Network Working Group Ken Morneault INTERNET-DRAFT Cisco Systems Malleswar Kalla Selvam Rengasami Telcordia Technologies Greg Sidebottom Nortel Networks Expires in six months Sep 2000 ISDN Q.921-User Adaptation Layer Status of This Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC 2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as 'work in progress'. The list of current Internet-Drafts can be accessed at http//www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http//www.ietf.org/shadow.html. To learn the current status of any Internet-Draft, please check the '1id-abstracts.txt' listing contained in the Internet- Drafts Shadow Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe), munnari.oz.au (Pacific Rim), ftp.ietf.org (US East Coast), or ftp.isi.edu (US West Coast). Abstract This Internet Draft defines a protocol for backhauling of ISDN Q.921 User messages over IP using the Stream Control Transmission Protocol (SCTP). This protocol would be used between a Signaling Gateway (SG) and Media Gateway Controller (MGC). It is assumed that the SG receives ISDN signaling over a standard ISDN interface. Morneault, Kalla, Rengasami, & Sidebottom [Page 1] Internet Draft ISDN Q.921 User Adaptation Layer Sep 2000 TABLE OF CONTENTS 1. Introduction.....................................................3 1.1 Scope.........................................................3 1.2 Terminology...................................................3 1.3 IUA Overview..................................................4 1.4 Services Provided by the IUA Layer............................9 1.5 Functions Implemented by the IUA Layer.......................11 1.6 Definition of IUA Boundaries.................................12 2. Conventions.....................................................12 3. Protocol Elements...............................................13 3.1 Common Message Header........................................13 3.2 IUA Message Header...........................................15 3.3 Description of Messages......................................16 4. Procedures......................................................33 4.1 Procedures to Support Service in Section 1.4.1...............34 4.2 Procedures to Support Service in Section 1.4.3...............34 4.3 Procedures to Support Service in Section 1.4.3...............34 5. Examples.........................................................40 5.1 Establishment of associations between SG and MGC examples.....40 5.2 ASP Traffic Fail-over Examples................................42 5.3 Q.921/Q.931 primitives backhaul Examples......................43 5.4 Layer Management Communication Examples.......................44 6. Security........................................................44 6.1 Threats.......................................................45 6.2 Protecting Confidentiality ...................................45 7. IANA Considerations.............................................45 8. Acknowledgements................................................46 9. References......................................................46 10. Author's Addresses..............................................46 Morneault, Kalla, Rengasami, & Sidebottom [Page 2] Internet Draft ISDN Q.921 User Adaptation Layer Sep 2000 1. Introduction In this document, the term Q.921 user refers to an upper layer which uses the services of Q.921, not the user side of ISDN interface [1]. Examples of the upper layer would be Q.931 and QSIG. This section describes the need for ISDN Q.921 User Adaptation (IUA) layer protocol as well as how this protocol shall be implemented. 1.1 Scope There is a need for Switched Circuit Network (SCN) signaling protocol delivery from an ISDN Signaling Gateway (SG) to a Media Gateway Controller (MGC) as described in the Framework Architecture for Signalling Transport. The delivery mechanism should meet the following criteria: * Support for transport of the Q.921 / Q.931 boundary primitives * Support for communication between Layer Management modules on SG and MGC * Support for management of active associations between SG and MGC This draft supports both ISDN Primary Rate Access (PRA) as well as Basic Rate Access (BRA) including the support for both point-to-point mode and point-to-multipoint modes of communication. QSIG adaptation layer requirements do not differ from Q.931 adaptation layer, hence the procedures described in this draft are also applicable for a QSIG adaptation layer. For simplicity, only Q.931 will be mentioned in the rest of this document. 1.2 Terminology Interface - For the purposes of this document an interface supports the relevant ISDN signalling channel. This signalling channel may be a 16 kbps D channel for an ISDN BRA as well as 64 kbps primary or backup D channel for an ISDN PRA. For QSIG, the signalling channel is a Qc channel. Q.921-User - Any protocol normally using the services of the ISDN Q.921 (e.g., Q.931, QSIG, etc.). Backhaul - A SG terminates the lower layers of an SCN protocol and backhauls the other layer to MGC for call processing. For the purposes of this draft the SG terminates Q.921 and backhauls Q.931 to MGC. Association - An association refers to a SCTP association. The association will provide the transport for the delivery of Q.921-User protocol data units and IUA adaptation layer peer messages. Stream - A stream refers to an SCTP stream; a uni-directional logical channel established from one SCTP endpoint to another associated SCTP endpoint, within which all user messages are delivered in-sequence except for those submitted to the un-ordered delivery service. Morneault, Kalla, Rengasami, & Sidebottom [Page 3] Internet Draft ISDN Q.921 User Adaptation Layer Sep 2000 Application Server (AS) - A logical entity serving a specific application instance. An example of an Application Server is a MGC handling the Q.931 and call processing for D channels terminated by the Signaling Gateways. Practically speaking, an AS is modeled at the SG as an ordered list of one or more related Application Server Processes (e.g., primary, secondary, tertiary). Application Server Process (ASP) - A process instance of an Application Server. Examples of Application Server Processes are primary or backup MGC instances. Fail-over - The capability to re-route signalling traffic as required between related ASPs in the event of failure or unavailability of the currently used ASP (e.g. from primary MGC to back-up MGC). Fail-over also applies upon the return to service of a previously unavailable process. Layer Management û Layer Management is a nodal function that handles the inputs and outputs between the IUA layer and a local management entity. Network Byte Order - Most significant byte first, a.k.a Big Endian. Host - The computing platform that the ASP process is running on. 1.3 IUA Overview The architecture that has been defined [5] for SCN signaling transport over IP uses multiple components, including an IP transport protocol, a signaling common transport protocol and an adaptation module to support the functions expected by a particular SCN signaling protocol from its underlying protocol layer. This document defines an adaptation module that is suitable for the transport of ISDN Q.921 User (Q.931). Morneault, Kalla, Rengasami, & Sidebottom [Page 4] Internet Draft ISDN Q.921 User Adaptation Layer Sep 2000 1.3.1 Example - SG to MGC In a Signaling Gateway, it is expected that the ISDN signaling is received over a standard ISDN network termination. The SG then provides interworking of transport functions with IP Signaling Transport, in order to transport the Q.931 signaling messages to the MGC where the peer Q.931 protocol layer exists, as shown below: ****** ISDN ****** IP ******* * EP *---------------* SG *--------------* MGC * ****** ****** ******* +-----+ +-----+ |Q.931| (NIF) |Q.931| +-----+ +----------+ +-----+ | | | | IUA| | IUA | | | | +----+ +-----+ |Q.921| |Q.921|SCTP| |SCTP | | | | +----+ +-----+ | | | | IP + | IP | +-----+ +-----+----+ +-----+ NIF - Nodal Interworking Function EP - ISDN End Point SCTP - Stream Control Transmission Protocol (Refer to [3]) IUA - ISDN User Adaptation Layer Protocol It is recommended that the IUA use the services of the Stream Control Transmission Protocol (SCTP) as the underlying reliable common signalling transport protocol. The use of SCTP provides the following features: - explicit packet-oriented delivery (not stream-oriented) - sequenced delivery of user messages within multiple streams, with an option for order-of-arrival delivery of individual user messages, - optional multiplexing of user messages into SCTP datagrams, - network-level fault tolerance through support of multi-homing at either or both ends of an association, - resistance to flooding and masquerade attacks, and - data segmentation to conform to discovered path MTU size There are scenarios without redundancy requirements and scenarios in which redundancy is supported below the transport layer. In these cases, the SCTP functions above may not be a requirement and TCP can be used as the underlying common transport protocol. Please refer to RFC XXXX/Appendix X for more guidance on the Adaptation Layer operation when using TCP as the underlying transport layer. Morneault, Kalla, Rengasami, & Sidebottom [Page 5] Internet Draft ISDN Q.921 User Adaptation Layer Sep 2000 1.3.2 Support for the management of SCTP associations between the SG and ASPs. The IUA layer at the SG maintains the availability state of all configured remote ASPs, in order to manage the SCTP Associations and the traffic between the SG and ASPs. As well, the active/inactive state of remote ASPs is also maintained - Active ASPs are those currently receiving traffic from the SG. The IUA layer may be instructed by local management to establish an SCTP association to a peer IUA node. This can be achieved using the M- SCTP ESTABLISH primitive to request, indicate and confirm the establishment of an SCTP association with a peer IUA node. The IUA layer may also need to inform local management of the status of the underlying SCTP associations using the M-SCTP STATUS request and indication primitive. For example, the IUA may inform local management of the reason for the release of an SCTP association, determined either locally within the IUA layer or by a primitive from the SCTP. Also the IUA layer may need to inform the local management of the change in status of an ASP or AS. This can be achieved using the M-ASP STATUS or M-AS STATUS primitives. 