1. 15-744: Computer Networking L-1 Intro to Computer Networks

2. L -1; 9-11-02© Srinivasan Seshan, 20022 Outline Administrivia Whirlwind tour of networking

3. L -1; 9-11-02© Srinivasan Seshan, 20023 Who’s Who? Professor: Srinivasan Seshan http://www.cs.cmu.edu/~srini srini@cmu.edu Office hours: Wed 1:30-2:30pm TA: Amit Manjhi manjhi@cs.cmu.edu Office hours: Mon 3:00-4:00pm Course info http://www.cs.cmu.edu/~srini/15-744/F02/

4. L -1; 9-11-02© Srinivasan Seshan, 20024 Objectives Understand the state-of-the-art in network protocols, architectures and applications Understand how networking research is done Teach the typical constraints and thought process for networked systems How is class different from undergraduate networking (15-441) Training network programmers vs. training network researchers

5. L -1; 9-11-02© Srinivasan Seshan, 20025 Web Page Check regularly!! Course schedule Reading list Lecture notes Announcements Assignments Project ideas Exams Student list

6. L -1; 9-11-02© Srinivasan Seshan, 20026 Course Materials Research papers Links to ps or pdf on Web page Combination of classic and recent work ~40 papers Optional readings Recommended textbook For students not familiar with networking Peterson & Davie 2 nd edition 2 copies on reserve Kurose & Ross (preferably 2 nd edition) I have some spare (1 st ed) that I can lend out

7. L -1; 9-11-02© Srinivasan Seshan, 20027 Grading Homework assignments Problem sets & hands-on assignments (15%) Hand-ins for readings (10%) Class participation (5%) 2 person project (30%) Midterm exam (20%) Final (2 nd Midterm) exam (not cumulative) (20%)

8. L -1; 9-11-02© Srinivasan Seshan, 20028 Waitlist & HW 0 HW 0 – due next Thursday in class If you are trying to add class HW 0 is due on Tuesday in class I will email enrollment decisions by next Friday

9. L -1; 9-11-02© Srinivasan Seshan, 20029 Outline Administrivia Whirlwind tour of networking

10. L -1; 9-11-02© Srinivasan Seshan, 200210 What is the Objective of Networking? Communication between applications on different computers Must understand application needs/demands Traffic data rate Traffic pattern (bursty or constant bit rate) Traffic target (multipoint or single destination, mobile or fixed) Delay sensitivity Loss sensitivity

11. L -1; 9-11-02© Srinivasan Seshan, 200211 Four Steps to Networking Communicating across a link Connecting together multiple links (internetworking) Finding and routing data to nodes on internetwork Matching application requirements

12. L -1; 9-11-02© Srinivasan Seshan, 200212 A First Step Creating a link between nodes Link: path followed by bits Wired or wireless Broadcast or point-to-point (or both) Node: any device connected to a link

13. L -1; 9-11-02© Srinivasan Seshan, 200213 Types of Links Point-to-PointMultiple Access …

14. L -1; 9-11-02© Srinivasan Seshan, 200214 Packet Transmission Modes Unicast Transmission to single specific receiver Broadcast Transmission to all network nodes Multicast Transmission to specific subset of nodes Anycast Transmission to one of a specific subset of nodes

15. L -1; 9-11-02© Srinivasan Seshan, 200215 Switched Network What are Switched Networks? Switch: moves bits between links Packet switching Circuit switching

16. L -1; 9-11-02© Srinivasan Seshan, 200216 Back in the Old Days…

17. L -1; 9-11-02© Srinivasan Seshan, 200217 Then Came TDM… Multiplex (mux)Demultiplex (demux) Synchronous time division multiplexing

18. L -1; 9-11-02© Srinivasan Seshan, 200218 TDM Logical Network View

19. L -1; 9-11-02© Srinivasan Seshan, 200219 Packet Switching (Internet) Packets

20. L -1; 9-11-02© Srinivasan Seshan, 200220 Packet Switching Interleave packets from different sources Efficient: resources used on demand Statistical multiplexing General Multiple types of applications Accommodates bursty traffic Addition of queues

21. L -1; 9-11-02© Srinivasan Seshan, 200221 Statistical Multiplexing Gain 1 Mbps link; users require 0.1 Mbps when transmitting; users active only 10% of the time Circuit switching: can support 10 users Packet switching: with 35 users, probability that >=10 are transmitting at the same time < 0.0017

22. L -1; 9-11-02© Srinivasan Seshan, 200222 Characteristics of Packet Switching Store and forward Packets are self contained units Can use alternate paths – reordering Contention Congestion Delay

23. L -1; 9-11-02© Srinivasan Seshan, 200223 Internet[work] Second Step: Internet[work] A collection of interconnected networks Host: network endpoints (computer, PDA, light switch, …) Router: node that connects networks Internet vs. internet

24. L -1; 9-11-02© Srinivasan Seshan, 200224 Challenge Many differences between networks Address formats Performance – bandwidth/latency Packet size Loss rate/pattern/handling Routing How to translate between various network technologies

25. L -1; 9-11-02© Srinivasan Seshan, 200225 Third Step: How To Find Nodes? Internet Computer 1Computer 2

26. L -1; 9-11-02© Srinivasan Seshan, 200226 Naming Humans use readable host names E.g. www.cmu.eduwww.cmu.edu Globally unique (can correspond to multiple hosts) Naming system translates to physical address E.g. DNS translates name to IP Address (e.g. 128.2.11.43) Address reflects location in network

27. L -1; 9-11-02© Srinivasan Seshan, 200227 Domain Name System What’s the IP address for www.cmu.edu? It is 128.2.11.43 DNS server address manually configured into OS Local DNS ServerComputer 1

