1 CSE524: Lecture 2 Protocols in practice, Internet history (Part 1)

2 Administrative Reading assignment –Chapter 1, due by Monday 10/1/2001 Homework assignments –

3 Administrative Results of diagnostic quiz –Majority Have not had an Internet networking course (or slept through the one you took) This course will be directed at you –A small handful In danger of being very very bored OK, if you need easy credits, but don’t sleep

4 A day in the life of an Internet host… Booting –Dynamically configure network settings DHCP, BOOTP UDP (unreliable datagrams) IP and data-link broadcast IP address, DNS server and route configuration

5 A day in the life of an Internet host… Web request –Find DNS server ARP (IP to hardware address mapping) Data-link broadcast Reply often broadcast back and cached on each host of network

6 A day in the life of an Internet host… Send DNS request –UDP, IP, data-link header

7 A day in the life of an Internet host… Send HTTP request “GET index.html HTTP/1.0” HTTP (application request data) TCP (reliable byte stream) IP, data-link header

8 A day in the life of an Internet host… Role of TCP and UDP? Demultiplex at end hosts. –Which process gets this request? FTPHTTPTFTPNV TCPUDP IP NET 1 NET 2 NET n … TCP/UDPIP IPX Port Number Network Protocol Field Type Field

9 A day in the life of an Internet host…. What about…. –Reliability Corruption Lost packets –Flow and congestion control –Fragmentation –Out-of-order delivery The beauty of TCP, IP, and layering –All taken care of transparently

10 What if the Data gets Corrupted? Internet GET windex.htmlGET index.html Solution: Add a checksum Problem: Data Corruption 0,996,7,8214,571,2,36 X

11 What if the Data gets Lost? Internet GET index.html Problem: Lost Data Internet GET index.html Solution: Timeout and Retransmit GET index.html

12 What if receiver has no resources (flow control)? Internet PUT remix.mp3 Problem: Overflowing receiver buffers Internet Solution: Receiver advertised window PUT remix.mp3 16KB free

13 What if Network is Overloaded? Problem: Network Overload Short bursts: buffer What if buffer overflows? –Packets dropped and retransmitted –Sender adjusts rate until load = resources Called “Congestion control” Solution: Buffering and Congestion Control

14 Problem: Packet size Solution: Fragment data across packets What if the Data Doesn’t Fit? On Ethernet, max IP packet is 1.5kbytes Typical web page is 10kbytes GETindex.html GET index.html

15 Solution: Add Sequence Numbers Problem: Out of Order What if the Data is Out of Order? GETx.thindeml GET x.thindeml GET index.html ml4inde2x.th3GET1

16 Internet History Those who ignore the past are doomed to repeat it cerfs_up/ cerfs_up/ Where did it come from? Who built it? Why does it work?

17 Packet switching Kleinrock, MIT (July 1961) –Theoretical feasibility of communications using packets instead of circuits –L. Kleinrock, "Information Flow in Large Communication Nets", RLE Quarterly Progress Report, July –L. Kleinrock, Communication Nets: Stochastic Message Flow and Delay, Mcgraw-Hill (New York), 1964.

18 Conceptual “Internet” J.C.R. Licklider, W. Clark, MIT (August 1962) –“On-line Man Computer Communication” –“Galactic network” concept of globally interconnected set of computers –Licklider goes to DARPA as head of computer research program (Oct. 1962)

19 First WAN Roberts, (1966) –Licklider convinces Roberts of internetworking –Kleinrock convinces Roberts of packet switching –First WAN TX-2 computer in Massachusetts connected to the Q-32 in California with a low speed dial-up telephone L. Roberts, T. Merrill, “Toward a Cooperative Network of Time- Shared Computers”, Fall AFIPS Conf., Oct –Roberts goes to DARPA as program manager Plans for building “ARPANET” based on system L. Roberts, "Multiple Computer Networks and Intercomputer Communication", ACM Gatlinburg Conf., October 1967.

20 ARPANET Roberts finishes ARPANET structure and specification (August 1968) –RFQ for implementation of IMPs (Interface Message Processors) –Packet switches which route packets –BBN (Bolt, Beranek, and Newman) wins contract –Kahn at BBN updates ARPANET design Run over any fabric Multiple independent networks

21 ARPANET First ARPANET node UCLA (Sept. 1969) –SRI second node Part of a project which includes early hypertext system NLS Initial hostname/address database –First message from UCLA to SRI –UCSB and Univ. of Utah add nodes –4 node ARPANET (Dec. 1969)

22 RFCs 1969: Crocker establishes RFC series of notes –Informal distribution of ideas –Printed on paper and snail mailed at first –Then available via ftp and now http –Jon Postel RFC editor and protocol number assignment –Open and free access to RFCs –Positive feedback loop

23 NCP Crocker leads Network Working Group –Host-to-Host protocol standard for two ends to talk to each other –NCP (Network Control Protocol) defined (Dec. 1970) –Precursor to TCP –Deployed from –Allows applications to be developed on top of network

24 BBN’s Tomlinson (Mar. 1972) –Time-shared systems at the time –Idea: leave messages to each other on shared systems, extend to remote systems –Writes first application to send and read –Infamous used –Roberts later updates with listing, filing, forwarding, selective read, reply

25 Internetting International Network Working Group (Sept. 1973) –Goal: run protocols over packet satellite net, packet radio net, and wired ARPANET –Problems NCP can only address networks connected to IMPs on ARPANET NCP relied on ARPANET for end2end reliability NCP assumed no packet loss: applications halt upon loss NCP had no end-end host error control –Kahn redesigns protocols for internetworking

26 Internetting Kahn’s Architecture –Each network stands alone. No changes required to connect to Internet. –Communication on a “best-effort” basis –Source in charge of retransmission –Black boxes connecting networks (gateways and routers) have no per-flow information Simple Avoids complicated adaptation and recovery from failure –No global control at the operations level –Host-to-Host flow control (sliding windows and acks)

27 Internetting Other issues –Host-to-Host data pipelining (multiple packets en route) –Gateway interprets IP headers for routing and performs fragmentation to other networks –End2end checksums, reassembly of fragments, duplicate detection (virtual circuit model) –Global addressing via 32-bit address 8-bit network number, 24 bit host number Fails to forsee development of the LAN –Interfaces to operating systems R. Kahn, Communications Principles for Operating Systems. Internal BBN memo, Jan

28 Internetting Kahn brings in Cerf (Stanford) to help implement ideas on multiple OS platforms –V. Cerf, R. Kahn “A protocol for packet network intercommunication” IEEE Transactions on Communications, May 1974 –TCP draft produced (includes IP) Dec ARPA sponsors 3 groups to implement on hosts –Stanford (Cerf), BBN (Tomlinson), UCL (Kirstein) –All interoperate IP later separated (not all apps need reliability) –UDP added

29 Internetting IP –Internet Protocol (Sept. 1981) Postel – TCP –Transmission Control Protocol (Sept. 1981) Postel – Initial applications –Goal is resource sharing of systems on ARPANET File transfer Remote login (telnet) Packet voice, packet video (late 1970s)

30 Internetting NCP replaced by TCP/IP ( ) –Implementations of TCP/IP on many platforms (Clark) –Mandate from to switch all users on ARPANET from NCP to TCP/IP (1980) Not well received One-day shutoff of NCP in mid-1982 makes people angry, but not sufficiently convincing January 1983: NCP banned from ARPANET Some older computers allowed to operate with old NCP for a short time Full transition takes several months, finishes at end of 1983 “I survived the TCP/IP transition” buttons (Y2K bug?) –MILNET created for military