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Problem Solving Report

Question 1

a). In computer science, polling is whereby one device or program continuously checks the state of other devices or programs to ascertain if they are still connection or in need of connection. Polling is specifically used in multidrop or multipoint communication where there are multiple devices connected to a controlling device. The controlling device communicates with each device one at a time to ascertain if there is need for communication. In this case scenario, the traffic of data in the router can be prevented by polling the data in queues and it is transmitted systematically. One advantage of polling is that many of its characteristics can be centrally determined. The second advantage is that with increase in traffic, and then the demand increases simultaneously and hence there cannot be oversaturation in the polled channels. Polling has some disadvantages too for instance, polling causes delays and hence some application may malfunction. Polling involves sending and receiving many messages and hence it consumes a lot of bandwidth.

b). token bus network and token bus network are more or less the same except the fact that in a token bus network, the network ends do not meet to form a ring. Instead, the network in both ends is cut off. Prior to network usage, a node requires a token. The data to be sent and the destination should be included. In the token bus topology, the physical location of nodes doesn’t matter because the passage of tokens is numerically in a sequence of node addresses. The coax cable is used by the token bus system which has a transmission rate of 1 to 10 mbps. Since there are no packets of data passed during transmission, there is a protocol that determines the passage of tokens. In the token bus system, frames are transmitted systematically with each station taking turn in the transmission. This means that the time used to transmit frames although the network is even and hence an increase in speed of transmission means an increase in the performance and vice versa.

c). i) because only one computer can send data at a time in a bus topology, collisions happen when the network is overloaded and it becomes slower. The nature of depending on nodes to co-ordinate together fails at times and collision occurs. That is why an access control protocol (ACP) is needed to minimize collisions. Collision detection (CD) and carrier sense multiple accesses (CSMA) are examples of ACP. However, in the bus topology, if one computer fails, others will not be affected but if the cable fails then the whole network will be affected.

In bus topology, a broadcast message is sent from one device which acts as the sender and the receiver gets the message. However, because the devices share a backbone as a medium for communication, all devices are able to access the message. Hence, bus topology requires a few devices in order to function well so that the information exchanged by different devices cannot be overwhelming.

ii) Hubs and repeaters regenerate and amplify the signal between pairs of segments and restores strong signal levels during transmission. They allow connection of LAN cable segments and facilitate signal transmission over larger distances. When there is a failure of network, they provide electrical isolation and protect equipment from other segments of the LAN from being affected by the electrical fault. In case of a collision, a JAM signal is generated by a repeater to all connected output ports and this alerts the connected devices not to transmit during collision.

Bridges are found on Ethernet frames where they examine frame headers and send frames to their particular destination. The buffering of frames means that the collisions are isolated hence a high throughput with no limitation on the coverage geographically or number of nodes accessed. Switches allow switching of frames from one device to another simultaneously without collisions. With switches, there can be many interfaces.

Question 2

a). the main reason why a checksum only checks for errors in the IPv4 header is because speed matters. Due to the fact that the internet backbone routers transmit hundreds of thousands of packets per second, it is quite cumbersome to calculate a checksum in all the content because packet processing would be slowed down. Data encapsulation in an IPv4 datagram, consists of a checksum field that represents the entire packet.

The IP and TCP checksums and the Ethernet frame check sequence protects data from corruption but not all types of corruption. It is important to use the cyclic redundancy check which is a harsh function that makes sure the data is not corrupted by confirmation.

a). Subnet mask is

000 0 -> 000 00000 0 ->

001 1 001 00000 32

010 2 010 00000 64

011 3 011 00000 96 (64+32)

100 4 100 00000 128

101 5 101 00000 160 (128+32)

110 6 110 00000 192 (128+64)

111 7 111 00000 224 (128+64+32)

c). Fragmentation is a process in which a datagram is sub-divided in smaller sized datagrams in order to fit in a certain network frame. Each network has a unique MTU (maximum transfer unit) different from the others and hence routers have to fragment each datagram’s packet to fit in the destination network. With fragmentation, the host is able to choose reasonable sizes of data for transmission with the ability to transmit even larger data sizes. Protocols are able to be optimized for connections with high bandwidth.