28. L -1; 9-11-02© Srinivasan Seshan, 200228 Packet Routing/Delivery Each network technology has different local delivery methods Address resolution provides delivery information within network E.g., ARP maps IP addresses to Ethernet addresses Local, works only on a particular network Routing protocol provides path through an internetwork

29. L -1; 9-11-02© Srinivasan Seshan, 200229 Network:Address Resolution Protocol Ethernet Broadcast: who knows the Ethernet address for 128.2.11.43? Ethernet Unicast: Yes, it is 08-00-2c-19-dc-45

30. L -1; 9-11-02© Srinivasan Seshan, 200230 Internetwork: Datagram Routing R R R R R H H H H R R H R Routers send packet to next closest point H: Hosts R: Routers

31. L -1; 9-11-02© Srinivasan Seshan, 200231 Routing Forwarding tables at each router populated by routing protocols. Original Internet: manually updated Routing protocols update tables based on “cost” Exchange tables with neighbors or everyone Use neighbor leading to shortest path

32. L -1; 9-11-02© Srinivasan Seshan, 200232 Fourth Step: Application Demands Reliability Corruption Lost packets Flow and congestion control Fragmentation In-order delivery Etc…

33. L -1; 9-11-02© Srinivasan Seshan, 200233 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

34. L -1; 9-11-02© Srinivasan Seshan, 200234 What if Network is Overloaded? Problem: Network Overload Short bursts: buffer What if buffer overflows? Packets dropped Sender adjusts rate until load = resources Called “congestion control” Solution: Buffering and Congestion Control

35. L -1; 9-11-02© Srinivasan Seshan, 200235 What if the Data gets Lost? Internet GET index.html Problem: Lost Data Internet GET index.html Solution: Timeout and Retransmit GET index.html

36. L -1; 9-11-02© Srinivasan Seshan, 200236 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

37. L -1; 9-11-02© Srinivasan Seshan, 200237 Solution: Add Sequence Numbers Problem: Out of Order What if the Data is Out of Order? GETx.htindeml GET x.htindeml GET index.html ml4inde2x.ht3GET1

38. L -1; 9-11-02© Srinivasan Seshan, 200238 Network Functionality Summary Link Multiplexing Routing Addressing/naming (locating peers) Reliability Flow control Fragmentation Etc….

39. L -1; 9-11-02© Srinivasan Seshan, 200239 What is Layering? Modular approach to network functionality Example: Link hardware Host-to-host connectivity Application-to-application channels Application

40. L -1; 9-11-02© Srinivasan Seshan, 200240 Protocols Module in layered structure Set of rules governing communication between network elements (applications, hosts, routers) Protocols define: Interface to higher layers (API) Interface to peer Format and order of messages Actions taken on receipt of a message

41. L -1; 9-11-02© Srinivasan Seshan, 200241 Layering Characteristics Each layer relies on services from layer below and exports services to layer above Interface defines interaction Hides implementation - layers can change without disturbing other layers (black box)

42. L -1; 9-11-02© Srinivasan Seshan, 200242 Layering Host Application Transport Network Link User AUser B Layering: technique to simplify complex systems

43. L -1; 9-11-02© Srinivasan Seshan, 200243 Layer Encapsulation Get index.html Connection ID Source/Destination Link Address User AUser B

44. L -1; 9-11-02© Srinivasan Seshan, 200244 Protocol Demultiplexing Multiple choices at each layer FTPHTTPTFTPNV TCPUDP IP NET 1 NET 2 NET n … TCP/UDPIP IPX Port Number Network Protocol Field Type Field

45. L -1; 9-11-02© Srinivasan Seshan, 200245 E.g.: OSI Model: 7 Protocol Layers Physical: how to transmit bits Data link: how to transmit frames Network: how to route packets Transport: how to send packets end2end Session: how to tie flows together Presentation: byte ordering, security Application: everything else

46. L -1; 9-11-02© Srinivasan Seshan, 200246 OSI Layers and Locations Switch Router Host Application Transport Network Data Link Presentation Session Physical

47. L -1; 9-11-02© Srinivasan Seshan, 200247 Example: Transport Layer First end-to-end layer End-to-end state May provide reliability, flow and congestion control

48. L -1; 9-11-02© Srinivasan Seshan, 200248 Example: Network Layer Point-to-point communication Network and host addressing Routing

49. L -1; 9-11-02© Srinivasan Seshan, 200249 Is Layering Harmful? Sometimes.. Layer N may duplicate lower level functionality (e.g., error recovery) Layers may need same info (timestamp, MTU) Strict adherence to layering may hurt performance

50. L -1; 9-11-02© Srinivasan Seshan, 200250 Class Coverage No coverage of physical and data link layer Students expected to know this Focus on network to application layer We will deal with: Protocol rules and algorithms Investigate protocol trade-offs Why this way and not another?

51. L -1; 9-11-02© Srinivasan Seshan, 200251 Lecture Topics Traditional Layering Internet architecture Routing (IP) Transport (TCP) Queue management (FQ, RED) Naming (DNS) Recent Topics Multicast Mobility Active networks QOS Security Network measurement Overlay networks P2P applications

52. L -1; 9-11-02© Srinivasan Seshan, 200252 Next Lecture: Design Considerations How to determine split of functionality Across protocol layers Across network nodes Assigned Reading [Cla88] Design Philosophy of the DARPA Internet Protocols [SRC84] End-to-end Arguments in System Design [Cla02] Tussle in Cyberspace: Defining Tomorrow’s Internet