Lecture No. 12
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Fiber Distributed Data Interface-Advance Computer Networking-Lecture Slides, Slides of Computer Networks
This course is about introduction to network programming. Topics covered in this are direct link networks, packet switching, internetworking, end-to-end protocols, congestion control and resource, allocation, end-to-end data, applications. This lecture includes: Fiber, Distributed, Data, Interface, Token, Rings, Dual, Self, healing, Concentrator, Optical, Bypass, Isolate, Variable, Buffer
Typology: Slides
2011/2012
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- Lecture No.
3
Fiber Distributed Data Interface
-^
Similar to 802.5/IBM token rings but runs on
fiber
-^
Consists of a
dual ring
: two independent rings that
transmit data in opposite directions at 100Mbps
-^
Tolerates a single link break or node failure (
self-
healing
ring)
(a)
(b)
5
FDDI – Physical Properties
Variable size buffer
(9 - 80 bits)
between input and outputinterfaces (10 ns bit time)– Not required to fill buffer before
starting transmission
- Maximum
500 stations
, maximum
2 km
distance between any pair of
stations
6
FDDI – Physical Properties
- Total
200 km fiber
: dual nature
implies 100 km cableconnecting all stations
- Physical media can be coax or
twisted pair cable
- Uses 4B/5B encoding
8
Timed Token Algorithm
- Target Token Rotation Time
TTRT
–“agreed-upon” or negotiated
upper bound on TRT
9
MAC Algorithm
- Each node measures TRT
between successive tokenarrivals
- If
measured-TRT > TTRT
–Token is late–Can not send data
11
FDDI MAC Issue
- If a node has lots of data, it
holds the token for the maximum allowed
time
- When a downstream neighbor
gets the token, its
measured
TRT >= TTRT^ –It cannot transmit its frame!
12
FDDI MAC Issue
- What if the
downstream neighborhas some
urgent
data
to send?
14
FDDI Traffic Classes
Asynchronous
traffic
–Sensitive to throughput rather
than delay –Lower priority–Can send only
if token is early
- May cause the time to exceed by
one FDDI frame
15
Bounded Priority Traffic
- If a node has large amount of
synchronous data– It will send regardless of measured TRT– TTRT will become meaningless !!!
- Therefore, total synchronous data
during one token rotation is
bounded
by TTRT
17
Token Maintenance
- Monitoring for the
lost token
–No token when initializing ring–Bit errors corrupt token pattern–Node holding the token crashes
18
Token Maintenance
- Monitoring for a
valid token
–Should periodically see valid
transmission (frame or token) –Max. gap = ring latency + max
frame <= 2.5ms
- Set 2.5ms timer; start
negotiations
if it fires
20
Token Maintenance Procedure
- A node sends a
claim frame
including
its TTRT
bid
- When a node receives a claim frame, it
compares the bid
with its own bid
- If its bid is higher, it updates TTRT &
forward the frame
- If its bid is lower, it replaces with its own
claim frame
- If bids are equal, higher address node wins
21
Token Maintenance Procedure
- If a node’s claim frame
returns back to it, it knows:–Its bid was the