PowerPoint Presentation
Introduction
All material copyright 1996-2012
J.F Kurose and K.W. Ross, All Rights Reserved
George Parisis
School of Engineering and Informatics
University of Sussex
About
Networks are everywhere!
You must understand the principles even if you don’t want to be a network administrator
Most programmers access the network through a high-level API
We will use Java for socket programming
Web applications –> next year
50% coursework (2 assignments) – 50% unseen exam
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About
Everything will be on the Canvas website
Slides
Recorded lectures
Lab exercises
Library Reading List
Forum to discuss stuff
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Lab classes
Lab classes will be
Wireshark, programming
connected with lectures
important to understand the technologies and work with your assignments
NetBeans
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Coursework
1st assignment – week 7 – programming transport layer
2nd assignment – week 11 – socket programming
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My Expectations
You will attend lectures and lab classes
You will attempt to complete each lab exercise during the week, if insufficient time is available in class
You will ask questions if you don’t understand
during the lecture
drop-in sessions
post on forum
send me an email
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Course Outline
Week Lecture Lecture Lab Class Assignment
1 Introduction Introduction –
2 Principles, SMTP, POP3, IMAP The World Wide Web and HTTP Wireshark Introduction, SMTP, POP3
3 The World Wide Web and HTTP DNS and Socket Programming HTTP and Cookies
4 Transport Layer Services, UDP Transport Layer Principles UDP Socket Programming
5 Transport Layer Principles Go-Back-N, Selective Repeat TCP Socket Programming
6 Transmission Control Protocol Transmission Control Protocol –
7 Transmission Control Protocol Network Layer, Virtual Circuit and Datagram Networks TCP and UDP with Wireshark Assignment 1
8 IP, IP Addressing, DHCP, Routers NAT, ICMP, IPv6 IP Addressing and Subnetting
9 Routing Algorithms Routing Algorithms IP with Wireshark
10 RIP, OSPF BGP, Broadcast Routing NAT and DHCP with Wireshark
11 Link Layer, Error Detection, Multiple Access Protocols Ethernet, Ethernet Sources Ethernet and ARP with Wireshark Assignment 2
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Books
Computer Networking, James F. Kurose, Keith W. Ross, Pearson Education, 7th Edition
Library reading list (see Canvas)
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Introduction
Introduction
Goal:
get “feel” and terminology
more depth, detail later in course
Overview:
What is the Internet?
What is a protocol?
network edge: hosts, access net, physical media
performance: loss, delay, throughput
network core: packet/circuit switching, Internet structure
protocol layers, service models
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Introduction
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Introduction
Roadmap
what is the Internet?
delay, loss, throughput in networks
network edge
end systems, access networks, links
network core
packet switching, circuit switching, network structure
protocol layers, service models
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Introduction
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Introduction
What is the Internet: “nuts and bolts” view
billions of connected computing devices:
hosts = end systems
running network apps
communication links
fiber, copper, radio, satellite
transmission rate: bandwidth
Packet switches: forward packets (chunks of data)
routers and switches
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wired
links
wireless
links
router
mobile network
global ISP
regional ISP
home
network
institutional
network
smartphone
PC
server
wireless
laptop
Introduction
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Introduction
Internet: “network of networks”
Interconnected ISPs
protocols control sending, receiving of messages
e.g., TCP, IP, HTTP, Skype, 802.11
Internet standards
RFC: Request for comments by Internet Engineering Task Force (IETF)
Institute of Electrical and Electronics Engineers (IEEE)
What is the Internet: “nuts and bolts” view
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mobile network
global ISP
regional ISP
home
network
institutional
network
Introduction
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What is the Internet: a service view
Infrastructure that provides services to applications:
Web, VoIP, email, games, e-commerce, social nets, …
provides programming interface to apps
hooks that allow sending and receiving, app programs to “connect” to Internet
provides service options, analogous to postal service
Introduction
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mobile network
global ISP
regional ISP
home
network
institutional
network
Introduction
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Introduction
What is 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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Introduction
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Introduction
a human protocol and a computer network protocol:
Hi
Hi
TCP connection
response
TCP connection
request
Wha is a protocol?
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Got the
time?
2:00
Get http://www.awl.com/kurose-ross
time
Introduction
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Introduction
Roadmap
what is the Internet?
delay, loss, throughput in networks
network edge
end systems, access networks, links
network core
packet switching, circuit switching, network structure
protocol layers, service models
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Introduction
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Introduction
How do loss and delay occur?
packets queue in router buffers
packet arrival rate to link (temporarily) exceeds output link capacity
packets queue, wait for turn
A
B
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packet being transmitted (delay)
packets queueing (delay)
free (available) buffers: arriving packets
dropped (loss) if no free buffers
Introduction
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Introduction
Four sources of packet delay
dproc: processing delay
check bit errors
determine output link
typically < msec
A
B
propagation
transmission
nodal
processing
queueing
dqueue: queueing delay
time waiting at output link for transmission
depends on congestion level of router
dtotal = dproc + dqueue + dtrans + dprop
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Introduction
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Introduction
dtrans: transmission delay:
L: packet length (bits)
R: link bandwidth (bps)
dtrans = L/R
dprop: propagation delay:
d: length of physical link
s: propagation speed in medium (~2x108 m/sec)
dprop = d/s
Four sources of packet delay
propagation
nodal
processing
queueing
dnodal = dproc + dqueue + dtrans + dprop
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A
B
transmission
dtrans and dprop
very different
Introduction
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Introduction
“Real” Internet delays and routes
what do “real” Internet delay & loss look like?
traceroute program: provides delay measurement from source to router along end-end Internet path towards destination. For all i:
sends three packets that will reach router i on path towards destination
router i will return packets to sender
sender times interval between transmission and reply.
