A SIP trunk is setup by the carrier to port a subscriber's number(s) into its own exchange network or hosting platform, which will be located in a secure data centre. This centre’s around the use of soft switches and Session Border Controllers (SBCs). These numbers are then re-presented across a private IP network (MPLS, VPLS) or Internet connection back to the subscriber's premises. Quality of Service (QoS) is paramount and can be effected over different types of IP connection including Leased lines, MPLS or VPLS networks. Thus a leased line is provided to connect into the MPLS 'cloud', which in turn is linked to the carrier, who will have their links into the PSTN. In addition Virtual Route Forwarding can be set up to provide Internet access from the same leased line connection to reduce costs.
SIP Trunks can be configured in many ways, including:
- A Managed Service, where the Service Provider supplies the CPE (Customer Premises Equipment) to monitor and guarantee SLAs (Service Level Agreements) in addition to basic voice services
- An Unmanaged Service, which is similar to an analog phone line, providing basic voice services
The impetus for SIP trunking is the move from the traditional circuit switched telephone world to packet switching. In other words, the traditional PBX system is giving way to the iPBX, IP PBX or VoIP telephone system.
SIP trunking often still uses traditional T1 / E1 lines, but in a configuration where the TDM Channelisation is unnecessary, and just becomes effectively a 2 Mbps IP pipe.
SIP or Session Initiation Protocol is a switching system, signaling system and call setup and clearing system used for IP telephony, also known as VoIP. SIP is becoming more popular, supplanting other switching protocols in VoIP phone systems.
Both T1 / E1 PRI and SIP trunks connect between your phone system and your telephone service provider. Which you select depends on your system's capabilities and the provider that terminates your calls to the PSTN or Public Switched Telephone Network. It is not necessarily true that a new VoIP phone system will automatically use a SIP trunk for service. In fact, many IP PBX systems are ordered with T1 or E1 PRI interface cards because the best service deal may well be from a competitive supplier providing PRI local and/or long distance telephone service.