ensuring voip quality starts at home

The search has produced evident results. Voice quality on most broadband VoIP services is close to the PSTN, and often better, with the greatest challenges caused by contention in access networks.

Many VoIP service providers maintain they do not get many quality complaints. “I’ve got customers saying the voice quality they are getting with our system is better than what they get with traditional systems,” says Bill Bollinger, vice president of engineering, Appia Communications Inc., a Michigan provider of hosted PBX services for small and medium businesses.

Michael Burrell, head of enterprise telephony at Equant, a subsidiary of France Telecom that provides VoIP and VPN services to multinational companies, says, “As we travel to various offices, we ask, ‘What do you think about the phone service,’” and often they give us a quizzical look and ask, ‘What do you mean?’ so we say, ‘Do you realize that you are using VoIP,’ and often they did not know.”

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Nevertheless, service providers continue to push to eliminate the remaining glitches and imperfections to make sure their networks match the PSTN and even outdo it in voice clarity.

Service providers have developed various strategies and techniques for quality, based on the kinds of services they offer. For those offering services directly to end users, such as consumer VoIP or hosted PBX services, those strategies usually involve trying to manage the parts of the network that are under their control, while minimizing effects of something they often do not control: the access network.

“The low-hanging fruit to ensure goodquality conversation is the last mile between the customer and the Internet, specifically the upstream connection,” says Louis Mamakos, CTO of consumer VoIP provider Vonage Holdings Corp. “That upstream pipe is the bottleneck that voice traffic is going to encounter on its way to its destination. The good news is that it is the part of the whole problem that is easiest to deal with. The amount of traffic on that bottleneck is under the control of the customer at home. You can have the cable or DSL router box prioritize traffic for you as it is being injected into the network.”

If a residential customer has a LAN with a couple of PCs as well as a VoIP terminal adaptor, Mamakos says, the service provider needs to make sure that voice is “not competing against and losing against” other upstream traffic. “If they are doing just Web browsing, the amount of traffic that they send into the network is small,” says Mamakos. “When you have symmetric applications, like peer-to-peer file sharing or a really big e-mail upstream, that is where you need to start to manage how that capacity gets used.” Vonage recommends a router from a company such as Linksys (a Cisco Systems Inc. company), that can prioritize VoIP traffic over other applications.

For those providing hosted PBX services to small businesses, often voice is delivered over the LAN. However, “bandwidth issues typically don’t happen within the LAN,” says Appia’s Bollinger. “On a LAN you have 100 megs of availability. When you are talking about 12kbps or 24kbps for voice, you’re talking about a mosquito flying through the Holland Tunnel in terms of bandwidth.”

“Usually the quality issues are lower, and the quality is better,” with voice over the LAN, agrees Equant’s Burrell, whose company has done deployments for large enterprises worldwide.

Moving to the WAN, however, says Bollinger, “You go from 100 megs to a T1 or DSL” as the access bandwidth. “We are not having an issue with voice quality unless there is contention for bandwidth in a private T1 environment,” says Bollinger.

Once you get beyond that first hop into the network, managing quality of service becomes a non-issue, because there is adequate performance on the backbone of the Internet, Mamakos says. Vonage manages its Internet bandwidth, and then manages its gateway capacity to the PSTN (obtained from other service providers) to be sure it has enough.

Termination to the PSTN also is not a significant quality issue, service providers say, except for some international destinations. “We do tend to see a bit more variation in quality,” says Mamakos. For that reason, Vonage, like most VoIP providers, has multiple contracts for each destination, where possible.

However, the choice of endpoint can make a significant difference in quality. “We are getting fairly far along in the learning curve in making VoIP devices,” says Mamakos. “The variability is not that large anymore.” Some service providers, such as Vonage, are offering endpoints that let the user choose the codec. If the end user is connecting using dialup, rather than broadband, the quality will be best using the G.729 or G.726 codecs, which compress more and use less bandwidth.