3 probes
3 probes
3 probes
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Introduction
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Introduction
“Real” Internet delays, routes
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
16 194.214.211.25 (194.214.211.25) 126 ms 128 ms 126 ms
17 * * *
18 * * *
19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136 ms
traceroute: gaia.cs.umass.edu to www.eurecom.fr
3 delay measurements from
gaia.cs.umass.edu to cs-gw.cs.umass.edu
* means no response (probe lost, router not replying)
trans-oceanic
link
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Introduction
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Introduction
Packet loss
queue (aka buffer) preceding link in buffer has finite capacity
packet arriving to full queue dropped (aka lost)
lost packet may be retransmitted by previous node, by source end system, or not at all
A
B
packet being transmitted
packet arriving to
full buffer is lost
buffer
(waiting area)
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Introduction
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Introduction
Throughput
throughput: rate (bits/time unit) at which bits transferred between sender/receiver
instantaneous: rate at given point in time
average: rate over longer period of time
server, with
file of F bits
to send to client
link capacity
Rs bits/sec
link capacity
Rc bits/sec
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server sends bits
(fluid) into pipe
pipe that can carry
fluid at rate
Rs bits/sec)
pipe that can carry
fluid at rate
Rc bits/sec)
Introduction
Introduction
Throughput (more)
Rs < Rc What is the average end-to-end throughput?
Rs bits/sec
Rs > Rc What is the average end-to-end throughput?
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Rc bits/sec
link on end-end path that constrains end-to-end throughput
bottleneck link
Rs bits/sec
Rc bits/sec
Introduction
Introduction
Throughput: Internet scenario
Rs
Rs
Rs
Rc
Rc
Rc
R
per-connection end-end throughput
in practice: Rc or Rs is often bottleneck
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Introduction
Introduction
Roadmap
what is the Internet?
delay, loss, throughput in networks
network edge
end systems, access networks, links
network core
packet switching, circuit switching, network structure
protocol layers, service models
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Introduction
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Introduction
A closer look at network structure
network edge:
hosts: clients and servers
servers often in data centers
access networks, physical media: wired, wireless communication links
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mobile network
global ISP
regional ISP
home
network
institutional
network
Introduction
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Introduction
Access networks and physical media
Q: How to connect end systems to edge router?
residential access nets
DSL
Cable
FTTH
institutional access networks (school, company)
mobile access networks
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Introduction
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Introduction
Access net: digital subscriber line (DSL)
central office
telephone
network
DSLAM
use existing telephone line to central office DSLAM
data over DSL phone line goes to Internet
voice over DSL phone line goes to telephone net
A high-speed downstream channel, in the 50 kHz to 1 MHz band
A medium-speed upstream channel, in the 4 kHz to 50 kHz band
An ordinary two-way telephone channel, in the 0 to 4 kHz band
DSL
modem
splitter
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ISP
voice, data transmitted
at different frequencies over
dedicated line to central office
DSL access
multiplexer
Introduction
Introduction
Access net: home network
to/from headend or central office
wireless
devices
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cable or DSL modem
router, firewall, NAT
wired Ethernet (1 Gbps)
wireless access
point (54 Mbps)
often combined
in single box
Introduction
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Introduction
Enterprise access networks (Ethernet)
typically used in companies, universities, etc
10 Mbps, 100Mbps, 1Gbps, 10Gbps transmission rates
today, end systems typically connect into Ethernet switches
Ethernet
switch
institutional mail,
web servers
institutional router
institutional link to
ISP (Internet)
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Introduction
Introduction
Wireless access networks
shared wireless access network connects end system to router
via base station aka “access point”
wireless LANs:
within building (100 ft)
802.11b/g (WiFi): 11, 54 Mbps transmission rate
wide-area wireless access
provided by telco (cellular) operator, 10’s km
between 1 and 10 Mbps
3G, 4G: LTE
to Internet
to Internet
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Introduction
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Introduction
Physical media
bit: propagates between
transmitter/receiver pairs
electromagnetic waves or optical pulses across a physical medium
physical link: what lies between transmitter & receiver
guided media:
signals propagate in solid media: copper, fiber, coax
unguided media:
signals propagate freely, e.g., radio
twisted pair (TP)
two insulated copper wires
each about 1 mm thick, arranged in a regular spiral pattern (to reduce the electrical interference from similar pairs close by)
Category 5: 100 Mbps, 1 Gpbs Ethernet
Category 6: 10Gbps
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Introduction
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Introduction
Physical media: coaxial, fiber
coaxial cable:
two concentric copper conductors
bidirectional
fiber optic cable:
glass fiber carrying light pulses, each pulse a bit
high-speed operation:
high-speed point-to-point transmission (e.g., 10’s-100’s Gpbs transmission rate)
low error rate:
repeaters spaced far apart
immune to electromagnetic noise
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Introduction
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Introduction
Physical media: radio
signal carried in electromagnetic spectrum
no physical “wire”
bidirectional
propagation environment effects:
reflection
obstruction by objects
interference
radio link types:
terrestrial microwave
e.g. up to 45 Mbps channels
LAN (e.g., WiFi)
11Mbps, 54 Mbps
wide-area (e.g., cellular)
3G cellular: ~ few Mbps
satellite
Kbps to 45Mbps channel (or multiple smaller channels)
270 msec end-end delay
geosynchronous versus low altitude
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Introduction
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Introduction
Summary
Internet overview
what’s a protocol?
delay, throughput
network edge, access networks
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Introduction
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