A communications network consists of network elements, nodes (senders and receivers) and connecting communications media. Among several criteria for classifying networks we use two: transmission technology and scale. The scale or distance also determines the technique used in a network: wireline or wireless. The connection of two or more networks is called internetwork. The most widely known internetwork is the Internet.
According to transmission technology we can broadly classify networks as broadcast and point-to-point networks:
In broadcast networks a single communication channel is shared by every node. Nodes communicate by sending packets or frames received by all the other nodes. The address field of the frame specifies the recipient or recipients of the frame. Only the addressed recipient(s) will process the frame. Broadcast technologies also allow the addressing of a frame to all nodes by dedicating it as a broadcast frame processed by every node in the network. It is also possible to address a frame to be sent to all or any members of only a group of nodes. The operations are called multicasting and any casting, respectively.
Point-to-point networks consist of many connections between pairs of nodes. A packet or frame sent from a source to a destination may have to first traverse intermediate nodes where they are stored and forwarded until it reaches the final destination.
Regarding our other classification criterion, the scale of the network, we can classify networks by their physical area coverage:
Personal Area Networks (PANs) support a person's needs. For instance, a wireless network of a keyboard, a mouse, and a personal digital assistant (PDA) can be considered as a PAN.
Local area networks (LANs), typically owned by a person, department, a smaller organisation at home, on a single floor or in a building, cover a limited geographic area. LANs connect workstations, servers, and shared resources. LANs can be further classified based on the transmission technology, speed measured in bits per second, and topology. Transmissions technologies range from traditional 10 Mbps LANs to today's 10 Gbps LANs. In terms of topology, there are bus and ring networks and switched LANs.
Metropolitan area networks (MANs) span a larger area, such as a city or a suburb. A widely deployed MAN is the cable television network distributing not just one-way TV programs but two-way Internet services as well in the unused portion of the transmission spectrum. Other MAN technologies are the Fiber Distributed Data Interface (FDDI) and IEEE wireless technologies as discussed below.
Wide area networks (WANs) cover a large geographical area, a state, a country or even a continent. A WAN consists of hosts (clients and servers) connected by subnets owned by communications service providers. The subnets deliver messages from the source host to the destination host. A subnet may contain several transmission lines, each one connecting a pair of specialised hardware devices called routers. Transmission lines are made of various media; copper wire, optical fiber, wireless links, etc. When a message is to be sent to a destination host or hosts, the sending host divides the message into smaller chunks, called packets. When a packet arrives on an incoming transmission line, the router stores the packet before it selects an outgoing line and forwards the packet via that line. The selection of the outgoing line is based on a routing algorithm. The packets are delivered to the destination host(s) one-by-one where the packets are reassembled into the original message.
Wireless networks can be categorised as short-range radio networks, wireless LANs, and wireless WANs.
In short range radio networks, for instance Bluetooth, various components, digital cameras, Global Positioning System (GPS) devices, headsets, computers, scanners, monitors, and keyboards are connected via short-range radio connections within 20–30 feet. The components are in primary-secondary relation. The main system unit, the primary component, controls the operations of the secondary components. The primary component determines what addresses the secondary devices use, when and on what frequencies they can transmit.
A wireless LAN consists of computers and access points equipped with a radio modem and an antenna for sending and receiving. Computers communicate with each other directly in a peer-to-peer configuration or via the access point that connects the computers to other networks. Typical coverage area is around 300 feet. The wireless LAN protocols are specified under the family of IEEE 802.11 standards for a range of speed from 11 Mbps to 108 Mbps.
Wireless WANs comprise of low bandwidth and high bandwidth networks. The low bandwidth radio networks used for cellular telephones have evolved through three generations. The first generation was designed only for voice communications utilising analog signalling. The second generation also transmitted only voice but based on digital transmission technology. The current third generation is digital and transmits both voice and data at most 2Mbps. Fourth and further generation cellular systems are under development. High-bandwidth WANs provides high-speed access from homes and businesses bypassing the telephone systems. The emerging IEEE 802.16 standard delivers services to buildings, not mobile stations, as the IEEE 802.11 standards, and operates in much higher 10-66 GHz frequency range. The distance between buildings can be several miles.
Wired or wireless home networking is getting more and more popular connecting various devices together that can be accessible via the Internet. Home networks may consists of PCs, laptops, PDAs, TVs, DVDs, camcorders, MP3 players, microwaves, refrigerator, A/C, lights, alarms, utility meters, etc. Many homes are already equipped with high-speed Internet access (cable modem, DSL, etc.) through which people can download music and movies on demand.
The various components and types of communications networks correspond to the modelling constructs and the different steps of building a simulation model. Typically, a network topology is built first, followed by adding traffic sources, destinations, workload, and setting the parameters for network operation. The simulation control parameters determine the experiment and the running of the simulation. Prior to starting a simulation various statistics reports can be activated for analysis during or after the simulation. Statistical distributions are available to represent specific parameterisations of built-in analytic distributions. As the model is developed, the modeller creates new model libraries that can be reused in other models as well.