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CSE 330: Advanced Computer Networks

Bing WangComputer Science & Engineering

DepartmentFall 2006

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Course info

Instructor: Bing Wang, bing@engr.uconn.edu

Office: ITEB 367 Lecture: 3:30-4:45pm, MW, ITEB 127 Office hours: by appointment

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Course Goals

Advanced, fundamental networking principles foundational material: longer life mix of theory and practice a second course: i.e., assumes a first course on both wired and wireless networks

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Course Topics

common themes: randomization, indirection, virtualization, multiplexing, scalability, optimization

network algorithmics: routing algorithms network control: congestion control, TCP network simulation, performance analysis network measurement/management topics in wireless networks: MAC,

measurement, performance, management, security, TCP in wireless networks Difference & synergy between wired & wireless

network

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Course mechanics

class www site: www.engr.uconn.edu/~bing/cse330

textbook: none papers, all posted on www site

prereq: previous course in networking some knowledge of probability,

optimization theory, algorithms workload:

2 written homeworks 1 programming assignment (on using ns-2) 1 semester-long project

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Grading

Class participation (10%) Notes & reading online

Homework (30%) Semester-long project (60%)

Goal: hand-on experiences through a well-defined research problem

Team of 2 students Topic (your background, preference)

• Fill in background survey Proposal (due 5th class) Midterm report/presentation (14th class) Final report/presentation (last class)

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Part 0: Networking Review Goals: review key topics

from intro networks course equalize

backgrounds identify remedial

work ease into course

Overview: overview error control flow control congestion control routing LANs addressing synthesis:

“a day in the life” control timescales

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What’s a network: “nuts and bolts” view

network edge: millions of end-system devices: pc’s workstations,

servers PDA’s, phones, toastersrunning network apps

network core: routers, switches forwarding data packets: packet switching calls: circuit switching

communication links fiber, copper, radio, …

local net

companynet

regional net

router workstation

servermobile

Web-enabled toaster+weather forecasterhttp://dancing-man.com/robin/toasty/

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What’s a protocol?a human protocol and a computer network protocol:

Hi

Hi

Got thetime?

2:00

TCP connection req.

TCP connectionreply.Get http://www.cse.uconn.edu/index.html

<file>time

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What’s a protocol?

human protocols: “what’s the time?” “I have a question” introductions

… specific msgs sent… specific actions

taken when msgs received, or other events

network protocols: machines rather than

humans all communication

activity in Internet governed by protocols

protocols define format, order of msgs sent and

received among network entities, and actions taken on msg transmission, receipt

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A closer look at network structure: network edge:

applications and hosts network core:

routers network of networks

access networks, physical media: communication links

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The network edge:

end systems (hosts): run application programs e.g., WWW, email at “edge of network”

client/server model client host requests,

receives service from server e.g., WWW client (browser)/

server; email client/server

peer-peer model: host interaction symmetric e.g.: Gnutella, KaZaA

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Network edge: connection-oriented service

Goal: data transfer between end systems

handshaking: setup (prepare for) data transfer ahead of time Hello, hello back

human protocol set up “state” in two

communicating hosts

TCP - Transmission Control Protocol Internet’s connection-

oriented service

TCP service [RFC 793] reliable, in-order byte-

stream data transfer loss: acknowledgements

and retransmissions

flow control: sender won’t overwhelm

receiver

congestion control: senders “slow down

sending rate” when network congested

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Network edge: connectionless service

Goal: data transfer between end systems same as before!

UDP - User Datagram Protocol [RFC 768]: Internet’s connectionless service unreliable data

transfer no flow control no congestion

control

App’s using TCP: HTTP (WWW),

BitTorrent (file transfer), Telnet (remote login), SMTP (email)

App’s using UDP: streaming media,

teleconferencing, Internet telephony

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The Network Core

mesh of interconnected routers

fundamental question: how is data transferred through net? circuit switching:

dedicated circuit per call: telephone net

packet-switching: data sent thru net in discrete “chunks”

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Network Core: Circuit Switching

End-end resources reserved for “call”

link bandwidth, switch capacity

dedicated resources: no sharing

circuit-like (guaranteed) performance

call setup required

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Network Core: Packet Switching

each end-end data stream divided into packets

user A, B packets share network resources

each packet uses full link bandwidth

resources used as needed,

resource contention: aggregate resource

demand can exceed amount available

congestion: packets queue, wait for link use

store and forward: packets move one hop at a time transmit over link wait turn at next

link

Bandwidth division into “pieces”Dedicated allocationResource reservation

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Access networks and physical media

Q: How to connect end systems to edge router?

residential access nets institutional access

networks (school, company)

mobile access networks

Keep in mind: bandwidth (bits per

second) of access network?

shared or dedicated?

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Example access net: home network

Typical home network components: ADSL or cable modem router/firewall Ethernet wireless access point

wirelessaccess point

wirelesslaptops

router/firewall

cablemodem

to/fromcable

headend

Ethernet(switched)

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We have seen “pieces” of network edge, core, links protocols

How do we talk about “structure” of network and its architecture? layered architecture

structure allows identification, relationship of complex system’s pieces: layered reference model for discussion

layer N builds on services provided by layer N-1 layer N provides service to layer N+1

physical topology, interconnection

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Internet protocol stack application: supporting network

applications ftp, smtp, http, BitTorrent

transport: host-host data transfer tcp, udp

network: routing of datagrams from source to destination ip, routing protocols

link: data transfer between neighboring network elements ppp, ethernet

physical: bits “on the wire”

application

transport

network

link

physical

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Layering: logical communication

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical

networklink

physical

data

E.g.: transport take data from

app add addressing,

reliability check info to form “datagram”

send datagram to peer

wait for peer to ack receipt

analogy: post office

data

transport

transport

data

ack

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Layering: physical communication

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical

networklink

physical

data

data

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Internet structure: network of networks

roughly hierarchical at center: “tier-1” ISPs (e.g., UUNet, BBN/Genuity,

Sprint, AT&T), national/international coverage treat each other as equals

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

Tier-1 providers interconnect (peer) privately

NAP

Tier-1 providers also interconnect at public network access points (NAPs)

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Internet structure: network of networks

“Tier-2” ISPs: smaller (often regional) ISPs Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

NAP

Tier-2 ISPTier-2 ISP

Tier-2 ISP Tier-2 ISP

Tier-2 ISP

Tier-2 ISP pays tier-1 ISP for connectivity to rest of Internet tier-2 ISP is customer oftier-1 provider

Tier-2 ISPs also peer privately with each other, interconnect at NAP

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Internet structure: network of networks

“Tier-3” ISPs and local ISPs last hop (“access”) network (closest to end systems)

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

NAP

Tier-2 ISPTier-2 ISP

Tier-2 ISP Tier-2 ISP

Tier-2 ISP

localISPlocal

ISPlocalISP

localISP

localISP Tier 3

ISP

localISP

localISP

localISP

Local and tier- 3 ISPs are customers ofhigher tier ISPsconnecting them to rest of Internet

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Internet structure: network of networks

a packet passes through many networks!

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

NAP

Tier-2 ISPTier-2 ISP

Tier-2 ISP Tier-2 ISP

Tier-2 ISP

localISPlocal

ISPlocalISP

localISP

localISP Tier 3

ISP

localISP

localISP

localISP

Try a traceroute!