INTRODUCTION OF MEMBER GROUP

Being in groups is part of everyday life and many of us will belong to a wide range of groups, for example: family groups, social groups, sports groups, committees, etc.
This page concentrates on group that have been specially formed to fulfil some purpose, or groups that are drawing together of people with shared experience. This type of group is often also referred to as a team.
Introduce our group members:

"The strength of the team is each individual member. The strength of each member is the team."

OSI LAYER

The content in this page :

What Is The OSI Layer?

OSI layer is also known as OSI Model. The International Organization for Standardization devised the open systems interconnection (OSI) model, which allows different communication systems to communicate using standard protocols. In layman's terms, the OSI establishes a standard for computer systems to communicate with one another. In the year 1984. It is a 7 layer architecture with each layer having specific functionality to perform. All these 7 layers work collaboratively to transmit the data from one person to another across the globe.

The OSI Model can be thought of as a universal computer networking language. It's based on the idea of breaking down a communication system into seven abstract layers that are piled on top of each other.

Each layer of the OSI Model handles a specific job and communicates with the layers above and below itself. The application layer attacks target layer 7, while the protocol layer attacks target layers 3 and 4.

Why Does The OSI Model Matter Or Still Relevant Today?

1. The OSI enables you to spot vulnerabilities throughout your whole technology stack. The OSI model has been used for decades to help IT experts understand networking and troubleshoot issues that may arise at any stage in the networking process.

2. You can use the OSI model to keep a data-centric security posture. With the OSI model providing a framework for conducting an inventory of your organization's assets, it's also useful in helping you understand where the biggest data security risks lie within your organization.

3. The OSI model is critical for fostering a security-first approach to cloud adoption. Given that the OSI model can be indispensable for conducting an inventory of your security resources and assets, it's no surprise that keeping the OSI model in mind when migrating to the cloud can also be useful. This is because the OSI model will help you understand the specific types of data security risks that cloud adoption might bring to your organization. This allows you to be more strategic about the types of cloud systems you adopt.

4. The OSI Model is still very useful for debugging network problems, even if the modern Internet does not fully follow it (it instead follows the simpler Internet protocol suite). The OSI Model can assist break down a problem and finding the cause of what's down for thousands of users. A lot of unneeded work can be avoided if the problem can be focused down to one specific layer of the model.

What Are The Seven Layers Of the OSI Model?

The seven abstraction layers of the OSI model can be defined as follows, from bottom to top:

v Layer 1 – Physical Layer

v Layer 2 – Data Link Layer

v Layer 3 – Network Layer

v Layer 4 – Transport Layer

v Layer 5 – Session Layer

v Layer 6 – Presentation Layer

v Layer 7 – Application Layer

👉 LAYER 1 - Physical Layer

The lowest layer of the OSI reference model is the physical layer. It is responsible for the actual physical connection between the devices. The physical layer contains information in the form of bits which is a string of 1s and 0s. It is responsible for transmitting individual bits from one node to the next. When receiving data, this layer will get the signal received and convert it into 0s and 1s and send them to the Data Link layer, which will put the frame back together.

The functions of the physical layer are:

Bit synchronization: The physical layer provides the synchronization of the bits by providing a clock. This clock controls both sender and receiver thus providing synchronization at the bit level.

Bit rate control: The physical layer also defines the transmission rate i.e. the number of bits sent per second.

Physical topologies: Physical layer specifies the way in which the different, devices/nodes are arranged in a network i.e. bus, star, or mesh topology.

Transmission mode: Physical layer also defines the way in which the data flows between the two connected devices. The various transmission modes possible are Simplex, half-duplex and full-duplex.

Note:
*Hub, Repeater, Modem, and Cables are Physical Layer devices.

