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TCP/IP Lecture 2

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  1. TCP/IPLecture 2 cs193i – Internet Technologies Summer 2004 Stanford University

  2. Announcements • Lab #1 due Wednesday • HW #1 assigned • Extra perl session tomorrow • Tuesday, June 29, 2:15-3:05pm, Skilling 193 • Broadcast live on E2, Stanford Online • Silas’ Thursday office hours moved to Wednesday this week • Sweet Hall, 6:30-8:30pm

  3. Communicating with Anyone

  4. Local Area Network (LAN) • High speed, data network over small region • Few thousand meters • Network technologies: • Ethernet • FDDI • Token ring • Data link layer • Packets routed based on physical address (MAC) LAN 1 LAN 2

  5. Local Area Network (LAN) • High speed, data network over small region • Few thousand meters • Network technologies: • Ethernet • FDDI • Token ring • Data link layer • Packets routed based on physical address (MAC) LAN 1 ? LAN 2

  6. Connecting Below Internet Level • Hub • Center of star topology • In Ethernet, multiport repeater or concentrator • Bridge • Connects 2 networks of same technology – extended LAN • Filters/forwards/floods based on MAC • Link layer - frames • Switch • Connects 2+ networks – packet-switched network • Reduces collisions Hub Bridge Switch

  7. Connecting at the Internet Level • Router • Originally gateway • Forwards packets based on network layer info (IP) • Separate broadcast domains • In each domain, IP packet encapsulated in domain-specific packet Router

  8. Internet Society • Governing body for Internet since 1992 • http://www.isoc.org • Domain names and addresses assigned • Upper level: Internet Assigned Numbers Authority • Regional: • Latin America / Caribbean • Asia Pacific • America • Europe

  9. How Does Everyone Work Together? • Networks • MCI Worldcom, Sprint, Earthlink, … • Exchange points provide connections between networks • Network Access Points – open access policies • Network Service Provider • Build national or global networks • Lease space at NAPs • Sell bandwidth to regional NSPs • Regional NSP sell bandwidth to ISP • Internet Service Provider sells bandwidth to end users

  10. How Does Everyone Work Together?

  11. OSI Reference Model for Network Design Application (Layer 7) Presentation Session Transport Network Data Link Physical (Layer 1)

  12. Layering: FTP Example Application FTP Application Presentation ASCII/Binary Session Transport TCP Transport Network Network IP Link Link Ethernet Physical The 4-layer Internet model The 7-layer OSI Model OSI vs. TCP/IP Stack

  13. Internet Protocol

  14. Header 10101011101010101010010101010100101010100 11010010101010010101111111010000011101111 10100001011101010100110101011110100000101 00100000000010101000011010000111111010101 ......... 1011011001010100011001001010110 Data IP Datagram

  15. A B C 0 nethost 1 0net host 110nethost 1724 bits 21416 bits 3218 bits IP Addresses • 4 8-bit numbers (Hierarchical) • Specifies both network and host • Number of bits allocated to specify network varies • Three classes: 18.26.0.1 host network 32-bits

  16. IP Addresses • IP (Version 4) Addresses are 32 bits long • IP Addresses Assigned Statically or Dynamically (DHCP) • IPv6 addresses are 128 bits long

  17. IP Address Space • Originally, 3 Classes • A, B, C • Problem • Classes too rigid (C too small, B too big) • Solution • Subnetting (e.g. within Stanford) • Classless Interdomain Routing (CIDR)

  18. Subnetting • IP Address plus subnet mask (netmask) • IP Addr: 171.64.15.82Netmask: 0xFFFFFF00 (111...1100000000) • First 24 bits are the Subnet ID (the neighborhood) • Last 8 bits are Host ID (the street address) • Can be written as “Prefix + Length” • 171.64.15.0/24 or 171.64.15/24

  19. Subnetting at Stanford

  20. IP Routing • Routers are not omniscient • Next-Hop • Hop-by-Hop • Thus IP makes no guarantees • except to try it’s best (”Best Effort”) • packets may get there out of order, garbled, duplicated • may not get there at all! • Unreliable datagram service

  21. IP Routing Hop-by-Hop How a Router Forwards Datagrams

  22. 232-1 0 Classless Interdomain Routing (CIDR)

  23. 128.9.0.0 142.12/19 65/8 128.9/16 0 2 -1 32 2 16 128.9.16.14 Classless Interdomain Routing (CIDR)

  24. 128.9.19/24 128.9.25/24 128.9.16/20 128.9.176/20 128.9/16 0 2 -1 32 128.9.16.14 Classless Interdomain Routing (CIDR)

  25. 128.9.19/24 128.9.25/24 128.9.16/20 128.9.176/20 128.9/16 0 2 -1 32 128.9.16.14 Classless Interdomain Routing (CIDR)

  26. Five Minute Break

  27. Network Programs • host • ping • traceroute • nslookup

  28. Summary of IP • Connectionless/Datagram • Unreliable/Best Effort

  29. Transmission Control Protocol

  30. Characteristics • Connection-Oriented • Reliable • Byte-Stream • Flow Control (aka Congestion Control)

  31. Three Phases • Establish Connection • Data Transfer • Terminate Connection

  32. Establishing the Connection

  33. Host A Byte 0 Byte 1 Byte 2 Byte 3 Byte 80 Host B Byte 0 Byte 1 Byte 2 Byte 3 Byte 80 Data Transfer

  34. Host A Byte 0 Byte 1 Byte 2 Byte 3 Byte 80 TCP Data TCP Data Host B Byte 0 Byte 1 Byte 2 Byte 3 Byte 80 Data Transfer

  35. IP Data IP Hdr TCP Data TCP Hdr 0 15 31 Src port Dst port Sequence # Src /dst port numbers Ack Sequence # and IP addresses Flags Window Size RSVD HLEN uniquely identify socket PSH SYN URG RST ACK FIN 6 4 Checksum Urg Pointer (TCP Options) TCP Data Maintaining the “Connection”

  36. (Active) (Passive) Client Server Fin (Data +) Ack Fin Ack Connection Close/Teardown 2 x 2-way handshake Terminating the Connection

  37. Connection-Oriented • Reliable • Byte-Stream • Flow Control (aka Congestion Control)

  38. Reliability & Flow Control • Sequence numbers & Acknowledgements (ACKs) • Receiver detects Corrupt, Lost, Duplicated, Out-of-order • Tell sender which packets it has received correctly • Sender can resend • In Flight Window (Window Size) • Sender only has N unacknowledged packets “in

  39. Arachne . Berkeley .edu Leland.Stanford.edu Application Layer Leslie Ron Transport Layer O.S. O.S. Data Header Data Header Network Layer D H D H D H D H D H Link Layer D H Sending a Message

  40. Connection-Oriented • Reliable • Byte-Stream • Flow Control (aka Congestion Control)

  41. UDP

  42. User Datagram Protocol (UDP) • Like TCP, in the Transport Layer • Characteristics • Connectionless, Datagram, Unreliable • Adds only application multiplexing/demultiplexing and checksumming to IP • Good for Streaming Media, Real-time Multiplayer Networked Games, VoIP

  43. Summary • IP is the basis of Internetworking • TCP builds on top of IPadds reliable, congestion-controlled, connection-oriented byte-stream. • UDP builds on top of IPallows access to IP functionality