The Cisco Unified Communications Manager supports the popular Session Initiation Protocol, or SIP. What is SIP, and how does it work? SIP trunks are used by businesses who desire to use their IP-PBX as an external as well as an internal communications device. Whenever you want to call someone who is not located within your enterprise, you must have a Session Initiation Protocol trunk that will enable you to connect to the traditional Public Switch Telephone Network, or PSTN. Instead of relying upon telephone wires for a call centre solution, this PSTN connectivity comes to you from SIP trunking.

SIP works by setting up video and voice calls over the Internet. As a signalling protocol, SIP also tears down these multimedia communication sessions. This method works extremely well, and is virtually undetectable to those on the other end of the telephone. No one will realize that you are not using a local provider such as AT&T or Verizon when they speak with you via an Internet voice call.

You will be connected to one of many SIP trunk providers when you make a call. These providers are also known as Internet Telephony Service Providers, or ITSP. An ITSP has the ability to provide a telephone number or numbers in most area codes worldwide. When using an Internet Telephony Service Provider, you also have access to features such as Direct Inward Dial (DID) and Caller ID. An ITSP is reminiscent of the Vonage service, but instead of one subscriber per home, you have an entire corporation as users.

Many people become confused whenever someone tries to explain an SIP trunk to them. The part that seems to confuse them the most is the fact that the SIP trunk is not a physical connection, but a logical one. A T1 connection and a PRI connection are both physical connections. Physical connections are guided by something, such as cables and wires. A logical connection is wireless.

The usual way to connect to the Internet Telephony Service Provider is via the Internet, but some people do use a private MPLS circuit. However, using the Internet can have its limitations. The lack of QOS, or Quality of Service, can mean that your connection may be less than stellar. Noise on the line and dropped connections can happen, but most people are surprised and pleased at how well the Internet can work for them. The ITSP can also connect with the PSTN, or Public Switched Telephone Network, and in this way can communicate with both fixed landline phones as well as cell phones.

Since the Cisco Unified Communications Manager has used SIP trunks for quite some time now, it was decided that some changes were imminent to keep the system flowing smoothly. It is known that there are some limits to the direct configuration of the SIP trunks into the UCM, so Cisco recently took the step of adding expanded support for Session Initiation Protocol on all of their routers.

This support is a feature that you may be interested in adding to your voice gateway. It is called CUBE, which is short for Cisco Unified Border Element. You do have to pay an additional amount in order to make use of this software for your virtual call centre, but devotees of CUBE have found that it can save your business money.