Part 1: Introduction

CSE 3461/5461
Reading: Chapter 1, Kurose and Ross

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 Part I: Introduction
Our goal: Overview:
• Get context, overview, • What’s the Internet
“feel” of networking • What’s a protocol?
• More depth, detail later • Network edge
in course • Network core
• Approach: • Access net, physical media
– Descriptive • Performance: loss, delay
– Use Internet as • Protocol layers, service models
example
• Backbones, NAPs, ISPs
• History

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 Outline
• What is the Internet?
• Network Edge
• Network Core
• Delay, Loss, Throughput in Networks
• Protocol Layers, Service Models
• History

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What’s the Internet: “Nuts and bolts” view
PC Mobile network
• Millions of connected
Server
computing devices:
Wireless Global ISP
laptop – Hosts = end systems
Smartphone
– Running network apps
Home
• Communication links network Regional ISP

Wireless
– Fiber, copper,
links radio, satellite
Wired
links – Transmission rate:
bandwidth

• Packet switches: forward

packets (chunks of data)
Router Institutional
– Routers and switches network
 “Cool” Internet Appliances

Web-enabled toaster +
weather forecaster

IP picture frame
http://www.ceiva.com/

Tweet-a-watt:
monitor energy use

Slingbox: watch,
control cable TV remotely
Internet
refrigerator Internet phones
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 What’s the Internet: “Nuts and Bolts” View
• Internet: “network of Mobile network

networks”
Global ISP
– Loosely hierarchical
– Public Internet versus private
intranet Home
network
• Protocols: control sending, Regional ISP

receiving of messages
– e.g., TCP, IP, HTTP, FTP, PPP
• Internet standards
– RFC: Request For Comments
– IETF: Internet Engineering Task
Force
Institutional
network

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 What’s the Internet: A Service View
• Infrastructure that Mobile network

provides services to
Global ISP
applications:
– Web, VoIP, email, games,
Home
e-commerce, social nets, … network Regional ISP
• Provides programming
interface to apps
– Hooks that allow sending and
receiving app programs to
“connect” to Internet
– Provides service options, Institutional
network
analogous to postal service
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 What’s a Protocol? (1)
Human Protocols: Network Protocols:
• “What’s the time?” • Machines rather than
• “I have a question” humans
• Introductions • All communication
activity in Internet
… specific msgs sent governed by protocols
… specific actions taken Protocols define format, order of
when msgs received, or messages sent and received
other events among network entities, and
actions taken on message
transmission, receipt

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 What’s a Protocol? (2)
Human protocol and computer network protocol:

Hi TCP connection
req.
Hi
TCP connection
Got the reply.
time? GET
2:00 http://gaia.cs.umass.edu/index.htm
<file>

time

Q: Other human protocols?

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 Outline
• What is the Internet?
• Network Edge
• Network Core
• Delay, Loss, Throughput in Networks
• Protocol Layers, Service Models
• History

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 Closer Look at Network Structure

• Network edge:
Applications and
hosts
• Access networks,
physical media:
Wired, wireless
communication links
• Network core:
– Routers
– Network of networks
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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-to-peer model:
– Host interaction symmetric
– e.g.: Gnutella, KaZaA

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Network Edge: Connection-Oriented Service

Goal: Data transfer between endTCP service [RFC 793]

systems
• Handshaking: setup (prepare for) data transfer
• Reliable, ahead
in-order of time
byte-
– Hello, hello back human protocol
stream data transfer
– Set up “state” in two communicating hosts
– Loss: acknowledgements and
• TCP - Transmission Control Protocolretransmissions
– Internet’s connection-oriented service
• 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 Apps using TCP:

end systems • HTTP (WWW), FTP (file
– Same as before! transfer), Telnet (remote
• UDP - User Datagram login), SMTP (email)
Protocol [RFC 768]:
Internet’s connectionless
service Apps using UDP:
– Unreliable data • Streaming media,
teleconferencing, Internet
transfer telephony
– No flow control
– No congestion
control 14
Access Networks and Physical Media
Q: How to connect end
systems to edge router?
• Residential access nets
– Cable modem
• Institutional access
networks (school, company)
– Local area networks
• Mobile access networks
Physical media
• Coax, fiber
• Radio (e.g., WiFi)

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 Outline
• What is the Internet?
• Network Edge
• Network Core
• Delay, Loss, Throughput in Networks
• Protocol Layers, Service Models
• History

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 The Network Core
• Mesh of interconnected
routers
• The fundamental question:
how is data transferred
through network?
– Circuit switching:
dedicated circuit per
call – telephone
network
– Packet switching:
data sent through
network in discrete 17
Network Core: Circuit Switching (1)
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: Circuit Switching (2)
Network resources (e.g., bandwidth) divided
into “pieces”
• Pieces allocated to calls
• Resource piece idle if not used by owning call (no
sharing)
• Dividing link bandwidth into “pieces”
– Frequency division
– Time division

