Lesson 5: Understanding LAN Switching

Shared LAN Technology | LAN Switching Basics | Key Switching Technologies

Switching Technology: Full Duplex

Another concept that we have in LAN switching that allows us to dramatically improve the scalability, is something known as full duplex transmission. And that effectively doubles the amount of bandwidth between nodes.This can be important, for example, between high bandwidth consumers such as between a switch and a server connection, for example. It provides essentially collision free transmissions in the network.

And what this provides, for example, in 10 megabit per second connections, it effectively provides 10 meg of transmit capacity, and 10 megabit of receive capacity, for effectively 20 megabits of capacity on a single connection.Likewise, for a 100 megabit per second connection, we can get effectively 200 megabits per second of throughput

Switching Technology: Two Methods

Another concept that we have in switching is that we have actually two different modes of switching. And this is important because it can actually effect the performance or the latency of the switching through our network.

     Cut-through

First of all we have something known as cut through switching. What cut through switching does, is, as the traffic flows through the switch, the switch simple reads the destination MAC address, in other words we find out where the traffic needs to go through, go to.And as the data flows through the switch we don't actually look at all of the data. We simply look at that destination address, and then, as the name implies, we cut it through to its destination without continuing to read the rest of the frame.

     Store-and-forward

And that allows to improve performance over another method known as store and forward. With store and forward switching, what we do is we actually read, not only the destination address, but we read the entire frame of data.As we read that entire frame we then make a decision on where it needs to go, and send it on it's way. The obvious trade-off there is, if we're going to read the entire frame it takes longer to do that.

But the reason that we read the entire frame is that we can do some error correction, or error detection, on that frame, that may increase the reliability if we're having problems with that in a switched network.So cut through switching is faster, but the trade-off is that we can't do any error detection in our switched network.

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