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SPECIFICATION (a) Describe the characteristics and relative advantages of network and stand-alone

environments. (b) Describe the difference between a Local area and a Wide area network. (c) Describe the elements of network environments. Chapter 29 (d) network topologies (e) characteristics and relative advantages of server and peer-to-peer networks (f) factors which affect rate and manner data can be transmitted (g) factors affecting compatibility between different systems (h) functions of gateways (i) need for portability (j) ease of transferring numerical, graphical and textual data between applications (k) need for standards(protocols) for interchange of text, numeric data and graphics for

hardware and software, for common operating systems (l) Emergence of de facto standards based on history and sales in comparison to formal

standards NETWORK or STAND-ALONE? A computer network allows sharing of resources and information among devices connected to the network. The Advanced Research Projects Agency (ARPA) funded the design of the Advanced Research Projects Agency Network (ARPANET) for the United States Department of Defense. It was the first operational computer network in the world.

NETWORKING is linking computers through telecommunications hardware, software and media to share resources and data.

Computer networks can be used for several purposes:

• Facilitating communications. Using a network, people can communicate efficiently and easily via e-mail, instant messaging, chat rooms, telephony, video telephone calls, and videoconferencing.

• Sharing hardware. In a networked environment, each computer on a network can access and use hardware on the network. Suppose several personal computers on a network each require the use of a laser printer. If the personal computers and a laser printer are connected to a network, each user can then access the laser printer on the network, as they need it.

• Sharing files, data, and information. In a network environment, any authorized user can access data and information stored on other computers on the network. The capability of providing access to data and information on shared storage devices is an important feature of many networks.

• Sharing software. Users connected to a network can access application programs on the network.

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ADVANTAGES FROM NETWORKS (see p.158) • Being able to share software, data and hardware resources such as printers, file storage,

image scanners, routers etc. • Sharing processing activity • Connecting devices that would otherwise be incompatible e.g. from different platforms. • Accessible services for security, user support, systems maintenance • Allows sending e-mail, EDI etc.

By-products of networking are • Improved operational efficiency, speed and accuracy • Better control of resources (just-in-time) • Improved productivity DISADVANTAGES FROM NETWORKS (see p.158) • Users become dependent on them. • May be impossible to continue the business if the system fails. • Relies upon skills of the network manager. • Security issues. • Needs careful design to cope with increases in traffic. A RELIABLE NETWORK REQUIRES • to be accessible when needed by users • not lose or corrupt data • be able to recover quickly from disasters such as power failure • to be used by staff following codes of conduct • Be regularly maintained and modified. Networks to be effective must • Ensure response time is adequate • Be reliable i.e. hardware, software and operator skills are regularly upgraded • Maintain procedures to ensure data privacy and data integrity. • Be run maintaining standards and ethics A LOCAL AREA AND A WIDE AREA NETWORK.P.158

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PrinterNetwork

File Serv er

ComputerComputer

Printer

Network

LAN

LAN

LAN

Computer

Computer

Computer

LAN Technologies - Ethernet, Appletalk, Token Ring, Arcnet

Characteristics of a LAN (Local Area Network) A collection of computers and peripherals • In a limited area usually one building or several buildings in close proximity. • Can be connected to other LANs or WANs see routers, bridges, gateways • Usually physically cabled using Ethernet with cable length of 500m before a repeater is

needed. • LANs generally have bus or ring topologies and a high bandwidth. (256kps to 100mps). • Can share resources - e-mail, video conferencing, graphics, printers etc. Characteristics of a WAN (Wide Area Network) Connects computers or networks • over a wide geographical area • may consist of a combination of switched and dedicated lines and microwave and satellite

communication VAN (Value Added Network) Videotext, e-mail, fax, bulletin boards, specialist databases. 1. What does Windows Server 2003 do? 2. Why is networking of mission-critical importance in the following areas? B2B Company Intranets Health Service Education Administration Police e-Commerce 3. Discuss the following concerns in network security Item Accountability Threats from Possible

