Saturday, 31 August 2013

SIP trunking - interesting how much is involved when you sit down and think!

I've recently spent a little over 3 days working on a new set of training material on SIP Trunking as part of my Wraycastle work. It amazing how much you hold in your head about topics. It's only when you start to put "pen to paper" so to speak that you realise there's a lot more about a topic than you superficially had in the front of your mind.

It turns out 33 slides later there is actually a great deal more than the SIP Forum's SIPConnect 1.1 specification when you start to consider all the facets of SIP trunks in their broadest sense, i.e. both Carrier to Carrier - Network to Network Interface (NNI) and Carrier to customer - User to Network Interface (UNI).

From a customer /Enterprise view-point I can see two main scenarios playing out:

Existing TDM PBX where the customer doesn't want to upgrade to a new IP-PBX, so chooses the media gateway route to terminate a carrier SIP interconnection with their TDM PBX.

And Scenario two where a customer has invested in the IP-PBX or Unified comms platform and builds a separate network and connection for their voice infrastructure.

I then went on to consider the following areas:

•Why SIP Trunking
Brief market look at SIP trunking – why customers are moving from PRI to SIP trunks
Carriers Perspective Why SIP trunks make sense

Customer Scenarios
  • E-SBC and IP-PBX Interconnect
  • VoIP Gateway to Traditional PBX (AudioCodes, Sonus, Cisco CUBE)
  • Multi-site
  • IP-PBX or Microsft Lync
  • Contact Centres (Queue-ing – SIP Response 182 Call Queued)
  • Emergency Services access

•Carrier Scenarios
• Example TalkTalk Business & Virgin Media Business, BTWholesale IPVoice and IPExchange
• Emergency Services Provision

Technical standards and overview of delivery
What a SIP trunk in technically (SIP Forum Standard – SIPConnect)
Design Options from a carriers perspective
Authentication (IP address based vs. SIP Registrations, SSL SIPS and SRTP)
Transcoding, Codec Support
Session Management
SIP interworking with ISDN (Q.931, Q.SIG – RFC4497 - rfc4497)
QoS monitoring

Gotchas – 
Point Of Sales devices,
Franking machines 
and Alarm systems
Multisite and Bursting
CAC and capacity planning
Optimal Routing (REFER and 302 Redirect, vs 486 Busy and 603 Decline)
Site Failure (detection) 
and redirection (SIP OPTIONS messages)
Security Considerations (SPIT – SPam over IP Telephony)

If anyone is interested in knowing more about any of these areas - or even the whole course, then contact Wraycastle - you'll find them at:


Andrew J. Prokop said...

I teach a two and a half day on SIP fundamentals and each time I think of something new to add to the course for my next batch of students. This is only an introductory class, but I can't help but dig deeper and deeper.

Neill Wilkinson said...

And there lies the problem, or may be the fun. There's always something new to learn and explore.