The objective of this document is to provider entry point for people to understand srTCM and trTCM (single / two rate Tree Color Marker). This document will explain algorithm described in below RFCs, and compare two different algorithm used for trTCM. RFC 2697 - A Single Rate Three Color Marker RFC 2698 - A Two Rate Three Color Marker RFC 4115 - A Differentiated Service Two-Rate, Three-Color Marker with Efficient Handling of in-Profile Traffic

1. Introduction to
Single / Two Rate Three Color Marker
(srTCM / trTCM)
Kentaro Ebisawa / 海老澤 健太郎
Twitter: @ebiken

2. Preface
• The objective of this document is to provider entry point for people to
understand srTCM and trTCM (single / two rate Tree Color Marker).
• This document will explain algorithm described in below RFCs, and
compare two different algorithm used for trTCM.
• RFC 2697 - A Single Rate Three Color Marker
• https://tools.ietf.org/html/rfc2697
• RFC 2698 - A Two Rate Three Color Marker - IETF Tools
• https://tools.ietf.org/html/rfc2698
• RFC 4115 - A Differentiated Service Two-Rate, Three-Color Marker with
Efficient Handling of in-Profile Traffic
• https://tools.ietf.org/html/rfc4115
2Intro to Single Rate / Two Rate Three Color Marker (srTCM/trTCM) | 2015/02/06 | @ebiken

3. List of contents
• Intro to metering
• color-blind vs. color-aware modes
• 3 types of meter algorithm using Token Bucket
• RFC 2697 - A Single Rate Three Color Marker
• RFC 2698 - A Two Rate Three Color Marker
• RFC 4115 - A Differentiated Service Two-Rate, Three-Color Marker with
Efficient Handling of in-Profile Traffic
• Comparison between RFC2698 and RFC4115
• Notes
Intro to Single Rate / Two Rate Three Color Marker (srTCM/trTCM) | 2015/02/06 | @ebiken 3

4. Metering … what is it and where would it be used?
• Meter will be applied to flow of
packets assigned to each meter
by classifier.
• Meter will measure rate of
packet belonging to the meter,
and mark packet for further
processing.
• An implementation can use any
method for accounting rate.
However, token bucket is widely
used due to difficulty of
accounting rate by storing raw
historical stats data of flow.
Intro to Single Rate / Two Rate Three Color Marker (srTCM/trTCM) | 2015/02/06 | @ebiken 4
RFC2475: https://tools.ietf.org/html/rfc2475
Fig. 1 : Logical View of a Packet Classifier and Traffic Conditioner
Packets Classifier
Meter
Marker
Shaper/
Dropper

5. color-blind vs. color-aware modes
• Both RFC 2698 and RFC 4115 has 2 modes, color-blind and aware mode.
• The following slides only describes algorithm of color-blind mode to keep simplicity.
• If you found needs to differentiate packet marking after reading description below, refer to the original RFCs for details.
• RFC 2698
• color-blind mode
• Packet will be evaluated against remaining tokens and tokens are consumed.
• color-aware mode
• If packet has been pre-colored in then it would be marked with the color without evaluating nor consuming remaining tokens.
• If packet was not pre-colored, it will be treated same as in color-blind mode.
• RFC 4115
• color-blind mode
• The meter assumes that all incoming packets are green.
• The operation of the meter is similar to that in the color-aware operation for green packets.
• color-aware mode
• red packets are always marked red.
• yellow packets could be marked yellow or red as result of evaluation.
• green packets could be marked any color as result of evaluation.
Intro to Single Rate / Two Rate Three Color Marker (srTCM/trTCM) | 2015/02/06 | @ebiken 5

6. RFC 2697 - A Single Rate Three Color Marker (srTCM)
• Parameters
• Committed Information Rate (CIR) … Bytes per second
• Committed Burst Size (CBS) … Bytes
• Excess Burst Size (EBS) … Bytes
• Descriptions
• CIR defines how fast token will be refilled.
• CBS/EBS defines size of token buckets named Tc and Te whose max size is
CBS/EBS.
• Tc(t) and Te(t) stands for amount of tokens in the buckets at time “t”.
• CBS and/or EBS must be greater than 0 and should be larger than MTU.
Intro to Single Rate / Two Rate Three Color Marker (srTCM/trTCM) | 2015/02/06 | @ebiken 6

