Jay's Blog

SIP Versus PRI Costs

The PRI has been the standard for connecting PBXs to the public switched telephone network (PSTN) for years. A PRI in North America multiplexes twenty three 64 Kbps voice channels and one 64 Kbps signaling channel across a T1 link. Because this is done via time division multiplexing (TDM), it does not take advantage of the gaps in conversations when no traffic is sent. Packetized IP traffic can take advantage of the statistical nature of traffic flow, and conversation gaps do not consume bandwidth. Experience with SIP trunking suggests that at least 50 conversations can be supported on a single T1 line; some customers have attained 70 conversations with no audible impact. Our high-level calculations suggest that there is at least a 28% savings when migrating to SIP trunking, but the savings could be greater when considering that a SIP trunk can support twice as many sessions as a PRI. The challenge has been that not all central offices support SIP trunking, and not all enterprises have SIP trunking capabilities on their voice systems.

The following example (for North America) compares the costs of PRI facilities with SIP trunk facilities that can carry the equivalent traffic. Potential operating expenditure (opex) reductions result from fewer trunk requirements and lower rates (see Table 1).

PRI Cost

• About $1,325 per PRI per month with 20,000 long distance (LD) minutes
• About $57.60 per channel per month with 870 LD minutes

SIP Trunk Cost

• $450 per access, plus $15 per channel per month plus $0.02 LD per minute off network
• $41.40 per session per month with 870 off network LD minutes

Source: Gartner (June 2010)

LightBound, and Indiana VoIP service provider, offers across America with SIP, PRI or Analog. LightBound can provide voice service to over 98% of the populated country.  This is a great option for companies wanting to have virtual numbers in other cities. Connecting multiple offices with a centralized IP PBX phone system.

Let us take care of technology, so you can take care of business.