#2 1
Victor S. FrostDan F. Servey Distinguished Professor Electrical Engineering and Computer
ScienceUniversity of Kansas2335 Irving Hill Dr.
Lawrence, Kansas 66045Phone: (785) 864-4833 FAX:(785) 864-
7789 e-mail: [email protected]
http://www.ittc.ku.edu/
Review of Networking Principles#2
All material copyright 2006Victor S. Frost, All Rights Reserved
#2 2
Review of Networking Principles
• Who is communicating?• What is being communicated?• How are network functions
structured?• What is the architecture of the
Internet?• What is being shared?
#2 3
Who is Communicating
• Internet
Source: Pew Internet & American Life Project, February
15 – April 6, 2006 TrackingSurvey. N=4,001 adults, 18 and older. Margin of error is
±2% for results based onthe full sample and ±2% for results based on internet
users.Please note that prior to our January 2005 survey, the
question used to identify internet users read, “Do you ever go online to access the Internet or World Wide Web or to send and receive email?” The current
two-part question wordingreads, “Do you use the internet, at least occasionally? and
“Do you send or receive email, at least occasionally?”Last updated April 26, 2006.
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Who is Communicating
Adult Teen
Cell Phone 73% 45%
Laptop 30% 32%
MP3 Palyer 20% 47%
From: Lee Rainie Director, Pew Internet & American Life Project 5/9/06 How the Internet is Changing Consumer Behavior and Expectations Speech to SOCAP Symposium (Society of Consumer Affairs Professionals in Business)
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What is being Communicated
• Entertainment– Music– Video
• Rea-time• Non Real-time
– Games• Speech• Information
– News– Stock quotes– Education/Training– Product information– Job search– Health information– Government information
• Transactions– Customer-to-Business
• On-line banking• Purchase
products/services– Business-to-Business
• Transducer data– Temperature– Motion– Other…..
• Scientific data
#2 6
What is being CommunicatedSource: Pew Internet & American Life Project Tracking surveys
(March 2000 – April 2006). Please note that thewording for some items has been abbreviated. For full question
wording, please refer to the questionnaire.*Prior to January 2005, item wording was slightly different for the
items marked with an asterisk. questionnaires for question wording changes.
**Percentage of internet users who do these activities on a typical day is less than 1%
Last updated: April 26, 2006 – Daily Internet Activities were not asked in the January 2006 or May-June 2005
Tracking Survey.
From: Lee Rainie Director, Pew Internet & American Life Project 5/9/06 How the Internet is Changing Consumer Behavior and
Expectations Speech to SOCAP Symposium (Society of Consumer Affairs Professionals in Business)
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Where are the communicating end-points
• Homes• Offices• Vehicles
– Cars– Trucks
• Trains• Planes• Laboratories• In the field
From: John B. Horrigan, BROADBAND ADOPTION AT HOME IN THE UNITED STATES:GROWING BUT SLOWING, 33rd Annual TELECOMMUNICATIONS POLICY RESEARCH CONFERENCE September 24, 2005
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Networking Basics :Information Flow
Internet
AccessMedia
Information Flow
#2 9
Network architectures and the Reference Models
• Open systems are build upon a Layered Architecture of the network
• Layered Architecture is the “structuring” of network functions
• Reference models provide:– A conceptual framework to
characterize networks– A mechanism to control/describe the
complexity of networks– Required for open systems
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Internet protocol stack• application: supporting network
applications– FTP, SMTP, STTP
• 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
From: Computer Networking: A Top Down Approach Featuring the Internet, 2nd edition. Jim Kurose, Keith Ross Addison-Wesley, July 2002.
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Layering: logical communication
applicationtransportnetwork
linkphysical
applicationtransportnetwork
linkphysical
applicationtransportnetwork
linkphysical
applicationtransportnetwork
linkphysical
networklink
physical
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
transport
transport
From: Computer Networking: A Top Down Approach Featuring the Internet, 2nd edition. Jim Kurose, Keith Ross Addison-Wesley, July 2002.
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Layering: physical communication
applicationtransportnetwork
linkphysical
applicationtransportnetwork
linkphysical
applicationtransportnetwork
linkphysical
applicationtransportnetwork
linkphysical
networklink
physical
data
data
From: Computer Networking: A Top Down Approach Featuring the Internet, 2nd edition. Jim Kurose, Keith Ross Addison-Wesley, July 2002.
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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
applicationtransportnetwork
linkphysical
applicationtransportnetwork
linkphysical
source destination
M
M
M
M
Ht
HtHn
HtHnHl
M
M
M
M
Ht
HtHn
HtHnHl
message
segment
datagram
frame
From: Computer Networking: A Top Down Approach Featuring the Internet, 2nd edition. Jim Kurose, Keith Ross Addison-Wesley, July 2002.
