Download 23-wrapup

CS 268: Computer Networking
L-23 Course Wrap-up
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
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Traditional
Layering
Internet architecture
Routing (IP)
Transport (TCP)
Queue management
(FQ, RED)
Naming (DNS)
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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]
• A collection of
interconnected
networks
• Host: network
endpoints (computer,
PDA, light switch, …)
• Router: node that
connects networks
• Internet vs. internet
Internet[work]
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Challenge
• Many differences between networks
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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
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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
Computer 1
Local DNS Server
Translates human readable names to logical endpoints
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Extensions to the Network Architecture
• Naming
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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
Routers send
packet towards
destination
H
R
R
R
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H
R
R
R
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R
R
H
H: Hosts
R: Routers
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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, policyaware switching, network measurement
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Meeting Application Demands
• Reliability
• Corruption
• Lost packets
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Flow and congestion control
Fragmentation
In-order delivery
Etc. …
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What if the Data gets Corrupted?
Problem: Data Corruption
GET index.html
Internet
GET windex.html
Solution: Add a checksum
0,9 9
6,7,8 21
X
4,5 7
1,2,3 6
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What if Network is Overloaded?
Problem: Network Overload
Solution: Buffering and Congestion Control
• Short bursts: buffer
• What if buffer overflows?
• Packets dropped
• Sender adjusts rate until load = resources  “congestion control”
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What if the Data gets Lost?
Problem: Lost Data
GET index.html
Internet
Solution: Timeout and Retransmit
GET index.html
Internet
GET index.html
GET index.html
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What if the Data Doesn’t Fit?
Problem: Packet size
• On Ethernet, max IP packet is 1.5kbytes
• Typical web page is 10kbytes
Solution: Fragment data across packets
ml
x.ht
inde
GET
GET index.html
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What if the Data is Out of Order?
Problem: Out of Order
ml
inde
x.ht
GET
GET x.htindeml
Solution: Add Sequence Numbers
ml 4
inde 2
x.ht 3
GET 1
GET index.html
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Lots of Functions Needed
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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:
Application
Application-to-application channels
Host-to-host connectivity
Link hardware
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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
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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
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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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