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WAN Services for the Host-Your-Own-VoIP Enterprise

Select Carefully to Get the Most from Converged Services Networks
By Todd Kiehn


A number of sophisticated enterprise IT professionals have accepted the challenge of internally hosting Voice over Internet Protocol (VoIP) services instead of outsourcing IP PBX and enhanced feature servers to telecommunications service providers. These ambitious IT shops are managing VoIP hardware and software implementations themselves, rolling out sophisticated VoIP services to headquarters and branch offices across the enterprise and maintaining hands-on development of enhanced VoIP features.

In the course of this initiative, host-your-own-VoIP (define - news -alerts) enterprises also must acquire reliable, secure, wide area network (WAN) local access and backbone transport to interconnect far-flung enterprise locations as well as provide connectivity to the public switched telephone network.

There are several technology criteria that IT managers need to consider when selecting WAN services, including the networks ability to provide security for enterprise communications as well as provide cost-efficient converged services for all voice, data, and video traffic. Management must also consider the WAN networks Quality of Service (QoS) capabilities and its ability to back them up with meaningful service level agreements. Finally, enterprises should insist on partnering with a WAN provider that fully leverages the latest standards to ensure interoperability, improve flexibility, and reduce cost.

Secure Data
One of the most significant developments in WAN services is the migration to Multi-Protocol Label Switched (MPLS) backbone technology. MPLS enables relatively easy provisioning of virtual private network (VPN) connections among enterprise locations as well as to partner and supplier locations.

For data applications, MPLS-based WAN service enables an enterprise to consolidate file sharing, daily point-of-sale transmissions, Internet access, storage, Web commerce, and other types of data traffic onto a single, enterprise-wide private network offered by a single provider.

Although MPLS by itself provides some security, enterprises considering using an MPLS WAN for VoIP should also insist on a truly private MPLS network, isolated (or firewalled) from the public Internet. A private MPLS network provides service providers and enterprises with better capability to manage QoS and mitigate security risks.

Integrating Voice
Many of the most enterprising IT managers are pursuing self hosted VoIP services to eliminate the administrative and capital costs of maintaining local PBXs at several offices, including the costs of local procurement and local staffing. They are also consolidating applications over a single service providers MPLS backbone network to reduce overall network costs by eliminating expensive point-to-point links and increasing the enterprises utilization of available network bandwidth.

However, until recently, voice communications has been conspicuously absent from the converged WAN services model, limiting the cost benefits of a multi-service network. With current VoIP implementations, enterprises typically run site-to-site traffic over the WAN, but access the PSTN via separate local voice connections from each site. This means IT managers have had to continue to manage numerous local voice circuits and multiple off-network vendors as well as wasting available WAN bandwidth.

Two key barriers have stood in the way of integrating voice with other applications in a converged network: signaling incompatibility between enterprise and service provider VoIP networks, and the lack of an ability to guarantee voice QoS and security on corporate WANs. These challenges have forced enterprises to continue to use TDM connections separate from their converged WANs to access the PSTN.

Now that these barriers are beginning to fall, thanks to efforts by enterprises, service providers, and equipment vendors to deploy IP-enabled PBXs and adopt common signaling protocols and by service provider efforts to transform wholesale PSTN gateway services into integrated components of retail converged WAN access and transport services. Leading WAN service providers can now offer cost-efficient converged services access for all VoIP, data, and video traffic over a single multiservice access infrastructure

Session Initiation Protocol
One of the most critical criteria for selecting a VoIP service provider is its conformance to the Session Initiation Protocol (SIP), a VoIP signaling protocol which is enjoying rapid adoption by both enterprises and service providers.

In the enterprise, virtually all major IP PBX suppliers now offer SIP-based solutions. Enterprises are adopting SIP in great part for its compatibility with common Internet standards such as TCP/IP, DNS, and DHCP, allowing voice to fit seamlessly into existing routing and address schemes including IPv4 and IPv6. Further, because SIP is an application layer protocol, it presents a common session control mechanism not only for VoIP, but also for instant messaging, presence and a multitude of additional IP multimedia applications.

For these same reasons, the service provider community also is now largely committed to SIP as the signaling protocol of choice not only for VoIP, but also for IP Multimedia Subsystem (IMS) fixed/mobile convergence architectures. Traditional telephone companies have begun to deploy SIP at the core of their networks, using border elements such as signaling and media gateways to provide interworking with other protocols, including the PSTNs SS7.

