Cisco Networking Academy Program CCNA 1 and 2 Companion Guide, Revised part 38 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. | Page 339 Tuesday May 20 2003 2 53 PM Gigabit 10-Gb and Future Ethernet 339 Bit patterns from the MAC sublayer are converted into symbols with symbols sometimes controlling information such as start frame end frame and medium idle conditions . The entire frame is broken up into control symbols and data symbols data code groups . All of this extra complexity is necessary to achieve the tenfold increase in network speed over Fast Ethernet. For 1000BASE-T the first part of the encoding uses a technique called 8Bit-1Quinary quarter 8B1Q4 the second part of the encoding is the actual line encoding specific to copper called 4-dimensional 5 level pulse amplitude modulation 4D-PAM5 . The 8B1Q4 encoding followed by the 4D-PAM5 line encoding provide the synchronization bandwidth and SNR characteristics needed to make possible the four wire pairs working in parallel running full duplex on each wire pair simultaneously. For 1000BASE-X 8-bit 10-bit 8B 10B encoding similar to the 4B 5B concept is used followed by the simple NRZ line encoding of light on optical fiber. 1000BASE-T Goals for 1000BASE-T introduced as 1000BASE-T Gigabit Ethernet over twisted-pair included these Capability to function over existing Category 5 copper cable plants Assurance that this cable would work by passing a Category 5e test which most cable can pass after a careful retermination Interoperability with 10BASE-T and 100BASE-TX Applications such as building backbones interswitch links wiring closet applications server farms and high-end desktop workstations Provision of 10x bandwidth of Fast Ethernet which became very widely installed by end users helping to necessitate more speed upstream in the network To achieve this speed running over Category 5e copper cable 1000BASE-T needed to use all four pairs of wires. Category 5e cable reliably can carry up to 125 Mbps of traffic. Using sophisticated circuitry full-duplex transmissions on the same wire pair allow 250 Mbps per pair .
