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Some calls fail after upgrade of IOS gateway - new H323 versions can not communicate with older ones

Core Issue

The newer H323 versions 3 and 4, found in Cisco IOS 12.2(8)T and later, have some difficulty in communicating with some devices using some older H323 version stacks. In particular, NetMeeting connections may not complete with this version.


To correct this issue, disable the H245 tunnel, allowing additional TCP sessions rather than requiring use of the existing one.

The two bold IOS commands below may correct this issue. These commands are hidden and will not be seen by normal parsing operations.

router(config)# voice service voip
router(conf-voi-serv)# h323
router(conf-serv-h323)# h245 caps mode restricted
router(conf-serv-h323)# h245 tunnel disable

For more information, refer to Third Party H323 Calls Fail with Cisco IOS Later than 12.2(8)T.

Problem Type

Call connection (Connection quality: One-way audio, no busy tone, dropped calls, etc.)

Call Connection

Call connection establishment

Common Software and Product Issues

Problems after an upgrade

When Problem Occurs

While call is connecting

End Where Problem is Heard or Device Type Involved

IP phone

Signaling Protocol


Voice Gateways

IOS gateways
Version history
Revision #:
1 of 1
Last update:
‎06-22-2009 05:04 PM
Updated by:
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