Upload
arsenio-carter
View
28
Download
1
Tags:
Embed Size (px)
DESCRIPTION
Network Protocols: Design and Analysis. Polly Huang EE NTU http://cc.ee.ntu.edu.tw/~phuang [email protected]. Introduction. [Hanson99a] [Jamin97b] [Levin83a] Internet Overview. What you’re up against. 40 papers about 3 per class (!) plus supplementary if you want :-) - PowerPoint PPT Presentation
Citation preview
Network Protocols: Design and Analysis
Polly Huang
EE NTU
http://cc.ee.ntu.edu.tw/~phuang
Introduction
[Hanson99a]
[Jamin97b]
[Levin83a]
Internet Overview
Polly Huang, NTU EE 3
What you’re up against
• 40 papers– about 3 per class (!)– plus supplementary if you want :-)
• Written for experts• Written for the time (not now)• All having to show how cool they are
– as opposed to a completely objective overview
• Some good, some not
Polly Huang, NTU EE 4
What’s on your side
• Some overview in lectures• Discussion with peers
– Reading groups are good!
• Use context– Related papers, reference textbook, own
background
• Hinds in the first 3 papers– [Hanson99a], [Jamin97b], [Levin83a]
[Hanson99a]
Polly Huang, NTU EE 6
Hints: In the Reading
• Skim first, then read in depth– Abstract
– Introduction
– Conclusion
• While going through the paper, takes notes– Highlight key-words/phrases/sentences
– Numerate points
– Summarize sections/paragraphs
– Scribble thoughts
Polly Huang, NTU EE 7
Hints: After Reading
• Write a 1-2 paragraph summary• Keep a database (bibilography) of all your papers
– Authors, paper title, publisher, date, location– List of keywords– Your summary/assessment of the papers– Location of your on-line copy
• Good for a research-oriented career– Will save lots of time when you write a paper– Will save lots of hair when you want to know somethin
g
[Jamin97b]
Polly Huang, NTU EE 9
Telling Good from Bad
• New idea– Really new? how do you know?– Related work & context
• The problem– Clearly stated?
• Evaluation– Do their experiments back up their claims?– Are their experiments statistically sound?
Polly Huang, NTU EE 10
On the Review Forms
• Novelty– New idea
• Clarity– The problem
• Reality (practicality)– Evaluation
• Importance, significance, relevance– How much impact?– Would things change?
Polly Huang, NTU EE 11
OK for Beginners
• Clarity– Easiest– Judging the writing
• Evaluation– Easy– Judging the experiments and technical content
Polly Huang, NTU EE 12
Challenging for the Advanced
• Novelty– Hard– Need to follow/read enough papers in the area
• Importance– Hardest– Need to have breadth and know enough
development in the area
[Levin83a]
Polly Huang, NTU EE 14
Kinds of Papers• Idea papers
– Better have good insight into something! implementable?
• Systems papers– Is their system really new? solid? insight? lessons? al
ternatives?
• Analysis papers– Are their models clean? relevant?
• Evaluation papers– Traces or experiments of existing systems– Do they show insight into something new?
Polly Huang, NTU EE 15
Context
• SOSP is a top OS conference – SIGCOMM, SIGMETRICS, MOBILCOM
• Give guidance to writers about systems papers
• From the reviewer’s perspective
Polly Huang, NTU EE 16
Trying to Address 2 Questions
• What makes a paper important?
• What makes a paper clear?– This should not over-shadow the technical
merit– It, however, may influence (sometimes
critically) the reviewer’s impression on the paper
– Just keep in mind that the reviewers are busy!