1.3.3 Signaling Network Architecture A Signaling Gateway is used to support the transport of Q.921-User signaling traffic to one or more distributed ASPs (e.g., MGCs). Clearly, the IUA protocol description cannot in itself meet any performance and reliability requirements for such transport. A physical network architecture is required, with data on the availability and transfer performance of the physical nodes involved in any particular exchange of information. However, the IUA protocol must be flexible enough allow its operation and management in a variety of physical configurations that will enable Network Operators to meet their performance and reliability requirements. To meet the ISDN signaling reliability and performance requirements for carrier grade networks, these Network Operators should ensure that there is no single point of failure provisioned in the end-to-end network architecture between an ISDN node and an IP ASP. Depending of course on the reliability of the SG and ASP functional elements, this can typically be met by the provision of redundant QOS-bounded IP network paths for SCTP Associations between SCTP End Points, and redundant Hosts, and redundant SGs. The distribution of ASPs within the available Hosts is also important. For a particular Application Server, the related ASPs should be distributed over at least two Hosts. An example physical network architecture relevant to carrier-grade operation in the IP network domain is shown in Figure 1 below: Morneault, Kalla, Rengasami, & Sidebottom [Page 6] Internet Draft ISDN Q.921 User Adaptation Layer Sep 2000 Host1 ******** ************** * *_________________________________________* ******** * * * _________* * ASP1 * * * SG1 * SCTP Associations | * ******** * * *_______________________ | * * ******** | | ************** | | ******** | | * *_______________________________| * * | * SG2 * SCTP Associations | * *____________ | * * | | Host2 ******** | | ************** | |_________________* ******** * |____________________________* * ASP1 * * * ******** * * * ************** . . . Figure 2 - Physical Model Example For carrier grade networks, the failure or isolation of a particular ASP should not cause stable calls to be dropped. This implies that ASPs need, in some cases, to share the call state or be able to pass the call state between each other. However, this sharing or communication of call state information is outside the scope of this document. 1.3.4 ASP Fail-over Model and Terminology The IUA supports ASP fail-over functions in order to support a high availability of call processing capability. All Q.921-User messages incoming to an SG are assigned to a unique Application Server, based on the Interface Identifier of the message. The Application Server is, in practical terms, a list of all ASPs configured to process Q.921-User messages from certain Interface Identifiers. One or more ASPs in the list are normally active (i.e., handling traffic) while any others may be unavailable or inactive, to be possibly used in the event of failure or unavailability of the active ASP(s). The fail-over model supports an n+k redundancy model, where n ASPs is the minimum number of redundant ASPs required to handle traffic and k ASPs are available to take over for a failed or unavailable ASP. Note that 1+1 active/standby redundancy is a subset of this model. A simplex 1+0 model is also supported as a subset, with no ASP redundancy. Morneault, Kalla, Rengasami, & Sidebottom [Page 7] Internet Draft ISDN Q.921 User Adaptation Layer Sep 2000 To avoid a single point of failure, it is recommended that a minimum of two ASPs be in the list, resident in separate hosts and therefore available over different SCTP Associations. For example, in the network shown in Figure 2, all messages from a particular D Channel could be sent to ASP1 in Host1 or ASP1 in Host2. The AS list at SG1 might look like the following: Interface Identifiers - Application Server #1 ASP1/Host1 - State Up, Active ASP1/Host2 - State Up, Inactive In this 1+1 redundancy case, ASP1 in Host1 would be sent any incoming message for the Interface Identifiers registered. ASP1 in Host2 would normally be brought to the active state upon failure of, or loss of connectivity to, ASP1/Host1. In this example, both ASPs are Up, meaning that the related SCTP association and far-end IUA peer is ready. The AS List at SG1 might also be set up in load-share mode as shown below: Interface Identifier (x) - Application Server #1 ASP1/Host1 - State Up, Active ASP1/Host2 - State Up, Active In this case, both the ASPs would be sent a portion of the traffic. In the process of fail-over or fail-back, it is recommended that in the case of ASPs supporting call processing, stable calls do not get released. It is possible that calls in transition may fail, although measures of communication between the ASPs involved can be used to mitigate this. For example, the two ASPs may share call state via shared memory, or may use an ASP to ASP protocol to pass call state information. The ASP to ASP protocol is outside the scope of this document. 1.3.5 Flow Control 1.3.6 Client/Server Model It is recommended that the SG and ASP be able to support both client and server operation. The peer endpoints using IUA should be configured so that one always takes on the role of client and the other the role of server for initiating SCTP associations. The default orientation would be for the SG to take on the role of server while the ASP is the client. In this case, ASPs should initiate the SCTP association to the SG. The SCTP (and UDP/TCP) Registered User Port Number Assignment for IUA is 9900. Morneault, Kalla, Rengasami, & Sidebottom [Page 8] Internet Draft ISDN Q.921 User Adaptation Layer Sep 2000 1.4 Services Provided by the IUA Layer 1.4.1 Support for transport of Q.921/Q.931 boundary primitives In the backhaul scenario, the Q.921/Q.931 boundary primitives are exposed. IUA layer needs to support all of the primitives of this boundary to successfully backhaul Q.931. This includes the following primitives [1]: DL-ESTABLISH The DL-ESTABLISH primitives are used to request, indicate and confirm the outcome of the procedures for establishing multiple frame operation. DL-RELEASE DL-RELEASE primitives are used to request, indicate, and confirm the outcome of the procedures for terminating a previously established multiple frame operation, or for reporting an unsuccessful establishment attempt. DL-DATA The DL-DATA primitives are used to request and indicate SDUs containing Q.931 PDUs which are to be transmitted, or have been received, by the Q.921 layer using the acknowledged information transfer service. DL-UNIT DATA The DL-UNIT DATA primitives are used to request and indicate SDUs containing Q.931 PDUs which are to be transmitted, by the Q.921 layer using the unacknowledged information transfer service. 1.4.2 Support for communication between Layer Management modules on SG and MGC It is envisioned that the IUA layer needs to provide some services that will facilitate communication between Layer Management modules on the SG and MGC. These primitives are pointed out in [2], which are shown below: MIUA-TEI STATUS The MIUA-TEI STATUS primitives are used to request, confirm and indicate the status (assigned/unassigned) of a TEI. To facilitate reporting of errors that arise because of backhauling Q.931 scenario, the M-ERROR primitive is defined: Morneault, Kalla, Rengasami, & Sidebottom [Page 9] Internet Draft ISDN Q.921 User Adaptation Layer Sep 2000 M-ERROR The M-ERROR primitive is used to indicate an error with a received IUA message (e.g., interface identifier value is not known to the SG). 1.4.3 Support for management of active associations between SG and MGC A set of primitives between the IUA layer and the Layer Management are defined below to help the Layer Management manage the SCTP association(s) between the SG and MGC. The IUA layer can be instructed by the Layer Management to establish SCTP association to a peer IUA node. This procedure can be achieved using the M-SCTP ESTABLISH primitive. M-SCTP ESTABLISH The M-SCTP ESTABLISH primitives are used to request, indicate, and confirm the establishment of SCTP association to a peer IUA node. M-SCTP RELEASE The M-SCTP RELEASE primitives are used to request, indicate, and confirm the release of SCTP association to a peer IUA node. The IUA layer may also need to inform the status of the SCTP associations to the Layer Management. This can be achieved using the M-SCTP STATUS primitive M-SCTP STATUS The M-SCTP STATUS primitives are used to request and indicate the status of the underlying SCTP association(s). The Layer Management may need to inform the IUA layer of a AS/ASP status (i.e., failure, active, etc.), so that messages can be exchanged between IUA layer peers to stop traffic to the local IUA user. This can be achieved using the M-ASP STATUS primitive. M-ASP STATUS The ASP status are stored inside IUA layer on both the SG and MGC sides. The M-ASP STATUS primitive can be used by Layer Management to request the status of the Application Server Process from the IUA layer. This primitive can also be used to indicate the status of the Application Server Process. M-ASP MODIFY The M-ASP MODIFY primitive can be used by Layer Management to modify the status of the Application Server Process. In other words, the Layer Management on the ASP side uses this primitive to initiate the ASPM procedures. Morneault, Kalla, Rengasami, & Sidebottom [Page 10] Internet Draft ISDN Q.921 User Adaptation Layer Sep 2000 M-AS STATUS The M-AS STATUS primitive can be used by Layer Management to request the status of the Application Server. This primitive can also be used to indicate the status of the Application Server. 1.5 Functions Implemented by the IUA Layer 1.5.1 Mapping The IUA layer must maintain a map of the Interface ID to a physical interface on the Signaling Gateway. A physical interface would be a T1 line, E1 line, etc. and could include the TDM timeslot. In addition, for a given interface the SG must be able to identify the associated signalling channel. IUA layers on both SG and MGC need to maintain the status of TEIs and SAPIs. The SG maps an Interface Id to an SCTP association/stream only when an ASP sends an ASP Active message for a particular Interface Id. It must be noted, however, that this mapping is dynamic and could change at any time due to a change of ASP state. This mapping could even temporarily be invalid, for example during failover of one ASP to another. Therefore, the SG must maintain the states of AS/ASP and reference them during the routing of an messages to an ASP. 1.5.2 Status of ASPs The IUA layer on the SG must maintain the state of the ASPs it is supporting. The state of an ASP changes because of reception of peer-to-peer messages (ASPM messages as described in Section 3.3.2) or reception of indications from the local SCTP association. ASP state transition procedures are described in Section 4.3.1. At an SG, an Application Server list may contain active and inactive ASPs to support ASP load-sharing and fail-over procedures. When, for example, both a primary and a back-up ASP are available, IUA peer protocol is required to control which ASP is currently active. The ordered list of ASPs within a logical Application Server is kept updated in the SG to reflect the active Application Server Process(es). 