Understanding Transport Layer Protocols

Computer networks Module-04 Ch-06 THE TRANSPORT LAYER The Transport Service Elements of transport protocols Congestion control The internet transport protocols By- Dr. SANTOSH K C Assoc. Professor CSE Dept. B.I.E.T., Davangere-04

6.1 THE TRANSPORT SERVICE 2

Introduction and Transport-Layer Services A transport-layer communication between application processes running on different hosts. protocol provides for logical As shown in Figure 3.1, transport-layer protocols are implemented in the end systems but not in network routers. On the sending side, the transport layer converts the application-layer messages it receives from a sending application process into transport-layer packets, known as transport-layer segments. Note that network routers act only on the network-layer 3

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A Transport-layer protocol provides logical communication between processes running on different hosts, a Network-layer protocol provides logical communication between hosts. Household Analogy: 12 kids in Ann s house sending letters to 12 kids in Bill s house: Hosts = Houses Processes = Kids/cousins Application messages = Letters in envelopes Transport-layer protocol = Ann and Bill who mux/demux to in-house siblings Network-layer protocol = Postal service 5

6.1.2 Transport Service Primitives 6

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6.2 ELEMENTS OF TRANSPORT PROTOCOLS Connection Establishment Three-way handshake 9

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ErrorControlandFlowControl CRC or checksum ARQ (Automatic Repeat reQuest). Stop-and-wait Sliding window 12

Multiplexing 13

6.3 CONGESTION CONTROL Regulating the Sending Rate Regulating the Sending Rate 14

6.4 THE INTERNET TRANSPORT PROTOCOLS: UDP 15

THE INTERNET TRANSPORT PROTOCOLS: TCP UDP UDP is is a a simple such such as as client most most Internet needed needed. . simple protocol protocol and client- - server server interactions Internet applications, applications, reliable, and it it has interactions and reliable, sequenced has some some very and multimedia, multimedia, but sequenced delivery very important important uses, uses, but for delivery is is for UDP UDP cannot called called TCP cannot provide TCP and and is is the provide this, the main this, so main workhorse workhorse of of the so another another protocol protocol is is required the Internet Internet. .. . required. . It It is is 16

The TCP Service Model TCP service is obtained by both the sender and the receiver creating end points, called sockets sockets. . Each socket has a socket number (address) consisting of the IP address of the host and a 16-bit number local to that host, called a port port. . 17

Port numbers below 1024 are reserved for standard services that can usually only be started by privileged users (e.g., root in UNIX systems). They are called well well- -known known ports The list of well-known ports is given at www.iana.org. Over 700 have been assigned. A few of the better-known ones are listed inFig.6-34. ports. . 18

The TCP Segment Header 19

TCP Connection Establishment Connections are established in TCP by means of the three way hand shake discussed in Sec.6.2.2. To establish a connection, one side, say, the server, passively waits for an incoming connection by executing the LISTEN LISTEN and ACCEPT ACCEPT primitives in that order. The other side, say, the client ,executes a CONNECT specifying the IP address and port to which it wants to connect. CONNECT primitive, 20

(a) TCP connection establishment in the normal case.

TCP Connection Management Modelling 22

End of Transportation Layer 23