COMP 562: “Advanced Topics in Networking” Qian Zhang Spring 2009 HKUST Introduction 1-1

Course Info  Instructor: Qian Zhang  Course web site /comp562-index.htm /comp562-index.htm contains all notes, announcements, etc. Check it regularly!  Lecture schedule  Tuesday/Thursday 12:00-13:20 Rm 2463 Introduction 1-2

Course Info  Textbook: James Kurose and Keith Ross  Computer Networking: A Top Down Approach, 4 th ed. Addison Wesley, 2007  with useful resource material  The reading materials online for paper reading and reviewing  Experience networking research through team projects (1-2 students)  Understand what is good research  Hands-on experience in networking research  Appreciate team work / collaborations  Survey oriented (own idea is encouraged) Introduction 1-3

Course Info  Grading scheme  Homework (2) 30 points  Paper presentation (1) 15 points  Project report (1) 15 points  Final Exam 40 points  Paper presentation  Everyone reviews and presents 1 paper  me ids of 3 papers that you’d like to present by Feb. 27  Present the paper and give your own comments on the selected paper Introduction 1-4

More about Class Project  Can be individual project or group project (at most 2 in a group)  Two types I can see:  Survey a problem in depth (read several papers related to the problem and summarized/ discuss)  Do some research on a given problem  Sample project topics:  Most commercial systems (e.g. PPlive) are not based on open source. Try to deduce the algorithm for specific p2p streaming applications Introduction 1-5

Course Schedule  Review of the basic principles of computer networking  Broadcasting and Multicasting  Peer-to-Peer Networking  Wireless Networking  Multimedia Networking and Quality of Service Provision  Advanced Topics for Congestion Control  Network Security  Student presentation Introduction 1-6

Introduction 1-7 Chapter 1 Introduction Computer Networking: A Top Down Approach, 4 th edition. Jim Kurose, Keith Ross Addison-Wesley, July A note on the use of these ppt slides: The notes used in this course are substantially based on powerpoint slides developed and copyrighted by J.F. Kurose and K.W. Ross, 2007

Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge  End systems, access networks, links 1.3 Network core  Circuit switching, packet switching, network structure 1.4 Delay, loss and throughput in packet-switched networks 1.5 Protocol layers, service models 1.6 Networks under attack: security Introduction 1-8

What’s the Internet: “nuts and bolts” view  Millions of connected computing devices: hosts = end systems  Running network apps Introduction 1-9 Home network Institutional network Mobile network Global ISP Regional ISP router PC server wireless laptop cellular handheld wired links access points  Communication links  Fiber, copper, radio, satellite  Transmission rate = bandwidth  Routers: forward packets (chunks of data)

What’s the Internet: “nuts and bolts” view  Protocols control sending, receiving of msgs  E.g., TCP, IP, HTTP, Skype, Ethernet  Internet: “network of networks”  Loosely hierarchical  Public Internet versus private intranet  Internet standards  RFC: Request for comments  IETF: Internet Engineering Task Force Introduction 1-10 Home network Institutional network Mobile network Global ISP Regional ISP

What’s the Internet: A Service View  Communication infrastructure enables distributed applications:  Web, VoIP, , games, e- commerce, file sharing  Communication services provided to apps:  Reliable data delivery from source to destination  “Best effort” (unreliable) data delivery Introduction 1-11

Chapter 1: Roadmap 1.1 What is the Internet? 1.2 Network edge  End systems, access networks, links 1.3 Network core  Circuit switching, packet switching, network structure 1.4 Delay, loss and throughput in packet-switched networks 1.5 Protocol layers, service models 1.6 Networks under attack: security Introduction 1-12

A Closer Look at Network Structure:  Network edge: applications and hosts Introduction 1-13  Access networks, physical media: wired, wireless communication links  Network core:  Interconnected routers  Network of networks

The Network Edge:  End systems (hosts):  Run application programs  E.g. Web,  At “edge of network” Introduction 1-14 client/server peer-peer  Client/server model  Client host requests, receives service from always-on server  E.g. Web browser/server; client/server  Peer-peer model:  Minimal (or no) use of dedicated servers  E.g. Skype, BitTorrent

