Vendors such as Packeteer and Sitara (now Converged Access) are providing appliances for traffic management that mainly work at the network edge, because network vendors have not adequately addressed these issues, says Bjarne Munch, senior analyst, META Group. "I see this as being more of a short term value proposition."
These edge devices can be good if you have congested links that would be costly to expand (eg, communications between Australia and Fiji) or that are already high bandwidth (eg, Melbourne to Sydney) and you want to avoid buying more capacity just to cope with peak loads, he says. Packet shaping will prioritise the most important traffic and let the rest wait.
Such appliances are also good for monitoring and reporting, as gaining an understanding of the applications being run is a non-trivial task for a large organisation where not all purchases are centralised. Once profiles are created that identify applications' network requirements, the location of users, etc, it is possible to manage the traffic properly.
"First and foremost, you have to understand your network, then you can control it," says Steve House, Packeteer's senior manager -- product management. Packet shaping requires collection of application-specific information, so Packeteer's products now report that information, identifying response times and causes of problems for individual applications.
This information can already be fed into BMC's management software, HP's OpenView and IBM's autonomic computing model.
This understanding of the data flowing through a network can also be used to support compression. Traffic awareness means the appliance only attempts to compress the compressible traffic, and applies different algorithms according to the traffic type. This approach can "effectively double or triple the bandwidth of an existing pipe," says House.
Deep packet inspection tools "are evolving very quickly," according to Boland, and are becoming more application aware. These tools permit the network fabric to take action according to the contents of data packets, for example applying rate shaping or changing the VPN. They might apply policies to determine access rights (eg, access to certain servers might be prohibited if the request comes from an outside IP address), or they could redirect URL requests to a cache.
Policy servers can redirect traffic as necessary to maintain the required quality of service, he says, basing these decisions on data collected by service assurance agents. By using open interfaces, Cisco's policy servers are able to operate with other vendors' products.
"We are beyond transmission... the real intelligence is in the areas of measuring, control, and dynamic function," he says.
Time-critical applications such as VoIP require end-to-end traffic management, says Munch, so it will need to be implemented throughout the network, for example with quality of service support in each router. In such cases, the router must be able to handle all traffic types. Some applications are very "chatty" and require low latency for good results, which means proper management is essential. VoIP and similar traffic requires all switches and routers to queue all traffic types correctly, and network equipment vendors are adding this capability to their products, he says.
House has a different opinion. He suggests that if too much high priority traffic (eg, too many voice calls) is directed across one link, QoS mechanisms will attempt to handle them all, overloading the link and giving poor performance for each stream. A Packeteer appliance will instead guarantee the required bandwidth for each call and completely deny attempted calls that would cause overload.
Another issue with QoS is that dropping lesser queues to give priority to voice or video packets can cause problems with other applications. Packet shaping can guarantee minimum bandwidth allocation for those other functions, he says.
The objective is to give "good" applications the highest priority and let "bad" ones have what's left -- in this context, bad could mean something innocuous as a large, once-off FTP transfer. "The general network will always survive with Packeteer," claims House.
Boland points out that some applications may need intelligent degradation. For example, MPEG streams consist of syncing frames followed by a series of difference frames. If you have to drop packets, you don't want to drop them from syncing frames. "We can degrade gracefully," he says.
Jonathan Spellman, IP network specialist with Damovo, agrees with Munch about the need for QoS support in the network infrastructure but warns that it is easy to make inconsistent settings on different switches, which can lead to dropped VoIP calls.
Furthermore, such switches aren't very smart in that any changes to the overall system (even something as simple as an application upgrade) may disturb its equilibrium and prevent proper data flows. This means ongoing monitoring -- whether in-house or on a managed service basis -- is required, using tools such as those from NetIQ.
According to Boland, another attribute of VoIP is that the digital signal processor (DSP) chips used in VoIP gateways and other devices are able to measure the quality of a call, and any deviation below the norm may indicate a network problem. This information should be accessible to the network management system.
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