Protocol Layers

KS3 Computer Science

11-14 Years Old

48 modules covering EVERY Computer Science topic needed for KS3 level.

GCSE Computer Science

14-16 Years Old

45 modules covering EVERY Computer Science topic needed for GCSE level.

A-Level Computer Science

16-18 Years Old

66 modules covering EVERY Computer Science topic needed for A-Level.

KS3 Network Protocols and Layers (14-16 years)

  • An editable PowerPoint lesson presentation
  • Editable revision handouts
  • A glossary which covers the key terminologies of the module
  • Topic mindmaps for visualising the key concepts
  • Printable flashcards to help students engage active recall and confidence-based repetition
  • A quiz with accompanying answer key to test knowledge and understanding of the module

A-Level Network Protocols and Layers (16-18 years)

  • An editable PowerPoint lesson presentation
  • Editable revision handouts
  • A glossary which covers the key terminologies of the module
  • Topic mindmaps for visualising the key concepts
  • Printable flashcards to help students engage active recall and confidence-based repetition
  • A quiz with accompanying answer key to test knowledge and understanding of the module

Protocol Layers

A set of rules defined for communication among the devices using a network is known as a protocol. The rules contain guidelines that are used to regulate specific attributes in a network. These attributes include access method, the permission of physical topologies, kind of cables, and data transfer rate.

Open Systems Interconnection (OSI) Model

Devices connected to the internet follow specific patterns of layers for communication. One of the well-known examples is the Open system interconnection (OSI) reference model. The model was presented with a set of standard layers as well as protocols of communication that occur in between the devices connected to the web globally. Computer networking started to conceive in 1970. In 1983, two networking models were merged, and the OSI model was formed. The presented model has been working since 1984. Although it is not declared a universal model to adopt, it is extensively used as a standard. The OSI reference model is quite distinctive as compared with the TCP/IP model.

Layers are used to classify the work done quickly in a network. Therefore, protocols are used as a hierarchy that divides the tasks of communications into different layers.


The set of rules used for communication inside the layer are known as protocols. Although, one layer is unaware of the issues lying in the other layer.


One layer that gives service to the layer lying above it is known as the interface.

1. The OSI Model Layers

A network in the OSI model is classified into seven layers. Each layer at its end characterizes networking in accordance with software and hardware to transfer the data using the network. Interoperability, the aim of establishing a standard protocol model, arises from consistency between the protocol stack of one system or the protocol stack of another. Each layer has the ability to correspond with a similar layer during communication at the receiving end.

The OSI model’s learning provides assistance to managers for the troubleshooting of the systems professionally. Moreover, it assists those who are going to develop programs and application developers (how layers perform and the functionality of each layer). Fig. 1 depicts the OSI model layers. The OSI model’s description is mostly carried out in top to bottom order as the number moves from Layer 7 and down towards Layer 1. A brief description of the model is as given.

Protocol Layers: OSI Model
Figure 1: OSI Model Layers

1. Application Layer (Layer – 7):

The “application layer” is the top layer in the OSI model. In the model, the application layer is the closest layer with the client using the network. The layer provides a kind of interface to the end-user. The layer directly collects the information from the client and pursue further. Moreover, this layer displays the incoming information coming from the other ends. However, applications are not themselves residing on this layer. This layer enables communications via lower layers to connect its system with the applications running on the other end. Mozilla Firefox, Safari, Internet Explorer, Google Chrome, TelNet are communications’ examples that depend on the “application layer.”

2. Presentation Layer (Layer – 6):

The layer signifies the field that is free of data representation in the “application layer”. Usually, it is used to present or perform translation of application-layer data to network format. As well as performs translation formatting from network to application format during the reception. Therefore, we can say that the presentation layer works to “present” the data for the “application layer” or the “network layer”. Data encryption from the transmission end or data decryption is a good example of this layer at the receiving end.

3. Session Layer (Layer – 5):

A session needs to be established when devices “speak” with each other, which is done by the “session layer” assistance. Performance of session layers required setup along with strong coordination. Termination at the end of the session must be intimated via this layer. Waiting time for response is a real example of a session layer.

4. Transport Layer (Layer – 4):

Data transferring between end systems and hosts are carried out by employing a “transport layer”. It decides the amount of data to be sent, the rate of data sending, the data route, etc. One of the most prevalent examples of the transport layer is the Transport Control Protocol (TCP). TCP is built on Internet Protocol (IP). The integrated model we called TCP/IP.  TCP & UDP performs on the “transport layer”, whereas the IP address performs at the “network layer” (layer – 3).

5. Network Layer (Layer – 3):

The layer enables the actual communication means used for forwarding the data packets. The packet forwarding is carried out by using various routers. Your PC present in the lab at Manchester needs to be connected with a server in London. The system has millions of paths for connection with the server. The router will find the most effective route for you on its own.

