3.3. Essential Media System Timing

While signals travel very fast on an Ethernet, they still take a finite amount of time to propagate over the entire media system. The longer the cables used in the media system, the more time it takes for signals to travel from one end of the system to the other. The total round-trip time used in the slot time includes the time it takes for frame signals to go through all of the cable segments. It also includes the time it takes to go through all other devices, such as transceiver cables, transceivers and repeaters.

The maximum length for cable segments are carefully designed so that the essential signal timing of the system is preserved, even if you use maximum-length segments everywhere and the system is the largest allowed. The guidelines for each media variety incorporate the essential timing and round-trip signal delay requirements needed to make any half-duplex Ethernet up to the maximum-size system work properly. The cable segment guidelines are described in the media system chapters located in Part II. The correct signal timing is essential to the operation of the MAC protocol, so let's look at the slot time in more detail.