Hi Jacob CRC check is done at the Ethernet MAC layer(or Data Link Layer conceptually). This error detection process is to detect the errors at the MAC layer packets, which is the errors caused by the physical layer or MAC layer. In some products single big TCP/IP packet(Jumbo Packet) can broken into the small packets at the MAC layer depending on the maximum size of the packet that link supports(Some thing like MRU). So the error in the datapackets which are broken and sent by the MAC layer, is detected by the CRC in the MAC layer. When sender sends the broken data packets each separately, at the reciever side also, these all packets are joined into single packet again before passing it to TCP/IP layer. To check the errors in joined TCP/IP packet, frame check is used at that layer. This is to detect the errors occuring in the TCP/IP packets due to breaking up and joining up. So both has relevant significance at each layer. Chandra ----- Original Message ----- From: jacob mathews <[EMAIL PROTECTED]> Date: Tuesday, August 28, 2001 1:35 pm Subject: TCP/IP check sum > Hi, > On a etherent frame CRC is used for error detection. > For TCP/IP frames frame check is done by using 16bit > 1's complemet addtion. > Why is TCP/IP frame check required when the same is > verified by the ethernet MAC? > What is then the motivation of providing TCP/IP > checksum overload by some products? > > Waiting for responses. > thanking you, > jacob > > ____________________________________________________________ > Do You Yahoo!? > Send a newsletter, share photos & files, conduct polls, organize > chat events. Visit http://in/ groups.yahoo.com > >
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