Chapter 3 Transport Layer Chapter 3: Transport Layer Our goals: - PowerPoint PPT Presentation

Chapter 3 Transport Layer Chapter 3: Transport Layer Our goals:  learn about transport  l n b t t nsp t  understand principles d t d i i l  layer protocols in the behind transport Internet: layer services: y  UDP: connectionless  multiplexing/ transport, unreliable demultiplexing delivery of segments  reliable data transfer  reliable data transfer  TCP: connection-oriented  flow control transport, reliable delivery  congestion control of byte stream 10/17/2017 Transport Layer (SSL) 3-1 1

Chapter 3 outline Chapter 3 outl ne  3.1 Transport-layer p y  3.5 Connection-oriented services transport: TCP  3.2 Multiplexing and  segment structure demultiplexing d lti l i  reliable data transfer  reliable data transfer  flow control  3.3 Connectionless  connection management transport: UDP tran p rt D  3.6 Principles of  3.4 Principles of congestion control reliable data transfer  3 7 TCP congestion  3.7 TCP congestion (my slides for Section control 3.4 do not follow Kurose & Ross) Kurose & Ross) 10/17/2017 Transport Layer (SSL) 3-2 2

Transport services and protocols Transport serv ces and protocols application transport  provide logical communication network data link between app processes on between app processes on phys cal physical different hosts  transport protocol runs in end systems (primarily) end systems (primarily)  send side: breaks app messages into segments , passes to network layer passes to network layer  rcv side: reassembles application transport segments into messages, network data link passes to app layer passes to app layer physical 10/17/2017 Transport Layer (SSL) 3-3 3

Internet transport-layer protocols  unreliable, unordered application transport network datagram delivery by UDP datagram delivery by UDP d data link li k physical network  no-frills extension of “best- data link network physical effort” IP data link physical  reliable, in-order byte delivery by TCP network data link physical  connection setup  connection setup network d data link li k physical  flow control network data link  congestion control application physical network transport data link network  services not available: i il bl physical h i l data link physical  delay guarantees  bandwidth guarantees g 10/17/2017 Transport Layer (SSL) 3-4 4

Chapter 3 outline Chapter 3 outl ne  3.1 Transport-layer p y  3.5 Connection-oriented services transport: TCP  3.2 Multiplexing and  segment structure d demultiplexing lti l i  reliable data transfer  reliable data transfer  flow control  3.3 Connectionless  connection management transport: UDP tran p rt D  3.6 Principles of  3.4 Principles of congestion control reliable data transfer  3 7 TCP congestion  3.7 TCP congestion control 10/17/2017 Transport Layer (SSL) 3-5 5

Multiplexing/demultiplexing Multiplexing/demultiplexing Multiplexing at send host: Demultiplexing at rcv host: gather data from multiple deliver received segments deliver received segments sockets, encapsulate data with to correct sockets header (later used for demultiplexing) socket k t process/thread /th d P4 application P1 P2 P3 application P1 application transport transport transport network network network link link link physical physical physical host 3 host 2 host 1 10/17/2017 Transport Layer (SSL) 3-6 6

How demultiplexing works m p g 32 bits  host receives IP datagrams source port # dest port #  It uses IP addresses in layer- y other header fields 3 header & port numbers in layer-4 header to direct segment to appropriate socket application data (message) ( g ) TCP/UDP segment format 10/17/2017 Transport Layer (SSL) 3-7 7

Connectionless demultiplexing Connect onless demult plex ng  UDP socket identified by  UDP socket identified by  IP datagrams from  IP datagrams from two-tuple: different sources directed to same UDP ( dest IP address, dest port number) socket k t  When host receives UDP segment: segment:  directs UDP segment to socket with destination port number number 10/17/2017 Transport Layer (SSL) 3-8 8

