CS 4119: Computer Networks Prof. Henning Schulzrinne Dept. of Computer Science Columbia University http://www.cs.columbia....
Why learn about computer networks? <ul><li>Almost all modern software applications are distributed </li></ul><ul><ul><li>f...
CS4119 as Foundation <ul><li>Lots of Columbia Computer Science classes build on this: </li></ul><ul><ul><li>COMS 4180  Net...
Course Information <ul><li>Introductory  (first) course in computer networking </li></ul><ul><li>Who is this course for? <...
Course Information (more) <ul><li>Class WWW site:  http://www.cs.columbia.edu/4119 </li></ul><ul><li>Web bulletin board </...
Teaching assistants <ul><li>Sangho Shin  <ss2020@cs.columbia.edu>   </li></ul><ul><li>Manmohan Voniyadka  <mv2147@cs.colum...
Honesty policy <ul><li>See  http:// www.cs.columbia.edu /academics/honesty </li></ul><ul><li>Please read and ask if questi...
A bit about myself <ul><li>UMass Amherst (student of Jim Kurose’s…), Bell Labs, GMD Fokus (now Fraunhofer), Columbia Unive...
Part 1: Introduction <ul><li>What is the Internet? </li></ul><ul><li>What is a protocol?  </li></ul><ul><li>The network ed...
Part 2: Application Layer <ul><li>Principles of application-layer protocols  </li></ul><ul><li>The World Wide Web: HTTP  <...
Part 3: Transport Layer <ul><li>Transport-layer services and principles  </li></ul><ul><li>Multiplexing and demultiplexing...
Part 4: Network Layer <ul><li>Introduction and network service model  </li></ul><ul><li>Routing principles  </li></ul><ul>...
Part 5: Link Layer & LANs <ul><li>Introduction, services  </li></ul><ul><li>Error detection and correction  </li></ul><ul>...
Time permitting <ul><li>Security </li></ul><ul><ul><li>see  Network Security </li></ul></ul><ul><li>Multicast </li></ul><u...
Part I: Introduction <ul><li>Our goal:   </li></ul><ul><li>get context, overview, “feel” of networking </li></ul><ul><li>m...
What is a network? Main Entry:  1 net·work      Pronunciation: 'net-&quot;w&rk Function:  noun Date: 1560 1   :  a fabric ...
Communication Link Network
What’s the Internet: “nuts and bolts” view <ul><li>millions of connected computing devices:  hosts, end-systems </li></ul>...
What’s the Internet: “nuts and bolts” view <ul><li>protocols :  control sending, receiving of messages </li></ul><ul><ul><...
Internet Standardization <ul><li>International Telecommunications Union (ITU) </li></ul><ul><ul><li>United Nations treaty ...
IETF <ul><li>Open membership </li></ul><ul><li>Meets three times a year, about 2,000+ people </li></ul><ul><li>Most work d...
What’s the Internet: a service view <ul><li>communication  infrastructure  enables distributed applications: </li></ul><ul...
What’s a protocol? <ul><li>human protocols: </li></ul><ul><li>“ what’s the time?” </li></ul><ul><li>“ I have a question” <...
What’s a protocol? <ul><li>a human protocol and a computer network protocol: </li></ul>Q:  Other human protocol?  Hi Hi TC...
A closer look at network structure <ul><li>network edge:  applications and hosts </li></ul><ul><li>network core:   </li></...
The network edge <ul><li>end systems (hosts): </li></ul><ul><ul><li>run application programs </li></ul></ul><ul><ul><li>e....
Network edge: connection-oriented service <ul><li>Goal:  data transfer between end sys. </li></ul><ul><li>handshaking:  se...
Network edge: connectionless service <ul><li>Goal: data transfer between end systems </li></ul><ul><ul><li>same as before!...
The Network Core <ul><li>mesh of interconnected routers </li></ul><ul><li>the  fundamental question:  how is data transfer...
Network Core: Circuit Switching <ul><li>End-end resources reserved for “call” </li></ul><ul><li>link bandwidth,  switch ca...
Network Core: Circuit Switching <ul><li>network resources (e.g., bandwidth)  divided into “pieces” </li></ul><ul><li>piece...
Circuit Switching: FDM and TDM FDM frequency time TDM frequency time 4 users Example:
Aside: spectrum <ul><li>AM: 535 kHz to 1.7 MHz </li></ul><ul><li>TV: 54-88 (VHF, channels 2-6) and 174-220 (UHF, channels ...
Numerical example <ul><li>How long does it take to send a file of 640,000 bits from host A to host B over a circuit-switch...
Network Core: Packet Switching <ul><li>each end-end data stream divided into  packets </li></ul><ul><li>user A, B packets ...
Network Core: Packet Switching <ul><li>Packet-switching:  </li></ul><ul><li>store and forward behavior </li></ul>
Packet Switching: Statistical Multiplexing <ul><li>Sequence of A & B packets does not have fixed pattern     statistical ...
Packet switching versus circuit switching <ul><li>1 Mb/s link </li></ul><ul><li>each user:  </li></ul><ul><ul><li>100 kb/s...
Packet-switching: store-and-forward <ul><li>Takes  L/R  seconds to transmit (push out) packet of  L  bits on to link or  R...
Packet switching versus circuit switching <ul><li>Great for bursty data </li></ul><ul><ul><li>resource sharing – go as fas...
Reality: a hybrid of CO and CL End-to-end Datagram (UDP) End-to-end  Connection (TCP) Datagram (IP) Virtual Circuit (ATM, ...
Packet-switched networks: routing <ul><li>Goal:  move packets among routers from source to destination </li></ul><ul><ul><...
Network Taxonomy Telecommunication networks <ul><li>Datagram network is  not  either connection-oriented  </li></ul><ul><l...
Chapter 1: roadmap <ul><ul><li>1.1  What  is  the Internet? </li></ul></ul><ul><ul><li>1.2  Network edge </li></ul></ul><u...
Access networks and physical media <ul><li>Q: How to connection end systems to edge router? </li></ul><ul><li>residential ...
Residential access: point to point access <ul><li>Dialup via modem </li></ul><ul><ul><li>up to 56Kbps direct access to rou...
Residential access: cable modems <ul><li>HFC: hybrid fiber coax </li></ul><ul><ul><li>asymmetric: up to 10 Mb/s upstream, ...
Residential access: cable modems Diagram: http://www.cabledatacomnews.com/cmic/diagram.html
Cable Network Architecture: Overview home cable headend cable distribution network (simplified) Typically 500 to 5,000 homes
Cable Network Architecture: Overview home cable headend cable distribution network (simplified)
Cable Network Architecture: Overview home cable headend cable distribution network server(s)
Cable Network Architecture: Overview home cable headend cable distribution network FDM: Channels V I D E O V I D E O V I D...
Institutional access: local area networks <ul><li>company/university  local area network  (LAN) connects end system to edg...
Wireless access networks <ul><li>shared  wireless  access network connects end system to router </li></ul><ul><li>wireless...
Home networks <ul><li>Typical home network components:  </li></ul><ul><li>ADSL or cable modem </li></ul><ul><li>router/fir...
Physical Media <ul><li>physical link:  transmitted data bit propagates across link </li></ul><ul><li>guided media:   </li>...
Physical Media: coax, fiber <ul><li>Coaxial cable: </li></ul><ul><li>wire (signal carrier) within a wire (shield) </li></u...
Physical media: radio <ul><li>signal carried in electromagnetic spectrum </li></ul><ul><li>no physical “wire” </li></ul><u...
Other network media <ul><li>Power lines </li></ul><ul><li>Home phone lines – bus vs. star </li></ul><ul><li>Infrared (IR) ...
<ul><li>Capacity has theoretical limit </li></ul><ul><ul><li>Shannon’s Law: capacity limit given by  </li></ul></ul><ul><u...
