1. Token Bucket

2. Traffic regulator Receiver Sender Traffic regulator
Goal: Traffic entering the network should comply to a given envelope

3. Traffic regulators Traffic exceeding the envelope is non-compliant.
What do to with non-compliant traffic ?
Buffer  Traffic shaping
Drop  Traffic policing
Allow, but assign low priority  Traffic marking
We focus on Traffic shapers
© Jörg Liebeherr, 2006
ECE 1545

4. Traffic shapers Envelope
Traffic shaper enforces that the departures D comply to a traffic envelope E
Non-compliant traffic is stored in a FIFO buffer
Buffered traffic is released as soon as allowed
 This type of shaper is called “Greedy Shaper”
Envelope

5. Token Bucket
Token Bucket is a traffic regulation mechanism to enforce that departures comply to the envelope
Traffic
Time interval b
Slope r

6. Token Bucket
Tokens are added at rate r up to a maximum size of TBmax

7. Token Bucket Assume: Packet can depart if enough tokens are available.
Tokens are removed tokens when packet departs (Here: 10 tokens are needed)

8. Token Bucket Assume: Packet removes 10 tokens from buffer
(Number of tokens is associated with packet size)

9. Token Bucket
Packet must wait until enough tokens are available

10. Token Bucket (fluid flow version)
For an analysis we work with a fluid flow version of the token bucket (Traffic can depart in arbitrary small chunks)

11. TBmax = b = 2 r = 1

12. TBmax = b = 2 r = 1
A+TB-B

13. Implementation

14. Implementation in Lab 2 (a+b)
TokenBucket

15. Token Bucket in Lab 2 (a+b)
TokenBucketReceiver (BR)
TokenBucketSender (BS)
if (buffer_is_empty && not(sendingInProgress) && enough_tokens_available) consume tokens; send packet; else add packet to buffer;
If (buffer_is_not_empty) if (enough_tokens) consume tokens; sendingInProgress = true; remove packet from buffer; send packet; sendingInProgress = false; else get expected time when there will be enough tokens; sleep for this time; wait for packet to arrive to buffer;

16. Alternative implementation for Token Bucket?
Idea: instead of counting tokens (and compute timestamps from tokens), work directly with timestamps
VC : release time of packet (init: VC = 0) l : packet size
now : current time TDTp : Target departure time of packet p b
TokenBucketSender (BS)
TokenBucketReceiver (BR)
If (buffer_is_not_empty) if (TDThead_of_buffer ≤ now) sendingInProgress = true; remove packet from buffer; send packet; sendingInProgress = false; else sleep for now - TDThead_of_buffer ; wait for packet to arrive to buffer;
VC = max {VC, now} + l/r;
if ( buffer_is_empty && not(sendingInProgress) && VC - b/r ≤ now )
send packet;
else
Set TDTp = VC - b/r;
add packet to buffer;

17. Peak Rate Constrained Token Bucket
Adds a constraint on the maximum (“peak”) rate of traffic:
Is implemented with 2 token buckets in series.
Traffic
Slope r b
Slope P
Time interval