chu02_2

Home Network Technologies

家庭網路相關網路技術

Computer

TV

Broadband Access Technology

Internet

ISP

Home Networking Technology

Home Network

Broadband Access Technologies

• Digital Subscriber Line (DSL)

• Cable Modem

• Broadband Over Power Line (BOPL)

• Fiber-to-the-Home (FTTH)

• IEEE 802.16 (WiMax)

• GPRS; 3.5G

Outlines

• Broadband Over Power Line

• Digital Subscriber Line (DSL) Technology

• Cable Modem

Broadband Over Power Line (BOPL)

• Use existing electrical lines to provide the medium for a high speed communications network

• Superimposing voice or data signals onto the line carrier signal using OFDM

• Two categories– In-house– access

In-House BPL

• connecting machines within a building

• HomePlug: an alliance for in-house BPL

Access BPL

• Delivers the last mile of broadband to the home

Access BPL Architecture

InternetVoIP

Medium-voltage lines

Low-voltage lines

Backhaul

Coupler

Bridge

Backhaul Point

Wireless link

Coupler

Bridge

Coupler

Backhaul Point

Coupler

Advantages of BPL

• Power lines are our most ubiquitous infrastructure

• Lower cost of deployment– Existing wires

Main Concerns

• Radio Frequency Interference (RFI) to licensed service

• power lines are inherently a very noisy environment

– Every time a device turns on or off, it introduces a pop or click into the line.

– Energy-saving devices often introduce noisy harmonics into the line

Digital Subscriber Line (DSL) Technology

• The key in DSL technology is modulation, a process in which one signal modifies a properties of another.

• Hardware: DSL requires modems and splitters for end-users; carriers use DSLAMs (digital subscriber line access multiplexers)

• Differences between xDSL technologies: speed, operating distance, applications, ratio between up and downstream

• Different approaches: ATM-based ADSL, ISDN DSL.

• The important thing is what is running over xDSL...

xDSL - Digital Subscriber Line Technology

ADSL: Asymmetric Digital Subscriber Line

• twisted pair copper (single loop)

• asymmetric: most commonly:

– downlink: 256 Kbps - 8 Mbps

– uplink : 64 Kbps - 2 Mbps

• limited distance (18000 feet over 26-gauge copper)

RADSL: Rate-Adaptive Digital Subscriber Line

• varying speeds depending upon line quality; asymmetric

– downlink: 1.5 Mbps - 8 Mbps

– uplink : 176 Kbps - 1 Mbps

• limited distance (18000 feet over 26-gauge copper)

HDSL: High-speed Digital Subscriber Line

• full-duplex, symmetric

– 1.544 Mbps or 2.048 Mbps in each direction

• two twisted pairs (for T1) and 3 pairs (for E1)

• max distance 12,000 feet

VDSL: Very-high-bit-rate Digital Subscriber Line (known as

BDSL)• asymmetric

– downlink: 12.96-51.84 Mbps

– uplink : 1.6 - 2.3 Mbps

• max 4,500 - 1,000 feet

• applications: High definition TV, multimedia

Cable Modem

• primarily used to deliver broadband Internet access on Hybrid Fibre-Coaxial (HFC)

Computer

TV

Cable Modem

Cable

TelevisionCompany

Cable

Internet

CMTS

Cable Modem Standards

• DOCSIS (Data Over Cable Service Interface Specification)

– 1.0 (1997): typical 2 Mbps upstream

– 1.1 (1999): 10 Mbps upstream

– 2.0 (2002) : 30 Mbps upstream

Hybrid Fibre-Coaxial (HFC)

• combines optical fiber and coaxial cable

The Downstream & Upstream Path• The downstream data path of the cable modem uses a SINGLE

6mhz TV channel, which is typically in the higher frequencies range (550 MHz and above) because higher frequencies can carry information faster.

• The lower end of the radio frequency spectrum (5MHz – 42 MHz) is used for the upstream or the return path.

• In terms of data bandwidth, the typical upstream channel usually has a capacity of around 5 Mbps.

• The total downstream bandwidth for a single channel is around 30 Mbps.

5-42MHz

Upstreamsignaling

50 MHz - 550 MHz 550 MHz - 750 and up MHz

. . .

Multiple TV Channels Downstream Channel

Cable TV Spectrum

Cable Modem: Modulation & Demodulation Phase

• Demodulation Phase: – tunes to the appropriate 6 MHz downstream channel (42 MHz –

850 MHz).

– demodulates the signal and extracts the downstream data that is destined for it

– converts the data into an Ethernet or USB signal to be fed into the user’s computer.

