For PIX firewall (with VoIP application-layer gateway [ALG] or fixup protocol), the following version/feature combinations are supported:
Version 5.2: Supports H.323 version 2, Registration and Status (RAS), and NAT (no PAT).
Version 6.0 and 6.1: Adds SIP with NAT (no PAT), Skinny Client Control Protocol (SCCP) with NAT (no PAT), and no Media Gateway Control Protocol (MGCP) support.
Version 6.2: PAT support for H.323 version 2 and SIP.