1.5.3 SCTP Stream Management SCTP allows a user specified number of streams to be opened during the initialization. It is the responsibility of the IUA layer to ensure proper management of these streams. Because of the unidirectional nature of streams, IUA layers are not aware of the stream information from the peer IUA layers. The use of SCTP streams within IUA is recommended in order to minimize transmission and buffering delay. A separate stream should be used for each D channel. Morneault, Kalla, Rengasami, & Sidebottom [Page 11] Internet Draft ISDN Q.921 User Adaptation Layer Sep 2000 1.5.4 Seamless Network Management Interworking The IUA layer on the SG should pass an indication of unavailability of the IUA-User (Q.931) to the local Layer Management, if the currently active ASP moves from the ACTIVE state. The Layer Management could instruct Q.921 to take some action, if it deems appropriate. Likewise, if an SCTP association fails, the IUA layer on both the SG and ASP sides MAY generate Release primitives to take the D channels out-of-service. 1.5.5 Congestion Management If the IUA layer becomes congested (implementation dependent), it MAY stop reading from the SCTP association to flow control from the peer IUA. 1.6 Definition of IUA Boundaries 1.6.1 Definition of IUA/Q.921 boundary DL-ESTABLISH DL-RELEASE DL-DATA DL-UNIT DATA 1.6.2 Definition of IUA/Q.931 boundary DL-ESTABLISH DL-RELEASE DL-DATA DL-UNIT DATA 1.6.3 Definition of SCTP/IUA Boundary An example of the upper layer primitives provided by SCTP are available in Reference [3] section 9. 1.6.4 Definition of IUA/Layer-Management Boundary M-ERROR M-SCTP ESTABLISH M-SCTP RELEASE M-SCTP STATUS M-ASP STATUS M-AS STATUS MIUA-TEI STATUS 2.0 Conventions The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, SHOULD NOT, RECOMMENDED, NOT RECOMMENDED, MAY, and OPTIONAL, when they appear in this document, are to be interpreted as described in [RFC2119]. Morneault, Kalla, Rengasami, & Sidebottom [Page 12] Internet Draft ISDN Q.921 User Adaptation Layer Sep 2000 3.0 Protocol Elements This section describes the format of various messages used in this protocol. 3.1 Common Message Header The protocol messages for Q.921 User Adaptation require a message header which contains the adaptation layer version, the message type, and message length. All types of messages contain this header. This message header is common among all SCN signaling protocol adaptation layers. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Version | Reserved | Message Class | Message Type | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Message Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1 Common Header Format All fields in an IUA message MUST be transmitted in the network byte order, unless otherwise stated. 3.1.1 Version The version field (vers) contains the version of the IUA adaptation layer. The supported versions are the following: Release 1.0 0x1 3.1.2 Message Classes and Types The following List contains the valid Message Classes: Message Class: 8 bits (unsigned integer) 0 Management (MGMT) Message 1 Reserved 2 Reserved 3 ASP State Maintenance (ASPSM) Messages 4 ASP Traffic Maintenance (ASPTM) Messages 5 Q.921/Q.931 Boundary Primitives Tranport (QPTM) Messages 6 to 255 Reserved Morneault, Kalla, Rengasami, & Sidebottom [Page 13] Internet Draft ISDN Q.921 User Adaptation Layer Sep 2000 The following list contains the message names for the defined messages. Q.921/Q.931 Boundary Primitives Transport (QPTM) Messages Data Request Message 0x01 Data Indication Message 0x02 Unit Data Request Message 0x03 Unit Data Indication Message 0x04 Establish Request 0x05 Establish Confirm 0x06 Establish Indication 0x07 Release Request 0x08 Release Confirm 0x09 Release Indication 0x0a Application Server Process State Maintenance (ASPSM) messages ASP Up 0x01 ASP Down 0x02 Heartbeat 0x03 ASP Up Ack 0x04 ASP Down Ack 0x05 Application Server Process Traffic Maintenance (ASTM) messages ASP Active 0x01 ASP Inactive 0x02 ASP Active Ack 0x03 ASP Inactive Ack 0x04 Management (MGMT) Messages Error Indication 0x00 Notify 0x01 TEI Status Request 0x02 TEI Status Confirm 0x03 TEI Status Indication 0x04 3.1.3 Message Length The Message length defines the length of the message in octets, not including the Common header. 3.1.4 Variable-Length Parameter Format IUA messages consist of a Common Header followed by zero or more variable-length parameters, as defined by the message type. The variable-length parameters contained in a message are defined in a Tag-Length-Value format as shown below. Morneault, Kalla, Rengasami, & Sidebottom [Page 14] Internet Draft ISDN Q.921 User Adaptation Layer Sep 2000 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Parameter Tag | Parameter Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ \ \ / Parameter Value / \ \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Parameter Tag: 16 bits (unsigned integer) The Type field is a 16 bit identifier of the type of parameter. It takes a value of 0 to 65534. The value of 65535 is reserved for IETF-defined extensions. Values other than those defined in specific parameter description are reserved for use by the IETF. Parameter Length: 16 bits (unsigned integer) The Parameter Length field contains the size of the parameter in bytes, including the Parameter Tag, Parameter Length, and Parameter Value fields. Thus, a parameter with a zero-length Parameter Value field would have a Length field of 4. The Parameter Length does not include any padding bytes. Parameter Value: variable-length The Parameter Value field contains the actual information to be transferred in the parameter. The total length of a parameter (including Tag, Parameter Length and Value fields) MUST be a multiple of 4 bytes. If the length of the parameter is not a multiple of 4 bytes, the sender pads the Parameter at the end (i.e., after the Parameter Value field) with all zero bytes. The length of the padding is NOT included in the parameter length field. A sender should NEVER pad with more than 3 bytes. The receiver MUST ignore the padding bytes. 3.2 IUA Message Header In addition to the common message header, there will be a specific message header for QPTM and the TEI Status MGMT messages. The IUA message header will immediately follow the Common header in these messages. This message header will contain the Interface Identifier and Data Link Connection Identifier (DLCI). The Interface Identifier identifies the physical interface terminating the signalling channel at the SG for which the signaling messages are sent/received. The format of the Interface Identifier parameter can be text or integer. The Interface Idnetifiers are assigned according to network operator policy. The integer values used are of local significance only, coordinated between the SG and ASP. Morneault, Kalla, Rengasami, & Sidebottom [Page 15] Internet Draft ISDN Q.921 User Adaptation Layer Sep 2000 The integer formatted Interface Identifier MUST be supported. The text formatted Interface Identifier MAY optionally be supported. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Tag (0x1) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Interface Identifier (integer) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | DLCI | Spare | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2 IUA Message Header (Integer Interface Id) The Tag value for Interface Identifier is 0x1. The length is always set to a value of 8. The DLCI format is shown below in Figure 3. 0 1 2 3 4 5 6 7 +-----+-----+-----+-----+-----+-----+-----+-----+ | 0 | SPR | SAPI | +-----------------------------------------------+ | 1 | TEI | +-----------------------------------------------+ Figure 3 DLCI Format SPR Spare, 2nd bit in octet 1 SAPI Service Access Point Identifier, 3rd thru 8th bits in octet 1 TEI Terminal Endpoint Identifier, 2nd thru 8th bits in octet 2 The DLCI field (including the SAPI and TEI) is coded in accordance with Q.921. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Tag (0x3) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Interface Identifier (text) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | DLCI | Spare | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 4 IUA Message Header (Text Interface Id) The Tag value for Interface Identifier is 0x1. The length is variable. 3.3 IUA Messages The following section defines the messages and parameter contents. The IUA messages will use the common message header (Figure 2) and the IUA message header (Figure 3). Morneault, Kalla, Rengasami, & Sidebottom [Page 16] Internet Draft ISDN Q.921 User Adaptation Layer Sep 2000 3.3.1 Q.921/Q.931 Boundary Primitives Transport (QPTM) Messages 3.3.1.1 Establish Messages (Request, Confirm, Indication) The Establish Messages are used to establish a data link on the signalling channel or to confirm that a data link on the signalling channel has been established. The MGC controls the state of the D channel. When the MGC desires the D channel to be in-service, it will send the Establish Request message. The SG will respond with an Establish Confirm if the Q.921 layer indicates a DL-ESTABLISH Confirm. The SG will respond with an Establish Indication if the Q.921 layer indicates a DL-ESTABLISH Indication. The Establish messages contain the common message header followed by IUA message header. It does not contain any additional parameters. 