• Modulation Phase: The cable modem receives data on its Ethernet or USB interface and modulates the data onto the upstream carrier frequency, negotiates channel access with the CMTS and sends the data.

Protecting the Downstream Channel (and the upstream as well)

• A component of the DOCSIS 1.1 standard called Baseline Privacy Initiative+ (BPI+) is bi-directional encryption between cable modem and the CMTS

• Each DOCSIS 1.1 compliant cable modem has a digital certificate stored in its firmware. This allows for the cable modem to be authenticated onto the network.

• The authentication takes place when the CMTS verifies the certificate presented by the modem. (The certificate is signed by the manufacturer’s private key).

• Encryption is based on 56-bit Triple-DES

• This scheme effectively renders any sniffing attempts useless, unless cracking of the Triple-DES scheme is possible

DOCSIS Security OverviewDOCSIS Security Overview-- BPI+ ---- BPI+ --

CMTS

CM

PC

Internet

Data Encryption(DES)

Key Management(RSA, Tri-DES)

CM Authentication(X.509 Certificates)

Secure Software Download

(X.509 Certificate)

TFTP Server New CM Code

......

Digitally Signed by: Manufacturer

Mfg Certificate......

Digitally Signed by: DOCSCSIS Root CM Certificate......

Digitally Signed by: Mfg CA

CM Code File

x$a9E!

abcdef

abcdef

The Device

• The cable modem bridges Ethernet frames between a customer LAN and the coax cable network

• It does, however, also support functionalities at other layers– Ethernet PHY and DOCSIS PHY– IP address– UDP, port-based packet filtering– DHCP, SNMP, TFTP

Fiber-to-the-Home(FTTH)

CopperFiber

24 kbps - 1.5 MbpsOld networks, optimized for voice

CO/HE

19 Mbps - 1 Gbps +Optical networks, optimized for voice, video and data

CO/HE//

CO/HE//

//

Note: network may be aerial or underground

FTTH Characteristics

• FTTH is an optical access network in which the optical network unit is on or within the customer’s premise.

• Although the first installed capacity of a FTTH network varies, the upgrade capacity of a FTTH network exceeds all other transmission media.

CO/HE//

Optical Network

Unit

Optical Line Termination

Source: www.ftthcouncil.org

Optical Access Network

Why FTTH?

• Enormous information carrying capacity• Easily upgradeable• Ease of installation• Allows fully symmetric services• Reduced operations and maintenance costs • Benefits of optical fiber:

– Very long distances– Strong, flexible, and reliable– Allows small diameter and light weight cables– Secure – Immune to electromagnetic interference (EMI)

Fiber versus Copper

Glass• Uses light• Transparent• Dielectric material-

nonconductive– EMI immune

• Low thermal expansion• Brittle, rigid material• Chemically stable

Copper• Uses electricity• Opaque• Electrically conductive

material– Susceptible to EMI

• High thermal expansion• Ductile material• Subject to corrosion and

galvanic reactions• Fortunately, it’s

recyclable

Architecture and Transport

CO/HE

Architecture (Electronics)• PON• Active node• Hybrid

Transport:ATM orEthernet

//

FTTH Architectures

• Passive Optical Networks (PONs)– Shares fiber optic strands for a portion of the networks

distribution

– Uses optical splitters to separate and aggregate the signal

– Power required only at the ends

• Active Node– Subscribers have a dedicated fiber optic strand

– Many use active (powered) nodes to manage signal distribution

• Hybrid PONs– Literal combination of an Active and a PON architecture

FTTH Technical Considerations

• Data– How much per home?– How well can you share the channel?– Security – how do you protect the subscriber’s data?– What kind of QoS parameters do you specify?– Compatible business services?

• SLAs• T1

• Support for voice?• Support for video?

– Broadcast– IPTV

FTTH Technical Considerations

• Data– How much per home?– How well can you share the channel?– Security – how do you protect the subscriber’s

data?– What kind of QoS parameters do you specify?

