Transcript An Overview of Broadband Over Power Line

Home Network Technologies
家庭網路相關網路技術
Home Networking
Technology
Computer
Home
Network
Internet
Broadband Access
Technology
ISP
TV
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
Coupler
Internet
VoIP
Backhaul
Backhaul
Point
Coupler
Wireless
link
Bridge
Medium-voltage
lines
Low-voltage
lines
Coupler
Coupler
Bridge
Backhaul
Point
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 endusers; 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)
Internet
Cable Modem
Computer
CMTS
Cable
TV
Television
Company
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.
Downstream Channel
Multiple TV Channels
Upstream
signaling
5-42
MHz
...
50 MHz - 550 MHz
550 MHz - 750 and up MHz
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 Overview
-- BPI+ -Internet
CM Authentication
(X.509 Certificates)
Key Management
(RSA, Tri-DES)
abcdef
CMTS
Data Encryption
(DES)
Mfg Certificate
......
Digitally Signed by:
DOCSCSIS Root
CM Certificate
......
Digitally Signed by:
Mfg CA
x$a9E!
abcdef
TFTP Server Secure Software Download CM
New CM Code
......
(X.509 Certificate)
CM Code
File
Digitally Signed by:
Manufacturer
PC
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)
//
Copper
Fiber
CO/HE
CO/HE
//
Old networks, optimized for voice
24 kbps - 1.5 Mbps
CO/HE
//
Optical networks, optimized for voice,
video and data
Note: network may be aerial
or underground
19 Mbps - 1 Gbps +
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.
Optical Access Network
CO/HE
//
Optical Line
Termination
Source: www.ftthcouncil.org
Optical
Network
Unit
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
Copper
• Uses light
• Transparent
• Dielectric materialnonconductive
– EMI immune
• Low thermal expansion
• Brittle, rigid material
• Chemically stable
• 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
Architecture
(Electronics)
• PON
• Active node
• Hybrid
Transport:
ATM or
Ethernet
CO/HE
//
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
FTTH Technical considerations:
Security
• 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 Data Flow and Security:
Downstream
Time division
multiplex (TDM) –
each subscriber’s
data gets its turn.
T
D
//
//
//
H
//
//
T
//
Tom
//
Box 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.
H
Harry
D
Dick
FTTH Data Flow and Security:
Upstream
Time division multiple
access (TDMA) – similar to
downstream, with gap for
laser start/stop
T
D
//
//
//
H
//
//
Tom
//
//
Due 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
H
Harry
Dick
FTTH Data Flow and QoS
If Dick has paid for
more bandwidth, he
gets more
T
D
//
//
//
//
H
//
T
//
Tom
//
If Tom’s packets need higher
priority (e.g., telephone), they
go first
H
Harry
D
Dick
Video Delivery with FTTH
• 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
IPTV Unicast (VOD)
Router B
Router A
(headend)
Router E
In-hom e
routing
Router C
(network)
VOD server
Router D
(NID)
Program
stream
Program
request
In-hom e
routing
In-hom e
routing
In-hom e
routing
Set top
term inal
Subscriber's TV
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
10 Mbps
100 Mbps
1000 Mbps
1000 Mbps
Gigabit Ethernet
Full-duplex Switch
1000BaseT
1000 Mbps
100BaseT
100 Mbps
1000BaseT
1000 Mbps
Gigabit Ethernet Communication
Structure
Ethernet Upper Layers
Logical Link Control (LLC)
Media Access Control (MAC)
Gigabit Media Independent Interface (GMII)
1000BASE-T
Codec
8B/10B Coding/Decoding
1000BASE-LX
1270-1355 nm
光傳送接收器
SMF
3 km
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
MMF
50 um
MMF
62.5 um
Balance Shielded
Copper
Cat-5
UTP
550m 550m
300m
25m
100m
MMF
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 halfduplex 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
transmission time

frame_ size
transmission _ rate
time
A
maximum
hub
distance
B
round trip
propagation delay
space
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.
7
1
Preamble SFD
6
6
DA
SA
2
LEN
46
4
Data
FCS
Minimum Frame Length (512 bits)
bytes
Network Extent
• For a given minimum-length frame, the extent of
a network scales inversely with data rate.
10,000 m
~ 2800m
1,000 m
~ 205m
100 m
~ 20m
10m
10Mbps
100 Mbps
1000 Mbps
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 carrierextension field so that they are exactly one
slotTime long.