Internet structure: network of networks <ul><li>roughly hierarchical </li></ul><ul><li>at center: “tier-1” ISPs  (e.g., UU...
Tier-1 ISP: e.g., Sprint Sprint US backbone network
Internet structure: network of networks <ul><li>“ Tier-2” ISPs: smaller (often regional) ISPs </li></ul><ul><ul><li>Connec...
Internet structure: network of networks <ul><li>“ Tier-3” ISPs and local ISPs  </li></ul><ul><ul><li>last hop (“access”) n...
Internet structure: network of networks <ul><li>a packet passes through many networks! </li></ul>Tier 1 ISP Tier 1 ISP Tie...
National Backbone Provider e.g. Genuity/GTE US backbone network
Internet2 weather map
How big is the Internet? “ The Domain Survey attempts to discover every host on the Internet by doing a complete search of...
Chapter 1: roadmap <ul><ul><li>1.1  What  is  the Internet? </li></ul></ul><ul><ul><li>1.2  Network edge </li></ul></ul><u...
How do loss and delay occur? <ul><li>packets  queue  in router buffers   </li></ul><ul><li>packet arrival rate to link exc...
Four sources of packet delay <ul><li>1. nodal processing:   </li></ul><ul><ul><li>check bit errors </li></ul></ul><ul><ul>...
Delay in packet-switched networks <ul><li>3. Transmission delay: </li></ul><ul><li>R=link bandwidth (bps) </li></ul><ul><l...
Caravan analogy <ul><li>Cars “propagate” at  100 km/hr </li></ul><ul><li>Toll booth takes 12 sec to service a car (transmi...
Caravan analogy (more) <ul><li>Cars now “propagate” at  1000 km/hr </li></ul><ul><li>Toll booth now takes 1 min to service...
Nodal delay <ul><li>d proc  = processing delay </li></ul><ul><ul><li>typically a few microseconds or less </li></ul></ul><...
Queueing delay (revisited) <ul><li>R=link bandwidth (b/s) </li></ul><ul><li>L=packet length (bits) </li></ul><ul><li>a=ave...
“ Real” Internet delays and routes <ul><li>What do “real” Internet delay & loss look like?  </li></ul><ul><li>Traceroute  ...
“ Real” Internet delays and routes 1  cs-gw (128.119.240.254)  1 ms  1 ms  2 ms 2  border1-rt-fa5-1-0.gw.umass.edu (128.11...
Traceroute: NJ (DSL) to Columbia Tracing route to www.cs.columbia.edu [128.59.23.100] over a maximum of 30 hops: 1  1 ms  ...
Packet loss <ul><li>queue (aka buffer) preceding link in buffer has finite capacity </li></ul><ul><li>when packet arrives ...
Chapter 1: roadmap <ul><ul><li>1.1  What  is  the Internet? </li></ul></ul><ul><ul><li>1.2  Network edge </li></ul></ul><u...
Protocol “Layers” <ul><li>Networks are complex!  </li></ul><ul><li>many “pieces”: </li></ul><ul><ul><li>hosts </li></ul></...
Organization of air travel <ul><li>a series of steps </li></ul>ticket (purchase) baggage (check) gates (load) runway takeo...
Layering of airline functionality <ul><li>Layers:  each layer implements a service </li></ul><ul><ul><li>via its own inter...
Why layering? <ul><li>Dealing with complex systems: </li></ul><ul><li>explicit structure allows identification, relationsh...
Internet protocol stack <ul><li>application:  supporting network applications </li></ul><ul><ul><li>FTP, SMTP, STTP </li><...
Internet protocols <ul><li>In addition, many “supporting actors” </li></ul><ul><ul><li>mapping various identifiers: number...
Example: Cisco 7960 phones <ul><li>Used in CS department </li></ul><ul><li>Protocols implemented: </li></ul><ul><ul><li>DH...
Encapsulation message segment datagram frame source application transport network link physical destination application tr...
Chapter 1: roadmap <ul><ul><li>1.1  What  is  the Internet? </li></ul></ul><ul><ul><li>1.2  Network edge </li></ul></ul><u...
Internet History <ul><li>1961:  Len Kleinrock - queuing theory shows effectiveness of packet-switching </li></ul><ul><li>1...
Internet History <ul><li>1970:  ALOHAnet satellite network in Hawaii </li></ul><ul><li>1973:  Metcalfe’s PhD thesis propos...
Internet History <ul><li>1983:  deployment of TCP/IP </li></ul><ul><li>1982:  smtp e-mail protocol defined  </li></ul><ul>...
Internet History <ul><li>Early 1990’s: ARPAnet decommissioned </li></ul><ul><li>1991: NSF lifts restrictions on commercial...
Introduction: Summary <ul><li>Covered a “ton” of material! </li></ul><ul><li>Internet overview </li></ul><ul><li>what’s a ...
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  • Two simple multiple access control techniques. Each mobile’s share of the bandwidth is divided into portions for the uplink and the downlink. Also, possibly, out of band signaling. As we will see, used in AMPS, GSM, IS-54/136
  • 4119-lec1.ppt

    1. 1. CS 4119: Computer Networks Prof. Henning Schulzrinne Dept. of Computer Science Columbia University http://www.cs.columbia.edu/~hgs slides based on material by Jim Kurose and Keith Ross, © 1996-2004 used by permission, with extensions by H. Schulzrinne
    2. 2. Why learn about computer networks? <ul><li>Almost all modern software applications are distributed </li></ul><ul><ul><li>from enterprise applications to video games </li></ul></ul><ul><li>General useful principles: </li></ul><ul><ul><li>dealing with asynchronicity </li></ul></ul><ul><ul><li>unreliable components  predictable end systems </li></ul></ul><ul><ul><li>(network) life is random and unpredictable </li></ul></ul><ul><ul><li>work with other implementations that you have never met before </li></ul></ul><ul><li>Theory: </li></ul><ul><ul><li>congestion control </li></ul></ul><ul><ul><li>routing </li></ul></ul><ul><li>How does the world really work? </li></ul><ul><ul><li>email, the web, P2P applications, DSL, … </li></ul></ul><ul><li>Learning to create professional-grade network applications </li></ul><ul><ul><li>not just use libraries as black boxes </li></ul></ul>
    3. 3. CS4119 as Foundation <ul><li>Lots of Columbia Computer Science classes build on this: </li></ul><ul><ul><li>COMS 4180 Network Security </li></ul></ul><ul><ul><li>COMS 6181 Advanced Internet Services </li></ul></ul><ul><ul><li>COMS 6998 Advanced Internet Routing </li></ul></ul><ul><ul><li>COMS 6180 Modeling & Performance Evaluation </li></ul></ul><ul><ul><li>COMS 6125 Web-enhanced Information Management </li></ul></ul><ul><ul><li>ELEN 6950 & 6951 Wireless & Mobile Networks </li></ul></ul><ul><ul><li>+ projects in a variety of research groups </li></ul></ul>
    4. 4. Course Information <ul><li>Introductory (first) course in computer networking </li></ul><ul><li>Who is this course for? </li></ul><ul><ul><li>Undergraduates (senior) </li></ul></ul><ul><ul><li>MS students </li></ul></ul><ul><ul><li>first-year PhD students </li></ul></ul><ul><li>Prerequisites: </li></ul><ul><ul><li>Algorithms, operating systems, programming skills in C </li></ul></ul><ul><li>Course materials: </li></ul><ul><ul><li>text: Computer Networking: A Top Down Approach Featuring the Internet , Jim Kurose & Keith Ross, Addison Wesley, 3rd edition 2005 </li></ul></ul><ul><ul><li>web readings </li></ul></ul><ul><ul><li>class notes at http://www.cs.columbia.edu/4119 </li></ul></ul>
    5. 5. Course Information (more) <ul><li>Class WWW site: http://www.cs.columbia.edu/4119 </li></ul><ul><li>Web bulletin board </li></ul><ul><li>Workload </li></ul>20% 1 midterm 30% 1 final exam 10% 1-2 lab assignments 20% 3 programming assignments 20% 4 written homework assignments
    6. 6. Teaching assistants <ul><li>Sangho Shin <ss2020@cs.columbia.edu> </li></ul><ul><li>Manmohan Voniyadka <mv2147@cs.columbia.edu> </li></ul><ul><li>Office hours TBA </li></ul>
    7. 7. Honesty policy <ul><li>See http:// www.cs.columbia.edu /academics/honesty </li></ul><ul><li>Please read and ask if questions </li></ul>
