Happiness is not something ready made. It comes from your own actions
– The Dalai Lama
I recently wrote about an Omdia study that described how enterprises are rapidly moving from TDM to SIP. While I cannot know what is in the mind of every IT leader when it comes to “why SIP,” I certainly have a list of my own. Off the top of my head, I can think of:
- Cost savings
- Shared resources
- New features
- New endpoints
- Simplified call recording
- Better redundancy and failover
- Trunk reduction
- SIP migration as the catalyst for improving WAN resiliency, increasing bandwidth, etc.
Of course, perceived benefits are not implementation and it’s essential that organizations carefully plan their SIP migration. To help with that task, I’ve created a series of high-level checklists for preparation, design decisions, choosing a SIP provider, planning, and avoiding pitfalls.
Planning
Everything begins with an inventory of the existing TDM infrastructure. This involves detailing voice circuits and DIDs. This should be easy to complete using configuration records and billing statements.
The next part is much harder. You may know all the DIDs owned by your enterprise but determining how they are used takes an examination of overall usage patterns, current costs, specific or location usages, and busy hour requirements. The goal is to not only meet the current needs, but right-size the organization following a centralization of trunks. For example, the number of required trunks may drop substantially once they become a shared resource spread across a large geographical area and over many time zones.
Security
Technology without security is a hacker’s paradise. I’ve written extensively about this, so rather than repeat myself, here are a couple articles that will help with this step.
Thinking Holistically About SIP
Attention and Vigilance: Securing Your SBC the Right Way
Technical
I am a big believer in designing for reliability, redundancy, and self-healing. In other words, you need a really good reason not to deploy everything in high availability pairs. This means that everything has a backup. One SBC becomes an HA pair. That HA pair is backed up by another HA pair in a geographically distributed disaster recovery data center. The same holds true for WAN circuits, carrier connections, session managers, power, etc.
Other technical concerns include:
- Optimizing network regions — What may have been considered best practices years ago needs to be reexamined for SIP.
- Implementing voice quality monitoring — Be prepared to proactively solve problems before your users flood the helpdesk with complaints about lousy sounding phone calls.
- Examine or create bandwidth needs, codec requirements, and call admission control policies
- Determine the required number of DSPs — The number may go up or possibly down after moving to SIP.
Key Decisions
SIP comes with a lot of flexibility, but at some point, you need to put a stake in the ground and choose a path. Some of the decision points include:
- Codecs — G.711 vs. G.729. Do you sacrifice call quality for reduced bandwidth?
- How will branch survivability be implemented (if at all)?
- Shared vs. dedicated MPLS circuits
- Redundant carriers
- What do you do with all those analog devices — fax machines, modems, etc.?
- What is the right SBC for your enterprise?
- Who does the work — PBX vendor, reseller, or internal resources?
Carrier Selection
Choosing your SIP carrier should never be an afterthought. Although it’s tempting to stick with your current TDM provider, this is the time when you need to consider the following:
- NPA NXX footprint — Who delivers the services exactly where they are needed?
- Failover capabilities for active calls. If resiliency is paramount, consider multiple links at every ingress/egress point. Understand how BGP is supported by the carrier.
- Don’t make bursting a hard requirement. Rather, do your homework ahead of time in determining your organization’s busy call hour.
Carrier Costs
As a technologist, I hate having to think about money, but as a practical person, I can’t ignore it. Here, the following should be considered:
- Non-recurring costs:
- Initial Implementation (circuits, features, etc.)
- DID porting
- Monthly recurring costs:
- DID numbers
- Toll-free numbers
- Toll-free features
- Toll-free talk paths
- Talk paths for redundancy
- Incoming Caller ID Name delivery
Planning the Work
You’ve done your due diligence and determined what you want and who you want it from. You now need to come up with a clear and concise plan on how to implement everything. This includes:
- A verification and test lab
- Create test DIDs
- Port individual DIDs for selected users (e.g. telecom team)
- Prepare a detailed implementation process, cut sheet templates, and test plan(s)
- Assign implementers and checkers. Make sure that every change is checked for accuracy
- Cut outbound local/toll at each site a week or more before DID port
- Determine support model — onsite or remote
- Port toll-free traffic last
Potential Pitfalls
Even the best laid plans sometimes go awry. Here are a few potential problem areas that must be considered:
- Call recording — often a nightmare if not carefully planned
- Fax
- Modems
- TDD
- Carrier screening of outbound Caller ID for certain call types
- 911
- Long carrier lead times on circuits and/or features
- Number porting
- DTMF recognition on inbound calls
Test Plan
You won’t know if it works if you don’t properly test everything. Areas of high concern include:
- Inbound
- DID to station
- Toll-free
- IVR and call vectoring
- DID with blocked or unavailable Caller ID
- DID to voicemail
- Outbound (include on-net locations and lots of DTMF)
- Tandem (extend to mobile, call forward, carrier take back and transfer, etc.)
- Fax (inbound and outbound)
- Failover
- SIP circuits
- SBCs
- Session managers
Mischief Managed
Life doesn’t come with guarantees, and Murphy has a way of showing up when he’s least expected, but the better the plan, the more likely you will have a positive outcome. These tips will take you a long way to achieving the results you want, but it’s up to you to customize the approach to one that delivers the results that make sense for your organization.