COMP 562: Advanced Topics in Networking

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

Course Info Instructor: Qian Zhang www.cs.ust.hk/~qianzh Course web site http://www.cs.ust.hk/~qianzh/comp562 2009/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 Other research papers online The reading materials online for paper reading and reviewing Grading scheme Homework (2) 30 points Paper presentation (1) 15 points Project report (1) 15 points Final Exam 40 points Introduction 1-3

Course Info Paper presentation Everyone reviews and presents 1 paper Email me ids of 3 papers that you d like to present by Feb. 27 Present and give your own comments on the selected paper Experience networking research through team projects (1 2 students) 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 1-4

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 1-5

Chapter 1 Introduction 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 Computer Networking: A Top Down Approach, 4 th edition. Jim Kurose, Keith Ross Addison-Wesley, July 2007. Introduction 1-6

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 1-7

What s the Internet: nuts and bolts view PC server wireless laptop cellular handheld access points wired links Millions of connected computing devices: hosts = end systems Running network apps Communication links Fiber, copper, radio, satellite Transmission rate = bandwidth Mobile network Global ISP Home network Regional ISP Institutional network router Routers: forward packets (chunks of data) Introduction 1-8

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 Mobile network Global ISP Home network Regional ISP Institutional network Introduction 1-9

What s the Internet: A Service View Communication infrastructure enables distributed applications: Web, VoIP, email, games, e commerce, file sharing Communication services provided to apps: Reliable data delivery from source to destination Best effort (unreliable) data delivery Introduction 1-10

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 1-11

A Closer Look at Network Structure: Network edge: applications and hosts Access networks, physical media: wired, wireless communication links Network core: Interconnected routers Network of networks Introduction 1-12

The Network Edge: End systems (hosts): Run application programs E.g. Web, email At edge of network peer-peer Client/server model Client host requests, receives service from always on server E.g. Web browser/server; email client/server Peer peer model: Minimal (or no) use of dedicated servers E.g. Skype, BitTorrent client/server Introduction 1-13

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 bytestream data transfer Loss: acknowledgements and retransmissions Flow control: Sender won t overwhelm receiver Congestion control: Senders slow down sending rate when network congested Introduction 1-14

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 (email) App s using UDP: streaming media, teleconferencing, DNS, Internet telephony Introduction 1-15

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 1-16

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 1-18

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 1-19

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) Dividing link bandwidth into pieces Frequency division Time division Introduction 1-20

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 Bandwidth division into pieces Dedicated allocation Resource reservation 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 Introduction 1-21

Packet Switching: Statistical Multiplexing A 100 Mb/s Ethernet statistical multiplexing C B queue of packets waiting for output link 1.5 Mb/s D E 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 1-22

Packet Switching versus Circuit Switching Is packet switching a slam dunk winner? 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 Introduction 1-23

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 Tier-1 providers interconnect (peer) privately Tier 1 ISP Tier 1 ISP Tier 1 ISP Introduction 1-24

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 Tier-2 ISP pays tier-1 ISP for connectivity to rest of Internet Tier-2 ISP is customer of tier-1 provider Tier-2 ISP Tier-2 ISP Tier 1 ISP Tier 1 ISP Tier 1 ISP Tier-2 ISPs also peer privately with each other. Tier-2 ISP Tier-2 ISP Tier-2 ISP Introduction 1-25

Internet Structure: Network of Networks Tier 3 ISPs and local ISPs Last hop ( access ) network (closest to end systems) Local and tier- 3 ISPs are customers of higher tier ISPs connecting them to rest of Internet local ISP local ISP Tier 3 ISP Tier-2 ISP Tier 1 ISP Tier-2 ISP local ISP local ISP Tier 1 ISP local ISP Tier-2 ISP Tier 1 ISP Tier-2 ISP local ISP local ISP Tier-2 ISP local ISP Introduction 1-26

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 packet being transmitted (delay) A B packets queueing (delay) free (available) buffers: arriving packets dropped (loss) if no free buffers Introduction 1-28

Four Sources of Packet Delay 1. Nodal processing: Check bit errors Determine output link 2. Queueing Time waiting at output link for transmission Depends on congestion level of router A B nodal processing queueing Introduction 1-29

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 A transmission propagation Note: s and R are very different quantities! B nodal processing queueing Introduction 1-30

Nodal Delay d = d + d + d + nodal proc queue trans d prop 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 1-31

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 A buffer (waiting area) packet being transmitted B packet arriving to full buffer is lost Introduction 1-32

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 server server, sends with bits (fluid) file of into F pipe bits to send to client pipe link that capacity can carry R fluid s bits/sec at rate R s bits/sec) pipe link that capacity can carry Rfluid c bits/sec at rate R c bits/sec) Introduction 1-33

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 application transport network link physical Introduction 1-35

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 1-37

What Can Bad Guys Do: Malware? Spyware: Virus Infection by downloading web page with spyware Records keystrokes, web sites visited, upload info to collection site Infection by receiving object (e.g., e mail attachment), actively executing Self replicating: propagate itself to other hosts, users 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) Introduction 1-38

Denial of Service Attacks Attackers make resources (server, bandwidth) unavailable to legitimate traffic by overwhelming resource with bogus traffic 1. Select target 2. Break into hosts around the network (see malware) 3. Send packets toward target from compromised hosts target Introduction 1-39

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 A C src:b dest:a payload B Ethereal software used for end of chapter labs is a (free) packet sniffer More on modification, deletion later Introduction 1-40

Masquerade as you IP spoofing: send packet with false source address A C src:b dest:a payload B Introduction 1-41

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 A C src:b dest:a user: B; password: foo B Introduction 1-42

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 A later.. C src:b dest:a user: B; password: foo B Introduction 1-43

Introduction: Summary Covered a ton of material! Internet overview What s a protocol? Network edge, core, access network Packet switching versus circuitswitching Internet structure Performance: loss, delay, throughput Layering, service models Security Introduction 1-44