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Switching your data

Are you serious about running your network to its maximum potential? Then you need to replace your hub with a switch. Here are few guidelines to follow when buying a switch. by Mahesh Rathod

The main job of an Ethernet switch is to divide networks into segments and providing each segment with dedicated bandwidth

As a network grows and new users are added, the network's bandwidth becomes more crowded and traffic slows down. For example, if a network has 100 Mbps of bandwidth, and 4 users are using the network heavily, each user will receive only 25 Mbps of bandwidth (100 divided by 4). Because everyone on the network is sharing the same space, this shared network can grind to a halt during peak network activity.

This problem can be addressed by using a switch. Similar to a hub, a switch transforms a shared network into a switched network, giving all users access to the network's full bandwidth. In the example above, all of the users would enjoy true 100 Mbps bandwidth instead of 20 Mbps. Since a switch helps users make the most of a network's potential, most 10/100 network looking for maximum performance should have one, especially in areas of high traffic. Power-hungry workgroups requiring maximum bandwidth should definitely be connected to a switch.

What is a Switch?
Usually in a LAN, all devices attached to the network share that network's bandwidth. As more devices are attached to the network and as bandwidth requirements expand, network congestion also increases. The main job of an Ethernet switch is to divide networks into segments and providing each segment with dedicated bandwidth. The switch transfers traffic between network segments to allow a station on one segment to address a station on another segment.

Like bridges, switches subdivide larger networks and prevent the unnecessary flow of network traffic from one segment to another, or in the case of cross-segment traffic, switches direct the frames only across segments containing the source and destination hosts.

How Do Ethernet Switches Work?
Ethernet switches mainly work at the Layer 2 (Data Link Layer) of the OSI model. They check the destination media access control (MAC) address on each incoming frame, and look up the address in their tables to find out whether it is local to that port or is destined for another port. If the address is not local, they switch the frame to its appropriate destination port.

How different are switches?
Switches themselves are hardware devices that look similar to routers, hubs or bridges. However, three important factors separate switches from their networking cousins: overall speed (switches are much faster); forwarding methodology or electronic logic (smarter); and higher port counts. In contrast to the functionality of bridges and routers, which traditionally utilize the less effective and more expensive microprocessor and software methods, switches direct data frames across the various segments in a faster and more efficient manner through an extensive reliance upon on-board logic, through Application-Specific Integrated Circuits (ASICs).

When to buy a switch?
A switch isn't necessary for every network. A decision to buy a switch is influenced by two factors: to improve network performance and to run high-speed bandwidth heavy applications like multimedia.

To enhance performance: A switch will improve performance for any file servers or workstations connected directly to it. Small network can use a switch instead of a hub to give workstations maximum speed. If a network is large, it should have at least one switch in every high-traffic workgroup. As a general rule, try to get every file server, critical workstations, and print server connected directly to a switch.

To run high-speed applications: When a network will be using high-speed applications like multimedia or video generally speaking, every workstation and file server that will be using multimedia or video should be connected to a switch to avoid transmission delays.

Anywhere a 10/100 Fast Ethernet hub is required small workgroups and large network alike will benefit more from using a 10/100 switch to maximize performance over a mere 10/100 hub alone.

Types of switches
Switches can be classified according to the way they forward data packets or the manner in which they handle network traffic.

Store and Forward switches
Store-and-forward switches, take an entirely different approach. Instead of the faster send-it-as-soon-as-you-can rule used by cut-through devices, store-and-forward devices wait until the entire packet is received by the switch, only then sending it on to its destination.

Dynamic switches
Dynamic switches not only forward packets to their proper destination, but also maintain a table that associates individual nodes with the specific ports to which they are connected. This information is updated each time a particular machine transmits data across the network, allows the switch to quickly direct frames across the proper segments, rather than across all segments on the switch.

Segment switches
Segment switches can handle the traffic from an entire network segment on each port, allowing you to connect a higher number of workstations or segments with fewer switches/physical ports. The aspect behind segment switches is that they are also capable of handling a single workstation on each port (in essence, a segment with one node).

Port switches
Port switches are designed to accommodate a single device on each physical port. However, implementing a port-switching solution demands a good deal of capital for additional wiring (cable runs are needed from each device directly to the switch) and enough switches to provide the requisite number of physical ports.

Features to look for in a switch

• 16 or 24-Ports switches should run at 10/100 Full Duplex and have an auto sensing capability
• Should be perfect for running 10BaseT, 100BaseTX and 100BaseFX hardware seamlessly
• Data flow control should be able to filter out faulty data packets
• Must be capable of advanced store-and-forward data packet switching

Mahesh Rathod can be reached at rathodmp@hotmail.com