3.3.1.2 Release Messages (Request, Indication, Confirmation) The Release Request message is used to release the data link on the signalling channel. The Release Confirm and Indication messages are used to indicate that the data link on the signaling channel has been released. The Release messages contain the common message header followed by IUA message header. The Release confirm message is in response to a Release Request message and it does not contain any additional parameters. The Release Request and Indication messages contain the following parameter: REASON 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reason | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The valid values for Reason are shown in the following table. Define Value Description RELEASE_MGMT 0x0 Management layer generated release. RELEASE_PHYS 0x1 Physical layer alarm generated release. RELEASE_DM 0x2 Specific to a request. Indicates Layer 2 should release and deny all requests from far end to establish a data link on the signalling channel (i.e. if SABME is received send a DM) RELEASE_OTHER 0x3 Other reasons Note: Only RELEASE_MGMT, RELEASE_DM and RELEASE_OTHER are valid reason codes for a Release Request message. Morneault, Kalla, Rengasami, & Sidebottom [Page 17] Internet Draft ISDN Q.921 User Adaptation Layer Sep 2000 3.3.1.3 Data Messages (Request, Indication) The Data message contains an ISDN Q.921-User Protocol Data Unit (PDU) corresponding to acknowledged information transfer service. The Data messages contain the common message header followed by IUA message header. The Data message contains the following parameters: PROTOCOL DATA 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Protocol Data | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The protocol data contains upper layer signalling message e.g. Q.931, QSIG. The Data message should NOT contain any padding bytes. 3.3.1.4 Unit Data Messages (Request, Indication) The Unit Data message contains an ISDN Q.921-User Protocol Data Unit (PDU) corresponding to unacknowledged information transfer service. The Unit Data messages contain the common message header followed by IUA message header. The Unit Data message contains the following parameters PROTOCOL DATA 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Protocol Data | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3.3.2 Application Server Process Maintenance (ASPM) Messages The ASPM messages will only use the common message header. 3.3.2.1 ASP Up (ASPUP) The ASP Up (ASPUP) message is sent by an ASP to indicate to an SG that it is ready to receive traffic or maintenance messages. Morneault, Kalla, Rengasami, & Sidebottom [Page 18] Internet Draft ISDN Q.921 User Adaptation Layer Sep 2000 The ASPUP message contains the following parameters Adaptation Layer Identifier (optional) Info String (optional) The format for ASPUP Message parameters is as follows: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Tag (0x2) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Adaptation Layer Identifier* | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Tag (0x4) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | INFO String* | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The Adaptation Layer Identifier (ALI) is a string that identifies the adaptation layer. This string must be set to "IUA" which results in a length of 7. The ALI would normally only be used in the initial ASP Up message across a new SCTP association to ensure both peers are assuming the same adaptation layer protocol. The optional INFO String parameter can carry any meaningful 8-bit ASCII character string along with the message. Length of the INFO String parameter is from 0 to 255 characters. No procedures are presently identified for its use but the INFO String may be used for debugging purposes. 3.3.2.2 ASP Up Ack The ASP Up Ack message is used to acknowledge an ASP Up message received from a remote IUA peer. The ASPUP Ack message contains the following parameters: Adaptation Layer Identifer (optional) INFO String (optional) Morneault, Kalla, Rengasami, & Sidebottom [Page 19] Internet Draft ISDN Q.921 User Adaptation Layer Sep 2000 The format for ASPUP Ack Message parameters is as follows: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Tag (0x2) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Adaptation Layer Identifier* | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Tag (0x4) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | INFO String* | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The format and description of the optional Info String parameter is the same as for the ASP Up message (See Section 3.3.3.1.). The format and description of the optional Adaptation Layer Identifier (ALI) parameter is the same as for the ASP Up message (See Section 3.3.2.1). 3.3.2.3 ASP Down (ASPDN) The ASP Down (ASPDN) message is sent by an ASP to indicate to an SG that it is NOT ready to receive traffic or maintenance messages. The ASPDN message contains the following parameters: Reason INFO String (Optional) The format for the ASPDN message parameters is as follows: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reason | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Tag (0x4) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | INFO String* | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The format and description of the optional Info String parameter is the same as for the ASP Up message (See Section 3.3.3.1.). Morneault, Kalla, Rengasami, & Sidebottom [Page 20] Internet Draft ISDN Q.921 User Adaptation Layer Sep 2000 The Reason parameter indicates the reason that the remote IUA adaptation layer is unavailable. The valid values for Reason are shown in the following table. Value Description 0x1 Management Inhibit If a ASP is removed from Management Inhibit, the ASP will send an ASP Up message. 3.3.2.4 ASP Down Ack The ASP Down Ack message is used to acknowledge an ASP Down message received from a remote IUA peer. The ASP Down Ack message contains the following parameters: Reason INFO String (Optional) The format for the ASP Down Ack message parameters is as follows: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reason | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Tag (0x4) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | INFO String* | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The format and description of the optional Info String parameter is the same as for the ASP Up message (See Section 3.3.2.1.). The format of the Reason parameter is the same as for the ASP Down message (See Section 3.3.2.3). 3.3.2.5 ASP Active (ASPAC) The ASPAC message is sent by an ASP to indicate to an SG that it is Active and ready to be used. The ASPAC message contains the following parameters Traffic Mode Type (Mandatory) Interface Identifier (Optional) - Combination of integer and integer ranges, OR - string (text formatted) INFO String (Optional) The format for the ASPAC message using integer formatted Interface Identifiers is as follows: Morneault, Kalla, Rengasami, & Sidebottom [Page 21] Internet Draft ISDN Q.921 User Adaptation Layer Sep 2000 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Traffic Mode Type | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Tag (0x1=integer) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Interface Identifiers* | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Tag (0x8=integer range) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Interface Identifier Start1* | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Interface Identifier Stop1* | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Interface Identifier Start2* | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Interface Identifier Stop2* | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Additional Interface Identifiers | | of Tag Type 0x1 or 0x8 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Tag (0x4) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | INFO String* | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Morneault, Kalla, Rengasami, & Sidebottom [Page 22] Internet Draft ISDN Q.921 User Adaptation Layer Sep 2000 The format for the ASPAC message using text formatted (string) Interface Identifiers is as follows: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Traffic Mode Type | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Tag (0x3=string) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Interface Identifier* | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Additional Interface Identifiers | | of Tag Type 0x3 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Tag (0x4) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | INFO String* | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The Traffic Mode Type parameter identifies the traffic mode of operation of the ASP within an AS. The valid values for Type are shown in the following table: Value Description 0x1 Over-ride 0x2 Load-share Within a particular Interface Identifier, only one Traffic Mode Type can be used. The Over-ride value indicates that the ASP is operating in Over-ride mode, where the ASP takes over all traffic in an Application Server (i.e., primary/back-up operation), over-riding any currently active ASPs in the AS. In Load-share mode, the ASP will share in the traffic distribution with any other currently active ASPs. The optional Interface Identifiers parameter contains a list of Interface Identifier integers (Type 0x1 or Type 0x8) or text strings (Type 0x3)indexing the Application Server traffic that the sending ASP is configured/registered to receive. If integer formatted Interface Identifiers are being used, the ASP can send also ranges of Interface Identifiers (Type 0x8). Interface Identifier types Integer (0x1) and Integer Range (0x8) are allowed in the same message. Text formatted Interface Identifiers (0x3) cannot be used with either Integer (0x1) or Integer Range (0x8) types. There is one-to-one relationship between an Interface Identifier and an AS Name. If no Interface Identifiers are included, the message is for all provisioned Interface Identifiers. Morneault, Kalla, Rengasami, & Sidebottom [Page 23] Internet Draft ISDN Q.921 User Adaptation Layer Sep 2000 The format and description of the optional Info String parameter is the same as for the ASP Up message (See Section 3.3.2.1.). An SG that receives an ASPAC with an incorrect Traffic Mode Type for a particular Interface Identifier will respond with an Error Message (Cause: Invalid Traffic Handling Mode). 