Network Edge: Reliable Data Transfer Service Goal: data transfer between end systems  Handshaking: setup (prepare for) data transfer ahead of time  Hello, hello back human protocol  Set up “state” in two communicating hosts  TCP - Transmission Control Protocol  Internet’s reliable data transfer service TCP service [RFC 793]  Reliable, in-order byte- stream data transfer  Loss: acknowledgements and retransmissions  Flow control:  Sender won’t overwhelm receiver  Congestion control:  Senders “slow down sending rate” when network congested Introduction 1-15

Network Edge: Best Effort (Unreliable) Data Transfer Service Goal: data transfer between end systems  same as before!  UDP - User Datagram Protocol [RFC 768]:  Connectionless  Unreliable data transfer  No flow control  No congestion control App’s using TCP:  HTTP (Web), FTP (file transfer), Telnet (remote login), SMTP ( ) App’s using UDP:  streaming media, teleconferencing, DNS, Internet telephony Introduction 1-16

Access Networks and Physical Media Q: How to connect end systems to edge router?  Residential access nets  Institutional access networks (school, company)  Mobile access networks Keep in mind:  Bandwidth (bits per second) of access network?  Shared or dedicated? Introduction 1-17

Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge  End systems, access networks, links 1.3 Network core  Circuit switching, packet switching, network structure 1.4 Delay, loss and throughput in packet-switched networks 1.5 Protocol layers, service models 1.6 Networks under attack: security Introduction 1-18

The Network Core  Mesh of interconnected routers  The fundamental question: how is data transferred through net?  Circuit-switching: dedicated circuit per call: telephone net  Packet-switching: data sent thru net in discrete “chunks” Introduction 1-19

Network Core: Circuit Switching End-end resources reserved for “call”  Link bandwidth, switch capacity  Dedicated resources: no sharing  Circuit-like (guaranteed) performance  Call setup required Introduction 1-20

Network Core: Circuit Switching Network resources (e.g., bandwidth) divided into “pieces”  Pieces allocated to calls  Resource piece idle if not used by owning call (no sharing) Introduction 1-21  Dividing link bandwidth into “pieces”  Frequency division  Time division

Network Core: 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 Introduction 1-22 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  Node receives complete packet before forwarding Bandwidth division into “pieces” Dedicated allocation Resource reservation

Packet Switching: Statistical Multiplexing Sequence of A & B packets does not have fixed pattern, shared on demand  statistical multiplexing TDM: each host gets same slot in revolving TDM frame Introduction 1-23 A B C 100 Mb/s Ethernet 1.5 Mb/s D E statistical multiplexing queue of packets waiting for output link

Packet Switching versus Circuit Switching  Great for bursty data  Resource sharing  Simpler, no call setup  Excessive congestion: packet delay and loss  Protocols needed for reliable data transfer, congestion control  Q: How to provide circuit-like behavior?  Bandwidth guarantees needed for audio/video apps  Still an unsolved problem Is packet switching a “slam dunk winner?” Introduction 1-24

Internet Structure: Network of Networks  Roughly hierarchical  At center: “tier-1” ISPs (e.g., Verizon, Sprint, AT&T, Cable and Wireless), national/international coverage  Treat each other as equals Introduction 1-25 Tier 1 ISP Tier-1 providers interconnect (peer) privately

Internet Structure: Network of Networks  “Tier-2” ISPs: smaller (often regional) ISPs  Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs Introduction 1-26 Tier 1 ISP Tier-2 ISP Tier-2 ISP pays tier-1 ISP for connectivity to rest of Internet  Tier-2 ISP is customer of tier-1 provider Tier-2 ISPs also peer privately with each other.

Internet Structure: Network of Networks  “Tier-3” ISPs and local ISPs  Last hop (“access”) network (closest to end systems) Introduction 1-27 Tier 1 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

Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge  End systems, access networks, links 1.3 Network core  Circuit switching, packet switching, network structure 1.4 Delay, loss and throughput in packet-switched networks 1.5 Protocol layers, service models 1.6 Networks under attack: security Introduction 1-28

How do Loss and Delay Occur? Packets queue in router buffers  Packet arrival rate to link exceeds output link capacity  Packets queue, wait for turn Introduction 1-29 A B packet being transmitted (delay) packets queueing (delay) free (available) buffers: arriving packets dropped (loss) if no free buffers

Four Sources of Packet Delay  1. Nodal processing:  Check bit errors  Determine output link Introduction 1-30  2. Queueing  Time waiting at output link for transmission  Depends on congestion level of router A B nodal processing queueing