FTTH Technical Considerations: Speed

• Data requirements– Competition: ADSL, cable modem ~0.5 to ~1.5

Mb/s shared, asymmetrical– FTTH ~10 to 30 Mb/s non-shared or several 100

Mb/s shared, symmetrical– SDTV video takes 2-4 Mb/s today at IP level– HDTV takes maybe 5 times STDV requirement– Pictures can run 1 MB compressed– 5.1 channel streaming audio would run ~380

kb/s

• Security– Data is shared in the downstream direction in most

systems– Your Gateway filters out all packets not intended for you– But there is fear that someone will snoop on your data– FSAN has a low-complexity, low-security encryption

scheme– 802.3ah has formed a committee to study security– Manufacturers have taken their own tacks on security,

from none to robust

FTTH Technical considerations: Security

FTTH Data Flow and Security: Downstream

//

//

//

//

////

//

Tom Dick

Harry

T D H

T D

HBox on side of home separates out only the data bound for that subscriber. But the fear is that someone will fool his box into giving data intended for another subscriber. Solution is to encrypt the data.

Time division multiplex (TDM) – each subscriber’s data gets its turn.

FTTH Data Flow and Security: Upstream

//

//

//

//

////

//

Tom Dick

Harry

T D H

HDue to the physics of the network, Harry’s data flows upstream but does not come to Tom’s box, so Tom cannot see Harry’s data

Time division multiple access (TDMA) – similar to downstream, with gap for

laser start/stop

FTTH Data Flow and QoS

//

//

//

//

////

//

Tom Dick

Harry

T D H

T D

H

If Dick has paid for more bandwidth, he gets more

If Tom’s packets need higher priority (e.g., telephone), they go first

• several different ways

– Broadcast (cable TV standards)

• Analog or Digital

• Benefit from high volume and rich applications of cable boxes

– IPTV – TV transmitted over Internet Protocol

• Feasible, and some people are doing it in place of broadcast

• Bandwidth hog, but statistics can work for you

– Interesting hybrid model awaits hybrid STTs, but can give the best of both worlds

Video Delivery with FTTH

IPTV Unicast (VOD)

Router A(headend)

Router B

Router C(network)

Router D(NID)

Router E

Program request

Program stream

In-home routing

In-home routing

In-home routing

Subscriber's TVSet top terminal

In-home routing

VOD server

Home Networking Technologies

• IEEE 802.3/Ethernet

• IEEE 802.11 a/b/g/n (WiFi)

• Bluetooth

• In-House BPL (HomePlug)

IEEE 802.3 Family

• Original IEEE 802.3 (Ethernet)– 10 Mbps

• Fast Ethernet– 1000 Mbps

• Gigabit Ethernet – 1 Gbps

• 10 G Ethernet– 10 Gbps

Gigabit Ethernet Networks

• 1000 Mbps transmission rate

• IEEE 802.3 CSMA/CD frame format

• Medium: Twisted pair (UTP, STP) or Fiber

• Hub- or switch-based topology

• Do not support priority scheme

• Bandwidth utilization is not guaranteed to be fair

• Do not support guaranteed delay service

• Low bandwidth utilization under heavy loads

• Suitable for multimedia communications

Gigabit Ethernet Architecture

1000 Mbps

10 Mbps 100 Mbps 1000 Mbps

Gigabit Ethernet Full-duplex Switch

100 Mbps 1000 Mbps

1000 Mbps

1000BaseT 100BaseT 1000BaseT

Gigabit Ethernet Communication Structure

1000BASE-LX1270-1355 nm 光傳送接收器

1000BASE-SX 770-860 nm 光傳送接收器

1000BASE-CX STP 傳送接收器

1000BASE-T 4-Pair 傳送接收器

SMF MMF MMF 50 um

MMF 62.5 um

Balance Shielded Copper

Cat-5 UTP

3 km 550m 550m 300m 25m 100m

8B/10B Coding/Decoding 1000BASE-T Codec

Gigabit Media Independent Interface (GMII)

Media Access Control (MAC)

Logical Link Control (LLC)

Ethernet Upper Layers

Gigabit Ethernet Physical Layer

• 1000BASE-T (UTP, IEEE 802.3ab)

• 1000BASE-CX (Short copper jumpers, IEEE 802.3z)

• 1000BASE-SX (Shortwave fiber, IEEE 802.3z)

• 1000BASE-LX (Longwave fiber, IEEE 802.3z)

Gigabit Ethernet Characteristics

• Good fault tolerance

– Hub/Repeater architecture

• Carrier Extension for short frames.

• Frame Bursting to increase performance (optional).

Half-Duplex vs. Full-Duplex

• Gigabit Ethernet can operate in either half-duplex or full-duplex mode.

• Half-duplex poses some difficult problems that can result in restrictions on the allowable topologies and/or changes to the Ethernet MAC algorithm.

