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Considerations Needed for SIP Trunking

Tuesday, June 23, 2015 - 09:15
Considerations Needed for SIP Trunking

Enterprises that are ready to upgrade their phone systems have a variety of options and setups from which to choose.  One of the “buzz phrases” you may have heard about is trunking – or more specifically SIP trunking.  But what does this phrase mean and how can it become part of your new and improved enterprise phone system?

What is SIP Trunking?

SIP stands for Session Initiation Protocol – the framework for establishing a communication session on a data network.  SIP communication sessions could include a VoIP call between two users, or a conference call between several users.

A SIP Trunk supplies the same service as a traditional analog phone line.  It enables you to extend VoIP telephony past your organization’s firewall without requiring a separate PSTN circuit.  Where there are separate physical wires required for typical analog service, a SIP Trunk is a virtual phone line provided by an Internet Telephony Service Provider (ITSP) or SIP trunk provider.  This provider uses your data circuit (cable, DSL, fiber, or T1 line, etc.) to connect your phone system with their network.

Over 75% of companies say they will be using SIP by 2016, according to a recent Podcast: SIP Trunking 101 – Business Benefits and Implementation Considerations.  In this informative podcast interview with Marcus Schmidt, the Senior Director of Product Management from West Unified Communications, the basics of Session Initiation Protocol (SIP) are reviewed, with a focus on the benefits to businesses.

Advantages of SIP Trunks

So why should your enterprise go with SIP trunking?  There are a multitude of reasons.  Traditional legacy PBX systems often carry with them higher costs as a result of so many separate billing items.  For instance, monthly phone bills may have line items that contain charges for each incoming phone line, long-distance charges, and maintenance fees, to name a few.

With an SIP Trunk, there is no direct physical connection from the business to the phone company – so there are no costs incurred for adding hardware, installing circuits, or running lines to maintain a connection to the PSTN.  SIP Trunking enables organizations to pay only for the number of lines they really need versus paying for extra analog lines or under-utilized Primary Rate Interface (PRI) circuits that only come in 23-channel blocks.   Because SIP Trunks can be customized to provide any number of channels based on organizational need, businesses are able to realize cost-savings by only paying for the communication channels and resources they actually need.

And fewer phone lines merged into one virtual connection point reduces IT involvement and associated support costs as well.  Each individual phone number or Direct Inward Dialing (DID) number typically costs less from an SIP provider since traditional DIDs from phone companies are packed with additional charges for hardware and support of their physical infrastructure.  Without these added costs, DIDs obtained through a SIP provider typically cost less.

Contact Centers can leverage many benefits after implementing SIP trunking. SIP trunking can provide cloud announcements to alert callers to major outages, without the need to tie up call center resources.  SIP also allows for routing options that TDM trunks cannot provide, such as routing local calls in one city to another halfway across the country.

Another advantage of SIP trunking is that it allows for better disaster recovery and business continuity.  With a traditional on-premises PBX with physical connections to the PSTN, there are few recovery and redundancy options if that equipment were to fail.  On the other hand, SIP trunking utilizing VoIP means that when failures occur, SIP providers can reroute the connection and associated services to an alternate data line.  This allows for continued business communications in the event of a disaster or failure scenario.

Communication Considerations and Requirements

So now that we understand some of the reasons to implement SIP trunks, how do we go about determining our business’s communication requirements for proper SIP trunking scalability?  Starting with a basic checklist will make the process for implementing SIP trunking much simpler and help the process to go smoothly.  Here are some simple questions to get the ball rolling:

How many phones do you have across the business?

The answer to this question may help to assess whether your organization would be better off purchasing a specific number of trunks versus a specific number of minutes.  SIP trunk pricing can be billed per trunk + cost/minute or at a flat fee per SIP trunk with unlimited usage.  For example, in this second pricing model, the limiting factor is the call paths; a company could purchase 50 channels and use as many minutes as they need across those channels, but they would be limited to 50 simultaneous calls.

How many people are on the phone at the same time during core business hours?

Since one SIP trunk will generally cover 2-3 users if only one of those users is making a call at any given time, you can calculate the number of trunks based on the answer to this question.  The answer to this question also helps to determine the best SIP trunk pricing model for the enterprise.

How does the enterprise determine trunk capacity?

The process of calculating the required trunk capacity starts with determining the grade of service (GoS) – the probability of a caller experiencing a busy signal at a call center, enterprise office, etc. This first step uses an Erlang B formula and calculation. Erlang B can determine the number of trunks, or lines, needed to handle a calling load during a one-hour period.  The second step is to calculate the bandwidth necessary to support the number of SIP trunk sessions determined by the Erlang calculations. Trunks in this case are the number of lines/sessions needed to carry the calls.

Speed and Type of Data Connection

An important consideration for SIP trunk planning is reviewing the speed and type of your data connection (MPLS, cable, DSL, fiber, T1, etc.), and whether or not it’s expandable.  Moreover, you will need to analyze your call volume to ensure the existing available bandwidth is sufficient for implementing SIP trunks.

SIP trunks utilize a moderate amount of bandwidth, so in evaluating your company’s call volume, it’s possible that it will be necessary to increase the bandwidth on your data circuit, or replace it with a pipe that will be sufficient for all call traffic, flow, and data usage.  Nowadays, many carriers provide web portals that can give customers the power to grow or shrink the bandwidth utilization of their trunk circuits as the need arises.

Companies need a way to connect and integrate existing voice equipment with SIP trunks.  SIP Trunking can use VoIP across shared lines like a company’s internet connection, but legacy/older systems that aren’t set up for VoIP will require VoIP gateways to implement SIP trunking, so additional equipment may be necessary.

Quality of Service Requirements

First a quick definition of QoS

Since SIP trunks support voice services over data lines, it is important to make sure that there is a network router in place that can be configured with Virtual LANs (VLANs) that route data and voice traffic with the proper prioritization.  QoS Analytics – voice analytics that include historical and real-time reporting – may need to be performed and reviewed for bottlenecks.  If there are any issues in the network set up, additional bandwidth may be required.

A firewall should be installed to properly secure the data and voice networks when using SIP trunking.  It should be configured for maximum throughput without compromising on the security of your networks.  Even though typical latency or delay doesn’t normally cause audio quality issues, if the latency is above 150ms, it can be noticeable to users.  So, proper configuration of your network routers and firewalls is a vital part of setting up SIP trunking.

For enterprises looking to the present and future of voice communications, West UC offers MaxxConnect, a suite of SIP trunking solutions designed to provide enterprise clients with the carrier–grade service they have come to expect from traditional providers.  West UC provides many options for voice system upgrades, and can help your organization navigate all of the considerations that can occur with SIP trunking.


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