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CIS 6930: Review on Network Technology

Jonathan C.L. Liu, Ph.D.Department of Computer, InformationScience and Engineering (CISE),University of Florida

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Network HardwareLocal Area NetworksMetropolitan Area NetworksWide Area NetworksWireless NetworksHome NetworksInter-networks

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Local Area Networks

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Metropolitan Area Networks

A metropolitan area network based on cable TV.

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Wide Area Networks

A stream of packets from sender to receiver.

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Wireless Networks

(a) Bluetooth configuration(b) Wireless LAN

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Network SoftwareProtocol HierarchiesDesign Issues for the LayersConnection-Oriented and Connectionless ServicesService PrimitivesThe Relationship of Services to Protocols

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Connection-Oriented and Connectionless Services

Six different types of service.

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Service PrimitivesPackets sent in a simple client-server interaction on a connection-oriented network.

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Fiber Optic Networks

A fiber optic ring with active repeaters.

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The Electromagnetic Spectrum

The electromagnetic spectrum and its uses for communication.

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Global Star

(a) Relaying in space.(b) Relaying on the

ground.

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Structure of the Telephone System

A typical circuit route for a medium-distance call.

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Time Division Multiplexing

The T1 carrier (1.544 Mbps).

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Time Division Multiplexing (3)

Multiplexing T1 streams into higher carriers.

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Packet Switching

A comparison of circuit switched and packet-switched networks.

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Functions of the Data Link Layer

•Provide service interface to the network layer

•Dealing with transmission errors

•Regulating data flow• Slow receivers not swamped by fast senders

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Elementary Data Link Protocols

•An Unrestricted Simplex Protocol•A Simplex Stop-and-Wait Protocol•A Simplex Protocol for a Noisy

Channel

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Unrestricted Simplex Protocol

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Simplex Stop-and-Wait Protocol

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For a Noisy Channel

A positive acknowledgement

with retransmission protocol.

Continued

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For a Noisy Channel (2)

A positive acknowledgement with retransmission protocol.

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Sliding Window Protocols•A One-Bit Sliding Window Protocol

•A Protocol Using Go Back N•A Protocol Using Selective Repeat

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Dynamic Channel Allocation

Station Model.Single Channel Assumption.Collision Assumption.

(a) Continuous Time.(b) Slotted Time.

(a) Carrier Sense.(b) No Carrier Sense.

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Pure ALOHA

In pure ALOHA, frames are transmitted at completely arbitrary

times.

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Pure ALOHA (2)Vulnerable period for the shaded

frame.

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Pure ALOHA (3)

Throughput versus offered traffic for ALOHA systems.

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Performance Comparison

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CSMA with Collision Detection

CSMA/CD can be in one of three states: contention, transmission, or idle.

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Ethernet Cabling

The most common kinds of Ethernet cabling.

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Ethernet MAC Sublayer Protocol

Collision detection can take as long as 2 .

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Ethernet Performance

Efficiency of Ethernet at 10 Mbps with 512-bit slot times.

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Switched EthernetA simple example of switched Ethernet.

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Fast Ethernet

The original fast Ethernet cabling.

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Some Wireless Networks

384 Kbps384 Kbps

56 Kbps56 Kbps

54 Mbps54 Mbps

5-11 Mbps5-11 Mbps

1 Mbps1 Mbps

802.15

802.11b

802.11{a,g}

IS-95 CDMA, GSM

UMTS/WCDMA, CDMA2000

.11 p-to-p link

2G

3G

Indoor

10 – 30m

Outdoor

50 – 200m

Mid rangeoutdoor

200m – 4km

Long rangeoutdoor

5km – 20km

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Wireless Link CharacteristicsDifferences from a wired link ….

decreased signal strength: radio signal attenuates as it propagates through matter (path loss)interference from other sources: standardized wireless network frequencies (e.g., 2.4 GHz) shared by other devices (e.g., phone); devices (motors) interfere as wellmultipath propagation: radio signal reflects off objects ground, arriving at destination with slightly different times

…. make communication across (even a point to point) wireless link much more “difficult”

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IEEE 802.11 Wireless LAN

802.11b2.4-5 GHz unlicensed radio spectrumup to 11 Mbpsdirect sequence spread spectrum (DSSS) in physical layer• all hosts use same

chipping codewidely deployed, using base stations

802.11a 5-6 GHz rangeup to 54 Mbps

802.11g 2.4-5 GHz rangeup to 54 Mbps

All use CSMA/CA for multiple accessAll have base-station and ad-hoc network versions

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Hidden-Node Problem

(a) The hidden station problem.

(b) The exposed station problem.

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IEEE 802.11: multiple accessavoid collisions: 2+ nodes transmitting at same time802.11: CSMA - sense before transmitting

don’t collide with ongoing transmission by other node

802.11: no collision detection!difficult to receive (sense collisions) when transmitting due to weak received signals (fading)can’t sense all collisions in any case: hidden nodes, and/or fadinggoal: avoid collisions: CSMA/C(ollision)A(voidance)

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Timing of the protocol

The use of virtual channel sensing using CSMA/CA.

