SIT202 - Computer Networks - TCP/IP Protocol - Assessment Answer

December 05, 2018
Author : Ashley Simons

Solution Code: 1IGE

Question:Computer Networks

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Computer Networks Assignment

Assignment Task

1 . Given the following network/s:

Client Server Switch Router Switch

Consider the problem of transferring a large file via the web:

a) Identify how many networks are illustrated and what topologies is/are used in each network identified. Explain how you identified the networks and topologies in your answer.

b) For each of the five devices illustrated, indicate which layers of the TCP/IP protocol suite are certain to be found on that device and briefly explain why.

c) In the Week 1 slides / prescribed reading, it is mentioned that addressing is required at all layers except the physical layer. If this is true, explain how the physical layer will be able to deliver/direct the data to its intended destination. Refer to the above scenario/network when explaining your answer.

2 . a) Given that electromagnetic waves can travel at the speed of light, briefly explain howdifferent signals can arrive at different times when transmitted at the same time. Consider both wired and wireless media in your answer.

b) Consider a digital signalling approach that uses only two voltage levels to represent binary data and achieves a data rate of 1Mbps. Explain how increasing the number of voltage levels could potentially increase the data rate and briefly discuss the potential problems that may be encountered.

c) A network administrator has identified that several paths throughout the organisation’s network are experiencing significant latency. Given that latency consists of propagation time, transmission time, queuing time, and processing delay, discuss how each of these could potentially be reduced, addressing the identified problem.

d) Consider the Manchester and Differential Manchester encoding schemes.

i.Using the same input of 8 bits, draw an illustration of both schemes. For the input sequence, you may choose any 8 bits however must include both 1 and 0 bits.

ii. Explain how these schemes achieve self-synchronization.

iii. Explain the relationship between DC components and baseline wandering and how these schemes resolve this problem.

e) Consider the frequency-division multiplexing and time-division multiplexing techniques. Give an example where these two techniques could be used at the same time and explain how they are used.

a) A colleague is developing a new protocol that will be implemented at the network layer. A key requirement of this new protocol is that data must be delivered in order. There are two data-link technologies to choose from, one is a datagram network and the other is a virtual-circuit network. Identify and discuss two advantages and two disadvantages of each technology.

b) Consider a scenario where a computer is attempting to send data to a device on the same network however the destination is not responding to ARP requests. Identify and briefly explain three reasons why this may occur. Note that the possibilities of the devices being turned off and/or not connected to the network have already been eliminated.

c) Refer to the figure shown on Week 3 Slide 49 for the calculation of CRC codes. Demonstrate the generation of the CRC code using the same approach (same divisor and number of redundant bits) using the 8-bit number 11001101 as input.

d) Consider the following three 16 bit data elements:

1100 1100 1100 1100

0101 1100 0101 1100

0001 0001 0001 0001

Demonstrate the calculation of the 16-bit Internet checksum for this input

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Solution:

Question 1:

  • In this architectural design, there are 4 networks used. File is transmitted from client machine to switch, again from switch to Router and at last from Router to another switch. The various network devices (IS, Intermediate system) are used to connect two sub networks. The first Switch is used to connect network1 and network2. The Router is used to connect network2 and network3. The second switch is used to connect network3 and network4. So, hence 4 sub networks are used.

In case of network1, the bus topology is the appropriate choice because if one client fails then another client can transmit the file in the switch. In case of network2, the bus topology is also chosen due to easily extendable of networks. In network3, star topology is used where central device is the router. In network4, the bus topology is used due to easily transfer the file to the server.

(b) In case of transferring file from Client device, the layer 4, Application Layer is used.

In case of switch device, the layer2 (Data Link Layer) of the OSI model but layer1 (Host-to-network Layer) of the TCP/IP model is used.

In case of Router device, the layer3 (Network Layer) of the OSI model but layer2 (Internet Layer) of the TCP/IP model is used.

In case of receiving file into Server device, the Application Layer (layer4) is also used.

The client and server device use the Application Layer (layer4) for sending and receiving the file. Because, FTP (File Transfer Protocol) is naturally used for transferring file amongst the client and server. The FTP resides on the Application Layer.

Switch operates at the lowest layer of the TCP/IP model. This protocol is used for connecting the hosts so packets can be easily sent over the network.

Router operates on the layer2 i.e. Internet layer of the TCP/IP model. The IP (Internet protocol) is used in this layer for transferring packets independently to the destination.

(c) There is a direct link between two devices in case of Physical layer. The raw bits are transmitted between two devices. The data is encoded as energy in the source device, and then transfers the encoded energy through the physical wire; again the transmitted energy is decoded at the destination to get the original data.

In the above scenario, the data is transferred over a carrier like cables. The cable sends the bit stream over the network at the mechanical and electrical level. The protocols like ATM, Fast Ethernet can be used in case of data transmission.

Question 2:

(a) In case of electromagneticwaves when passing with radio signals, the waves must actonobjectsand mediaat the time of travelling. Basically, the radio signalisreflected, refracted or diffracted. When the radio signals travel to a direct line, the interactions between the signals mightnot bedoable.

Reflection:

Reflectionof lightassociated degreeof prevalence. Mirrorsarea that mightbe seen inresidence and lots ofdifferentplaces.Radio wavesarea unitequallyreflectedbyseveralsurfaces.

At the time of reflection, incidence-angle iscapablethe reflection-angle for a surface that would be expected forlightweight.Oncean indicationismirroredthere'sunremarkablyseen the loss of the signal, either absorption, or signal passing through the medium.

Refraction:

Theconstructof wavesare refractedis incrediblyacquainted,particularlybecause itissimplyincontestablebyputtinga regionof water or in air.It’s doableto envisionthe apparentamendmentor bendas thestick pushes into the water.

