4. Networks Interconnection/Internet Concept of Network Interconnection
-First implemented in the Defense Advanced Research Project Agency Network (Arpanet), in 1966 in USA.
-Consists of connecting several computer networks based on different protocols
-Requires the definition of a common interconnection protocol on top the local protocols.
-The Internet Protocol (IP) plays this role, by defining unique addresses for a network and a host machine.
Internet Protocol (IP)
Overview
-The IP protocol provides two main functionality:
→Decomposition of the initial information flow into packets of standardized size, and reassembling at the destination.
→Routing of a packet through successive networks, from the source machine to the destination identified by its IP address.
-Transmitted packets are not guaranteed to be delivered (datagram protocol).
-The IP protocol does not request for connection (connectionless) before sending data and does not make any error detection. Functions
-Decompose the initial data (to be sent) into datagrams.
-Each datagram will have a header including, the IP address and the port number of the destination.
-Datagrams are then sent to selected gateways, e.g IP routers, connected at the same time to the local network and to an IP service provider network.
-Datagrams are transferred from gateways to gateways until they arrived at their final destination.
Structure of an IP packet
-The fields at the beginning of the packet, called the frame header, define the IP protocol’s functionality and limitations.
-32 bits are allocated for encoding source and destination addresses (32 bits for each of these address fields).
-The remainder of the header (16 bits) encodes various information such as the total packet length in bytes.
-Hence an IP packet can be a maximum of 64Kb long.
Transmission Control Protocol (TCP)
Overview
-TCP provides by using IP packets a basic service that does guarantee safe delivery:
→error detection
→safe data transmission
→assurance that data are received in the correct order
-Before sending data, TCP requires that the computers communicating establish a connection (connection-oriented protocol).
-TCP provides support for sending and receiving arbitrary amounts ofdata as one big stream of byte data (IP is limited to 64Kb).
-TCP does so by breaking up the data stream into separate IP packets.
-Packets are numbered, and reassembled on arrival, using sequence and sequence acknowledge numbers.
-TCP also improves the capability of IP by specifying port numbers.
→ There are 65,536 different TCP ports (sockets) through which every TCP/IP machine can talk.
User Datagram Protocol (UDP)
Overview
-Datagram protocol also built on top of IP.
-Has the same packet-size limit (64Kb) as IP, but allows for port number specification.
-Provides also 65,536 different ports.
-Hence, every machine has two sets of 65,536 ports: one for TCP and the other for UDP.
-Connectionless protocol, without any error detection facility.
-Provides only support for data transmission from one end to the other, without any further verification.
-The main interest of UDP is that since it does not make further verification, it is very fast.
-Useful for sending small size data in a repetitive way such as time information.
4.5 Internet Application Protocols On top of TCP/IP, several services have been developed in order to homogenize applications of same nature:
-FTP (File Transfer Protocol) allows the transfer of collection of files between two machines connected to the Internet.
-Telnet (Terminal Protocol) allows a user to connect to a remote host in terminal mode.
-NNTP (Network News Transfer Protocol) allows the constitution ofcommunication groups (newsgroups) organized around specific topics.
-SMTP (Simple Mail Transfer Protocol) defines a basic service forelectronic mails.
-SNMP (Simple Network Management Protocol) allows themanagement of the network.
