Media Gateway (MG) Stack

MG(4) provides an introductory manual page for MG Switching stack components and interfaces. You can also select one of the component or interface sections from the diagram below:

Components

Interfaces

Components

MG Stack Manager (MGLM)

This section provides a roadmap to Manual Pages for Voice over IP (VoIP) Stack Manager (VoIP SM).

Media Gateway (MG)

This section provides a roadmap to Manual Pages for Media Gateway (MG).

H.248/MEGACO

This section provides a roadmap to Manual Pages for Media Gateway Control (H.248/MEGACO).

Media Gateway Control Protocol (MGCP)

This section provides a roadmap to Manual Pages for Media Gateway Control Protocol (MGCP).

Channel Driver

This section provides a roadmap to Manual Pages for Multiplex/Channel (MX/CH).

Real-Time Transport Protocol (RTP)

This section provides a roadmap to Manual Pages for Real-Time Transport Protocol (RTP).

CHI

Section: Channel Interface (CHI) (7)
Updated: 2008-10-31
Index Return to Main Contents

NAME

chi - Channel Interface

SYNOPSIS

#include <ss7/chi.h>
#include <ss7/chi_ioctl.h>

int ch_stream = open(ch_device, flags);

DESCRIPTION

The Channel Interface, CHI, specifices a STREAMS(4)-based kernel-level instantiation of a Channel interface definition compatible with the Multiplex, mx(4), and Media Gateway mg(4), drivers. The Channel Interface (CHI) enables the user of a channel to access and use any variety of conforming communications media channels, without specific knowledge of the provider's protocol. The service interface is designed to support any media channel service provider, and does not address issues concerning channel management, protocol performance, and performance analysis tools. The specification assumes that the reader is familiar with ITU-T synchronous digital hierarchy and STREAMS(4).

CHI specifies an interface that supports the service provided by various low level device drivers such as the X400P-SS7 driver, x400p(4), and X100P-SS7 driver x100p(4). These specifications are targeted for use by developers and testers fo protocol modules that require channel service.

The Channel Services Provider

The Channel Services Provider provides the means to manage the connection and disconnection of channels. It is a local control protocol in the sense that there not necessarily any remote peer entitites. Communications is between the local user entity and the local provider entity.

Model of the CHI

The CHI defines the service provided by the channel services provider to channel services user at the boundary between the channel services provider and the channel services user entity. The interface consists of a set of primitives defined as STREAMS(4) messages that provide access to the channel services, and a transferred between the channel services user entity and the channel services provider entity. These primitives are of two types: ones that originate from the channel services user (CSU), and other tha originate from the channel services provider (CSP). The primitives that originate from the CSU make requests to the CSP, or respond to an indication or event of the CSP. The primitives that originate from the CSP are etiher confirmation of a requies or are indications to the CSU that an event has occured.

The CHI allows the CSP to be configured with any media streams (such as G.703/G.704 digital channels) that also conform to the CHI. A CSU can also be a user program that conforms to the CHI and accesses the CSP via putmsg(2) and getmsg(2) system calls.

CHI Services: The features of the CHI are defined in terms of services provided by the CSP, and the individual primitives that may flow between the CSU and CSP.
Local Management: The CHI specification also defines a set of local management functions. These services have significance only to the local stream.

CHI SERVICES DEFINITION

Local Management Services

The channel service provider provides the following local management services:

Information Service. The information service provides the channel service user with the ability to query the channel service provider concerning options and parameters specific to the channel service provider and associated with an attached channel. The information service uses the following primitives:

---: CH_INFO_REQ(7): Request information about the attached channel and channel service provider.
---: CH_INFO_ACK(7): Indicates information about the attached channel and channel service provider.

Options Management Service. The options management service provides a mechanism whereby the channel service user can query and change parameters associated with the attached channel and manage options associated with the channel service provider. The options management service uses the following primitives:

---: CH_OPTMGMT_REQ(7): Manage the specified options.
---: CH_OPTMGMT_ACK(7): Acknowledge that the management of the previously specified options is complete.

Channel Attachment Service. The channel attachment service provides the channel service user with the ability to attach a specified channel to the requesting stream for a stream associated with a CH_STYLE2 channel service provider. The channel attachment service is not available on a stream associated with a CH_STYLE1 channel service provider. The channel attachment service uses the following primitives:

---: CH_ATTACH_REQ(7): Attach the specified channel to the requesting stream.

Channel Detachment Service. The channel detachment service provides the channel service user with the ability to detach a previously attached channel from the requesting stream. The requesting stream must be associated with a CH_STYLE2 channel service provider and must have previously successfully executed a CH_ATTACH_REQ(7) primitive. The channel detachment service uses the following primitives:

---: CH_DETACH_REQ(7): Detach the currently attached channel from the requesting stream.