6. Data Link Layer (Layer – 2):

The layer gives node-to-node data transfer (with two connected nodes). Moreover, it tackles the error correction occurring in the “physical layer: (Layer – 1). Two sublayers are present here.

  1. Media Access Control (MAC)
  2. Logical Link Control (LLC)

In the domain of networking, switches commonly operate at the “data link layer”. However, few of the controls operate at the “Network Layer”.

7. Physical Layer (Layer – 1):

That is the bottom of the OSI model, where the physical layer exists. The layer shows some electrical and physical presentation. The layer consists of various elements, for instance, wireless connection (wi-fi), cables, voltages, the framework of pins, and other physical equipment. Whenever an issue occurs in networking, the problems are mostly captured from the physical layer that includes cables, checking the power of plugs, the voltage of routers and switches, etc.

How to remember OSI seven layers?

All People Seem To Need Data Processing (From top to down)

Please Do Not Throw Sausage Pizza Away (From down to top)

2. Internetwork Packet Exchange/Sequenced Packet Exchange (IPX/SPX):

(IPX/SPX) A series of network protocols, traditionally used on devices using Novell NetWare OS, provide packet switching and sequencing for small and large networks. Shortly after, when they substituted NetWare LANs, they became commonly used on networks deploying Microsoft Windows LANs.

The IPX/SPX-Compatible Protocol is adjusted to auto-detect the type of frame utilized on the NetWare network. The default 802.2 type is applied if a nil frame is found. The prevailing one is chosen if several frame forms are identified. Because of their supremacy in the network OS (with Novell Netware) from the 1980s to the mid-1990s, Novell is primarily responsible for using IPX as a standard computer networking protocol. For DOS-era multi-user network sports, IPX/SPX was traditional.

Netware Protocols:

1. Internetwork Packet Exchange (IPX):

IPX is applied for transferring packets.

2. Routing Information Protocol (RIP):

RIP retains the hop count as a routing metric.

3. Sequence Packet Exchange (SPX):

SPX works on the transport layer and assists by adding a connection-oriented service.

3. Multiple Link Interface Driver (MLID)

The ODI (Open Data-Link Interface) term for a LAN board driver built according to ODI requirements is Multiple Connection Device Driver. Currently, it is possible to interchange the words MLID and LAN pilot. The MLID executes all the previously stated LAN driver roles, and it is intended to communicate with the ODI Connection Support Layer. The MLID is not explicitly connected to a networking protocol stack, unlike the typically dedicated IPX engine.

4. Transfer Control Protocol / Internet Protocol (TCP/IP):

The Internet Protocol (IP) set is special because it is composed of protocols that are not patented; this suggests that they do not affiliate o any organization and that it is open for all to access the innovation. The illustration above integrates the contrast of a couple of models. The Internet model does not, as you can note, span the two layers of the OSI model; this suggests that TCP/IP is independent of hardware. As TCP/IP does not have protocols at the lower level, we will start with protocols at the middle level.

Internet Middle-Layer Protocol:

The network and transport layer of the OSI model is responsible for packet communication in a network. However, TCP/IP considers three forms of address for addressing the network.

  1. Physical address (employing TCP)
  2. Internet Protocol Address (utilizing IP)
  3. Logical Node Name (through DNS)

1. Transmission Control Protocol (TCP):

As implied in the term, TCP/IP has two layers. It is the top layer’s duty, TCP, to take massive volumes of data, compile it into packets and send them on their way to receive a fellow TCP layer, which transforms the packets into usable data/information.

2. Internet Protocol (IP):

The lower portion, IP, is the couple’s contextual feature that enables the time frame to be transmitted and retrieved to the right position. In terms of synthesis, if you think about IP, the IP layer acts as a GPS packet to locate the right destination. Each packet passes through a gateway computer (signs on the road), just like a car travelling on a highway, which helps to forward the packets to the correct location.

3. Domain Name Server (DNS):

A distributed storage framework interacts with the transport layer to give client applications with the name to number integration. In order to use conceptual names for system recognition, DNS servers build databases that comprise hierarchical name structures of the different domains.

Internet Upper-Layer Protocols:

1. File Transfer Protocol (FTP):

FTP, a peer to peer protocol, is used to transfer the files between connected nodes on the network. It also enables users on a remote host to start operations. It performs on the top three levels of the OSI model.

  1. FTP provides session administration on the session layer.
  2. FTP provides translation using computer independent file translation on the presentation layer.
  3. FTP provides network resources such as file services on the device layer.

2. Terminal Network (TelNet):

For remote access functionality, TelNet is required. It helps users, by imitating one of the host’s interfaces, to control host-based frameworks.  Telnet offers synchronization across OS that is different. It includes dialogue access at the session layer; telnet offers localization utilizing byte order and character codes at the presentation layer. The telnet provides facilities for remote operations at the device layer.