• Full-duplex is simpler to implement than a half-duplex MAC.

Limitations of Half-duplex Operation

• CSMA/CD implies an intimate relationship between the minimum length of a frame (L, measured in bit-times, not absolute time) and the maximum round-trip propagation delay (2a) of the network: L > 2a

round trippropagation delay

transmission timerateontransmissi

sizeframe_

_

maximumdistance

time

space

A

B

hub

10 Mbps Ethernet

• For the original 10 Mbps Ethernet, a compromise was struck.

• Minimum frame = 512 bits (64 bytes), not including the preamble and Physical Layer overhead.

• Minimum data field = 46 bytes rarely imposes a significant padding overhead (IP header + TCP header = 40 bytes).

• At 10 Mbps, 512 bit-times is 51.2us. Depends on the type of cable used and the network configuration, the extent of a 10 Mbps Ethernet can be on the order of from 2-3 Km.

Preamble SFD DA SA LEN Data FCS

7 1 6 6 2 46 4 bytes

Minimum Frame Length (512 bits)

Network Extent

• For a given minimum-length frame, the extent of a network scales inversely with data rate.

10Mbps 100 Mbps 1000 Mbps

10,000 m

1,000 m

100 m

10m

~ 2800m

~ 205m

~ 20m

100 Mbps Fast Ethernet

• For 100 Mbps Fast Ethernet, a conscious choice had to be made to do one or more of the following:Increase the minimum frame length so that large

networks (with multiple repeaters) could be supported.

Change the CSMA/CD algorithm to avoid the conflict.

Leave the minimum frame as is, and decrease the extent of the network accordingly.

Limitations of Half-duplex Operation

• For Hub-based configuration (1995 ~), the only truly important distance was from the user to the wiring closet (<100m, 200m diameter).

• A change to the minimum frame length would have required changes to higher-layer software, including device driver and protocol suite implementation. Also difficult to seamlessly bridge between 10 Mbps and 100 Mbps network with different minimum frame lengths.

• A change to the CSMA/CD algorithm would have significantly delayed the release of the Fast Ethernet standard.

Limitations of Half-duplex Operation

• Fast Ethernet uses The same 512-bit minimum frame.Decrease the network extent to the order of

200m, using twisted-pair cabling.No change to the CSMA/CD algorithm.

• For Gigabit Ethernet, network extent is only about 20m!!, if the same approach is used.

Carrier Extension

• For Ethernet/Fast Ethernet, the minimum frame length = slotTime = 512 bits.

• Gigabit Ethernet keeps the 512-bit minimum frame length but sets slotTime to 512 bytes

• In Gigabit Ethernet, frames that shorter than slotTime are extended by appending a carrier-extension field so that they are exactly one slotTime long.

• Frames longer than slotTime are untouched

Carrier Extended Frame Format

Preamble/SFD DA SA LEN Data FCS Extension

8 6 6 2 46 - 493 4 448 - 1 bytes

Minimum Nonextended Frame Length (64 bytes)

512-byte Short Frame

Carrier-Extended Frame (64-511 Bytes)

Preamble/SFD DA SA LEN Data FCS

8 6 6 2 494 - 1500 4 bytes

Non-Carrier-Extended Frame ( 512 Bytes)

Channel Efficiency

• The use of carrier extension for short frames imposes a significant performance degradation.

• In the worst-case (a stream of minimum length frames of 512 bits with a 64-bit preamble/SFD and a 96-bit interframe gap), the channel efficiency is

• For Ethernet (Fast Ethernet),

5124096 + 64 + 96

= 12%

512512 + 64 + 96

= 76%

length ofslot time

Frame Bursting

• The solution is to allow a station to send multiple frames, while extending only the first one with carrier extension (Frame Bursting).

• No additional frames are sent if a collision occurs before the slotTime expires.

• After that time, the station can begin sending additional frames without contending again.

• The interframe gap is filled with non-data symbols.• The bursting station may continue to start new frames for

up to one burstLength, which limits the maximum time that a station is allowed to dominate the channel.

Frame Bursting

Maximum Time to start of Last frame in Burst (8192 Bytes)

SlotTime(512 Bytes)

傳送訊框 frame 1 frame 2 frame 3 frame 4

Inter-Frame Spacing (96 bit time)

Preamble SFD DA SA LEN LLC PAD FCS

Carrier extension

Carrier detection

Frame Bursting

• Transmitters are not required to implement frame bursting.

