Understanding Computer Networking Topologies And Protocols

Network Topologies and their Advantages and Disadvantages

In computer networking, a network or physical topology represent the logical structure or outline used to connect computers or any other computational devices. Several methods or patterns can be used as discussed below:

The star topology- As the name suggests, this pattern invokes a star pattern where every device (computer) is connected to a central device used as a management hub. In most cases, this central device is usually a switch. Moreover, the star topology is the most used pattern because of its simplicity which makes it adequate for most networking purposes. Real life example; computers in a small laboratory connected to a central server.

Advantages

1.    As stated above the method is very simple to implement.
2.    It also can have a high tolerance to faults i.e. damage on one computer does not affect the rest.
3.    Moreover, it’s very easy to detect problems or faults.

Disadvantages

1.    Nevertheless, it’s quite expensive to install.
2.   Although it has independent components, it can fail of the central device is damaged (Zandbergen, 2017)
3. Bus topology– A topology where all devices are usually connected to a central connection characterised by a main cable i.e. the bus. Consider the connection of computers in a classroom where a central cable carrying the network is used to tap the connection. This method will use collision mitigation procedures as packets (from all the devices) are sent across the common bus.

Advantages

1.    Based on the description, it’s clear to see that it’s very easy to install.
2.    Moreover, it requires minimal resources to implement (Omnisecu, 2017).

Disadvantages

1.    It can never serve as a standalone connection method.
2.    Also susceptible to single point failure if the bus fails.
3. Mesh topology– Most probably the most notable pattern seen today because it’s characterised by advanced interconnections where each and every device is connected to each other, for instance, the internet. Basically, in this networking pattern, a device will have a connection to all the devices available in a given network. Furthermore, due to these connections (which are very many), it tends to be very expensive (Nizam, 2014).

Advantages

1.    Multiple connections constitute and resilient and robust system.
2.    Furthermore, you can add any device from any location.
3.    Finally, it can easily handle large amounts of data or traffic.

Disadvantages

1.    It’s very expensive to install and maintain.
2.    Secondly, it can sometimes be hard to manage and maintain (Certification kits, 2017). 

In today’s world, several telecommunication vendors exist and they produce many devices that perform similar functions but with varying operational systems. Therefore, to integrate these devices and their vendors standards such as the TCP/IP model are used to unify communication. TCP/IP will facilitate communication using a layered architecture that enables the integration of digital medium with physical mediums (Nizam, 2014). 

When transferring data from one device to another, several factors must be considered such as the destination, size of data and time of arrival among many others. These factors or variables are usually appended to the original data being transmitted using the process known as encapsulation. In essence, each layer of the TCP/IP model will add its relevant control information, known as a header file to the existing data. In the end, an extensive data size is produced after the addition of the control data at each given TCP/IP stage. Decapsulation is the reverse where control information is removed from the actual data to reveal the intended message (Omnisecu, 2017).

Having established the meaning and functionality of encapsulation and de-capsulation lets highlight the difference with multiplexing as well as de-multiplexing. Multiplexing is a process used to transfer multiple signals or data using a common channel. Therefore, a single medium is used to transfer data that is comprised of many and independent signals. At the receiver end, a similar operation known as demultiplexing is used to separate these signals (data) into their individual and respective forms (Nizam, 2014). 

Two variables are provided in this question; bandwidth (BW) and signal to noise ratio (SNR) Now, BW = 6.8 MHz whereas the SNR = 132

Two methods can be used to calculate the bit rate; Nyquist formula and Shannon capacity formula

Nyquist: Bit rate = 2 x Bandwidth x Log₂ Signal level (L)

TCP/IP Model and OSI Model

Shannon formula = bit rate = B x Log₂ (1 + SNR). Therefore,

But we only have BW and SNR, therefore;

= B x Log₂ SNR = 6800000 x Log₂ 132

Bit rate    = 47901880.01 = 47.9019 MHz

Signal level can be obtained from the Nyquist formula having identified the bit rate;

Bit rate = 2 x Bandwidth x Log₂ Signal level (L)

Our signal level is: 47901880.01 = 13600000 x Log₂ L

3.52219706 = Log₂ L, therefore, L = 2^3.52219706

= 11.48912529 Levels 

As stated before, standards were/are developed to unify technological devices and components used in our daily operations. The OSI model (Open Systems Interconnection model) is a similar model to TCP/IP that uses a layered structure to facilitate communication. However, unlike the TCP/IP model that has four main layers, it has seven layers (Frenzel, 2013). Moreover, the OSI model has a wider application as compared to the TCP/IP model as it defines the communication standards that integrate telecommunication systems. The TCP/IP model will define communication standards however, its application is mainly on internet communication where the operational protocols are defined such as HTTP (hypertext transfer protocol), SMTP (simple mail transfer protocol) and UDP (User datagram protocol) (Burke, 2017).

Furthermore, the functionalities of the TCP/IP model are defined by its name where the TCP is used to outline and define the communication channel i.e. connection establishment using a three-way handshake. On the other hand, IP defines the procedure used to develop communication information (addressing). Nevertheless, it has limited applications as compared to the OSI model which defines communication at any level where data has to go through the seven layer before transmission and also during the reception. This process facilitates the integration of digital signals (0s and 1s) with physical signals (electrical pulses) (Frenzel, 2013). Nevertheless, most communication seen today relies on internet protocols such as HTTP and IP which all are based on the TCP/IP model thus the reason it’s still used and not OSI model.

Advantages and disadvantages of the OSI model

1.    A basic and general model that defines the operation of devices based on the communication modules.
2.    A versatile approach to communication that supports all devices used in the telecommunication services.
3.    Its operational design facilitates a robust system that is highly independent of the technology in use.