Losing one fragment means losing the entire datagram on the other hand, if only minimum MTU datagrams are sent by the host over the internet, fragmentation would not be needed. This is because the internet supports large data sizes and hence fragmentation would not be necessary in most cases. Fragmentation would affect the speed and the performance because it cuts off datagrams into smaller sizes.

d). i) the negative acknowledgement (NACK) oriented reliable multicast (NORM) protocol can provide data transportation that is reliable from a sender to a receiver over an IP multicast network. NORM is primarily designed to provide scalable, robust and efficient bulk data across topologies and IP network. It provides support for multicast sessions with the receivers and senders having minimal coordination. The message headers of NORM protocols have common information which allows synchronization of receivers and senders. The protocol tolerates timings that are inaccurate and other bad conditions. It operates efficiently even when large sizes of packets are lost or in case of delays.

Problem Solving ReportProblem Solving Report 1Problem Solving Report 2Problem Solving Report 3Problem Solving Report 4Problem Solving Report 5Problem Solving Report 6Problem Solving Report 7Problem Solving Report 8Problem Solving Report 9Problem Solving Report 10ii).

In the diagrams above, the arrows from left to right represent the negative acknowledgement mechanism whereas the arrows from the left to the right show the data repair. The space between the arrows is the hold off period. As shown, the first repair is quick and successful while the second repair delays and it is unsuccessful – shown by the elbow connectors.

The first advantage of a negative acknowledgement mechanism detects a problem or a corruption in the message and alerts the system of the error. The protocol can continue working with no interruption until an error occurs that is when alert messages are sent. The disadvantage of a negative acknowledgement protocol is that it is expensive to implement and it consumes time hence causing delays by the interruptions while sending error messages.

Question 3

The information contained in RIPv2 updates include a maximum hop count of 15, with route updates sent every 30 seconds to multicast address with an administrative distance of 120. The OSPFv2 checks the available routers and gets the available link state information to construct the network’s topology map. OSPFv2 supports Internet Protocol Version 6 (IPv6) and Internet Protocol version 4 (IPv4) networks and the Classless Inter-Domain Routing (CIDR) addressing model. OSPFv2 detects topology problems very quickly like link breakages and within seconds, it converges a new loop-free looping structure. It uses a Dijkstra’s algorithm method to compute the shortest path tree for each route. 32-bit numbers identify the areas of the OSPFv2 network which are expressed in dot-decimal notation of octet base or in decimal.

RIPv2 is an example of classless routing protocols. In these types of protocols, during routing updates, there is exchange of subnet information. This means that the IP addresses are more efficiently utilized. The user manually controls network summarization. The distance vector finds its way using hops. It converges slowly. The knowledge of the router about each route is utilized and determines the direction/vector to use.

In the link state routing protocols, the event triggers the updates. Prompts (hellos) communicate with the neighbor. The link state is fast to converge compared to the distance vector. In link state, the network is fully visible because of the existence of information about the network in a database.










Destination Next Hop

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Problem Solving Report 15

c). i) IPv4 header is more complex than IPv6 header, however IPv6 header is larger in size than IPv4 header. This is because of the difference in address size. IPv6 address are 126 bits whereas IPv4 are 32bit binary numbers; this applies to the source and destination too. IPv4 options have space in the IPv4 header, IPv6 have extension header. The length of IPv4 datagram header is 20-byte. IPv6 headers does not contain flags, identification, and IHL(Internet Header Length) like IPv4 header.

ii). The protocol of IPv4 is connect less and cannot be used in packet-switched networks. The delivery is not guaranteed, sequencing that is proper is not assured and delivery of duplicate cannot be entirely avoided. The header following the IPv6 is identified by 8-bit header field and it is located at the beginning of the data field of the IPv6 data packet. The packet’s payload transport layer protocol is specified by this field. TCP 6 and UDP 17 are the most common next headers. The IPv4 protocol field is similar to the next header field.

iii) Persisting datagrams for instance the internet going round in circles is prevented by the 8-bit time to live field in IPv4. The lifetime of the datagram is limited to seconds specifications. Less than one second time intervals are rounded off to one. When the datagram gets to the router, there is a hop count, 1 is the decrement of the router at the TTL field at this juncture. The sender receives the ICMP time exceeded message from the router after the packet has been discarded following a 0 from the TTL field.


CCNA Study Notes: Routing Protocols. (2016). Retrieved 22 August 2016, from

Comparison between IPv4 Header and IPv6 Header. (2016). Retrieved 22 August 2016, from

(2016). Retrieved 22 August 2016, from

RIPv2 > CCDA Self-Study: RIP, IGRP, and EIGRP Characteristics and Design. (2016). Retrieved 22 August 2016, from