3.3.2.6 ASP Active Ack The ASPAC Ack message is used to acknowledge an ASP-Active message received from a remote IUA peer. The ASPAC Ack message contains the following parameters: Traffic Mode Type (Mandatory) Interface Identifier (Optional) - Combination of integer and integer ranges, OR - string (text formatted) INFO String (Optional) The format for the ASPAC Ack message is as follows: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Traffic Mode Type | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Tag (0x1=integer) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Interface Identifiers* | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Tag (0x8=integer range) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Interface Identifier Start1* | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Interface Identifier Stop1* | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Interface Identifier Start2* | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Interface Identifier Stop2* | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Additional Interface Identifiers | | of Tag Type 0x1 or 0x8 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Tag (0x4) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | INFO String* | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Morneault, Kalla, Rengasami, & Sidebottom [Page 24] Internet Draft ISDN Q.921 User Adaptation Layer Sep 2000 The format for the ASP Active Ack message using text formatted (string) Interface Identifiers is as follows: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Traffic Mode Type | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Tag (0x3=string) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Interface Identifier* | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Additional Interface Identifiers | | of Tag Type 0x3 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Tag (0x4) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | INFO String* | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The format of the Traffic Mode Type and Interface Identifier parameters is the same as for the ASP Active message (See Section 3.3.2.5). The format and description of the optional Info String parameter is the same as for the ASP Up message (See Section 3.3.2.1.). 3.3.2.7 ASP Inactive (ASPIA) The ASPIA message is sent by an ASP to indicate to an SG that it is no longer an active ASP to be used from within a list of ASPs. The SG will respond with an ASPIA message and either discard incoming messages or buffer for a timed period and then discard. The ASPIA message contains the following parameters Traffic Mode Type (Mandatory) Interface Identifiers (Optional) - Combination of integer and integer ranges, OR - string (text formatted) INFO String (Optional) The format for the ASP Inactive message parameters using Integer formatted Interface Identifiers is as follows: Morneault, Kalla, Rengasami, & Sidebottom [Page 25] Internet Draft ISDN Q.921 User Adaptation Layer Sep 2000 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Traffic Mode Type | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Tag (0x1=integer) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Interface Identifiers* | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Tag (0x8=integer range) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Interface Identifier Start1* | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Interface Identifier Stop1* | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Interface Identifier Start2* | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Interface Identifier Stop2* | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Additional Interface Identifiers | | of Tag Type 0x1 or 0x8 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Tag (0x4) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | INFO String* | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Morneault, Kalla, Rengasami, & Sidebottom [Page 26] Internet Draft ISDN Q.921 User Adaptation Layer Sep 2000 The format for the ASP Inactive message using text formatted (string) Interface Identifiers is as follows: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Traffic Mode Type | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Tag (0x3=string) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Interface Identifier* | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Additional Interface Identifiers | | of Tag Type 0x3 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Tag (0x4) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | INFO String* | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The Traffic Mode Type parameter identifies the traffic mode of operation of the ASP within an AS. The valid values for Traffic Mode Type are shown in the following table: Value Description 0x1 Over-ride 0x2 Load-share The format and description of the optional Interface Identifiers and Info String parameters is the same as for the ASP Active message (See Section 3.3.2.3.). The optional Interface Identifiers parameter contains a list of Interface Identifier integers or text strings indexing the Application Server traffic that the sending ASP is configured/registered to receive, but does not want to receive at this time. 3.3.2.8 ASP Inactive Ack The ASP Inactive (ASPIA) Ack message is used to acknowledge an ASP Inactive message received from a remote IUA peer. The ASPIA Ack message contains the following parameters: Traffic Mode Type (Mandatory) Interface Identifiers (Optional) - Combination of integer and integer ranges, OR - string (text formatted) INFO String (Optional) Morneault, Kalla, Rengasami, & Sidebottom [Page 27] Internet Draft ISDN Q.921 User Adaptation Layer Sep 2000 The format for the ASPIA Ack message is as follows: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Traffic Mode Type | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Tag (0x1=integer) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Interface Identifiers* | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Tag (0x8=integer range) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Interface Identifier Start1* | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Interface Identifier Stop1* | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Interface Identifier Start2* | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Interface Identifier Stop2* | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Additional Interface Identifiers | | of Tag Type 0x1 or 0x8 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Tag (0x4) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | INFO String* | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Morneault, Kalla, Rengasami, & Sidebottom [Page 28] Internet Draft ISDN Q.921 User Adaptation Layer Sep 2000 The format for the ASP Inactive Ack message using text formatted (string) Interface Identifiers is as follows: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Traffic Mode Type | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Tag (0x3=string) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Interface Identifier* | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Additional Interface Identifiers | | of Tag Type 0x3 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Tag (0x4) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | INFO String* | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The format of the Traffic Mode Type and Interface Identifier parameters is the same as for the ASP Inctive message (See Section 3.3.2.7). The format and description of the optional Info String parameter is the same as for the ASP Up message (See Section 3.3.2.1.). 3.3.2.9 Heartbeat (BEAT) The Heartbeat message is optionally used to ensure that the IUA peers are still available to each other. It is recommended for use when the IUA runs over a transport layer other than the SCTP, which has its own heartbeat. The BEAT message contains no parameters. 3.3.3 Layer Management (MGMT) Messages 3.3.3.1 Error (ERR) The Error message is used to notify a peer of an error event associated with an incoming message. For example, the message type might be unexpected given the current state, or a parameter value might be invalid. The ERR message contains the following parameters: Error Code Diagnostic Information (optional) Morneault, Kalla, Rengasami, & Sidebottom [Page 29] Internet Draft ISDN Q.921 User Adaptation Layer Sep 2000 The format for the ERR message is as follows: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Error Code | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Tag (0x7) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Diagnostic Information* | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The Error Code parameter indicates the reason for the Error Message. The Error parameter value can be one of the following values: Invalid Version 0x01 Invalid Interface Identifier 0x02 Invalid Adaptation Layer Identifier 0x03 Invalid Message Type 0x04 Unsupported Traffic Handling Mode 0x05 Unexpected Message 0x06 Protocol Error 0x07 Unsupported Interface Identifier Type 0x08 Invalid Stream Identifier 0x09 Unassigned TEI 0x0a Unrecognized SAPI 0x0b Invalid TEI, SAPI combination 0x0c The "Invalid Version" error would be sent if a message was received with an invalid or unsupported version. The Error message would contain the supported version in the Common header. The Error message could optionally provide the supported version in the Diagnostic Information area. The "Invalid Interface Identifier" error would be sent by a SG if an ASP sends a message with an invalid (unconfigured) Interface Identifier value. The "Unsupported Traffic Handling Mode" error would be sent by a SG if an ASP sends an ASP Active with an unsupported Traffic Handling Mode. An example would be a case in which the SG did not support load-sharing. The "Unexpected Message" error would be sent by an ASP if it received a QPTM message from an SG while it was in the Inactive state. The "Protocol Error" error would be sent for any protocol anomaly (i.e. a bogus message). The "Invalid Stream Identifier" error would be sent if a message was received on an unexpected SCTP stream (i.e. a stream that did not have an Interface Identifier associated with it). Morneault, Kalla, Rengasami, & Sidebottom [Page 30] Internet Draft ISDN Q.921 User Adaptation Layer Sep 2000 The "Unsupported Interface Identifier Type" error would be sent by a SG if an ASP sends a Text formatted Interface Identifier and the SG only supports Integer formatted Interface Identifiers. When the ASP receives this error, it will need to resend its message with an Integer formatted Interface Identifier. The "Unrecognized SAPI" error would handle the case of using a SAPI that is not recognized by the SG. The "Invalid TEI, SAPI combination" error identify errors where the TEI is assigned and the the SAPI is recognized, but the combination is not valid for the interface (e.g., on a BRI the MGC tries to send Q.921 Management messages via IUA when Layer Management at the SG should be performing this function). The optional Diagnostic information can be any information germane to the error condition, to assist in identification of the error condition. To enhance debugging, the Diagnostic information could contain the first 40 bytes of the offending message. 