In today`s high speed, high demand networks, switches play a pivotal role. They are key to the performance and functioning of the network and their selection is a critical element in the strategic purchasing process.
While networks are designed to support applications that can make businesses more effective and efficient, a combination of factors - such as server consolidation, rich media types, bandwidth-hungry applications - create situations in which the demand for applications out-strips the available bandwidth.
When this occurs, the network acts as a "funnel" - applications compete for bandwidth or are kept off the network altogether.
These networks are not able to ensure the smooth operation of important applications and must juggle the competing demands for application bandwidth from the various sources within the organisation.
The choke points in these "funnel" networks are at the aggregation spots - in wiring cabinets and backbones - where performance and services intersect.
Anywhere-to-anywhere
Legacy software-based routers which have traditionally occupied these aggregation points were not designed for the enormous traffic loads and the anywhere-to-anywhere traffic that is now the norm.
Gigabit Ethernet and switching routers eliminate these choke points, in a sense, flipping the "funnel" over.
By delivering a performance of more than 100 times traditional routers at a fraction of the cost, these devices offer true scalability, providing the bandwidth required for current applications and future applications as well.
Bandwidth: only one piece of the puzzle
But adding bandwidth is only one piece of the solution. As the mix of applications in a network becomes more complicated, the need to manage the traffic flowing through the network becomes more critical. In order to manage this traffic, traffic flows must first be measured and tracked. Once traffic patterns are understood, advanced services such as filtration and prioritisation can be used to optimise the network. It is the combination of performance and control at the heart of networks that delivers the competitive advantage so sought after by businesses operating in today`s global environment. In this regard, it is the ability to satisfy the dual requirements of performance and control that has created the excitement around the new breed of products called Layer-4 network switches.
Layer 4
Layer 4 of the OSI model is the Transport Layer. It is responsible for co-ordinating communication between network source and destination systems. Critical network management elements such as the TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) reside in Layer 4.
At Layer 4, each data packet contains information that can be used to uniquely identify the application that generated the packet. This is possible because the TCP and UDP headers include "port numbers" that identify which application protocols are included in each packet.
In combination, the port number information in the Layer 4 header and the source destination information in the Layer 3 header can be used to apply fine-grained control. Individual application conversation flows can be controlled between client and servers, and if the switching router is full function, all this can be done at wire speed.
By reading into the Layer 4 header, a Layer 4 switch can differentiate between applications when performing routing decisions. Applications can be assigned different forwarding rules, guaranteeing different Quality of Service (QoS), or have security filters applied to them providing application-level control over the network. Once this information is tracked, QoS, security and accounting can be applied to the individual flows using the source/destination/source-port/destination-port information.
It is important to realise that a single client/server pair can have many different application conversations open at the same time. Since an enterprise backbone sees many thousands of client/server pairs, a backbone class Layer 4 switch must have the table capacity to store in the order of millions of Layer 4 flows.
QOS, security, accounting
The demand for QoS is undeniable. Rich data types, mixed media, video conferencing, real-time audio and video multicasting, Internet telephony and interactive transaction processing combine with mission-critical applications to create the need for tight control over latency and throughput.
Layer 4 switching allows QoS policies to be set on application-level flows, thereby giving network managers complete control over bandwidth usage in the network backbone.
Layer 4 switching eliminates the performance loss associated with security features. A true Layer 4 switch should deliver wire-speed performance when all the advanced features including security are activated.
In Layer 4 switching, packets are processed in custom ASICs, and since the source and destination port information is tracked, application-level security can be coupled with wire-speed performance.
Accounting
Management requires measurement. When network traffic cannot be measured, it cannot be effectively managed. Layer 4 switching vastly improves measurement, accounting and performance monitoring capabilities by tracking application flows.
A Layer 4 switch tracks source/destination network addresses and source/destination port numbers for each flow. This allows a well-designed Layer 4 switch to collect accounting information for each and every flow that passes through it.
Protocols
For Internet enabled networks, switches must be able to accommodate directory protocols such as the Lightweight Directory Access Protocol (LDAP) and Lightweight Flow Admission Protocol (LFAP). LDAP provides a standard way for Internet clients, applications and Web servers to access directory listings of thousands of Internet users, while LFAP facilitates better network traffic control and alleviates congestion problems.
Switches and switching routers that do not support all these protocols will be relegated to providing partial solutions in future.
Conversely, devices that can deliver performance, functionality, and the rich mix of protocols will be the building blocks of durable networks.
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