• A trade-off between complexity and performance.

• Receiver must be prepared to receive bursted frames.

• Even if the first frame in a burst is longer than a slotTime (no carrier-extension), a station may still continue to burst frames up to the burstLength time.

• Normally, no collision should occur after the first slotTime during a burst of frames.

Half-Duplex Operational Parameters

Parameters

SlotTime 512 512 512 4096(Bit times)

interFrameGap 9.6 96 0.96 0.096 (us)

attempLimit 16 16 16 16

backoffLimit 10 10 10 10

jamSize 32 32 32 32

maxFrameSize 1518 1518 1518 1518

minFrameSize 64 64 64 64

extendSize 0 0 0 448

burstLength - - - 65,536 (bits)

Ethernet Type 10Mbps 1 Mbps 100 Mbps 1000 Mbps

Full-Duplex MAC

• When an Ethernet operates in full-duplex mode, all of the complexity of carrier sense, collision detection, carrier extension, frame bursting, backoff algorithm, and so on, has no bearing !!

• Only shared medium needs these.

• The full-duplex MAC is not really a MAC at all.

• With a dedicated channel, a station may transmit at will.

Limitations of Full-duplex Operation

• The underlying physical channel must be capable of supporting simultaneous, bi-directional communications without interference (1000BASE-X and 1000BASE-T families).

• Exactly two devices on the LAN segment.

• The interfaces in both devices must be capable of and configured to use full-duplex mode.

• If all of these conditions are met, then full-duplex mode not only can be used, it should be used.

Operation of Full-Duplex MAC

• A station can send a frame any time there is a frame in its transmit queue and it is not currently sending a frame.

• Stations should similarly receive frames at any time, subject to interframe spacing.

• Do not defer transmissions to received traffic.• No need for carrier-extension in full-duplex mode !!• No explicit need for frame bursting !!• Full-duplex MAC can “burst” at any time (not just after an

extended carrier) and for any length of time (not just for a burstLength period) !!

Gigabit Ethernet Protocol Stack• CS: Convergence Sublayer• MDI: Medium Dependent Interface• MII: Medium Independent Interface• GMII: Gigabit Medium Independent Interface

Physical

LLC

MAC

CS

PCSPMAPMD

Medium

CS

PCSPMAPMD

Medium

CS

PLS

PMA

Medium

PLS

PMD

Medium

MII MII GMII

AUIAUI

MDI MDI MDIMDI

Data link

Higher Layers&

Netrotk

1 Mbps, 10 Mbps 10 Mbps 100 Mbps 1000 Mbps

PHY

10 Gigabit Ethernet Protocol Stack

Physical

LLC

MAC

Data link

Higher Layers&

Netrotk

Reconciliation Sublayer (RS)

64B/66B PCS

64B/66B PCS

8B/10B PCS

PMA

PMD

Medium

PMA

PMD

Medium

WIS

XGMIIXGMII

PMA

PMD

Medium

XGMII

Proposed IEEE 802.3ae Layers

10GBase-R 10GBase-W 10GBase-X

OSI Ref.

IEEE 802.11 Family

• Differs in Physical Layer• IEEE 802.11b

– 2.45 GHz / 11 Mbps (100 m)

• IEEE 802.11a– 5.8 GHz / 54 Mbps (70 m)

• IEEE 802.11g– 2.4 GHz / 54 Mbps (100 m)

• IEEE 802.11n– 2.4/5 GHz / 100+ (max. 600) Mbps (100+ m)

IEEE 802.11Standard for WLAN operations at data rates up to 2 Mbps in the 2.4 GHz ISM band. DSSS modulation.

IEEE 802.11a

Standard for WLAN operations at data rates up to 54 Mbps in the 5 GHz band. Proprietary “rate doubling" has achieved 108 Mbps. Realistic rating is 20-26 Mbps.

IEEE 802.11bWi-Fi™ or “high-speed wireless” 1, 2, 5.5 and 11 Mbps in the 2.4 GHz band. All 802.11b systems are backward compliant. Realistic rating is 2 to 4 Mbps.

IEEE 802.11g802.11a backward compatible to the 802.11b 2.4 GHz band using OFDM.

Direct Sequence Spread Spectrum

Orthogonal Frequency Division Multiplexing

2.4 GHz Radio Licenses NOT required in these bands 5 GHz

Adaptive Rate Selection

• Performance of the network will also be affected by signal strength and degradation in signal quality due to distance or interference.

