SIP TRUNKING

SIP Education

SIP Trunking Attributes

1. Switched Access - A SIP trunk offers the CPE device switched access to a diverse set off PSTN and or on-net IP termination points via the ITSP on the network side of the SIP trunk.
   
   
2. Proxy at CPE - The SIP trunking attaches to a SIP device at the customer premise (CP) that is a proxy device, with one or more user agents (UAs) logically attached to it.
   
   
3. SIP Trunk is Switched - Incoming calls from the SIP trunk to the CPE device are switched to other devices sitting behind the interfacing CPE proxy device.
   
   
4. Multiple ENUM Termination - The ITSP should be able to route calls with any variant of DID or 800 numbers to a specific client on the SIP trunk; i.e. the SIP trunk should not be limited to a single 800 or DID number as it is a switched service that the CPE Proxy will finally route in its domain.
   
   
5. Bandwidth QoS Management - In conjunction with the ITSP proxy/soft switch and the CPE edge controller, bandwidth is managed such that any shared bulk traffic from the enterprise is throttled back, giving the VoIP media traffic priority, and in so doing attains a QoS for VoIP traffic over that SIP trunk.
   
   
6. Cause Code Management - In the event that usable bandwidth on the SIP trunk is exhausted, either the ITSP or CPE side device must be able to determine that the event exists. Either side must then be able to issue the correct SIP cause code so that notification can be sent upstream. Rerouting must then be done, or call progress tones played to the originating end user.
   
   
7. Firewall Traversal - At the CPE side, a border controller/firewall must be provisioned that allows scalability via manipulation at the level 5 layer (SIP layer). This allows calls to traverse and pass through the enterprise firewall seamlessly, and with no security issues (as is the case with STUN or manual pinhole techniques).
   
   
8. Security - Both the ITSP on the carrier side, and the enterprise SUA at the CPE side, must provide the necessary security to ensure that unauthorized users cannot gain access to SIP call facilities interworking between the enterprise and ITSP. This could include:
   
   
   • IP authentication between the CPESU and ITSP proxy
   • Registration and authentication via MD5
   • IPSEC tunnels (optional)
   • TLS (someday)