Local%20Area%20Networks%20(LANs)

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Local Area Networks (LANs)
- IEEE 802 - Ethernet - Wireless LAN
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1. IEEE 802

• IEEE 802.1 Higher layer LAN protocols
• IEEE 802.2 Logical link control
• IEEE 802.3 Ethernet
• IEEE 802.4 Token bus
• IEEE 802.5 Token Ring
• IEEE 802.6 Metropolitan Area Networks
• IEEE 802.7 Broadband LAN using Coaxial Cable
• IEEE 802.8 Fiber Optic TAG
• IEEE 802.9 Integrated Services LAN
• IEEE 802.10 Interoperable LAN Security
• IEEE 802.11 Wireless LAN (Wi-Fi)
• IEEE 802.12 demand priority
• IEEE 802.14 Cable modems

• IEEE 802.15 Wireless PAN
• IEEE 802.15.1 (Bluetooth)
• IEEE 802.15.4 (ZigBee)
• IEEE 802.16 Broadband Wireless Access (WiMAX)
• IEEE 802.16e (Mobile) Broadband Wireless Access
• IEEE 802.17 Resilient packet ring
• IEEE 802.18 Radio Regulatory TAG
• IEEE 802.19 Coexistence TAG
• IEEE 802.20 Mobile Broadband Wireless Access
• IEEE 802.21 Media Independent Handoff
• IEEE 802.22 Wireless Regional Area Network

3
IEEE 802 LAN Protocol Architecture

• Lower layers of OSI model
• IEEE 802 reference model
• Physical
• Logical link control (LLC)
• Media access control (MAC)

4
IEEE 802 Protocol Layers Compared to OSI Model
5
802 Layers - Physical

• Encoding/decoding
• Preamble generation/removal (for sync.)
• Bit transmission/reception
• Transmission medium and topology

6
802 Layers Medium Access Control

• Assemble data into frame
• Disassemble frame, and perform address
  recognition and error detection
• Govern access to the LAN transmission medium

802 Layers - Logical Link Control

• Interface to higher levels
• Flow and error control

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LAN Protocols in Context
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Logical Link Control

• Transmission of link level PDUs between two
  stations
• Relieved of some link access details by MAC layer
• Based on HDLC (High-Level Data Link Control)
• Three services
• Unacknowledged connectionless service
• Connection mode service
• Acknowledged connectionless service

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Medium Access Control

• Multiple devices shares the networks
  transmission capacity/medium
• Means of controlling access to the transmission
  medium
• MAC layer receives data from LLC layer
• LLC PDU is enclosed in a MAC frame

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2. Ethernet

• Developed by Xerox
• IEEE 802.3
• Classical Ethernet
• 10 Mbps
• Bus topology
• Medium Access Control
• CSMA/CD (carrier sense multiple access with
  collision detection)

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Bus Topology

• Stations attach to linear transmission medium
  (bus), via a tap
• Full-duplex between station and tap
• Transmission propagates length of medium in both
  directions
• Received by all other stations
• At each end of bus terminator, to absorb signal
• Need to indicate for whom transmission is
  intended
• Need to regulate transmission
• If two stations attempt to transmit at same time,
  signals will overlap and become garbled
• If one station transmits continuously access
  blocked for others
• Transmit data in small blocks (frames)
• Each station assigned unique address
• Destination address included in frame header

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Frame Transmission on a Bus LAN
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CSMA/CD

• With CSMA, collision occupies medium for duration
  of transmission
• Stations listen whilst transmitting
• If medium idle, transmit, otherwise, step 2
• If busy, listen for idle, then transmit
• If collision detected, send a jamming signal and
  then cease transmission
• After jam, wait random time (backoff) then start
  from step 1
• Binary exponential backoff
• Random delay is doubled (the first 10
  retransmission)
• After 16 unsuccessful attempts, give up

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IEEE 802.3 Frame Format
Max. frame size 1518 18 1500
Preamble 1010101010101010 SFD 10101011
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Ethernet Physical Layer

• Ethernet (10 Mbps)
• Fast Ethernet (100 Mbps)
• Gigabit Ethernet (GbE)
• 10 gigabit Ethernet (10GbE)
• 100 gigabit Ethernet (100GbE)

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10Mbps Ethernet
(hundreds of meters)
(Mbps)

• ltdata rategtltSignaling methodgtltMax segment lengthgt
• 10Base5 10Base2 10Base-T
• Medium Coaxial Coaxial UTP
• Signaling Baseband Baseband Baseband
• Manchester Manchester Manchester
• Topology Bus Bus Star
• Nodes 100 30 -