Consequences Precautions

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Data Privacy Data Integrity

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PEER-TO-PEER NETWORKS (p.159) • A peer is an equal i.e. each node in such a network is equal to any other node. • If the node is a computer it can also act as a stand-alone device • It is difficult to share data with other nodes.. • If the node is a fax, printer, modem, tape-backup drive etc. it can be used and shared

by any other node. Advantages Disadvantages Cheap and cheerful Performance is slow, only suitable for up to 10

nodes. No need for network manager Software updates difficult Security an issue File transfers difficult. CLIENT-SERVER NETWORKS (p.158) Networks with powerful file servers - in which different pieces of hardware work on the same processing problem. The network tries to use the full processing power of each computer in the network, including the file-server and the user workstations or clients. Advantages Disadvantages Power of client and servers are used jointly Network crash means all users must cease

activity. Administration e.g. backup and file-sharing can be dealt with by server Specialist servers such as proxy, print, e-mail servers can be used to reduce bottlenecks. Can store application programs on servers – much easier to update. File servers enable logging on any client Passwords/security – backups centralised. Less idle-time i.e. better use of resources. Very flexible – Host controls the communication protocol.

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THE ELEMENTS OF NETWORK ENVIRONMENTS • Network cards for each client and node which provides a physical interface an expansion board you insert into a computer so the computer can be connected to a network. • A Network server A computer or device on a network that manages network resources. For example, a file server is a computer and storage device dedicated to storing files. Any user on the network can store files on the server. A print server is a computer that manages one or more printers, and a network server is a computer that manages network traffic. A database server is a computer system that processes database queries. • Network operating system An operating system that includes special functions for connecting computers and devices into a local-area network (LAN). Some operating systems, such as UNIX and the Mac OS, have networking functions built in. The term network operating system, however, is generally reserved for software that enhances a basic operating system by adding networking features. • Communication Media (p.160) Transmission rate is measured in bits per second Medium Speed Twisted-pair (copper cable) 500bps to 10mps Coaxial cable (Ethernet) 56kps to 200mps Fibre-optic 500 kpbs to 10gbps Microwave 256 kbps to 100mps Satellite 256 kbps to 100mps • Suitable bandwidth The range of frequencies that can be accommodated on a particular telecommunications medium is called its bandwidth - The amount of data that can be transmitted in a fixed amount of time. For digital devices, the bandwidth is usually expressed in bits per second (bps) or bytes per second. For analog devices, the bandwidth is expressed in cycles per second, or Hertz (Hz).. What is Broadband Internet & how does it work? • Broadband v Modem Broadband provides users with a high-speed, always-connected Internet service - removing many of the current frustrations of standard dial-up access. Currently, most homes access the Internet via a standard dial-up modem, which is connected to a phone line. This delivers data at a speed of up to 56 kilobits per second (kbps). Additionally users have the frustration of waiting to dial-up (connect) to the Internet. Broadband, on the other hand, has a higher capacity to send more information at a much faster rate. For example, a motorway allows much more traffic to move quickly from town to town than a single lane country road does. Equally, Broadband Internet via cable modem allows more

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video, data and audio 'traffic' to pass faster. In addition, Broadband is always connected resulting in no more frustrating dial-up connections. How quickly would you like to access you pages, video clips, etc?

• Repeaters A network device used to regenerate or replicate a signal. Repeaters are used in transmission systems to regenerate analogue or digital signals distorted by transmission loss. Needed after .5K on a LAN. • Routers A device that forwards data packets along networks. A router is connected to at least two networks, commonly two LANs or WANs or a LAN and its ISP’s network. Routers are located at gateways, the places where two or more networks connect. Think Cisco. • Bridges (p.161) A device that connects two local-area networks (LANs), or two segments of the same LAN that use the same protocol, such as Ethernet or Token-Ring. • Gateway A node on a network that serves as an entrance to another network. In enterprises, the gateway is the computer that routes the traffic from a workstation to the outside network that is serving the Web pages. In homes, the gateway is the ISP that connects the user to the internet..

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• Protocols (p.162) An agreed-upon format or set of rules for transmitting data between two devices. TCP/IP Whereas the IP protocol deals only with packets, TCP enables two hosts to establish

a connection and exchange streams of data. X25 A popular standard for packet-switching networks. The X.25 standard was approved

by the CCITT (now the ITU) in 1976. • Type of transmission (p.162) ATM The small, constant cell size allows ATM equipment to transmit video,

audio, and computer data over the same network, and assure that no single type of data hogs the line.

