Layering and the Internet Model

Part 1: Layering and the Internet Model

Imagine that a technology organization has been in business for decades, and that the organization developed its own method of computer-to-computer communication. Because this method of communication only occurs within this organization, it is not layered, but rather is designed to operate as quickly and efficiently as possible on the custom hardware by using the least amount of overhead possible. The organization continues to create its own communication hardware and software that works with modern computers, but the CTO of the organization is considering replacing this custom communication solution with the adoption of the Internet Model in use today, along with its technologies. With this scenario in mind, address each of the topics below.

Topic 1: The Advantages of a Layered Model

Identify and describe the advantages that a layered solution would offer the technology organization when compared to its non-layered solution.

Advantages of layered model:

• The entire set of communications functions can be broken a series of layers, each of which can be defined separately.
• Software and hardware can be developed to provide the functions of each layer separately
• The software or hardware can work in any manner and can be easily updated and improved
• Each piece of hardware and software can then work together in the overall network

Reference:

FitzGerald, J., Dennis, A., Durcikova, A. (2014). Business Data Communications and Networking, 12th Edition. Page 7

Topic 2: The Disadvantages of a Layered Model

Identify and describe the disadvantages of a layered solution when compared to the organization’s non-layered solution.

Disadvantage of using layered model is that it is somewhat inefficient because there are several layers, each with its own software and protocol data unit, PDU, sending a message involves many software programs (one for each protocol) and many PDUs. (FitzGerald, Dennis & Durcikova, 2015)

In our case, since organization has developed many communication hardware and software, depend on level of service/level that will be switched to, may need to modify existing systems to work with new infrastructures. And also, organization may need to train its employee to manage/support new system and infrastructure.

Reference:

FitzGerald, J., Dennis, A., Durcikova, A. (2014). Business Data Communications and Networking, 12th Edition. Page 13

Topic 3: The Layers of the Internet Model

Identify the layers of the Internet Model, and explain what functionality each layer would provide for the organization, if adopted.

The Physical Layer: The physical layer is the physical connection between the sender and receiver. Its role is to transfer a series of electrical, radio, or light signals through the circuit. The physical layer includes all the hardware devices (e.g., computers, modems, and switches) and physical media (e.g., cables and satellites).

The Data Link Layer: The data link layer is responsible for moving a message from one computer to the next computer in the network path from the sender to the receiver.

The Network Layer: The network layer performs routing, in that it selects the next computer to which the message should be sent.

The Transport Layer: The transport layer performs two functions. First, it is responsible for linking the application layer software to the network and establishing end-to-end connections between the sender and receiver when such connections are needed. Second, it is responsible for breaking long messages into several smaller messages to make them easier to transmit and then recombining the smaller messages back into the original larger message at the receiving end. The transport layer can also detect lost messages and request that they be resent.

Application Layer: The application layer is the application software used by the network user and includes much of what the OSI model contains in the application, presentation, and session layers. It is the user’s access to the network. By using the application software, the user defines what messages are sent over the network.

Reference:

FitzGerald, J., Dennis, A., Durcikova, A. (2014). Business Data Communications and Networking, 12th Edition. Page 9 - 10

Topic 4: Other Advantages

Are there advantages, for the organization, to adopting the Internet Model beyond those mentioned in Topic 1? If so, describe them.

In layered model, software and hardware can be developed to provide the functions of each layer separately, it will be easier to perform an upgrade compare to current system and stay up to date. Since servers could be on vendor side, most likely, organization may not need to perform any hardware upgrade for the physical layer in future.

Part 2: Application Architecture

Assume that an organization’s employees have each been given a computer to perform their work. Each computer accesses the organization’s applications via a powerful mainframe computer in the server room. When an employee types a key, the keystroke is sent to the mainframe, which in turn decides what action to take, and transmits that action back to their computer. Every keystroke is sent to the mainframe, and all decisions are made by the mainframe. Each employee’s computer acts only as an input and display device. The CTO is considering switching from its current architecture, to another architecture. With this scenario in mind, address each of the topics below.