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 Circuit Switching: FDM and TDM
Example:
FDM
4 users

frequency

time
TDM

frequency

time
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Network Core: Packet Switching (1)
Each end-end data stream Resource contention:
divided into packets • Aggregate resource
• Users A, B packets share demand can exceed
network resources amount available
• Each packet uses full link • Congestion: packets queue,
bandwidth wait for link use
• Resources used as needed • Store and forward: packets
move one hop at a time
– Transmit over link
Bandwidth division into “pieces” – Wait turn at next link
Dedicated allocation
Resource reservation

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Network Core: Packet Switching (2)
10 Mbs
A Ethernet Statistical multiplexing C

1.5 Mbps
B
Queue of packets 45 Mbps
waiting for output
link

D E

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 Packet Switching Versus Circuit Switching
Packet switching allows more users to use network!
• 1 Mbit link
• Each user:
– 100 Kbps when “active”
– Active 10% of time

N users
• Circuit switching:
1 Mbps link
– 10 users
• Packet switching:
– With 35 users,
Probability{>10 active} < .0004

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 Packet-Switched Networks: Routing
• Goal: Move packets among routers from source to
destination
– We’ll study several path selection algorithms (chapter 4)
• Datagram network:
– Destination address determines next hop
– Routes may change during session
– Analogy: driving, asking directions
• Virtual circuit network:
– Each packet carries tag (virtual circuit ID), tag determines next hop
– Fixed path determined at call setup time, remains fixed thru call
– Routers maintain per-call state

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 Internet Structure: Network of Networks
• Roughly hierarchical
• National/international
local
backbone providers (NBPs) ISP
– e.g. BBN/GTE, Sprint, AT&T, regional ISP
IBM, UUNet
– Interconnect (peer) with each NBP B
other privately, or at public
Network Access Point (NAPs) NAP NAP
• Regional ISPs NBP A
– connect into NBPs regional ISP
• Local ISP, company local
– connect into regional ISPs ISP

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 National Backbone Provider
e.g. Sprint US backbone network
POP: point-of-presence

to/from backbone

peering
… … …
…

to/from customers

Example: Sprint 26
 Outline
• What is the Internet?
• Network Edge
• Network Core
• Delay, Loss, Throughput in Networks
• Protocol Layers, Service Models
• History

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 Delay in Packet-Switched Networks (1)
Packets experience delay on • Nodal processing:
end-to-end path – Check bit errors
• Four sources of delay at – Determine output link
each hop • Queueing
– Time waiting at output link
for transmission
– Depends on congestion
Transmission level of router
A Propagation

B
Nodal
processing Queueing

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 Delay in Packet-Switched Networks (2)
Transmission Delay: Propagation Delay:
• R = Link bandwidth (bps) • d = Length of physical link
• L = Packet length (bits) • s = propagation speed in
• Time to send bits into link medium (~2×108 m/sec)
= L/R • propagation delay = d/s

Note: s and R are very

different quantities!
Transmission
A Propagation

B
Nodal
Processing Queueing 29
 Queueing delay (revisited)

• R = Link bandwidth (bps)

• L = Packet length (bits)
• a = Average packet arrival
rate

Traffic intensity = La/R

 La/R ~ 0: Average queueing delay small

 La/R → 1: Delays become large
 La/R > 1: More “work” arriving than can be
serviced, average delay infinite!
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 “Real” Internet Delays and Routes
traceroute (or tracert): Routers, round-trip delays on
source-dest path
Also: pingplotter, various Windows programs
1 cs-gw (128.119.240.254) 1 ms 1 ms 2 ms
2 border1-rt-fa5-1-0.gw.umass.edu (128.119.3.145) 1 ms 1 ms 2
ms
3 cht-vbns.gw.umass.edu (128.119.3.130) 6 ms 5 ms 5 ms
4 jn1-at1-0-0-19.wor.vbns.net (204.147.132.129) 16 ms 11 ms 13
ms
5 jn1-so7-0-0-0.wae.vbns.net (204.147.136.136) 21 ms 18 ms 18 ms
6 abilene-vbns.abilene.ucaid.edu (198.32.11.9) 22 ms 18 ms 22
ms
7 nycm-wash.abilene.ucaid.edu (198.32.8.46) 22 ms 22 ms 22 ms
8 62.40.103.253 (62.40.103.253) 104 ms 109 ms 106 ms
9 de2-1.de1.de.geant.net (62.40.96.129) 109 ms 102 ms 104 ms
10 de.fr1.fr.geant.net (62.40.96.50) 113 ms 121 ms 114 ms
11 renater-gw.fr1.fr.geant.net (62.40.103.54) 112 ms 114 ms
112 ms
12 nio-n2.cssi.renater.fr (193.51.206.13) 111 ms 114 ms 116 ms
13 nice.cssi.renater.fr (195.220.98.102) 123 ms 125 ms 124 ms
14 r3t2-nice.cssi.renater.fr (195.220.98.110) 126 ms 126 ms
124 ms
15 eurecom-valbonne.r3t2.ft.net (193.48.50.54) 135 ms 128 ms
133 ms
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16 194.214.211.25 (194.214.211.25) 126 ms 128 ms 126 ms
 Outline
• What is the Internet?
• Network Edge
• Network Core
• Delay, Loss, Throughput in Networks
• Protocol Layers, Service Models
• History