    8. 8. A bit about myself <ul><li>UMass Amherst (student of Jim Kurose’s…), Bell Labs, GMD Fokus (now Fraunhofer), Columbia University </li></ul><ul><li>Research interest in networking (IRT research group at Columbia) </li></ul><ul><ul><li>performance and reliability </li></ul></ul><ul><ul><li>multimedia systems </li></ul></ul><ul><ul><li>security </li></ul></ul><ul><li>Active in Internet protocol standardization </li></ul><ul><ul><li>IETF, NENA </li></ul></ul>
    9. 9. Part 1: Introduction <ul><li>What is the Internet? </li></ul><ul><li>What is a protocol? </li></ul><ul><li>The network edge, core, and access networks </li></ul><ul><li>Physical media </li></ul><ul><li>Delay and loss in Packet-Switched Networks </li></ul><ul><li>Protocol layers, service models </li></ul><ul><li>Internet backbones, NAPs and ISPs </li></ul><ul><li>Standardization </li></ul><ul><li>A brief history of computer networking & Internet </li></ul>
    10. 10. Part 2: Application Layer <ul><li>Principles of application-layer protocols </li></ul><ul><li>The World Wide Web: HTTP </li></ul><ul><li>File transfer: FTP </li></ul><ul><li>Electronic mail in the Internet </li></ul><ul><li>The Internet's directory dervice: DNS </li></ul><ul><li>Socket programming </li></ul>
    11. 11. Part 3: Transport Layer <ul><li>Transport-layer services and principles </li></ul><ul><li>Multiplexing and demultiplexing applications </li></ul><ul><li>Connectionless transport: UDP </li></ul><ul><li>Principles of reliable of data transfer </li></ul><ul><li>TCP case study </li></ul><ul><li>Principles of congestion control </li></ul><ul><li>TCP congestion control </li></ul>
    12. 12. Part 4: Network Layer <ul><li>Introduction and network service model </li></ul><ul><li>Routing principles </li></ul><ul><li>Hierarchical routing </li></ul><ul><li>IP: the Internet Protocol </li></ul><ul><li>Routing in the Internet </li></ul><ul><li>What is inside a router? </li></ul>
    13. 13. Part 5: Link Layer & LANs <ul><li>Introduction, services </li></ul><ul><li>Error detection and correction </li></ul><ul><li>Multiple access protocols and LANs </li></ul><ul><li>LAN addresses and ARP </li></ul><ul><li>Ethernet </li></ul><ul><li>Hubs, Bridges and Switches </li></ul><ul><li>Wireless LANs: IEEE 802.11 </li></ul><ul><li>PPP: the Point-to-Point Protocol </li></ul><ul><li>ATM </li></ul>
    14. 14. Time permitting <ul><li>Security </li></ul><ul><ul><li>see Network Security </li></ul></ul><ul><li>Multicast </li></ul><ul><li>Overlay and peer-to-peer networks </li></ul><ul><li>Multimedia </li></ul><ul><ul><li>see Advanced Internet Services </li></ul></ul>
    15. 15. Part I: Introduction <ul><li>Our goal: </li></ul><ul><li>get context, overview, “feel” of networking </li></ul><ul><li>more depth, detail later in course </li></ul><ul><li>approach: </li></ul><ul><ul><li>descriptive </li></ul></ul><ul><ul><li>use Internet as example </li></ul></ul><ul><li>Overview: </li></ul><ul><li>what’s the Internet </li></ul><ul><li>what’s a protocol? </li></ul><ul><li>network edge </li></ul><ul><li>network core </li></ul><ul><li>access net, physical media </li></ul><ul><li>performance: loss, delay </li></ul><ul><li>protocol layers, service models </li></ul><ul><li>backbones, NAPs, ISPs </li></ul><ul><li>history </li></ul>
    16. 16. What is a network? Main Entry: 1 net·work    Pronunciation: 'net-&quot;w&rk Function: noun Date: 1560 1 : a fabric or structure of cords or wires that cross at regular intervals and are knotted or secured at the crossings 2 : a system of lines or channels resembling a network 3 a : an interconnected or interrelated chain, group, or system <a network of hotels> b : a system of computers, terminals, and databases connected by communications lines 4 a : a group of radio or television stations linked by wire or radio relay b : a radio or television company that produces programs for broadcast over such a network
    17. 17. Communication Link Network
    18. 18. What’s the Internet: “nuts and bolts” view <ul><li>millions of connected computing devices: hosts, end-systems </li></ul><ul><ul><li>pc’s workstations, servers </li></ul></ul><ul><ul><li>PDA’s phones, toasters </li></ul></ul><ul><ul><li>running network apps </li></ul></ul><ul><li>communication links </li></ul><ul><ul><li>fiber, copper, radio, satellite </li></ul></ul><ul><li>routers: forward packets (chunks) of data thru network </li></ul>local ISP company network regional ISP router workstation server mobile
    19. 19. What’s the Internet: “nuts and bolts” view <ul><li>protocols : control sending, receiving of messages </li></ul><ul><ul><li>e.g., TCP, IP, HTTP, FTP, PPP </li></ul></ul><ul><li>Internet: “network of networks” </li></ul><ul><ul><li>loosely hierarchical </li></ul></ul><ul><ul><li>public Internet versus private intranet </li></ul></ul><ul><li>Internet standards </li></ul><ul><ul><li>RFC: Request for comments </li></ul></ul><ul><ul><li>IETF: Internet Engineering Task Force </li></ul></ul>local ISP company network regional ISP router workstation server mobile
    20. 20. Internet Standardization <ul><li>International Telecommunications Union (ITU) </li></ul><ul><ul><li>United Nations treaty organization </li></ul></ul><ul><ul><li>Transmission standards (e.g., modem: V.90) </li></ul></ul><ul><ul><li>Traditional telephone services, fax </li></ul></ul><ul><li>Internet Engineering Task Force (IETF) </li></ul><ul><ul><li>Core: Internet Protocol, transport (TCP) </li></ul></ul><ul><ul><li>Applications: email, HTTP, ftp, ssh, NFS, VoIP </li></ul></ul><ul><ul><li>Not: HTML, APIs </li></ul></ul><ul><li>W3C </li></ul><ul><ul><li>HTML, XML, schema, SOAP, semantic web, … </li></ul></ul><ul><li>OASIS </li></ul><ul><ul><li>XML schema for specific applications </li></ul></ul><ul><li>Lots of other organizations: component vs. system engineering </li></ul>
    21. 21. IETF <ul><li>Open membership </li></ul><ul><li>Meets three times a year, about 2,000+ people </li></ul><ul><li>Most work done on mailing lists (see www.ietf.org) </li></ul><ul><li>Working groups produce technology </li></ul><ul><li>No formal voting at WG level, but review by “area directors” </li></ul><ul><li>Emphasis on interoperability and deployment </li></ul><ul><li>Internet drafts  Proposed Standard (RFC) </li></ul><ul><li>See www.rfc-editor.org for RFC directory </li></ul>
    22. 22. What’s the Internet: a service view <ul><li>communication infrastructure enables distributed applications: </li></ul><ul><ul><li>WWW, email, games, e-commerce, databases, voting, telephony, multimedia, IM, … </li></ul></ul><ul><ul><li>more? </li></ul></ul><ul><li>communication services provided: </li></ul><ul><ul><li>connectionless </li></ul></ul><ul><ul><li>connection-oriented </li></ul></ul><ul><li>cyberspace [Gibson]: </li></ul><ul><ul><li>“ a consensual hallucination experienced daily by billions of operators, in every nation, ....&quot; </li></ul></ul>
    23. 23. What’s a protocol? <ul><li>human protocols: </li></ul><ul><li>“ what’s the time?” </li></ul><ul><li>“ I have a question” </li></ul><ul><li>introductions </li></ul><ul><li>… specific msgs sent </li></ul><ul><li>… specific actions taken when msgs received, or other events </li></ul><ul><li>network protocols: </li></ul><ul><li>machines rather than humans </li></ul><ul><li>all communication activity in Internet governed by protocols </li></ul>Protocols define format & order of messages sent and received among network entities, and actions taken on message transmission and receipt .