Receipt Acknowledgment Service. The receipt acknowlegment service provides an indication to the channel service user of the positive or negative acknowledgment of the previous primitive issued by the channel service user. The receipt acknowledgement service uses the following primitives:

---: CH_OK_ACK(7): Successful receipt acknowledgment.
---: CH_ERROR_ACK(7): Unsuccessful receipt acknowledgement.

Connection Services

The channel service provider provides the following connection services:

Enable Service. The enable service provides the channel service user with the ability to enable the attached channel. Some channel service providers can enable channels (prepare them for operation) locally, and others will require exchanges with the transmission peer that will take some time before the channel can be enabled. The enable service uses the following primitives:

---: CH_ENABLE_REQ(7): Request that the attached channel be enabled. This primitives requires local acknowledgment.
---: CH_ENABLE_CON(7): Confirms that the attached channel has been enabled as requested.

Disable Service. The disable service provides the channel service user with the ability to disable the attached channel. Some channel service providers can disable channels (remove them from operation) locally, and others will require exchanges with the transmission peer that may take some time before the channel can be disabled. In addition, it is possible tha an autonomous disabling of the channel occurs without the request of the channel service user. In this case, the channel disable service is used to indicate to the channel service user that an autonomous disabling of the channel has occured. The disable service uses the following primitives:

---: CH_DISABLE_REQ(7): Request that the attached enabled channel be disabled. This primitives requires local acknowledgment.
---: CH_DISABLE_CON(7): Confirms that the attached channel has been enabled as requested.
---: CH_DISABLE_IND(7): Indicates that the attached channel has autonomously been disabled.

Connect Service. The connect service provides the channel service user iwth the ability to connect an enabled channel in the receive and/or transmit directions. Some channel service providers can connect channels locally, and others will required exchanges with the transmission peer that will take some time before the channel can be connected in the specified direction. The connect service uses the following primitives:

---: CH_CONNECT_REQ(7): Requests that the attached and enabled channel be connected in the specified direction. This primitives requires local acknowledgment.
---: CH_CONNECT_CON(7): Confirms that the attached and enabled channel has been connected in the indicated directions as requested.

Disconnect Service. The disconnect service provides the channe service user with the ability to disconnect a connected channel in the specified receive or transmit directions. Some channel service providers can disconnect channels locally, and others will require exchanges with the transmission peer tha may take some time before the channel can be disconnected in the specified direction. In addition, it is possible that an autonomous disconnection occurs without the request of the channel service user. In this case, the channel disconnect service is used to indicate to the channel service user that an autonomous disconnection has occurred in the indicated directions. The disconnect service uses the following primitives:

---: CH_DISCONNECT_REQ(7): Requests that the attached, enabled and connected channel be disconnected in ths specified directions. This primitives requires local acknowledgment.
---: CH_DISCONNECT_CON(7): Confirms that the attached, enabled and connected channel has been disconnected in the indicated directions as requested.
---: CH_DISCONNECT_IND(7): Indicates that the channel has been autonomously disconnected in the indicated directions.

Event Services

The channel service provider provides the following event services:

Notification Service. The notification service is used by the channel service provider to inform the channel service user that a specific event has occured. The notification service uses the following primitives:

---: CH_EVENT_IND(7): Indicates that the indicated event has occured.

Media Services

The channel service provider provides the following media services:

Data Transfer Service. The data transfer service is used by the channel service user to request the transmission of channel media data on the channel. It is also used by the channel service provider to indicate the reception of channel media data on the channel. The data transfer service uses the following primitives:

---: CH_DATA_REQ(7): Requests that the specified media data be transmitted.
---: CH_DATA_IND(7): Indicates that the indicated media data was received.

OPTIONS

The Channel Interface (CHI) does not define any general options at this time. Options specific to the underlying CH provider will be defined in the manual page for the specific CH provider.

CAVEATS

This documentation is not complete and needs some work before it is finalized.

FILES

The Channel Interface (CHI) is defined in the <sys/chi.h> and <sys/chi_ioctl.h> header files. Additional header files are specified by specific providers of the CHI interface.

DEVICES

The Channel Inteface (CHI) does not provide any devices of its own. Specific providers of the interface will provide their own devices.

MODULES

Some generic STREAMS(4) modules can be provided that convert between the CHI interface and other interfaces (such as the MXI).

VERSIONS

This manpage was written for CHI Version 1.

REFERENCES

[1]: CHI, Channel Interface (CHI) Specification, Revision 0.9.2, Draft 2, July 15, 2007, (Edmonton, Canada), B. Bidulock, OpenSS7 Corporation. <http://www.openss7.org/specs/chi.pdf>