• Frames longer than slotTime are untouched
Carrier Extended Frame Format
512-byte Short Frame
8
Preamble/SFD
6
6
2
DA
SA
LEN
46 - 493
Data
4
FCS
448 - 1 bytes
Extension
Minimum Nonextended
Frame Length (64 bytes)
Carrier-Extended Frame (64-511 Bytes)
8
Preamble/SFD
6
6
2
DA
SA
LEN
494 - 1500
Data
Non-Carrier-Extended Frame ( 512 Bytes)
4 bytes
FCS
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
512
length of
= 12%
slot time
4096 + 64 + 96
• For Ethernet (Fast Ethernet),
512
512 + 64 + 96
= 76%
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)
Carrier
detection
傳送
訊框
Carrier extension Inter-Frame Spacing (96 bit time)
frame 1
Preamble
frame 2
frame 3
SFD DA SA LEN LLC PAD FCS
frame 4
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
(Bit times)
interFrameGap
(us)
attempLimit
backoffLimit
jamSize
maxFrameSize
minFrameSize
extendSize
burstLength
(bits)
Ethernet Type
10Mbps
1 Mbps
512
512
9.6
100 Mbps
1000 Mbps
512
4096
96
0.96
0.096
16
10
32
1518
64
0
16
10
32
1518
64
0
16
10
32
1518
64
0
16
10
32
1518
64
448
-
-
-
65,536
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
LLC
MAC
Higher Layers
&
Netrotk
PLS
CS
MII
AUI
MII
PLS
PMD
MDI
PMA
MDI
Medium
1 Mbps, 10 Mbps
CS
GMII
PCS
PMA
PMD
AUI
Data link
Physical
CS
MDI
PCS
PMA
PMD
MDI
Medium
Medium
Medium
10 Mbps
100 Mbps
1000 Mbps
PHY
10 Gigabit Ethernet Protocol Stack
OSI Ref.
Proposed IEEE 802.3ae Layers
LLC
MAC
Higher Layers
&
Netrotk
Reconciliation Sublayer (RS)
XGMII
XGMII
XGMII
64B/66B PCS
Data link
Physical
64B/66B PCS
WIS
8B/10B PCS
PMA
PMA
PMA
PMD
PMD
PMD
Medium
Medium
Medium
10GBase-R
10GBase-W
10GBase-X
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)
2.4 GHz Radio Licenses NOT required in these bands 5 GHz
Direct Sequence Spread Spectrum
IEEE 802.11
Standard 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 802.11b
Wi-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 802.11g
802.11a backward compatible to the 802.11b 2.4 GHz band
using OFDM.
Orthogonal Frequency Division Multiplexing
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
fixed terminal
mobile terminal
server
infrastructure network
access point
application
Application
TCP
TCP
IP
IP
LLC
LLC
LLC
802.11 MAC
802.11 MAC 802.3 MAC
802.3 MAC
802.11 PHY
802.11 PHY 802.3 PHY
802.3 PHY
Basic Service Set (BSS)
Coordinated
function
BSS
Independent Basic Service Set
(IBSS)
A BSS without
Access Point
IBSS
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)
A cell
Access
Point
91.44 to 152.4 meters
BSS
ESS: BSS’s with Wired Distribution
System (DS)
20-30% overlap
BSS
BSS
ESS: BSS’s with Wireless
Distribution System (DS)
BSS
BSS
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
Access Point
Client
Probe Request
Probe Response
Authentication Request
Authentication Response
Probing
802.11
Authentication
Association Request
Association Response
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
AP
MN
probe request with SSID
probe response
If SSID matches
Service Set Identifier (SSID)
Passive Scanning
AP
MN
beacon with SSID
Service Set Identifier (SSID)
Full Scanning
MN
AP 1
AP 2
Scan channel 1
AP 3
MinChannelTime
Scan channel 2
Beacon or Probe Resp
Scan channel 3
…
Scan channel 11
MaxChannelTime
Authentication and Association Types
WLAN authentication occurs at Layer 2.
It is the process of authenticating the
device not the user.
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
Access Point
Client
Authentication Request
Authentication response
Shared Key Authentication
• Requires that the client configures a static WEP key
Access Point
Client
Authentication Request
Authentication response (challenge)
Authentication Request(encrypted challenge)
Authentication response(Success/Failure)
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
Client
Access Point
Auth. Request
Auth. Response (Success/Reject)
RADIUS
Server
Access-Request
(MAC sent as RADIUS req.)
Access-Success/Reject
實際驗證
Open
Authentication
WEP Encapsulation
1.
2.
3.
4.
P = M || checksum(M)
KeyStream = RC4 (IV || k)
C = XOR (P, KeyStream)
Transmit (IV, C)
{p=plaintext}
{k=shared-key}
{c=ciphertext}
{IV=init-vector}
IV
Initialization
Vector (IV)
||
seed
WEP Key
Plaintext
RC4
PRNG
Key Stream

||
C
Ciphertext
P
CRC-32
Integrity Check Value (ICV)
Message
WEP Decapsulation
1.
