Home on the range: the wild world of quality of service on the WAN

The wide-area network (WAN) presents more challenges than does the local-area network (LAN). That’s why David Komaromi, data and telecommunications manager for law firm Fraser Milner Casgrain LLP in Toronto, would rather control how his voice packets travel over the WAN than leave it up to a carrier. This is because quality of service (QoS) is a must for any voice or video traffic over IP networks, and Komaromi’s firm relies on a voice over IP phone system. Smaller customers or those without much technical expertise may prefer to have the carrier do it all, Komaromi says, but it's more efficient to control your voice or video traffic end to end. The best arrangement is one where packets are prioritized on the firm's network and the carrier simply accepts the priorities assigned by the customer.The reasons for that are fairly simple. Bandwidth is usually scarcer on the WAN, and latency – delay in getting a packet from point A to point B – is more of an issue, says Ian Gallagher, consulting systems engineer with Cisco Systems Canada. When there is less bandwidth to spare, packets are more likely to be lost, resulting in choppy conversations or at worst, dropped calls. Latency can cause annoying delays between one party speaking and the other hearing, and can contribute to echo.And the technical issues are often complicated by the fact that the enterprise IT and telecommunications people have less control over the WAN than the LAN. "When the traffic leaves the enterprise and hits the wide-area network, you may or may not be working with a private network," says Tracy Fleming, director of emerging technology at Avaya Inc. in Toronto.If the WAN is private, then you manage your own quality of service much the same way as in the LAN. It's just more important because there's usually less bandwidth to spare."The WAN definitely stands out as ... a bottleneck in terms of bandwidth," says Jay Angl, a research analyst at Info-Tech Research Group in London, ON. While LANs today typically have at least 100 megabits if not a gigabit per second of capacity, WANs are significantly slower. And geographical distance makes latency more of a concern. "Just because of the sheer physics involved," says Angl, "there's a natural latency in transmitting data across the country."Call management must work with QoS toolsOne of the first steps in any voice or video over IP project should be to analyze the existing network. If the network has only been used for data, Angl says, there's a good chance no such analysis has ever been done. The analysis will determine how much traffic is going over the network and whether problems are likely to arise at peak periods. If so, the links may need added capacity. Then there should be monitoring tools to keep an eye on traffic moving over the network, to identify points of congestion and help troubleshoot whatever problems arise."In some cases the tools are quite expensive," Angl warns. It may make sense to turn to an outside consultant or systems integrator who already has the necessary equipment.Quality of service provisions allowing voice and video packets to be tagged so that they get priority over data packets (for which delays usually have little visible effect) are essential on the WAN.Besides implementing quality of service, a network administrator can improve performance by tracking down the specific points or devices on the network where problems are occurring, says Catalin Dinulescu, managed services product line manager for Nortel Networks Corp. of Brampton, ON. Then it may be possible either to replace or tune the problem device or to route some of the traffic – particularly voice or video traffic – around the bottleneck.In fact, says Gallagher, call management – which can control how many calls are routed over a given network link – is an important complement to quality of service technology. "If you send five calls down a WAN connection that was provisioned for three calls, you're going to have problems."Compression is another possible way to manage bandwidth, Dinulescu adds. And Fleming suggests that varying the packet size can help; essentially, the smaller the packets, the less noticeable the loss of an individual voice or video packet will be.The buck stops with the WAN ownerWith a private WAN link, the responsibility for all this falls on the business. The responsibility comes with control, but dedicated links are also fairly costly and inflexible, and often not an option for operations with multiple small locations to connect.As well, if the WAN belongs to a carrier, it may be hard both to monitor what's going on across the network and to control the priority given to different types of traffic. One option is to rely on the carrier who operates the WAN link to manage quality of service and, as Komaromi says, this can be the best option for those who don't want to tackle the job themselves.But another option is services that let the WAN operate almost as an extension of the customer's local network. Multiprotocol label switching (MPLS) essentially creates what looks like a LAN link over the WAN. "Many organizations that had an expensive frame-relay network are moving toward MPLS," Angl says.MPLS provides guaranteed classes of service for different types of traffic over the WAN, explains Dinulescu. Another advantage of MPLS is that it provides point-to-point connectivity among multiple locations, rather than requiring a hub-and-spoke architecture that creates heavy bandwidth demands around a central hub.On the other hand, MPLS is tricky to manage, so even organizations that are quite technically sophisticated often rely on their carriers to manage MPLS services for them.

Home on the range: the wild world of quality of service on the WAN

News | 06/23/2008 3:09 pm EDT

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