unit-09-p1p2m1-2012(task 1-4)

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Task 1 Network Systems & Protocols

• In pairs, investigate different types of network topologies. In each caseimport an image and identify with clear reasons the likely environmentswhere each network may be installed.

• Include in the above reasons any advantages and disadvantages for each network system and how they relate to particular networkstandards and protocols.

Expand boxes below

Explanation Image

Bus topology uses a common backbone to connect all thenetwork devices in a network. A single cable functions asthe shared communication medium for all the devicesattached with this cable with an interface connector. Thedevice, which wants to communicate, sends thebroadcast message to all the devices attached with theshared cable but only the intended recipient actuallyaccepts and processes that message.Ethernet bus topologies are easy to install and don’trequire much cabling and only a main shared cable is

used for network communication.

Ethernet cables used in the Bus topology. Also, Busnetwork works with very limited devices. Performanceissues are likely to occur in the Bus topology if more than12-15 computers are added in a Bus Network.Additionally, if the Backbone cable fails then all networkbecomes useless and no communication fails among allthe computers.

Advantages

• Easy to implement and extend.• Easy to install.• Well-suited for temporary or small networks not

requiring high speeds (quick setup), resulting infaster networks.

• Cheaper than other topologies• Cost effective; only a single cable is used.• Easy identification of cable faults.

Disadvantages

• Limited cable length and number of stations.• If there is a problem with the cable, the entire

network breaks down.• Performance degrades as additional computers

are added or on heavy traffic (shared bandwidth).

Bus Topology

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• Significant Capacitive Load (each bus transactionmust be able to stretch to most distant link).

• It works best with limited number of nodes.• Commonly has a slower data transfer rate than

other topologies.

In ring Network, every computer or device has twoadjacent neighbours for communication. In a ringnetwork, all the communication messages travel in thesame directory whether clockwise or anti clockwise. Anydamage of the cable of any cable or device can result inthe breakdown of the whole network. Ring topology nowhas become almost obsolete.FDDI, SONET or Token Ring Technology can be used toimplement Ring Technology. Ring topologies can befound in offices, schools or small buildings.

Advantages

• Very orderly network where every device hasaccess to the token and the opportunity totransmit

• Performs better than a bus topology under heavynetwork load

• Does not require network server to manage theconnectivity between the computers

Disadvantages

• One malfunctioning workstation or bad port in theMAU can create problems for the entire network

• Moves, adds and changes of devices can affect thenetwork

• Network adapter cards and MAU's are much moreexpensive than Ethernet cards and hubs

• Much slower than an Ethernet network undernormal load

Ring Topology

Mesh topology work on the concept of routes. In Meshtopology, message sent to the destination can take anypossible shortest, easiest route to reach its destination. Inthe previous topologies star and bus, messages areusually broadcasted to every computer, especially in bustopology. Similarly in the Ring topology message can

travel in only one direction i.e. clockwise or anticlockwise.Internet employs the Mesh topology and the messagefinds its route for its destination. Router works in find theroutes for the messages and in reaching them to theirdestinations. The topology in which every deviceconnects to every other device is called a full Meshtopology unlike in the partial mesh in which every deviceis indirectly connected to the other devices.

Advantages

• There are dedicated links used in the topology,which guarantees, that each connection is able to

carry its data load, thereby eliminating trafficproblems, which are common, when links are

Mesh Topology

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shared by multiple devices.• It is a robust topology. When one link in the

topology becomes unstable, it does not cause theentire system to halt.

• If the network is to be expanded, it can be donewithout causing any disruption to current users of

the network.• It is possible to transmit data, from one node to a

number of other nodes simultaneously• Troubleshooting, in case of a problem, is easy as

compared to other network topologies.• This topology ensures data privacy and security,

as every message travels along a dedicated link.Disadvantages

• It requires a lot more hardware (cables, etc.) ascompared to other Local Area Network (LAN)topologies.

• The installation and configuration of this topology

is very complicated and can get very messy. Alarge number of Input / Output (I/O) ports arerequired.

• It is an impractical solution, when large numbersof devices are to be connected to each other in anetwork.