    24. 24. What’s a protocol? <ul><li>a human protocol and a computer network protocol: </li></ul>Q: Other human protocol? Hi Hi TCP connection req. Got the time? 2:00 TCP connection reply. Get http://www.cs.columbia.edu/index.html <file> time
    25. 25. A closer look at network structure <ul><li>network edge: applications and hosts </li></ul><ul><li>network core: </li></ul><ul><ul><li>routers </li></ul></ul><ul><ul><li>network of networks </li></ul></ul><ul><li>access networks, physical media: communication links </li></ul>
    26. 26. The network edge <ul><li>end systems (hosts): </li></ul><ul><ul><li>run application programs </li></ul></ul><ul><ul><li>e.g., WWW, email </li></ul></ul><ul><ul><li>at “edge of network” </li></ul></ul><ul><li>client/server model </li></ul><ul><ul><li>client host requests, receives service from server </li></ul></ul><ul><ul><li>e.g., WWW client (browser)/ server; email client/server </li></ul></ul><ul><li>peer-peer model: </li></ul><ul><ul><li>host interaction symmetric </li></ul></ul><ul><ul><li>host can act as both client and server or no real request/response notion </li></ul></ul><ul><ul><li>e.g.: teleconferencing </li></ul></ul>
    27. 27. Network edge: connection-oriented service <ul><li>Goal: data transfer between end sys. </li></ul><ul><li>handshaking: setup (prepare for) data transfer ahead of time </li></ul><ul><ul><li>Hello, hello back human protocol </li></ul></ul><ul><ul><li>set up “state” in two communicating hosts </li></ul></ul><ul><li>TCP - Transmission Control Protocol </li></ul><ul><ul><li>Internet’s connection-oriented service </li></ul></ul><ul><li>TCP service [RFC 793] </li></ul><ul><li>reliable, in-order byte-stream data transfer </li></ul><ul><ul><li>loss: acknowledgements and retransmissions </li></ul></ul><ul><li>flow control: </li></ul><ul><ul><li>sender won’t overwhelm receiver </li></ul></ul><ul><li>congestion control: </li></ul><ul><ul><li>senders “slow down sending rate” when network congested </li></ul></ul>
    28. 28. Network edge: connectionless service <ul><li>Goal: data transfer between end systems </li></ul><ul><ul><li>same as before! </li></ul></ul><ul><li>UDP - User Datagram Protocol [RFC 768]: Internet’s connectionless service </li></ul><ul><ul><li>unreliable data transfer </li></ul></ul><ul><ul><li>no flow control </li></ul></ul><ul><ul><li>no congestion control </li></ul></ul><ul><li>Applications using TCP: </li></ul><ul><ul><li>HTTP (WWW), FTP (file transfer), ssh (remote login), SMTP (email) </li></ul></ul><ul><li>Applications using UDP: </li></ul><ul><ul><li>streaming media </li></ul></ul><ul><ul><li>teleconferencing, Internet telephony </li></ul></ul>
    29. 29. The Network Core <ul><li>mesh of interconnected routers </li></ul><ul><li>the fundamental question: how is data transferred through net? </li></ul><ul><ul><li>circuit switching: dedicated circuit per call: telephone net </li></ul></ul><ul><ul><li>message switching: application units </li></ul></ul><ul><ul><li>packet-switching: data sent thru net in discrete “chunks” </li></ul></ul>
    30. 30. Network Core: Circuit Switching <ul><li>End-end resources reserved for “call” </li></ul><ul><li>link bandwidth, switch capacity </li></ul><ul><li>dedicated resources: no sharing </li></ul><ul><li>circuit-like (guaranteed) performance </li></ul><ul><li>call setup required </li></ul>
    31. 31. Network Core: Circuit Switching <ul><li>network resources (e.g., bandwidth) divided into “pieces” </li></ul><ul><li>pieces allocated to calls </li></ul><ul><li>resource piece idle if not used by owning call (no sharing) </li></ul><ul><li>dividing link bandwidth into “pieces” </li></ul><ul><ul><li>frequency division </li></ul></ul><ul><ul><li>time division </li></ul></ul><ul><ul><li>space division </li></ul></ul>
    32. 32. Circuit Switching: FDM and TDM FDM frequency time TDM frequency time 4 users Example:
    33. 33. Aside: spectrum <ul><li>AM: 535 kHz to 1.7 MHz </li></ul><ul><li>TV: 54-88 (VHF, channels 2-6) and 174-220 (UHF, channels 7-13) </li></ul><ul><li>Unlicensed vs. licensed </li></ul><ul><ul><li>cell phone (800 MHz, 1800/1900 MHz) </li></ul></ul><ul><ul><li>Wi-Fi (2.4 GHz, 5 GHz) </li></ul></ul>
    34. 34. Numerical example <ul><li>How long does it take to send a file of 640,000 bits from host A to host B over a circuit-switched network? </li></ul><ul><ul><li>All links are 1.536 Mb/s </li></ul></ul><ul><ul><li>Each link uses TDM with 24 slots </li></ul></ul><ul><ul><li>500 ms to establish end-to-end circuit </li></ul></ul><ul><li>Work it out! </li></ul>
    35. 35. Network Core: Packet Switching <ul><li>each end-end data stream divided into packets </li></ul><ul><li>user A, B packets share network resources </li></ul><ul><li>each packet uses full link bandwidth </li></ul><ul><li>resources used as needed , </li></ul><ul><li>resource contention: </li></ul><ul><li>aggregate resource demand can exceed amount available </li></ul><ul><li>congestion: packets queue, wait for link use </li></ul><ul><li>store and forward: packets move one hop at a time </li></ul><ul><ul><li>transmit over link </li></ul></ul><ul><ul><li>wait turn at next link </li></ul></ul>Bandwidth division into “pieces” Dedicated allocation Resource reservation
    36. 36. Network Core: Packet Switching <ul><li>Packet-switching: </li></ul><ul><li>store and forward behavior </li></ul>
    37. 37. Packet Switching: Statistical Multiplexing <ul><li>Sequence of A & B packets does not have fixed pattern  statistical multiplexing . </li></ul><ul><li>In TDM each host gets same slot in revolving TDM frame. </li></ul>A B C 10 Mb/s Ethernet 1.5 Mb/s statistical multiplexing queue of packets waiting for output link D E
    38. 38. Packet switching versus circuit switching <ul><li>1 Mb/s link </li></ul><ul><li>each user: </li></ul><ul><ul><li>100 kb/s when “active” </li></ul></ul><ul><ul><li>active 10% of time </li></ul></ul><ul><li>circuit-switching: </li></ul><ul><ul><li>10 users </li></ul></ul><ul><li>packet switching: </li></ul><ul><ul><li>with 35 users, probability > 10 active less that .004 </li></ul></ul><ul><li>Packet switching allows more users to use network! </li></ul>N users 1 Mb/s link
    39. 39. Packet-switching: store-and-forward <ul><li>Takes L/R seconds to transmit (push out) packet of L bits on to link or R b/s </li></ul><ul><li>Entire packet must arrive at router before it can be transmitted on next link: store and forward </li></ul><ul><li>delay = 3L/R </li></ul><ul><li>Example: </li></ul><ul><li>L = 7.5 Mbits </li></ul><ul><li>R = 1.5 Mb/s </li></ul><ul><li>delay = 15 sec </li></ul>R R R L
