Information Technology Reference
In-Depth Information
In Figure 3-6, H.225 call control signaling is used to set up a call between Endpoint 2 and Endpoint 1 (messages 1[nd]4). The Connect
message is used to communicate the IP address and TCP port that will be used to set up a connection for H.245.
The two endpoints now negotiate terminal capabilities, such as DTMF relay, hookflash relay, and supported codecs using Terminal
Capability Set and Terminal Capability Set Ack messages.
At this point, the endpoints also determine the master/slave relationship using Master Slave Determination and Master Slave
Determination Ack messages. The endpoint that becomes the master controls the session.
After capabilities exchange and master/slave determination takes place, the next step is for the endpoints to begin logical channel
establishment.
Logical channel establishment comprises the initiation of unidirectional RTP/RTCP streams between the endpoints. Logical channel
establishment is initiated using the Open Logical Channel and Open Logical Channel Ack message types.
The Open Logical Channel messages specify media channel parameters, such as UDP ports for RTP/RTCP, codec, DTMF support,
and so on. Open Logical Channel Ack is used to indicate that the endpoint will accept the media, as well as to confirm IP addresses
and ports to use for RTP.
As you can see from Figure 3-6, regular call setup can be involved. Call setup can be expedited by using a method called H323 Fast
Start (or Fast Connect), which involves carrying H.245 information in H.225 messages.
The following example shows the configuration of an IOS H.323 gateway that's integrated with CUCM:
voice service voip
h323
ccm-compatible
!
interface GigabitEthernet1/0
ip address 10.2.2.1 255.255.255.0
h323-gateway voip bind srcaddr 10.2.2.1
!voice class h323 1
h225 timeout tcp establish 3
!
dial-peer voice 20 voip
preference 1
destination-pattern 5...
 
Search WWH ::




Custom Search