Cisco Networking Academy Program CCNA 1 and 2 Companion Guide, Revised part 39 is the Cisco approved textbook to use alongside version of the Cisco Networking Academy Program CCNA 1 and CCNA 2 web-based courses. The topics covered provide you with the necessary knowledge to begin your preparation for the CCNA certification exam (640-801, or 640-821 and 640-811) and to enter the field of network administration. | B Page 349 Tuesday May 20 2003 2 53 PM Gigabit 10-Gb and Future Ethernet 349 to expect that its evolution will cease. The higher speeds and greater transmission distances that are making Ethernet both a LAN and a MAN protocol are not the only additions to the Ethernet standard that we are likely to see. Because fiber is being used as the transmission medium the likelihood that an error in the data might occur during the passage of the Ethernet packet across the network is very low much lower than in the original Ethernet. On a network with a very low error rate it makes sense to transmit larger packets of data. The upper limit on the amount of data that can be carried in an Ethernet packet a frame is 1500 bytes. Sending more data than that in a frame would make it an invalid Ethernet frame and cause the network to discard it. This has been the standard since Ethernet was created. Given a low likelihood of errors on a network large files could be moved over the network more efficiently if a larger amount of data could be carried in each frame. The reason for this is that it takes time for computers to generate and to process Ethernet headers and trailers. Each Ethernet frame must have a header and a trailer. For example if six times as much data could be sent per frame there would be fewer frames only one sixth as many needed to carry all the data in a file. This means that fewer headers and trailers would have to be generated by the transmitter and processed by the receiver. The result is a shorter amount of time needed to move a large file over a network between two computers. WANs that use fiber as their transmission medium routinely transmit large data packets. For this reason especially when multigigabit LANs are connected to WANs it is likely that we will see the use of Jumbo Ethernet frames. A Jumbo frame is any Ethernet frame that is carrying more than 1500 bytes of data. The proposed upper limit for the amount of data carried in a Jumbo frame is .