Packet Switching Refers to protocols in which messages are divided into packets before they are sent. Each packet is then transmitted individually and can even follow different routes to its destination. Once all the packets forming a message arrive at the destination, they are recompiled into the original message. Most modern Wide Area Network (WAN) protocols, including TCP/IP, X.25, and Frame Relay, are based on packet-switching technologies.

NETWORK TOPOLOGIES A topology is the shape or configuration of the network i.e. the way nodes are connected. BUS NETWORK - a number of computers are linked by single loop circuit - all messages are passed to the entire network and can flow in either direction

Bus

PC PC

PC

Printer

File Server

Bus Networks have no central computer but share other network resources such as printers in the same way as star networks

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RING NETWORK

Ring

PC

PC

PC

File Server

Printer

In a ring network, individual computers are connected serially to one another. This arrangement is expensive but provides many routing possibilities

STAR NETWORK - central host is connected to several smaller computers and/or terminals; all communications between the smaller computers must pass through host/hub.

Star

PC PC PC

File ServerController

Printer

Star networks give many users access to central files and system resources through a host CPU

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Transmission modes

A given transmission on a communications channel between two machines can occur in several different ways. The transmission is characterised by:

• the direction of the exchanges

• the transmission mode: the number of bits sent simultaneously

• synchronisation between the transmitter and receiver

Simplex, half-duplex and full-duplex connections

There are 3 different transmission modes characterised according to the direction of the exchanges:

• A simplex connection is a connection in which the data flows in only one direction, from the transmitter to the receiver. This type of connection is useful if the data do not need to flow in both directions (for example, from your computer to the printer or from the mouse to your computer...).

• A half-duplex connection (sometimes called an alternating connection or semi-duplex) is a connection in which the data flows in one direction or the other, but not both at the same time. With this type of connection, each end of the connection transmits in turn. This type of connection makes it possible to have bidirectional communications using the full capacity of the line.

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• A full-duplex connection is a connection in which the data flow in both directions simultaneously. Each end of the line can thus transmit and receive at the same time, which means that the bandwidth is divided in two for each direction of data transmission if the same transmission medium is used for both directions of transmission.

Serial and parallel transmission

The transmission mode refers to the number of elementary units of information (bits) that can be simultaneously translated by the communications channel. In fact, processors (and therefore computers in general) never process (in the case of recent processors) a single bit at a time; generally they are able to process several (most of the time it is 8: one byte), and for this reason the basic connections on a computer are parallel connections.

Parallel connection

Parallel connection means simultaneous transmission of N bits. These bits are sent simultaneously over N different channels (a channel being, for example, a wire, a cable or any other physical medium). The parallel connection on PC-type computers generally requires 10 wires.

These channels may be:

• N physical lines: in which case each bit is sent on a physical line (which is why parallel cables are made up of several wires in a ribbon cable)

• one physical line divided into several sub-channels by dividing up the bandwidth. In this case, each bit is sent at a different frequency...

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Since the conductive wires are close to each other in the ribbon cable, interference can occur (particularly at high speeds) and degrade the signal quality...

Serial connection

In a serial connection, the data are sent one bit at a time over the transmission channel. However, since most processors process data in parallel, the transmitter needs to transform incoming parallel data into serial data and the receiver needs to do the opposite.

These operations are performed by a communications controller (normally a UART (Universal Asynchronous Receiver Transmitter) chip). The communications controller works in the following manner:

• The parallel-serial transformation is performed using a shift register. The shift register, working together with a clock, will shift the register (containing all of the data presented in parallel) by one position to the left, and then transmit the most significant bit (the leftmost one) and so on:

• The serial-parallel transformation is done in almost the same way using a shift register. The shift register shifts the register by one position to the left each time a bit is received, and then transmits the entire register in parallel when it is full:

Synchronous and asynchronous transmission

Given the problems that arise with a parallel-type connection, serial connections are normally used. However, since a single wire transports the information, the problem is how to synchronise the transmitter and receiver, in other words, the receiver can not necessarily distinguish the characters (or more generally the bit sequences) because the

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bits are sent one after the other. There are two types of transmission that address this problem:

• An asynchronous connection, in which each character is sent at irregular intervals in time (for example a user sending characters entered at the keyboard in real time). So, for example, imagine that a single bit is transmitted during a long period of silence... the receiver will not be able to know if this is 00010000, 10000000 or 00000100... To remedy this problem, each character is preceded by some information indicating the start of character transmission (the transmission start information is called a START bit) and ends by sending end-of-transmission information (called STOP bit, there may even be several STOP bits).

