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Lecture 10: Token Ring and FDDI Networks

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Lecture 10: Token Ring and FDDI Networks Homework for Chapter 2: All problems, particularly time lines for sliding window protocol Exam 2: October 16, 2000 – PowerPoint PPT presentation

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Title: Lecture 10: Token Ring and FDDI Networks


1
Lecture 10 Token Ring and FDDI Networks
  • Homework for Chapter 2 All problems,
    particularly time lines for sliding window
    protocol
  • Exam 2 October 16, 2000

2
Token Ring Review
  • Shared medium similar to ethernet
  • Distributed algorithm controls transmission
  • All nodes see all frames

Tokensmall (24 bit) circulating frame To send
Remove token and send frame Sender removes
message when it comes around and reinserts token
3
Key Concept
  • Token Holding Time (THT)gttransmission time of a
    packet
  • Token Rotation Time (TRT)lt ActiveNodes x
    THTRingLatency Note TRT is load dependent

4
Fiber Distributed Data Interface (FDDI)
5
Single Attachment Stations (SAS) attached to a
concentrator (DAS)Star-like topology
6
FDDI physical properties
  • 100 Mbpsbit time is only 10 ns
  • Network adaptor buffers-9-80 bits-retransmit when
    half full
  • Queuing delay50 ns for 10 bit buffers
  • Up to 500 stations
  • 2 km between stations (propagation delay10 ms)
  • 100 km ring circumference--200 km total fiber
    length
  • 4B/5B encoding
  • Packet size18,200 bytes

7
FDDI physical properties (cont.)
  • Complete Ring
  • Ring Latency24 (10 ns)50050 ns0.5 ms0.53 ms
  • Packet transmission time1.45 ms
  • Every node should see a valid transmission (token
    or data frame) every 1.98 ms (or less). This is
    called the idle time
  • Broken ring
  • Ring Latency 24 (10ns)100050ns1.0ms1.05 ms
  • Idle time2.5 ms

8
Key Parameters
  • Target token rotation time (TTRT)-upper bound to
    TRT as seen from any node
  • So, TTRT is a measure of the maximum possible
    delay as seen by each station
  • TTRT is negotiatedthe station with the most
    sensitive application sets TTRT (more later)
  • Measured TRT-every station measures current value
    of TRT

9
Media Access Algorithm(Timed Token Algorithm)
  • If Measured TRT gt TTRT, the token is
    delayedstation is not permitted to send
  • Measured TRT lt TTRT, station can send
    TTRT-Measured TRTTHT
  • Ideally, this algorithm provides feedback needed
    to keep the ring from being overloaded

10
Access Problems
  • Station are allowed to start packets that cause
    THTgt TTRT-Measured TRT
  • If you are downstream from such a node, you may
    never be able to send your packets
  • Two traffic categories
  • Synchronouse.g. time sensitive-Total synchronous
    traffic limited TTRT per ring rotation
  • Asynchronous-governed by Timed Token Algorithm

11
Worst Case Performance
  • Token Rotation Time2TTRT
  • Does not happen on successive rotations

12
FDDI Token Maintenance
  • Recall idle time of a broken ring is 2.5 ms
  • Stations send claim if idle longer than 2.5 ms
  • Claim contains a bid for TTRT that is the maximum
    that is acceptable to by sending station
  • Bid is passed on by nodes with higher TTRT-they
    reset their TTRT to the bid value
  • Bid is replaced by nodes with lower TTRT
    requirements
  • Eventually, TTRT is set to the largest value that
    satisfies all stations.

13
FDDI frame format
14
Wireless LAN - 802.11
  • LAN - Local Area Network. A network based on any
    physical network technology that is designed to
    span distances of up to a few thousand meters.
  • IEEE 802 LAN-Shared mediumpeer-to-peer
    communications network that broadcasts
    information to all stations to communicate

15
Wireless LAN - 802.11
  • OSI Layer 1 - Physical
  • Encoding/Decoding
  • Preamble generation/removal
  • Bit transmission/reception
  • OSI Layer 2 - Data Link
  • Medium Access Control/Arbitration
  • Addressing
  • Protocol Data Unit/Frame

16
Wireless LAN - 802.11
  • Design issues
  • Distance
  • Performance
  • Reliability
  • Security
  • Administration
  • Scalable

17
Wireless LAN - 802.11
  • Technology
  • LAN Emulation
  • Frequency Hopping
  • Direct Sequencing
  • Collision
  • Distribution
  • Frame Format
  • Other

18
Wireless LAN - 802.11
  • Frequency Hop Spread Spectrum
  • 2.4Ghz, 1 and 2 Mbps transmission
  • Hop over 79 channels (N.America)
  • Pseudo-random hopping
  • Interference Immunity

19
Wireless LAN - 802.11
  • Direct Sequence Spread Spectrum
  • 2.4Ghz, 1 and 2 Mbps transmission
  • 11 Chip Barker Sequnce
  • Interference Immunity

20
Wireless LAN - 802.11
  • Baseband Diffuse Infrared
  • 1 and 2 Mbps transmission
  • Interference Immunity
  • Light
  • Reflection

21
Wireless LAN - 802.11
  • Baseband Diffuse Infrared
  • 1 and 2 Mbps transmission
  • Interference Immunity
  • Light
  • Reflection

22
Wireless LAN - 802.11
  • Direct Sequencing
  • Chipping Code
  • Spread signal across frequency
  • Increase in bandwidth determined by bit size of
    chipping code
  • 802.11 chipping code 11-bits

23
Four-bit chipping sequence
24
Wireless LAN - 802.11
  • Collision Avoidance
  • Unlike Ethernet, not all nodes can see each
    others signal
  • Use of RTS/CTS/ACK handshake between sender and
    receiver

25
Example of a wireless network
26
Wireless LAN - 802.11
  • Components
  • Access Point
  • Central wireless base Unit
  • Client
  • Remote Node
  • Distribution System
  • Interconnecting LAN (Like Ethernet)

27
Access points connected to a distribution network
28
Node Mobility
29
IEEE 802.11 frame format
30
Wireless LAN - 802.11
  • Other related Topics
  • IEEE 802.11b - 11Mbps Wireless LAN
  • Currently only DSS support from vendors
  • IEEE 802.11a - Future (51Mbps?) Wireless LAN

31
Wireless LAN - 802.11
Other References (outside of class
text) http//grouper.ieee.org/groups/ 802/11/
Tutorial/index.html Stallings, W Data and
Computer Communications - 5th ed.,
Prentice-Hall, 1997
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