– Layered Architecture
- Need of a Layered Architecture
- Functional Details of OSI Layers
- Design Philosophy of Layered Architecture
- The complex task of communication is broken into simpler sub-tasks or modules
- Each layer performs a subset of the required communication functions
- Each layer relies on the next lower layer to perform more primitive functions
- Each layer provides services to the next higher layer
- Changes in one layer should not require changes in other layers
- Helps in troubleshooting and identifying the problem
An example Sending a letter
- To standardize the design of communication
- system, the ISO created the OSI model.
- Open Systems Interconnection
- Developed by the International Organization
- for Standardization (ISO)
- It describes the functions to be performed at
- ISO standard that covers all aspects of network communications is the Open Systems Interconnection ( OSI ) model.
- First introduced in the late 1970s.
- Each layer performs a subset of the required
- Each layer relies on the next lower layer to
- perform more primitive functions
- Each layer provides services to the next
- Changes in one layer should not require
ISO is the organization. OSI is the model. Note
OSI Model Application Presentation Session Transport Network Data Link Physical
An exchange using the OSI model
OSI Model – Physical Layer
- Physical interface between devices
- handles the transmission of bits over a
- Choice of Wired / wireless medium
- Data is converted into signals
- Includes voltage levels, connectors, media choice
The physical layer is responsible for movements of individual bits from one hop (node) to the next. Note
OSI Model – Data Link Layer
- – Transforms data into a frame
- – Means of activating, maintaining and
- deactivating a reliable link
- – Error detection and control
- – Higher layers may assume error free
- Examples :- Ethernet, Frame Relay, FDDI.
Data Link Layer
The data link layer is responsible for moving frames from one hop (node) to the next. Note
OSI Model – Network Layer
- – Transport of information
- – Higher layers do not need to know
- about underlying technology
- – Responsible for creating, maintaining
- and ending network connections
- – Transfers a data packet from node to
- node within the network .
- – Not needed on direct links
- Examples :- IP, IPX, AppleTalk.
The network layer is responsible for the delivery of individual packets from the source host to the destination host. Note
- – Exchange of data between end
- systems (end to end flow control)
- Layer 4 protocols include TCP (Transmission Control Protocol) and UDP (User Datagram Protocol).
The transport layer is responsible for the delivery of a message from one process to another. Note
OSI Model – Session Layer
- – Control of dialogues between
- – Synchronization Points (backup points)
- Examples :- SQL, ASP(AppleTalk Session Protocol), NETBIOS, RPC, PAP.
The session layer is responsible for dialog control and synchronization. Note
OSI Model – Presentation Layer
- – Data formats and coding
- Examples :- JPEG, MPEG, ASCII, EBCDIC, HTML.
The presentation layer is responsible for translation, compression, and encryption. Note
OSI Model – Application Layer
- – Layer where the application using the
- – Common network applications include
- – Means for applications to access OSI environment
The application layer is responsible for providing services to the user. Note
Summary of layers
The OSI Environment
The OSI Environment
TCP/IP Protocol Suit
- TCP/IP suite is the set of protocols that implement the protocol stack on which the Internet runs. It is sometimes called the Internet Model.
- This model consists of five ordered layers
- In a protocol stack, each layer solves a set of problems involving the transmission of data, and provides a well-defined service to the higher layers
- Developed by research foundation by US department of defense
TCP/IP Protocol Architecture Model
Some Protocols in TCP/IP Suite