Home Network Technologies

1
Home Network Technologies
2
??????????
Home Networking Technology
Internet
Home Network
Broadband Access Technology
Computer
ISP
TV
3
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

4
Outlines

• Broadband Over Power Line
• Digital Subscriber Line (DSL) Technology
• Cable Modem

5
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

6
In-House BPL

• connecting machines within a building
• HomePlug an alliance for in-house BPL

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Access BPL

• Delivers the last mile of broadband to the home

8
Access BPL Architecture
Coupler
Backhaul
Backhaul Point
Medium-voltage lines
Low-voltage lines
Coupler
Wireless link
Bridge
9
Coupler
Coupler

Bridge
Backhaul Point
10
Advantages of BPL

• Power lines are our most ubiquitous
  infrastructure
• Lower cost of deployment
• Existing wires

11
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

12
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...

13
xDSL - Digital Subscriber Line Technology
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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)

15
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)

16
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

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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

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Cable Modem

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

Internet
Cable Modem
Computer
Cable
CMTS
Cable
TV
Television Company
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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

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Hybrid Fibre-Coaxial (HFC)

• combines optical fiber and coaxial cable

21
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
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Cable TV Spectrum
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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 users 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.

24
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 manufacturers
  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

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DOCSIS Security Overview-- BPI --
Internet
CM Authentication (X.509 Certificates)
Mfg Certificate ...... Digitally Signed by
DOCSCSIS Root
Key Management (RSA, Tri-DES)
CM Certificate ...... Digitally Signed by Mfg CA
CMTS
PC
Data Encryption (DES)
abcdef
xa9E!
abcdef
CM
TFTP Server
Secure Software Download (X.509 Certificate)
New CM Code ...... Digitally Signed by
Manufacturer
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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

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Fiber-to-the-Home(FTTH)
Copper
Fiber
//
24 kbps - 1.5 Mbps
Old networks, optimized for voice
Note network may be aerial or underground
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FTTH Characteristics

• FTTH is an optical access network in which the
  optical network unit is on or within the
  customers 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
Optical Network Unit
Source www.ftthcouncil.org
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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)

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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, its recyclable

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Architecture and Transport

• Architecture
• (Electronics)
• PON
• Active node
• Hybrid

Transport ATM or Ethernet
CO/HE
//
32
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

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FTTH Technical Considerations

• Data
• How much per home?
• How well can you share the channel?
• Security how do you protect the subscribers
  data?
• What kind of QoS parameters do you specify?
• Compatible business services?
• SLAs
• T1
• Support for voice?
• Support for video?
• Broadcast
• IPTV

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FTTH Technical Considerations

• Data
• How much per home?
• How well can you share the channel?
• Security how do you protect the subscribers
  data?
• What kind of QoS parameters do you specify?

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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

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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

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FTTH Data Flow and Security Downstream
Time division multiplex (TDM) each subscribers
data gets its turn.
//
//
Tom
Dick
//
//
//
Harry
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.
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FTTH Data Flow and Security Upstream
Time division multiple access (TDMA) similar to
downstream, with gap for laser start/stop
//
//
Tom
Dick
//
//
//
Harry
Due to the physics of the network, Harrys data
flows upstream but does not come to Toms box, so
Tom cannot see Harrys data
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FTTH Data Flow and QoS
If Dick has paid for more bandwidth, he gets more
//
//
Tom
Dick
//
//
//
Harry
If Toms packets need higher priority (e.g.,
telephone), they go first
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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

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IPTV Unicast (VOD)
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Home Networking Technologies

• IEEE 802.3/Ethernet
• IEEE 802.11 a/b/g/n (WiFi)
• Bluetooth
• In-House BPL (HomePlug)

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IEEE 802.3 Family

• Original IEEE 802.3 (Ethernet)
• 10 Mbps
• Fast Ethernet
• 1000 Mbps
• Gigabit Ethernet
• 1 Gbps
• 10 G Ethernet
• 10 Gbps

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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

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Gigabit Ethernet Architecture
46
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 ??????
1000BASE-SX 770-860 nm ??????
1000BASE-CX STP ?????
1000BASE-T 4-Pair ?????
Cat-5 UTP
MMF 62.5 um
Balance Shielded Copper
MMF 50 um
SMF
MMF
3 km 550m 550m 300m 25m
100m
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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)

48
Gigabit Ethernet Characteristics

• Good fault tolerance
• Hub/Repeater architecture
• Carrier Extension for short frames.
• Frame Bursting to increase performance
  (optional).

