SIP Trunking

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SIP Trunking is the mechanism used to interconnect SIP Enabled PBXes and/or SIP User Agents to each other to establish voice sessions between each other over an IP Network. Utilizing the now ubiquitous SIP Standard for signaling, SIP Trunking has emerged as a viable alternative to legacy (TDM) and fixed-line circuits for the establishment and transmission of voice communications. There are several applications of SIP Trunking with the most popular being interconnecting SIP-enabled PBXes to each other and allowing the offloading of off net traffic to the PSTN.

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[edit] SIP – The De-facto VoIP Standard

The proliferation of SIP Based PBX’es and the commitment among major PBX manufactures including Avaya™, 3COM™, Nortel™, Cisco™ among many other small and larger players, to the protocol serves as tangible evidence that the telephony industry is in the midst of a paradigm shift not unlike the transition from analog interconnectivity to ISDN in the 1990’s. Although most PBX manufactures have concentrated on leveraging the advanced functionality and inherent simplicity of SIP based PBX’es bringing such powerful new features such as Instant Messaging; Presence Management; centralized call control; and simplified moves, adds and changes; most of this functionality has been relegated to the enterprise’s private data network. Large Telephone Companies, burdened with billions of dollars of traditional ISDN infrastructure and the complex integration of disparate and legacy OSS systems have been slow to adopt SIP Trunking to the PSTN to afford enterprises utilizing SIP-based PBX’es to displace legacy PRI and POT’s infrastructure with direct end to end SIP interconnectivity thus mitigating the need and expense of legacy infrastructure.

[edit] The Anatomy of a Legacy Telephone Call

Although many enterprise telephony and IT managers may not be aware, a significant, if not majority, of their telephone calls to the PSTN are already traversing VoIP networks for at least a portion of their transport. Traditional Telcos typically serve customers with a Class 4 or 5 switch providing trunks or business lines to the customer premise. The little known fact is that most Telcos back-end these switches with VoIP gateways/switches such as Sonus™ to transport the calls over their data backbones therefore maintaining optimal use of their network infrastructure. Once calls reach their target destinations, they are then converted back to TDM by the VoIP Gateway and handed off to the legacy switch for last mile transport to the customer premise.

With the advent of SIP telephony at the customer premise, it becomes readily apparent that the aforementioned scenario is both illogical and inefficient. Nonetheless, traditional Telcos for myriad reasons have not as of yet been enable to deliver viable last-mile SIP solutions.

[edit] The Telephony Service Provider Landscape

While traditional telephony service providers including RBOC’s, ILEC’s, CLEC’s and nascent Internet Telephony Service Providers (ITSP) have to some extent embraced SIP in their service offerings, most of them are targeting the residential market (i.e. Vonage™) and have chosen to address the business market with Hosted PBX solutions which may commonly be referred to as IP Centrex (i.e. Covad). Although the technology is sound, demographics including the robust sales of IP and IP Hybrid PBX’es have overwhelmingly demonstrated that the business market, and in particular the enterprise market, has clearly chosen premise-based solutions; however very few service providers have chosen to address this growing market.

[edit] The Benefits of SIP Trunking

Although pricing for SIP Trunking is typically 40 – 70% below legacy Telco offerings, features and functionality that enhance SIP based IP PBX’es and indeed solve multiple issues related to large-scale enterprise deployments, are the key considerations in the deployment of SIP Trunking. Among the several benefits we will explore are Disaster Recovery, On Demand provisioning of lines, DID’s and toll free numbers, and finally – the geographic abstraction of local DID’s.

[edit] Disaster Recovery

Given recent natural disasters, and the general need for enterprises to assure business continuity, disaster recovery of voice networks is a critical consideration. Given the ubiquity, robustness and distributed nature of IP Networks, it is understood that IP Networks can be engineered to a higher degree of fault tolerance, than their fixed line, circuit-switched counter parts.

[edit] On Demand Addition of PSTN Access Lines

One of the most challenging responsibilities of a telephony manager is to insure the proper balance between cost and available lines to assure capacity for seasonal peaks and valleys; and short run marketing campaigns. In a traditional telephony environment where Telco facilities such as PRI’s may take up to forty-five days to provision and typically require one to three year term commitments, the telephony manager was typically forced to deploy sufficient facilities to insure capacity at the highest busy hour usage for the year, or risk callers receiving busy signals. Naturally, this inefficient method involves significant monthly recurring costs for under-utilized circuits.

[edit] Geographic Abstraction of DIDs

The advent of IP Telephony has allowed enterprises to consolidate PBXes in data centers and serve remote branches and tele-workers from centralized locations. However, this emerging configuration poses a significant challenge – how do you provide local telephone numbers to branch offices and tele-workers when the centralized PBX is not in the same calling area. Legacy Telcos due to technical and regulatory issues are not able to provide these local numbers via traditional facilities to the centralized PBX. Current solutions include the deployment of costly gateway elements at branch offices and even for tele-workers.

The aforementioned solution, while in common practice today is both impractical and inefficient as it creates greater hardware expenditures, increased telephony network costs, and provides greater complexity in managing additional network element.

With SIP Trunking, the telephony manager can now simply choose DIDs from around the country an have them served to the central PBX, mitigating all the complexity associated with centralized PBXes. Furthermore, if the enterprise is deploying multiple centralized PBXes, they can leverage the inherent disaster recovery capabilities.

[edit] See also

[edit] External links

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