IGNOU BCA 5th sem Solved Assignment - What are layers in the TCP/IP Model? Discuss the main functions and services of each layer?

What are layers in the TCP/IP Model? Discuss the main functions and services of each  layer?

Ans                 

Like OSI network model, TCP/IP also has a network model. TCP/IP was on the path of development when the OSI standard was published and there was interaction between the designers of OSI and TCP/IP standards. The TCP/IP model is not same as OSI model. OSI is a seven-layered standard, but TCP/IP is a four layered standard. The OSI model has been very influential in the growth and development of TCP/IP standard, and that is why much OSI terminology is applied to TCP/IP. The following figure compares the TCP/IP and OSI network models.

TCP/IP Model   
There are four layers :      
Application    

Transport

Internet

Network Access         

The TCP/IP model, similar to the OSI model, is comprised of layers.  The OSI has seven layers and the TCP/IP model has four or five layers depending on different preferences.  Some people use the Application, Transport, Internet and Network Access layers.  Others split the Network Access layer into the Physical and Data Link components.

LAYER 4 - APPLICATION

Application layer is the top most layer of four layer TCP/IP model. Application layer is present on the top of the Transport layer. Application layer defines TCP/IP application protocols and how host programs interface with transport layer services to use the network.

Application layer includes all the higher-level protocols like DNS (Domain Naming System),HTTP (Hypertext Transfer Protocol), Telnet, FTP (File Transfer Protocol), TFTP (Trivial File Transfer Protocol), SNMP (Simple Network Management Protocol), SMTP (Simple Mail Transfer Protocol) , DHCP (Dynamic Host Configuration Protocol), X Windows, RDP (Remote Desktop Protocol) etc.

LAYER 3 - TRANSPORT

This layer acts as the delivery service used by the application layer.  Again the two protocols used are TCP and UDP.  The choice is made based on the application's transmission reliability requirements.  The transport layer also handles all error detection and recovery.  It uses checksums, acknowledgements, and timeouts to control transmissions and end to end verification.  Unlike the OSI model, TCP/IP treats reliability as an end-to-end problem.

LAYER 2 - INTERNET

The routing and delivery of data is the responsibility of this layer and is the key component of this architecture.  It allows communication across networks of the same and different types and carries out translations to deal with dissimilar data addressing schemes.  It inject packets into any network and deliver them to the destination independently to one another.  Because the path through the network is not predetermined, the packets may be received out of order.  The upper layers are responsible for the reordering of the data.  This layer can be compared to the network layer of the OSI model.  IP and ARP⁶ are the major protocols used at this layer.

LAYER 1 - NETWORK ACCESS

This a combination of the Data Link and Physical layers of the OSI model which consists of the actual hardware.  This includes wires, network interface cards, etc.  Other related details within this layer are connectors, signal strength, and wavelength along with various others. It will use the required LAN operating algorithms, such as Carrier Sense Multiple Access with Collision Detect (CMSA/CD)⁷ or IBM Token Passing⁸ etc. and is responsible for placing the data within a frame.  The frame format is dependent on the system being used, for example Ethernet LAN, Frame relay⁹, etc. The frame is the package that holds the data, in the same way as an envelope holds a letter.  The frame holds the hardware address of the host and checking algorithms for data integrity.  This layer has actually not been specified in details because it depends on which technology is being used such as Ethernet.  So freedom is given to this layer as far as implementation is concerned.