Delay in Packet-Switched Networks 3. Transmission delay:  R=link bandwidth (bps)  L=packet length (bits)  Time to send bits into link = L/R 4. Propagation delay:  d = length of physical link  s = propagation speed in medium (~2x10 8 m/sec)  propagation delay = d/s Introduction 1-31 propagation transmission Note: s and R are very different quantities! A B nodal processing queueing

Nodal Delay  d proc = processing delay  Typically a few microsecs or less  d queue = queuing delay  Depends on congestion level in the router  d trans = transmission delay  = L/R, significant for low-speed links  d prop = propagation delay  A few microsecs to hundreds of msecs Introduction 1-32

Packet Loss  Queue (aka buffer) preceding link in buffer has finite capacity  Packet arriving to full queue dropped (aka lost)  Lost packet may be retransmitted by previous node, by source end system, or not at all Introduction 1-33 A B packet being transmitted packet arriving to full buffer is lost buffer (waiting area)

Throughput  Throughput: rate (bits/time unit) at which bits transferred between sender/receiver  Instantaneous: rate at given point in time  Average: rate over long(er) period of time Introduction 1-34 server, with file of F bits to send to client link capacity R s bits/sec link capacity R c bits/sec pipe that can carry fluid at rate R s bits/sec) pipe that can carry fluid at rate R c bits/sec) server sends bits (fluid) into pipe

Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge  End systems, access networks, links 1.3 Network core  Circuit switching, packet switching, network structure 1.4 Delay, loss and throughput in packet-switched networks 1.5 Protocol layers, service models 1.6 Networks under attack: security Introduction 1-35

Internet Protocol Stack  Application: supporting network applications  FTP, SMTP, HTTP  Transport: process-process data transfer  TCP, UDP  Network: routing of datagrams from source to destination  IP, routing protocols  Link: data transfer between neighboring network elements  PPP, Ethernet  Physical: bits “on the wire” Introduction 1-36 application transport network link physical

Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge  End systems, access networks, links 1.3 Network core  Circuit switching, packet switching, network structure 1.4 Delay, loss and throughput in packet-switched networks 1.5 Protocol layers, service models 1.6 Networks under attack: security Introduction 1-37

Network Security  Attacks on Internet infrastructure:  Infecting/attacking hosts: malware, spyware, worms, unauthorized access (data stealing, user accounts)  Denial of service: deny access to resources (servers, link bandwidth)  Internet not originally designed with (much) security in mind  Original vision: “a group of mutually trusting users attached to a transparent network”  Internet protocol designers playing “catch-up”  Security considerations in all layers! Introduction 1-38

What Can Bad Guys Do: Malware?  Spyware:  Infection by downloading web page with spyware  Records keystrokes, web sites visited, upload info to collection site  Virus  Infection by receiving object (e.g., attachment), actively executing  Self-replicating: propagate itself to other hosts, users Introduction 1-39  Worm:  Infection by passively receiving object that gets itself executed  Self-replicating: propagates to other hosts, users Sapphire Worm: aggregate scans/sec in first 5 minutes of outbreak (CAIDA, UWisc data)

Denial of Service Attacks  Attackers make resources (server, bandwidth) unavailable to legitimate traffic by overwhelming resource with bogus traffic Introduction Select target 2. Break into hosts around the network (see malware) 3. Send packets toward target from compromised hosts target

Sniff, Modify, Delete Your Packets Packet sniffing:  Broadcast media (shared Ethernet, wireless)  Promiscuous network interface reads/records all packets (e.g., including passwords!) passing by Introduction 1-41 A B C src:B dest:A payload  Ethereal software used for end-of-chapter labs is a (free) packet-sniffer  More on modification, deletion later

Masquerade as you  IP spoofing: send packet with false source address Introduction 1-42 A B C src:B dest:A payload

Masquerade as you  IP spoofing: send packet with false source address  Record-and-playback : sniff sensitive info (e.g., password), and use later  Password holder is that user from system point of view Introduction 1-43 A B C src:B dest:A user: B; password: foo

Masquerade as you  IP spoofing: send packet with false source address  Record-and-playback : sniff sensitive info (e.g., password), and use later  Password holder is that user from system point of view Introduction 1-44 A B later ….. C src:B dest:A user: B; password: foo

Introduction: Summary Covered a “ton” of material!  Internet overview  What’s a protocol?  Network edge, core, access network  Packet-switching versus circuit- switching  Internet structure  Performance: loss, delay, throughput  Layering, service models  Security Introduction 1-45