    40. 40. Packet switching versus circuit switching <ul><li>Great for bursty data </li></ul><ul><ul><li>resource sharing – go as fast as you can and then get out of the way </li></ul></ul><ul><ul><li>no call setup </li></ul></ul><ul><li>Excessive congestion: packet delay and loss </li></ul><ul><ul><li>protocols needed for reliable data transfer, congestion control </li></ul></ul><ul><ul><li>GWB at rush hour  everybody loses </li></ul></ul><ul><li>Q: How to provide circuit-like behavior? </li></ul><ul><ul><li>prioritization </li></ul></ul><ul><ul><li>bandwidth guarantees needed for audio/video apps </li></ul></ul><ul><ul><li>still an unsolved problem (chapter 6) </li></ul></ul><ul><li>Is packet switching a “slam dunk winner?” </li></ul>
    41. 41. Reality: a hybrid of CO and CL End-to-end Datagram (UDP) End-to-end Connection (TCP) Datagram (IP) Virtual Circuit (ATM, MPLS) Circuit (SONET) FDM TDM message switching (SMTP, IM)
    42. 42. Packet-switched networks: routing <ul><li>Goal: move packets among routers from source to destination </li></ul><ul><ul><li>we’ll study several path selection algorithms (chapter 4) </li></ul></ul><ul><li>datagram network: </li></ul><ul><ul><li>destination address determines next hop </li></ul></ul><ul><ul><li>routes may change during session </li></ul></ul><ul><ul><li>analogy: driving, asking directions </li></ul></ul><ul><li>virtual circuit network: </li></ul><ul><ul><li>each packet carries tag (virtual circuit ID), tag determines next hop </li></ul></ul><ul><ul><li>fixed path determined at call setup time , remains fixed thru call </li></ul></ul><ul><ul><li>routers maintain per-call state </li></ul></ul>
    43. 43. Network Taxonomy Telecommunication networks <ul><li>Datagram network is not either connection-oriented </li></ul><ul><li>or connectionless. </li></ul><ul><li>Internet provides both connection-oriented (TCP) and </li></ul><ul><li>connectionless services (UDP) to apps. </li></ul>Circuit-switched networks FDM TDM Packet-switched networks Networks with VCs Datagram Networks
    44. 44. Chapter 1: roadmap <ul><ul><li>1.1 What is the Internet? </li></ul></ul><ul><ul><li>1.2 Network edge </li></ul></ul><ul><ul><li>1.3 Network core </li></ul></ul><ul><ul><li>1.4 Network access and physical media </li></ul></ul><ul><ul><li>1.5 Internet structure and ISPs </li></ul></ul><ul><ul><li>1.6 Delay & loss in packet-switched networks </li></ul></ul><ul><ul><li>1.7 Protocol layers, service models </li></ul></ul><ul><ul><li>1.8 History </li></ul></ul>
    45. 45. Access networks and physical media <ul><li>Q: How to connection end systems to edge router? </li></ul><ul><li>residential access nets </li></ul><ul><li>institutional access networks (school, company) </li></ul><ul><li>mobile access networks </li></ul><ul><li>Keep in mind: </li></ul><ul><li>bandwidth (bits per second) of access network? </li></ul><ul><li>shared or dedicated? </li></ul>
    46. 46. Residential access: point to point access <ul><li>Dialup via modem </li></ul><ul><ul><li>up to 56Kbps direct access to router (often less) </li></ul></ul><ul><ul><li>Can’t surf and phone at same time: can’t be “always on” </li></ul></ul><ul><li>ADSL: asymmetric digital subscriber line </li></ul><ul><ul><li>up to 1 Mb/s upstream (today typically < 256 kb/s) </li></ul></ul><ul><ul><li>up to 8 Mb/s downstream (today typically < 1 Mb/s) </li></ul></ul><ul><ul><li>FDM: 50 kHz - 1 MHz for downstream </li></ul></ul><ul><ul><li>4 kHz - 50 kHz for upstream </li></ul></ul><ul><ul><li>0 kHz - 4 kHz for ordinary telephone </li></ul></ul>
    47. 47. Residential access: cable modems <ul><li>HFC: hybrid fiber coax </li></ul><ul><ul><li>asymmetric: up to 10 Mb/s upstream, 1 Mb/s downstream </li></ul></ul><ul><li>network of cable and fiber attaches homes to ISP router </li></ul><ul><ul><li>shared access to router among home </li></ul></ul><ul><ul><li>issues: congestion, dimensioning </li></ul></ul><ul><li>deployment: available via cable companies </li></ul>
    48. 48. Residential access: cable modems Diagram: http://www.cabledatacomnews.com/cmic/diagram.html
    49. 49. Cable Network Architecture: Overview home cable headend cable distribution network (simplified) Typically 500 to 5,000 homes
    50. 50. Cable Network Architecture: Overview home cable headend cable distribution network (simplified)
    51. 51. Cable Network Architecture: Overview home cable headend cable distribution network server(s)
    52. 52. Cable Network Architecture: Overview home cable headend cable distribution network FDM: Channels V I D E O V I D E O V I D E O V I D E O V I D E O V I D E O D A T A D A T A C O N T R O L 1 2 3 4 5 6 7 8 9
    53. 53. Institutional access: local area networks <ul><li>company/university local area network (LAN) connects end system to edge router </li></ul><ul><li>Ethernet: </li></ul><ul><ul><li>shared or dedicated cable connects end system and router </li></ul></ul><ul><ul><li>10 Mb/s, 100 Mb/s for PCs and enterprise networks </li></ul></ul><ul><ul><li>Gigabit Ethernet (GigE) for servers </li></ul></ul><ul><ul><li>10 Gb/s for servers and backbones </li></ul></ul><ul><li>deployment: institutions, home LANs </li></ul><ul><ul><li>wide area emerging </li></ul></ul><ul><li>LANs: chapter 5 </li></ul>
    54. 54. Wireless access networks <ul><li>shared wireless access network connects end system to router </li></ul><ul><li>wireless LANs: </li></ul><ul><ul><li>radio spectrum replaces wire </li></ul></ul><ul><ul><li>e.g., 802.11 a/b/g/n </li></ul></ul><ul><ul><ul><li>nominally, 1 to 100 Mb/s </li></ul></ul></ul><ul><li>wider-area wireless access </li></ul><ul><ul><li>through cell phone network </li></ul></ul><ul><ul><li>CDPD: old, slow wireless access to ISP router via cellular network (fill speech gaps) -- obsolete </li></ul></ul><ul><ul><li>EVDO, 1xRTT: emerging </li></ul></ul>base station mobile hosts router
    55. 55. Home networks <ul><li>Typical home network components: </li></ul><ul><li>ADSL or cable modem </li></ul><ul><li>router/firewall/NAT </li></ul><ul><li>Ethernet </li></ul><ul><li>wireless access </li></ul><ul><li>point </li></ul>wireless access point wireless laptops router/ firewall cable modem to/from cable headend Ethernet
    56. 56. Physical Media <ul><li>physical link: transmitted data bit propagates across link </li></ul><ul><li>guided media: </li></ul><ul><ul><li>signals propagate in solid media: copper, fiber </li></ul></ul><ul><li>unguided media: </li></ul><ul><ul><li>signals propagate freely, e.g., radio </li></ul></ul><ul><li>Twisted Pair (TP) </li></ul><ul><li>two insulated copper wires </li></ul><ul><ul><li>Category 3: traditional phone wires, 10 Mb/s Ethernet </li></ul></ul><ul><ul><li>Category 5 TP: 100 Mb/s Ethernet </li></ul></ul><ul><ul><li>Category 6 TP: </li></ul></ul><ul><ul><ul><li>1 Gb/s Ethernet </li></ul></ul></ul>