Polly Huang, NTU EE 17
About Importance
• Novelty– Idea new and original
• Practicality– Applicable, implementable, deployable– For system papers, yes– Not necessary true for general papers
Polly Huang, NTU EE 18
And Impact Factor
• Lessons learned
• New problems identified
• Previous results contradicted
• Things changed– For a lot of people– A lot but for few people
Polly Huang, NTU EE 19
About Clarity
• Clearly states lessons learned– Reasoning (why, not just what)
• Puts results in context– Related work, premise
• Avoids extra baggage– Irrelevant technical details– Less critical analytical elaboration
Polly Huang, NTU EE 20
The Communication Interface
• Clear presentation– Organization, good abstract
• Good writing– Readability
Polly Huang, NTU EE 21
If you are writing…
• Think the criteria– Novelty, reality, impact, and clarity
• My advise to this class– Start from Clarity– English is the bottleneck for most of you– Practice makes perfect– Without this, the organization, sometimes even the
work could well be effort in vain– When this is done reasonably well, your advisor will be
able to help you with the rest
Polly Huang, NTU EE 22
Theory vs. Implementation
• Theory is incredibly important– Can predict general results
– Help understand systems
• Implementation is incredibly important– Explore real-world constraints (sometimes abstracted
away in theory)
Polly Huang, NTU EE 23
Embrace Them Both
• Best papers tend to have both• Neither is sufficient
– (some) assumptions in the theory are not all that realistic
– Ex. Ethernet cannot reach more than 36% utilization [but it fails to consider higher levels]
– (some) systems work is just trees, no forest
– Ex. distributed.net broke the RC5-64 challenge in 1757 [but what does that say about security in general]
Polly Huang, NTU EE 24
This’s Why Teamwork is Good
• Some are – good at grasp symbols, abstract notations– keen in detecting patterns in random
phenomena– experienced in implementations
• This team can be great
Polly Huang, NTU EE 25
Science vs. Engineering• The roles of science and engineering in networking
and systems• Huge amount of engineering (“construction”)
– What can we really build?
– Ex. Napster or WWW were engineering triumphs
• Really important science (“discovery”)– The Internet is a complex system with many interactions
we don’t understand
– There are principals that affect all possible systems
Questions?
The Overview
The Internet
Now and Beyond
Polly Huang, NTU EE 29
The Internet, Circa 1969
Polly Huang, NTU EE 30
A 1999 Internet ISP Map
[data courtesy of Ramesh Govindan and ISI’s SCAN project]
Polly Huang, NTU EE 31
The Internet, Posterized, Circa 2000
[data courtesy of UCSD’s caida]
Polly Huang, NTU EE 32
Internet Development Mantra
“We reject kings, presidents and voting. We believe in rough consensus and running code.”
- Dave ClarkQuote from a T-shirt commonly worn at IETF meetings
Polly Huang, NTU EE 33
Glimpses of the Future?
http://www.picoweb.net/(an 8-bit web server with Ethernet) a sensor network
(tracking the truck)
cell-phones:millions ofIP-enabledhandsetstoday
UCB mote:an 8-bit sensor nodewith non-IP basednetworking
home entertainment:Onkyo’s network-enabledstereo receiver
USCRobo-Mote
[Rahimi, Sukhatme, et al., 2002]
PC/104
Polly Huang, NTU EE 34
Some Definitions
• Host: computer, desktop, PDA, light switch, etc. (also a node)
• Link: path followed by bits.– Wire or wireless– Broadcast, point-to-point, and in-between
• Switch: moves bits between alternate links– Packet switching: stateless, store and forward– Circuit switching: stateful, cut through– other terms: hub, router, base-station
Polly Huang, NTU EE 35
Networks
…
Point-to-Point
Multiple Access
…
wired or wireless
Polly Huang, NTU EE 36
Internetworks
– Two or more nodes connected by a link, or
– Two or more networks connected by two or more nodes
• A network can be defined recursively as...
Polly Huang, NTU EE 37
The Global Network
• Structure– Getting started
– What and where?
– Getting data there
• Metrics
Polly Huang, NTU EE 38
Getting started: A Host
• Host configuration needs:– a physical network cable (Ethernet, etc.)