3.3.3.2 Notify (NTFY) The Notify message used to provide an autonomous indication of IUA events to an IUA peer. The NTFY message contains the following parameters: Status Type Status Identification Interface Identifiers (Optional) INFO String (Optional) Morneault, Kalla, Rengasami, & Sidebottom [Page 31] Internet Draft ISDN Q.921 User Adaptation Layer Sep 2000 The format for the NTFY message is as follows: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Status Type | Status Identification | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Tag (0x1) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Interface Identifiers* | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Tag (0x4) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | INFO String* | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The Status Type parameter identifies the type of the Notify message. The following are the valid Status Type values: Value Description 0x1 Application Server state change (AS_State_Change) 0x2 Other The Status Identification parameter contains more detailed information for the notification, based on the value of the Status Type. If the Status Type is AS_State_Change the following Status Indentification values are used: Value Description 0x1 Application Server Down (AS_Down) 0x2 Application Server Up (AS_Up) 0x3 Application Server Active (AS_Active) 0x4 Application Server Pending (AS_Pending) 0x5 Alternate ASP Active These notifications are sent from an SG to an ASP upon a change in status of a particular Application Server. The value reflects the new state of the Application Server. If the Status Type is Other, then the following Status Information values are defined: Value Description 0x1 Insufficient ASP resources active in AS This notification is not based on the SG reporting the state change of an ASP or AS. For the value defined the SG is indicating to an ASP(s) in the AS that another ASP is required in order to handle the load of the AS. Morneault, Kalla, Rengasami, & Sidebottom [Page 32] Internet Draft ISDN Q.921 User Adaptation Layer Sep 2000 The format and description of the optional Interface Identifiers and Info String parameters is the same as for the ASP Active message (See Section 3.3.2.3.). 3.3.3.3 TEI Status Messages (Request, Confirm and Indication) The TEI Status messages are exchanged between IUA layer peers to request, confirm and indicate the status of a particular TEI. The TEI Status messages contain the common message header followed by IUA message header. The TEI Status Request message does not contain any additional parameters. In the integrated ISDN Layer 2/3 model (e.g., in traditional ISDN switches), it is assumed that the Layer Management for the Q.921 Layer and the Q.931 layer are co-located. When backhauling ISDN, this assumption is not necessarily valid. The TEI status messages allow the two Layer Management entities to communicate the status of the TEI. In addition, knowing that a TEI is in service allows the ASP to request the SG to establish the Datalink to the terminal (via the IUA Establish message) for signaling if the ASP wants to be in control of data link establishment. Another use of the TEI status procedure is where the Layer Management at the ASP can prepare for to send/- receive signaling to/from a given TEI and confirm/verify the establishment of a datalink to that TEI. For example, if a datalink is established for a TEI that the ASP did not know was assigned, the ASP can check to see whether it was assigned or whether there was an error in the signaling message. Also, knowing that a TEI is out of service, the ASP need not request the SG to establish a datalink to that TEI. The TEI Status Indication, and Confirm messages contain the following parameter: STATUS 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Status | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The valid values for Status are shown in the following table. Define Value Description ASSIGNED 0x0 TEI is considered assigned by Q.921 UNASSIGNED 0x1 TEI is considered unassigned by Q.921 4.0 Procedures The IUA layers needs to respond to various primitives it receives from other layers as well as messages it receives from the peer-to-peer messages. This section describes various procedures involved in response to these events. Morneault, Kalla, Rengasami, & Sidebottom [Page 33] Internet Draft ISDN Q.921 User Adaptation Layer Sep 2000 4.1 Procedures to support service in section 1.4.1 These procedures achieve the IUA layer's "Transport of Q.921/Q.931 boundary" service. 4.1.1 Q.921 or Q.931 primitives procedures On receiving these primitives from the local layer, the IUA layer will send the corresponding QPTM message (Data, Unit Data, Establish, Release) to its peer. While doing so, the IUA layer needs to fill various fields of the common and specific headers correctly. In addition the message needs to be sent on the SCTP stream that corresponds to the D channel. 4.1.2 QPTM message procedures On receiving QPTM messages from a peer IUA layer, the IUA layer on an SG or MGC needs to invoke the corresponding layer primitives (DL-ESTABLISH, DL-DATA, DL-UNIT DATA, DL-RELEASE) to the local Q.921 or Q.931 layer. 4.2 Procedures to support service in section 1.4.2 These procedures achieve the IUA layer's "Support for Communication between Layer Managements" service. 4.2.1 Layer Management primitives procedures On receiving these primitives from the local layer, the IUA layer will send the corresponding MGMT message (TEI Status, Error) to its peer. While doing so, the IUA layer needs to fill various fields of the common and specific headers correctly. 4.2.2 MGMT message procedures On receiving MGMT messages the IUA layer needs to invoke the corresponding Layer Management primitives (MIUA-TEI STATUS, M-ERROR) to the local layer management. All MGMT messages are sent on a sequenced stream to ensure ordering. SCTP stream '0' SHOULD be used. 4.3 Procedures to support service in section 1.4.3 These procedures achieve the IUA layer's "Support for management of active associations between SG and MGC" service. 4.3.1 State Maintenance The IUA layer on the SG needs to maintain the states of each ASP as well as the state of the AS. 4.3.1.1 ASP States The state of the each ASP, in each AS that it is configured, is maintained in the IUA layer on the SG. The state of an ASP changes due to the following type of events: Morneault, Kalla, Rengasami, & Sidebottom [Page 34] Internet Draft ISDN Q.921 User Adaptation Layer Sep 2000 * Reception of messages from peer IUA layer at that ASP * Reception of some messages from the peer IUA layer at other ASPs in the AS * Reception of indications from SCTP layer * Switch-over Time triggers The ASP state transition diagram is shown in Figure 4. The possible states of an ASP are the following: ASP-DOWN Application Server Process is unavailable and/or the SCTP association is down. Initially all ASPs will be in this state. ASP-UP The remote IUA peer at the ASP is available (and the SCTP association is up) but application traffic is stopped. ASP-ACTIVE The remote IUA peer at the ASP is available and application traffic is active. Figure 4 ASP State Transition Diagram +-------------+ +----------------------| | | Alternate +-------| ASP-ACTIVE |<------------+ | ASP | +-------------+ | | Takeover | ^ | | | | ASP | | ASP | | | Active | | Inactive | ASP | | | v |Takeover | | +-------------+ | | | | |-------------+ | +------>| ASP-UP |-------------+ | +-------------+ | | ^ | | ASP Down/ | ASP | | ASP Down / | ASP SCTP CDI | Up | | SCTP CDI | Down/ | | v | SCTP | +-------------+ | CDI | | | | +--------------------->| |<------------+ | ASP-DOWN | +-------------+ SCTP CDI The local SCTP layer's Communication Down Indication to the Upper Layer Protocol (IUA) on an SG. The local SCTP will send this indication when it detects the loss of connectivity to the ASP's peer SCTP layer. Ts Switch-over Time Triggers. This timer is configurable by the Operator on a per AS basis. The default value of this timer should be three seconds. Morneault, Kalla, Rengasami, & Sidebottom [Page 35] Internet Draft ISDN Q.921 User Adaptation Layer Sep 2000 4.3.1.2 AS States The state of the AS is maintained in the IUA layer on the SG. The state of an AS changes due to events. These events include the following: * ASP state transitions * Recovery timer triggers The possible states of an AS are the following: AS-DOWN The Application Server is unavailable. This state implies that all related ASPs are in the ASP-DOWN state for this AS. Initially the AS will be in this state. AS-UP The Application Server is available but no application traffic is active (i.e., one or more related ASPs are in the ASP-UP state, but none in the ASP-Active state). AS-ACTIVE The Application Server is available and application traffic is active. This state implies that one ASP is in the ASP-ACTIVE state. AS-PENDING An active ASP has transitioned from active to inactive or down and it was the last remaining active ASP in the AS. A recovery timer T(r) will be started and all incoming SCN messages will be queued by the SG. If an ASP becomes active before T(r) expires, the AS will move to AS-ACTIVE state and all the queued messages will be sent to the active ASP. If T(r) expires before an ASP becomes active, the SG stops queuing messages and discards all previously queued messages. The AS will move to AS-UP if at least one ASP is in ASP-UP state, otherwise it will move to AS-DOWN state. Morneault, Kalla, Rengasami, & Sidebottom [Page 36] Internet Draft ISDN Q.921 User Adaptation Layer Sep 2000 Figure 5 AS State Transition Diagram +----------+ one ASP trans ACTIVE +-------------+ | |------------------------>| | | AS-UP | | AS-ACTIVE | | | | | | |< -| | +----------+ \ / +-------------+ ^ | \ Tr Trigger / ^ | | | \ at least one / | | | | \ ASP in UP / | | | | \ / | | | | \ / | | | | \ /---/ | | one ASP | | \ / one ASP | | Last ACTIVE ASP trans | | all ASP \-/----\ trans to | | trans to UP or to UP | | trans to / \ ACTIVE | | DOWN | | DOWN / \ | | (start Tr timer) | | / \ | | | | / \ | | | | /all ASP \ | | | v / trans to \ | v +----------+ / DOWN \ +-------------+ | |<--/ -| | | AS-DOWN | | AS-PENDING | | | | (queueing) | | |<------------------------| | +----------+ Tr Trigger no ASP +-------------+ in UP state Tr = Recovery Timer 4.3.2 ASPM procedures for primitives Before the establishment of an SCTP association the ASP state at both the SG and ASP is assumed to be "Down". As the ASP is responsible for initiating the setup of an SCTP association to an SG, the IUA layer at an ASP receives an M-SCTP ESTABLISH request primitive from the Layer Management, the IUA layer will try to establish an SCTP association with the remote IUA peer at an SG. Upon reception of an eventual SCTP-Communication Up confirm primitive from the SCTP, the IUA layer will invoke the primitive M-SCTP ESTABLISH confirm to the Layer Management. At the SG, the IUA layer will receive an SCTP Communication Up indication primitive from the SCTP. The IUA layer will then invoke the primitive M-SCTP ESTABLISH indication to the Layer Management. Once the SCTP association is establishedand assuming that the local IUA-User is ready, the local ASP IUA Application Server Process Maintenance (ASPM) function will initiate the ASPM procedures, using the ASP Up/-Down/-Active/-Inactive messages to convey the ASP-state to the SG - see Section 4.3.3. Morneault, Kalla, Rengasami, & Sidebottom [Page 37] Internet Draft ISDN Q.921 User Adaptation Layer Sep 2000 The Layer Management and the IUA layer on SG can communicate the status of the application server using the M-AS STATUS primitives. The Layer Managements and the IUA layers on both the SG and ASP can communicate the status of an SCTP association using the M-SCTP STATUS primitives. If the Layer Management on SG or ASP wants to bring down an SCTP association for management reasons, they would send M-SCTP RELEASE request primitive to the local IUA layer. The IUA layer would release the SCTP association and upon receiving the SCTP Communication Down indication from the underlying SCTP layer, it would inform the local Layer Management using M-SCTP RELEASE confirm primitive. If the IUA layer receives an SCTP-Communication Down indication from the underlying SCTP layer, it will inform the Layer Management by invoking the M-SCTP RELEASE indication primitive. The state of the ASP will be moved to "Down" at both the SG and ASP. At an ASP, the Layer Management may try to reestablish the SCTP association using M-SCTP ESTABLISH request primitive. 