Registration Request
The RRQ message is a request from a terminal or a gateway to a gatekeeper to register, as
shown in Figure 8-4.
452 Authorized Self-Study Guide: Cisco Voice over IP (CVOICE)
V
Gateway A
Gatekeeper
RCF RCF
RRQ RRQ
Terminal
Figure 8-4 Registration Request
If the gatekeeper responds with an RCF message, the terminal will use the responding
gatekeeper for future calls. If the gatekeeper responds with an RRJ message, the terminal
must seek another gatekeeper with which to register.
An H.323 gateway learns of a gatekeeper by using a static configuration or dynamic discovery.
Static configuration simply means configuring the gatekeeper’s IP address on an
interface used for H.323 signaling.
Following is an example of the information used to register an H.323 ID or an E.164
address:
■ H323 ID: gatewayname@domain.com
■ E.164 address: 4085551212
Lightweight Registration
Prior to H.323 version 2, Cisco gateways reregistered with the gatekeeper every 30 seconds.
Each registration renewal used the same process as the initial registration, even
though the gateway was already registered with the gatekeeper. This behavior generated
considerable overhead at the gatekeeper. H.323 version 2 defines a lightweight registration
procedure that still requires the full registration process for initial registration, but
uses an abbreviated renewal procedure to update the gatekeeper and minimize overhead.
Lightweight registration, as illustrated in Figure 8-5, requires each endpoint to specify a
Time to Live (TTL) value in its RRQ message. If the endpoint does not indicate a TTL, the
gatekeeper assigns one and sends it to the gateway in the RCF message. When a gatekeeper
receives an RRQ message with a TTL value, it returns an updated TTL timer value
in an RCF message to the endpoint. Shortly before the TTL timer expires, the endpoint
sends an RRQ message with the keepalive field set to True, which refreshes the existing
registration. No configuration changes are permitted during a lightweight registration, so
all fields are ignored other than the endpoint identifier, gatekeeper identifier, tokens, and
TTL. With H.323 version 1, endpoints cannot process the TTL field in the RCF. The gatekeeper
probes the endpoint with IRQs for a predetermined grace period to learn if the
endpoint is still alive.
Chapter 8: Configuring H.323 Gatekeepers 453
V
RCF
TTL
RRQ
RRQ
Keepalive
The gateway sends an
RRQ message with
Keepalive = True before
the TTL timer expires.
Gatekeeper sends a TTL
timer in an RCF message.
Figure 8-5 Lightweight Registration