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Remote SIP Phones and the New Interaction SIP Bridge

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Traditionally, when an organization had agents that worked remotely, whether from home or another location with internet access and VPN, they used the PSTN for the voice path. The disadvantages of this method are as follows:

  • Increased toll charges that the company incurs
  • Increased trunking costs, as the system needs to use 2 lines for each external call – one to the customer and one to the agent
  • Less flexibility and convenience for the remote user since their primary communications line may be tied up unless the company has provided another specifically for work – again an additional expense

Leveraging Voice over IP addresses the above concerns, and is a logical consideration if the corporate system is already SIP-based, but there are some challenges. The most important is the quality of the user’s internet connection, as it will be carying voice traffic. Once that has been addressed to the extent possible, then the voice endpoint must be determined.

The SIP Soft Phone is the least expensive solution as it leverages the PC’s existing internet and VPN connection for both voice and data traffic. The user connects a USB headset to the PC and uses the client software to manage calls. One drawback with this method is that voice quality is now dependent upon the performance of the PC in addition to the internet connection. In many cases it turns out to be a suitable solution, but when a hardware endpoint is preferred, you have to connect the SIP desktop phone to the server at the office.

The reason that you can’t simply plug in a SIP desktop phone at home and hope that it functions the same as when you are in the office is that most home routers are not SIP-aware, so the Network Address Translation (NAT) feaure of the router, which allows you to use 1 public IP address for all of your internal/private devices, prevents the phone from establishing SIP registration to the server or a functional audio path.

One way to get around this is to configure and ship a Small Office/Home Office router to the user that is able to maintain a VPN tunnel to the office. Then the user connects both their PC and SIP desktop phone to the router and everything connects as expected. This can be an expensive option, particularly from a support standpoint.

A second option is to deploy a SIP-aware firewall or Session Border Controller (SBC) on the corporate network. This devices performs NAT translation and allows remote SIP phones to communicate with internal devices. While this may still be the preferred method in many organizations, it does have some cost considerations.

Finally, with the release of Service Update 2 for CIC 4.0, Interactive Intelligence is offering the SIP Bridge application that users can install on their PC’s along with their existing Interaction Client components. The SIP Bridge serves as a relay for all RTP, SIP, and HTTP communications to and from the IP phone. Now, there are no additional devices required on the remote-user OR corporate side of the connection other than the VPN connectivity that is already in place to support client/server application traffic.


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