Diffraction:

Radio signalscan alsobearoptical phenomenon.It’sfound thatoncesignals encounterassociate degreeobstaclethey have an inclinationto travel around them.This couldmean thatan indicationcould also beobtained from a senderalbeitthisshouldbe pointed byan oversizedentity.Itcan besignificantlyobservable on fewradio radiationtransmissions.radiationtransmissionsaredetectedinmoreplaces than transmissions on VHF FM.

Theprimedifferencebetween wired vs. wireless networks is, the first oneutilizes cables (fiber optic, coaxial cable etc) and second utilizes radio signals. The wireddevicepermits for a speedy andinvolvingsecure communication over distances of less than 2,000 feet. But the wireless device is restricted by its transmission speeds from outside interference as well as it is less secured.Yet, more mobility is achieved in case of wirelessnetworking than wired networking where the covered area is approximately 150-300 feet and 1000 feet of indoors and outdoors respectively. Thewired networking is more expensive as it uses Ethernet cables, hubs and switches.

(b)The data rate gets larger with the increasing of the voltage levels because the increase in signal to noise ratio allows added bits to be sent in a particular time. This is because the larger signal to noise ratio makes it easier for the receiver to actuate what bits were sent. For example, if one sends 2 bits in one time breach (4 possibilities), the receiver have to actuate which of 4 altered levels were sent. If the voltage is increased, again the level shift amid the 4 possibilities increases. These will abatement the error rate of the same bit rate. However, one could as well forward added bits in one time breach with the same difference in signal level amid each accessible combination. This is why added signal level (voltage) allows an access in bit rate.

Potential Problem:

The potential problem arises when Digital data sent through a Wi-Fi signal is beatific in packets; the integrity checking is done with received packets to finish the data stream. This action assume data is kept as usual ; however, it does not affected the actuality the digital data accept to consistently transferred over air, light, electromagnetism, etc.

When the analog Wi-Fi signal quality degrades, the problem occurs for dropping connection.

(C )Propagation time:

There are several accidental sources for delaying transmitting a packet. In LAN, the most common term is bandwidth delay: the time bare for transmitter to get the packet assimilates the wire. Afterwards aggregate has been adapted to accepted units. There is as well propagation time, apropos to the propagation of the bits with the speed of light depending on the transmission media. The delay is measured as: distance/speed of the light.

Transmission time:

Transmission delay is measured by the total number of bits to be transferred / bandwidth of the pipe.

For example, if we acquire a pipe that can handle a bandwidth of 100Mbps, it agency that the pipe is accessible to acquire a max of 100Megabits per second, i.e., we can stuff 100Mbits into the pipe in any second. If we wish to forward 1000bits, the time the pipe will yield to acquire 1000/100M = 10 microseconds. This is the transmission delay/time. Let's say the propagation delay is 10ms. It agency that already you've pushed the bits, the packet will yield 10ms to ability the receiver. So the absolute delay for sending the packet and the receiver accepting it is 10 microseconds + 10ms = ~10ms. In case of high bandwidth networks, the transmission delay is very minimum.

Queuing time:

Queuing delay/ time(dqueue) is the complicated version of nodal delay. The queuing delay may alter from packet to packet. For example, if 15 packets access at an empty queue at the specified time, the first packet sent will ache no queuing delay, while the last one sent would suffer a larger queuing delay. Therefore, in measuring queue delay and reducing the delay, the statistical measures are needed like average queue delay, variance of queuing delay and probability of queuing delay.

Processing delay:

In case of networking environment, this delay is the elapsed interval for routers to process the packet header.

At the time of packet processing, routers analysis into bit-level errors in the packet and identify about the packet's next destination. By using high-speed and sophisticated routers, the processing delays can be minimized.

Processing delay:

ii)To decode the accustomed signal correctly, the bit breach of the accepter must be absolutely same or within transmitter limit. Synchronization from the receiving signal is done with the help of PLL (Phase Lock Loop) when clock is generated. It can be accomplished if the received signal is self-synchronizing by accepting frequent transitions in the signal.

 

iii)Zero frequency component in the signal spectrum is known as the direct-current (DC) component after line coding. DC component cannot enter through the some components of a networking. This leads to signal distortion as well as erroneous output. It also results energy loss on the line.

(e) Naturally, wireless network uses the TDM (Time-division Multiplexing) whereas wired networks use FDM (Frequency-division Multiplexing). So, the network that supports both LAN and WLAN must use both. On the other hand, broadband ISP connection taken by multiple users must use both at the same time. First, broadband uses FDM to spilt the connection over the phone line. Again, individual connected users access their packets by interleaving on to the total connection that is TDM.

FDM: This technique actually uses the analog signal and circuits through copper wire or microwave channels.

Processing delay:

TDM: This technique allows digital data combined from channels of low-bandwidth into a channel of single high-bandwidth. To occupy alternative time slots, digital data from different channels is multiplexed as per time.

TDM

Question 3:

(a)Datagram:

Advantages:

The datagram packet can transfer from any to any communication.

The network is flexible enough and even allocation of network fails, the consecutive packets by the surrounding nodes can send. In this case, there is no need for call setup and termination.

Disadvantages:

This network actually leads to timedelay, propagation delay as it can add the features for monitoring, re-ordering and recovering the packets.

Virtual circuit:

Advantages:

Data packets are delivered at the destination address in an orderly fashion with reliable connection where headers are very small. So, no need for storin the destination address for the header.

Disadvantages:

Load distribution over the network is quite impossible. If one device fails then the total network is disrupted. Handling lots of traffic is very problematic.

(d) Internet checksum:

Internet checksum:

Internet checksum

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