**Network Layer, Data Link Layer, and Physical Layer are also knowns as Lower Layers or Hardware Layers.

👉LAYER 2 - Data Link Layer (DLL)

The data link layer is very similar to the network layer, except the data link layer facilitates data transfer between two devices on the SAME network. The data link layer takes packets from the network layer and breaks them into smaller pieces called frames. Like the network layer, the data link layer is also responsible for flow control and error control in intra-network communication (The transport layer only does flow control and error control for inter-network communications)

The data link layer is responsible for the node-to-node delivery of the message. The main function of this layer is to make sure data transfer is error-free from one node to another, over the physical layer. When the packet arrives in a network, it is the responsibility of the DLL to transmit it to the Host using its MAC address. Data Link Layer is divided into two sublayers:

Logical Link Control (LLC)
Media Access Control (MAC)

The functions of the Data Link layer are:

Framing: Framing is a function of the data link layer. It provides a way for a sender to transmit a set of bits that are meaningful to the receiver. This can be accomplished by attaching special bit patterns to the beginning and end of the frame.

Physical addressing: After creating frames, the Data Link layer adds physical addresses (MAC address) of the sender and/or receiver in the header of each frame.

Error Control: Data link layer provides the mechanism of error control in which it detects and retransmits damaged or lost frames.

Flow Control: The data rate must be constant on both sides else the data may get corrupted thus, flow control coordinates the amount of data that can be sent before receiving an acknowledgment.

Access Control: When a single communication channel is shared by multiple devices, the MAC sub-layer of the data link layer helps to determine which devices have control over the channel at a given time.

Note:
*Packet in Data Link layer is referred to as Frame
**Data Link layer is handled by the NIC (Network Interface Card) and device drivers of host machines.
***Switch & Bridge are Data Link layer devices.

👉LAYER 3 - Network Layer

The network layer is responsible for facilitating data transfer between two different networks. If the two devices communicating are on the same network, then the network layer is unnecessary. The network layer breaks up segments from the transport layer into smaller units, called packets, on the sender's devices, and reassembles these packets on the receiving device. The network layer also finds the best physical path for the data to reach its destination; this is known as routing.

The functions of the Network layer are:

Routing: The network layer protocols determine which route is suitable from source to destination. This function of the network layer is known as routing.

Logical Addressing: In order to identify each device on internetwork uniquely, the network layer defines an addressing scheme. The sender and receiver's IP addresses are placed in the header by the network layer. Such an address distinguishes each device uniquely and universally.

Note:

*Segment in Network layer is referred to as Packet

👉LAYER 4 - Transport Layer

Layer 4 is responsible for end-to-end communication between the two devices. This includes taking data from the session layer and breaking it up into chunks called segments before sending it to layer 3. The transport layer on the receiving device is responsible for reassembling the segments into data the session layer can consume.

The transport layer provides services to the application layer and takes services from the network layer. The data in the transport layer is referred to as Segments. It is responsible for the End to End Delivery of the complete message. The transport layer also provides the acknowledgment of the successful data transmission and re-transmits the data if an error is found.

The functions of the transport layer are:
Segmentation and Reassembly: This layer accepts the message from the (session) layer, and breaks the message into smaller units. Each of the segments produces has a header associated with it. The transport layer at the destination station reassembles the message.

Service Point Addressing: In order to deliver the message to the correct process, the transport layer header includes a type of address called service point address or port address. Thus by specifying this address, the transport layer makes sure that the message is delivered to the correct process.

Note:
*Data in the Transport Layer is called Segments.
**Transport layer is operated by the Operating System. It is a part of the OS and communicates with the Application Layer by making system calls.

***Transport Layer is called as Heart of the OSI model.

👉LAYER 5 - Session Layer

This is the layer responsible for opening and closing communication between the two devices. The time between when the communication is opened and closed is known as the session. The session layer ensures that the session stays open long enough to transfer all the data being exchanged, and then promptly closes the session in order to avoid wasting resources. This layer also is responsible for the establishment of connection, maintenance of sessions, and authentication, and also ensures security.