(100m)
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10BASE-T

• Unshielded twisted pair (UTP) medium
• Also used for telephone
• Star-shaped topology
• Stations connected to central point, (multiport
  repeater)
• Two twisted pairs (transmit and receive)
• Repeater accepts input on any one line and
  repeats it on all other lines
• Link limited to 100 m on UTP
• Optical fiber 500 m
• Central element of star is active element (hub)
• Physical star, logical bus
• Multiple levels of hubs can be cascaded

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Fast Ethernet

• 100Mbps Fast Ethernet
• Star-wire topology (Similar to 10BASE-T)
• 100BASE-T Options

T twisted-pair wire
X 2 pair (transmit, receive)
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100BASE-TX

• 100BASE-TX runs over two pairs of wires
• Uses one pair of twisted wires in each direction
• 100 Mbit/s of throughput in each direction
  (full-duplex)
• STP and Category 5 UTP allowed

1 White/Orange 2 Orange 3 White/Green 4 5 6
Green 7 8
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Full Duplex Operation

• Traditional Ethernet half duplex
• Either transmit or receive but not both
  simultaneously
• With full-duplex, station can transmit and
  receive simultaneously
• 100-Mbps Ethernet in full-duplex mode,
  theoretical transfer rate 200 Mbps
• Attached stations must have full-duplex adapter
  cards
• Must use switching hub
• Each station constitutes separate collision
  domain
• In fact, no collisions
• CSMA/CD algorithm no longer needed
• 802.3 MAC frame format used
• Attached stations can continue CSMA/CD

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Gigabit Ethernet
(Short wavelength) (Long wavelength)
(log scale)
S 850 nm L 1,310 nm
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10-Gbps Ethernet
(log scale)
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Virtual LAN (VLAN) with Ethernet Switches
Server Broadcasting without VLANS
Servers Sometimes Broadcast Goes To All
Stations Latency Results
Server Broadcast
Client C
Client B
Client A
Server D
Server E
Destination MAC address FF-FF-FF-FF-FF-FF
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Virtual LAN (VLAN)with Ethernet Switches,
Continued
Server Broadcasting with VLANS
With VLANs, Broadcasts Only Go To a Servers
VLAN Clients Less Latency
Server Broadcast
No
No
Client C on VLAN1
Client B on VLAN2
Client A on VLAN1
Server D on VLAN2
Server E on VLAN1
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Tagged Ethernet Frame (802.1Q)
Tagged 802.3 MAC Frame
Basic 802.3 MAC Frame
Preamble (7 octets)
Preamble (7 octets)
Start-of-Frame Delimiter (1 Octet)
Start-of-Frame Delimiter (1 Octet)
Destination Address (6 Octets)
Destination Address (6 Octets)
Source Address (6 Octets)
Source Address (6 Octets)
Tag Protocol ID (2 Octets) 1000000100000000 81-00
hex 33,024 decimal. Larger than 1,500, So not a
Length Field
Length (2 Octets) Length of Data Field in
Octets 1,500 (Decimal) Maximum
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Tagged Ethernet Frame (802.1Q)
Basic 802.3 MAC Frame
Tagged 802.3 MAC Frame
Tag Control Information (2 Octets) Priority Level
(0-7) (3 bits) VLAN ID (12 bits) 1 other bit
Data Field (variable)
PAD (If Needed)
Length (2 Octets)
Data Field (variable)
Frame Check Sequence (4 Octets)
PAD (If Needed)
Frame Check Sequence (4 Octets)
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Hub Versus Switch
Hub Broadcasts Each Bit Out All Other
Ports --- If A Is Transmitting, B Must Wait to
Transmit
Ethernet Hub
X
C
D
A
B
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Hub Versus Switch
Switch Sends Frame Out One Port If A Is
Transmitting to C, B Can Transmit to
D Simultaneously
Ethernet Switch
C
D
A
B
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BusHub Switch
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3. Wireless LANs

• A wireless LAN uses wireless transmission medium
• To satisfy requirements for
• mobility
• relocation
• ad hoc networking
• coverage of locations difficult to wire
• Applications
• LAN Extension
• Cross-Building Interconnect
• Nomadic Access
• Ad Hoc Networking

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IEEE 802.11 WLAN (Wi-Fi)

• ??????
• Wireless Local Area Network (WLAN)
• Wi-Fi (Wireless Fidelity)
• Wi-Fi Alliance (http//wi-fi.org/)
• IEEE 802.11
• 802.11a/b/g/n

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WLAN???/??? (Access Point)
AP
Switch
Router
Internet/ Intranet
Router
Switch
Access Router
AP
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WLAN ?? (Hotspots)
Coffee Shop
Airport
WLAN Adapter
Internet
Access Point
Conference Center
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MIT iSPOTS http//ispots.mit.edu/
APs 2800 Users per 15 min 1000
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??WLAN?????
Dopod CHT9100
Linksys Video Camera
100 OLPC

• PDA / Laptop PC
• PDA/Smart Phone
• Printer
• Digital Camera
• Wireless Audio
• Projector
• Surveillance Camera
• Wireless Skype Phone
• Wii

Nikon Coolpix S50c
NEC LT265 Projector
Nintendo Wii
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Ad Hoc??

