H.248 Protocol Mechanism

Termination ID

A termination ID identifies a termination that is going to register or deregister a service. The termination ID of each termination is unique. During service configuration, the termination ID corresponding to each termination must be configured on the MG and MGC. The root termination ID represents an entire MG. The ServiceChange command executed on the root termination ID is effective on an entire MG. The wildcard can be used.

H.248 Interface Registration Mechanism

The MG sends the ServiceChangeRequest command to inform the MGC that a user or a group of users are about to register or deregister a service. After this command is executed successfully, the termination status is changed to InService or OutOfService. In addition, the MGC can unsolicitedly send the ServiceChangeRequest command to request the MG to register or deregister a service for a user or a group of users.

Figure 4-2 shows the registration flow of the H.248 AG.

• The MG sends the ServiceChangeRequest command to the MGC. In the command, TerminationId is Root, Method is Restart, and ServiceChangeReason is 901 (cold boot), 902 (warm boot), or 900 (in other cases).
• The MGC sends the Reply message to the MG indicating the successful registration.
• The MGC sends the Modify command to the MG requesting the MG to detect the offhook of all users (al/of).
• The MG responds to the MGC with the Reply message.

Figure 4-2 H.248 AG registration flow

H.248 Interface Heartbeat Mechanism

After the registration is successful, the MG and MGC maintain communication by sending each other the heartbeat message Notify (it/ito). By default, the heartbeat message is sent every 60s. The sending interval can be set within the range of 5s to 655s.

After the MG sends the first heartbeat message to the MGC, if the MG does not receive the heartbeat response from the MGC before the preset interface heartbeat timer (for example, the length of three sending intervals) times out, the MG sets the interface status to wait for response. Then, the MG keeps initiating a registration with the MGC. If dual-homing is configured, the MG initiates registration with the two MGCs alternatively.

H.248 Interface Deregistration Mechanism

Figure 4-3 shows the unsolicited deregistration flow of the MG.

• The MG sends the ServiceChangeRequest command to the MGC. In the command, TerminationId is Root, Method is Restart, and ServiceChangeReason is 905 (indicates that the termination is taken out of service because of maintenance operation, and now the MG uses 905 to initiate a deregistration request through command lines).
• The MGC sends the Reply message to the MG indicating a successful deregistration.

Figure 4-3 Unsolicited deregistration flow of the MG

Figure 4-4 shows the flow of the MGC unsolicitedly deregistering the MG.

• The MGC sends the ServiceChangeRequest command to the MG. In the command, TerminationId is Root, Method is Forced, and ServiceChangeReason is 905.
• The MG responds to the MGC with the Reply message. The MG supports the registration and deregistration of not only an entire MG but also a single termination. The service status of a single user can be changed through the registration and deregistration of a single termination.

Figure 4-4 Unsolicited deregistration flow of the MGC

H.248 Interface Authentication Mechanism

Figure 4-5 shows the authentication flow.

• The MG sends the ServiceChange command to register with the MGC. The command contains the digital signature of the MG.
• After receiving the ServiceChange command, the MGC verifies the MG and sends a reply.
• The MGC sends the Modify message to the MG. The message contains the required algorithm ID and random number.
• The MG verifies the message sent by the MGC and sends a reply.
• The MGC authenticates the MG periodically.
• The MG sends replies to the MGC.

Figure 4-5 Authentication flow