The functions of the session layer are:

Session establishment, maintenance, and termination: The layer allows the two processes to establish, use and terminate a connection.

Synchronization: This layer allows a process to add checkpoints which are considered synchronization points in the data. These synchronization points help to identify the error so that the data is re-synchronized properly, and ends of the messages are not cut prematurely and data loss is avoided.

Dialog Controller: The session layer allows two systems to start communication with each other in half-duplex or full-duplex.

Note:
*All the below 3 layers (including Session Layer) are integrated as a single layer in the TCP/IP model as "Application Laye".

**Implementation of these 3 layers is done by the network application itself. These are also known as Upper Layers or Software Layers.

👉LAYER 6 - Presentation Layer

The presentation layer is also known as the Translation layer. The data from the application layer is extracted here and manipulated as per the required format to transmit over the network. This layer is primarily responsible for preparing data so that it can be used by the application layer; in other words, layer 6 makes the data presentable for applications to consume. The presentation layer is responsible for the translation, encryption, and compression of data.

The functions of the presentation layer are:

Translation: such as ASCII to EBCDIC.

Compression: Reduces the number of bits that need to be transmitted on the network.

Encryption/Decryption: Data encryption translates the data into another form or code. The encryption data is known as the ciphertext and the decrypted data is known as plain text. A key value is used for encrypting as well as decrypting data.

👉LAYER 7 - Application Layer

The application layer is also known as the desktop layer. At the very top of the OSI Reference Model stack of layers, we find the Application layer which is implemented by the network applications. These applications produce the data, which has to be transferred over the network. This layer also serves as a window for the application services to access the network and display the received information to the user.
Ex: Application - Browsers, Skype Messenger, etc.

The function of the Application layer are:
Network Virtual Terminal
FTAM-File transfer access and management
Mail Services
Directory Services

How data flows through the OSI Model?

A Cobham's college student is trying to access the OnlineLearning System located in the Cobham's College network facilities. The student is using her modem to connect to the public network before able to connect to the Cobham's College facilities. From the Cobham's College network, the data then was forwarded to IT Center where the OnlineLearning System server located.

In order for human-readable information to be transferred over a network from one device to another, the data must travel down the seven layers of the OSI Model on the sending device and then travel up the seven layers on the receiving end.

Data flow from layer 7 down to layer 1 from the sender and then flows from layer 1 to layer 7 on the recipient device. The simplest example of communication flow through the OSI Model is an email application.

When a sender clicks "Send" on an email application, the message is sent to the presentation layer using a defined protocol (SMTP for outgoing email). The presentation layer compresses the data and sends the message to the session layer, which opens a session for communication between the sender's device and the outgoing server.

The message is sent to the transport layer where data is segmented, and then the network layer breaks the segments into packets. Then, the packets are sent from the network layer to the data link layer, where packets are further broken down into frames. The frames are sent to the physical layer where data is converted to bitstreams of ones and zeros and transferred across a medium such as wireless connections or cables.

When the message reaches the recipient, the process is reversed. Data is sent from the physical layer to the application layer, where data is converted from the bitstreams ones and zeros to the message available in the recipient's email client. When a message is sent back to the sender, the process is repeated, and communication flows down to layer 1 from layer 7 and back up the OSI Model when it reaches the recipient's device.

Based on the scenario: Explain how the data travels from the lecturer’s computer to reach the OnlineLearning System server which is in the Cobham College IT Center. The explanation should be related to the OSI Layer Model. Explain the possible network components involves throughout the communications. Illustrate the diagram to support your explanation.

APPLICATION LAYER

A Cobham College Lecturer type in the system website address and click the enter button on the browser, the link address send to the presentation layer using a defined protocol HTTP or HTTPS.

PRESENTATION LAYER

Receives link address from the application layer and converts the link address to machine-understandable binary formats such as 1s and 0s.
Reduce the number of bits that are used to represent the original data which is called Data Compression.
Encrypted the data before the transmission of data to the session layer.

