Transcript Local Area Networking. - University of South Wales

UNESCO PROJECT
Advanced Course on Networking
Professor Khalid Al-Begain
UNESCO/CISM SECOND ADVANCED SCHOOL OF
INFORMATICS
University of Damascus, Syria, 06 - 15 April 2004
I am
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Khalid Al-Begain
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School of Computing, University of Glamorgan,
Wales, UK
Professor in Mobile Networking
Head of the Mobile Computing and Networking
Research Group
– Performance evaluation Modelling, simulation and
analysis
– QoS Routing and Multicast Routing
– Resource Management and Call admission Control
– Traffic Engineering
– Mobile Services for next generation mobile and wireless
networks
Course Content
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Four Lectures
A combination of essential and advanced
topics
New compared with last year : WIRELESS
The Course covers
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LANs and WLAN standards
TCP/IP Theory : Protocols and Applications
Wireless and Cellular Networks: Channel
Allocation Schemes
LAN versus WAN -Revisited
Local Area Networks
Wide Area Networks
Geographical Coverage
Limited (room, building, campus)
Widespread (country, worldwide)
Data Rates
High - typically 1M to 1Gbps
Historically low <= 64Kbps.
Now much higher up to 2.4G
Transmission
Media
Private (coax, twisted-pairs, optic
fibres, radio)
Use of “Common Carriers”
(BT, Mercury)
(Fibres, microwaves, satellite…)
Error Rates
Low
Historically high
typically worse than 1 in 106.
Now comparable with LANs
Better than 1 in
1010
Types
Ethernet (IEEE 802.3)
Token Ring (IEEE 802.5)
Token Bus (IEEE 802.4)
Wireless (IEEE 802.11), Bluetooth
Packet Switching (ITU X.25)
Cell Switching (ATM)
Circuit Switching (ITU ISDN)
Access
Multiple Access
Individual Access Links
LANs:
Major medium access techniques
LANs:
Major medium access techniques
CD: Collision Detection
Ethernet, Fast Ethernet
LANs:
Major medium access techniques
CA: Collision Avoidance
WLAN, Bluetooth
IEEE 802 :LANs
The Data Link Layer
Logical Link Control Sublayer
Medium Access Sublayer
IEEE 802
Important
The future
will tell!
IEEE 802.3
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Classic Ethernet (10 Mbps)
(First Founded by Xerox in 1976)
Fast Ethernet (100Mbps) (IEEE 802.3u)
 Gigabit Ethernet (1Gbps) (IEEE 802.3z)
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Classical Ethernet
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The most common cabling methods
Classical Ethernet
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The most common cabling methods
Manchester Encoding
Used in Classical Ethernet
Ethernet : Frame Formats
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Two versions exist:
(a) DIX (Digital, Intel, Xerox)
(b) IEEE 802.3
Ethernet Medium Access CSMA
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All stations are connected to the cable
When a station wishes to transmit, it “listens” to the
cable - if there is no signal it starts to transmit,
otherwise it tries again later.
(Non-Persistent, 1-Persistent, p-Persistent)
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Whilst a station is transmitting it compares the signal
on the coax with the signal it is transmitting - if they
are different it stops and tries again later
CD: Collision Detection means when detects collision
then stop transmission  wait random time  try
again
The time to wait is calculated using the Binary
Exponential Backoff algorithm.
Collision Detection
Cause: Signals need time to propagate!
Binary Exponential Backoff
Time slot = 51.2μs
Binary Exponential Backoff:
• After 1st collision each participating station waits randomly 0 or 1 slot
• After 2nd collision each participating station waits 0,1,2, or 3 slots
• After n-th collision each participating station waits between 0 .. 2n-1 slots
• Maximum Backoff = 1023 slots
Beyond the 10Mbps
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The early1980s luxury:
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8 MHz PC
256 KByte RAM
10 MByte Hard Disk
Connected to the Dream 10Mbps LAN
But Parkinson’s Law is valid here too:
“Work Expands to fill the time available for its Completion”
In other words:
“Data expands to fill the bandwidth available for their transmission”
The 100Mbps LAN
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Many proposals came to have faster LANs or MANs
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FDDI : Fibre Distributed Data Interface
DQDB : Dual Queue Dual Bus
Fibre Channel
Common Feature :
Very complex
High Cost
 However for a technology to work, it must be follow
the KISS Law:
“Keep It Simple, Stupid”
Fast Ethernet
1992 : the IEEE 802.3 committee again.