• Ad Hoc Mode

• Infrastructure Mode

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4
2
1
3
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IEEE 802.11??
Protocol Release Date Op. Frequency (Unlicensed Band) Typ Max of Non- Overlapping Channels Range (Indoor)
Legacy 1997 2.4-2.5 GHz 1 Mbps 2 Mbps 3  ?
802.11a 1999 5.15-5.35 / 5.47-5.725 /5.725-5.875 GHz 25 Mbps 54 Mbps 24 30 m
802.11b 1999 2.4-2.5 GHz 6.5 Mbps 11 Mbps 3 50 m
802.11g 2003 2.4-2.5 GHz 25 Mbps 54 Mbps 3 30 m
802.11n 2006 draft 2.4 GHz or 5 GHz bands 200 Mbps 540 Mbps 3 / 24 50 m
- Data Rate -
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IEEE 802.11 Architecture

• MAC protocol and physical medium specification
  for wireless LANs
• Smallest building block is basic service set
  (BSS)
• Number of stations
• Same MAC protocol
• Competing for access to same shared wireless
  medium
• BSS generally corresponds to cell
• May be isolated or connect to backbone
  distribution system (DS) through access point
  (AP)
• AP functions as bridge
• DS can be switch, wired network, or wireless
  network
• MAC protocol may be distributed (DCF) or
  controlled (PCF) by central coordination function
  in AP

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IEEE 802.11??
ESS
BSS
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SSID

• SSID (Service Set Identifier)
• Service Set???
• ????????????,?????????SSID,????????
• SSID??
• AP?????SSID,?????????????????
• ???AP??SSID,??WLAN???

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802.11 ????/??

• 802.11?????????????????
• ISM??,2.4GHz, 5 GHz
• ??????1W,802.11 0.1W
• ????,????Bluetooth
• ??(Channel)
• 2.4-GHz- ISM?? 14???(??22 MHz)
• ???????111??

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Channel Nominal Frequency (MHz) Minimum (MHz) Maximum (MHz)
1 2412 2401 2423
2 2417 2405 2428
3 2422 2411 2433
4 2427 2416 2438
5 2432 2421 2443
6 2437 2426 2448
7 2442 2431 2453
8 2447 2436 2458
9 2452 2441 2463
10 2457 2446 2468
11 2462 2451 2473
22 MHz
5 MHz
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AP??????
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Typical 802.11 WLAN Operation
Ethernet Switch
802.11 Frame
802.3 Frame
UTP
Radio Transmission
AP
Laptop
802.3 Frame
Access points (APs) bridge the networks Translates
between the 802.11 wireless frame and the
Ethernet 802.3 frame used within the LAN
Client PC
Server
Large Wired LAN
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Typical 802.11 WLAN Operation, Continued
Ethernet Switch
UTP
AP A
Laptop
802.3 Frame
802.11 Frame
Client PC
Handoff or Roaming (if mobile computer moves to
another access point, it switches service to that
access point)
AP B
Server
Large Wired LAN
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IEEE 802.11 Services

• Association
• Establish an initial association between a
  station and an AP
• Reassociation
• Enables an established association to be
  transferred from one AP to another
• Disassociation
• Terminate an existing association
• Authentication
• Establish the identity of stations to each other
• Privacy
• Prevent eavesdropping

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A Scenario
(1) Association (2) Reassociation (3)
Disassociation
Internet
AP 2
AP 1
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Stations and Access Points Transmit in a Single
Channel
Collision if 2 Devices send Simultaneously
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Medium Access Control

• Reliable data delivery
• Noise, interference, and other propagation
  effects result in loss of frames
• Multiple Access
• Only one station or the access point can
  transmit at a time
• Security
• Authorized access
• Two MAC methods
• CSMA/CAACK (mandatory)
• RTS/CTS (optional)

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CSMA/CAACK

• CSMA/CA (Carrier Sense Multiple Access with
  Collision Avoidance)
• If there has been no traffic for a sufficiently
  long time, station or access point may send
  immediately.
• If there is current traffic or collision,
• the station sets a random timer
• If there is no traffic when the timer finishes,
  may send
• Receiver immediately sends back an
  acknowledgement (ACK) when it receives a frame.