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 Protocol “Layers”
Networks are Complex!
• Many “pieces”:
– Hosts Question:
– Routers Is there any hope of organizing
– Links of various structure of network?
media
Or at least our discussion of
– Applications networks?
– Protocols
– Hardware,
software
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 Internet Protocol Stack
• Application: supporting network
applications Application
– FTP, SMTP, HTTP
• Transport: host-host data transfer Transport
– TCP, UDP
• Network: routing of datagrams from
Network
source to destination
– IP, routing protocols
Link
• Link: data transfer between neighboring
network elements
– PPP, Ethernet Physical
• Physical: bits “on the wire”, “over the air”

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 Layering: Logical Communication (1)
Each layer: Application
Transport
• Distributed Network
• “Entities” Link
Physical
implement layer
Network
functions at each Application Link
node Transport Physical
Network
• Entities perform Link
actions, exchange Physical
Application Application
messages with Transport Transport
peers Network Network
Link Link
Physical Physical

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 Layering: Logical Communication (2)
Data
E.g.: Transport layer Application
Transport
Transport
• Take data from app
Network
• Add addressing, Link
reliability check info to Physical
form “datagram” ACK Network
• Send datagram to peer Application Link
• Wait for peer to ack Transport Data Physical
Network
receipt
Link Data
• Analogy: post office Physical
Application Application
Transport Transport
Transport
Network Network
Link Link
Physical Physical

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Layering: Physical Communication
Data
Application
Transport
Network
Link
Physical
Network
Application Link
Transport Physical
Network
Link
Physical Data
Application Application
Transport Transport
Network Network
Link Link
Physical Physical

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 Protocol Layering and Data
Each layer takes data from above
• Adds header information to create new data unit
• Passes new data unit to layer below

Source Destination
M Application Application M Message
HT M Transport Transport HT M Segment
HNHT M Network Network HNHT M Datagram
HL HNHT M Link Link HL HNHT M Frame
Physical Physical

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 Outline
• What is the Internet?
• Network Edge
• Network Core
• Delay, Loss, Throughput in Networks
• Protocol Layers, Service Models
• History

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 Internet History (1)
1961–1972: Early packet-switching principles
• 1961: Kleinrock – queueing • 1972:
theory shows effectiveness of – ARPAnet demonstrated
packet-switching publicly
• 1964: Baran – packet- – NCP (Network Control
switching in military nets Protocol) first host-host
• 1967: ARPAnet conceived by protocol
Advanced Research Projects – First e-mail program
Agency – ARPAnet has 15 nodes
• 1969: First ARPAnet node
operational

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 Internet History (2)
1972–1980: Internetworking, new and proprietary nets
• 1970: ALOHAnet satellite network Cerf and Kahn’s internetworking
in Hawaii principles:
• 1973: Metcalfe’s PhD thesis – Minimalism, autonomy - no
proposes Ethernet internal changes required to
• 1974: Cerf and Kahn - architecture interconnect networks
for interconnecting networks – Best effort service model
• late 70s: Proprietary architectures: – Stateless routers
DECnet, SNA, XNA
– Decentralized control
• late 70s: Switching fixed length
Define today’s Internet
packets (ATM precursor)
architecture
• 1979: ARPAnet has 200 nodes

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 Internet History (3)
1980–1990: New protocols, a proliferation of networks

• 1983: Deployment of • New national networks:

TCP/IP Csnet, BITnet, NSFnet,
• 1982: SMTP e-mail Minitel
protocol defined • 100,000 hosts connected
• 1983: DNS defined for to confederation of
name-to-IP-address networks
translation
• 1985: FTP protocol
defined
• 1988: TCP congestion
control
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 Internet History (4)
1990s: Commercialization, the WWW
• Early 1990’s: ARPAnet
decommissioned
Late 1990’s:
• 1991: NSF lifts restrictions on • Est. 50 million
commercial use of NSFnet computers on Internet
(decommissioned, 1995) • Est. 100 million+ users
• Early 1990s: WWW
• Backbone links
– hypertext [Bush 1945, Nelson
1960s] running at 1 Gbps
– HTML, http: Berners-Lee
– 1994: Mosaic, later Netscape
– Late 1990s: commercialization
of the WWW

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 Introduction: Summary
Covered a “ton” of material! You now have:
• Internet overview • Context, overview, “feel”
• What’s a protocol? of networking
• Network edge, core, access • More depth, detail later
network in course
– Packet switching versus
circuit switching
• Performance: loss, delay
• Layering and service models
• Backbones, NAPs, ISPs
• History

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