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Avoiding collisions (more)

idea: allow sender to “reserve” channel rather than random access of data frames: avoid collisions of long data framessender first transmits small request-to-send (RTS) packets to BS using CSMA

RTS may still collide with each other (but they’re short)BS broadcasts clear-to-send (CTS) in response to RTSRTS heard by all nodes

sender transmits data frame

other stations defer transmissions

Avoid data frame collisions completely using small reservation packets!

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Collision Avoidance: RTS-CTS exchange

APA B

time

RTS(A)RTS(B)

RTS(A)

CTS(A) CTS(A)

DATA (A)

ACK(A) ACK(A)

reservation collision

defer

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802.11: Channels, association802.11b: 2.4GHz-2.485GHz spectrum divided into 11 channels at different frequencies

AP admin chooses frequency for APinterference possible: channel can be same as that chosen by neighboring AP!

host: must associate with an APscans channels, listening for beacon frames containing AP’s name and MAC addressselects AP to associate withmay perform authenticationwill typically run DHCP to get IP address in AP’s subnet

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Broadband Wireless

•The 802.16 Protocol Stack•The 802.16 Physical Layer•The 802.16 MAC Sublayer

Protocol•The 802.16 Frame Structure

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The 802.16 Protocol Stack

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The 802.16 Physical Layer

The 802.16 transmission environment.

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The 802.16 Physical Layer (2)

Frames and time slots for time division duplexing.

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802.16 MAC Sublayer Protocol

Service Classes•Constant bit rate service•Real-time variable bit rate

service•Non-real-time variable bit

rate service•Best efforts service

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802.16 Frame Structure

(a) A generic frame. (b) A bandwidth request frame.

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Bluetooth

•Bluetooth Architecture•Bluetooth Applications•The Bluetooth Protocol Stack•The Bluetooth Radio Layer•The Bluetooth Baseband Layer•The Bluetooth L2CAP Layer•The Bluetooth Frame Structure

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Mradius ofcoverage

S

SS

P

P

P

P

M

S

Master device

Slave device

Parked device (inactive)P

802.15: personal area networkless than 10 m diameterreplacement for cables (mouse, keyboard, headphones)ad hoc: no infrastructuremaster/slaves:

slaves request permission to send (to master)master grants requests

802.15: evolved from Bluetooth specification

2.4-2.5 GHz radio bandup to 721 kbps

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The Bluetooth Protocol StackThe 802.15 version of the Bluetooth

protocol architecture.

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The Bluetooth Frame Structure

A typical Bluetooth data frame.

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IEEE 802.15.3 - Overview

High data rate WPANPotential future standardMotivation: The need for higher bandwidths currently supported with 802.15.1

100 Mpbs within 10 meter400 Mpbs within 5 meter

Data, High quality TV, Home cinema

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IEEE 802.15.3 - Overview

Dynamic topologyMobile devices often join and leave the piconetShort connection times

High spatial capacityMultiple Power Management modesSecure Network

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IEEE 802.15.3 - Overview

Based on piconetsData Devices (DEV) establish peer-to-peer communicationIncludes also a Piconet Coordinator (PNC)

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IEEE 802.15.3 - Topology

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IEEE 802.15.3 - Superframe

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IEEE 802.15.3 - Beacon

BeaconControl informationAllocates GTSSynchronization

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IEEE 802.15.3 - CAP

CAPAllows contention via CSMA/CACommand exchange between DEV and PNCFile transfers from DEV without request

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IEEE 802.15.3 - CFP

CFPTime slot allocation specified in the beaconReserved bandwidth for DEVMTS: Command, GTS: Data

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IEEE 802.15.3 - GTS

GTS reservationDEV sends a Channel Time Request (CTR) to PNC• Isochronous data: number and duration

of slot(s)• Asynchronous data: Total amount of data

PNC allocates GTSs to DEV via CTADEV is responsible of utilizing allocated GTSs

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IEEE 802.15.3 - GTS

Two types of GTSsDynamic GTS• Location within a superframe may change• PNC can optimize channel utilization

Pseudostatic GTS• Only for isochronous data• Fixed location within a superframe• May be changed, but only after a series

of notitications to the DEV

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IEEE 802.15.3

Starting a piconetDEV scans the for the best channel and sends out beacons -> the DEV becomes PNCIf no channels available: Establishes a child or neighbor piconet instead• Requests a private GTS from parent PNC• All communication takes place within

assigned GTS

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IEEE 802.15.3 - QoS

QoSIEEE 802.15.3 supports both synchronous and asynchronous dataCAP offers only best-effortThe PNC will allocate resources in the CFP• Through admission control• Synchronous data: Based on number of

time slots per superframe, duration of slot, priority and GTS type

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IEEE 802.15.3 - QoS• Asynchronous data: Based on total data

and priority

After performing admission control, GTSs may be allocated