Networking Technologies

802.x

Ethernet IEEE 802.3 Standard The 802.3 standard was based on the DIX Ethernet standard and incorporates the 802.2 Logical Link Control sub-layer standard to cover both the Physical and the Data Link layers of the OSI 7 Layer Model. The IEEE 802.3 standard specifies CSMA/CD (which allows packets to collide) as it's media access method, a network transmission speed of 10 Mbps, a logical bus topology and either a bus or star physical topology.

802.3 is a broadcast network with data packets going out in all directions. All machines receive every broadcast with only those to which the packets are addressed responding with acknowledgments. 802.3 defines two signaling modes: baseband and broadband.

Within the 802.3 standard several implementations are defined. The naming convention for these implementations denote the data rate, signaling mode and usually the distance of a segment or cabling media. These include: 10BASE2, 10BASE5, 10BASET, 10BROAD36, 10BASEF.

The packet frame format that has been specified by the IEEE contains a preamble of 7 bytes, a start of frame indicator (SOF) of 1 byte, destination and source addresses of 6 bytes each, a length field of 2 bytes which tells the length of the data field to follow, the data field and the frame check sequence (FCS) field of 4 bytes.

More recent standards are being drafted by the Fast Ethernet Alliance for 802.3u. It also uses a logical bus topology and CSMA/CD. Fast Ethernet may use one of 3 transceivers for its network connections: 100BASE-TX, 100BASE-T4 or 100BASE-FX.

100BASE-TX uses 2 pairs of category 5 UTP or category 1 STP cabling. 100BASE-T4 uses 4 pairs of category 3, 4 or 5 UTP and 100BASE-FX uses fiber optic cabling.

An 802.3z Gigabit Ethernet Task Force has been formed by the IEEE 802.3 Working Group. This standard will support full duplex and half duplex communications at 1,000 Bbps using the IEEE 802.3 frame format, CSMA/CD media access method and also will be backwards compatible with 10BASET and 100BASET. 802.3z will first be implemented using fiber optic cable and later on with category 5 UTP and coaxial cable.