BROCADE IP PRIMER

The Transport Layer (Layer 4)point, the receiver will send back a message to the sender to say, “Hey, I didn'tget segment number 6." The sender will then retransmit segment number 6.The receiver will acknowledge it, and the transport will continue.SourceSegment #3DestinationSegment #4Segment #6Segment #5RESEND“Hey, I didn’t getsegment #5!”AcknowledgementSegment #7“Okay, got it!”Segment #8I've talked a lot about connection-oriented transporting. What about connectionless?Connectionless transporting will break the data into segments aswell, but it doesn't really care whether the data gets to where it's going or not.It just sends it. There's no window. No acknowledgments. No flow control. Noretransmitting. The data is sent, and whether it actually gets to the destinationor not is not important.“What kind of a stupid transport method is that?” I hear you cry. It seemsundesirable on the surface, doesn't it? I mean, what's the point of the TransportLayer, if you can't make sure your data got there, right? One word: speed.The problem with connection-oriented transporting is there's a lot of overhead.There are acknowledgments to wait for, window sizes to maintain, flow controlto be conscious of, retransmits-it's a lot of extra work (and a lot of extra bandwidth).Overhead slows down the transmission. Now, if you're sending e-mail,you're typically more willing to sacrifice the small amount of speed differenceto make sure that your e-mail got there okay (and the way you wanted it). Butare there communications where it would actually be better for you to sacrificereliability for speed?Think of a sound file. One minute of CD-quality music contains approximately10 MB of data. You're thinking of using connectionless transport for speed.You know the network well enough to know that you have a small chance oflosing 0.001% of your segments, should you use connectionless transporting.That amounts to approximately 100 bytes of data lost. Now, I have audiophilefriends who would argue that they could tell the difference between the full 10Brocade IP Primer 15