0
Collision Free Protocol
Hemang Kothari
Assistant Professor
Computer Engineering Department
MEFGI, Rajkot.
Email: hemang.ko...
Motivation
• Pure ALOHA, slotted ALOHA, CSMA and
CSMA/CD are contention based protocols
– try. If collide, retry.
– No gua...
Motivation
Reservation Polling Against Corruption
Collision Free World
• Provides in order access to shared medium so
that every station has chance to transfer (fair
protoc...
Reservation – Bit Map
• Stations take turns transmitting a single
frame at a full rate ( R ) bps
• Each cycle begins with ...
Bit Map - Reservation Based
• When a station needs to send a data frame, it
makes a reservation in its own mini-slot.
• By...
Polling
• Stations take turns accessing the medium
• One device is assigned as primary station and the
others as secondary...
Polling
Binary Countdown
• Each station sends the address bits in some
order (from highest order bit to the lowest
order bit).
• T...
Example – Binary Countdown
Token Ring
Limited Contention Protocols
• Collision based protocols (ALOHA,CSMA/CD)
are good when the network load is low.
• Collisio...
Adaptive Tree Walk Protocol
• Trick: partition the group of station and limit the
contention for each slot.
• Under light ...
0
1
Example:
2
3 4 5 6
A B C* D E* F* G H*
Slot 0: C*, E*, F*, H* (all nodes under node 0 can try), conflict
slot 1: C* (a...
Review - 1
• Sixteen stations, numbered 1 through 16, are
contending for the use of a shared channel
• By using the adapti...
Solution
• Stations 2, 3, 5, 7, 11, and 13 want to send. Eleven slots
are needed, with the
– contents of each slot being a...
Lecture 5   collision free protocols
Upcoming SlideShare
Loading in...5
×

Lecture 5 collision free protocols

6,706

Published on

Published in: Education, Technology, Business
0 Comments
2 Likes
Statistics
Notes
  • Be the first to comment

No Downloads
Views
Total Views
6,706
On Slideshare
0
From Embeds
0
Number of Embeds
0
Actions
Shares
0
Downloads
159
Comments
0
Likes
2
Embeds 0
No embeds

No notes for slide

Transcript of "Lecture 5 collision free protocols"

  1. 1. Collision Free Protocol Hemang Kothari Assistant Professor Computer Engineering Department MEFGI, Rajkot. Email: hemang.kothari@marwadieducation.edu.in
  2. 2. Motivation • Pure ALOHA, slotted ALOHA, CSMA and CSMA/CD are contention based protocols – try. If collide, retry. – No guarantee of performance. – What happens if the network load is high? • Collision free protocols: – pay constant overhead to achieve performance guarantee – Good when network load is high
  3. 3. Motivation Reservation Polling Against Corruption
  4. 4. Collision Free World • Provides in order access to shared medium so that every station has chance to transfer (fair protocol) • Eliminates collision completely • Three methods for controlled access: – Reservation – Polling – Token Passing
  5. 5. Reservation – Bit Map • Stations take turns transmitting a single frame at a full rate ( R ) bps • Each cycle begins with a reservation interval that consists of (N) mini-slots. One mini-slot for each of the N stations
  6. 6. Bit Map - Reservation Based • When a station needs to send a data frame, it makes a reservation in its own mini-slot. • By listening to the reservation interval, every station knows which stations will transfer frames, and in which order. • The stations that made reservations can send their data frames after the reservation frame.
  7. 7. Polling • Stations take turns accessing the medium • One device is assigned as primary station and the others as secondary stations • All data exchanges are done through the primary • When the primary has a frame to send it sends a select frame that includes the address of the intended secondary • When the primary is ready to receive data it send a Poll frame for each device to ask if it has data to send or not. If yes, data will be transmitted otherwise NAK is sent. • Polling can be done in order (Round-Robin) or based on predetermined order
  8. 8. Polling
  9. 9. Binary Countdown • Each station sends the address bits in some order (from highest order bit to the lowest order bit). • The bits in each position from different stations are ORed.
  10. 10. Example – Binary Countdown
  11. 11. Token Ring
  12. 12. Limited Contention Protocols • Collision based protocols (ALOHA,CSMA/CD) are good when the network load is low. • Collision free protocols (bit map, binary Countdown) are good when load is high. • How about combining their advantages -- limited contention protocols. – Behave like the ALOHA scheme under light load – Behave like the bitmap scheme under heavy load.
  13. 13. Adaptive Tree Walk Protocol • Trick: partition the group of station and limit the contention for each slot. • Under light load, every one can try for each slot like aloha • Under heavy load, only a small group can try for each slot • how do we do it – treat stations as the leaf of a binary tree. – first slot (after successful transmission), all stations (under the root node) can try to get the slot. – if no conflict, fine. – if conflict, only nodes under a subtree get to try for the next one. (depth first search)
  14. 14. 0 1 Example: 2 3 4 5 6 A B C* D E* F* G H* Slot 0: C*, E*, F*, H* (all nodes under node 0 can try), conflict slot 1: C* (all nodes under node 1 can try), C sends slot 2: E*, F*, H*(all nodes under node 2 can try), conflict slot 3: E*, F* (all nodes under node 5 can try), conflict slot 4: E* (all nodes under E can try), E sends slot 5: F* (all nodes under F can try), F sends slot 6: H* (all nodes under node 6 can try), H sends.
  15. 15. Review - 1 • Sixteen stations, numbered 1 through 16, are contending for the use of a shared channel • By using the adaptive tree walk protocol. If all the stations whose addresses are prime numbers suddenly become ready at once, • how many bit slots are needed to resolve the contention?
  16. 16. Solution • Stations 2, 3, 5, 7, 11, and 13 want to send. Eleven slots are needed, with the – contents of each slot being as follows: – slot 1: 2, 3, 5, 7, 11, 13 – slot 2: 2, 3, 5, 7 – slot 3: 2, 3 – slot 4: 2 – slot 5: 3 – slot 6: 5, 7 – slot 7: 5 – slot 8: 7 – slot 9: 11, 13 – slot 10: 11 – slot 11: 13
  1. A particular slide catching your eye?

    Clipping is a handy way to collect important slides you want to go back to later.

×