of vendors. Most of these products featured low expansion of a distributed computing environment. speed, (under 1 Mbit/s), bus or serial connections between com- puters, with little if any software control of the network. As such, these early networks were complicated and difficult to use. 56.4.4 LAN characteristics The market today is very different. Vendors such as Novell, Banyan and Microsoft have produced software-driven network The key characteristics of a LAN are: operating systems that can function over a multitude of standards- based LANs. Standards such as IEEE 802.3 (Ethernet), and IEEE 1. Transmission medium. 802.5 (Token Ring), have provided reliable and functional methods 2. Signalling technique. Figure 56.9 Example of a typical LAN application 56/8 Local and Wide Area Networking 3. Access method. 4. Network topology. 56.4.4.1 Transmission media BASEBAND The transmission medium is the physical entity used to convey data over the LAN and includes any active hardware, such as amplifiers, required to regenerate the signal on the medium, and any passive BROADBAND hardware, such as taps and connectors, required to provide access to the medium. The most common types of installed media are (see also Chapter 1. Broadband coaxial cable. 2. Baseband coaxial cable. Figure 56.10 Signalling techniques on LANs 3. Twisted pair wire. In addition, optical fibre is emerging as an increasingly important able bandwidth is divided into separate channels, the use of a transmission medium. (See Chapter 53.) frequency division multiplexing (FDM) allows several 'conversa- tions' to coexist on the LAN simultaneously. Baseband LANs are generally less expensive and easier to install 56.4.4.2 Signalling techniques than broadband LANs. (See Figure 56.10.) LAN signalling techniques can be divided into baseband and broad- band transmission. 56.4.4.3 Access methods Baseband transmission utilises direct encoding to convey digital information in its digital form, to the transmission medium. In The method of access to the LAN permits a