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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.

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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 gt 2a

transmission time
time
A
maximum distance
hub
B
round trip propagation delay
space
51
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 6 6 2
46 4 bytes
Preamble SFD DA SA LEN
Data FCS
Minimum Frame Length (512 bits)
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Network Extent

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

10,000 m 1,000 m 100 m 10m
2800m
205m
20m
10Mbps 100 Mbps
1000 Mbps
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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.

?
54
Limitations of Half-duplex Operation

• For Hub-based configuration (1995 ), the only
  truly important distance was from the user to the
  wiring closet (lt100m, 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.

55
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.

56
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

57
Carrier Extended Frame Format
512-byte Short Frame
8 6 6
2 46 - 493 4 448 - 1
bytes
Preamble/SFD DA SA LEN
Data FCS Extension
Minimum Nonextended Frame Length (64 bytes)
Carrier-Extended Frame (64-511 Bytes)
8 6 6
2 494 - 1500
4 bytes
Preamble/SFD DA SA LEN
Data FCS
Non-Carrier-Extended Frame (? 512 Bytes)
58
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),

length of slot time
59
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.

60
Frame Bursting
Maximum Time to start of Last frame in Burst
(8192 Bytes)
SlotTime (512 Bytes)
Carrier detection
Inter-Frame Spacing (96 bit time)
Carrier extension
?? ??
frame 1
frame 2
frame 4
frame 3
Preamble SFD DA SA LEN LLC PAD FCS
61
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.

62
Half-Duplex Operational Parameters
Ethernet Type

Parameters
10Mbps 1 Mbps 100 Mbps
1000 Mbps
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)
63
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.

64
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.

65
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) !!

66
Gigabit Ethernet Protocol Stack

• CS Convergence Sublayer
• MDI Medium Dependent Interface
• MII Medium Independent Interface
• GMII Gigabit Medium Independent Interface

67
10 Gigabit Ethernet Protocol Stack
68
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)

69
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
70
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.

71
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

72
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
802.3 MAC
802.3 MAC
802.11 MAC
802.11 PHY
802.3 PHY
802.3 PHY
802.11 PHY
73
Basic Service Set (BSS)
Coordinated function
BSS
74
Independent Basic Service Set (IBSS)
A BSS without Access Point
IBSS
Ad hoc mode
75
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

76
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

77
ESS Single BSS (with integrated DS)
A cell
Access Point
91.44 to 152.4 meters
BSS
78
ESS BSSs with Wired Distribution System (DS)
20-30 overlap
BSS
Distribution System
BSS
79
ESS BSSs with Wireless Distribution System (DS)
BSS
Distribution System
BSS
80
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

81
ESSID
82
Connecting to the Network
Access Point
Client
Probing
802.11 Authentication
Association
83
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

84
Active Scanning
AP
MN
probe request with SSID
probe response
If SSID matches
Service Set Identifier (SSID)
85
Passive Scanning
AP
MN
beacon with SSID
Service Set Identifier (SSID)
86
Full Scanning
MN
AP 1
AP 2
AP 3
Scan channel 1
MinChannelTime
Scan channel 2
Beacon or Probe Resp
MaxChannelTime
Scan channel 3

Scan channel 11
87
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)
88
802.11 Authentication Methods

• Open Authentication (standard)
• Shared key authentication (standard)
• MAC Address authentication (commonly used)

89
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
90
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)
91
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

RADIUS Server
Client
Access Point
Access-Request (MAC sent as RADIUS req.)
Auth. Request
Access-Success/Reject
Auth. Response (Success/Reject)
92
????
Open Authentication
93
WEP Encapsulation