• As the signal becomes weaker, Adaptive Rate Selection (ARS) may be invoked.

Access Point (AP)

• Usually connects wireless and wired networks– if not wired

• acts as an extension point (wireless bridge)

• consists of a radio, a wired network interface (e.g., 802.3), and bridging software conforming to the 802.1d bridging standard

• Number of clients supported– device dependent

AP as a Wireless Bridge

mobile terminal

access point

server

fixed terminal

application

TCP

802.11 PHY

802.11 MAC

IP

802.3 MAC

802.3 PHY

Application

TCP

802.3 PHY

802.3 MAC

IP

802.11 MAC

802.11 PHY

LLC

infrastructure network

LLC LLC

Basic Service Set (BSS)

BSS

Coordinatedfunction

Independent Basic Service Set (IBSS)

IBSS

A BSS withoutAccess Point

Ad hoc mode

Extended Service Set (ESS)

• ESS: one or more BSSs interconnected by a Distribution System (DS)

• Traffic always flows via Access Point• allows clients to seamlessly roam

between APs

Distributed System (DS)

• A thin layer in each AP

– embodied as part of the bridge function

– keeps track of AP-MN associations

– delivers frames between APs

• Three types:

– Integrated: A single AP in a standalone network

– Wired: Using cable to interconnect APs

– Wireless: Using wireless to interconnect APs

ESS: Single BSS (with integrated DS)

BSS

AccessPoint

A cell

91.44 to 152.4 meters

ESS: BSS’s with Wired Distribution System (DS)

BSS

BSS

Distribution

System

20-30% overlap

ESS: BSS’s with Wireless Distribution System (DS)

BSS

BSS

Distribution

System

ESSID in an ESS

• ESSID differentiates one WLAN from another

• Client must be configured with the right ESSID to be able to associate itself with a specific AP

• ESSID is not designed to be part of security mechanism, and it is unfitted to be one

• AP broadcast the SSID(s) they support

• Client association requests contain the ESSID

• Transmitted in the clear

ESSID

Connecting to the Network

Client Access Point

Probe Request

Probe Response

Authentication Response

Authentication Request

Association Response

Association Request

Probing

802.11Authentication

Association

Probing Phase

• Find an available AP

• APs may operate at different channels (11 channels in total in case of 802.11a)

• Should scan a channel at least MinChannelTime

• If an AP is found, should last MaxChannelTime

Active Scanning

probe request with SSID

probe responseIf SSID matches

Service Set Identifier (SSID)

APMN

Passive Scanning

beacon with SSID

Service Set Identifier (SSID)

APMN

Full Scanning

MN AP 1

Scan channel 1

AP 2 AP 3

Scan channel 2

Beacon or Probe Resp

MinChannelTime

MaxChannelTime

Scan channel 3

Scan channel 11

…

WLAN authentication occurs at Layer 2. It is the process of authenticating the device not the user.

Authentication and Association Types

Authentication request

Authentication response(Accept or Reject)

802.11 Authentication Methods

• Open Authentication (standard)

• Shared key authentication (standard)

• MAC Address authentication (commonly

used)

Open Authentication

• The authentication request contain a NULL authentication protocol. It must have the AP SSID.

• The access point will grant any request for authentication

Client Access Point

Authentication Request

Authentication response

Shared Key Authentication• Requires that the client configures a static WEP key

Client Access Point

Authentication Request

Authentication response (challenge)

Authentication response(Success/Failure)

Authentication Request(encrypted challenge)

MAC Address Authentication

• Not specified in the 802.11 standard, but supported by many vendors (e.g. Cisco)

• Can be added to open and shared key authentication

Access-Request(MAC sent as RADIUS req.)

Auth. Request

Auth. Response (Success/Reject) Access-Success/Reject

ClientRADIUS ServerAccess Point

實際驗證

Open Authentication

WEP Encapsulation

1. P = M || checksum(M) {p=plaintext}

2. KeyStream = RC4 (IV || k( {k=shared-key}

3. C = XOR (P, KeyStream) {c=ciphertext}

4. Transmit (IV, C) {IV=init-vector}

WEP Key

Initialization Vector (IV)

Plaintext

Ciphertext

IV

seed

Message

Key Stream

CRC-32 Integrity Check Value (ICV)

RC4 PRNG

P

C

WEP Decapsulation1. KeyStream = RC4 (IV || k(2. P’ = XOR (C, KeyStream) = M’ || checksum(M)3. If checksum(M’) = (checksum(M))’

Then P’ is accepted

WEP Key

Plaintext Key stream

Message

Ciphertext

IV

ICV' = ICV?