• The cost of installation and maintenance is high,which is a major disadvantage.

Tree topologies are comprised of the multiple startopologies on a bus. Tree topologies integrate multiplestar topologies together onto a bus. Only the hub devicescan connect directly with the tree bus and each Hubfunctions as a root of a tree of the network devices. Thisbus/star/hybrid combination supports futureexpandability of the computer networks, much betterthan a bus or star.

Advantages

• It is the best topology for a large computernetwork for which a star topology or ring topologyis unsuitable due to the sheer scale of the entirenetwork. Tree topology divides the whole networkinto parts that are more easily manageable.

•

Tree topology makes it possible to have a point topoint network.• All computers have access to their immediate

neighbours in the network and also the centralhub. This kind of network makes it possible formultiple network devices to be connected with thecentral hub.

• It overcomes the limitation of star networktopology, which has a limitation of hub connectionpoints and the broadcast traffic induced limitationof a bus network topology.

• A tree network provides enough room for futureexpansion of a network.

Disadvantages

Tree Topology

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• Dependence of the entire network on one centralhub is a point of vulnerability for this topology. Afailure of the central hub or failure of the maindata trunk cable can cripple the whole network.

• With increase in size beyond a point, the

management becomes difficult.

The most commonly used topology in LAN is the startopology. Star topologies can be implemented in home,offices or even in a building. All the computers in the startopologies are connected to central devices like hub,switch or router. The functionality of all these devices isdifferent. Computers in a network are usually connectedwith the hub, switch or router with the Unshielded Twisted Pair (UTP) or Shielded Twisted Pair Cables.As compared to the bus topology, a star network requiresmore devices & cables to complete a network. The failureof each node or cable in a star network, won’t take down

the entire network as compared to the Bus topology.

Advantages

• Better performance: star topology prevents thepassing of data packets through an excessivenumber of nodes. At most, 3 devices and 2 linksare involved in any communication between anytwo devices

• Isolation of devices: Each device is inherentlyisolated by the link that connects it to the hub. This makes the isolation of individual devicesstraightforward and amounts to disconnectingeach device from the others. This isolation alsoprevents any non-centralized failure from affectingthe network.

• Simplicity: This topology is easy to understand,establish, and navigate. Its simplicity obviates theneed for complex routing or message passingprotocols. Also, as noted earlier, the isolation andcentralization it allows simplify fault detection, aseach link or device can be probed individually.

• Easy to install and wire.• Easy to detect faults and to remove parts.• No disruptions to the network when connecting or

removing devices.

Disadvantages

• High dependence of the system on the functioningof the central hub

• Failure of the central hub renders the networkinoperable

• The performance and scalability of the networkdepends on the capabilities of the hub

• Network size is limited by the number of connections that can be made to the hub

• Other nodes may see a performance drop if traffic

to another node occupies a significant portion of the central node's processing capability or

Star Topology

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throughput.• Wiring up of the system can be very expensive.

Task 2

Collision Issues

To overcome data collision issue, Ethernet has a solution calledCSMA/CD and is commonly referred to as the backoff algorithm.Create a diagram in Microsoft Visio and import into the box

provided. Refer to this diagram to help you explain how toovercome data collisions on a computer network system.

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Image: CSMA/CD (Carrier sense multiple access with collisiondetection)

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B

C

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Task 3 Peer-to-Peer & Client Server Networks

Create a PowerPoint comparing the benefits and thedisadvantages of peer-to-peer and client-server networks. Forevidence, you will need to demonstrate your presentation, importyour slides and presentations notes in the table below and alsorecord it as a short video.

Expand boxes to suit your presentation

PowerPoint Slide Presentation Notes Title Page

Peer to peer networks have no

server controlling the network. All

of the systems on the network are

joined together meaning that they

can share all of their information.

The security on peer-to-peer

networks is not the best, as you

can only put passwords on folders

but peer-to-peer networking is the

best way to either share a home

internet connection or play

networking games together otherthe network.

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How to overcome data collisions

Collision is very normal in Ethernet networks where only one networking device

can send data at one time. When two computers send the information out at the

same time same, the information collides and creates the collision. The collision

will cause the information to be lost and fail the transmission.