– an IP address
– a network mask
– a gateway
– a DNS server (and other servers)
– 2003: a mail server
• Automated with DHCP (and better still in IPv6)
Polly Huang, NTU EE 39
Getting started: A Network
• Network configuration needs:– a wire (from the phone or cable company)
– a router
– a firewall, a IP sharing or NAT machine?
– an ISP to connect you to the Internet
– network addresses (192.168.1.xxx)—a subnet
– plus whatever servers you want (DHCP, DNS, Email)
• Automated in IPv6
Polly Huang, NTU EE 40
Getting started: An ISP
• ISP needs:– a big block of addresses
– connections to one or more other ISPs, peerings
– multiple routers, probably at exchange point (a POP or MAE)
– servers for your users: mail, web, etc.
– servers for you: monitoring, etc.
– an AUP (Acceptable Use Policy)
– a lawyer
Polly Huang, NTU EE 41
Idealized Network Structure
Backbones
Regionals
Campus LANs
Polly Huang, NTU EE 42
The Global Network
• Structure– Getting started
– What and where?
– Getting data there
• Metrics
Polly Huang, NTU EE 43
How Do Computers Find Each Other?
Internet
Computer1 Computer 2
Polly Huang, NTU EE 44
Different Kinds of Addresses
• Will talk about names, addresses, binding in [Saltzer81a]
• For now, what are names and addresses in the Internet?– URL/URNs: http://www.isi.edu– Domain names www.isi.edu– IP address / port numbers: 128.125.1.1– MAC address: 12:34:45:67:ae:0a
Polly Huang, NTU EE 45
Finding IP Address:Domain Naming System (DNS)
Local DNS server
What’s the IP address for www.usc.edu?
Computer 1
It is 128.125.19.146
How does computer 1 know its address? either hard-coded, or gets it at boot time w/DHCP
How does the server know computer 1’s address? usually hard-coded, or via DNS updates, and requests
Polly Huang, NTU EE 46
Finding Ether Address:Address Resolution (ARP)
Ethernet
Broadcast: who knows the Ethernet address for 128.125.51.41?
Ethernet
Broadcast: Yes, I am08-00-2c-19-dc-45
Polly Huang, NTU EE 47
Finding Things: The USER’s Perspective
• http://cc.ee.ntu.edu.tw/~phuang/teach/net-protocol-fall-03/– http a protocol– cc.ee.ntu.edu.tw a web server name– ~phuang/…fall-03/ a path on that server
• Beware:– names vs. addresses at multiple layers
• Alternatively, using a search engine – Network Protocols Polly Teaching
Polly Huang, NTU EE 48
The Global Network
• Structure– Getting started
– What and where?
– Getting data there
• Metrics
Polly Huang, NTU EE 49
Packet Traveling Through the Internet
R
R
R
RRHH
H
H
H
R
RH
R
Routers send packet to next closest hop
H: Hosts
R: Routers
Polly Huang, NTU EE 50
How do the routers know where to send data?
• Forwarding tables at each router populated by routing protocols.– Routing tables optimize distance– Subject also to policies
• Will talk more about this in routing weeks.
Polly Huang, NTU EE 51
Why do the packets get there?(Internet Economics 101)
Backbones
Regionals
Campus LANs
When you get IP connectivity, you pay someone, who pays someone, who… a client-provider relationship
At higher levels, ISPs establish peering relationships with each other. They occasionally do settlements to pay for interactions.
Polly Huang, NTU EE 52
The Global Network
• Structure– Getting started
– What and where?
– Getting data there
• Metrics
Polly Huang, NTU EE 53
Network Metrics
• Bandwidth– Transmission capacity
– A.k.a. How many bits can fit in a section of a link?
• Delay– Queuing delay
– Propagation delay (limited by the c)
• Delay-bandwidth product– Important for control algorithms
Questions?
The Considerations
For designing or engineering
the Internet
Polly Huang, NTU EE 56
What Is the Problem?
Polly Huang, NTU EE 57
What Is the Problem?
Polly Huang, NTU EE 58
But scale in what sense?
