Secure Networking - Question 1 / Week 1

a). The concept of layered in networking used to accommodate the changes that happened in the technology every day. Each layer of the network has some specific functions to play and responsible for taking actions for distinct function of the network. Each layer of the network has to pass the information to the next layer, this is how the data and information is processed.

The OSI model simplifies how these protocols of network designed by separating the communication of network into smaller pieces. The OSI model is designed in such a way that it makes sure distinct kinds of tools like network adapters, hubs, and routers are all compatible.

Protocol layering is a common method to simplify the design of networking by separating them into functional layers and it assigned the protocols to them to carry out the task.

b). A network is the hub of various devices and that too large devices. All devices are dissimilar to each other. Dissimilar device can arise the issue of compatibility. To avoid these kinds of compatible issues and all other issues, standard network model is used for the communication. The most important network model is TCP/IP. This network model consists of various layers. The data that needs to transfer to new location pass through every layer. When this information reach to each layer, some information gets add to this data. This process is called encapsulation and when this data reaches to the destination, this added information has to unpacked in every layer. This process is called decapsulation

The main difference between the two is, in encapsulation, the data is move from top layer to bottom layer and every layer contains a lot of information which called header together with the original data while in decapsulation, the information moves from lower bottom layer to top layer and in each layer unpacks the added information to the corresponding header and to get the original data.

c). A layer required to communicate with all its peer layer at the receiver’s node and it is a need of protocol also that helps in passing the information to the layers whish is above to it and below to it. The header of the layer also contains the field of protocol. For instance, it is used to describe which protocols is used at the next layer. It will contain all the address information that is targeted to the peer layer at the receiver’s node, and checksum maybe present, or a length field to assist in the message and information integrity. Exchanging the protocol of layer with other has less impact on the side or adjacent layer as compared it has on the receiving layer on the other node. All the peer

nodes should be same, however as long is the layer which is adjacent should be compatible with it. For instance, if one created a network layer which is called roundabout, then one needs to get a protocol number to define it within the many 802.x protocols, and one required to incorporate a protocol field hence TCP or UDP can be identified.

d). The internet is an abstraction all the technologies of network that is underlying and resolution of physical address. A protocol stack is the layer of all the seven layers and these all layers are work together to perform all the hardware and software function. Layer 1 is the network layer that helps in combining the physical and data layer and it help in routing between the devices of the same network and also exchange the information among network and other devices.

Layer 2 is the internet layer that helps in connecting the computer with the internet and it is adjacent to network layer. It uses Ip address and also includes network identifier and host identifier. It used to make the connection with the LAN of home network

Layer 3 if the transport layer. It helps in asking the information other network of the model as it is willing to accept the information from the other local device. In this case, making a connection between printer and system is the work of transport layer.

Layer 4 is the application and a combination of presentation and application and session layer. It used to send emails and to transfer the files from one device to another. In this case, files and information can be transferred.

Secure Networking - Question 2 / Week 2

Virtual circuit is based on connection-oriented service and it has implementation of various resources like CPU, bandwidth, etc are used by the virtual circuit to transfer the data. On the other side, datagram provides the connection less service and it has no similar resources for transferring the data.

i. In virtual circuit, it has various resources and bandwidth that get reserved prior to transmission, the path that is used to send the first data packets and other data packets gets reserved and fixed and all the remaining and other data packets used the same resources and the same path to follow. On other side, datagram network’s path is not fixed and data packers are free to move in any direction, sometimes they may collide and these packets don’t have fixed routes and they change their route and go dynamically and keep changing their router table on routers. This is the reason why the packets get delayed in transmitting from sender to receiver.

ii. In virtual circuit, it has various resources and bandwidth that get reserved prior to transmission, the path that is used to send the first data packets and other data packets gets reserved and fixed and all the remaining and other data packets used the same resources and the same path to follow. On other side, datagram network’s path is not fixed and data packers are free to move in any direction, sometimes they may collide and these packets don’t have fixed routes and they change their route and go dynamically and keep changing their router table on routers. This is the reason why orders of packets get changed at the receiver side and the packets does not receive in a sequential manner at the receiver end.

iii. In virtual circuit network, the pat is fixed and it has assurance of fixed resources, so virtual circuits are more reliable for transferring the data as compared to the datagram network. On the other side, datagram network because of dynamic resource allocation and it also follows the path of dynamic which is more prone to error and it is very less reliable than the virtual circuit. So, there is no reliability to get the packets on the receiver side.

Secure Networking - Question 3 / Week 3

a) . the network layer is the third layer of the OSI model. It takes care of all the request that is received from the transport layer and it moves forward the services to the data link layer. The network layer receives the data from the PC from the left and translates the logical address into physical address. After translating the address, it determines the route from left PC to the right PC, from source to destination and it also takes care of the congestion and traffic if occurred like switching, routing and also controls the traffic of data packets. The main aim of the network layer is to transfer the data packet from host to the receiving end. There are some functions that network layer has to perform while going from left Pc to right PC.

First is routing, in routing packet reached at the input link of router and the router will help in moving the packets to the output link of the router. In this case left PC to router, the data packet moves. The layer also converts the physical address to logical address so that it can find out about the destination. It helps in maintaining the connection between different type of network.