4.3.3 ASPM procedures for peer-to-peer messages All ASPM messages are sent on a sequenced stream to ensure ordering. SCTP stream '0' SHOULD be used. 4.3.3.1 ASP Up After an ASP has successfully established an SCTP association to an SG, the SG waits for the ASP to send an ASP Up message, indicating that the ASP IUA peer is available. The ASP is always the initiator of the ASP Up exchange. When an ASP Up message is received at an SG and internally the ASP is not considered locked-out for local management reasons, the SG marks the remote ASP as Up. The SG responds with an ASP Up Ack message in acknowledgement. The SG sends an-Up Ack message in response to a received ASP Up message even if the ASP is already marked as "Up" at the SG. If for any local reason the SG cannot respond with an ASP Up, the SG responds to a ASP Up with a Notify (ASP Down) message. At the ASP, the ASP Up Ack message received from the SG is not acknowledged by the ASP. If the ASP does not receive a response from the SG, or an ASP Down is received, the ASP may resend ASP Up messages every 2 seconds until it receives a ASP Up Ack message from the SG. The ASP may decide to reduce the frequency (say to every 5 seconds) if an ASP Up Ack is not received after a few tries. The ASP must wait for the ASP Up Ack message from the SG before sending any ASP traffic control messages (ASPAC or ASPIA) or Data messages or it will risk message loss. If the SG receives QPTM, ASP Active or ASP Inactive messages before an ASP Up is received, the SG should discard these messages. Morneault, Kalla, Rengasami, & Sidebottom [Page 37] Internet Draft ISDN Q.921 User Adaptation Layer Sep 2000 4.3.3.2 ASP Down The ASP will send an ASP Down to an SG when the ASP is to be removed from the list of ASPs in all Application Servers that it is a member. Whether the ASP is permanently removed from an AS is a function of configuration management. The SG marks the ASP as "Down" and returns an ASP Down Ack message to the ASP if one of the following events occur: - an ASP Down message is received from the ASP, - another ASPM message is received from the ASP and the SG has locked out the ASP for management reasons. The SG sends an ASP Down Ack message in response to a received ASP Down message from the ASP even if the ASP is already marked as "Down" at the SG. If the ASP does not receive a response from the SG, the ASP may send ASP Down messages every 2 seconds until it receives an ASP Down Ack message from the SG or the SCTP association goes down. The ASP may decide to reduce the frequency (say to every 5 seconds) if an ASP Down Ack is not received after a few tries. 4.3.3.3 IUA Version Control If a ASP Up message with an unsupported version is received, the receiving end responds with an Error message, indicating the version the receiving node supports and notifies Layer Management. This is useful when protocol version upgrades are being performed in a network. A node upgraded to a newer version should support the older versions used on other nodes it is communicating with. Because ASPs initiate the ASP Up procedure it is assumed that the Error message would normally come from the SG. 4.3.3.4 ASP Active Any time after the ASP has received a ASP Up Ack from the SG, the ASP sends an ASP-Active (ASPAC) to the SG indicating that the ASP is ready to start processing traffic. In the case where an ASP is configured/- registered to process the traffic for more than one Application Server across an SCTP association, the ASPAC contains one or more Interface Identifiers to indicate for which Application Servers the ASPAC applies. When an ASP Active (ASPAC) message is received, the SG responds to the ASP with a ASPAC Ack message acknowledging that the ASPAC was received and starts sending traffic for the associated Application Server(s) to that ASP. The ASP must wait for the ASP-Active Ack message from the SG before sending any Data messages or it will risk message loss. If the SG receives QPTM messages before an ASP Active is received, the SG should discard these messages. Morneault, Kalla, Rengasami, & Sidebottom [Page 38] Internet Draft ISDN Q.921 User Adaptation Layer Sep 2000 There are two modes of Application Server traffic handling in the SG IUA - Over-ride and Load-balancing. The Type parameter in the ASPAC message indicates the mode used in a particular Application Server. If the SG determines that the mode indicates in an ASPAC is incompatible with the traffic handling mode currently used in the AS, the SG responds with an Error message indicating Invalid Traffic Handling Mode. In the case of an Over-ride mode AS, reception of an ASPAC message at an SG causes the redirection of all traffic for the AS to the ASP that sent the ASPAC. The SG responds to the ASPAC with an ASP-Active Ack message to the ASP. Any previously active ASP in the AS is now considered Inactive and will no longer receive traffic from the SG within the AS. The SG sends a Notify (Alternate ASP-Active) to the previously active ASP in the AS, after stopping all traffic to that ASP. In the case of a load-share mode AS, reception of an ASPAC message at an SG causes the direction of traffic to the ASP sending the ASPAC, in addition to all the other ASPs that are currently active in the AS. The algorithm at the SG for loadsharing traffic within an AS to all the active ASPs is implementation dependent. The algorithm could, for example be round-robin or based on information in the Data message, such as Interface ID, depending on the requirements of the application and the call state handling assumptions of the collection of ASPs in the AS. The SG responds to the ASPAC with a ASP-Active Ack message to the ASP. 4.3.3.5 ASP Inactive When an ASP wishes to withdraw from receiving traffic within an AS, the ASP sends an ASP Inactive (ASPIA) to the SG. In the case where an ASP is configured/registered to process the traffic for more than one Application Server across an SCTP association, the ASPIA contains one or more Interface Ids to indicate for which Application Servers the ASPIA applies. There are two modes of Application Server traffic handling in the SG IUA when withdrawing an ASP from service - Over-ride and Load-balancing. The Type parameter in the ASPIA message indicates the mode used in a particular Application Server. If the SG determines that the mode indicates in an ASPAC is incompatible with the traffic handling mode currently used in the AS, the SG responds with an Error message indicating Invalid Traffic Handling Mode. In the case of an Over-ride mode AS, where normally another ASP has already taken over the traffic within the AS with an Over-ride ASPAC, the ASP which sends the ASPIA is already considered by the SG to be "Inactive" (i.e., in the "Up" state). An ASPIA Ack message is sent to the ASP, after ensuring that all traffic is stopped to the ASP. In the case of a Loadshare mode AS, the SG moves the ASP to the "Inactive" state and the AS traffic is re-allocated across the remaining "active" ASPs per the load-sharing algorithm currently used within the AS. An ASPIA Ack message is sent to the ASP after all traffic is halted to the ASP. A NTFY(Insufficient ASPs) may be sent to all inactive ASPs, if required. Morneault, Kalla, Rengasami, & Sidebottom [Page 39] Internet Draft ISDN Q.921 User Adaptation Layer Sep 2000 If no other ASPs are Active in the Application Server, the SG sends a NTFY(AS-Inactive) to all inactive ASPs of the AS and either discards all incoming messages for the AS or starts buffering the incoming messages for T(r)seconds, after which messages will be discarded. T(r) is configurable by the network operator. If the SG receives an ASPAC from an ASP in the AS before expiry of T(r), the buffered traffic is directed to the ASP and the timer is cancelled. 4.3.3.6 Notify In the case where a Notify (AS-Inactive) message is sent by an SG that now has no ASPs active to service the traffic or a NTFY (Insufficient ASPs), the Notify message does not force the ASP(s) receiving the message to become active. The ASPs remain in control of what (and when) action is taken. 4.3.3.7 Heartbeat The optional Heartbeat procedures may be used when operating over transport layers that do not have their own heartbeat mechanism for detecting loss of the transport association (i.e., other than the SCTP). Once the ASP sends an ASP Up message to the SG, the ASP sends Beat messages periodically, subject to a provisionable timer T(beat). The SG IUA, upon receiving a BEAT message from the ASP, responds with a BEAT message. If no BEAT message (or any other IUA message), is received from the ASP within the timer 2*T(beat), the ASP will consider the remote IUA as 'Down". The SG will also send an ASP Down Ack message to the ASP. At the ASP, if no BEAT message (or any other IUA message) is received from the SG within 2*T(beat), the SG is considered unavailable. Transmission of BEAT messages is stopped and ASP Up procedures are used to re-establish communication with the SG IUA peer. Note: Heartbeat related events are not shown in Figure 4 "ASP state transition diagram". 