Topic 1: Architecture Identification

Identify the application architecture in use by the organization, and explain the basic mechanics of how that architecture works.

It is host-based architecture.  The basic mechanic of this architecture is the clients (usually terminals) enabled users to send and receive messages to and from the host computer. The clients merely captured keystrokes, sent them to the server for processing, and accepted instructions from the server on what to display.

Reference:

FitzGerald, J., Dennis, A., Durcikova, A. (2014). Business Data Communications and Networking, 12th Edition. Page 28

Topic 2: Switching to Client-Server

Identify and explain three issues the organization would need to address if it would like to switch from its current architecture to a two-tier, client-server architecture.

Issues:

• Cost to upgrade current computer used by employee to be able to run required applications efficiently
• Since applications will be on client PC, software version control could be complicated
• Performance could be degrade upon increasing the users

Topic 3: Advantages and Disadvantages of Client-Server

Identify the advantages and disadvantages, for the organization, of switching from the organization’s current architecture to a client-server architecture.

Advantages:

• Client-server architectures provide the best scalability
• Client-server architectures are also the most reliable. We can use multiple servers to perform the same tasks, so that if one server fails, the remaining servers continue to operate and users don’t notice problems.

Disadvantages:

• Data security could be at risk
• Applications and data logic will be de-centralized
• It could be costly to maintain servers and applications

Part 3: Digital Communication Rates

Imagine that we need to digitally download the text of a paperback book at the rate of 40 pages per minute.  The number of lines per page is 25, and the number of characters per line is 65.  With this scenario in mind, address each of the topics below.

1. Most of what is needed to calculate the number of bits sent per minute is present in the scenario above, but something is missing. What is it?

Number of bits used to encode each character

2. What are the common values for this missing item, and where do these values come from?

Coding schemes:

• ASCII (7 or 8 bits)
• Unicode (8 or 16 bits)
• ISO 8859 (8 bit)

3. Which value would you choose from #2? There is no one provably “correct” answer to this, but do make sure to justify your choice.

Unicode 16 bits

4. With your assumption in #3, calculate the bit rate needed, expressed as bits per second, to download the text of the book as described in the scenario. Recall that the bit-rate formula is:

R = b/t

where R is the bit-rate, b is the number bits, and t is the unit of time.

Number of pages:                   40

Number of line per page:       25

Number of char per line:        65

b = 65 x 25 x 40 x 16 = 1040000 bits

R = 1040000/60 = 17333.3333 bits/sec

5. Now that you have calculated the bit rate needed to download the book, let us consider how this relates to symbol transmission over a physical circuit. If a physical circuit encodes one bit per symbol, what would the minimum symbol rate need to be to download the book? Make sure to give the value and explain your reasoning.

Bit per symbol:            1

Symbol Rate = (1 symbol/1 bit) x 17333.3333 bits/sec = 17333.3333 symbols/sec

As circuit encodes one bit per symbol, symbol rate is same as bits rate calculated in #4.

6. If 256 Quadrature Amplitude Modulation (256-QAM) is used on the physical circuit, what would the minimum symbol rate on the circuit need to be to download the book at the given rate of 40 pages per minute? Make sure to give the value and explain your calculations.

256-QAM sends 8 bits per symbol.

Symbol Rate = (1 symbol/8 bit) x 17333.3333 bits/sec = (2166.6666 symbols/sec) x 60 = 129999.9997 symbols/min

To get rate of 40 pages per min:

Symbol Rate = (2166.6666 symbols/sec) x (60 sec/1 min) = 129999.9997 symbols/min

7. Lastly, if the bandwidth of the circuit is tripled, but all other factors including the signal strength and noise strength are kept equal, what would happen to the capacity of the circuit? Make sure to explain your reasoning.

Per Shannon’s formula C = B * log2(1 + S/N), channel and bandwidth are proportional. Hence, when bandwidth of circuit is tripled, capacity of the circuit will be triple as well.