Title: Lecture 10: Token Ring and FDDI Networks
1Lecture 10 Token Ring and FDDI Networks
- Homework for Chapter 2 All problems,
particularly time lines for sliding window
protocol - Exam 2 October 16, 2000
2Token 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
3Key Concept
- Token Holding Time (THT)gttransmission time of a
packet - Token Rotation Time (TRT)lt ActiveNodes x
THTRingLatency Note TRT is load dependent
4Fiber Distributed Data Interface (FDDI)
5Single Attachment Stations (SAS) attached to a
concentrator (DAS)Star-like topology
6FDDI 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
7FDDI 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
8Key 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
9Media 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
10Access 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
11Worst Case Performance
- Token Rotation Time2TTRT
- Does not happen on successive rotations
12FDDI 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.
13FDDI frame format
14Wireless 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
15Wireless 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
16Wireless LAN - 802.11
- Design issues
- Distance
- Performance
- Reliability
- Security
- Administration
- Scalable
17Wireless LAN - 802.11
- Technology
- LAN Emulation
- Frequency Hopping
- Direct Sequencing
- Collision
- Distribution
- Frame Format
- Other
18Wireless 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
19Wireless LAN - 802.11
- Direct Sequence Spread Spectrum
- 2.4Ghz, 1 and 2 Mbps transmission
- 11 Chip Barker Sequnce
- Interference Immunity
20Wireless LAN - 802.11
- Baseband Diffuse Infrared
- 1 and 2 Mbps transmission
- Interference Immunity
- Light
- Reflection
21Wireless LAN - 802.11
- Baseband Diffuse Infrared
- 1 and 2 Mbps transmission
- Interference Immunity
- Light
- Reflection
22Wireless 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
23Four-bit chipping sequence
24Wireless 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
25Example of a wireless network
26Wireless LAN - 802.11
- Components
- Access Point
- Central wireless base Unit
- Client
- Remote Node
- Distribution System
- Interconnecting LAN (Like Ethernet)
27Access points connected to a distribution network
28Node Mobility
29IEEE 802.11 frame format
30Wireless 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
31Wireless 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