Ans. The TCP/IP reference model is the network model used in the current Internet architecture. It was created in the 1970s by DARPA for use in developing the Internet’s protocols, and the structure of the Internet is still closely reflected by the TCP/IP model. It is considered as the grandfather of the Internet the ARPANET. The reference model was named after two of its main protocols, TCP (Transmission control Protocol) and IP(Internet Protocol).
There are versions of this model with four layers and with five layers. The original four-layer version of the model is shown below.
· Layer 4 – Process Layer or Application Layer: This is where the “higher level” protocols such as FTP, HTTP, etc. operate. The original TCP/IP specification described a number of different applications that fit into the top layer of the protocol stack. These applications include Telnet, FTP, SMTP and DNS.
Telnet is a program that supports the TELNET protocol over TCP, TELNET is a general two-way communication protocol that can be used to connect to another host and run applications on that host remotely.
FTP(File transfer Protocol) is a protocol that was originally designed to promote the sharing of files among computer users. It shields the user from the variations of file storage on deferent architectures and allows for a reliable and efficient transfer of data.
SMTP (Simple Mail transport Protocol) is the protocol used to transport electronic mail from one computer to another through a series of other computers along the route.
DNS (Domain Name System) resoles the numerical address of a network node into its textual name or vice-versa. It would translate www.yahoo.com to 126.96.36.199 to allow the routing protocols to find the host that the packet is destined for.
· Layer 3 – Host-To-Host (Transport) Layer: This is where flow-control and connection protocols exist,, such as TCP. This layer deals with opening and maintaining connection, ensuring that packet are in fact received the transport layer is the interface between the application layer and the complex hardware of the network it is designed to allow peer entities on the source and destination hosts to carry on conversations. Data may be user data or control data. Two modes are available, full-duplex and half duplex. In full-duplex operation, both sides can transmit and receive data simultaneously, whereas in half duplex, a side can only send or receive at one time.
· Layer 2 – Internet or Internetworking Layer: This layer defines IP addresses, with many routing schemes for navigating packets from one IP address to another. The job of the network layer is to inject packets into any network and have them travel independently to the destination. The layer defines IP (Internet Protocol) for its official packet format and protocol. Packet routing is a major job of this protocol.
· Layer 1 – Networking Access Layer: This layer describes the physical equipment necessary for communications, such as twisted pair cables, the signaling used on that equipment, and the low-level protocols using that signaling. That Host-to-Network layer interfaces the TCP/IP protocol stack to the physical network. The TCP/IP reference model does not specify in any great detail the operation of this layer, except that the host has to connect to the network using some protocol so it can send IP packets over it. As it is not officially defined, it varies from implementation to implementation, with vendors supplying their own version.
1. What are the advantages and disadvantages of layered architecture in a network?
Ans. Advantages of Layered Architecture
· Any given layer can be modified or upgraded without affecting the other layers.
· Modulazition by means of layering simplifies the overall design.
· Different layers can be assigned to different standards, committees, and design teams.
· The relation between different control functions can be better understood.
· Common lower levels may be shared by different higher levels.
· Functions (especially at lower levels) may be removed from software to hardware and micro-codes.
· Increases the compatibility of different machines.
Disadvantages of Layered Architecture
· Total overhead is higher.
· Two communicating machines may have to use certain functions which they could do without layers.As technology changes, the functions may not be in the most cost-effective layer.