H323 Gateway Configuration and Troubleshooting

H323 PROTOCOL:

• H.225 handles call setup and teardown and q.931 operations.
• H.225 RAS
• H.245 Feature negotiation (codec negotiation)
• H.261/H.263 -->Video Register admission status-->Handles the   gatekeeper conferencing
• H.450 Supplementary services (Hold etc)
• H323 Fast start(default)-->combining the H.225 and H.245 signalling in a single message.
• T.120-->Data Transfer 
•  Video codec -->H.261 & H.263 
•  H.245 Control signalling & Capabilities exchange 
•  H.225 Call signalling, Registration & RAS control  port 1720

Why would we use H323?

1) Widely supported and interoperated(h323 is the default protocol for Cisco)

2) It supports Fractional PRI

3) You want caller-id support on FXO or T1 CAS-->H323 Supports whereas MGCP doest not support.

Explanation: you are getting an incoming call from PSTN through FXO port on MGCP gateway and MGCP Gateway is connected to call manager. The caller id information you will not get when using the MGCP.

4) PRI Call preservation:

When the call agent CUCM goes down then h323 doesn’t not drop call.  In case of MGCP also call will not be dropped but for MGCP PRI backhaul the calls are dropped.

5) Many call routing and manipulation options

6) Supports NFAS( Non facility associated signaling): one signaling for multiple PRI lines--Result you will have more channels.

7) H.323 gatekeeper support-->Call admission control

H.323 configuration

Enabling  the H.323 service in the Voice Gateway

conf t

voice service voip

h323

no shutdown

Verify gateway status

show gateway

H323 Gateway Addition in call Manager:

·         H323 and SIP gateway never registers with the Call Manager.

·         Call Manager shows the status of the H323/SIP Gateway as Unknown.

·         When adding the H323 Gateway always select the option H323 Gateway in the add Gateway option. For MGCP Gateway addition you need to select the appropriate model.

Cisco CM Administration----->device menu--->Gateway--->Add new-->H323 gateway-->device name==>ip-address

·         Assign the gateway to the Route Pattern for routing the calls to the gateway

In the Main menu Call routing--->Route Hunt---> Route pattern-->Add new-->

Route Pattern ==>  e.g 5001

Gateway/Route list  ==> Ip-address of h323 gateway.

Configuration of H323 Gateway to communicate with CallManager:

Step 1: Create a Loop back interface

H323 Gateways do a recursive route table lookup for finding the destination network and use the router closest interface as the source address for commmunicating with the CUCM.

H323 bind command ensures the H323 gateway uses the same address every time it communicating with the CUCM.

conf  t

int loopback 0

ip address 192.168.1.19 255.255.255.255

h323-gateway voip interface

h323-gateway voip

Step 2: To route calls from the H323 Gateway to the CUCM --> Configure atleast one VOIP dial-peer

Step 3: Enabling the H323 Service

Enters voice-service voip configuration mode

Router(config)#voice service  voip   //This commands will let you to enable H.323 as VoIP service and enters h323 configuration mode

Roter(config-voi-serv)#h323

Router(config-serv-h323)#telephony-service ccm-compatible // This command will enable Call Manager compatibility for H323

 Step 4: Interaction between the call manager and the H323 Gateway

Router# conf t

Router(Config)# int fa0/0

Router(config-fa)# ip address 192.168.1.10 255.255.255.0

Router(config-fa)h323-gateway voip interface // This command will bind interface IP Address with H323 for signaling. It used because H323 signaling contains different source address so to make it a single ip address need to bind with interface

Router(config-fa)#h323-gateway voip h323-id HVoiceGW1 //Giving the  ID HVoiceGW1 to the gateway

Router(config-if)#h323-gateway voip bind srcaddr   // Assign the ip address of the interface connected to the call manager or the ip address of the Loop back interface

Note for H323 gateway

·         Fast connect(fast start) -->In a sense, this tunnels H.245 traffic inside H.225 messages-->enabled by default

·         For call to connect both the end points should support the fast start.

·         The IP phone communicates with its CallManager using Skinny Client Control Protocol (SCCP). The CallManager exchanges H.323 messages with the H.323 voice gateway using Fast Start.

