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Migrating to SIP Trunking: Is It Worth the Move?

There has been a great deal of buzz over the past few years surrounding Session Initiation Protocol (SIP) trunking for connection to the Public Switched Telephone Network (PSTN). Many companies have pondered moving away from the traditional time-division multiplexing (TDM) links (i.e., Basic Rate Interface/BRI, Primary Rate Interface/PRI and Plain Old Telephone Service/POTS) and going […]

There has been a great deal of buzz over the past few years surrounding Session Initiation Protocol (SIP) trunking for connection to the Public Switched Telephone Network (PSTN). Many companies have pondered moving away from the traditional time-division multiplexing (TDM) links (i.e., Basic Rate Interface/BRI, Primary Rate Interface/PRI and Plain Old Telephone Service/POTS) and going to SIP for PSTN access. However, there is still a slight bit of hesitation from many companies, namely larger companies, wondering if SIP is worth the move.

For many years, small and medium sized companies have leveraged SIP trunks for their ability to provide both data and voice capabilities with one connection. Gone are the days of SIP being only for “mom and pop shops” – all companies can realize the benefits and flexibility that are provided with SIP trunks.

Benefits of SIP vs. TDM Trunks

There are numerous benefits of SIP over TDM trunks, most notably: scalability, flexibility, redundancy and rapid return on investment.

Scalability – Unlike traditional POTS and T1/PRI lines that are limited to the amount of channels they can provide (i.e., 23 for T1 PRI), SIP trunks offer on-demand scalability. Both enterprises and small businesses can leverage SIP trunking to dynamically add or remove large amounts of capacity when and where required – a good example of this would be a company-wide meeting where multiple employees need to dial in for an extended period of time.

Management/Flexibility – SIP trunking eliminates the need for separate voice and data connections, allowing for faster site rollouts, fewer gateways to manage and faster geographic growth. Companies then have the ability to deploy multiple different architectures depending on their needs including centralized, distributed or hybrid PSTN designs. This flexibility makes transitioning away from TDM trunks much easier.

Redundancy – With most SIP trunking services, it is very easy to redirect traffic from one trunk to the next in the event of outage. Quickly moving calls to another SIP trunk increases business uptime and greatly reduces any impact to customers.

Rapid Return on Investment – With SIP, it is no longer necessary for every site to have a local gateway with PSTN connectivity (which often go underutilized). SIP can utilize a company’s existing data backbone to extend Voice over Internet Protocol (VoIP) connections to any site. Furthermore, because local gateway connectivity for all sites is not necessary, companies can realize a significant hardware cost savings not only in bringing up new sites, but also with hardware refresh intervals. Traditional TDM links, such as PRI connections, typically come with a substantial monthly expenditure, and when this is multiplied across the enterprise, the costs add up quickly. Customers can typically realize SIP cost savings almost immediately when they begin to look at their monthly TDM spending.

Enter Cisco CUBE

SIP trunks might be sounding pretty good at this point, but how does this all fit together? Cisco has made architecting, implementing and managing SIP trunks extremely efficient with their Cisco Unified Border Element (CUBE) offering. Cisco CUBE provides solutions for all businesses, from small to large, with a multitude of different deployment models. CUBE can be deployed on physical devices such as Cisco 800, 2900, 3900 or 4K Integrated Services Routers (ISR) series platforms and can even be deployed virtually on Unified Computing System(UCS) servers with vCUBE. The multiple deployment options provide the flexibility to migrate to SIP in a way that makes the most sense for the business, allowing control of the pace and architecture strategy for migrating away from TDM trunks.

CUBE performs the essential functions of a session border controller (SBC) at the edge of the network: session control, interworking, demarcation and security. As voice, video and mobile services become more prevalent collaboration elements, it is critical to have network components that are highly scalable and secure. Cisco CUBE provides box-to-box and in-box high availability redundancy options. Customers also have the ability to use multiple service providers’ SIP services on a single CUBE. The ability to utilize multiple service providers adds another layer of redundancy into the CUBE architecture for increased uptimes and reliability.

Not all SIP service providers speak the same dialect of the SIP language, but CUBE has the ability to perform SIP normalization and has multi-tenancy support to allow optimum interoperability with various SIP providers. CUBE also has the ability to deploy toll-fraud features to protect against hackers who target SIP ports. The capability to intelligently allow or deny and encrypt real-time traffic is becoming increasingly critical as incidents of attacks are becoming more common.

Questions and Answers with Your SIP Provider

I have discussed the benefits of SIP trunks vs. the traditional TDM trunk and have covered, albeit at a high level, how Cisco CUBE architecture makes the transition more efficient. What about the last piece — the SIP PSTN provider? Choosing the right SIP provider for your business needs is a critical step in the transition. Most companies have a provider that already handles their data backbone and can provide SIP services, but it is always a good idea to explore the options. During discussions with customers, one of the most common questions asked is, “What should I ask my carrier regarding SIP?” Here are a few things to consider when thinking about making the transition to SIP and choosing which service provider might be the right choice for your company.

Service Level Agreement (SLA) Uptime – What are the SLA uptimes for the SIP service? Although it is very rare, providers can have issues with their SIP backbone and this can cause SIP outages. Depending on the particular needs of your business, it might be worth having multiple SIP providers for high availability purposes.

Redundancy in Network – Does the carrier support multiple trunks in a trunk group (trunk pooling) for redundancy? Does the carrier support geographic redundancy? Can the provider support private (Multiprotocol Label Switching/MPLS) trunks and public trunks depending on the network architecture? These are all important questions to ask when beginning to think about the type of architecture that will make the most sense for the transition to SIP.

Enhanced 911 (E911) – Does the carrier have an E911 public safety answering point (PSAP) service? This is extremely important, especially with a centralized PSTN architecture, to ensure the proper emergency services are dispatched to the proper locations. Many customers decide to supplement SIP providers’ E911 capabilities with solutions like Cisco Emergency Responder.

Fax Capabilities and Codec Support – Does the carrier support G711 pass-through or T.38 fax pass-through? Yes, some claim faxing has gone the way of the dinosaurs, but it is still a critical function for many companies.

GTRI’s collaboration professionals have helped numerous customers integrate SIP solutions. If your company is looking for help with SIP architecture or TDM to SIP transition, we can assist.

Nick Fox is a Consulting Engineer in Professional Services at GTRI.

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