A Network Technology And Data Communications Information Technology Essay

A WAN, or Wide Area Network, is a network that covers a large area, for example computers on opposite sides of the planet communicating. Usually, WANs are 2 or more LANs (Local Area Networks) connected together. One of the most well-known examples of a WAN is something we all use every day: the Internet.

Types of WAN’s

PTO Switched Services

Here I will look at some of the most commonly known examples of PTO Switched Services.

Circuit Switching

Circuit switching is based on the sender and receiver making the most of the full communication channel for the length of the communication. This type of switching can be found in the Public Switched Telephone Network (PSTN) where telephone calls are started by the person dialling but aren’t completed until the person receiving the call answers.

The main advantage of circuit switching is that it is extremely reliable for what it does. Another advantage is that once the connection is set up, it is fast to use and relatively error-free.

The disadvantages include the cost of the initial set up and the time that it takes to set up the particular channel. There is also the chance of a failure at one point causing a disruption in all communications. Lastly, although there are many paths available, you can only communicate on one path at a time, meaning that if you want to talk to someone else you will have to start the process again, in the same vein once a path is established that channel will be unavailable to other users.

To attempt to overcome the problems of circuit switching, packet switching was introduced.

Examples of Circuit Switching

PSTN

PSTN, or Public Switched Telephone Network, is a circuit-switching network that uses internationally agreed codes and unique identifiers (telephone numbers) to operate.

The PSTN network was originally made for fixed-line analogue telephone systems but the PSTN is now almost completely digital and also incorporates mobile telephones alongside analogue ones.

ISDN

ISDN, or Integrated Services Digital Network, is a communications standard used internationally to send data, including voice and video, over digital or regular phone lines, at the same time.

One of the most well known uses of ISDN is for Internet access, with ISDN providing a maximum speed for upload and download of 128 Kbit/s.

Leased Lines

A leased line is a symmetric telecommunications line connecting two locations for voice and/or data communications. Unlike PSTN lines, leased lines don’t have a telephone number; instead each side of the line is permanently connected to the other.

Usually, leased lines are used by businesses to directly connect offices that are far apart, however shorter distances are also used for convenience. The main difference between leased lines and dial-up connections is that a leased line is always active. The main advantage of leased lines is the guarantee of a high level of quality, this is because the connection doesn’t carry anybody else’s data.

Packet Switching

Packet switching is a communications method that works by splitting the data being sent into smaller chunks, called packets.

When the data is sent it can end up being sent through different paths to arrive at its destination. Each time a packet goes through a switch, router or adapter it is buffered and queued, which can slow down how quick the packets arrive at their destination, which also means the order of delivery can also be different.

Examples of Packet Switching

X.25

X.25 is one of the oldest packet-switched services that are still available and used, although it is now being replaced by less complex protocols, like IP (internet Protocol). It was developed before the OSI Reference Model so the protocol suite is essentially just three layers, which are almost the same as the lower three layers of the seven-layer OSI model (Physical, Data and Network layers).

X.25 is designed to operate effectively regardless of which systems are connected to the network. It is typically used by telephone service providers which allows them to charge their customers based on their use of the network.

Frame Relay

Frame relay is a telecommunication service geared towards cost-efficient data transmission between local area networks and wide area networks. Frame relay sends packets at the data link layer of the OSI model rather than at the Network layer. A frame can use packets from different protocols such as Ethernet and X.25 and is also variable in size with some being as large as 1000bytes or more.

Frame Relay was originally a stripped-down version of X.25, but managed to distance itself from the error-correcting which is most commonly associated with X.25. Instead when Frame Relay finds an error, it just drops the packet. Frame Relay works on the basis of shared-access and uses a technique known as “best-effort”, where error-correction is almost obsolete however there is also no guarantee of reliable data delivery, instead it leaves the error correcting to each end of the connection.

SMDS

SMDS, or Switched Multimegabit Data Service, is a telecommunications service that provides connectionless, high-performance, packet-switched data transport. As SMDS is neither a protocol nor a technology, it means that it can support standard protocols and communications interfaces that are using current, as well as future, technology.

SMDS can use either fibre or copper-based lines and works on the data link and physical layers of the OSI model.

Mobile and Broadband Services

The greatest change to WAN’s and most internet services in the near future is expected to be the rise and increase of quality in mobile and broadband services and standards.

ATM

ATM, or Asynchronous Transfer Mode (ATM) is a data link as well as a network layer circuit switched protocol which is connection based. For example a logical connection has to be made between both end points before data can start to be sent or received.

ATM also divides the data being sent into small sized cells, each consisting of 53 bytes (48 Bytes for Data and 5 Bytes for Header Information).

The process of splitting the data into a fixed size is what makes ATM different from packet switched networks that use different length packets, like IP.

xDSL

DSL, or Digital Subscriber Line, provides customers with digital services through their telephone system. The ‘x’ simply means that there are a range of different DSL technology available.

DSL is probably the most used method for people to access digital services, such as the internet as it is cheaper than leased lines and also faster than ISDN, with speeds of upto 1.5Mb/s download speed and 128kb/s upload speed available on ADSL (Asymmetric DSL).

This is down to the fact that DSL uses a digital modem rather than an analogue one, meaning that the data doesn’t need to be converted before it is sent.