100BASE-T NETWORK Baseband Repeater DATA LINK PHYSICAL AUTONEG AUTONEG AUTONEG MEDIUM MEDIUM 100 Mb/s link segment 100 Mb/s link segment MDI = MEDIUM DEPENDENT INTERFACE PCS = PHYSICAL CODING SUBLAYER MII = MEDIA INDEPENDENT INTERFACE PMA = PHYSICAL MEDIUM ATTACHMENT PHY = PHYSICAL LAYER DEVICE PMD = PHYSICAL MEDIUM DEPENDENT MII is optional for 10 Mb/s DTEs and for 100 Mb/s systems and is not specified for 1 Mb/s systems. PMD is specified for 100BASE-X only; 100BASE-T4 does not use this layer. Use of MII between PCS and Baseband Repeater Unit is optional. AUTONEG is optional. Figure 11.10 Architectural positioning of 100BASE-T. (From Ref. 4, Figure 21-1, reprinted with permis- sion of the IEEE.) terminated with the coaxial cable characteristic impedance. The coaxial cable segments are marked at 2.5-m intervals. MAUs should only be attached at these 2.5-m interval points. This assures nonalignment at fractional wavelength boundaries. 11.6.2.3 Later Versions of Ethernet or CSMA/CD. The later versions of Ethernet came about when users demanded higher and higher data rates. We started at 10 Mbps, thence to 100 Mbps, 1000 Mbps, and finally 10,000 Mbps (10 Gbps). As these transmis- sion rates speeded up, there was less and less time to detect carrier presence or a collision occurrence. The velocity of propagation is essentially constant for all the transmission rates using the same transmission medium type. The frame lengths remained the same (1518 octets), but at 100 Mbps the time to transmit a frame is one-tenth that of 10 Mbps. would follow that 1 Gbps would be 100 times shorter than the 10-Mbps case. One way to improve the situation to permit the faster data rates is to reduce the maximum length of the medium. This shortens the roundtrip propagation time to detect carrier/collision. We remember that the maximum length of Ethernet at 10 Mbps was 2500 m with repeaters. This length dropped by an order of 10 to about 200 m for 100 Mbps using two repeaters instead of five. These maximum lengths can be increased to 412 