CSMA-CD (Carrier Sense Multiple Access with Collision Detection) control

mechanism is applied for enabling packet re-transmission after detecting the

collision. It is a set of rules which determines how network devices respond when

two devices attempt to use a data channel at the same time. This is the data

collision!

CSMA/CD is used to monitor the traffic on the line at all of the different

workstations. If there is no data being transmitted (information being sent) at that

time, the station can transmit the data across.

However, if two stations try to send the data at simultaneous times, this causes

the collision. This is detected by all of the workstations which are linked and after

a random time interval, the stations which collided attempt to send the

information again.

CSMA is most commonly used in half-duplex Ethernet connections. The protocol is

“half-duplex”, which implies that a station may either receive or transmit data, but

not at the same time.

Example:

Machine A and machine C both check to see if there is any traffic on the lines and

that they are clear to send data. When checking they both see that the lines are

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There are many advantages and

disadvantages of peer-to-peer

network compared to client-server,

depending on where you are using

your network and what it is being

used for. Peer-to-peer networking

works better with 2-8 systems

linked to the network. If there are

too many then it doesn’t always

work as fast and efficiently. The

security is also very poor (can only

put passwords on files) and

backup and data recovery on the

systems is difficult. Therefore each

computer should have its own

back up. Although there are a few

disadvantages there are also

advantages, the main one being

they are very easy and simple to

set up. Also if one computer fails

to work, all of the others will

continue to run. (Opposite toclient-server) The cost of building

and maintaining the peer-to-peer

network system is a lot less than

the client server networks. And

there is also no need for a system

administrator as users personally

administrate their machines.

Client-server networks allow

clients to be able to log onto the

network. This network allows a

large amount of systems on the

network, whereas the peer-to-peer

only works with 2-8 systems on

the network. These client-server

networks are very wide-ranging,

such as Facebook and Skype and

other communication systems,

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online gaming systems and web

servers being accessed by many

clients. The client server networks

need a better quality network as

the network will be a lot busierdue to the amount of systems on

the network. It may also need a

system with higher specification

computer.

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Client-server networks work in a

different way to peer-to-peer

networks. The security and back

up on the client-server network is

a lot more efficient. As all of the

data is stored on the server it is

easy to make a back up of it, and

can be very easily recovered if

data is lost. Security rights can be

set up and adjusted to suit the

needs of the user. Also changes to

the network can be made very

easily by upgrading the server.

There is a centralised control in

client-server networks, in which

the servers help administering the

whole set up. All of the access

rights and resource allocation is

done by the servers. Although

there are a lot of advantages to

the client-server networks the

disadvantages also balance them

out. The worst one being thatwhen one of the servers goes

down, all of the computers on the

system cannot be used. Also if

there are too many requests from

the clients it may lead to

congestion on the network. The

client-server network also costs a

considerable amount more than

peer-to-peer network to set up andto run! They are also a lot more

complicated to set up.Peer-to-peer networks should be

installed in homes or in very small

businesses where employees

interact regularly. They are also

inexpensive to set up compared to

the client-server network.

However, they offer almost no

security. On the other hand, client-server networks can become as

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big as you need them to be to

support the company. Some

support millions of users and offer

the best and most updated

security measures.

An example of a client-server

relationship is a file server.

Computer systems connect to the

server, which they then request a

file from and the server will then

deliver it. When this action is

performed in a peer-to-peer

network it is decentralized. The

computers which are on the

network all contact each other andagree between them to share files.

Both the Client-Server network

and Peer-to-Peer network are able

to download files or upload files to

the others.

Task 4 Network Protocols

Generate another presentation to answer the following questionslisted below in order to decide why different networks standardsare necessary.

To meet the P2 criteria, you must address all five points.

• Purpose of why TCP/IP model is used on

all types network system

• The benefit of a WAN standard (public and

private packet-switching networks)

• The benefit of a LAN standard (IEEE Standards,

Wireless etc)

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• What protocols are used on a WAN (layers 1 to

4)

• What protocols are used on a LAN (layers 5 to

7)

Note: You may consider the Internet to be an example of a WAN for thisassignment task.

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