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3 2 11 2
21
3 2 11 2
21
21
Medium
3 2 11 221
21
21
2 134 1 2 3 4
End System
End System
Network
1
2
Physical layer entity
Data link layer entity 3 Network layer entity
3 Network layer entity
Transport layer entity4
Modified from: Leon-Garcia & Widjaja: Communication Networks
Router
End-to-End System
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Layering for the Access Network
• Physical Layer– Responsible for the media interface,
e.g., radio interface, powerline or optical
– Characterized by – Capacity in b/s
• Quality in bit error rate
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Layering for the Access Network
• Data Link Layer– Medium Access Control (MAC)
sublayer• Controls transmissions on the physical
layer
– Link access control (LAC)• Manages the logical link
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Segmentation and Reassembly
• Segmentation Often lower layers breakup packets into smaller elements add overhead to the smaller elements for transmission
• Reassembly combines smaller elements to form packet
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Segmentation and Reassembly
• Example:
Hs
MH tH n Higher Layer Packet
MH tH n HL2
Link LayerHL2=Link Layer OverheadHs=Segment OverheadHMac= MAC Overhead
Hs Hs
Hs HMAC Hs HMAC Hs HMAC
Seg
men
tati
on
Reass
em
bly
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Segmentation and Reassembly
• Specific Example:
Hs
MH tH n Higher Layer Packet
MH tH n HL2
Radio ControlHRLC=Link Layer OverheadHs=RLC OverheadHMac= MAC OverheadHs Hs
Hs HMAC Hs HMAC Hs HMAC
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What’s the Internet: “nuts and bolts” view
• millions of connected computing devices: hosts, end-systems– PCs workstations, servers– PDAs phones, toasters
running network apps• communication links
– fiber, copper, radio, satellite
– transmission rate = bandwidth
• routers: forward packets (chunks of data)
local ISP
companynetwork
regional ISP
router workstation
servermobile
From: Computer Networking: A Top Down Approach Featuring the Internet, 2nd edition. Jim Kurose, Keith RossAddison-Wesley, July 2002.
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Architecture of the Internet
From: Computer Networks, A. S. Tannenbaum, 4th Ed, Prentice Hall, 2003
e.g., Sprint or ATT
or cable system
Voice, Image, Data, Video
e.g., Sprint or ATT
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Tier-1 ISP: e.g., Sprint
Sprint US backbone network
From: Computer Networking: A Top Down Approach Featuring the Internet, 2nd edition. Jim Kurose, Keith RossAddison-Wesley, July 2002.
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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
From: Computer Networking: A Top Down Approach Featuring the Internet, 2nd edition. Jim Kurose, Keith RossAddison-Wesley, July 2002.
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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
From: Computer Networking: A Top Down Approach Featuring the Internet, 2nd edition. Jim Kurose, Keith RossAddison-Wesley, July 2002.
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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
From: Computer Networking: A Top Down Approach Featuring the Internet, 2nd edition. Jim Kurose, Keith RossAddison-Wesley, July 2002.
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What is being shared?
• The are shared resources in access networks
• Sharing implies some form of access coordination
• Coordination must be based on some perception of the state on the “system”– Which nodes have packets to send?– Do nodes have a common clock?– Is a wireless node in a deep fade?
• In general the more state information the nodes have the more efficient the sharing
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Duplexing
• Transmit and receive information flows also share the physical connection.
• Half Duplex-transmit and then receive
• Full Duplex-transmit and receive at the same time, split physical connection into a– Transmit
resources– Receive
resources
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Downstream and Upstream
• Upstream and downstream can use different access technologies
• All information flows from the node go toward the Internet
• All information flows destine for the nodes come from the Internet
I nternetInternet
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What is being shared?
• On the physical connection: resources– Time– Frequency– Power/Code– Space
• System elements resources– Buffer– Processing
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FDMA and TDMA
FDMA= Frequency Division Multiple Access
frequency
timeTDMA= Time Division Multiple Access
frequency
4 users
Example:
From: Computer Networking: A Top Down Approach Featuring the Internet,
2nd edition. Jim Kurose, Keith RossAddison-Wesley, July 2002.
time
Channel
Time SlotFrame
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FDMA
• For N nodes and total Bandwidth = BT– Bandwidth per user = BT/N
• FDM must have guard bands between channels wastes resources
• Frequency Division Duplexing (FDD)– Downstream on one channel– Upstream on another channelFrequency
Guard bands
Time
W
1
2
M
M–1
…
Modified from: Leon-Garcia & Widjaja: Communication Networks
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TDMA• Peak transmission rate = R• Each station transmits at R bps for 1/M of the time• Frames must have bit patterns to indicate “start of
frame” or have a guard time account propagation delays wastes resources
• Time Division Duplexing (TDD)– Downstream on one time slot– Upstream on another time slot
• Stations must be synchronized to common clock
1
Time
Guard time
One cycle
12 3 MW
Frequency
...
