Network Protocols: Design and Analysis

Network Protocols: Design and Analysis

Polly Huang

EE NTU

http://cc.ee.ntu.edu.tw/~phuang

[email protected]

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


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]


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


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]


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?


On the Review Forms

• Novelty– New idea

• Clarity– The problem

• Reality (practicality)– Evaluation

• Importance, significance, relevance– How much impact?– Would things change?


OK for Beginners

• Clarity– Easiest– Judging the writing

• Evaluation– Easy– Judging the experiments and technical content


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]


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?


Context

• SOSP is a top OS conference – SIGCOMM, SIGMETRICS, MOBILCOM

• Give guidance to writers about systems papers

• From the reviewer’s perspective


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!


About Importance

• Novelty– Idea new and original

• Practicality– Applicable, implementable, deployable– For system papers, yes– Not necessary true for general papers


And Impact Factor

• Lessons learned

• New problems identified

• Previous results contradicted

• Things changed– For a lot of people– A lot but for few people


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


The Communication Interface

• Clear presentation– Organization, good abstract

• Good writing– Readability


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


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)


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]


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


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


The Internet, Circa 1969


A 1999 Internet ISP Map

[data courtesy of Ramesh Govindan and ISI’s SCAN project]


The Internet, Posterized, Circa 2000

[data courtesy of UCSD’s caida]


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


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


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


Networks

…

Point-to-Point

Multiple Access

…

wired or wireless


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...


The Global Network

• Structure– Getting started

– What and where?

– Getting data there

• Metrics


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)


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


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


Idealized Network Structure

Backbones

Regionals

Campus LANs


The Global Network


– What and where?


• Metrics


How Do Computers Find Each Other?

Internet

Computer1 Computer 2


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


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


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


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


The Global Network


– What and where?


• Metrics


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


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.


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.


The Global Network


– What and where?


• Metrics


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


What Is the Problem?


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!


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]


Reliable File Transfer

• Loss sensitive

• Not delay sensitive relative to round trip times

• Point-to-point or multipoint

• Bursty


Remote Login

• Loss sensitive

• Delay sensitive – Subject to interactive constraints– Can tolerate up to several hundreds of

milliseconds

• Bursty

• Point to point


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


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


Web

• Transactional traffic– Short requests, possibly large responses

• Loss (bug?) tolerant

• Delay sensitive– Human interactivity

• Point-to-point (multipoint is asynchronous)


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


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.


(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


Engineering Trade-offs

Network can be engineered to provide:

• Reliability

• Low delay / high bandwidth

• Low cost

Pick any two


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]


How does technology affect the net?

• Technology drives much of the Internet• Although marketing and politics also have

influence


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?


Conclusion

• The terminology• The global network

– Entities– Connectivity– Transportation

• The design considerations– Scale– Application– Robustness– Technology

Questions?

Network Protocols: Design and Analysis

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