• In a synchronous connection, the transmitter and receiver are paced by the same clock. The receiver continuously receives (even when no bits are transmitted) the information at the same rate the transmitter send it. This is why the transmitter and receiver are paced at the same speed. In addition, supplementary information is inserted to guarantee that there are no errors during transmission.

During synchronous transmission, the bits are sent successively with no separation between each character, so it is necessary to insert synchronisation elements; this is called character-level synchronisation.

The main disadvantage of synchronous transmission is recognising the data at the receiver, as there may be differences between the transmitter and receiver clocks. That is why each data transmission must be sustained long enough for the receiver to distinguish it. As a result, the transmission speed can not be very high in a synchronous link.

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EXAMINATION QUESTIONS 1996.6 (4 marks) and 2000 (Exemplar) Describe TWO differences between a Local Area Network (LAN) and other networks such as a Wide Area Network (WAN) LAN • normally within same building

• maximum cable length 2km • connection is by local physical cable

WAN • network is distributed nationally or internationally • transmission uses telecommunications network or even satellite links

1991.7 (2 marks) A particular database package claims to be usable over a network. What amplification of this claim would you require? Access to the same database by single users or many users? Record and field locking 1997.5 (8 marks) (a) Give two differences between a Local Area Network (LAN) and a Wide Area Network (WAN) (2) (b) Discuss the relative merits of server-based networks and peer to peer networks. (6) (a) Geographical extent Connections -LAN cable and physical, WAN non-physical LAN restricted to single site/building/campus etc. C/w WAN more than one site (1) LAN connection via direct line, physical link e.g. co-axial cable, UTP, fibre optic c/w WAN connection via modem, telephone line, satellite link etc. (1) (b) Server based - central backing store available to all users c/w peer-peer distributed resource shared by all users (2,1,0) Server based - centrally held and shared software resource c/w peer-peer individual copies of software (2,1,0) Server based - centrally controlled user attributes c/w more flexible working environment (2,1,0) Server based: high management overheads for a system manager c/w distributed responsibilities for management/fewer overheads (2,1,0) Server based - reliant on a central control system c/w peer to peer no reliance (2,1,0) Server based - requires a different back-up strategy c/w peer to peer Server based - longer and more complex set-up and installation c/w peer-to-peer (2,1,0) ALLOW: maintenance and complexity of set up, licensing and management overheads NOT server based needs a server, peer-to-peer does not. NOT cheaper or cost

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1998.10 and 2000.9 Exemplar (7 Marks) At the central office of a landscape gardening company there are six employees. Each employee has a stand-alone computer system and printer. The company director has commissioned a business survey, which indicated that it would be more efficient if the six PCs were formed into a peer to peer network.

(a) State three benefits that the company would gain from networking their computer systems as a peer to peer system rather than a server based system. (3) (b) What additional hardware would be needed to connect the six stand-alone computer systems as a peer to peer network system? State why each item is required (4)

(a) Data can be shared Data transfer is improved Team-working is more effective Communications are enhanced (Disallow those advantages which can only be gained only by use of a server based

system.) Max 3 (b) reduced cost i.e. no purchase cost for server reduced network management overheads. Network Interface Card + reason Data transmission media + reason Max 4 1999.7 (8 marks) Ring and Star are two common network topologies. (a) Explain what is meant by the term "network topology". (2) (b) Give two advantages for each of the ring and star topologies that are not held by the other. (4) (c) State two factors that affect the rate of data transfer between the computers in a network. (2) 7 (a) The way in which the elements of a network are interconnected (physical layout) [1] which determines the cabling and interfaces needed [1] maximum 2 (b) Star: Each computer is independent of the others, the system is unaffected if one computer or connection fails [1] Data transmission speeds may vary on each cabling link [1] Centralised control of message switching – security control [1] Easier to add new stations without disruption to the system [1] To a maximum of 2 Ring: Less dependence on a single central computer [1] Routing is simpler as a packet simply circles the ‘ring’ [1] Very high transmission rates can be possible [1] maximum 2 Note: Do not credit points given twice in different forms (c) Physical capacity of cables [1] Protocol limitations [1] Hardware limitations eg network cards, modems, etc [1] Difference between analogue and digital [1] Loading of network [1] maximum 2

