SIP Trunks – Simply Stated


What is a SIP Trunk?

A SIP Trunk is a concurrent call that is routed over the IP backbone of a carrier using VoIP technology. SIP Trunks are commonly used in conjunction with an IP-PBX and are thought of as replacements for traditional PRI or analog circuits. The popularity of SIP Trunks is due primarily to the cost savings of SIP, along with the increased reliability as backed by the SLAs of SIP Trunk Providers. SIP trunks/service may be plugged in directly to an IP-capable system without the use of circuit cards or gateways in some cases.  This results in reduced costs.

What are the advantages of SIP Trunks versus Analog Circuits?

SIP Trunks are usually cheaper than analog circuits while maintaining the same service quality that businesses expect from line quality. SIP Trunks typically cost approximately $15 to $25 per trunk, versus $35- $40 per analog circuit. In addition, long distance termination charges associated with SIP Trunks are much cheaper than traditional analog or TDM rates. With Comtel SIP, clients avoid the numerous optional taxes and surcharges imposed by the carriers today and instead only pay for mandated taxes/surcharges.

What are the advantages of SIP Trunks versus PRI?

SIP Trunks realize their primary benefit over PRIs from cost savings. SIP trunks typically cost $15 to $25 per trunk for unlimited inbound and local calling along with a long distance rate that can be under 3 cents per call. When coupled with line oversubscription (e.g. a 30 person company purchasing just as many SIP trunks as they anticipate having concurrent calls….typically 8 to 10) SIP Trunks are a very cost effective way for a business to save money. Lastly, a primary benefit of SIP Trunks over PRIs is that SIP Trunks can be purchased in increments of 1, whereas PRIs have to be purchased in increments of 23 channels. With an IP Telephony system like IPedge, SIP plugs directly into the network.  With PRI, it requires gateways and/or cards.

When should a business use SIP Trunking instead of hosted?

A business should look into purchasing SIP Trunks when they decide that their needs are best met with a premise-based system. This system is often referred to as an IP-PBX. Coupled with SIP Trunks, an IP-PBX serves up similar features to hosted solutions. SIP Trunks typically save a business customer money over a hosted solution in that a SIP Trunk can serve the needs of three to four employees (depending on oversubscription) while a hosted seat is needed for each employee.

What equipment do I need to be able to use SIP Trunking?

SIP Trunks can work with a SIP-ready PBX. SIP Trunks can also be made to work with traditional analog or key systems with an IAD (Integrated Access Device). The SIP Trunk service provider will need to interoperate with the underlying equipment manufacturer. However, it should be noted that with the advent of standards around RFC 3261 and SIP Connect, the challenge of finding SIP Trunk Service Providers with SIP Trunk compatible equipment is significantly decreased.

Will I need more Internet bandwidth when I buy SIP Trunks?

SIP Trunks are virtual circuits delivered over an Internet Access line. Depending on the number of SIP Trunks purchased, and the amount of excess Internet connectivity, a business should consider purchasing more Internet access. However, it’s important to know that when a SIP Trunk is not being used, the bandwidth otherwise allocated to a SIP Trunk is freed up for use in less intensive applications, such as e-mail and general web use. This dynamic allocation of bandwidth is yet another feature of SIP Trunks versus more traditional technologies, such as analog or PRI circuits. Analog/PRI tend to be “fixed”, whereas SIP is flexible.

Implementing SIP trunks with older key systems is a great way to optimize our relationship with a customer.  Reducing one’s bill while implementing today’s latest technology is a great advantage.  Comtel SIP trunks would have appropriate usage bundles to accommodate a client’s traffic.

SIP by nature is not a physical connection, but rather, a virtual path.  That said, while fixed PRI or analog lines have the limitation of a hard wired connection between a serving CO or datacenter and the customer’s premise, SIP can be available wherever the SIP provider offers service.  So, a client with multiple locations can easily accommodate SIP from diverse geographies, as well as handle overflow traffic resulting from an outage (e.g. from a loop failure, system down, etc.).

So, SIP tends to work in much the same way, except it usually has the following attributes when compared to analog or PRI:

  1. It is less expensive
  2. It leverages broadband infrastructure
  3. You can buy less paths than the 23 delivered with a PRI
  4. Your services may be flexible in terms of where they terminate
  5. SIP can be made to work as a replacement for analog on old systems
  6. SIP has built in disaster recovery options
  7. SIP is a great entrée to hosted services and lets a client experience cloud
  8. The Carrier network is largely SIP today. The irony is that most traffic today gets converted to SIP once it leaves the customer’s network anyway. So, SIP is how calls are getting processed anyway!

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