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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, 4th ed. Addison Wesley, 2007
http://wps.aw.com/aw_kurose_network_4/ 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 Email 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 1Introduction
Computer Networking: A Top Down Approach ,4th edition. Jim Kurose, Keith RossAddison-Wesley, July 2007.
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
wirelesslaptop
cellular handheld
wiredlinks
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, email, games, e-commerce, file sharing
Communication services provided to apps:
Reliable data delivery from source to destination
“Best effort” (unreliable) data delivery
Introduction 1-11
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, email 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; email
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 (email)
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 forwardingBandwidth division into
“pieces”Dedicated allocationResource 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
C100 Mb/sEthernet
1.5 Mb/s
D E
statistical multiplexing
queue of packetswaiting 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 ISP
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 1 ISP
Tier 1 ISP
Tier-2 ISPTier-2 ISP
Tier-2 ISP Tier-2 ISP
Tier-2 ISP
Tier-2 ISP pays tier-1 ISP for connectivity to rest of Internet Tier-2 ISP is customer oftier-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 1 ISP
Tier 1 ISP
Tier-2 ISPTier-2 ISP
Tier-2 ISP Tier-2 ISP
Tier-2 ISP
localISPlocal
ISPlocalISP
localISP
localISP Tier 3
ISP
localISP
localISP
localISP
Local and tier- 3 ISPs are customers ofhigher tier ISPsconnecting 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
Bnodal
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 (~2x108 m/sec) propagation delay = d/s
Introduction 1-31
propagation
transmission
Note: s and R are very different quantities!
A
Bnodal
processing queueing
Nodal Delay
dproc = processing delay Typically a few microsecs or less
dqueue = queuing delay Depends on congestion level in the router
dtrans = transmission delay = L/R, significant for low-speed links
dprop = propagation delay A few microsecs to hundreds of msecs
Introduction 1-32
proptransqueueprocnodal ddddd
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 tofull 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, withfile of F bits
to send to client
link capacity
Rs bits/sec
link capacity
Rc bits/sec pipe that can
carryfluid at rate
Rs bits/sec)
pipe that can carryfluid at rate
Rc 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., e-mail 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 1-40
1. Select target
2. Break into hosts around the network (see malware)
3. Send packets toward target from compromised hosts
target
Sniff, Modify, Delete Your PacketsPacket 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: SummaryCovered 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