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Will MPLS Be the Secret to VoIP's Success?

Voice services deployed over IP networks are growing steadily in the enterprise, by as much as 10 percent a year in some sectors, according to the Yankee Group. But noticeably absent in these much-ballyhooed enterprise offerings are industry-standard quality of service guarantees, networking experts say.

Without an improved networking protocol that helps converged voice and data networks scale properly, while giving priority to voice packets over, say, a joke-of-the-day e-mail, VoIP deployments risk chronic quality issues such as static and delays in transmission.

But one promising success lurking behind the rollout of VoIP -- as well as a coming array of IP-enabled telephony services -- is the networking protocol known as MPLS, or Multi-Protocol Label Switching .

Experts say MPLS-enabled networks give operators a great deal of flexibility to divert and route voice and data traffic around link failures, congestion, and bottlenecks in IP networks, both public and private.

MPLS, an initiative of standards-group IETF (The Internet Engineering Task Force) integrates Layer 2 information about network links (bandwidth, latency, utilization) into Layer 3 (IP) within a particular autonomous system--or ISP. It has been in use by major backbone providers for years as a management tool for simplifying and improving IP-packet exchange.

For carriers that found success offering layer 3 VPN services to enterprise customers with MPLS-based networks, the protocol has already proven its usefulness. Customers found new ways to provide network access to their employees; service providers, with the help of MPLS-based networking, built new revenues during turbulent times in the telecommunications industry.

Now, "we see many service providers deploying MPLS in their networks and we expect to see more MPLS support," says David Christophe, education working group chair for the MPLS/Frame Relay Alliance, a trade group of networking companies working to promote common MPLS standards.

"Right now, service providers have one network for voice, one for internet IP traffic, one for ATM or even Frame Relay-based (data networks)," Christophe says.

"It's tough to share resources across them. That can be tricky. This leads to the view on the part of many carriers that MPLS provides a good mechanism in the core of networks to provide connectivity between various types of (networking) services," he says.

Give a network the ability to give voice priority over other kinds of packets crowding into a data pike, goes some of the thinking, and a carrier or vendor is farther along the road to providing service level agreements and Quality of Service guarantees with VoIP.

But MPLS is not going to solve all the quality and routing issues involved with overlaying voice services on IP networks, adds Lisa Pierce, telecommunications analyst and research fellow for Forrester Research. "Anyone who thinks MPLS is a magic bullet -- as important as it is -- is seriously mistaken."

For one, she says, MPLS has many variations right now -- call them different dialects that can get in the way of how well one network communicates with another -- such as whose traffic is more important.

That's one reason inter-carrier agreements among different providers of MPLS-based VoIP rollouts have yet to happen, she notes.

But Pierce is quick to note that inter-carrier agreements "will first occur over managed VoIP networks, between two carriers privately --just for their high end customers" (think of a special "HOV" lane for voice packets traveling across the IP highway,) she says. "That could begin as early as 2004. But the public Internet will never likely be able to guarantee end-end per-call/transaction QoS."

For some time, Pierce has noted in research papers, "the gap between the ideal and the real [with VoIP] becomes very clear when one considers that no tier-one provider yet offers end-to-end applications-specific SLAs (service level agreements) for managed VoIP services."

In addition, "many providers don't even publish VoIP service-level objectives (SLOs), much less stand behind those metrics with service credits (the combination of SLOs and service credits yields SLAs)."

However, that view was published before AT&T recently upped its quality guarantees.

In late September, AT&T announced that by next year, it will be offering VoIP service for business customers as an option on its managed network Virtual Private Network (VPN) service for business customers.

AT&T says it is deploying the offerings via its MPLS-based network, which uses class of service traffic management to provide enterprises with applications such as voice "delivered securely, reliably and with high quality."

In something of a breakthrough for major backbone providers, AT&T has staked a claim to being the first in the industry to provide global VoIP-specific and ITU standards-based service level guarantee for voice quality, including quality reports of every call placed.

In addition, the service is promising dynamic real-time bandwidth allocation and prioritization between voice and data, which is designed to help customers trim their network and utilization costs.

The long distance and data backbone provider says it plans to initially service the domestic voice needs of United States-based multinational companies and U.S. government agencies with continued expansion to over 40 countries throughout 2004.

Lawrence Byrd, a convergence strategist with Avaya, a major provider of IP voice telephony, networking software and services, says although MPLS is gaining in use and moving closer to becoming more standardized, the protocol needs time to develop. But that won't slow down VoIP deployments, he adds.

"The driver here is actually going to come from IP Telephony," he tells internetnews.com.

He says if you take the example of customers deploying branch solutions with VoIP, such as a newspaper with 29 different locations, which it then wants to network through an integrated IP system, adding voice on that IP network becomes an attractive way to integrate all those branch offices for a lower cost.

"The business case is going to drive this, and will be driven by these kinds of business cases," says Byrd. "If a carrier can say 'I'll do that for you,' -- and since the driver here is voice and telephony -- we're going to arrive at [deploying] MPLS" as part of that effort.

At the same time, enterprises are finding that frame relay-based networks that they once deployed for their T1 data connections are not the most optimal solution to use for rolling out VoIP, Byrd adds, because frame relay's packet-switching protocols are not effective in traffic across a wide area network.

By contrast, adds Rohan Dwarkha, a network engineer with VoIP provider Vonage, MPLS is very scalable and can find the fastest path across a data network in order to get the call to its receiver as quickly as possible.

Christophe of the MPLS/Frame Relay Alliance agrees that much work awaits regarding standardizing MPLS protocols. But progress is happening, he says, pointing to a recent (though non-binding) agreement tha alliance hammered out on a new Voice Trunking Format over MPLS. The implementation "helps standardize the way in which voice packets are compressed over a converged MPLS backbone using existing ATM Adaptation Layer 2 (AAL2) technology."

The agreement also contributes to the design of carrier or edge PE routers, multi-service edge switches and dedicated gateway equipment.

David Sinicrope, system manager at Ericsson and the chairman of the alliance's working group on the issue, says the voice trunking agreement "provides an efficient means of transporting voice and related traffic from integrated access devices and wireless telephony networks over MPLS infrastructure networks."

In the meantime, while network architects figure out how to deploy carrier-grade VoIP services, Pierce recommends that enterprises continue to gravitate toward managed VoIP service providers that can "consistently demonstrate and warranty superior end-to-end per-call network performance.

"These providers will likely charge a higher fee for their services, but, depending on the premium and relative performance, paying a little more could be well worth the difference between a satisfactory and dissatisfactory VoIP service and support."