The Transport LayerOverviewTransport Layer in the InternetIntroSlide 5The TCP Service ModelSlide 7Slide 8The TCP ProtocolSlide 10Slide 11Slide 12The TCP Segment HeaderSlide 14Slide 15Slide 16Slide 17TCP Connection ManagementSlide 19Slide 20Slide 21TCP Congestion ControlSlide 23Slide 24TCP Timer ManagementSlide 26UDPSlide 28Slide 2911The Transport LayerThe Transport LayerThe Internet Transport Protocols – TCP and UDP22OverviewOverviewIntroIntroThe TCP Service ModelThe TCP Service ModelThe TCP ProtocolThe TCP ProtocolThe TCP Segment HeaderThe TCP Segment HeaderTCP Connection ManagementTCP Connection ManagementTCP Transmission PolicyTCP Transmission PolicyTCP Congestion controlTCP Congestion controlTCP Timer managementTCP Timer managementUDPUDP33Transport Layer in the InternetTransport Layer in the InternetThe Internet has two main protocols in The Internet has two main protocols in the transport layer – a the transport layer – a connection connection orientedoriented protocol, and a protocol, and a connectionlessconnectionless one. We will study both one. We will study both of them.of them.The connection oriented protocol is The connection oriented protocol is TCP.TCP.The connectionless is UDP. The connectionless is UDP. Because UDP is basically just IP with a Because UDP is basically just IP with a short header added, we will focus on short header added, we will focus on TCP.TCP.44IntroIntroTCP (Transmission Control Protocol)TCP (Transmission Control Protocol) was was specifically designed to provide a specifically designed to provide a reliable reliable end-to-end byte streamend-to-end byte stream over an unreliable over an unreliable internetwork.internetwork.An internetwork differs from a single An internetwork differs from a single network because different parts may have network because different parts may have quite different topologies, bandwidth, quite different topologies, bandwidth, delays, packet sizes, and other delays, packet sizes, and other parameters. TCP was designed to parameters. TCP was designed to dynamically adaptdynamically adapt to properties of the to properties of the internetwork and to be internetwork and to be robustrobust in the face in the face of many kinds of many kinds of failuresof failures..55IntroIntroEach machine supporting TCP has Each machine supporting TCP has TCP transport entityTCP transport entity, , either a user process or part of the kernel, which manages either a user process or part of the kernel, which manages TCP streams and interfaces to the IP layer.TCP streams and interfaces to the IP layer.A TCP entity accepts user data streams from local A TCP entity accepts user data streams from local processes, breaks them up into pieces not exceeding 64K processes, breaks them up into pieces not exceeding 64K bytes, and sends each piece as a separate IP datagram. bytes, and sends each piece as a separate IP datagram. When IP datagrams containing TCP data arrive at a When IP datagrams containing TCP data arrive at a machine, they are given to the TCP entity, which machine, they are given to the TCP entity, which reconstructs the original byte streams.reconstructs the original byte streams.The The IP gives not guaranteeIP gives not guarantee that datagrams will be delivered that datagrams will be delivered properly, so properly, so it is up the TCPit is up the TCP to time out and retransmit to time out and retransmit them as need be. Datagrams that do arrive may well be in them as need be. Datagrams that do arrive may well be in the wrong order; it is also up to the TCP to reassemble them the wrong order; it is also up to the TCP to reassemble them into messages in proper sequence. into messages in proper sequence.66The TCP Service ModelThe TCP Service ModelTCP Service is obtained by having both theTCP Service is obtained by having both the sender and receiver create end points, sender and receiver create end points, called called sockets. sockets. Each socket has a socket number Each socket has a socket number (address)(address) consisting of the IP address of the consisting of the IP address of the host and host and a 16-bit number local to that host, a 16-bit number local to that host, calledcalled a port. a port. To obtain TCP service,To obtain TCP service, a connection a connection must be must be explicitly established between a socket on the explicitly established between a socket on the sending machine and a socket on the receiving sending machine and a socket on the receiving machine. machine. A socket may be used for multiple connections A socket may be used for multiple connections at the same time. In other words, two or more at the same time. In other words, two or more connections may terminate at the same socket. connections may terminate at the same socket.77The TCP Service ModelThe TCP Service ModelPort numbers Port numbers below 1024below 1024 are called are called well-known portswell-known ports and and are reserved for standard services. For example, any process are reserved for standard services. For example, any process wishing to establish a connection to a host to transfer a file wishing to establish a connection to a host to transfer a file using FTP can connect to the destination host’s port 21 to using FTP can connect to the destination host’s port 21 to contact its FTP daemon/service. Similarly, to establish a contact its FTP daemon/service. Similarly, to establish a remote login session using TELNET, port 23 is used. Port 80 remote login session using TELNET, port 23 is used. Port 80 is used for HTTP, port 443 is used for SSL, etc.is used for HTTP, port 443 is used for SSL, etc.Ports Ports between 1024 and 5000between 1024 and 5000 are called are called ephemeralephemeral and are and are free to use (not reserved). The client’s socket would use free to use (not reserved). The client’s socket would use such port. such port. All TCP connections are All TCP connections are full-duplexfull-duplex and and point-to-pointpoint-to-point. Full . Full duplex means that traffic can go in both directions at the duplex means that traffic can go in both directions at the same time. Point-to-point means that each connection has same time. Point-to-point means that each connection has exactly two end points. TCP does not support multicasting or exactly two end points. TCP does not support multicasting or