Modified from: Leon-Garcia & Widjaja: Communication Networks
#2 33
Sharing Power:Code Division Multiple Access
• Each bit in original signal is represented by multiple symbols in the transmitted signal, these symbols are called “chips”
• Coding gain = # chips/bit• The pattern of chips is called the “spreading
code”• Because the chip rate >> bit rate the
transmitted signal uses more bandwidth, i.e., the signal is signal across a wider frequency band
• Spread is in direct proportion to number of chips used
• Spreading codes have special properties.
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Example
Modified from: W. Stallings, Wireless Communications & Networks, Pearson 2005
• Spreading code = 0110
• Receiver must– know the
spreading code and
– be in sync
Bit Chip
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Property of Spreading Codes
• Each channel uses a different pseudorandom code
• Codes should have low cross-correlation– If they differ in approximately half the bits the
correlation between codes is close to zero and the effect at the output of each other’s receiver is small
• As number of users increases, effect of other users on a given receiver increases as additive noise– this is why this is considered sharing power
• CDMA has gradual increase in BER due to noise as number of users is increased
• Interference between channels can be eliminated is codes are selected so they are orthogonal and if receivers and transmitters are synchronized
From: Leon-Garcia & Widjaja: Communication Networks
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Example: CDMA with 3 users
• Assume three users share same medium• Users are synchronized & use different 4-bit orthogonal codes:
{-1,-1,-1,-1}, {-1, +1,-1,+1}, {-1,-1,+1,+1}, {-1,+1,+1,-1},
+1 -1 +1
User 1 x
-1 -1 +1
User 2 x
User 3 x
+1 +1 -1 SharedMedium
+
Receiver
From: Leon-Garcia & Widjaja: Communication Networks
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Channel 1: 110 -> +1+1-1 -> (-1,-1,-1,-1),(-1,-1,-1,-1),(+1,+1,+1,+1)Channel 2: 010 -> -1+1-1 -> (+1,-1,+1,-1),(-1,+1,-1,+1),(+1,-1,+1,-1)Channel 3: 001 -> -1-1+1 -> (+1,+1,-1,-1),(+1,+1,-1,-1),(-1,-1,+1,+1)Sum Signal: (+1,-1,-1,-3),(-1,+1,-3,-1),(+1,-1,+3,+1)
Channel 1
Channel 2
Channel 3
Sum Signal
Sum signal is input to receiver
From: Leon-Garcia & Widjaja: Communication Networks
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Example: Receiver for Station 2
• Each receiver takes sum signal and integrates by code sequence of desired transmitter
• Integrate over T seconds to smooth out noise
x
SharedMedium
+
Decoding signal from station 2
Integrate over T sec
From: Leon-Garcia & Widjaja: Communication Networks
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Sum Signal: (+1,-1,-1,-3),(-1,+1,-3,-1),(+1,-1,+3,+1) Channel 2 Sequence: (-1,+1,-1,+1),(-1,+1,-1,+1),(-1,+1,-1,+1)Correlator Output: (-1,-1,+1,-3),(+1,+1,+3,-1),(-1,-1,-3,+1)Integrated Output: -4, +4, -4Binary Output: 0, 1, 0
Decoding at Receiver 2
Sum Signal
Channel 2Sequence
CorrelatorOutput
IntegratorOutput
-4
+4
-4
Sum Signal
Channel 2Sequence
CorrelatorOutput
IntegratorOutput
-4
+4
-4
From: Leon-Garcia & Widjaja: Communication Networks
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Frequency Hopping Spread Spectrum
• Signal is broadcast over seemingly random series of radio frequencies– A number of channels
allocated for the FH signal– Width of each channel
corresponds to bandwidth of input signal
• Signal hops from frequency to frequency at fixed intervals– Transmitter operates in one
channel at a time– Bits are transmitted using
some encoding scheme– At each successive interval,
a new carrier frequency is selected
Modified from: W. Stallings, Wireless Communications & Networks,
Pearson 2005
#2 42
Practical considerations for Spread Spectrum Systems
• Problems with orthogonal codes– There are a limited number of orthogonal codes– Obtaining synchronization for all users is complex.
