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Switch Over For Efficiency

Switches are hardware devices that look similar to routers, hubs, and 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

As your network grows in terms of nodes, users, and services provided, sooner or later you'll be faced with the monster of all network problems: insufficient bandwidth.

Performance will degrade, users will cry about slow network response times, and client/server applications will grind to a halt. This is not good for your network. You've got two options at this point--work for a company that doesn't care how much money you spend and can afford long spans of network downtime, or adopt switching.

Switches are smarter than hubs and offer more dedicated bandwidth to users or groups of users. A switch forwards data packets only to the appropriate port for the intended recipient, based on information in each packet header. To insulate the transmission from the other ports, the switch establishes a temporary connection between the source and destination, and then terminates the connection when the conversation is done.

How Do Switches Work?
In simple terms, switches function by breaking down greater, traffic-intensive networks into smaller, more controllable sub-networks. Instead of each device constantly vying for attention on a single saturated segment of 10Mbps Ethernet, switches allow single devices (or groups of devices) to "own" their own dedicated 10Mbps segments connected directly to the high-speed switch, which then facilitates inter-segment communication.

Although this sounds a lot like a bridge, there are some important distinctions that make switches much more dynamic and useful pieces of hardware.

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 the segments containing the source and destination hosts.

How Different Are Switches?
Switches themselves are hardware devices that look similar to routers, hubs, and 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).

Types Of Switches
By now you should be convinced of the important role that switches could play as part of your Ethernet network. Let us take a look at the various kinds of switches that are available.

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, updated each time, a particular machine transmits across the network, allows the switch to quickly direct frames across 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 great aspect of segment switches is that they are also capable of handling a single workstation on each port (in essence, a segment with one node). Because of the inevitable cost controls that you encounter on a daily basis, segment switching is the preferred and most readily implemented solution because it requires little in the way of additional expenditures for hardware, additional cabling, and so on.

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. Additionally, as your network grows, you'll face significantly increased expansion costs because you'll need new cable runs and possibly entirely new switches every few months. If you've got lots of cash, this is a great option; you'll have quite an impressive network.

Cut-Through Switches
Cut-through switches help speed network communication by forwarding packets much sooner than traditional switches will allow. This is achieved by forwarding packets to their destination machine prior to receiving them in their entirety, sending them on as soon as the switch is able to determine the destination address. Unfortunately, if yours is an extraordinarily busy network, the benefits of cut-through switching will be less noticeable, and will reach their limits much sooner than in a less intensive environment.

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.

Although this doesn't strictly increase network performance, it does eliminate the additional transmissions that must occur as a result of packet errors that otherwise would have occupied network resources, thus providing an associated speed increase.

By including switches as part of your greater network, you'll gain a wide variety of benefits, including decreased latency, faster file transfers, fewer collisions and other transmission errors, and significantly easier management of the greater network.

Benefits Of Switches

  • Relatively inexpensive compared to other options such as fast Ethernet or FDDI.
  • Improves network performance.
  • Can be implemented in a proportionately shorter period of time.
  • Can regain lost bandwidth and allows for full duplex (20Mbps) networking.

Mahesh Rathod can be reached at rathodmp@hotmail.com

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