4.12.1. Performing Registration Operations

Global Call provides a number of options for registration and manipulation of registration information. The Global Call API simplifies and abstracts the network RAS messages in H.323 and Registrar messages in SIP. The following functionality is supported:

• Locating a registration server (gatekeeper in H.323 or registrar in SIP) via unicast or multicast (RAS messages: LRQ/LCF/LRJ, GRQ/GCF/GRJ)
• Registration (RAS message: RRQ)
• Specifying one-time or periodical registration (RAS message: RRQ)
• Changing registered information (RAS message: RRQ)
• Removing registered information by value (RAS message: RRQ)
• Sending non-standard registration message (RAS message: NonStandardMessage)
• Deregistering (RAS messages: URQ/UCF/URJ)
• Handling calls according to the gatekeeper policy for directing and routing calls (RAS messages: ARQ/ACF/ARJ, DRQ/DCF/DRJ)

Note: For detailed information on RAS negotiation, see ITU-T Recommendation H.225.0.

Locating a Registration Server

A Global Call application can choose to use a known address for the registration server (gatekeeper in H.323 or registrar in SIP) or to discover a registration server by multicasting to a well-known address on which registration servers listen. This choice is determined by the IP address specified as the registration address during registration.

The registration address is specified in the IPPARM_REG_ADDRESS parameter of the IPSET_REG_INFO parameter set. The IPPARM_REG_ADDRESS is of type IP_REGISTER_ADDRESS which contains the reg_server field that is the address value. A specific range of IP addresses are reserved for multicast transmission:

• If the application specifies an address in the range of multicast addresses or specifies the default multicast address (IP_REG_MULTICAST_DEFAULT_ADDR), then registration server discovery is selected.
• If the application specifies an address outside the range of multicast addresses, then registration with a specific server is selected.

Notes:

1. The application can specify the maximum number of hops (connections between routers) in the max_hops field of the IP_REGISTER_ADDRESS structure. This field applies only to H.323 applications using gatekeeper discovery (H.225 RAS) via the default multicast registration address.
2. When using H.323, the port number used for RAS is one less than the port number used for signaling. Consequently, to avoid a conflict when configuring multiple IPT board devices in the IPCCLIB_START_DATA structure, do not assign consecutive H.323 signaling port numbers to IPT board devices. See Section 3.4.19, gc_Start( ) for more information.

Registration

An application can use the gc_ReqService( ) function to register with a gatekeeper/registrar. The registration information in this case is included in the GC_PARM_BLK associated with the gc_ReqService( ) function. See Section 4.12.4, Registration Code Example for more information.

Specifying One-Time or Periodic Registration

Global Call enables an application to specify a one-time registration or periodic registration where information is re-registered with the gatekeeper/registrar at the interval (in seconds) specified by the application. This is achieved by setting the time_to_live parameter in the IP_REGISTER_ADDRESS structure. If the parameter is set to zero, then the stack uses one-time registration functionality. If the parameter is set to a value greater than zero, for example 5, then each registration with the server is valid for 5 seconds and the stack will automatically refresh its request before timeout. Registered applications are not notified of the refresh transactions.

When using SIP, periodic registration is also supported. The behavior depends on the time_to_live value specified in the IP_REGISTER_ADDRESS structure as follows:

• If the time_to_live value is specified, registration is done with this value set in the Expires header.
• If the time_to_live value is zero, the call control library automatically sets the Expires header to a value of 3600 seconds, which is treated as an application-specified time_to_live value.

Note: The actual expiration time for registration is determined by the registrar. The expiration time received from the registrar is stored and when half of this time expires, re-registration occurs.

Changing Registered Information

Global Call provides the ability to modify or add to the registration information after it has been registered with the gatekeeper/registrar. To change registration information, use the gc_ReqService( ) function. The GC_PARM_BLK in this context should contain an element with a set ID of IPSET_REG_INFO and a parameter ID of IPPARM_OPERATION_REGISTER with a value of:

• IP_REG_SET_INFO - To override existing registration.
• IP_REG_ADD_INFO - To add to existing registration information.

The overriding or additional information is contained in other elements in the GC_PARM_BLK. The elements that can be included are given in Table 3, Registration Information.

Removing Registered Information by Value

When an application needs to delete one (or more) of its aliases or supported prefixes from the list, it may use the gc_ReqService( ) function. The GC_PARM_BLK in this context should contain an element with a set ID of IPSET_REG_INFO and a parameter ID of IPPARM_OPERATION_REGISTER with a value of IP_REG_DELETE_BY_VALUE. If the string is registered, it will be deleted from the database and an updated list will be sent to the gatekeeper.

Note: When using IPPARM_OPERATION_REGISTER, the value IP_REG_DELETE_ALL is prohibited.

Sending Nonstandard Registration Messages

Global Call provides the ability to send nonstandard messages to and receive nonstandard messages from the gatekeeper or registrar. To send nonstandard messages, the application uses the gc_Extension( ) function. The first element must be set as described in Section 6.13, IPSET_MSG_REGISTRATION Parameter Set. Other elements are set as in conventional nonstandard messages; see Section 6.14, IPSET_NONSTANDARDDATA Parameter Set.

Deregistering

Global Call provides the ability to deregister from a gatekeeper/registrar. To deregister, an application uses the gc_ReqService( ) function. When deregistering, the application can decide whether to keep the registration information locally or delete it. The GC_PARM_BLK in this context should contain an element with a set ID of IPSET_REG_INFO and a parameter ID of IPPARM_OPERATION_DEREGISTER with a value set to either:

• IP_REG_MAINTAIN_LOCAL_INFO - To keep the registration information locally.
• IP_REG_DELETE_ALL - To delete the registration information stored locally.

See Section 4.12.5, Deregistration Code Example for more information.

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