    57. 57. Physical Media: coax, fiber <ul><li>Coaxial cable: </li></ul><ul><li>wire (signal carrier) within a wire (shield) </li></ul><ul><ul><li>baseband: single channel on cable </li></ul></ul><ul><ul><li>broadband: multiple channel on cable </li></ul></ul><ul><li>bidirectional </li></ul><ul><li>formerly common use in 10 Mb/s Ethernet </li></ul><ul><li>Fiber optic cable: </li></ul><ul><li>glass fiber carrying light pulses </li></ul><ul><li>typically dozens bundled into one cable </li></ul><ul><li>high-speed operation: </li></ul><ul><ul><li>100 Mb/s Ethernet </li></ul></ul><ul><ul><li>high-speed point-to-point transmission (e.g., 40 Gb/s) </li></ul></ul><ul><li>low error rate: repeaters spaced far apart; immune to electromagnetic noise </li></ul>
    58. 58. Physical media: radio <ul><li>signal carried in electromagnetic spectrum </li></ul><ul><li>no physical “wire” </li></ul><ul><li>bidirectional </li></ul><ul><li>propagation environment effects: </li></ul><ul><ul><li>reflection </li></ul></ul><ul><ul><li>obstruction by objects </li></ul></ul><ul><ul><li>interference </li></ul></ul><ul><li>Radio link types: </li></ul><ul><li>terrestrial microwave </li></ul><ul><ul><li>e.g. up to 45 Mb/s channels </li></ul></ul><ul><li>LAN (e.g., WiFi) </li></ul><ul><ul><li>2Mbps, 11Mb/s </li></ul></ul><ul><li>wide-area (e.g., cellular) </li></ul><ul><ul><li>e.g. 3G: hundreds of kb/s </li></ul></ul><ul><li>satellite </li></ul><ul><ul><li>up to 50 Mb/s channel (or multiple smaller channels) </li></ul></ul><ul><ul><li>270 msec end-end delay </li></ul></ul><ul><ul><li>geosynchronous versus low altitude (Iridium) </li></ul></ul>
    59. 59. Other network media <ul><li>Power lines </li></ul><ul><li>Home phone lines – bus vs. star </li></ul><ul><li>Infrared (IR) </li></ul><ul><li>BlueTooth – piconet </li></ul><ul><li>Serial lines (RS232, RS485) </li></ul><ul><li>Firewire (IEEE 1394) </li></ul>
    60. 60. <ul><li>Capacity has theoretical limit </li></ul><ul><ul><li>Shannon’s Law: capacity limit given by </li></ul></ul><ul><ul><li>C = B log 2 (1 + S/N) with spectral bandwidth B </li></ul></ul><ul><ul><li>E.g., phone has B = 3000 Hz, S/N = 35 dB, C = 34.8 kb/s </li></ul></ul><ul><ul><li>dB = </li></ul></ul><ul><ul><li>E.g., 25 dB = </li></ul></ul><ul><ul><li>Radio: typically 1 b/s per Hz of bandwidth </li></ul></ul><ul><li>Speed has physical limits: c in free space, 0.66 c in fiber </li></ul>Physical media: capacity
    61. 61. Internet structure: network of networks <ul><li>roughly hierarchical </li></ul><ul><li>at center: “tier-1” ISPs (e.g., UUNet, BBN/Genuity, Sprint, AT&T), national/international coverage </li></ul><ul><ul><li>treat each other as equals </li></ul></ul>Tier 1 ISP Tier 1 ISP Tier 1 ISP Tier-1 providers interconnect (peer) privately NAP Tier-1 providers also interconnect at public network access points (NAPs)
    62. 62. Tier-1 ISP: e.g., Sprint Sprint US backbone network
    63. 63. Internet structure: network of networks <ul><li>“ Tier-2” ISPs: smaller (often regional) ISPs </li></ul><ul><ul><li>Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs </li></ul></ul>Tier 1 ISP Tier 1 ISP Tier 1 ISP NAP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP <ul><li>Tier-2 ISP pays tier-1 ISP for connectivity to rest of Internet </li></ul><ul><li>tier-2 ISP is c ustomer of </li></ul><ul><li>tier-1 provider </li></ul>Tier-2 ISPs also peer privately with each other, interconnect at NAP
    64. 64. Internet structure: network of networks <ul><li>“ Tier-3” ISPs and local ISPs </li></ul><ul><ul><li>last hop (“access”) network (closest to end systems) </li></ul></ul>Tier 1 ISP Tier 1 ISP Tier 1 ISP NAP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP local ISP local ISP local ISP local ISP local ISP Tier 3 ISP local ISP local ISP local ISP Local and tier- 3 ISPs are customers of higher tier ISPs connecting them to rest of Internet
    65. 65. Internet structure: network of networks <ul><li>a packet passes through many networks! </li></ul>Tier 1 ISP Tier 1 ISP Tier 1 ISP NAP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP local ISP local ISP local ISP local ISP local ISP Tier 3 ISP local ISP local ISP local ISP
    66. 66. National Backbone Provider e.g. Genuity/GTE US backbone network
    67. 67. Internet2 weather map
    68. 68. How big is the Internet? “ The Domain Survey attempts to discover every host on the Internet by doing a complete search of the Domain Name System.”
    69. 69. Chapter 1: roadmap <ul><ul><li>1.1 What is the Internet? </li></ul></ul><ul><ul><li>1.2 Network edge </li></ul></ul><ul><ul><li>1.3 Network core </li></ul></ul><ul><ul><li>1.4 Network access and physical media </li></ul></ul><ul><ul><li>1.5 Internet structure and ISPs </li></ul></ul><ul><ul><li>1.6 Delay & loss in packet-switched networks </li></ul></ul><ul><ul><li>1.7 Protocol layers, service models </li></ul></ul><ul><ul><li>1.8 History </li></ul></ul>
    70. 70. How do loss and delay occur? <ul><li>packets queue in router buffers </li></ul><ul><li>packet arrival rate to link exceeds output link capacity </li></ul><ul><li>packets queue, wait for turn </li></ul>A B packet being transmitted (delay) packets queueing (delay) free (available) buffers: arriving packets dropped ( loss ) if no free buffers
    71. 71. Four sources of packet delay <ul><li>1. nodal processing: </li></ul><ul><ul><li>check bit errors </li></ul></ul><ul><ul><li>determine output link </li></ul></ul><ul><li>2. queueing </li></ul><ul><ul><li>time waiting at output link for transmission </li></ul></ul><ul><ul><li>depends on congestion level of router </li></ul></ul>A B propagation transmission nodal processing queueing
    72. 72. Delay in packet-switched networks <ul><li>3. Transmission delay: </li></ul><ul><li>R=link bandwidth (bps) </li></ul><ul><li>L=packet length (bits) </li></ul><ul><li>time to send bits into link = L/R </li></ul><ul><li>4. Propagation delay: </li></ul><ul><li>d = length of physical link </li></ul><ul><li>s = propagation speed in medium (~2x10 8 m/sec) </li></ul><ul><li>propagation delay = d/s </li></ul>Note: s and R are very different quantities! A B propagation transmission nodal processing queueing
