|  | 7.2 |
| Gigabit and 10-Gigabit Ethernet
|  | 7.2.4 |
| Gigabit Ethernet architecture
The distance limitations of full-duplex links are only limited by the medium, and not the round-trip delay. Since most Gigabit Ethernet is switched, the values in Figures and are the practical limits between devices. Daisy-chaining, star, and extended star topologies are all allowed. The issue then becomes one of logical topology and data flow, not timing or distance limitations. A 1000BASE-T UTP cable is the same as 10BASE-T and 100BASE-TX cable, except that link performance must meet the higher quality Category 5e or ISO Class D (2000) requirements. Modification of the architecture rules is strongly discouraged for 1000BASE-T. At 100 meters, 1000BASE-T is operating close to the edge of the ability of the hardware to recover the transmitted signal. Any cabling problems or environmental noise could render an otherwise compliant cable inoperable even at distances that are within the specification. It is recommended that all links between a station and a hub or switch be configured for Auto-Negotiation to permit the highest common performance. This will avoid accidental misconfiguration of the other required parameters for proper Gigabit Ethernet operation.
Web Links
Gigabit Networking Gigabit Ethernet Solutions http://www.cisco.com/en/US/tech/tk389/ tk214/ technologies_white_ paper09186a0080092951.shtml