Core Issue
The PIX h225 fixup routine is causing the Transmission Control Protocol (TCP) zero byte keepalives between the voice gateway and the Cisco CallManager to fail. Consequently, the voice call gets terminated exactly five minutes after the call setup due to unacknowleged TCP keepalive packets.
Resolution
Upgrade to a PIX Firewall version that contains a fix for the problem in Cisco bug ID CSCdy13293.
Another workaround is to downgrade to PIX version 6.1.3 or earlier. You may also disable fixup protocol h323 and h225 if Network Address Translation (NAT) is not used.
Problem Type
Call connection (Connection quality: One-way audio, no busy tone, dropped calls, etc.)
Call Connection
Dropped or disconnected calls
Frequency and Scope of Symptom
Occurs at regular intervals
When Problem Occurs
During conversation
Call Topology and Direction
IP network > IP network
Bug ID Number
CSCdy13293
Security Features
Firewall