    73. 73. Caravan analogy <ul><li>Cars “propagate” at 100 km/hr </li></ul><ul><li>Toll booth takes 12 sec to service a car (transmission time) </li></ul><ul><li>car~bit; caravan ~ packet </li></ul><ul><li>Q: How long until caravan is lined up before 2nd toll booth? </li></ul><ul><li>Time to “push” entire caravan through toll booth onto highway = 12*10 = 120 sec </li></ul><ul><li>Time for last car to propagate from 1st to 2nd toll both: 100km/(100km/hr)= 1 hr </li></ul><ul><li>A: 62 minutes </li></ul>ten-car caravan 100 km 100 km toll booth toll booth
    74. 74. Caravan analogy (more) <ul><li>Cars now “propagate” at 1000 km/hr </li></ul><ul><li>Toll booth now takes 1 min to service a car </li></ul><ul><li>Q: Will cars arrive to 2nd booth before all cars serviced at 1st booth? </li></ul><ul><li>Yes! After 7 min, 1st car at 2nd booth and 3 cars still at 1st booth. </li></ul><ul><li>1st bit of packet can arrive at 2nd router before packet is fully transmitted at 1st router! </li></ul><ul><ul><li>See Ethernet applet at AWL Web site </li></ul></ul>ten-car caravan 100 km 100 km toll booth toll booth
    75. 75. Nodal delay <ul><li>d proc = processing delay </li></ul><ul><ul><li>typically a few microseconds or less </li></ul></ul><ul><li>d queue = queuing delay </li></ul><ul><ul><li>depends on congestion </li></ul></ul><ul><li>d trans = transmission delay </li></ul><ul><ul><li>= L/R, significant for low-speed links </li></ul></ul><ul><li>d prop = propagation delay </li></ul><ul><ul><li>a few microsecs to hundreds of msecs </li></ul></ul>
    76. 76. Queueing delay (revisited) <ul><li>R=link bandwidth (b/s) </li></ul><ul><li>L=packet length (bits) </li></ul><ul><li>a=average packet arrival rate </li></ul>traffic intensity = La/R <ul><li>La/R ~ 0: average queueing delay small </li></ul><ul><li>La/R  1: delays become large </li></ul><ul><li>La/R > 1: more “work” arriving than can be serviced, average delay infinite! </li></ul>
    77. 77. “ Real” Internet delays and routes <ul><li>What do “real” Internet delay & loss look like? </li></ul><ul><li>Traceroute program: provides delay measurement from source to router along end-end Internet path towards destination. For all i: </li></ul><ul><ul><li>sends three packets that will reach router i on path towards destination </li></ul></ul><ul><ul><li>router i will return packets to sender </li></ul></ul><ul><ul><li>sender times interval between transmission and reply. </li></ul></ul>3 probes 3 probes 3 probes
    78. 78. “ Real” Internet delays and routes 1 cs-gw (128.119.240.254) 1 ms 1 ms 2 ms 2 border1-rt-fa5-1-0.gw.umass.edu (128.119.3.145) 1 ms 1 ms 2 ms 3 cht-vbns.gw.umass.edu (128.119.3.130) 6 ms 5 ms 5 ms 4 jn1-at1-0-0-19.wor.vbns.net (204.147.132.129) 16 ms 11 ms 13 ms 5 jn1-so7-0-0-0.wae.vbns.net (204.147.136.136) 21 ms 18 ms 18 ms 6 abilene-vbns.abilene.ucaid.edu (198.32.11.9) 22 ms 18 ms 22 ms 7 nycm-wash.abilene.ucaid.edu (198.32.8.46) 22 ms 22 ms 22 ms 8 62.40.103.253 (62.40.103.253) 104 ms 109 ms 106 ms 9 de2-1.de1.de.geant.net (62.40.96.129) 109 ms 102 ms 104 ms 10 de.fr1.fr.geant.net (62.40.96.50) 113 ms 121 ms 114 ms 11 renater-gw.fr1.fr.geant.net (62.40.103.54) 112 ms 114 ms 112 ms 12 nio-n2.cssi.renater.fr (193.51.206.13) 111 ms 114 ms 116 ms 13 nice.cssi.renater.fr (195.220.98.102) 123 ms 125 ms 124 ms 14 r3t2-nice.cssi.renater.fr (195.220.98.110) 126 ms 126 ms 124 ms 15 eurecom-valbonne.r3t2.ft.net (193.48.50.54) 135 ms 128 ms 133 ms 16 194.214.211.25 (194.214.211.25) 126 ms 128 ms 126 ms 17 * * * 18 * * * 19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136 ms traceroute: gaia.cs.umass.edu to www.eurecom.fr Three delay measements from gaia.cs.umass.edu to cs-gw.cs.umass.edu * means no reponse (probe lost, router not replying) trans-oceanic link
    79. 79. Traceroute: NJ (DSL) to Columbia Tracing route to www.cs.columbia.edu [128.59.23.100] over a maximum of 30 hops: 1 1 ms <1 ms <1 ms 192.168.0.1 2 15 ms 15 ms 15 ms 10.5.61.1 3 17 ms 19 ms 17 ms at-4-0-0-1713.CORE-RTR2.NWRK.verizon-gni.net [130.81.7.45] 4 18 ms 18 ms 18 ms 130.81.18.78 5 20 ms 20 ms 20 ms so-5-0-0-0.BB-RTR1.NY5030.verizon-gni.net [130.81.7.189] 6 17 ms 18 ms 18 ms so-7-0-0-0.BB-RTR2.NY5030.verizon-gni.net [130.81.8.74] 7 21 ms 18 ms 22 ms so-6-0-0-0.BB-RTR1.NY60.verizon-gni.net [130.81.8.250] 8 17 ms 19 ms 17 ms so-1-0-0-0.PEER-RTR1.NY60.verizon-gni.net [130.81.4.210] 9 19 ms 17 ms 17 ms jfk-edge-20.inet.qwest.net [65.116.172.85] 10 20 ms 19 ms 17 ms jfk-core-03.inet.qwest.net [205.171.230.18] 11 24 ms 24 ms 23 ms dca-core-03.inet.qwest.net [205.171.8.218] 12 23 ms 23 ms 23 ms 205.171.209.114 13 24 ms 23 ms 23 ms dcx-edge-01.inet.qwest.net [205.171.251.46] 14 26 ms 25 ms 23 ms 67.133.246.238 15 25 ms 25 ms 25 ms g2-0-0.a1.wash.broadwing.net [216.140.8.169] 16 25 ms 23 ms 23 ms 216.140.8.161 17 30 ms 29 ms 32 ms 216.140.17.122 18 29 ms 31 ms 71 ms so-4-2-0.a1-6-NWYK.broadwing.net [216.140.10.78] 19 31 ms 29 ms 31 ms 216.140.200.162 20 30 ms 29 ms 30 ms phi-core-1-x-nyser111-gw-1.net.columbia.edu [128.59.255.13] 21 29 ms 29 ms 31 ms mudd-edge-1-vlan502-1.net.columbia.edu [128.59.2.41] 22 31 ms 29 ms 31 ms shadow.cs.columbia.edu [128.59.23.100]
    80. 80. Packet loss <ul><li>queue (aka buffer) preceding link in buffer has finite capacity </li></ul><ul><li>when packet arrives to full queue, packet is dropped (aka lost) </li></ul><ul><li>lost packet may be retransmitted by previous node, by source end system, or not retransmitted at all </li></ul>
    81. 81. Chapter 1: roadmap <ul><ul><li>1.1 What is the Internet? </li></ul></ul><ul><ul><li>1.2 Network edge </li></ul></ul><ul><ul><li>1.3 Network core </li></ul></ul><ul><ul><li>1.4 Network access and physical media </li></ul></ul><ul><ul><li>1.5 Internet structure and ISPs </li></ul></ul><ul><ul><li>1.6 Delay & loss in packet-switched networks </li></ul></ul><ul><ul><li>1.7 Protocol layers, service models </li></ul></ul><ul><ul><li>1.8 History </li></ul></ul>
    82. 82. Protocol “Layers” <ul><li>Networks are complex! </li></ul><ul><li>many “pieces”: </li></ul><ul><ul><li>hosts </li></ul></ul><ul><ul><li>routers </li></ul></ul><ul><ul><li>links of various media </li></ul></ul><ul><ul><li>applications </li></ul></ul><ul><ul><li>protocols </li></ul></ul><ul><ul><li>hardware, software </li></ul></ul><ul><li>Question: </li></ul><ul><li>Is there any hope of organizing structure of network? </li></ul><ul><li>Or at least our discussion of networks? </li></ul>
    83. 83. Organization of air travel <ul><li>a series of steps </li></ul>ticket (purchase) baggage (check) gates (load) runway takeoff airplane routing ticket (complain) baggage (claim) gates (unload) runway landing airplane routing airplane routing