The layer is also used fragmentation and break the packets into smaller parts so that all packets of data can be reaches from left PC to right PC. Now the link layer helps in getting the packets in the form of data stream. The main aim of the link layer is to convert the data stream into signal bit by bit and to send all the signals to the underlying hardware that is left PC.

Link layer takes the packet from network layer and make them in the form of frames and then send bit by bit to the hardware, here hardware is the right PC. This is how data can be transferred from left PC to right PC.

b). when data moves from top to bottom through the different layers, this is called encapsulation and when data moves from bottom to up and the data that gets added, unpacks, this process is called decapsulation. Encapsulation is used at the left PC because the data gets collected from this PC and it is used when data is being sent and encapsulation is used when data is being received. When the signal goes out from the host computer to the network, data decapsulation is used. So, encapsulation occurs at the left PC and decapsulation occurs at the right PC.

Secure Networking - Question 4 / Week 4

a). the switches of ethernet is made of two forms, first is managed and second is unmanaged. The switches which are managed can be configured directly and or it can be enabled and disabled or supervises by the operator of network. Ethernet is simply a connection of various systems that is used to connect to a LAN to prevent any kind of simultaneous transmission. Yes, modern ethernet make use of switches which when only one device is used to connect to switch in wireless network port and it enables CSMA/CD to be disabled and full duplex communication is used rather than.

CSMA/CD is used in the ethernet networks to avoid all the kinds of collisions by checking if the medium is idle prior to sending the packets. CSMA/CA is used almost all wireless connections such as wifi as it is a wireless network and CSMA/CA is used to avoid collisions by checking prior if the channel is idle prior to sending the packets.

Carrier sense is an initial idea that helps participants sending the data over the network if the medium is not full. The carrier sense checks the channel anytime and data send if medium is free.

CSMA/CA helps in reducing the frequencies of the collision and avoid a plan at the same time if the medium is not free. This protocol is very necessary in wireless networks to transmit the data in the sequential order. It is necessary in the decentralized network to follow a set of rules while transmitting the data and organise the communication. This is the reason why CSMA/CA is used in Wi-Fi. Collision can occur in wireless network also because two devices try to access the access point simultaneously. So CSMA/CA is very useful.

b). Yes, the CSMA/CA is used in the WIFI reduce the likelihood of Collison but it in unable to reduce the Collison 100 percent because two devices try to access the same or different data from the same access point and that too simultaneously. It is unreliable because its all nodes are hidden. It is a protocol that operates on the data link layer. It check the station before sending the data and if the station is free then it sends the data and it is true for other, the other can also check at the same time when first one is checking and both check at that same time that the station is free and they both send the

data at the same time. So this is the reason why it is not secure always while transmitting the data. First it checks the station and if station is free, it transfer the data and noted down the time and then transfer the next data without checking bit according to time. So, this can be the other reason for not avoiding the traffic always.

Secure Networking - Question 5 / Week 5

a). & b). Fragmentation is done with the help of network layer when the size of the datagram is greater than the maximum so that it can hold a frame which is known as maximum transmission unit. The network layer separates the data obtains from the transport layer into various fragments so that this data in fragments can be flow without any disruption.

  • As there are 16 bits is the total length of the IP header, and maximum size can be 2^16-1=65,536 bytes.
  • This is done through the network layer at the destination and this is done with the help of routers.
  • The side of source do not require fragmentation because of good segmentation by the transport layer.
  • At the receiver end, the receiver knows about the frame as 16 bits in IP header. Every frame in the fragmentation contain same identification number.
  • The receiver searches about the sequence of all the frames that is used in the fragment offset which is of 13-bit field in IP header.
  • An overhead is there at the layer of network that is exist because of header introduction because of fragmentation.

Fields used in IP header for fragmentation:

  • Identification which is of 16 bits
  • Fragment offset which is of 13 bits
  • More fragment which is only 1 bit
  • Don’t fragment which is also 1 bit.


Reassembly can be done at the destination side and it is not carried out at the routers as packets take different path, so all can be meet at a router. So, need of fragmentation arise for the second time.


  • First, destination identifies the datagram which needs fragmentation from MF, Fragment offset field.
  • Second, Destination identifies about all the fragments according to the similar datagram from field of Identification.
  • Third, Identifies the 1st fragment (offset = 0).
  • Fourth, Identifies following fragment with the help of header length, fragment offset.
  • Fifth, Repeat until MF = 0.

c). when a host transmit a packet to the network, this packet should not be greater than the maximum size according the support of local network. The size of the local network can be determined by the data link and maximum transmission unit of IP, these two are generally same. The presence of fragmentation would influence the decision to validate only the IP header instead of the entire datagram because of following points:

  • If the single fragment loss then it results that all the fragments have to be resent to a relevant transport layer. It is common in fragmentation, of sender resends one packet then fragmentation occur again because of this one packet.
  • The first fragment includes a header of high layer that can raise issues with many such as firewalls, middle-boxes and routers because they are entirely dependent on header’s inspection.
  • The fragmentation may outcome in out of orders in the delivery of packets and requirement for reordering.

Remember, at the center of any academic work, lies clarity and evidence. Should you need further assistance, do look up to our Computer Science Assignment Help

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