COMMUNICATION SYSTEMS
Communication systems enable people and systems to share and exchange data andinformation electronically. This communication occurs between transmitting and receiving hardware and software over a network – each device on a network is called a node.
. As each message leaves its source it is encoded into a form suitable for transmission along the communication medium,which could be a wired or wireless connection. During its travels, the message may follow a variety of different paths through many different networks and connection devices.
Different types of connection device use different strategies to determine which path each message will follow – switches decide based on the MAC address,whilst routers use the IP address, for example. Eventually the message arrives at thereceiver, who decodes the message as it arrives at its destination. The network could be a local area network (LAN), a wide area network (WAN), it could be the Internet,an intranet, extranet or any combination of network types.For communication to be successful requires components to agree on a set of rulesknown as protocols. Establishing and agreeing on which set of protocols will be usedand the specific detail of each protocol must occur before any data can be transmittedor received – this process is known as handshaking. Protocols are classified according to the level or layer in which they operate. In the IPT course we classify protocols into three levels, namely; Application Level, Communication Control and Addressing Level, and Transmission Level
As messages pass through the interface between sender and transmitter they are encoded, meaning they descend the stack of protocols and are finally transmitted – each message is progressively encoded using the protocol (or protocols) operating at each level. Conversely, as messages are received they pass through the interface between receiver and destination – the original message is decoded by each protocol in turn as it ascends through each level of the protocol stack.In the IPT syllabus three levels of protocols are defined; this framework provides a simplified view of the more detailed OSI (Open Systems Interconnection) model. The OSI model defines seven layers, where each layer can be further expanded into sub- layers. Layers specified within the OSI model are combined to form the levels of the IPT model
In IPT the OSI Presentation and Application layers (layer 6and 7) are combined to form the IPT Application Level. OSI layers 3, 4 and 5, the network, transport and session layers are combined to form the IPT Communication Control and Addressing Level. Finally, protocols operating within the Physical and Data link layers (layer 1 and 2) of the OSI model are included in the IPT Transmission level. Throughout this chapter we focus on the IPT version with reference to the OSI model when appropriate. Note that in most cases communication occurs in both directions, even when the actual message only travels in one direction. The receiver transmits data back to the transmitter including data to acknowledge receipt, request more data or to ask for the data to be resent should it not be received correctly. The details of such exchanges are specific to the particular protocol being used. In this chapter we consider:
•Characteristics of communication systems, including an overview of each protocol level based on the OSI model, details of how messages pass from source to destination, examples of protocols operating at each level, measurements of transmission speed and common error checking methods.
•Examples of communication systems including teleconferencing, messaging systems and financial systems.
•Network communication concepts including client-server architecture, network physical and logical topologies and methods for encoding and decoding digital and analog data.
•Network hardware including transmission media, network hardware devices such as hubs, switches and routers, and also servers such as file, print, email and web servers.
•Software to control networks including network operating software, network administration tasks and other network-based applications.
•Finally we consider issues related to communication systems and current and emerging trends in communication
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