Considerations for Implementing SIP

In a recent Computer World article I discussed how the real cost savings associated with VoIP in the corporate enterprise comes from the implementation of Sesion Initiation Protocol (SIP). With most organizations paying very low long distance rates, justifying VoIP investments on long distance savings becomes a real challenge. SIP on the other hand allows you to get rid of local loop charges through a reduction in the number of PRI's you have dedicated to voice at remote and field locations. There are big savings to be had in SIP but in order to understand what your net savings will be you need to think through some of the following basic factors.

SIP Provider Pricing

Unlike traditional TDMS services, pricing for SIP is far less standardized. Different carriers will charge for the service in different ways. For example, PAETEC charges a flat fee for the bandwidth of the MPLS connection used to provide the SIP service plus $1.50/"virtual DID". On the other hand Time Warner Telecom charges more on an actual call volume basis. There really is no "best" way for a company to price its SIP service, what works best for you will depends on the dynamics of your particular organization. Make sure you understand the pricing scheme of the SIP providers you are evaluating and match that model to your organizations typical call dynamics.

Understand Where You Can Truly Remove Services

The implementation of SIP in your network is not the end to your PRI based TDMS service. Several factors will likely limit your ability to remove PRI's in certain areas. For example, make sure you understand for which of your remote locations your SIP provider can provide the virtual DID's. Not every SIP provider can provide local numbers in all markets, for those markets not covered by your SIP provider you will need to maintain your PRI service to maintain that locations local DID's. Also, consider services like faxing that may be riding on PRI's through FXO ports today. What will you do about this? How many local lines will you need to maintain for systems such as building security, fire alarms etc..? It may be that the need to maintain support for an antiquated technology such as faxing (my opinion) may hamper your ability to leverage modern network designs for financial gains. You may find yourself using your SIP implementation as a good time to rationalize the continued support for older communications mediums.

How Much Bandwidth Will You Need At Remote Sites?

Your current data link at each of your remote sites is running at some percent of utilization today. What will that be once you add voice traffic over the circuit? You need to make some estimates about a locations call volume combined with the type of voice compression you plan to use in order to determine if you will need to increase the bandwidth on your locations data pipe. This is significant because you could find yourself simply shifting costs around, from PRI to Data circuit. In order for SIP to represent a true cost savings at your field site, make sure the overall net spend decreases after PRI removal, additional services for local lines and potential increased data bandwidth.

Understand the Best Technical Architecture for your Organization

The technical details of a network design for SIP can be daunting. At the end of the day, there are really two major types of designs you will likely choose from. In a centralized model, all remote locations receive SIP trunks and thus call trunks through a centralized connection to the SIP provider. The SIP provider will deliver some type of connection to your corporate HQ or data center where you will connect to them through a CUBE. You can see an image of this here..
A distributed model requires each location to peer with the SIP provider. The distributed model provides a slightly more robust design in terms of backup and redundancy but at a higher CAPEX and OPEX cost. You can see the distributed model diagram here..

This is not an exhaustive list of considerations but thinking throh these things will help you to solidify your thinking on both the technical and financial benefits of SIP in your organization. I recommend that for evaluating SIP providers and doing your cost/benefit analysis, you utilize a third party who specializes in Telco analysis. It is critical that for you to make good decisions about SIP that you understand your current state. The SIP market is still young and services are still often tailored to your specific needs. Make sure you truly understand the net of it all before jumping in.