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TCP/IP

TCP/IP is transfer control protocol. TCP/IP is important because it provides the underlying technology for the internet. Intranet also employ  TCP/IP technology.

What is TCP/IP

TCP/IP is a set of related protocols that define how nodes intercommunicate on the Internet . The name is derived from the two main protocols. TCP is the transmition control protocol that defines the rules for the end to end communication.  IP is the internet protocol that is responsible for network addressing and routing.

The four layers of TCP/IP are

1. Application
2. Transport 
3. Network
4. Link

Application 

This layer is equivalent to the three layers of the OSI model. Common protocols are SMTP, FTP, HTTP.

Transport 

This layer is equivalent to the transport layer of the OSI model. Common protocols such as TCP and UDP are in this layer. Responsible for end to end reliability. Port address are provided by the TCP and UDP

Network 

Equivalent to the network layer of the OSI model. Common protocols such as IP, ICMP, ARP. IP addresses are provided in this layer.

Link

Equivalent to the bottom two layers of the OSI model. Common protocols such as SLIP, PPP, Ethernet and Token ring. Ethernet and Token ring networks provide their own addresses often known as media access control (MAC).

Encapsulation

Each layer has its own format for packets. Encapsulation is the process in which a higher layer packet is placed into the packet of the lower layer . For example TCP segments go inside IP datagrams. IP datagrams may then be placed inside Ethernet frames so that they can traverse an Ethernet network. 
A set of protocols that have been designed to work together is called a stack.

An example of a stack

De multiplexing

At the receiver end the process  of creating a stack is reversed . For example the IP datagram is removed from the Ethernet frame. TCP and UDP can be extracted from IP and FTP can be removed from TCP. 

Addressing IP

The addresses are used for end to end communication sessions, and both must be unique. The address has two parts  IP No, and Port No. The combination of these two is called a socket. The 32 bits IP addresses used to identify the interface. the 16 bit port number used to provide a unique identifier to the server.

Internet addresses 

This is often called  an IP address. 32 bits addresses subdivided between the Network identifier and the Host identifier. There are three main classes A, B, C and a forth one reserved for multicasting groups.

Classes of IP addresses.

For example the university of Western Sydney (UWS) IP address is 137.154.148.10. 

IP ( Internet Protocol)

Provides universal addressing. Defines the format of packet on the virtual network IP packets are routed through the virtual network. This is a network layer protocol. Packets are called Datagrams and are sent with all care but no responsibility. IP datagram are encapsulated in data link layer frames. Encapsulates transport layer data, the protocols TCP and UDP.

Routing IP 

IP's main task is the routing of packet from the source node to the destination node. Routing is based on the network ID and the node ID. The node ID can be used to identify sub network using the process called masking.  The maximum datagram size is 64Kb.

Network MTU (maximum transfer unit )

Each network hardware imposes its own fixed limit on the encapsulated packet. E.g. 802.3 frames are 1518 bytes and the maximum data load of 1500 bytes. The size limit is called network maximum transfer unit. What happens when the datagram is larger than the network MTU? . Well then the datagram is fragmented into smaller datagrams that fit the network MTU. The fragmentation is done by the IP router. These fragments are transmitted independently and are reassembled at the destination end.

Transport layer protocols.

TCP always requires two main transport layer protocols; TCP and UDP.
TCP protocol is the heavy duty protocol, is more reliable and is connection oriented. It is the major transport protocol in the Internet, it has a full duplex connection, provides a flow control and the TCP receiver node acknowledgements to sender. The sender will re transmit if there is no acknowledgment. 

UDP is the unreliable protocol. It is a connectionless  protocol. UDP messages are encapsulated in IP datagrams. 

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Last modified: October 03, 2004