1. 1 Minseok Kwon Department of Computer Science Rochester Institute of Technology jmk@cs.rit.edu http://www.cs.rit.edu/~jmk Week 1: Internet Architecture

2. 2 Internet Architecture What made the Internet THE WINNER? Packet switching Hourglass design End-to-end argument Layered structure Distributed control Superior organizational process

3. 3 The Network Core What is the networks? Mesh of interconnected routers How is data transferred through net? Circuit switching: dedicated circuit per call, e.g., telephone net Packet-switching: data sent thru net in discrete “chunks”, e.g., data net

4. 4 Circuit Switching End-to-end resources are reserved for call. Link bandwidth, switch capacity Dedicated resources: no sharing Circuit-like performance (guaranteed) Call setup required

5. 5 Packet Switching Each end-end data stream divided into packets User A, B packets share network resources Each packet uses full link bandwidth Resources used as needed Resource contention: Aggregate resource demand can exceed amount available Congestion: packets queue, wait for link use Store and forward: packets move one hop at a time Bandwidth division into “pieces” Dedicated allocation Resource reservation

6. 6 Packet Switching A B C 10 Mb/s Ethernet 1.5 Mb/s D E statistical multiplexing queue of packets waiting for output link

7. 7 Circuit or Packet? Which one you like between circuit-switching and packet-switching? Which one is simpler? Which one is good for bursty traffic? Which one is good for real-time traffic?

8. 8 Routing and Forwarding Goal: move packets through routers from source to destination Datagram network: Destination address in packet determines next hop Routes may change during session Virtual circuit network: Each packet carries tag (virtual circuit ID), tag determines next hop Fixed path determined at call setup time, remains fixed thru call Routers maintain per-call state

9. 9 Hourglass Design

10. 10 Hourglass Design Intelligence IP (Internet Protocol) Unreliable datagram service Addressing and connectionless Fragmentation and Reassembly Phone network: dumb edge device, intelligent network

11. 11 Hourglass Design Why is the hourglass design good? How about with multi-vendor, multi-provider public network? Is this independent of hardware? Which layer in fact provides reliable data transfer?

12. 12 Hourglass Design Which application protocols use TCP? HTTP, FTP, Telnet, SMTP, NNTP, BGP, IMAP, POP Which uses (mainly) UDP? SNMP, NTP, NFS, RTP, DNS Streaming media, IP telephony, teleconferencing More questions Are these enough? How can we provide more sophisticated services such as security, quality-of-service, controlling greedy sources, accounting and pricing? We have IPSec, DiffServ, SCTP, etc.

13. 13 The End-to-End Argument Adding checks during transit may make the system complex, error-prone, or uneconomical. In contrast, what about end-to-end checks and retry? Use checksums at the application level. Suppose that node A sends a file to node B. One concern is the file may be corrupted during this file transfer. Where should we check errors, in the network or at the edge? A B

14. 14 The End-to-End Argument Application knows best! The communication subsystems need to be reliable within reason, but should not provide these “application” features. Example: delivery guarantees, data encryption, duplicate suppression Reliability versus performance?

15. 15 The End-to-End Argument

16. 16 Layered Structure Networks are complex! Is there any hope of organizing structure of network? The answer is layering! Why layering? Effective to deal with complex systems. Explicit structure allows identification, relationship of complex system’s pieces. Modularization eases maintenance, updating of system. Each layer relies on services from layer below and exports services to layer above.

17. 17 Example: Air Travel Organization ticket (purchase) baggage (check) gates (load) runway takeoff airplane routing ticket (complain) baggage (claim) gates (unload) runway landing airplane routing Is there a way to organize structure of network?

18. 18 Internet Protocol Stack Application: supporting network applications Transport: host-host data transfer Network: routing of datagrams from source to destination Link: data transfer between neighboring network elements Physical: bits “on the wire” application transport network link physical

19. 19 Data Communication application transport network link physical application transport network link physical application transport network link physical application transport network link physical network link physical data

20. 20 Protocol Layering and Data Each layer takes data from above Adds header information to create new data unit Passes new data unit to layer below application transport network link physical application transport network link physical source destination M M M M H t H t H n H t H n H l M M M M H t H t H n H t H n H l message segment frame

21. 21 Distributed Control Requirements from DARPA Must survive a nuclear attack Reliability Intelligent aggregation of unreliable components Alternate paths, adaptivity Distributed management & control of networks Exceptions DNS: Top Level Domain (TLD) server IP address assignment (ICANN)

22. 22 Superior Organizational Process IAB/IETF process allowed for quick specification, implementation, and deployment of new standards Rough consensus and removing features Free and easy download of standards 2 interoperable implementations Bake-offs http://www.ietf.org/ How about ISO/OSI compared to IAB/IETF?

