VoIP – Engineering Behind Creating a SIP Trunk

1. On a 2900/3900 platform, the UC license is required to use the CUCME/SRST functionality. It is in addition to the base OS. Once unlocked the commands will be available (no upgrade needed).

2. As of Unity express 7.0.2, the CUE modules are licensed separately for a given number of mailboxes.

3. Spare phones (with an = in the part number) are technically unlicensed. You can use them with the system, as the CUCME router platform is licensed to a specific number of phones per hardware platform. While you don't need the licenses to operate the phones, you should probably purchase them to stay on Cisco's good side.

4. CUBE should be unlocked with the UC licenses on the 2900/3900 platform.

5. For 30 phones, you probably want a 2911 or 2921.

Brett is right in that you probably need to contact a Cisco VAR/Partner to sort out the licensing issues. They have people on staff that can take care of that for you and probably get you discount off list pricing.

To answer your question: it is possible to run a SIP trunk under your circumstances because your circumstances are no different than those of any other cable subscriber.

DOCSIS is a Layer 1 & 2 protocol, while SIP trunks essentially operate over IP & UDP which are Layer 3 protocols. I don't think it helps to mix them.

With most SIP trunking providers, when the PBX on your LAN registers with the SBC, the SBC uses NAT punching techniques to find the right private IP, if there is a NAT to cross.

Your deployment concerns are going to be:

• Making sure your router doesn't interfere with SIP traffic (disable SIP ALGs - most implementations break SIP)
• Hoping that your ISP doesn't traffic shape SIP
• Checking that your connection to the SBC is solid enough (<30ms RTT, <1% packet loss, <10ms jitter)

Since you are concerned about QOS - this is something that is simply not possible with packets over the internet. Many SIP trunking providers will sell a managed service product that comes with private data T1 connectivity to their backbone - so essentially they're taking & owning the QOS problem.