Such widespread adoption of IP PBXs and SIP, both inside and outside the enterprise, is making seamless peering between enterprise and service provider VoIP networks possible. Using SIP-compliant IP PBXs, businesses can extend the reach and functionality of a single IP PBX across an entire geographically distributed enterprise via MPLS-based IP VPNs, without an expensive PSTN gateway card in every branch office router. The enterprise can migrate its internal voice communication to IP by routing intra-company voice traffic over a private WAN or managed MPLS network, allowing it to eliminate intra-company toll and tariff charges.

Further, off-net calls to the PSTN can be handed off to the service provider via a logical SIP trunk between the enterprise IP PBX and carrier softswitch enabling enterprises to create an IP connection to the PSTN and eliminate those separate connections to the PSTN at each office. Further solutions will enable enterprises and service providers to create SIP peering interconnections between communities of enterprises, further reducing toll charges and allowing shared private dial plans to enable extension dialing between companies.

The wide adoption of the SIP standard overcomes variances in interoperability between carrier and enterprise voice equipment as well as easing the task of troubleshooting problems.

QoS and Security
With several different types of communications traffic now able to run over a converged network, it becomes important to select a WAN service provider who supports hard, deterministic QoS for each type with strict priority queuing. This is in recognition that different types of enterprise communications traffic will have differing QoS requirements.

Voice and video applications require rigorous timing control and performance metrics. Priority data includes mission-critical business applications with lower delay sensitivity than voice/video applications, such as surveillance video and applications with flow-control capable transport layers, while standard data includes sporadic LAN-to-LAN traffic. Internet-class applications like e-mail and Web browsing have the lowest QoS requirements.

A fully converged WAN network should offer the enterprise customizable and controllable bandwidth per port. The enterprise need only purchase the bandwidth required, maximizing flexibility and cost-effectiveness.

Security is a growing consideration as well. Enterprises should look for service providers with private VoIP WANs not directly exposed to the Internet. The VoIP WAN should have access to it controlled via session border controllers, which are essentially purpose-built VoIP firewalls to ensure that only authorized signaling and media packets reach the core VoIP network. This network arrangement helps to secure enterprise communications end-to-end from eavesdropping, denial of service, and other hacker attacks.

Retail PSTN Gateway Services In the Cloud
Given broad adoption of SIP in the IP PBX realm, service providers are well positioned to turn wholesale PSTN gateway services into retail gateway services in support of SIP-based enterprise WANs.

On the service providers side, on-net calls are sent over the enterprises private IP or MPLS backbone, while off-net SIP calls to the PSTN ride the carrier IP network to a service provider owned SIP gateway that converts VoIP to TDM for calls to PSTN parties. The service providers economies of scale have replaced a cost structure based on TDM gateways at every enterprise location with a handful of regional gateways interconnected by low-cost, high-quality IP circuits.

Such gateway services in the cloud are all the more efficient if the service provider operates both a national IP/MPLS network and a national TDM voice network complete with robust circuit switch support of E911, local number portability, and other vital telephony services.

This SIP-enabled scenario enables transport of all data and voice traffic over a single converged WAN connection and the centralization of all PSTN calling through a single VoIP connection to a national carrier.

In terms of capital and operating costs, on-net and off-net SIP voice connections remove the need for on-premise PSTN gateway equipment. The converged WAN connection removes the need to contract with a local phone company in each market for local PRI lines to the PSTN, while also reducing toll charges to the PSTN for on-net long distance and local access calls that are now carried over the WAN. On top of this, nationwide pooling of VoIP ports allows enterprises to aggregate PSTN capacity on large circuits rather than manage channels on many different individual trunks, resulting in greater oversubscription, higher port utilization, and lower costs.

Additionally, data WAN access options, such as per-application QoS offerings, now also apply to VoIP as well as to any other WAN data application, thereby moving the enterprise toward a usage-based access and transport capacity model for voice. As a critical bonus, the SIP-based WAN positions the enterprise to exploit the coming integration of voice with IM, presence, multimedia conferencing, IP video and other SIP-based IP multimedia applications for enhanced enterprise mobility, productivity, and business agility.

A WAN to Match Your Enterprise-Hosted VoIP Network
Given the large investment enterprise IT managers are making in implementing hosted VoIP networks, it is important to take the next step and select a WAN service provider who can offer the best match in security, converged services, QoS, and network protocols. Only then will the enterprise gain the full benefits of IP communications technology. IT

Todd Kiehn is senior product manager of VoIP services at Broadwing. For more information, please visit the company online at (news - alerts).

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