SESSION LAYER

Setting up and managing connections that will enable sending data from the lecturer to OnlineLearning System
Server will authenticate the lecturer by require a user ID and Password, if both are correct a session is established student's computer and server.

TRANSPORTATION LAYER

Data divided into small data units called segments.

NETWORK LAYER

Breaks the data segment into packets.

DATA LINK LAYER

Breaks the data packets into data frames.

PHYSICAL LAYER

Convert to bitstreams of 1s and 0s and transferred across wireless connections.
Then the data will be send into the system.

SUBNETTING

What is IP Address

IP address stands for Internet Protocol Address which is a collection of rules that regulate the speed over the internet or a local network. A device on the internet or a local network is identified by its IP address, which is a unique address.

IP addresses, in essence, are the identifier that allows data to be exchanged between devices on a network that contains location information and makes devices reachable for communication. The internet requires a method of distinguishing between various computers, routers, and webpages. IP addresses are a crucial aspect of how the internet operated and provide a means of doing so.

An IP address is a string of numbers separated by periods. IP addresses are made up of four numbers. For example, 192.158.1.38. The set of numbers can vary from 0 to 255. As a result, the entire IP addressing range is 0.0.0.0 to 255.255.255.255.

What is IPv4 Addressing

TCP/IP used a two-level addressing scheme when it was first launched in the 1980s. This system had acceptable scalability at the time. As shown in the Figure below the 32-bit IPv4 address identifies a network number and a host number.

The network number and the host number, when combined, uniquely identify all hosts connected over the internet. A tiny, networked community, such as LAN might be able to get with merely host addresses. Network addresses, on the other hand, are required for end systems on different networks to communicate with one another. The network part of an address is used by routers to make routing decisions and to allow communication between hosts on different networks.

Working with strings of 32 1s and 0s is tiresome and cumbersome for humans, unlike routers. As a result, dotted-decimal notation is used to write 32-bit IP addresses. Each 32-bit address is broken into four octets or groups of eight. Each octet is decimalized and then separated by decimal points or dots.

A class system was used to specify the network and host elements of the address in the early days of TCP/IP. IPv4 addresses were divided into five categories. The value of the first few bits in the first octet of the address was used to determine this. Although the class system can still be applied to IP addresses. Today's networks prefer to use a classless IP scheme instead.

What is a classful addressing

In a class system, IP addresses can be grouped into one of five different classes:

Class A
Class B
Class C
Class D
Class E

Each of the address classes has a different subnet mask. The class of an IP address can be identified by looking at its first octet.

For host addresses, IP addresses from the first three classes (A, B, and C) can be utilized. The other two classes, class D for multicast and class E for experimental reasons, are utilized for different purposes.

The IP address classes system was created for the purpose of assigning Internet IP addresses. The classes that were developed were dependent on the size of the network. Class A, for example, was established for a small number of networks with a big number of hosts. Class C was designed for small networks with a lot of hosts.

The first 8 bits (the first decimal number) of IP addresses from class A reflect the network, while 24 bits represent the host. The network part of class B is represented by the first 16 bits (the first two numbers), while the host part is represented by the remaining 16 bits. The first 24 bits of class C indicate the network, whereas the following 8 bits represent the host.

Class A

For networks with a large number of total hosts, Class A addresses are used. The first byte of the network ID in Class A allows for 126 networks. This octet's first bit is always zero. The network ID is completed by the remaining seven bits in this octet. The host's ID is represented by the remaining 24 bits in the last three octets, allowing for about 17 million hosts per network. Class A network number of values ranges from 1 to 127.

Class B

Class B addresses are for networks of a medium to large size. The first two octets of the network ID in class B allow for 16,384 networks. In the first octet, the first two bits are always 1 0. The network ID is completed by the remaining six bits and the second octet. The host ID is represented by the 16 bits in the third and fourth octets, allowing for about 65,000 hosts per network. The class B network number ranges from 128 to 191.

