Ref. [9] Broadband Telecommunications Technologies and Management 100 Mbps 1 Gbps 10 Gbps 100 Gbps 10 Mbps 100 Mbps 1 Gbps 10 Gbps Figure 7.12 Ethernet transmission rate requirements over a period of time (10 Mbps to 10 Gbps) for a server to switch to a local node A number of these standards were developed to operate over category 5 and later on category 6 twisted pair copper wires. Initially the local area networks of many offices used coaxial cables. These were however difficult to use and expensive. The category 5 wires are cheaper, the sockets and connecter are smaller and since the mid-1990s have been the common medium for office networking. Most computers and network equip- ment are manufactured with sockets associated with these wires. However, as Figure 7.12 demonstrates, transmission rate requirements have been increasing over the years for the server to switch to a local node. Higher order modulation techniques help the existing wiring infrastructure to support these faster transmission rate requirements. The bandwidth of category 5 and category 6 wires can be extended and higher modulation rates can be employed to satisfy faster required transmission rates. Office infrastructure can be re-used and only network cards need to be replaced. However, this is not necessary as the network equipment is regularly upgraded. Case Study Questions Why are there different Ethernet standards? What has been the driver for higher transmission rate Ethernet standards? Why is the 'twisted pair copper wire' a suitable medium for Ethernet? What are the advantages and disadvantages vis-à-vis optical fibres? How does digital modulation technology support the local area network business? What do you see as the limit of the present infrastructure? Phase Shift Keying Referring back to the carrier signal A cos (2 ft+0), modulating information can also be embedded in the carrier phase O. In phase modulation, the transmitted signal is written as A cos [2 ft+q (t) where Q (t) denotes the offset phase of the signal at the beginning 