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June 2001.8 In a solicitor’s practice there are ten employees working in three offices. Each employee has a standalone computer system and there is a shared printer in each office. The head of the practice has been advised that it would be more efficient if the ten computers were formed into a server-based network. (a) State three benefits that the practice would gain from networking their computer systems. (3 marks) (b) Give two reasons for choosing a server-based system rather than a peer-to-peer system. (2 marks) (c) State two items of hardware that will be needed to connect these ten computers as a server-based network. State why each item is required. (4 marks) (a) • Data/information can be shared without need for duplication • Software can be shared • Data transfer is improved • Communications are improved/Team-working is more effective • Centralised upgrading/installation of software • Improved sharing of peripherals e.g. printers • Central control of security • Central control of backup Any 3 °— 1 3 (b) • Central pool of data/printer available to all employees • Central control of security (if not given in (a)) • Central control of backup (if not given in (a)) • Centralised upgrading/installation of software (if not given in (a)) • Dedicated servers usually provide faster access to network resources • Users are freed from network management tasks • Computers may be of different types Any 2 °— 1 2 (c) • Server (1) plus reason (1) • Network Interface cards (1) plus reason (1) • Transmission media/cabling (1) plus reason (1) • Hub/switch (1) plus reason (1) • Modem/Terminal adapter (1) plus reason (1) Any 2 °— (2, 1, 0) 4

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January 2001.2 Describe two differences between a Local Area Network (LAN) and a Wide Area Network (WAN). (4 marks) 2 Topic 11.9 Network environments NB QUESTION IS DESCRIBE • LAN restricted to a single site/building/campus (1) WAN more than one site/geographically remote locations (1) • LAN connected via direct line/physical link/co-axial cable/UTP/fibre optic cable (1) WAN connection via satellite link, modem, telephone line (1) Any 2 °— (2, 1, 0) 4 January 2003 5 The term used to describe the arrangement of computers in a network is topology.

a. Name and draw diagrams to illustrate, two different Local Area Network (LAN) topologies. (4 marks)

b. State one different advantage for each topology that you have chosen (2 marks) a. Bus (Allow Line), Star or ring must be diagram (allow other topologies if correct e.g mesh, hybrid etc) • Name • Structure (only one mark if name contradicts structure) b. STATE • Bus - cost effective in certain installations/easy to install/easy to add stations to • Ring - very fast transmission rates possible/fault tolerant • Star - speed of transmission does not degrade under load/fault tolerant/extra computers can

be added without disturbing the network • Other - suitable advantage must be clear 2 x (1,0) 2 must match (a) if not labelled use same order January 2002. 9 A small company is installing a computer network. Employees are to be issued with a handbook to help them to understand the networking terms. Provide an explanation of the following terms for the handbook: a. Local Area Network and Wide Area Network; (5 marks) b. Server and peer-to-peer. (5 marks) a. • Network a set of computers and peripherals connected together • Network enables sharing of data and resources • All the computer systems are relatively close to each other e.g. the same building or cluster

of buildings (LAN) • Direct physical connection is possible (LAN) e.g. fibre optic/coax cables or Wireless

Network • Network connections are normally cables (LAN) Computers are geographically remote

(WAN) • A range of connection methods can be used e.g. satellite link, modem, telephone line, router,

gateway (WAN) b.

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• A computer/station on a network that provides a resource that can be used by any client station -server

• Provides access to storage file server • Provides access to network printer and print spooling print server • Provides access to shared information -database server • Server not working means that clients do not have access to server controlled resources or

(p-w-p) a station not working only means that the other stations do not have access to the resources on that station

• Clients/stations have access to resources/data controlled by other clients/stations (p-to-p) • All stations on the network lhave similar status (p-to-p) • Provides access to shared resources e.g. printers and storage (p-to-p) (if not given in (a)) June 2003.6 Describe two features of each of the following types of Local Area Network (LAN):

a. peer-to-peer network (4 marks) b. client-sever network (4 marks)

A level Questions on Networking

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June 03 P1 no 7

(a) Explain the difference between

i. serial and parallel,

ii. simplex and duplex

modes of transmission.