Connect on or ented demux Connection-oriented demux  Server has welcome and  Server may support y pp connection sockets many simultaneous TCP connection sockets with  welcome socket is clients: identified by server’s IP address and a port dd d  each connection socket number and the welcome socket  TCP connection socket have the same port number in server host b i s h st identified by 4-tuple: id tifi d b 4 t l  receiving host uses all  source IP address four values to direct  source port number segment to appropriate segment to appropriate  dest IP address connection socket  dest port number 10/17/2017 Transport Layer (SSL) 3-9 9

Connection-oriented demux ( (cont) t) P4 P1 P2 P1 P3 SP: 5775 DP: 80 S-IP: B D IP C D-IP:C SP: 9157 SP: 9157 client client DP: 80 DP: 80 DP: 80 DP: 80 Client Client server IP: A IP:B S-IP: A S-IP: B IP: C D-IP:C D-IP:C 10/17/2017 Transport Layer (SSL) 3-10 10

Chapter 3 outline Chapter 3 outl ne  3.1 Transport-layer p y  3.5 Connection-oriented services transport: TCP  3.2 Multiplexing and  segment structure d demultiplexing lti l i  reliable data transfer  reliable data transfer  flow control  3.3 Connectionless  connection management transport: UDP tran p rt D  3.6 Principles of  3.4 Principles of congestion control reliable data transfer  3 7 TCP congestion  3.7 TCP congestion control 10/17/2017 Transport Layer (SSL) 3-11 11

UDP: User Datagram Protocol [RFC 768] g [ ]  “best effort” service, UDP Length, in bytes of UDP segments (aka datagrams) segment including header g g may be: b 32 bits  lost source port # dest. port #  delivered out of order to appl checksum length  connectionless:  no handshaking between no handshak ng between UDP sender, receiver  each UDP segment Application handled independently p y data data of others (message) UDP segment format 10/17/2017 Transport Layer (SSL) 3-12 12

UDP (more)  suitable for interactive streaming multimedia applications pp Advantages of UDP Adv nt s f UDP  loss tolerant  no congestion control: UDP  min rate required can blast away as fast as  other UDP uses e g  other UDP uses, e.g. desired d i d  DNS  small segment header  SNMP  no connection establishment (which can  DHCP add delay)  reliable transfer over  simple: no connection state UDP? at sender, receiver t d i add reliability in application layer  application-specific pp p f error recovery 10/17/2017 Transport Layer (SSL) 3-13 13

Internet checksum S nd Sender: : Receiver:  treat segment as a sequence of 16-bit  compute 1’s complement sum integers (with checksum field i t of received segment (checksum initialized to zero) field included)  add integers using 1’s  check if computed sum equals complement arithmetic complement arithmetic si t sixteen 1’s: 1’s: and take 1’s complement  NO - error detected of the sum  YES - no error detected  put result as checksum  put result as checksum But maybe errors value into checksum field nonetheless? More later  detail: pseudoheader …. consisting of protocol no consisting of protocol no., IP IP addresses, segment length field (again) included in checksum calculation 10/17/2017 Transport Layer (SSL) 3-14 14

Internet Checksum Example  Notes N  In ones complement arithmetic, a negative integer -x is represented as the complement of x , i.e., each bit of x is p p , , inverted  When adding numbers, a carryout from the most significant bit needs to be added to the result g  Example: add two 16-bit integers 1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 1 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 wraparound 1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1 sum 1 1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 0 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 0 checksum 1 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1 10/17/2017 Transport Layer (SSL) 3-15 15

Chapter 3 outline Chapter 3 outl ne  3.1 Transport-layer p y  3.5 Connection-oriented services transport: TCP  3.2 Multiplexing and  segment structure demultiplexing d lti l i  reliable data transfer  reliable data transfer  flow control  3.3 Connectionless  connection management tran p rt transport: UDP D  3.6 Principles of  3.4 Principles of congestion control reliable data transfer  3 7 TCP congestion  3.7 TCP congestion (my slides do not control follow Kurose & Ross) 10/17/2017 Transport Layer (SSL) 3-16 16

Principles of Reliable data transfer p f f  important in application, transport, link layers  top-10 list of important networking topics!  top-10 list of important networking topics! 10/17/2017 Transport Layer (SSL) 3-17 17