• CDMA systems require synchronization– Code sync– Bit sync– Often carrier sync
• Example assumed that all signals arrive with the same power thus CDMA systems require power control– Base station monitors power from each node and
send explicit commands to increase/decrease the transmit power
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Comparison FDMA, TDMA, CDMA
Characteristic FDMA TDMA CDMA
For maximum resource utilization
No guard bands No timing errors(complex for
distributed users)
Orthogonal codes
Practical consideration
Guard bands Guard times PN codes
Transmission Continuous Need to wait for time slot (buffer)
Continuous
Resource assigned Frequency Band Time slot Code
Ease of adding new users
Complex Complex EasyGraceful
Degradation
Transmit Power Average Power Peak Power Average Power
Resistance to multipath
No No Inherent
Broadcast capability
Need common frequency band
Need common time slot
Need common code
Modified from: B. Bing, “Broadband Wireless Access”, Kluwer Academic Press, 2000
#2 44
Other Spread Spectrum Facts
• Hybrids: Direct Sequence/Frequency hop systems
• Spread Spectrum systems were originally developed for:– Anti-jamming (AJ)– Low probability of intercept (LPI)
#2 45
Sharing Space
• Radiated power drops off at as a function of distance – 1/D2 for free space– 1/Dn for other environments, e.g., k=4
for the common two-ray model
• Inter-channel interference will result if users are assigned the same frequency and are “too close”
#2 46
Sharing Space• Defining “too close” for a one dimensional case*
Following: M. Schwartz, “Mobile Wireless Communications” Cambridge Press, 2005
Desired signalMSC transmitting PT watts
on channel i
R1 Meters R2 Meters
Interfering signalMSC transmitting PT watts
on channel i
n-2
n-1
n-2T
n-1T
-n2T
-n1T
RR
(SIR) Ratio ceinterferen-to-Signal
RP phone cell at received power signal Desired
RP phone cell at received power signal Desired
RPRP phone cell at received Power Total
SIR>Minimum threshold for
proper operationSIR>7-12 dB for GSM
power ginterferin normalizedP where
P
RSIR general In
int
int
-n
#2 47
Sharing Space• Example 1-d model 4-cell reuse• Total number of Channels = N• Each cell uses N/4 different channels• So three cells separating the same set of interfering
channels• Consider first tier interferes
Worst case location for cell phone using a channel from group 1
D Meters
1 2 3 4 1 2 3 41 2 3 4R Meters
dB 23SIR
3n assuming
8RD Here
R)(DR)(DR
P
RSIR nn
-n
int
-n
Analysis assumes power control
#2 48
Sharing Space
Modified from: W. Stallings, Wireless Communications & Networks,
Pearson 2005
Cellular systems most oftenanalyzed with an Hexagonal
pattern
#2 49
Sharing Space
• Reducing interference and increasing capacity with sectoring using directional antennas
From: T.S. Rappaport Wireless Communications Principles and Practice, 2nd Edition
#2 50
Sharing Space
• Sharing in the spatial domain– Distance– Angle
#2 51
System element resources
Packet Buffershared by all
downstream nodes
I nternetInternet
Processor
Power limiteddevices
#2 52
Sharing Buffers: Statistical Multiplexing
• No Dedicated path• Address information is added to the Packet• Store if output port is busy• Trade off delay for blocking• If message is corrupted then retransmit entire
Packet
StoreStore&&
ForwardForward
StoreStore&&
ForwardForward
StoreStore&&
ForwardForward
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Sharing Buffers: Statistical Multiplexing
• If packet arrives to empty system then it is transmitted at the FULL LINE RATE
• Transmission at the FULL LINE RATE is shared among the all the users
• If a packet arrives to a busy system it waits
BufferBuffer ServerServer
MessageMessage
)/(/)( sbrateLinkbitslengthPacket
timeclockingAverageTC
#2 54
Sharing Buffers: Statistical Multiplexing
• Time measured from entering the queue to completion of clocking on to the link is the delay
• Load = C• Where = arrival rate in
packets/sec• Under common
assumptions:– Message lengths have a
exponential probability density function
– Interarrival times have a exponential probability density function
1CT
DelayAverage
M/M/1 Delay
0
510
15
20
2530
35
0 0.2 0.4 0.6 0.8 1
Load
De
lay
#2 55
I nternetInternetPower limited
devices
Sharing Buffers: Statistical Multiplexing
One Queue perNode
Server
Algorithm Selects Node
Contention AlgorithmUsed in upstream to
allocate resources