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Dated: Jun. 22, 2012
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Networking In General
Overview of LAN Switches
LAN switches, which are also sometimes called intelligent hubs, are the networking devices that have completely dominated and replaced Hubs. The reason behind this is that unlike Hubs, that only used to regenerate the received packets and forward them to all the ports that they had, LAN switches create one-to-one virtual circuits directly to the ports to which the destination computers are connected. This reduces the time consumed while transferring the data packets from the source computers to the destination ones.
LAN switches maintain lookup tables that contain MAC addresses of the computers that are connected to the switch ports. LAN switches always refer to their lookup tables before they forward data packets to the destination computers. This helps LAN switches create virtual circuits directly to the ports to which the destination computers are connected.
Hubs vs. LAN Switches
As mentioned above, after regenerating the received packets, Hubs used to forward them to every port that they had, every computer that was connected to the Hub was forced to receive them at the Physical layer before it can accept or deny the packets according to the destination information contained in them. This hardware level broadcasting decreased the network efficiency by over populating the ports and central devices with unnecessary data packets. This process also increased the collisions that used to take place when two machines initiated the transfer process simultaneously. Because of the collisions, network congestions were increased, hence providing a slow network performance.
On the other hand, because of lookup tables and virtual circuits in LAN switches, all the drawbacks that the Hubs had were eliminated, hence providing comparatively efficient and collision free network environments.
Types of LAN Switches
There are three types of LAN switches that transfer data packets in their own ways. The types of LAN switches are:
Cut-Through Switches: These LAN switch types start transferring the frames to the destination computers as soon as they receive them (bit by bit) and the destination MAC addresses are located. Since these switches do not wait to receive the entire data frame, these are considered Real-Time switches that provide decent transfer speed.
Fragment Free Switches: These types of LAN switches wait till the first 64 bytes of a frame is received before they actually start transferring it to the destination computer. The first 64 bytes of the frames are completely received before the transmission process takes place in order to avoid collisions. Because these switches work in a semi-real-time mode, but with more efficiency, these are also referred as Modified Cut-Through switches.
Store and Forward: These switch types wait till the entire data frame is received before they start transferring it to the destination computer. These switches are considered more accurate as compared to the above two because they check the received frames for Cycle Redundancy Check (CRC) errors. If the errors are found, the packets are dropped instantaneously; hence no transmission takes place whatsoever.
Since LAN switches identify source and destination computers on the basis of their MAC addresses, they work on Data Link layer, which is the 2nd layer of Open System Interconnect (OSI) reference model. However, nowadays Layer 3 LAN switches are also available that have capabilities of both LAN switches and the Routers. Most organizations now prefer to have Layer 3 switches over Routers as they are comparatively cheaper to them and work exactly the way Routers do.
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