Intelligent switching - the key to quality of service

The network is slow ... what can we do to get better response times? Do we install bigger "pipes", in other words upgrade the network backbone from 100Mbps to 1Gbps?

Or can we look to intelligent switches to make a difference?

Intelligent switching opens up possibilities to extend the natural life of a network backbone, by allowing the network manager to fully exploit the bandwidth available to him through prioritisation.

Prioritisation means the ability to identify certain traffic streams and "fast track" these data streams through the switch architecture, so that delay sensitive applications do not suffer.

Intelligent switching refers to the capability of networking hardware to look into the packets of traffic the network is carrying and to make forwarding decisions based on the type of traffic and the priority that has been assigned to that traffic.

Intelligent switching is really the basis of a policy-enabled, quality of service-ready network. The different layers as specified by the Open Systems Interconnect (OSI) model relate to the degree to which a switch is aware of the type traffic that it is carrying.

For example, a Layer 2 switch is aware of a packet`s MAC address and possibly the Layer 2 priority setting (802.1p header, and the VLAN association), while a Layer 4 switch, such as 3Com`s 4400 series, is able to identify the application that is being carried by looking at the layer 4 TCP header.

The ability of the switch to identify the traffic empowers the network administrator to either block or prioritise the specific traffic depending on its importance, optimising the network for maximum efficiency for mission-critical applications.

Another function of intelligent switching (beyond blocking and prioritising) is for the switch to redirect certain traffic streams to different ports based on the protocol.

The most common application is Web traffic, which can transparently be re-directed to a Web cache sitting off a Layer 4 aware switch.

There are different ways of identifying the traffic on a network, according to the layers as specified by the OSI model. However, because the model is a theoretical one, in practice there is a fair amount of overlap in terms of functionality from that which is specified per layer by the OSI model, and that which exists in reality.

With TCP/IP, the theoretical functionality of the OSI Layers 5 and 6 are incorporated into the 5 Layers of the TCP/IP suite. The important layers within TCP/IP are Layer 4 and what is referred to as Layer 7, the application layer. While Layer 7- aware products are available on the market, these are niche devices for specific circumstances - and are usually on the periphery of the network.

Essentially, the difference between a Layer 4-application aware device and a Layer 7-application aware device is the way the product identifies the traffic it is carrying.

With Layer 4 devices, the application is identified by the port through which the traffic is being switched, while a Layer 7 device will look into the application layer within the packets of data to achieve the same goal. While it can be argued that the Layer 7 device will be more accurate in identifying data streams, the applications are easily identified through well known Layer 4 port numbers, making Layer 4 just as efficient in identifying the application type.

The added functionality that intelligent switching brings to the network does result in increased complexity. However, to empower users, companies like 3Com develop software that alleviates the difficulty of configuration.

Its true that the more a box can do the more there is to configure, but through the use of wizards a lot of the complexity is removed.

Not all networks require the functionality that intelligent switching delivers. However, as the pricing of Layer 4 enabled devices is around 20% to 30% more than non-intelligent devices, such products are within the reach of most budgets and allow future-proof networks to be built. An investment in intelligence is a sound strategy.