VoiceCon: Cisco SIP upgrade could require broader network tweaking

Cisco’s update to its CallManager IP PBX – introduced this week with native SIP support – will require broader upgrades to other network infrastructure gear beyond the data center were the CallManager sits, according to Cisco.

Unified CallManager 5.0 introduces native SIP support, which allows the platform to interact with other SIP-based client and server presence applications, such as Microsoft Office Communicator, as well Cisco’s own Unified Presence Server and client software, being introduced this week. But an upgrade to 5.0 could have ripple affects across other gear, including IOS software upgrades routers in branch offices, as well as IP phone firmware, and possibly server configurations and corporate dial plans, the vendor says.

Along with the new CallManager, Cisco is also introducing a new version of its Survivable Remote Site Telephony (SRST) technology, which runs on branch office routers, tying in remote IP phones to a centralized CallServer infrastructure. Upgrading the CallManager in a data center will also require wide-scale upgrades to both SRST and the IOS versions running on Cisco routers in the field, the vendor says.

“What we’ve done with SRST is build SIP natively into IOS,” says Barry O’Sullivan, vice president and general manager of Cisco’s voice technology group. In the instance of a WAN failure in a branch, the integrated SIP features allow end users to continue using SIP-based applications, while SRST provides local call control and phone access to the PSTN, he says. However, “you would have to upgrade the routers you want to have SRST to version 3.4 to add SIP support,” says Alex Hadden-Boyd, director of marketing for IP Communications at Cisco.

Cisco also released Unified CallManager Express 3.4 – software which runs in a blade inside Cisco routers, providing local call control and telephony features beyond SRST’s emergency failover support. An upgrade to the Version 3.4 is needed to integrate CallManager Express nodes with an upgraded CallManager 5.0 at a central site, Cisco says.

In a data center, administrators will be able to cluster Unified CallManager 5.0 similar to past CallManager servers, but with some caveats. To support large-scale CallManager networks with tens of thousands of phones, Cisco uses a proprietary clustering software to tie together separate CallManagers as one large system.

However, CallManager 5.0 servers cannot be clustered together with severs running older versions of CallManager, Cisco says. Unified CallManager 5.0 servers running Windows and Linux also cannot be clustered.

“You can have [older versions] of CallManager and CallManager 5.0 under the same dial plan, but the must be on separate clusters,” says O’Sullivan, Cisco’s voice group manager. An inter-cluster trunk, which runs over a Gigabit Ethernet link, allows software in one cluster to communicate with software in another, he says.

“Another thing you can do for a migration plan is to move SIP phones and [older] Cisco IP phones on the same cluster,” O’Sullivan says.

Any IP phone connecting to a new CallManager 5.0 also have to upgrade its firmware. This is less of a challenge, O’Sullivan says, since checking for software updates is part of the registration process that happens automatically when IP phones are brought online. However, phones may have to be turned on and off to force them to re-registration with CallManager 5.0 and download the new software. (Previous versions of Cisco IP phones that ran a SIP stack – the 7960 version, in particular – won’t work with the new SIP-based CallManager, and will have to re-register to upgrade).

(Cisco says CallManager 5.0 can also support its proprietary Skinny Call Control Protocol – SCCP, known as just “Skinny,” – used in previous versions, but IP phones would still need to re-register with the new CallManager in order to work.)

Lastly, with CallManager 5.0, the new platform also offers a choice of server operating systems on which to run the IP PBX software. CallManager hardware can now be pre-configured with either Microsoft Windows Server 2003 or a specialized appliance version of Linux.

“Up until now, CallManager was available only on an open windows platform. Now they have a choice. The Linux model is more closed and contained and a lot of customers wanted that. But certain amount of customers want us to continue with the Microsoft platform as well,” O’Sullivan says.

One CallManager user tracking the 5.0 release says the switch to a Linux-based server is a welcome move, but not a reason to run out and upgrade right away.

“We won’t be the first out of the chute,” with CallManager 5.0 says Glen Waltman, principal IT technician at Air Products, which installed a converged Cisco VoIP/data network two years ago.

“CallManager has been running fine on Windows, except for all the patches that go with running a Microsoft System,” he says. “I don’t know if that would change with a Linux platform… but probably not.” Waltman says since Linux would also requires patching and software maintenance. “Nothing’s perfect,” he adds.