Maintaining session across network address/port translation firewall in the event of an address change with a session manager

摘要

Voice over IP and multimedia sessions can use session controllers. These can be thought of as comprising a back to back user agent (B2BUA) [10] dealing with SIP message and a media proxy (MP) [20] dealing with the media stream. SIP allows clients [40] to change their address/port during a session. This would result in a change in the external address presented by the network address/port translation firewall (NAPT) [30]. The B2BUA will be informed of the address change by SIP. If it instructs the MP to immediately latch to the new address packets already in transit with the old address may cause the MP to latch back to that old address. The B2BUA therefore instructs the MP to "re-latch" whereby it continues to use the old address until it detects packets using a new address, at which point it re-latches to this new address.