Lesson 2. OSI and TCP Network Layers

Open Systems Interconnection

• 7-layered framework for designing and implementing computer networks.

OSI LAYERS

1. Physical (Layer 1) -  Frames are converted into bits and transmitted physically

2. Data Link (Layer 2) - Packets are framed and sent to the next device.

3. Network (Layer 3) - Segments are packaged into packets and routed

4. Transport (Layer 4) - Data is broken into segments for reliable delivery.

5. Session (Layer 5) - Connections are established and managed.

6. Presentation (Layer 6) - Data is formatted and encrypted.

7. Application (Layer 7) - Creates the data

Physical Layer

• lowest layer of the OSI reference mode

• Responsible for the actual physical connection

  • contains information in the form of bits.

Bit Synchronization, Bit Rate Control, Physical Topologies, Transmission Mode

Functions - Physical Layer

Bit Synchronization

• It 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

This Physical layer also defines the transmission rate i.e. the number of bits sent per second

Physical Topologies

Physical layer specifies how the different, devices/nodes are arranged in a network

Transmission Mode

• Physical layer also defines how the data flows between the two connected devices.

• The various transmission modes possible are Simplex, half-duplex and full duplex.

DATA LINK LAYER

• responsible for the node-to-node delivery of the message.

• to make sure data transfer is error-free from one node to another.

• Packet in the ____________ is referred to as FRAME

• NIC

• ARP

Data Link Layer

1. LLC

2. MAC

FRAMING, PHYSICAL ADDRESSING, ERROR CONTROL, FLOW CONTROL, ACCESS CONTROL

FUNCTIONS of DDL

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.

Physical Addressing

• After creating frames, the Data link layer adds physical addresses (MAC addresses) of the sender and/or receiver in the header of each frame.

Error Control

The 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.

• ___________ coordinates the amount of data that can be sent before receiving an acknowledgment.

Access Control

• A single communication channel is shared by multiple devices

• the MAC sub-layer of the data link layer helps to determine which device has control over the channel at a given time.

Layer 3 – Network Layer

• The transmission of data from one host to the other located in different networks.

• Segment is referred to as Packet.

FUNCTIONS of the NL

1. ROUTING

2. LOGICAL ADDRESSING

ROUTING

• The network layer protocols determine which route is suitable from source to destination.

Logical Addressing

To identify each device inter-network uniquely, the network layer defines an addressing scheme.

Transport Layer

• It provides services to the application layer and takes services from the network layer.

• Data is referred to as Segments

• It is responsible for the end-to-end delivery of the complete message.

• performs sequencing and reassembling of the segmented data.

FUNCTIONS of TL

1. SEGMENTATION AND REASSEMBLY

2. SERVICE POINT ADDRESSING

Segmentation and Reassembly

This layer accepts the message from the (session) layer and breaks the message into smaller units.

Service Point Addressing

To deliver the message to the correct process, the transport layer header includes a type of address called port address.

Service Provided by Transport Layer, Connection-Oriented Services, Connectionless Services

Transport Layer - Steps

SESSION LAYER

Responsible for the establishment of connections, management of connections, terminations of sessions between two devices

Functions of the SL

1. Session Establishment, Maintenance, and Termination

2. Synchronization

3. Dialog Controller

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 that are considered synchronization points in the data.

Dialog Controller

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

Presentation Layer

• called the Translation layer.

• The data is extracted here and manipulated as per the required format to transmit over the network.

  • Protocols used are JPEG, MPEG, GIF, TLS/SSL, etc.

Translation, Encryption/Decryption, Compression

Functions of the PL

TRANSLATION

For example, ASCII to EBCDIC.

Encryption/ Decryption

• Data encryption translates the data into another form or code.

• Encrypted Data - known as the ciphertext,

  • ecrypted data is known as plain text

Compression

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

Layer 7 – Application Layer

•  Reference Model stack of layers

• we find the Application layer which is implemented by the network applications

Network Virtual Terminal, File Transfer Access Management, Mail Services, Directory Services

Application Layer - Functions

Network Virtual Terminal

It allows a user to log on to a remote host.

File Transfer Access or Management

This application allows a user to access files in a remote host, retrieve files in a remote host, and manage or control files from a remote computer.

DIRECTORY SERVICES

This application provides distributed database sources and access for global information about various objects and services.

Transmission Control Protocol

• fundamental framework for computer networking.

• The core protocols of the Internet.

• consists of four layers: the Link Layer, the Internet Layer, the Transport Layer, and the Application Layer.

TCP/IP - department of defense

• 1960s - designed and developed by the DOD

• concise version of the OSI model.

• the creation of the ARPANET

• the foundation of the modern internet.

Layers of TCP/IP Model

• Application Layer

• Transport Layer(TCP/UDP)

• Network/Internet Layer(IP)

• Network Access Layer

Network Access Layer

• a collection of applications that require network communication.

• receiver’s end processes and manages incoming data.

• Error prevention and “framing”

  • Point-to-Point Protocol (PPP) framing and Ethernet IEEE 802.2

  • it is known as NAL

Internet/Network Layer

• This layer parallels the functions of OSI’s Network layer.

•  It defines the protocols which are responsible for the logical transmission of data over the entire network.

Internet Protocol

• Delivering packets from the source host to the destination host by looking at the IP addresses in the packet headers.

• Two type of IP protocols

  • IPV4 - Website

  • IPV6 - Addresses is limited in number

Internet Control Message Protocol

It is encapsulated within IP datagrams and is responsible for providing hosts with information about network problems.

Address Resolution Protocol

Its job is to find the hardware address of a host from a known IP address

• ARP

Transport Layer

It exchange data receipt acknowledgments and retransmit missing packets to ensure that packets arrive in order and without error.

TCP

Applications can interact with one another using TCP as though they were physically connected by a circuit.

User Datagram Protocol

The datagram delivery service is provided by UDP , the other transport layer protocol.

 Application Layer

• TCP/IP mode combines the functions of three layers from the OSI model: the Application, Presentation, and Session layers.

• analogous to the transport layer of the OSI model.

Hypertext transfer protocol

• It is used by the World Wide Web to manage communications between web browsers and servers. HTTPS stands for HTTP-Secure.

SECURE SHELL

• It is a terminal emulations software similar to Telnet.

• stands for SSH

Network Time Protocol

• It is used to synchronize the clocks on our computer to one standard time source.

• Stands for NTP