• Numbers of hosts
• Amount bandwidth to each host
• Number of concurrent users
• Kinds of applications
• Numbers of links
• Number of independent equipment vendors
• Globally routable
• Geographic distance
• Versions of hw, sw
• App needs (QoS, etc.)
• Levels of trust/admin boundaries
• Hardware price-points
• … etc.
Always define what kind of scale you mean!
Polly Huang, NTU EE 60
Application Considerations
• Application input to network: traffic…– data rate– pattern (bursty or constant bit rate)– destination (multipoint or single destination, mobile or
fixed)
• Network service delivered to application– delay, jitter sensitivity– loss sensitivity– price sensitive
• More about specific app classes in [Clark88a]
Polly Huang, NTU EE 61
Reliable File Transfer
• Loss sensitive
• Not delay sensitive relative to round trip times
• Point-to-point or multipoint
• Bursty
Polly Huang, NTU EE 62
Remote Login
• Loss sensitive
• Delay sensitive – Subject to interactive constraints– Can tolerate up to several hundreds of
milliseconds
• Bursty
• Point to point
Polly Huang, NTU EE 63
Network Audio
• Relatively low bandwidth– Digitized samples, packetized
• Delay variance sensitive
• Loss tolerant
• Possibly multipoint, long duration sessions– Natural limit to number of simultaneous sender
s
Polly Huang, NTU EE 64
Network Video
• High bandwidth
• Compressed video, bursty
• Loss tolerance function of compression
• Delay tolerance a function of interactivity
• Possibly multipoint
• Larger number of simultaneous sources
Polly Huang, NTU EE 65
Web
• Transactional traffic– Short requests, possibly large responses
• Loss (bug?) tolerant
• Delay sensitive– Human interactivity
• Point-to-point (multipoint is asynchronous)
Polly Huang, NTU EE 66
Robustness
• Becoming a critical issue– cf. the microsoft memo about “trusted computin
g” (security robustness)– phone networks promise “5 nines” of reliability:
99.999% uptime• (= 5 minutes of outage per year
– the Internet is not there
Polly Huang, NTU EE 67
Network Failures
• Packet loss– queue overflows (due to congestion)– transmission noise
• Node or link failures• Routing transients or failures• Application-level service failures • Some failure (ex. congestive loss) is
expected, but too much (>5%) is very bad.
Polly Huang, NTU EE 68
(Lack of) Security in the Network
• Many things are too easy:– eavesdropping: credit card numbers, or passwords in pa
ckets– using other people’s resources: worms, DDoS– breaking into machines: software bugs, poor configurati
on, Trojan horses– other things? physical security, social engineering
• But strong security is possible– requires all of good protocols, implementations, and pe
ople
Polly Huang, NTU EE 69
Engineering Trade-offs
Network can be engineered to provide:
• Reliability
• Low delay / high bandwidth
• Low cost
Pick any two
Polly Huang, NTU EE 70
Some Backsliding About Robustness
• NAT boxes
• Application-level gateways
• Layer-3 caches
• User tweaking
• All violate the end-to-end principle, and can reduce robustness
• We’ll see this in [Saltzer81a]
Polly Huang, NTU EE 71
How does technology affect the net?
• Technology drives much of the Internet• Although marketing and politics also have
influence
Polly Huang, NTU EE 72
Examples• Telecom-considering voice-over-IP• Video-on-demand (tech OK, market demand not)• Getting Internet to “grandma” pushed DHCP and autoconfig• New protocols (web, Napster) change usage patterns (and ult
imately industries)• New devices (handsets) enables SMS messaging• Wireless/802.11 enables new modes of operation (wireless “
hot spots”)• Streaming music => the Internet in your stereo• Digital cameras plus on-line photos => the Internet in your p
icture frame• Embedded computing… the Internet in your refrigerator?
Polly Huang, NTU EE 73
Conclusion
• The terminology• The global network
– Entities– Connectivity– Transportation
• The design considerations– Scale– Application– Robustness– Technology
Questions?