    84. 84. Layering of airline functionality <ul><li>Layers: each layer implements a service </li></ul><ul><ul><li>via its own internal-layer actions </li></ul></ul><ul><ul><li>relying on services provided by layer below </li></ul></ul>ticket (purchase) baggage (check) gates (load) runway (takeoff) airplane routing departure airport arrival airport intermediate air-traffic control centers airplane routing airplane routing ticket (complain) baggage (claim gates (unload) runway (land) airplane routing ticket baggage gate takeoff/landing airplane routing
    85. 85. Why layering? <ul><li>Dealing with complex systems: </li></ul><ul><li>explicit structure allows identification, relationship of complex system’s pieces </li></ul><ul><ul><li>layered reference model for discussion </li></ul></ul><ul><li>modularization eases maintenance, updating of system </li></ul><ul><ul><li>change of implementation of layer’s service transparent to rest of system </li></ul></ul><ul><ul><li>e.g., change in gate procedure doesn’t affect rest of system </li></ul></ul><ul><ul><li>also found in operating systems and languages </li></ul></ul><ul><li>layering considered harmful? </li></ul>
    86. 86. Internet protocol stack <ul><li>application: supporting network applications </li></ul><ul><ul><li>FTP, SMTP, STTP </li></ul></ul><ul><li>transport: host-host data transfer </li></ul><ul><ul><li>TCP, UDP </li></ul></ul><ul><li>network: routing of datagrams from source to destination </li></ul><ul><ul><li>IP, routing protocols </li></ul></ul><ul><li>link: data transfer between neighboring network elements </li></ul><ul><ul><li>PPP, Ethernet </li></ul></ul><ul><li>physical: bits “on the wire” </li></ul>application transport network link physical
    87. 87. Internet protocols <ul><li>In addition, many “supporting actors” </li></ul><ul><ul><li>mapping various identifiers: numbers and names </li></ul></ul><ul><ul><li>configuring end systems </li></ul></ul><ul><ul><li>managing network elements </li></ul></ul><ul><ul><li>providing security </li></ul></ul><ul><ul><li>setting up sessions </li></ul></ul><ul><ul><li>authorizing users </li></ul></ul><ul><ul><li>synchronizing clocks </li></ul></ul><ul><li>Typical router or host implements dozens of protocols </li></ul>
    88. 88. Example: Cisco 7960 phones <ul><li>Used in CS department </li></ul><ul><li>Protocols implemented: </li></ul><ul><ul><li>DHCP, DNS, TFTP, RTP, HTTP, ICMP, IP, SDP, SNTP, UDP, TCP, Ethernet </li></ul></ul><ul><li>each often with sub-protocols or extensions </li></ul>
    89. 89. Encapsulation message segment datagram frame source application transport network link physical destination application transport network link physical router switch H t H n H l M H t H n M H t M M H t H n H l M H t H n M H t M M network link physical link physical H t H n H l M H t H n M H t H n H l M H t H n M H t H n H l M H t H n H l M
    90. 90. Chapter 1: roadmap <ul><ul><li>1.1 What is the Internet? </li></ul></ul><ul><ul><li>1.2 Network edge </li></ul></ul><ul><ul><li>1.3 Network core </li></ul></ul><ul><ul><li>1.4 Network access and physical media </li></ul></ul><ul><ul><li>1.5 Internet structure and ISPs </li></ul></ul><ul><ul><li>1.6 Delay & loss in packet-switched networks </li></ul></ul><ul><ul><li>1.7 Protocol layers, service models </li></ul></ul><ul><ul><li>1.8 History </li></ul></ul>
    91. 91. Internet History <ul><li>1961: Len Kleinrock - queuing theory shows effectiveness of packet-switching </li></ul><ul><li>1964: Paul Baran - packet-switching in military networks </li></ul><ul><li>1967: ARPAnet conceived by Advanced Research Projects Agency </li></ul><ul><li>1969: first ARPAnet node operational </li></ul><ul><li>1972: </li></ul><ul><ul><li>ARPAnet demonstrated publicly </li></ul></ul><ul><ul><li>NCP (Network Control Protocol) first host-host protocol </li></ul></ul><ul><ul><li>first e-mail program </li></ul></ul><ul><ul><li>ARPAnet has 15 nodes </li></ul></ul>1961-1972: Early packet-switching principles
    92. 92. Internet History <ul><li>1970: ALOHAnet satellite network in Hawaii </li></ul><ul><li>1973: Metcalfe’s PhD thesis proposes Ethernet </li></ul><ul><li>1974: Cerf and Kahn - architecture for interconnecting networks </li></ul><ul><li>late70’s: proprietary architectures: DECnet, SNA, XNA </li></ul><ul><li>late 70’s: switching fixed length packets (ATM precursor) </li></ul><ul><li>1979: ARPAnet has 200 nodes </li></ul><ul><li>Cerf and Kahn’s internetworking principles: </li></ul><ul><ul><li>minimalism, autonomy - no internal changes required to interconnect networks </li></ul></ul><ul><ul><li>best effort service model </li></ul></ul><ul><ul><li>stateless routers </li></ul></ul><ul><ul><li>decentralized control </li></ul></ul><ul><li>define today’s Internet architecture </li></ul>1972-1980: Internetworking, new and proprietary nets
    93. 93. Internet History <ul><li>1983: deployment of TCP/IP </li></ul><ul><li>1982: smtp e-mail protocol defined </li></ul><ul><li>1983: DNS defined for name-to-IP-address translation </li></ul><ul><li>1985: ftp protocol defined </li></ul><ul><li>1988: TCP congestion control </li></ul><ul><li>new national networks: Csnet, BITnet, NSFnet, Minitel </li></ul><ul><li>100,000 hosts connected to confederation of networks </li></ul>1980-1990: new protocols, a proliferation of networks
    94. 94. Internet History <ul><li>Early 1990’s: ARPAnet decommissioned </li></ul><ul><li>1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995) </li></ul><ul><li>early 1990s: WWW </li></ul><ul><ul><li>hypertext [Bush 1945, Nelson 1960’s] </li></ul></ul><ul><ul><li>HTML, http: Berners-Lee </li></ul></ul><ul><ul><li>1994: Mosaic, later Netscape </li></ul></ul><ul><ul><li>late 1990’s: commercialization of the web </li></ul></ul><ul><li>Late 1990’s: </li></ul><ul><ul><li>est. 50 million computers on Internet </li></ul></ul><ul><ul><li>est. 100 million+ users </li></ul></ul><ul><ul><li>backbone links runnning at 1 Gb/s </li></ul></ul><ul><li>2000’s: </li></ul><ul><ul><li>backbones at 10 Gb/s </li></ul></ul><ul><ul><li>wireless networks </li></ul></ul><ul><ul><li>broadband home </li></ul></ul><ul><ul><li>IP telephony </li></ul></ul>1990’s: commercialization, the WWW
    95. 95. Introduction: Summary <ul><li>Covered a “ton” of material! </li></ul><ul><li>Internet overview </li></ul><ul><li>what’s a protocol? </li></ul><ul><li>network edge, core, access network </li></ul><ul><ul><li>packet-switching versus circuit-switching </li></ul></ul><ul><li>Internet/ISP structure </li></ul><ul><li>performance: loss, delay </li></ul><ul><li>layering and service models </li></ul><ul><li>history </li></ul><ul><li>You now have: </li></ul><ul><li>context, overview, “feel” of networking </li></ul><ul><li>more depth, detail to follow! </li></ul>

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