CRC 32

RC4 PRNG

ICV’

ICV

Seed

P’

M’

802.1X

• based on EAP (extensible authentication protocol, RFC 2284)

– still one-way authentication

– initially, MN is in an unauthorized port

– an “authentication server” exists

– after authorized, the MH enters an authorized port

– 802.1X ties it to the physical medium, be it Ethernet, Token Ring or wireless LAN.

Three Main Components

• supplicant: usually the client software

• authenticator: usually the access point

• authentication server: usually a Remote Authentication Dial-In User Service (RADIUS) server

Extensible Authentication Protocol (EAP)

• the AP does not provide authentication to the client, but passes the duties to a more sophisticated device, possibly a dedicated server, designed for that purpose.

Authenticationrequest

Authenticationresponse

Authenticationrequest

Authenticationresponse

Authenticationserver

802.1X – How it works

Auth Server“RADIUS”

APClient

Let me in! (EAP Start)

What’s your ID? (EAP-request identity message)

ID = xxx@yyy.local (EAP Response)Is xxx@yyy.local OK?

Prove to me that you are xxx@yyy.local

The answer is “47”

Let him in. Here is the session key.

Come in. Here is the session key.

http://yyy.local\index.htmnetwork

EAP Challenge/Authentication

Encryptedsession

Distributed Coordination Function: CSMA/CA

• CSMA: Carrier Sense Multiple Access– physical carrier sense: physical layer

– virtual carrier sense: MAC layer• network allocation vector (NAV)

• CA: Collision Avoidance– random backoff procedure

• shall be implemented in all stations and APs

Contention Window

DIFS

contention windowbusy

All stations must wait DIFSafter medium is free

The winnerdata frame

random 1

random 2

random 3time

SIFS: Giving Priority to RTS/CTS/ACK

busy

DIFS

ACK

data frame

SIFSSIFS

DIFS

contention window

Source

Destination

OthersDefer access

SIFS: Transmitting Fragments

Source

Destination

Others

ACK ACK

SIFS

DIFS

ContentionWindow

Defer access

SIFS

Fragment 1SIFS

SIFS

Fragment 2

EIFS: Low Priority Retransmission

busy

data frame

SIFS

DIFS

SIFS

DIFS

contention window

Source

Destination

OthersDefer access

EIFS

NoACK

canresend

contension

CSMA/CA with RTS/CTS

busy

DIFS

ACK

data frame

SIFSSIFS

Source

Destination

Others NAV (RTS)

RTS

CTS

NAV (CTS)

contentionwindow

SIFS SIFS

RTS/CTS is Optional

• system parameter RTSThread– RTS/CTS is used only when frame size

RTSThread

Throughput Issues

• When a source node sends a frame, the receiving node returns a positive acknowledgment (ACK). – This can consume 50% of the available bandwidth.

• This overhead, combined with the collision avoidance protocol (CSMA/CA) reduces the actual data throughput to a maximum of 5.0 to 5.5 Mbps on an 802.11b wireless LAN rated at 11 Mbps.

What is Bluetooth?

• Major joint computing and telecomm industry initiative

• Plan to deliver a revolutionary radio-based solution– Cable replacement, no line of sight restrictions– Prefect for mobile devices - small, low power, low cost– Open specification (license free)

Bluetooth Characteristics

• Data/voice access

• Cable replacement technology

• 1 Mbps symbol rate

• Range 10+ meters

• Low cost

• Low power

Ultimate Headset(Voice Access)

Cordless Computer(Cable Replacement)

Automatic Synchronization

In the Office

At Home

Bluetooth World

Application of Bluetooth

• Integrated in– mobile phones– PDA/handhelds– Computers– Wireless peripherals

• Handsets

• cameras

– Network access devices• universal bridge to other networks or internet

Masters and Slaves

• Each Bluetooth device may be either a Master or Slave at any one time, thought not simultaneously.

• Master — the device which initiates an exchange of data.

• Slave — the device which responds to the master.

s m

Piconet

• Two or more units sharing the same hopping sequence form a piconet (similar to a LAN).

• Each piconet can have – only one master.

– up to seven slaves.• Each piconet has max

capacity (1 Mbps).s s s

m

Piconet Structure

Master

Active Slave

Parked Slave

Standby

Scatternet

• Multiple piconets form a scatternet.