1. P ?M checksum(M)? pplaintext
2. KeyStream RC4 (IV k( kshared-key
3. C XOR (P, KeyStream) cciphertext
4. Transmit (IV, C) IVinit-vector

IV

Initialization
seed

Key Stream


Vector (IV)

RC4

C
PRNG

WEP Key

Å



Ciphertext
Plaintext

P



CRC
-
32

Integrity Check Value (ICV)

Message

94
WEP Decapsulation

• KeyStream RC4 (IV k(
• P XOR (C, KeyStream) ?M checksum(M)?
• If checksum(M) (checksum(M))
• Then P is accepted

M

WEP Key



Key stream


Plaintext
RC4
P
IV


Seed

PRNG
ICV
CRC
32

Å

ICV' ICV?

Ciphertext
ICV

Message
95
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.

96
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

97
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
98
802.1X How it works
AP
Client
Auth ServerRADIUS
Let me in! (EAP Start)
Whats your ID? (EAP-request identity message)
ID xxx_at_yyy.local (EAP Response)
Is xxx_at_yyy.local OK?
Prove to me that you are xxx_at_yyy.local
EAP Challenge/Authentication
The answer is 47
Let him in. Here is the session key.
Come in. Here is the session key.
network
http//yyy.local\index.htm
Encryptedsession
99
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

100
Contention Window
data frame
random 1
The winner
contention window
busy
DIFS
random 2
random 3
time
101
SIFS Giving Priority to RTS/CTS/ACK
data frame
Source
contention window
busy
Destination
ACK
DIFS
DIFS
SIFS
SIFS
Others
Defer access
102
SIFS Transmitting Fragments
Source
DIFS
Contention Window
SIFS
Fragment 2
Destination
SIFS
ACK
Others
Defer access
103
EIFS Low Priority Retransmission
data frame
can resend
Source
contention window
EIFS
busy
DIFS
Destination
DIFS
No ACK
SIFS
SIFS
Others
Defer access
contension
104
CSMA/CA with RTS/CTS
SIFS
SIFS
data frame
Source
RTS
busy
ACK
Destination
contention window
CTS
DIFS
SIFS
SIFS
NAV (RTS)
Others
NAV (CTS)
105
RTS/CTS is Optional

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

106
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.

107
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)

108
Bluetooth Characteristics

• Data/voice access
• Cable replacement technology
• 1 Mbps symbol rate
• Range 10 meters
• Low cost
• Low power

109
Ultimate Headset(Voice Access)
110
Cordless Computer(Cable Replacement)
111
Automatic Synchronization
In the Office
At Home
112
Bluetooth World
113
Application of Bluetooth

• Integrated in
• mobile phones
• PDA/handhelds
• Computers
• Wireless peripherals
• Handsets
• cameras
• Network access devices
• universal bridge to other networks or internet

114
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
115
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 maxcapacity (1 Mbps).

116
Piconet Structure
117
Scatternet

• Multiple piconets form a scatternet.
• Same device can be shard by two different
  piconets

s
m
s
m
s
s
m
s
s
s
s
s
Max 256 piconets
118
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

119
Time Division Duplex (TDD)

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

Slot k
Slot k1
Slot k2
master
slave
625?s
120
Multi-Slot Packets

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

f(k)
f(k1)
f(k2)
f(k3)
f(k4)
f(k5)
f(k6)
1-slot packet
3-slot packet
5-slot packet
121
Time Division Multiplexing

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

Master
Slave 1
Slave 2
122
Putting It Altogether
channel
78
77
76
75
Master

Slave 1
5
Slave 2
4
3
2
1
time
0
123
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.

124
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.

125
SCO Traffics

• Master reserves slots for SCO links

0
0
1
2
3
4
5
1
2
Slot no
master
Slave 1
Slave 2
126
Mixed Link Packets
MASTER
SLAVE 1
SLAVE 2
SLAVE 3
127
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

128
An RFID System
129
RF Tag
130
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)

131
RFID Frequencies