E l e c t r i c a l    &   C o m p u t e r
Department of
Electrical & Computer Engineering
1
EE 586 Communication andSwitching Networks
Lecture 2
E l e c t r i c a l    &   C o m p u t e r
Department of
Electrical & Computer Engineering
Chapter 1: introduction
our goal:
get feel andterminology
more depth, detaillater in course
approach:
use Internet asexample
overview:
history
whats the Internet?
whats a protocol?
network edge; hosts, access net,physical media
network core: packet/circuitswitching, Internet structure
performance: loss, delay,throughput
security
protocol layers, service models
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1-2
(modified by Cheung for EE586; based on K&R original)
E l e c t r i c a l    &   C o m p u t e r
Department of
Electrical & Computer Engineering
Internet history
1961: Kleinrock - effectiveness of packet-switching
1964: Baran - packet-switching in military nets
1967: ARPAnet conceived
1972: 15-node ARPAnet public demo: email
1961-1972: Early packet-switching principles
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1-3
1972-1980:  Internetworking, new and proprietary nets
1970:  ALOHAnet satellite network in Hawaii
1974:  Cerf and Kahn - interconnecting networks
1976:  Ethernet at Xerox PARC
late70s: proprietary architectures: DECnet, SNA, XNA
1979:  ARPAnet has 200 nodes
(modified by Cheung for EE586; based on K&R original)
http://laughingsquid.com/wp-content/uploads/lenonard-klenrock-imp-20090902-082723.jpg
http://upload.wikimedia.org/wikipedia/en/2/27/Paul_Baran.jpg
http://www.computerhistory.org/internet_history/full_size_images/1969_4-node_map.gif
http://wikipcpedia.com/wp-content/uploads/2011/06/ALOHAnet_islands.jpg
http://www.cubadebate.cu/wp-content/uploads/2013/12/Vint-Cerf-And-Bob-Kahn.jpg
http://bogpeople.com/networking/metcalfe-enet.gif
E l e c t r i c a l    &   C o m p u t e r
Department of
Electrical & Computer Engineering
1982: smtp e-mail protocol defined
1983: deployment of TCP/IP
1983: DNS defined for name-to-IP-address translation
1985: ftp protocol defined
1988: TCP congestion control
1980-1990: new protocols, a proliferation of networks
Internet history
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1-4
(modified by Cheung for EE586; based on K&R original)
1990, 2000s: commercialization, the Web, new apps
early 1990s:  Berners-Lee: HTML,  HTTP
1994: Mosaic, later Netscape
late1990s:  commercialization of the web
2000s:
more killer apps: instant messaging, P2P file sharing
network security to forefront
backbone links running at Gbps
http://upload.wikimedia.org/wikipedia/commons/thumb/c/c2/Tim_Berners-Lee_2012.jpg/640px-Tim_Berners-Lee_2012.jpg
http://upload.wikimedia.org/wikipedia/en/b/b7/NCSA_Mosaic.PNG
http://upload.wikimedia.org/wikipedia/en/f/f5/Netscape9.png
E l e c t r i c a l    &   C o m p u t e r
Department of
Electrical & Computer Engineering
2005-present
~750 million hosts
Smartphones and tablets
Aggressive deployment of broadband access
Increasing ubiquity of high-speed wireless access
Emergence of online social networks:
Facebook: soon one billion users
Service providers (Google, Microsoft) create their ownnetworks
Bypass  Internet, providing instantaneous accessto search, emai, etc.
E-commerce, universities, enterprises running theirservices in cloud (eg, Amazon EC2)
Internet of things
Internet history
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1-5
(modified by Cheung for EE586; based on K&R original)
E l e c t r i c a l    &   C o m p u t e r
Department of
Electrical & Computer Engineering
“Nuts & Bolts” of Internet
millions of connectedcomputing devices:
hosts = end systems
running network apps
communication links
fiber, copper, radio,satellite
transmission rate:bandwidth
Packet switches: forwardpackets (chunks of data)
Internet: network edge +network core
wired
links
wireless
links
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router
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mobile network
global ISP
regional ISP
home
network
institutional
       network
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smartphone
PC
server
wireless
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(modified by Cheung for EE586; based on K&R original)
E l e c t r i c a l    &   C o m p u t e r
Department of
Electrical & Computer Engineering
A closer look at network structure:
network edge:
hosts: clients and servers
servers often in data centers
service driven
access networks:
gateway to network core
different physical mediumsand technologies
network core:
interconnected routers
network of networks
standard driven
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mobile network
global ISP
regional ISP
home
network
institutional
       network
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(modified by Cheung for EE586; based on K&R original)
E l e c t r i c a l    &   C o m p u t e r
Department of
Electrical & Computer Engineering
Network Protocols
Internet  standards
IETF: Internet Engineering Task Force
RFC: Request for comments
e.g. TCP, IP, HTTP
Find out what RFC 793 is.