• Same device can be shard by two different piconets

s s

sms

mss

ss

s

m

Max 256 piconets

Frequency Hop Spread-Spectrum

• Bluetooth channel is represented by a pseudo random hopping sequence through the entire 79 RF frequencies

• Nominal hop rate of 1600 hops per second

• Channel Spacing is 1 MHz

Time Division Duplex (TDD)

• Bluetooth is a Time Division Multiplexed system• 625 s/slot

Slot k Slot k+1 Slot k+2

master

slave

625s

Multi-Slot Packets

• Bluetooth defines data packets which are 1, 3, or 5 slots long

f(k) f(k+1) f(k+2) f(k+3) f(k+4) f(k+5) f(k+6)1-slotpacket

3-slotpacket

5-slotpacket

Time Division Multiplexing

• Slaves must listen to the master• A slave can send only after receiving a poll

Master

Slave 1

Slave 2

RX

RX RX

RXTX

TX TX

TX

RX RX RX RX

1

TX

2

TX

2

TX

1

TX

Putting It Altogether

0123

78

757677

45

…

time

Master

Slave 1

Slave 2

channel

Asynchronous Connection-Less (ACL) Links

• One ACL link can exist between any two devices.

• No slots are reserved.

• Every even-slot is Master transmission & every old-slot is Slave response

• Broadcast packets are ACL packets not addressed to any specific slaves.

Synchronous Connection Oriented (SCO) Links

• a symmetric link between Master and Slave with reserved channel bandwidth and slots.

• Typically used for voice connection• A Master can support up to three SCO links.• A slave can support

– up to 3 SCO links from the same master– two SCO links if the links are originated from different

masters.

• SCO packets are never retransmitted.

SCO Traffics

• Master reserves slots for SCO links

master

Slave 1

Slave 2

Slot no 0

TX

TX

RX

RX

TX

TX RX

RX

0SCOTX

RXSCO

TXSCO

RXSCO

1 2 3 4 5 1SCOTX

RXSCO

TXSCO

RXSCO

2

Mixed Link Packets

MASTER

SLAVE 1

SLAVE 2

SLAVE 3

ACLSCO SCO SCO SCOACLACL ACL

RFID

• What is RFID?– RFID is an ADC (Automatic Data Capture)

technology that uses radio-frequency waves to transfer data between a reader and a movable item to identify, categorize, track …

– RFID is fast, reliable, and does not require physical sight or contact between reader/scanner and the tagged item

An RFID System

Reader

RF ModuleTag

Antenna

Host ComputerHost Computer

Interrogation UnitTx/RxMicro

Computer

Computer Network

AntennaOne or more RF tagsTwo or more antennasOne or more interrogatorsOne or more host computersAppropriate software

RF Tag

Chip

Antenna

Tag

Radio Tx/Rx

RAM ROM

CPU I/O

Pwr Supply

Radio Tx/Rx

RAM ROM

CPU I/O

Pwr Supply

Radio Tx/Rx

RAM ROM

CPU I/O

Pwr Supply

Radio Tx/Rx

RAM ROM

CPU I/O

Pwr Supply

Chip + Antennae + Packaging = Tag

Variations of RF Tags

• Basic types: active vs. passive• Memory

– Size (16 bits - 512 kBytes +)– Read-Only, Read/Write or WORM

• Arbitration (Anti-collision)• Ability to read/write one or more tags at a time• Frequency : 125KHz - 5.8 GHz• Physical Dimensions

– Thumbnail to Brick sizes– Incorporated within packaging or the item

• Price ($0.50 to $150)

RFID Frequencies

Frequency Regulation Range Data Speed Comments

125-150 kHz Basically unregulated

? 10 cm Low Animal identification and factory data collection systems

13.56 MHz ISM band, differing power levels and duty cycle

< 1 m Low to moderate

Popular frequency for I.C. Cards (Smart Cards)

433 MHz

Non-specific Short Range Devices (SRD), Location Systems

1 – 100 m Moderate DoD Active

860-960 MHz

ISM band (Increasing use in other regions, differing power levels and duty cycle

2 – 5 m Moderate to high

EAN.UCC GTAG, MH10.8.4 (RTI), AIAG B-11 (Tires), EPC (18000-6’)

2450 MHz ISM band, differing power levels and duty cycle

1 – 2 m High IEEE 802.11b, Bluetooth, CT, AIAG B-11

Regulating Authority : ITU and Geo Organizations