(b) When data is transmitted it is subject to corruption. Explain how a parity check could be used

to determine whether corruption has taken place.

November 03 P1 no 7

A college has a number of standalone machines. The decision is taken to turn them into a LAN.

(a) State two items of hardware and one of software that will be necessary for the

conversion.

(b) Explain why students find the access to text based files does not cause a problem,

while graphics files download very slowly.

(c) State two advantages and two disadvantages of the college converting to a network

system.

(d) (i) Explain why a protocol is needed for this network.

(ii) Give a reason why such a protocol should be arranged in a layered fashion.

June 04 p1 no 5

(a) Explain the following modes of data transmission.

i. Simplex

4

4

3

2

4

4

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ii. Duplex

iii. Half-Duplex

(b) (i) Describe how buffers and interrupts are used in the transfer of data from primary

memory to secondary storage.

(ii) State which of the modes of data transmission would be most suitable for

the procedure in (i), justify your answer.

June 05 p1 no 6

(a) Draw simple sketches to illustrate

i. bus,

ii. star

network topologies.

(b) A school computer room is to be equipped with a network of machines. Give three advantages and one disadvantage of installing a network compared to stand alone machines.

June 05 P1 no 12

(a) State the meaning of

i. serial

ii. parallel

iii. simplex

iv. half duplex

v. modes of transmission

(b) One of the company’s computers is connected to a printer. Explain why data transmission is half-duplex.

November 2005 p1 no 5

3

5

2

4

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5 (a) Errors can occur when data is transmitted from one device to another. Explain how a

checksum can be used to monitor a transmission for errors. [3]

(b) Data is transmitted from one computer to another by using packet switching.

(i) Explain how packet switching works. [3]

(ii) Give one advantage and one disadvantage of using packet switching rather than circuit

switching. [2]

June 2006 P1 no 4

4 (a) State two ways in which a local area network (LAN) differs from a wide area network (WAN).

[2]

(b) Describe

(i) a bus network,

(ii) a star network

and give an advantage of each. [4]

(c) (i) Explain what is meant by the term protocol. [2]

(ii) Explain why the bit rate is an important part of any protocol. [2]

November 2006 P1 no 5 5 (a) State what is meant by the following types of data transmission. (i) Simplex. (ii) Half duplex. (iii) Serial. (iv) Parallel. [4] (b) Explain how buffers and interrupts are used in the transfer of data from primary memory to a hard drive. [6] (c) State two of the modes of data transmission mentioned in part (a) which would be used to transfer data from primary memory to a hard drive. Give reasons for your answers. [4] June 2007 P1 no 10 10 (a) State a difference between a local area network (LAN) and a wide area network (WAN). [1] (b) (i) Use examples from this application to explain the relationship between bit rates and the way that the data in the files is used. [4]

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(ii) The human computer interface (HCI) used on the computers in the showroom is menubased. Describe the interface that customers will use. [3] (c) State two health and safety issues that may arise due to the use of the computers. Give a different solution for each of the two issues which you have mentioned. [4] June 2008 P1 no 6 A large store has a number of departments, each selling different types of goods. Each department has its own computer system. It is decided to network the computers. A bus topology and a star topology are considered. Describe these topologies and give an advantage of each in this application. [8] June 2009 P1 no 6. (a) State what is meant by the following types of data transmission.

(i) Simplex. (ii) Half duplex. (iii) Serial. (iv) Parallel. [4]

(b) In a certain computer system parity checking is used to check the data has been transferred correctly. the type of parity checking used is even parity. Using the byte 01101001 as an example:

1. explain what is meant by an even parity [2] 2. give an example of an error which would not be detected [1]

November 2009 P1 no 8 (a) The machines in the tax office are networked. State two differences between a local area network (LAN) and a wide area network (WAN). (b) The machines in the tax office are networked using a star topology. (i) By drawing a diagram, or otherwise, describe a star topology. (ii) State one advantage and one disadvantage of using a star topology as opposed to a different type of topology.