Web standards
W3C: World Wide Web Consortium
REC: Recommendation
e.g. HTML, XML, SOAP
Other standard bodies
IEEE, ITU, ISO, ANSI, ETSI, …
Proprietary standards
Skype
“Language” of Internet
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mobile network
global ISP
regional ISP
home
network
institutional
       network
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1-8
(modified by Cheung for EE586; based on K&R original)
E l e c t r i c a l    &   C o m p u t e r
Department of
Electrical & Computer Engineering
Alice
Bob
Hi
Hi
Got the
time?
2:00
TCP connection
response
Get http://www.google.com
<file>
time
TCP connection
request
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What is a protocol?
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Protocols define formatorder of messenges sent and received amongnetwork entities, and actions taken on messenge transmission, receipt
(modified by Cheung for EE586; based on K&R original)
E l e c t r i c a l    &   C o m p u t e r
Department of
Electrical & Computer Engineering
Host: sends packets of data
host sending function:
breaks data into smallerchunks, known as packets,of length L bits
transmits packet intoaccess network attransmission rate R
How fast can a hostsend data?
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R: link transmission rate
host
1
2
two packets,
L bits each
packet
transmission
delay
time needed to
transmit L-bit
packet into link
L (bits)
R (bits/sec)
=
=
1-10
(modified by Cheung for EE586; based on K&R original)
Not to confuse withlatency – how long ittakes to get to receiver!
E l e c t r i c a l    &   C o m p u t e r
Department of
Electrical & Computer Engineering
end-end delay = 2L/R (assumingzero propagation delay)
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Packet-switching: store-and-forward
takes L/R seconds to transmit(push out) L-bit packet into linkat R bps
store and forward: entire packetmust  arrive at router before itcan be transmitted on next link
one-hop numerical example:
L = 7.5 Mbits
R = 1.5 Mbps
How long does it taketo traverse 2 hops?
1-11
source
R bps
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destination
1
2
3
L bits
per packet
R bps
(modified by Cheung for EE586; based on K&R original)
E l e c t r i c a l    &   C o m p u t e r
Department of
Electrical & Computer Engineering
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Packet Switching: queueing delay, loss
A
B
C
R = 100 Mb/s
R = 1.5 Mb/s
D
E
queue of packets
waiting for output link
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queuing and loss:
If arrival rate (in bits) to link exceeds transmission rate oflink for a period of time:
packets will queue, wait to be transmitted on link
packets can be dropped (lost) if memory (buffer) fills up
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(modified by Cheung for EE586; based on K&R original)
E l e c t r i c a l    &   C o m p u t e r
Department of
Electrical & Computer Engineering
(modified by Cheung for EE586; based on K&R original)
13
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Clarification of Transmission Rate
Transmission Rate (similar to bandwidth sometimes*)
= how many bits (balls) that can be sent (kicked) out in 1 second
Even with high transmission rate, it might take a longtime for the first bit to arrive (long propagation delay)but the subsequent bits will come at transmission rate.
E l e c t r i c a l    &   C o m p u t e r
Department of
Electrical & Computer Engineering
Alternative core: circuit switching
end-end resources allocatedto, reserved for callbetween source anddestination:
In diagram, each link has fourcircuits.
call gets 2nd circuit in toplink and 1st circuit in rightlink.
dedicated resources: no sharing
circuit-like (guaranteed)performance
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circuit segment idle if not usedby call (no sharing)
Commonly used in telephonenetworks and network core
(modified by Cheung for EE586; based on K&R original)
E l e c t r i c a l    &   C o m p u t e r
Department of
Electrical & Computer Engineering
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Circuit switching: FDM versus TDM
Freq. Division Multiplexing
frequency
time
Time Division Multiplexing
frequency
time
4 users
Example:
1-15
(modified by Cheung for EE586; based on K&R original)
E l e c t r i c a l    &   C o m p u t e r
Department of
Electrical & Computer Engineering
Example
How long does it take to send a file of 640,000bits from host A to host B over a circuit-switchednetwork?
All links have transmission rate 1.536 Mbps
Each link uses TDM with 24 slots/sec
500 msec to establish end-to-end circuit
The bandwidth 1.536Mbps is equally divided up between the24 users. Each user gets 1.536Mbps/24 = 64 kbps.
Note that the choice of TDM is immaterial here!
Time = setup time (500msec) + transmission time(640kb/64kbps) = 10.5s
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(modified by Cheung for EE586; based on K&R original)
1-16
E l e c t r i c a l    &   C o m p u t e r
Department of
Electrical & Computer Engineering
Access networks and physical media
Q: How to connect endsystems to edge router?
residential access nets
institutional accessnetworks (school,company)
mobile access networks
They differ in mainly:
bandwidth (bits per second)and delay (bits travel time)
shared or dedicated?