 Task: make faster LAN.
 Results:
Fast Ethernet (IEEE 802.3u) which is in
principle identical to Ethernet except
that bit time is 10ns instead of 100ns.
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Fast Ethernet Cabling
• Fast Ethernet uses either HUBs or Switches
• No Manchester Encoding
Gigabit Ethernet
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1995: the same idea: make Ethernet 10
time faster.
The Ethernet real Competitor:
Let us Go Wireless
Who is interested?
Desktop and laptop systems
 Handheld devices
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 PCs,
scanners, data collection devices
PDAs
 Palmtops
 etc
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WLAN implications
Multiple propagation pathways
 Signal interference
 Lifetime of battery
 Security
 Path loss
 Installation and connectivity
 Health
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IEEE 802.11
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1997 standard
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2.4GHz
1Mbit/s and 2Mbit/s
FHSS and DSSS
Logical Link
1999 standard
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802.11a
5 GHz - Orthogonal FDM
up to 54 Mbit/s
802.11b
2.4 GHz - DSSS
up to 11 Mbit/s
Control (LLC)
Data
Link
layer
Media Access
Control (MAC)
Frequency Direct
Hopping
Infrared
Sequence light
Physical
Layer
IEEE 802.11a,b Pros & Cons!
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IEEE 802.11a
+ Very high data rates
- 5 GHz licensing problem
- Competition with ETSI HiperLAN 2
- Illegal in Europe
- Higher cost
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IEEE 802.11b
+ Works in the Unlicensed band of 2.4 GHz
~ Data rates comparable with LANs
- Interference with Cordless phones and Microwave ovens
+ Cheaper devices
WLAN
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Two modes of operation
(a)
(b)
Centralised
Ad hoc
A multicel 802.11 network
IEEE 802.11 MAC
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The hidden Station problem:
Distributed Coordination Function (DCF)
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To solve the problem of Hidden station
Use DCF:
 Uses CSMA/CA (Collision Avoidance)
 It is based on virtual channel sensing
All WLANs must support DCF.
For centralised WLANs, there is also PCF
(Point Coordination Function)
Virtual Channel Sensing using CSMA/CA
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Example: A, B, C, and D stations (D out
of the range of A)
Request To Send
Clear To Send
Network Allocation Vector
Due to unreliable medium
Frame Fragmentation
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Because the radio link is unreliable
short frames are needed  long frames
has to be fragmented.
Interframe Spacing in 802.11
IEEE802.11 Frame Structure
IEEE802.11 MAC Services
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Distribution system services
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Association
Disassociation
Re-association
Distribution
Integration
Station services
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Authentication
De-authentication
Privacy
Data Delivery
What else in Wireless
Bluetooth (IEEE 802.15)
 Broadband Wireless (IEEE 802.16)
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And the Cellular Wireless Technologies
 GSM,
GPRS, and UMTS
What else in Wireless
Bluetooth (IEEE 802.15)
 Broadband Wireless (IEEE 802.16)
(will follow but very briefly)
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And the Cellular Wireless Technologies
 GSM,
GPRS, and UMTS
Bluetooth
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1994: Ericsson SIG started
(with IBM, Intel, Nokia and Toshiba)
Named after Viking King Harald Blaatand
(Bluetooth) who unified Denmark and Norway
without wires!!
Goal: Short-range, inexpensive (<$5) method to
connect devices without wires (E.g., mobile-PDA)
July 1999, PAN (Personal Area Network) standard
IEEE 802.15
Bluetooth Characteristics
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Works in the 2.4 GHz band (together with
WLANs and microwave ovens)
Low range (< 10m)
79 channels each with 1MHz 1Mbps
Organised into pico-cells (1 Master and 7
slaves)
Uses FHSS (Frequency Hopping) controlled
by Master (1600 hops/sec)
Uses same Frequency band and hoping as
WLAN (problem!!!)
Bluetooth Architecture
Scatternet, 255 parked slaves, Ad hoc
Bluetooth Services
Broadband Wireless IEEE802.16
Wireless MAN or Wireless Local Loop
 High data rates to Buildings
 Can be seen as Wireless Cable TV
network.
 Uses bandwidth between 10-66 GHz
 Uses sophisticated modulation to
achieve high rates
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IEEE 802.16 Transmission Environment
For example: with 25MHz spectrum rates are : 150, 100, 50 Mbps