2.
3.
WEP Key
IV
Ciphertext
Message
KeyStream = RC4 (IV || k)
P’ = XOR (C, KeyStream) = M’ || checksum(M)
If checksum(M’) = (checksum(M))’
Then P’ is accepted
M’
||
Seed
RC4
PRNG
Key stream
P’

Plaintext
CRC 32
ICV
ICV’
ICV' = ICV?
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.
Authentication
server
Authentication
request
Authentication
request
Authentication
response
Authentication
response
802.1X – How it works
Client
AP
Auth Server
“RADIUS”
Let me in! (EAP Start)
What’s your ID? (EAP-request identity message)
ID = [email protected] (EAP Response)
The answer is “47”
Is [email protected] OK?
Prove to me that you are
[email protected]
EAP Challenge/
Authentication
Let him in. Here is the session key.
Come in. Here is the session key.
network
http://yyy.local\index.htm
Encrypted
session
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
data frame
random 1
The winner
contention
window
busy
DIFS
random 2
All stations must wait DIFS
after medium is free
random 3
time
SIFS: Giving Priority to
RTS/CTS/ACK
data frame
Source
busy
Destination
contention
window
ACK
DIFS
DIFS
SIFS
SIFS
Others
Defer access
SIFS: Transmitting Fragments
Source
DIFS
SIFS
Fragment 1
SIFS
Fragment 2
Destination
SIFS
ACK
Others
Defer access
SIFS
ACK
Contention
Window
EIFS: Low Priority
Retransmission
data frame
Source
busy
Destination
contention
window
DIFS
SIFS
can
resend
EIFS
DIFS
No
ACK
SIFS
Others
Defer access
contension
CSMA/CA with RTS/CTS
SIFS
SIFS
data frame
Source
RTS
busy
Destination
ACK
contention
window
CTS
DIFS
SIFS
SIFS
Others
NAV (RTS)
NAV (CTS)
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.
s
m
• Master — the device which initiates an
exchange of data.
• Slave — the device which responds to the
master.
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).
m
s
s
s
Piconet Structure
Master
Active Slave
Parked Slave
Standby
Scatternet
• Multiple piconets form a scatternet.
• Same device can be shard by two different
piconets
m
s
s
m
s
s
m
s
s
Max 256 piconets
s
s
s
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
master
slave
625s
Slot k+1
Slot k+2
Multi-Slot Packets
• Bluetooth defines data packets which are 1, 3, or
5 slots long
1-slot
packet
3-slot
packet
5-slot
packet
f(k)
f(k+1)
f(k+2)
f(k+3)
f(k+4)
f(k+5)
f(k+6)
Time Division Multiplexing
• Slaves must listen to the master
• A slave can send only after receiving a poll
1
2
Master
TX
RX
Slave 1
RX
TX
Slave 2
TX
RX
2
RX
TX
TX
RX
1
RX
TX
TX
RX
RX
TX
Putting It Altogether
channel
78
77
76
75
Master
…
Slave 1
5
4
3
2
1
0
Slave 2
time
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
Slot no
master
0
1
SCO
TX
SCO
RX
Slave 1
Slave 2
SCO
RX
SCO
TX
2
3
TX
RX
RX
TX
4
TX
RX
5
0
1
RX
SCO
TX
SCO
RX
TX
SCO
RX
SCO
TX
2
Mixed Link Packets
SCO
MASTER
SLAVE 1
SLAVE 2
SLAVE 3
ACL
SCO
ACL
ACL
SCO
SCO
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
Antenna
RF Module
Tag
Reader
Host Computer
Interrogation Unit
Micro
Computer
Computer Network
Tx/Rx
Antenna
One or more RF tags
Two or more antennas
One or more interrogators
One or more host computers
Appropriate software
RF Tag
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
Regulating Authority : ITU and Geo Organizations
Frequency
125-150 kHz
13.56 MHz
433 MHz
860-960 MHz
2450 MHz
Regulation
Basically
unregulated
ISM band, differing
power levels and
duty cycle
Non-specific Short
Range Devices
(SRD), Location
Systems
ISM band
(Increasing use in
other regions,
differing power
levels and duty
cycle
ISM band, differing
power levels and
duty cycle
Range
Data Speed
Comments
Animal identification
and factory data
collection systems
Popular frequency for
I.C. Cards (Smart
Cards)
? 10 cm
Low
<1m
Low to
moderate
1 – 100 m
Moderate
DoD Active
Moderate to
high
EAN.UCC GTAG,
MH10.8.4 (RTI),
AIAG B-11 (Tires),
EPC (18000-6’)
High
IEEE 802.11b,
Bluetooth, CT,
AIAG B-11
2–5m
1–2m