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1-17
(modified by Cheung for EE586; based on K&R original)
E l e c t r i c a l    &   C o m p u t e r
Department of
Electrical & Computer Engineering
Access net: cable network
cable
modem
splitter
tv
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tv
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tv
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tv
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Channels
V
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D
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frequency division multiplexing: different channels transmitted
in different frequency bands
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(modified by Cheung for EE586; based on K&R original)
The Comcast logo
Time Warner Cable logo
22 mil
Cox logo.svg
Charter logo.png
Cablevision.svg
cable headend
12 mil
4.5 mil
E l e c t r i c a l    &   C o m p u t e r
Department of
Electrical & Computer Engineering
data, TV transmitted at different
frequencies over shared cable
distribution network
cable
modem
splitter
tv
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tv
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CMTS
ISP
cable modem
termination system
HFC: hybrid fiber coax
asymmetric: up to 30Mbps downstream, 2 Mbps upstream
network of cable, fiber attaches homes to ISP router
homes share access network to cable headend
downstream: broadcast
upstream: multiple access protocol to arbitrate usage
Access net: cable network
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(modified by Cheung for EE586; based on K&R original)
cable headend
E l e c t r i c a l    &   C o m p u t e r
Department of
Electrical & Computer Engineering
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Access net: digital subscriber line (DSL)
central office
ISP
telephone
network
DSLAM
voice, data transmitted
at different frequencies over
dedicated line to central office
use existing & dedicated telephone line to central office
data over DSL phone line goes to Internet
voice over DSL phone line goes to telephone net
< 2.5 Mbps upstream transmission rate (typically < 1 Mbps)
< 24 Mbps downstream transmission rate (typically < 10 Mbps)
DSL
modem
splitter
DSL access
multiplexer
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(modified by Cheung for EE586; based on K&R original)
E l e c t r i c a l    &   C o m p u t e r
Department of
Electrical & Computer Engineering
Access net: home network
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to/from headend orcentral office
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cable or DSL modem
router, firewall, NAT
wired Ethernet (up to 100 Gbps)
wireless access
point (300 Mbps – 7 Gbps)
wireless
devices
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often combined
in single box
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(modified by Cheung for EE586; based on K&R original)
E l e c t r i c a l    &   C o m p u t e r
Department of
Electrical & Computer Engineering
Enterprise access networks (Ethernet)
typically used in companies, universities, etc
10 Mbps, 100Mbps, 1Gbps, 10Gbps transmission rates
today, end systems typically connect into Ethernet switch
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Ethernet
switch
institutional mail,
web servers
institutional router
institutional link to
ISP (Internet)
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(modified by Cheung for EE586; based on K&R original)
Network layerdevice
Link layerdevice
E l e c t r i c a l    &   C o m p u t e r
Department of
Electrical & Computer Engineering
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Physical media
bit: propagates betweentransmitter/receiver pairs
physical link: what liesbetween transmitter &receiver
guided media:
signals propagate in solidmedia: copper, fiber, coax
unguided media:
signals propagate freely,e.g., radio
twisted pair (TP)
two insulated copperwires
Category 5: 100 Mbps, 1Gpbs Ethernet
Category 6: 10Gbps
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(modified by Cheung for EE586; based on K&R original)
http://multihow.net/wp-content/uploads/2011/08/twist-comparison.png
E l e c t r i c a l    &   C o m p u t e r
Department of
Electrical & Computer Engineering
1-24
Physical Media: coax, fiber
Coaxial cable:
two concentric copperconductors
bidirectional
baseband:
single channel on cable
legacy Ethernet
broadband:
 multiple channels on cable
 HFC
Fiber optic cable:
glass fiber carrying lightpulses, each pulse a bit
high-speed operation:
high-speed point-to-pointtransmission (e.g., 10’s-100’sGps)
low error rate: repeatersspaced far apart ; immune toelectromagnetic noise
f-pict
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(modified by Cheung for EE586; based on K&R original)
E l e c t r i c a l    &   C o m p u t e r
Department of
Electrical & Computer Engineering
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Physical media: radio
signal carried inelectromagnetic spectrum
no physical wire
bidirectional
propagation environmenteffects:
reflection
obstruction by objects
Interference
radio link types:
terrestrial  microwave
e.g. up to 45 Mbps channels
LAN (e.g., WiFi)
Mbps - Gbps
wide-area (e.g., cellular)
3G cellular: ~ few Mbps
4G cellular: up to Gbps
satellite
Kbps to 45Mbps channel (ormultiple smaller channels)
270 msec end-end delay
geosynchronous versus lowaltitude
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(modified by Cheung for EE586; based on K&R original)