IP endpoints have seen “significant improvement over years in MOS (mean opinion score, a standard measure of quality)” says Burrell. “We started measuring MOS as a service-level objective, and now we are evaluating PESQ, perceptual evaluation of speech quality,” a more stringent measure of quality.

The only exception in endpoint quality, Mamakos says, was in the quality of echo cancellers, although there has been significant improvement in the last year. “Now echo tends to be a configuration issue more than the quality of the echo cancellation,” he says. Where there are unexpectedly long loops in getting to the PSTN handoff, sometimes Vonage will have to turn on echo cancellation for that particular loop. “We wouldn’t turn it on if it were just a short local handoff,” Mamakos says.

In addition to similar measures, Appia uses “low-latency queuing (a technique implemented in routers) to make sure that we get quality of voice,” says Bollinger. “If you don’t have any packet loss issues or bandwidth issues, you’re golden. Low-latency quality of service kicks in only when we are in a bandwidth-contentious situation.”

Bollinger sees quality of service in the access network as a business opportunity for service providers. “The carrier that steps up to the plate and provides some level of prioritization [for voice] over Internet and typically on the last mile, they will be the winners in this environment,” says Bollinger. “But no one is willing to do that. I have talked to a half-dozen providers about that, and they all refuse.”

Some service providers that offer both VoIP and IP connectivity mark packets for different levels of service. Masergy Communications Inc. specializes in controlled quality of service, supporting high-bandwidth, real-time services.

“We are selling converged services, and any other application that will have a serious impact on voice, if the line gets congested,” says Jim Brunetti, director, IP engineering, Masergy. “We know if someone makes a voice call on a regular T1, and someone is also using it to get out to the Internet, the voice quality will generally suffer.”

To solve the issue, voice packets are marked “from when they leave the [customer’s] router onto a T1 line and over a backbone network. ... any place where there is a possibility of congestion,” Brunetti says.

SBC Communications Inc. also has engineered its backbone network using MPLS “to ensure quality of service and in order to be able to use VPNs,” says Nancy Lambros, lead member of technical staff, SBC.

SBC is taking quality a step further, developing an entire network service, called Hosted IP Network Service (HIPNS), using the ToS (type of service) bits in an IP packet header to differentiate services. “Now we want every critical network device react to that ToS bit,” Lambros says. “Phones have been doing that for a while, and we want to do it on the network equipment too.”

The issue is becoming more important as SBC prepares to launch a hosted PBX service based on its own infrastructure, rather than the wholesale product from Level 3 Communications Inc. that it has been offering.

To get the level of service SBC wants will require a significant upgrade in the network. “We had to upgrade a lot of edge devices,” Lambros says. “The problem is the device at the edge of the core backbone. All those critical points need to have the ability to do quality-of-service recognition and prioritization based on that marking.”

“Maybe it’s not needed yet,” says Lambros, “but we want to be able to have voice marked from endpoint to endpoint.”

For Equant, which often works with large corporate PBXs, many issues have been with those devices, says Burrell. “If we are going to have a problem, it is right at the start with the device we are connecting to.” He adds, “Usually if it is a newer PBX and a PRI in, often it goes off without a problem or hitch.”

Like Vonage, Equant occasionally will see issues with delay when the route to a destination is long. A recent problem on a service to India was solved simply by changing the route.

Other delays are caused by processing. “In video, if we are doing a video conference and it is going through ISDN switches, sometimes in those handoffs there are places where we can have a chance of call failure,” says Burrell.

Like many enterprise providers, Equant qualifies the customer’s own network, particularly if it’s a LAN VoIP service that will be deployed. “We do a site survey to be sure they have the right connection,” says Burrell. “We showed up at one pharmaceutical company in New Jersey and discovered that they had analog access.” Equant also will do traffic studies, as much to prevent overengineering as to be sure the network has enough bandwidth.

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