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Session Initiation Protocol (SIP)

IP Office supports SIP trunking. SIP trunks allow IP Office users to take advantage of new telephony services being offered by ‘Internet Telephony Service Providers (ITSPs)’. In many cases, these telephony services can offer substantial savings in comparison to traditional exchange lines. The IP Office solution allows all users, regardless of their phone type, to make and receive SIP calls. SIP trunks are handled like any other line on IP Office, affording all the call routing and toll control needed to manage inbound and outbound calls.

SIP trunks on IP Office require the provisioning of voice compression channels through the installation of VCM modules within the control unit.  RTP Relay is also supported to allow the IP stream through SIP after call setup.  A license for the maximum required number of simultaneous SIP calls is also needed. Up to 128 simultaneous calls are supported.

IP Office also supports the T38 protocol which allows Fax over IP.

There are several possible network topologies for SIP trunk systems, as shown in the following diagrams.

Option 1: Service provider with a Session Border Controller (SBC), which solves NAT traversal issues – this is the most reliable and preferred method.


Option 2: Direct connection from the IP Office’s second Ethernet port to the internet via a DMZ (demilitarized zone) port on the router. To make this configuration secure, the IP Office firewall is set to drop all packets except SIP.


Option 3: Connection to the ITSP over NAT using 3rd party STUN (Simple Traversal of UDP through NAT) servers in the network to discover the NAT mechanism being used.


Option 4: Connection to the ITSP through a router equipped with an Application Level Gateway (ALG) which transparently resolves all NAT issues.


For details on SIP ITSPs which have been tested by Avaya, please see the Technical Bulletin for the IP Office 4.0 release and/or IP Office Knowledge Base at .

© 2010 AVAYA
15-601041 Issue 20.f.-
18:14, 25 February 2010

Performance figures, data and operation quoted in this document are typical and must be specifically confirmed in writing by Avaya before they become applicable to any particular order or contract. The company reserves the right to make alterations or amendments at its own discretion. The publication of information in this document does not imply freedom from patent or any other protective rights of Avaya or others.

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Last Modified: 21/12/2009