·         After creating the h323 gateway in the call manager press the reset button and reset the gateway otherwise it will not work

Enable Call survivability on all the VOIP dial-peers on the Router

voip service voip

h323

call preserve

ISSUES FACED IN H323 gateway:

1) Calls not connecting from gateway to another gateway

conf t

voice service voip

allow-connections h323 to h323

allow-connections h323 to sip

allow-connections sip to h323

2) SRST issue with H323 gateway:

An H.323 gateway exchanges H.225 keepalives with CallManager.

To prevent active calls from being terminated when the CallManager becomes unreachable, turn off H.225 keepalives between the gateway and CallManager.

GW1(config)#voice service voip

GW1(conf-voi-serv)#h323

GW1(conf-serv-h323)#no h225 timeout keepalive

3)Inbound calls not failovering to backup callmanager:

Especially if the gateway has a PRI connection for inbound calls. When a call comes in that should be forwarded to a CallManager, the router attempts to set up an H.225 TCP session to its preferred VoIP dial peer.

The TCP session must time out before it will try another dial peer. This takes 30 seconds by default. ISDN Q.931 has a Call Proceeding timeout of 10 seconds. A call that comes in over a PRI line will time out before the router can fail over to an alternate CallManager. Even without a PRI connection, 15 seconds might be longer than you want to wait.

To remedy this, change the H.225 TCP session establishment timer. The voice class h323 10 command creates a voice class in global configuration mode that reduces the timer to three seconds:

NYCgateway(config)#voice class h323 10

NYCgateway(configs-class)#h225 timeout tcp establish 3

4) Calls are Dropped

When the call manager Fails then H323 Gateway is configured for SRST--->H323 gateway drops the active calls. When the Call Manager comes online again the calls are droppped.

CUBE (Cisco border element has no effect by enabling the no h225 timeout keepalive)-->IP to IP calls will be traversing the CUBE

voice service voip

no h225 timeout keepalive ---> disabels the keepalive messages.

voice class h323 1

h225 timeout tcp establish 2

h225 timeout setup 2

call preserve

H323 Gateway Failover Configuration

Cisco IOS gateways also handle Cisco CallManager failover situations. By using several enhancements to the dial-peer and voice class commands in Cisco IOS Release 12.1(2)T, Cisco IOS gateways can support redundant Cisco CallManagers. The command, h225 tcp timeout seconds, specifies the time that it takes for the Cisco IOS gateway to establish an H.225 control connection for H.323 call setup.

The following example shows the configuration for H.323 gateway failover:

interface FastEthernet0/0

ip address 10.1.1.10 255.255.255.0  --->10.1.1.10 (Ip address of CUCM)

voice class h323 1

h225 timeout tcp establish 3

h225 timout setup 2

dial-peer voice 101 voip

destination-pattern 1111

session target ipv4:10.1.1.101

preference 0                     ---->Preference 0 (This is the primary route for connecting with CUCM)

voice class h323 1

dial-peer voice 102 voip

destination-pattern 1111

session target ipv4:10.1.1.102

preference 1                     ---->(Backup route)

voice class h323 1

h225 timeout tcp establish 3 -->If the H323 Gateway cannot establish a TCP connection with CUCM within 3 seconds then it will try the next dial-peer with inferior preference.

h225 timeout tcp setup 2 --> The H.225 setup message is sent to the CUCM and the CUCM is not responding for the setup message within 2 seconds then next dial-peer with inferior preference is used. H.225 message is sent after establishment of TCP connection.

H323 Gateway Status Verification

·         show h323 gateway

·         clear h323 gateway --clears the statistics

·         show debug --->command to display the debug commands applied

·         show dial-peer voice summary  --->shows the summary of the dial peers

·         show dialplan number 9790523431 --->shows which dial peers are matched.

·         csim start phone-number command--->You can simulate a phone call from the router

Debugging a H323 Call:

·         debug cch323 h225 and debug cch323 h245 -->call setup and tear down checking.

·         debug  voip dialpeer --->good one for troubleshooting

·         debug ip tcp transaction ----> to make sure that the TCP session for H.225 and H.245 is being established.

Other configurations on H323:

·         call service stop --->Stops the h323 call processing

·         The faststart is enabled by default

call start slow ---> disable the h323 faststart.