TCP IP Protocol Suite

At the transport layer, TCP/IP defines three protocols: Transmission Control

Protocol (TCP), User Datagram Protocol (UDP), and Stream Control Transmission

Protocol (SCTP). At the network layer, the main protocol defined by TCP/IP is the

Internetworking Protocol (IP); there are also some other protocols that support data

movement in this layer.

Physical and Data Link Layers

At the physical and data link layers, TCPIIP does not define any specific protocol. It

supports all the standard and proprietary protocols. A network in a TCPIIP internetwork

can be a local-area network or a wide-area network.

Network Layer

At the network layer (or, more accurately, the internetwork layer), TCP/IP supports

the Internetworking Protocol. IP, in turn, uses four supporting protocols: ARP,

RARP, ICMP, and IGMP

Internetworking Protocol (IP)

The Internetworking Protocol (IP) is the transmission mechanism used by the TCP/IP

protocols. It is an unreliable and connectionless protocol-a best-effort delivery service.

The term best effort means that IP provides no error checking or tracking. IP assumes

the unreliability of the underlying layers and does its best to get a transmission through

to its destination, but with no guarantees.

IP transports data in packets called datagrams, each of which is transported separately.

Datagrams can travel along different routes and can arrive out of sequence or be

duplicated. IP does not keep track of the routes and has no facility for reordering datagrams

once they arrive at their destination.

Address Resolution Protocol

The Address Resolution Protocol (ARP) is used to associate a logical address with a

physical address. On a typical physical network, such as a LAN, each device on a link

is identified by a physical or station address, usually imprinted on the network interface

card (NIC). ARP is used to find the physical address of the node when its Internet

address is known.

Reverse Address Resolution Protocol

The Reverse Address Resolution Protocol (RARP) allows a host to discover its Internet

address when it knows only its physical address. It is used when a computer is connected

to a network for the first time or when a diskless computer is booted.

Internet Control Message Protocol

The Internet Control Message Protocol (ICMP) is a mechanism used by hosts and

gateways to send notification of datagram problems back to the sender. ICMP sends

query and error reporting messages.

Internet Group Message Protocol

The Internet Group Message Protocol (IGMP) is used to facilitate the simultaneous

transmission of a message to a group of recipients.

Transport Layer

Traditionally the transport layer was represented in TCP/IP by two protocols: TCP and

UDP. IP is a host-to-host protocol, meaning that it can deliver a packet from one

physical device to another. UDP and TCP are transport level protocols responsible

for delivery of a message from a process (running program) to another process. A new

transport layer protocol, SCTP, has been devised to meet the needs of some newer

applications.

User Datagram Protocol

The User Datagram Protocol (UDP) is the simpler of the two standard TCPIIP transport

protocols. It is a process-to-process protocol that adds only port addresses, checksum

error control, and length information to the data from the upper layer.

Transmission Control Protocol

The Transmission Control Protocol (TCP) provides full transport-layer services to

applications. TCP is a reliable stream transport protocol. The term stream, in this context,

means connection-oriented: A connection must be established between both ends

of a transmission before either can transmit data.

At the sending end of each transmission, TCP divides a stream of data into smaller

units called segments. Each segment includes a sequence number for reordering after

receipt, together with an acknowledgment number for the segments received. Segments

are carried across the internet inside of IP datagrams. At the receiving end, TCP collects

each datagram as it comes in and reorders the transmission based on sequence

numbers.

Stream Control Transmission Protocol

The Stream Control Transmission Protocol (SCTP) provides support for newer

applications such as voice over the Internet. It is a transport layer protocol that combines

the best features of UDP and TCP.

Application Layer

The application layer in TCPIIP is equivalent to the combined session, presentation,

and application layers in the OSI modeL Many protocols are defined at this layer.