Layers of protocols, TCP/IP example

TCP/IP is made up of two acronyms, TCP, for Transmission Control Protocol, and IP, for Internet Protocol. TCP handles packet flow between systems and IP handles the routing of packets. However, that is a simplistic answer that we will expound on further.

All modern networks are now designed using a layered approach. Each layer presents a predefined interface to the layer above it. By doing so, a modular design can be developed so as to minimise problems in the development of new applications or in adding new interfaces.

The ISO/OSI protocol with seven layers is the usual reference model. Since TCP/IP was designed before the ISO model was developed it has four layers; however the differences between the two are mostly minor. Below, is a comparison of the TCP/IP and OSI protocol stacks:

   7. Application   -- End user services such as email.
   6. Presentation  -- Data problems and data compression
   5. Session       -- Authentication and authorisation
   4. Transport     -- Guarantees end-to-end delivery of packets
   3. Network       -- Packet routing
   2. Data Link     -- Transmit and receive packets
   1. Physical      -- The cable or physical connection itself.
	  
	  

   5. Application   -- Authentication, compression, and end user services.
   4. Transport     -- Handles the flow of data between systems and 
                       provides access to the network for applications via
                       the (BSD socket library)
   3. Network       -- Packet  routing
   2. Link          -- Kernel OS/device driver interface to the network 
                       interface on the computer.
	  

Major difference between the OSI and TCP/IP:

• The application layer in TCP/IP handles the responsibilities of layers 5,6, and 7 in the OSI model.

• The transport layer in TCP/IP does not always guarantee reliable delivery of packets as the transport layer in the OSI model does. TCP/IP offers an option called UDP that does not guarantee reliable packet delivery.

Software Components of TCP/IP

Application Layer

Some of the applications we will cover are SMTP (mail), Telnet, FTP, Rlogin, NFS, NIS, and LPD

Transport Layer

The transport uses two protocols, UDP and TCP. UDP which stands for User Datagram Protocol does not guarantee packet delivery and applications which use this must provide their own means of verifying delivery. TCP does guarantee delivery of packets to the applications which use it.

Network Layer

The network layer is concerned with packet routing and used low level protocols such as ICMP, IP, and IGMP. In addition, routing protocols such as RIP, OSPF, and EGP will be discussed.

Link Layer

The link layer is concerned with the actual transmittal of packets as well as IP to ethernet address translation. This layer is concerned with Arp, the device driver, and Rarp.

To know more about TCP/IP...