Simple Mail Transfer Protocol (SMTP):

The internet is used for maintaining connections. One of the most excessively used applications used over the internet is e-mail. The application-level protocol used for e-mail is the Simple Mail Transfer Protocol (SMTP) based on text. However, SMTP is link oriented, unlike HTTP. SMTP is a complex protocol as compared with the HTTP. But the variety of commands is wide in SMTP.

Miscellaneous Protocols:

Serial Line Internet Protocol (SLIP):

SLIP is applied for dial-up connections that mostly perform functionality on the physical layer of the OSI model. This protocol is an advanced version of the Point-to-Point Protocol (PPP).

Point-to-Protocol (PPP):

This protocol also performs functions over a dial-up connection. The model works on OSI Physical Layer and Data Link Layer. It provides error controlling and is responsible for the physical address of the device.

Integrated Services Digital Network (ISDN):

The protocol considers voice and video types of data communication on phone lines. This protocol also performs OSI’s model Physical layer, Data-Link layer, and Transport layer.

Advantages of Protocol Layering:

  • Layering allows effective interoperability between systems from various vendors and machines of the same form.
  • The greater connectivity between computers, applications, and networks that this offer is one of the best of all the advantages of utilizing a hierarchical or layered approach.
  • Protocols confirm greater compatibility; it enables help to promote physical, network engineers, and managers.
  • Enhanced working life intentions of the manufacturer as backward compatibility is rendered even simpler. Products from successive iterations of technology will coexist because they are not automatically scrapped when modern systems are introduced.
  • The study has confirmed that a layered or hierarchical method to develop networking protocols scales easier than a horizontal approach.
  • Whenever we follow layered and partitioned techniques in our structural architecture, greater mobility is achieved more quickly.
  • When the whole framework has been developed using a layered philosophy, it is simpler to integrate and introduce value-added functionality into goods or services.
  • The layered method has proved time is the most feasible way to build and enforce any interface(s) that makes little sense, whether small, basic, big, or complicated.
  • Layering makes it possible to integrate inherent plasticity into systems and phases from get-go to execution, through improvement and update cycles over the complete useful insight lifecycle of a system
  • As per the networking protocol requirements, the layered method encourages a more streamlined and more straightforward method of standardization and validation, ensuring a better quality because of the enterprise.
  • Ranging a vast, complicated structure into shorter, more functional sub-components makes it possible for innovative technology to be created and applied and promotes human awareness of what can be very disparate and complicated structures.
  • It is also simpler to switch Layered Networking Protocols with one device or framework to another.
  • The reductionism or layering of systems, methods, and data networks enable designers to focus on a particular layer or essential functions within the area of duty of that layer without requiring some other layer to be significantly concerned or changed.

Disadvantages of Protocol Layering:

  • Often it can be hard to incorporate a network framework into this system. This is because, before the invention of either of these protocols, this model was developed.
  • For configuration control, the session layer is used. The presentation layer interacts with contact between users. At the same time, they are useful, in the OSI model, less than others.
  • On multiple levels, there is some overlap of resources. E.g., both the transport and data link layers have structures for error management.
  • In the layers, there is often interconnection. Such layers do not function in tandem. They are on hold to collect their previous administration results.

Summary and Facts:

What do you mean by protocol?

A set of rules defined for communication among the devices using a network is known as the protocol.

Enlist the prevalent protocols used in networking?

  1. Open Systems Interconnection (OSI) Model
  2. Internetwork Packet Exchange/Sequenced Packet Exchange (IPX/SPX)
  3. Multiple Link Interface Driver (MLID)
  4. Transfer Control Protocol / Internet Protocol (TCP/IP)

List down the seven Layers of the OSI Model?

  1. Application Layer (Layer – 7)
  2. Presentation Layer (Layer – 6)
  3. Session Layer (Layer – 5)
  4. Transport Layer (Layer – 4)
  5. Network Layer (Layer – 3)
  6. Data Link Layer (Layer – 2)
  7. Physical Layer (Layer – 1)

What are the middle layer protocols in the TCP/IP?

  1. Transmission Control Protocol (TCP)
  2. Internet Protocol (IP)
  3. Domain Name Server (DNS)

What are the upper layer protocols in the TCP/IP?

  1. File Transfer Protocol (FTP)
  2. Terminal Network (TelNet)
  3. Simple Mail Transfer Protocol (SMTP)

Name the misc. Protocols of the internet?

  1. Serial Line Internet Protocol (SLIP)
  2. Point-to-Protocol (PPP)
  3. Integrated Services Digital Network (ISDN)

What are the advantages of layering in networking?

  • Interoperability
  • Compatibility
  • Higher Flexibility
  • Enhanced life Expectancy
  • Scalability
  • Mobility
  • Value Added Characteristics
  • Cost-Effectiveness
  • Modularity
  • Blended Approach for Migration
  • Standardized and Certified
  • Task Classification
  • Portability

What are the disadvantages of layering in networking?

  • Redundancy at few points
  • Difficulty in adjusting new protocol
  • Few layers are not as much use in the OSI model (Transport & Data Link Layer)
  • Independency of layers