Examples of communication systems
In this section we consider three broad types of communication system. Firstly, teleconferencing systems where real time audio, video and/or other data is shared between participants. Secondly, messaging systems including traditional phone and fax as well as voice mail and email systems. Finally, we examine electronic commerce systems, specifically EFTPOS and Internet or electronic banking. Before we commence, we first describe relevant characteristics of three large wide area networks used to transmit data within the above communication systems – namely, the Internet, the public switched telephone network (PSTN) and intranets and extranets.
Internet
The Internet is a worldwide packet switched public network based on the Internet Protocol where all data moves between nodes within IP datagrams. As we learnt previously, there is no guarantee that IP datagrams will reach their destination. Furthermore the Internet is “connectionless” meaning there is no connection maintained between the sender and receiver – in effect each IP datagram is on its own and may follow a different path to its destination. As a consequence IP datagrams can arrive out of sequence or not arrive at all. These issues are insignificant when the communication between participants is asynchronous. However these are significant issues when real time (synchronous) communication is required. Synchronous in this context refers to the ability of participants to hold a real time conversation whilst asynchronous refers to systems where there is (or can be) a pause between sending and receiving processes. The Internet was designed for asynchronous rather than synchronous transfers
Public Switched Telephone Network
The PSTN is the network that carries traditional telephone calls throughout the world – it is also known as the “Plain Old Telephone Service” or POTS. The PSTN differs from the Internet because it creates and maintains an individual circuit between the participants during each conversation. When a phone call begins a single direct connection is created between the two telephones. This connection or circuit is used for the duration of the call – hence the PSTN is known as a “connection-based” or “circuit switched” network. This connection-based system was designed for real time synchronous voice communication using telephones as the collection and display devices. The significant infrastructure of the PSTN has been in place for many years and is owned and maintained by governments and large telecommunication companies. Somewhat confusingly, much of the data transferred over the Internet actually travels across the PSTN. Most Internet service providers, rather than installing their own dedicated lines, lease connections on the PSTN. This means many connectionless IP datagrams actually travel along network hops alongside connection-based data.
Intranet and Extranet
An intranet is a private network maintained by a company or government organisation and is based on the Internet protocol (IP). Many intranets include leased high-speed lines to connect their local area networks (LANs) into a private wide area network (WAN). The leased lines are dedicated to traffic on a specific private intranet. Such leased lines mean that the amount of data transferred is under the direct control of the intranet owner. This control becomes significant when real time synchronous applications are used. Some intranets connect LANs using the public Internet where all messages are encrypted during transmission to ensure privacy is maintained. Extranets are an extension of an intranet to allow access to customers and other users outside the organisation. The interface between the extranet and the intranet must be secure – commonly firewalls, user names and passwords and also encryption is used. Extranets allow companies to share their services with other companies. For instance a large bank may provide online banking services to other smaller banks via its extranet. Both intranets and extranets can also include virtual private networks (VPNs). VPNs use the infrastructure of the public Internet to provide secure and private connections to a company’s internal network. A VPN allows employees to securely communicate with their company’s network using any Internet connection. VPNs include tunnelling Transmission protocols, which not only encrypt and secure messages but also encrypt all internal network addresses. Examples of tunnelling protocols include Microsoft’s Point to Point Tunnelling Protocol (PPTP), Cisco’s Layer 2 Forwarding protocol(L2F) and the Layer 2 Tunnelling Protocol (L2TP) which is a standard that aims to combine the benefits and functions within both PPTP and L2F
In this section we consider three broad types of communication system. Firstly, teleconferencing systems where real time audio, video and/or other data is shared between participants. Secondly, messaging systems including traditional phone and fax as well as voice mail and email systems. Finally, we examine electronic commerce systems, specifically EFTPOS and Internet or electronic banking. Before we commence, we first describe relevant characteristics of three large wide area networks used to transmit data within the above communication systems – namely, the Internet, the public switched telephone network (PSTN) and intranets and extranets.
Internet
The Internet is a worldwide packet switched public network based on the Internet Protocol where all data moves between nodes within IP datagrams. As we learnt previously, there is no guarantee that IP datagrams will reach their destination. Furthermore the Internet is “connectionless” meaning there is no connection maintained between the sender and receiver – in effect each IP datagram is on its own and may follow a different path to its destination. As a consequence IP datagrams can arrive out of sequence or not arrive at all. These issues are insignificant when the communication between participants is asynchronous. However these are significant issues when real time (synchronous) communication is required. Synchronous in this context refers to the ability of participants to hold a real time conversation whilst asynchronous refers to systems where there is (or can be) a pause between sending and receiving processes. The Internet was designed for asynchronous rather than synchronous transfers
Public Switched Telephone Network
The PSTN is the network that carries traditional telephone calls throughout the world – it is also known as the “Plain Old Telephone Service” or POTS. The PSTN differs from the Internet because it creates and maintains an individual circuit between the participants during each conversation. When a phone call begins a single direct connection is created between the two telephones. This connection or circuit is used for the duration of the call – hence the PSTN is known as a “connection-based” or “circuit switched” network. This connection-based system was designed for real time synchronous voice communication using telephones as the collection and display devices. The significant infrastructure of the PSTN has been in place for many years and is owned and maintained by governments and large telecommunication companies. Somewhat confusingly, much of the data transferred over the Internet actually travels across the PSTN. Most Internet service providers, rather than installing their own dedicated lines, lease connections on the PSTN. This means many connectionless IP datagrams actually travel along network hops alongside connection-based data.
Intranet and Extranet
An intranet is a private network maintained by a company or government organisation and is based on the Internet protocol (IP). Many intranets include leased high-speed lines to connect their local area networks (LANs) into a private wide area network (WAN). The leased lines are dedicated to traffic on a specific private intranet. Such leased lines mean that the amount of data transferred is under the direct control of the intranet owner. This control becomes significant when real time synchronous applications are used. Some intranets connect LANs using the public Internet where all messages are encrypted during transmission to ensure privacy is maintained. Extranets are an extension of an intranet to allow access to customers and other users outside the organisation. The interface between the extranet and the intranet must be secure – commonly firewalls, user names and passwords and also encryption is used. Extranets allow companies to share their services with other companies. For instance a large bank may provide online banking services to other smaller banks via its extranet. Both intranets and extranets can also include virtual private networks (VPNs). VPNs use the infrastructure of the public Internet to provide secure and private connections to a company’s internal network. A VPN allows employees to securely communicate with their company’s network using any Internet connection. VPNs include tunnelling Transmission protocols, which not only encrypt and secure messages but also encrypt all internal network addresses. Examples of tunnelling protocols include Microsoft’s Point to Point Tunnelling Protocol (PPTP), Cisco’s Layer 2 Forwarding protocol(L2F) and the Layer 2 Tunnelling Protocol (L2TP) which is a standard that aims to combine the benefits and functions within both PPTP and L2F