CS 268: Computer Networking - BNRGbnrg.eecs.berkeley.edu/~randy/Courses/CS268.F08/lectures/23... ·...
Transcript of CS 268: Computer Networking - BNRGbnrg.eecs.berkeley.edu/~randy/Courses/CS268.F08/lectures/23... ·...
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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
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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 Server Computer 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
R R H
H
H
H
R
R H
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?
Internet GET windex.html GET index.html
Solution: Add a checksum
Problem: Data Corruption
0,9 9 6,7,8 21 4,5 7 1,2,3 6 X
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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?
Internet GET index.html
Problem: Lost Data
Internet GET index.html
Solution: Timeout and Retransmit
GET index.html GET 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
GET inde x.ht ml
GET index.html
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Solution: Add Sequence Numbers
Problem: Out of Order
What if the Data is Out of Order?
GET x.ht inde ml
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)
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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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