Subject Name Computer Communication Networks Subject Code 10

Subject Name: Computer Communication Networks Subject Code: 10 EC 71 Prepared By: Kala H S & Megha Gupta Department: ECE Date: 1/5/2022

Unit - 8 TRANSPORT LAYER: Process to Process Delivery 1/5/2022

TOPICS TO BE COVERED • Process to Process Delivery • UDP • TCP • Domain Name System • Resolution 1/5/2022

PROCESS to PROCESS DELIVERY • Data link layer is responsible for node-to-node delivery of frames between neighboring nodes. • Network layer is responsible for host-to-host delivery of datagrams between two different hosts. • However at any time several processes may be running on source host and destination host. To complete the communication we need delivery of data from one process running on source host to another running on destination host. This is called process-to-process delivery and is done by the transport layer. 1/5/2022

IANA Ranges The Internet Assigned Number Authority has divided port numbers into three ranges: 1. Well – known ports: These port numbers range from 0 to 1023 and are assigned and controlled by IANA. 2. Registered ports: Ranging from 1024 to 49151 and are not assigned or controlled by IANA. They can only be registered with IANA to prevent duplication. 3. Dynamic ports: Ranging from 49152 to 65535 are neither controlled nor registered by IANA. They can be used by any process and are ephemeral ports. 1/5/2022

Socket Address Process – to – process delivery requires IP address and port address. The combination of IP address and port number is called socket address. A transport layer protocol needs a pair of socket addresses: the client socket address and the server socket address. The IP header contains the IP addresses; the UDP or TCP header contains the port numbers 1/5/2022

Multiplexing and Demultiplexing Multiplexing At the sender site, there may be several processes that need to send packets but there is only one transport layer protocol. So a multiplexing scheme is required. The protocol accepts messages from different processes having different port numbers, adds the header and passes the packet to the network layer. Demultiplexing At receiver the data must be delivered to a single process among many through a single transport layer protocol. So demultiplexing is required. The transport layer receives datagrams from the network layer, after error checking and dropping of the header, it delivers each message to the appropriate process based on the port number. 1/5/2022

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Connection-less vs. Connection-oriented Service Connectionless service In connectionless service there is no need for connection establishment or connection release to send packets from one party to another. The packets are not numbered. There is no acknowledgement. The packets may be delayed or lost or may arrive out of order. UDP is connectionless protocol. Connection-Oriented service In this service a connection must first be established between sender and receiver the data can be transferred. At the end of communication the connection can be released. TCP and SCTP are connection – oriented protocols. 1/5/2022

Reliable vs. Unreliable If the application layer program needs reliability, we use a reliable transport layer protocol by implementing flow and error control at the transport layer. The service will be slower and more complex. If the application program does not need reliability because it uses its own flow and error control mechanism or it needs fast service or the nature of the service does not demand flow and error control (real-time applications), then an unreliable protocol can be used. UDP is connectionless and unreliable; TCP and SCTP are connection-oriented and reliable. 1/5/2022

USER DATAGRAM PROTOCOL (UDP) • The User Datagram Protocol (UDP) is called a connectionless, unreliable transport protocol. • It does not add anything to the services of IP except to provide process-toprocess communication instead of host-to-host communication. • Well known ports for UDP are listed in the table. 1/5/2022

User Datagram Format • Source Address • Destination Address • Length • Checksum 1/5/2022

TRANSMISSION CONTROL PROTOCOL (TCP) • TCP is a connection-oriented protocol; it creates a virtual connection between two TCPs to send data. In addition, TCP uses flow and error control mechanisms at the transport level. • Well known ports for TCP are listed in the table. 1/5/2022

DOMAIN NAME SPACE The domain name space is hierarchical in design. The names are defined in an inverted-tree structure with the root at the top. The tree can have 128 levels: level 0 (root) to level 127. 1/5/2022

Domains A domain is a subtree of the domain name space. The name of the domain is the domain name of the node at the top of the subtree. 1/5/2022

RESOLUTION Mapping a name to an address or an address to a name is called nameaddress resolution. DNS is designed as a client-server application. A host that needs to map an address to a name or a name to an address calls a DNS client called a resolver. Three methods: recursive resolution, iterative resolution and cache. Cache: when a server asks a mapping from another server and receives the responds, it stores this information in its cache memory before sending to the client. If the same or another client asks for the same mapping, it can check its cache memory and resolve the problem. 1/5/2022

Recursive resolution The client (resolver) can ask for a recursive answer from a name server. This means that the resolver expects the server to supply the final answer. If the server is the authority for the domain name, it checks its database and responds. If the server is not the authority, it sends the request to another server and waits for the response. mcgraw. com 1/5/2022

Iterative resolution If the client does not ask for a recursive answer, the mapping can be done iteratively. If the server is an authority for the name, it sends the answer. If it is not, it returns the IP address of the server it thinks can resolve the query mcgraw. com 1/5/2022

Acknowledgement : MY SINCERE THANKS TO • THE AUTHOR PROF. BEHROUZ A FOROUZAN. BECAUSE THE ABOVE PRESENTATION MATERIALS ARE HEAVILY BORROWED FROM HIS TEXTBOOK “DATA COMMUNICATION & NETWORKING” 4 TH EDITION, PUBLISHER TATA MCGRAW HILL • SURESHA V. PROFESSOR, DEPT. OF E&C, KVG COLLEGE OF ENGINEERING. SULLIA, D. K - 574 327 By Kala H S & Megha Gupta Assistant Professor 1/5/2022