5.0 Examples 5.1 Establishment of Association and Traffic between SGs and ASPs 5.1.1 Single ASP in an Application Server (1+0 sparing) This scenario shows the example IUA message flows for the establishment of traffic between an SG and an ASP, where only one ASP is configured within an AS (no backup). It is assumed that the SCTP association is already set-up. Morneault, Kalla, Rengasami, & Sidebottom [Page 40] Internet Draft ISDN Q.921 User Adaptation Layer Sep 2000 SG ASP1 | |<---------ASP Up----------| |--------ASP Up Ack------->| | | |<-------ASP Active--------| |------ASP Active Ack----->| | | 5.1.2 Two ASPs in Application Server (1+1 sparing) This scenario shows the example IUA message flows for the establishment of traffic between an SG and two ASPs in the same Application Server, where ASP1 is configured to be Active and ASP2 a standby in the event of communication failure or the withdrawal from service of ASP1. ASP2 may act as a hot, warm, or cold standby depending on the extent to which ASP1 and ASP2 share call state or can communicate call state under failure/withdrawal events. The example message flow is the same whether the ASP-Active messages are Over-ride or Load-share mode although typically this example would use an Over-ride mode. SG ASP1 ASP2 | | | |<--------ASP Up----------| | |-------ASP Up Ack------->| | | | | |<-----------------------------ASP Up----------------| |----------------------------ASP Up Ack------------->| | | | | | | |<-------ASP Active-------| | |-----ASP Active Ack----->| | | | | 5.1.3 Two ASPs in an Application Server (1+1 sparing, load-sharing case) This scenario shows a similar case to Section 5.1.2 but where the two ASPs are brought to active and load-share the traffic load. In this case, one ASP is sufficient to handle the total traffic load. SG ASP1 ASP2 | | | |<---------ASP Up---------| | |--------ASP Up Ack------>| | | | | |<------------------------------ASP Up---------------| |-----------------------------ASP Up Ack------------>| | | | | | | |<--ASP Active (Ldshr)----| | |----ASP Active Ack------>| | | | | |<----------------------------ASP Active (Ldshr)-----| |-----------------------------ASP Active Ack-------->| | | | Morneault, Kalla, Rengasami, & Sidebottom [Page 41] Internet Draft ISDN Q.921 User Adaptation Layer Sep 2000 5.1.4 Three ASPs in an Application Server (n+k sparing, load-sharing case) This scenario shows the example IUA message flows for the establishment of traffic between an SG and three ASPs in the same Application Server, where two of the ASPs are brought to active and share the load. In this case, a minimum of two ASPs are required to handle the total traffic load (2+1 sparing). SG ASP1 ASP2 ASP3 | | | | |<------ASP Up-------| | | |-----ASP Up Ack---->| | | | | | | |<--------------------------ASP Up-------| | |------------------------ASPUp Ack)----->| | | | | | |<---------------------------------------------ASP Up--------| |--------------------------------------------ASP Up Ack----->| | | | | | | | | |<-ASP Act (Ldshr)---| | | |----ASP Act Ack---->| | | | | | | |<---------------------ASP Act (Ldshr)---| | |----------------------ASP Act Ack------>| | | | | | 5.2 ASP Traffic Fail-over Examples 5.2.1 (1+1 Sparing, withdrawal of ASP, Back-up Over-ride) The following example shows a case in which an ASP withdraws from service: SG ASP1 ASP2 | | | |<-----ASP Inactive-------| | |----ASP Inactive Ack---->| | |-------------------NTFY(AS-Pending) (Optional)----->| | | | |<------------------------------ ASP Active----------| |-----------------------------ASP Active Ack)------->| | | In this case, the SG notifies ASP2 that the AS has moved to the Down state. The SG could have also (optionally) sent a Notify message when the AS moved to the Pending state. Note: If the SG detects loss of the IUA peer (IUA heartbeat loss or detection of SCTP failure), the initial SG-ASP1 ASP Inactive message exchange would not occur. Morneault, Kalla, Rengasami, & Sidebottom [Page 42] Internet Draft ISDN Q.921 User Adaptation Layer Sep 2000 5.2.2 (1+1 Sparing, Back-up Over-ride) The following example shows a case in which ASP2 wishes to over-ride ASP1 and take over the traffic: SG ASP1 ASP2 | | | |<-------------------------------ASP Active----------| |-----------------------------ASP Active Ack-------->| |----NTFY( Alt ASP-Act)-->| | (optional) | | In this case, the SG notifies ASP1 that an alternative ASP has overridden it. 5.2.3 (n+k Sparing, Load-sharing case, withdrawal of ASP) Following on from the example in Section 5.1.4, and ASP1 withdraws from service SG ASP1 ASP2 ASP3 | | | | |<----ASP Inact------| | | |---ASP Inact Ack--->| | | | | | | |---------------------------------NTFY(Ins. ASPs)(Optional)->| | | | | |<-----------------------------------------ASP Act (Ldshr)---| |-------------------------------------------ASP Act (Ack)--->| | | | | The Notify message to ASP3 is optional, as well as the ASP Active from ASP3. The optional Notify can only occur if the SG maintains knowledge of the minimum ASP resources required for example if the SG knows that n+k = 2+1 for a load-share AS and n currently equals 1. Note: If the SG detects loss of the ASP1 IUA peer (IUA heartbeat loss or detection of SCTP failure), the first SG-ASP1 ASP Inactive message exchange would not occur. 5.3 Q.921/Q.931 primitives backhaul Examples An example of the message flows for establishing a data link on a signalling channel, passing PDUs and releasing a data link on a signalling channel is shown below. An active association between MGC and SG is established (section 5.1) prior to the following message flows. Morneault, Kalla, Rengasami, & Sidebottom [Page 43] Internet Draft ISDN Q.921 User Adaptation Layer Sep 2000 SG ASP <----------- Establish Request Establish Confirm ----------> <----------- Data Request Data Indication -----------> <----------- Data Request Data Indication -----------> <----------- Data Request <----------- Data Request Data Indication -----------> <----------- Release Request (RELEASE_MGMT) Release Confirm ----------> An example of the message flows for a failed attempt to establish a data link on the signalling channel is shown below. In this case, the gateway has a problem with its physical connection (e.g. Red Alarm), so it cannot establish a data link on the signalling channel. SG ASP <----------- Establish Request (ESTABLISH_START) Release Indication ----------> (RELEASE_PHYS) 5.4 Layer Management Communication Examples An example of the message flows for communication between Layer Management modules between SG and ASP is shown below. An active association between ASP and SG is established (section 5.1) prior to the following message flows. SG ASP <----------- Data Request Error Indication ----------> (INVALID_TEI) <----------- TEI Status Request TEI Status Confirm ----------> (Unassigned) 6.0 Security IUA is designed to carry signaling messages for telephony services. As such, IUA must involve the security needs of several parties the end users of the services; the network providers and the applications involved. Additional requirements may come from local regulation. While having some overlapping security needs, any security solution should fulfill all of the different parties' needs. Morneault, Kalla, Rengasami, & Sidebottom [Page 44] Internet Draft ISDN Q.921 User Adaptation Layer Sep 2000 6.1 Threats There is no quick fix, one-size-fits-all solution for security. As a transport protocol, IUA has the following security objectives: * Availability of reliable and timely user data transport. * Integrity of user data transport. * Confidentiality of user data. IUA runs on top of SCTP. SCTP [3] provides certain transport related security features, such as * Blind Denial of Service Attacks * Flooding * Masquerade * Improper Monopolization of Services When IUA is running in professionally managed corporate or service provider network, it is reasonable to expect that this network includes an appropriate security policy framework. The "Site Security Handbook" [6] should be consulted for guidance. When the network in which IUA runs in involves more than one party, it may not be reasonable to expect that all parties have implemented security in a sufficient manner. In such a case, it is recommended that IPSEC is used to ensure confidentiality of user payload. Consult [7] for more information on configuring IPSEC services. 6.2 Protecting Confidentiality Particularly for mobile users, the requirement for confidentiality may include the masking of IP addresses and ports. In this case application level encryption is not sufficient; IPSEC ESP should be used instead. Regardless of which level performs the encryption, the IPSEC ISAKMP service should be used for key management. 7.0 IANA Considerations A request will be made to IANA to assign an IUA value for the Payload Protocol Identifier in SCTP Payload Data chunk. The following SCTP Payload Protocol Identifier will be registered: IUA 0x1 The SCTP Payload Protocol Identifier is included in each SCTP Data chunk, to indicate which protocol the SCTP is carrying. This Payload Protocol Identifier is not directly used by SCTP but may be used by certain network entities to identify the type of information being carried in a Data chunk. The User Adaptation peer may use the Payload Protocol Identifier as a way of determining additional information about the data being presented to it by SCTP. Morneault, Kalla, Rengasami, & Sidebottom [Page 45] Internet Draft ISDN Q.921 User Adaptation Layer Sep 2000 8.0 Acknowledgements The authors would like to thank Alex Audu, Ming-te Chao, Keith Drage, Norm Glaude, Nikhil Jain, Ming Lin, Stephen Lorusso, John Loughney, Barry Nagelberg, Neil Olson, Lyndon Ong, Heinz Prantner, Michael Tuexen and Hank Wang for their valuable comments and suggestions. 9.0 References [1] ITU-T Recommendation Q.920, 'Digital Subscriber Signalling System No. 1 (DSS1) - ISDN User-Network Interface Data Link Layer - General Aspects' [2] T1S1.7/99-220 Contribution, 'Back-hauling of DSS1 protocol in a Voice over Packet Network' [3] Stream Control Transmission Protocol, draft-ietf-sigtran-sctp-13.txt, Sep 2000 [4] Media Gateway Control Protocol (MGCP), draft-huitema-megaco-mgcp-v1-03.txt, August 1999 [5] Architectural Framework for Signaling Transport, RFC 2719 , October 1999 [6] Site Security Handbook, RFC 2196, September 1997 [7] Security Architecture for the Internet Protocol, RFC 2401 10.0 Author's Addresses Ken Morneault Tel +1-703-484-3323 Cisco Systems Inc. EMail kmorneau@cisco.com 13615 Dulles Technology Drive Herndon, VA. 20171 USA Malleswar Kalla Tel +1-973-829-5212 Telcordia Technologies EMail kalla@research.telcordia.com MCC 1J211R 445 South Street Morristown, NJ 07960 USA Selvam Rengasami Tel +1-732-758-5260 Telcordia Technologies EMail srengasa@telcordia.com NVC-2Z439 331 Newman Springs Rd Red Bank, NJ 07701 USA Greg Sidebottom Tel +1-613-763-7305 Nortel Networks EMail gregside@nortelnetworks.com 3685 Richmond Rd, Nepean, Ontario Canada K2H5B7 Morneault, Kalla, Rengasami, & Sidebottom [Page 46]