A 24 AWG twisted pair cable, such as CAT-5, is the cable of choice for these standards, and the notation “UTP” in the following diagrams stands for “unshielded twisted pair.” Noise pick up in twisted pair cables is typically common mode, which is effectively rejected by the differential receiver. Shielded cables improve EMI susceptibility and radiation at the expense of price and capacitance. The low data rate 4,000’ (or 1,220m) maximum cable length is set by DC attenuation of the signal, so better cables like 22 AWG, or high output voltage drivers, allow for longer transmission distances. High data rate length limitations are set by a cable’s high frequency characteristics, with jitter often being the limiting parameter. Using encoded data streams (like return-to-zero or Manchester encoding), or low capacitance cables can increase the data rate or the transmission distance. Most networks use a master-slave protocol, where a master device sequentially polls each slave device, and a slave device accesses the bus only after being polled. This provides for a very orderly communication structure – and likely higher throughput - but at the cost of increased latency, since once polled, a device that subsequently needs to transmit data must wait until it is polled again before transferring its data. Another advantage of polling is its deterministic nature. For example, high priority nodes can be polled more often than low priority nodes, and the lack of bus collisions guarantees that the data is delivered to the master when requested. The issue is that polling wastes processor bandwidth in the master device, since it has to poll each slave, even when the slave does not have data to transmit. If a network requires low latency (for example when bus access is event driven to ensure near real-time communication), then any device must be allowed to access the bus autonomously, as soon as it has data to transmit. This approach guarantees that bus collisions will occur, which must be detected and resolved. The cost is increased software complexity, and lower throughput due to data retransmission after collisions.