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Executive Editor

Sonus touts network border switch

Jan 05, 20044 mins
Network SwitchesNetworkingVoIP

New software key to linking carriers' IP networks.

New software key to linking carriers’ IP networks

Sonus Networks is introducing software that lets its switching gear connect phone calls between IP networks run by different carriers even if the networks use different protocols.

In doing so, Sonus is naming a new category of network device – the network border switch – that it says is needed to link carrier IP-voice networks in a streamlined fashion.

While carriers can tie the signaling and control for phone call sessions and internetwork security using existing session controller gear, Sonus says its new software called Network Border Switching is better suited to the task.

The software runs on Sonus’ existing GSX 9000 Open Services switch and its Insignus Softswitch hardware platforms, boxes that also can perform switching functions, avoiding the need for extra devices in their networks.

The software can translate signaling from a network that uses the H.323 standard and one that uses Session Initiation Protocol. This is necessary if the two networks are to set up and control calls.

Carriers must resolve private IP addresses of IP phones with those of the firewall that protects them, something some firewalls can handle and that can be resolved by session controllers, which are separate devices.

These separate controllers also handle signaling protocol translations. They are made by companies such as Acme PacketKagoor NetworksNetrakeNexTone Communications and SnowShore Networks.

Using network border switches can avoid the need for traditional voice switches at the junction of carrier networks. Typically, a carrier using IP to carry voice on its network converts the traffic to TDM in a tandem switch that connects to a similar TDM tandem in the other carrier’s network.

Carriers can accomplish the same ends, but it takes multiple devices, Sonus says. Putting the features of many such devices on one piece of hardware simplifies networks and reduces maintenance costs, along with the need for power and space. It also can reduce provisioning time because there are fewer devices to configure. 

IP-to-IP isn’t easy

Carriers trying to connect their IP voice networks with those of other carriers face a string of challenges.
Maintaining quality of service: Carriers must understand markers used by their peers to designate voice-quality service and tag packets accordingly.
Keeping call records: Details of which customers make use of the networks must be gathered, maintained and shared in a format compatible with billing software.
Resolving addresses: The networks must support  network address translation to deliver traffic to  devices with private IP addresses that sit behind firewalls.
Handling signaling differences: Calls initiated  using H.323 signaling must be able to cross networks where Session Initiation Protocol signaling is used.
Minimizing delay: Protocol conversions and re-forming of packets can’t be allowed to introduce enough delay to hurt voice quality.

Network simplicity is key to major carriers because they are faced with layoffs to improve their profits, says Christine Hartman, research director for voice over packets at Probe Group. “What they want is fewer boxes, and they want the right ones in the right places,” she says.

IP-to-IP peering can cost as little as 20% of the price to convert the traffic to TDM and then back to IP to cross network boundaries, she says.

Carriers have yet to work out IP voice peering between their networks, she says, mostly because of business reasons rather than technical reasons. “The hard part is coming to agreements on security, isolating trouble and who pays whom, more or less. Once the first few agreements are set, the others will fall in,” she says.

She credits Sonus with being the first softswitch vendor with this border switching ability. She says carrier phone switch vendors Lucent and Nortel have told her it is on their to-do list.

Pricing for the software has not been set, but the company says it will be based on how many simultaneous sessions the customer wants to support. The price for small deployments will be similar to the price of session border controllers, but will be less per session for larger deployments.