23. 23 Internet History: Starring Vint Cerf Robert Kahn Leonard Kleinrock Lawrence Roberts “Where Wizards Stay Up Late: The Origins of the Internet,” K. Hafner, M. Lyon, Simon & Schuster.

24. 24 Internet History 1961: Kleinrock - queueing theory shows effectiveness of packet-switching 1964: Baran - packet- switching in military nets 1967: ARPAnet conceived by Advanced Research Projects Agency 1969: First ARPAnet node operational (UCLA, UCSB, Utah, SRI) 1972: ARPAnet demonstrated publicly NCP (Network Control Protocol) first host-host protocol First e-mail program ARPAnet has 15 nodes 1961-1972: Early packet-switching principles

25. 25 ARPANET ARPANET -- L. Roberts (1966) Galactic computer network + packet switching DARPA program manager Structure and specification (August 1968) Kahn at BBN updates ARPANET design Run over any fabric (separation of hardware and network addresses) Support for multiple independent networks First node UCLA (Sept. 1969) 4 node ARPANET (Dec. 1969) SRI, UCSB, Utah Initial hostname/address database (flat file: hosts.txt)

26. 26 RFCs 1969: Crocker establishes RFC series of notes Official protocol documentation Printed on paper and snail mailed at first Then available via ftp and now http Open and free access to RFCs mandated Effective, positive feedback loop Key to quick development process (“time-to-market”) Has changed considerably as of late... Jon Postel: RFC editor and protocol number assignment

27. 27 E-mail BBN’s Tomlinson (Mar. 1972) Time-shared systems at the time allow users to leave messages for each other Extended to remote systems Writes first e-mail application to send and read Infamous “@” used

28. 28 Internet History 1970: ALOHAnet satellite network in Hawaii 1973: Metcalfe’s PhD thesis proposes Ethernet 1974: Cerf and Kahn - architecture for interconnecting networks late70’s: proprietary architectures: DECnet, SNA, XNA late 70’s: switching fixed length packets (ATM precursor) 1979: ARPAnet has 200 nodes Cerf and Kahn’s internetworking principles: minimalism, autonomy - no internal changes required to interconnect networks best effort service model stateless routers decentralized control Define today’s Internet architecture 1972-1980: Internetworking, new and proprietary nets

29. 29 Meanwhile … Other non-interoperable networks from jealous government agencies and companies DOE: MFENet (Magnetic Fusion Energy scientists) DOE: HEPNet (High Energy Physicists) NASA: SPAN (Space physicists) NSF: CSNET (CS community) NSF: NSFNet (Academic community) 1985 AT&T: USENET with Unix, UUCP protocols Academic networks: BITNET (Mainframe connectivity) Xerox: XNS (Xerox Network System) IBM: SNA (System Network Architecture) Digital: DECNet UK: JANET (Academic community in UK) 1984

30. 30 Internet History Early 1990’s: ARPAnet decommissioned 1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995) early 1990s: Web hypertext [Bush 1945, Nelson 1960’s] HTML, HTTP: Berners-Lee 1994: Mosaic, later Netscape late 1990’s: commercialization of the Web Late 1990’s – 2000’s: More killer apps: instant messaging, P2P file sharing Network security to forefront Est. 50 million host, 100 million+ users Backbone links running at Gbps 1990, 2000’s: commercialization, the Web, new apps

31. 31 TCP/IP software proliferation Widespread dispersal leads to critical mass Case study: Berkeley Unix Unix TCP/IP available at no cost (DoD) Incorporates BBN TCP/IP implementation Large-scale dissemination of code base Eventual economies of scale

32. 32 WWW CERN (European Organization for Nuclear Research) Berners-Lee, Caillau work on WWW (1989) First WWW client (browser-editor running under NeXTStep) Defines URLs, HTTP, and HTML Berners-Lee goes to MIT and LCS to start W3C Responsible for evolving protocols and standards for the web NCSA (National Center for Supercomputing Applications) Federally funded research center at UIUC Andreessen: Mosaic and eventually Netscape (1994)

33. 33 Internet Growth

34. 34 Growing Pains Explosion of networks Routing initially flat, each node runs the same distributed routing algorithm Moved to hierarchical model to match commercial reality (IGP, EGP) Address depletion, Classless addressing (CIDR) Congestion Network “brown-outs”, congestion collapse Add congestion control to TCP protocol, not IP Security Viruses, worms, denial-of-service attacks Privacy, authentication, and many more.

35. 35 Acknowledgements Many parts of this lecture are taken from course slides by Kurose/Ross and course slides by Wu-chang Feng.