CS 268: Computer Networking

L-23 Course Wrap-up

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Goals and Objectives

• Understand state-of-the-art in network protocols, architectures, and applications

• Process of networking research• Constraints and thought processes for networking

research• Problem Formulation—Approach—Analysis—Results

• Different from undergraduate networking (EECS 122)• i.e., training network programmers vs. training

network researchers

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Class Topic Coverage

• Little on physical and data link layer• Little on undergraduate material

• Supposedly you already know this, though some revisiting/overlap is unavoidable

• Focus on the why, not the what

• Focus on network-to-application layer• We dealt with:

• Protocol rules and algorithms, tradeoffs, rationale• Routing, transport, DNS resolution, …

• Network extensions and next generation architecture• Wireless, mobile, sensor, …

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Lecture Topics

Traditional• Layering• Internet architecture• Routing (IP)• Transport (TCP)• Queue management

(FQ, RED)• Naming (DNS)

Recent Topics• Multicast• Mobility/wireless• Active networks• QoS• Network measurement• Overlay networks• P2P applications• Datacenter networking

Italics topics on Quiz #2

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What is the Objective of Networking?

• Communication between applications on different computers

• Must understand application needs/demands• Traffic data rate, pattern (bursty or constant bit

rate), target (multipoint or single destination, mobile or fixed)

• Delay and loss sensitivity• Other application-support services

• Overlays, Active Networks, Data-oriented, …

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Back in the Old Days…

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Packet Switching (Internet)

Packets

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Packet Switching

• Interleave packets from different sources• Statistical multiplexing to use resources on demand• Supports multiple applications types• Accommodates bursty traffic via queues

• Store and forward• Packets are self contained units• Can use alternate paths – reordering• Effects of contention: congestion and delay

• Semester readings on Fair Queuing, Router Design, Network Topology and Network Measurement

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Internet[work]

Internet[work]

• A collection of interconnected networks

• Host: network endpoints (computer, PDA, light switch, …)

• Router: node that connects networks

• Internet vs. internet

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Challenge

• Many differences between networks• Address formats• Performance – bandwidth/latency• Packet size• Loss rate/pattern/handling• Routing

• How to translate between various network technologies?• Gateways

Extensions to the Network

• New kinds of networks within the Internet• Mobile• Wireless• Sensor• Delay Tolerant• Content Distribution/Data Oriented Networks

• Semester readings on Roofnet, Ad hoc and sensor net routing, DTNs, CDNs, DOT, etc.

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How To Find Nodes?

Internet

Computer 1 Computer 2

Need naming and routing

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Naming

What’s the IP address for www.cmu.edu?

It is 128.2.11.43

Translates human readable names to logical endpoints

Local DNS ServerComputer 1

Extensions to the Network Architecture

• Naming• DNS as an Overlay Network• Problems with Host-to-IP Address bindings• Problems with Service-to-Host bindings• Solutions based on the idea of an extra level of

indirection: flat identifiers plus resolution based on DHT lookup

• Semester readings on DNS and on flat names and DHTs in the context of i3, DOA, etc.

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Routing

R

R

R

RRH

H

H

H

R

RH

R

Routers send packet towards

destination

H: Hosts

R: Routers

Extensions to the Network Architecture

• Forwarding• Problems with Internet routing• Beyond point-to-point routing: multicast, mobility,

alternative schemes and metrics for wireless/sensor nets, delay tolerant nets, etc.

• Indirection schemes and intermediaries (“performance enhancing proxies”) to implement new forms of forwarding

• Semester readings on Internet topology, multicast, wireless, i3, DTN, DOA, policy-aware switching, network measurement

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Meeting Application Demands

• Reliability• Corruption• Lost packets

• Flow and congestion control

• Fragmentation

• In-order delivery

• Etc. …

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What if the Data gets Corrupted?

InternetGET windex.htmlGET index.html

Solution: Add a checksum

Problem: Data Corruption

0,9 9 6,7,8 21 4,5 7 1,2,3 6X

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What if Network is Overloaded?

Problem: Network Overload

• Short bursts: buffer• What if buffer overflows?

• Packets dropped• Sender adjusts rate until load = resources “congestion control”

Solution: Buffering and Congestion Control

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What if the Data gets Lost?

InternetGET index.html

Problem: Lost Data

InternetGET index.html

Solution: Timeout and Retransmit

GET index.htmlGET index.html

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Problem: Packet size

Solution: Fragment data across packets

What if the Data Doesn’t Fit?

• On Ethernet, max IP packet is 1.5kbytes• Typical web page is 10kbytes

GETindex.html

GET index.html

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Solution: Add Sequence Numbers

Problem: Out of Order

What if the Data is Out of Order?

GETx.htindeml

GET x.htindeml

GET index.html

ml 4 inde 2 x.ht 3 GET 1

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Lots of Functions Needed

• Link

• Multiplexing

• Routing

• Addressing/naming (locating peers)

• Reliability

• Flow control

• Fragmentation

• Etc. …

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What is Layering?

• Modular approach to network functionality

• Example:

Link hardware

Host-to-host connectivity

Application-to-application channels

Application

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Protocols

• Module in layered structure

• Set of rules governing communication between network elements (applications, hosts, routers)

• Protocols define:• Interface to higher layers (API) • Interface to peer

• Format and order of messages• Actions taken on receipt of a message

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Layering Characteristics

• Each layer relies on services from layer below and exports services to layer above

• Interface defines interaction

• Hides implementation - layers can change without disturbing other layers (black box)

Application-Oriented Networking

• All kinds of new application-specific routing and transport layers• Sensor network dissemination protocols• Content distribution/data oriented networks• Overlay networks • Active networks• Middleboxes/”Performance Enhancing Proxies”

• Layering and E2E assumptions questioned and revised

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Quo Vadis Networking?

• GENI: new architecture for Next Generation• New naming and forwarding as foundation• Security and authenticity from first principles• Experimentation in upper layers, e.g., DTN

• Refocus from wide-area to local-area• Unified telephony and data, wired/wireless• Datacenters for web and batch parallel apps• O(10,000) node DC and enterprise networks• New addressing, transport opportunities

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What Next?

• Thursday, 4 December: Quiz #2

• Friday, 12 December: Research Project Poster Session -- 12-2 PM in Soda 6th Floor• Poster more or less equivalent to 9 slide

research talk• Remember the Heilmeyer Questions!

• Monday, 15 December: 5 PM Project Reports• Specification on the web, 10-20 pages

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