52
CSMA/CAACK

• ACK (Acknowledgement)
• Receiver immediately sends back an acknowledgment
  when it receives a frame
• Does not wait to send an ACK
• This avoids interference with other stations,
  which must wait
• If sender does not receive the acknowledgement,
  it retransmits the frame using CSMA/CA
• 802.11 with CSMA/CAACK is a reliable protocol!

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RTS/CTS
CSMA/CA
D
RTS
A
B
CTS
C
http//media.pearsoncmg.com/aw/aw_kurose_network_2
/applets/csma-ca/withhidden.html
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Four Frame Exchange

• Basic data transfer involves exchange of two
  frames
• To further enhance reliability, four-frame
  exchange may be used
• Source issues a Request to Send (RTS) frame to
  destination
• Destination responds with Clear to Send (CTS)
• After receiving CTS, source transmits data
• Destination responds with ACK
• RTS alerts all stations within range of source
  that exchange is under way
• CTS alerts all stations within range of
  destination

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Request to Send/Clear to Send (RTS/CTS)
Switch
RTS
Radio Link
Access Point B
Laptop
Client PC
Server
1. Device that wishes to transmit may send
a Request-to-Send message
Large Wired LAN
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Request to Send/Clear to Send (RTS/CTS)
Must Wait
Switch
CTS
Radio Link
WAP
May Send Frames
Client PC
Server
Large Wired LAN
2. Wireless access point broadcasts a
Clear-to-Send message. Station that sent the
RTS may transmit unimpeded. Other stations
hearing the CTS must wait
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WLAN????

• WLAN????
• ?????????
• WLAN??????????
• ??????
• WLAN????
• ???? (Encryption)
• ???? (Authentication)

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WLAN????

• ??
• ??????
• ???? (Denial of Service, DoS)
• WEP Key??
• ????? (Man in the Middle)
• ????? (Rouge AP)
• ???? (Session Hijacking)

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Man-In-Middle??

• ????????( Mutual Authentication)

2. Associates As Legitimate Client
Legitimate AP
Evil Twin AP
Legitimate Client
1. Associates
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????? (Rouge AP)
Switch
Router
Internet/ Intranet
?? AP SSID 7Eleven
Router
Rouge AP SSID 7Eleven
Switch
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Session Hijacking
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WLAN????

• ??SSID??
• MAC????
• Shared Key ??
• WEP (Wired Equivalent Privacy)
• WPA (Wi-Fi Protected Access)
• 802.11i (WPA2)

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Wii Wireless Connection Setting
http//www.nintendo.com/consumer/systems/wii/en_na
/online.jsp
WPA Wi-Fi Protected Access PSK pre-shared
key WEP Wired Equivalent Privacy TKIP
Temporal Key Integrity Protocol Reference
IEEE 802.11i Wi-Fi Alliance
64
??SSID??
65
MAC????
66
Shared Key ??
Open System ?????
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Shared Key ??
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WEP (Wired Equivalent Privacy)
69
(No Transcript)
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WEP Encryption
0011 0101 0110
? XOR
( A ? B ? B A )
Plain Text
010111001011100101001101...
?
RC4
key
IV
?
110101100101010011001001...
?
Cipher Text
100010101110110110000100...
?
RC4
key
IV
?
110101100101010011001001...
?
Plain Text
010111001011100101001101...
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WPA (Wi-Fi Protected Access) - PSK (Pre-Shared
Key)
5j6 g0 is "Chu Shan".

• WPA-PSK
• Encryption TKIP

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• Key
• Password
• Dictionary attack
• Passphrase
• Phrase
• life is good in NCNU

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WPA (Wi-Fi Protected Access) - 802.1X
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IEEE 802.1X

• EAP-MD5
• EAP-TLS

EAP Extended Authentication Protocol RADIUS Rem
ote Authentication Dial In User Service
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802.11i (WPA2) - PSK
WPA2-PSK Encryption AES-CCMP
AES-CCMP AES-Counter Mode CBC-MAC Protocol
CBC-MAC Cipher Block Chaining-Message
Authentication Code
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802.11i (WPA2) - 802.1X
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WLAN??????
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WLAN??????
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WLAN??????????

• ????PDA?????WLAN?????
• Web-Based
• ????????
• ?????????????
• ????????????

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(No Transcript)