The IEEE's 802.1 Lab Task Force has selected 5-level pulse-amplitude-modulation (PAM-5) as the line code transmission scheme for l000Base-T, its proposed 1.0 GB Ethernet over copper standard. PAM-5 calls for four copper pairs and operates in both half and full-duplex. The group hopes to get a standard ratified by late 1998. The standard will be closely related to the 802.3 Lab Task Force standard for 1.0 GB over fiber optic cable.
Gigabit Ethernet will use the same frame format, full-duplex operation, and flow-control methods as 10 and 100 MBps Ethernet. This will reduce complexity when implementing a LAN which combines two or more bandwidths as there will be no need to translate frame formats, and it will simplify upgrading to a higher bandwidth.
Until such time as a standard for 1.0 GB transmission over Category S unshielded twisted pair is published, libraries should be wary of claims by companies selling Category 5+ and 5++. These are non-standard implementations.
When purchasing Category 5, be aware that it comes in both UTP (unshielded twisted pair) and STP (shielded twisted pair) . The latter, which is more expensive, is necessary only in environments where there is a great deal of radio-frequency interference and/or electro-magnetic interference. The libraries most likely to encounter this type of problem are those located in hospitals.