Class C

In tiny local area networks, Class C addresses are utilized (LANs). The first three octets of the network ID in Class C allow for about 2 million networks. The first three bits of the first octet in a Class C IP address are always 1 1 0. The network ID is completed by the remaining 21 bits of the first three octets. The host ID is represented by the last octet (8 bits), which allows for a total of 254 hosts per network. The values for Class C network numbers range from 192 to 223.

Class D

Class D IP addresses are used for multicasting and are not assigned to hosts. Multicasting allows a single host to simultaneously deliver a single stream of data to thousands of other hosts over the internet. It's commonly utilized in IP-based cable TV networks for audio and video transmission. Another example is the distribution of real-time stock market data from a single source to a large number of brokerage firms.

Class E

IP addresses in Class E are not assigned to the host and are not available for general use. These are just to be used for research.

What is Network Id

The network id specifies the network's unique identification number. The networks section also specifies the network class that has been assigned.

What is Host Id

This is the portion of the IPv4 address that each host gets. This machine on your network is identified by the host component. The network component of the address must be the same for each host on your network, but the host part must be different.

What is Subnetting

Subnetting is a technique for splitting a single physical network into multiple logical sub-networks (subnets). A network segment and a host segment make up an IP address. Subnets are created by taking bits from the host component of an IP address and utilizing them to create several smaller sub-networks within the larger network. Subnetting allows a company to expand its network without having to obtain a new network number from their internet service provider (ISP). Subnetting reduces network traffic while also hiding network complexity. When a single network number must be assigned to several portions of a local area network, subnetting is required (LAN).

Subnetting Calculation

Student are required to suggest a private addressing scheme used in Cobham College network. There are three faculties in Cobham College and one IT center for the OnlineLearning server. Given IP address 181.21.0.0. By using FLSM method, identify the IP address for the faculties and the IT center.

IP Address: 181.21.0.0

Class Address: Class B

Default Subnet Mask: 255.255.0.0

Needed Network/ Number of Subnets: 4 (3 faculties + 1 IT Center)

Quantity of Host per Subnet: 16832 host

Based on the given IP address which is 181.21.0.0, we can know that the class address is class B. As the class B IP addresses are mostly used for medium and large-sized networks in enterprises and organization. The class B IP address is suitable to use in the university network.

As the Class Address that being used is Class B, we also can know the default subnet mask for class B is 255.255.0.0. As the first octet and second octet is being used for the network address and the third octet and fourth octet is being used for host address.

The number of needed network or number of subnets can be obtains from the situation given as it said that there are three faculties and one IT Center. Therefore there are 4 network or 4 subnets. From the number of subnets, we also can obtain the quatity of bits borrowed as the formula used is 2^bb = subnet. As the subnets is 4 so we can obtain the quantity of bits borrowed is 2 bits.

As the bit borrowed is equal to 2 bits. The bits left is 14. This is because the total bits that can be used for the host address is 16 bits. Therefore 16 bits minus with 2 bits is equal to 14 bits. With the bit left we can obtain the quantity of host per subnets which is 16832 host using the formula 2^bl - 2.

No	Network Id	Valid Host Range	Broadcast Id	Subnet
1	181.21.0.0	181.21.0.1 – 181.21.63.254	181.21.63.255	Faculty 1
2	181.21.64.0	181.21.64.0.1 – 181.21.127.254	181.21.127.255	Faculty 2
3	181.21.128.0	181.21.128.1 – 181.21.191.254	181.21.191.255	Faculty 3
4	181.21.192.0	181.21.192.1 – 181.21.255.254	181.21.255.255	IT Center

As we can see for the IT Center the range of valid host is from 181.21.192.1 until 181.21.255.254. The OnlineLearning Server will belong to any of the host address within the range.

TCP/IP CONFIGURATION

In this section , we will give a manual guidance or step-by-step manual on how to cnfigure the IP address on the server by using the window operating system.

STEP 1 :