1.    OSI model does not have any operational protocols hence its dependence on the TCP/IP model.
2.    To some level, all layers depend on each other thus a faulty layer can hold operations (communication) at ransom.

Advantages and disadvantages of TCP/IP model

1.    The TCP/IP model operates independently of the communication system which makes it easy to install.
2.    A revolutionary model that defines communication protocols more so, routeing and internet protocols.

Disadvantages

1.    It’s an old model whose operation speeds are slow as compared to other recent models.
2.    Secondly, it has an extended overhead that requires extra resources to operate (Jayasundara, 2017). 

Several values are given:

Frame size = 5 million bits    Processing time = 1.8 µs

Number of routers = 10        length of the link = 1900 km

Queuing time = 3.5 µs, c as 2.2 x 10⁸ m/s      bandwidth = 8 Mbps

To calculate delay or the latency involved, we add all the values associated with time:

Processing + queuing + transmission + propagation time

Bandwidth Calculation and Encapsulation vs Multiplexing

Now, the Processing time = 10 x 1.8µ = 1.8 x 10^-5 s (accounting for 10 routers)

Queuing time = 10 x 3.5µ = 3.5 x 10^-5 s

Transmission time = Frame size/Bandwidth

= 5000000/8000000 = 5/8, approximately 0.625 s

Propagation time = Link length/speed of light

= 1900000/2.2 x 10⁸ = 8.636364 x 10^-3 s

Latency = 1.8 x 10^-5 + 3.5 x 10^-5 + 0.625 + 8.636364×10^-3 = 0.63369 s

Transmission time is the most dominant time since it’s bigger than the rest (packet size).

In comparison with this value, the queuing and Processing time are negligible (packet values are the smallest).  

Based on the TCP/IP model identified above, several protocols exist and are available for the transmission and reception of message information (Mail). POP3 which is the Post Office Protocol is one such protocol that is used to access messages stored in remote locations (i.e. remote servers). These servers usually host mailboxes that basically store the mails used by different users. POP3 has limited capabilities as compared to other protocols as it only able to access the intended locations (mailboxes) and nothing more (NCC, 1998).

As shown in the diagram above, POP3 operations are governed by four main states; closed, authorization, transaction and update.

Closed – The initial state exhibited by the POP3 session, this state signifies zero operations as the client (user intending to access their messages) usually has not provided the necessary credentials to access the mailbox.

Authorization – This state represents the initiation of communication, in essence, the client as the POP3 session must provide the necessary authentication parameters to access the remote server. First, the server using a greeting message starts the communication process with the client. In return, the client provides the requested verification details to have access to its intended mailbox (Kozierok, 2015

Transaction – Soon after verification, the client accesses the mailbox and is able to see the stored messages. Moreover, it’s able to conduct other activities such as listing the mails and even highlighting mails that are to be deleted.

Update – The final POP3 session state where the client will signal the state by sending a QUIT command which alerts the server which terminates operations. Furthermore, this state is entered automatically without any other operations as soon as the QUIT command is provided. As stated before, the POP3 protocol has limited functionalities and will rely on the server to execute operations such as deleting the designated deletion messages (mails). This operation is done at the update state.  

References

Burke. J. (2017). What is the difference between TCP/IP model and OSI model? Tech target. Retrieved 01 May, 2017, from: https://searchnetworking.techtarget.com/answer/What-is-the-difference-between-OSI-model-and-TCP-IP-other-than-the-number-of-layers

Certification Kits. (2017). CCNA – Bus, Ring, Star & Mesh Topologies. Retrieved 01 May, 2017, from: https://www.certificationkits.com/cisco-certification/ccna-articles/cisco-ccna-physical-networking-concepts-layer-1/ccna-bus-ring-star-a-mesh-topologies/

Chaudhari. A. (2016). 12 Advantages and Disadvantages of OSI model Layered Architecture. CSE stack. Retrieved 01 May, 2017, from: https://www.csestack.org/advantages-disadvantages-of-osi-model-layered-architecture/

Frenzel. L. (2013). What’s The Difference between the OSI Seven-Layer Network Model and TCP/IP? Electronic design. Retrieved 01 May, 2017, from: https://www.electronicdesign.com/what-s-difference-between/what-s-difference-between-osi-seven-layer-network-model-and-tcpip

Jayasundara. M. (2017). Advantages and disadvantages of TCP/IP and OSI model. Retrieved 01 May, 2017, from: https://msccomputernetworks.blogspot.co.ke/2016/08/advantages-and-disadvantages-of-tcpip.html

Kozierok. C. (2005). POP3 General Operation, Client/Server Communication and Session States. The TCP/IP guide. Retrieved 01 May, 2017, from: https://www.tcpipguide.com/free/t_POP3GeneralOperationClientServerCommunicationandSe-2.htm

Netscape Communications Corporation. (1998). Receiving Mail with POP3. Messaging Access SDK Guide. Retrieved 01 May, 2017, from: https://docs.oracle.com/cd/E19957-01/816-6027-10/asdk5.htm

Nizam. A. (2014). Advantages and Disadvantages of Using Mesh Topology. Networking basics. Retrieved 01 May, 2017, from: https://www.networking-basics.net/mesh-topology/

Omnisecu. (2017). TCP/IP Data Encapsulation and Decapsulation. Retrieved 01 May, 2017, from: https://www.omnisecu.com/tcpip/tcpip-encapsulation-decapsulation.php

Zandbergen. P. (2017). How Star, Bus, Ring & Mesh Topology Connect Computer Networks in Organizations. Retrieved 01 May, 2017, from: https://study.com/academy/lesson/how-star-topology-connects-computer-networks-in-organizations.html