Using a SIP trunk to connect a Cisco Call Manager to a carrier

Connecting a Cisco Call Manager

Cisco Call Manager (CCM) has support for SIP trunks. A SIP trunk provides connectivity to a carrier over the Internet and the carrier handles, via the carrier PSTN gateway the connection to the PSTN.

The most common method today to connect the Cisco Call Manager to a carrier is by a local PSTN gateway on the LAN.

Use a SIP trunk to connect to a carrier

Today more and more carriers offer one single connection for both voice and data. For enterprises this solution offers several benefits:

• Not having to pay charges for BRI/PRI connections
• Not having to buy and maintain the local PSTN gateway
• Not having to buy additional PSTN gateway hardware as the need for more lines grows
• Obtain better redundancy of the PSTN connectivity

For enterprises to make full use of the SIP trunk, the SIP traffic, as all other data traffic, needs to traverse the enterprise firewall. This can often be a problem as most firewalls cannot handle SIP-traffic. Another common issue when connecting a Cisco Call Manager to a carrier's SIP trunk is that carriers often require authentication. This is something that the firewall seldom can handle.

These issues need be solved in a controlled and secure way. In addition to this, intelligent SIP routing should be applied to get the most out of this solution.

Connecting to a carrier with Ingate

The Ingate Firewall® or Ingate SIParator® (in conjunction with any existing enterprise firewall) solves the problem of firewall and NAT traversal using a SIP proxy-based implementation. The SIP proxy is a complete solution to the firewall and NAT traversal issues introduced by the enterprise firewall. Ingate can also handle the authentication at the carrier's side. This allows the enterprise to make full use of the Cisco Call Manager in a flexible, controlled and cost effective way. Ingate’s SIP trunking solution provides the enterprise with the ability to connect to different carriers in different countries, making it possible to have the PSTN breakouts in the countries being called. This can lower costs for international calls.

Connecting remote users

The business professionals of today are some of the earliest adopters of convergence technology; most, in fact, find themselves connected to the Internet around the clock, whether they are working from their homes or any other place in the world. Wouldn’t it be ideal to take the last part of the office – the fixed phone - with them wherever they were? Enable them to be in the office without really being in the office.

Ingate’s Remote SIP Connectivity (RSC) software module allows remote users to traverse most SIP-unaware residential firewalls and NAT devices and use SIP communications through the Ingate product installed at the enterprise edge. The solution works for most common remote NATs, even symmetric ones, and for remote residential firewalls not being too tight (e.g. having critical ports closed from the inside of the remote LAN).

With RSC installed in the Ingate Firewall or SIParator the enterprise can offer the remote user to leverage all the functionality in the CCM 5.0 as if they were in the office.

Cisco Call Manager 4.x does not have support for SIP clients. But with Ingate’s built in SIP registrar and advanced SIP routing features remote users traveling or from a home office can be connected to CCM 4.x as if they were in the office. This solution is limited to support basic calls only since the remote user registers at Ingate SIParator free-standing from the CCM 4.x environment. Then Ingate’s advanced SIP routing capabilities is used to fork incoming calls from the SIP trunk both to the CCM 4.x and to the registered SIP clients simultaneously. Outgoing calls from the SIP clients will be routed to CCM 4.x which in turn routs the call to the internal Skinny client or to the SIP trunk for external calls.

For additional information on SIP trunking a Cisco Call Manager to a carrier using Ingate, please contact info@ingate.com.