7. RFC 2697 - srTCM algorithm (diagrams in following slides)
• Bucket update algorithm
• Initially both buckets are full.
• Tc(0) = CBS, Te(0) = EBS
• Tc and Te are updated CIR times per second as below.
• If Tc is less than CBS, Tc is incremented by one, else
• if Te is less then EBS, Te is incremented by one, else
• neither Tc nor Te is incremented.
• Marking and Bucket update when Packet arrives.
• Packet size B arrives.
• If Tc(t)-B >= 0, the packet is green and Tc is decremented by B
• if Te(t)-B >= 0, the packets is yellow and Te is decremented by B
• the packet is red and neither Tc nor Te is decremented.
Intro to Single Rate / Two Rate Three Color Marker (srTCM/trTCM) | 2015/02/06 | @ebiken 7

8. Intro to Single Rate / Two Rate Three Color Marker (srTCM/trTCM) | 2015/02/06 | @ebiken 8
Tc Te
1. Tc += CIR*Δt
Tc(t) < CBS
(not full)
2. Te += CIR*Δt
Te(t) < CBS
(not full)
Loop
Every Δt
do nothing
(both buckets
are full)
1. Fill Token to Tc
(if Tc is not full)
2. Fill Token to Te
(if Tc was full & Te is not full)
EBSCBS
How Tokens are added
(single rate TCM)
• CBS: Committed Burst Size (Bytes)
• EBS: Excess Burst Size (Bytes)
• CIR: Committed Information Rate
(Bytes per sec)
• Updates happens every Δt time
(different from RFC)
srTCM
YES
NO
YES
NO

9. Intro to Single Rate / Two Rate Three Color Marker (srTCM/trTCM) | 2015/02/06 | @ebiken 9
Tc Te
Tc(t) - B >= 0
Te(t) - B >=0
Packet Arrives
(Size B Bytes)
c. Mark RED
a. Mark GREEN
Tc(t) -= B
b. Mark YELLOW
Te(t) -= B
EBSCBS
How Packets are Colored & Tokens are Consumed
(single rate TCM)
• CBS: Committed Burst Size (Bytes)
• EBS: Excess Burst Size (Bytes)
• CIR: Committed Information Rate
(Bytes per sec)
• Updates happens every Δt time
(different from RFC)
srTCM
a. If Tc has enough token
Consume from Tc
Mark GREEN
b. If Te has enough token
Consume from Te
Mark YELLOW
c. Mark RED
(if no token)
Packet arrives
(B bytes)
YES
NO
YES
NO

10. RFC 2698 - A Two Rate Three Color Marker (trTCM)
• Parameters
• PIR: Peak Information Rate … Bytes per second
• PBS: Peak Burst Size … Bytes (Burst size of PIR)
• CIR: Committed Information Rate … Bytes per second
• CBS: Committed Burst Size … Bytes (Burst size of CIR)
• Descriptions
• PIR/CIR defines how fast token will be refilled.
• PIR must be equal to or greater than the CIR.
• PBS/CBS defines max size of token buckets named Tp and Tc.
• Tp(t) and Tc(t) stands for amount of tokens in the buckets at time “t”.
• PBS and/or CBS must be greater than 0 and should be larger than MTU.
Intro to Single Rate / Two Rate Three Color Marker (srTCM/trTCM) | 2015/02/06 | @ebiken 11

11. Intro to Single Rate / Two Rate Three Color Marker (srTCM/trTCM) | 2015/02/06 | @ebiken 12
Tc Tp
2. Fill Token to Tc
(if Tc is not full)
1. Fill Token to Tp
(if Tp is not full)
PBSCBS
1. Tp += PIR*Δt
if Tp(t) < PBS (not full)
Loop
Every Δt
trTCM
RFC2698
2. Tc += CIR*Δt
if Tc(t) < CBS (not full)
How Tokens are added : RFC 2698 (trTCM)

12. Intro to Single Rate / Two Rate Three Color Marker (srTCM/trTCM) | 2015/02/06 | @ebiken 13
Tc Tp
Tp(t) - B < 0
Tc(t) - B < 0
Packet Arrives
(Size B Bytes)
c. Mark GREEN
Tp(t) -= B
Tc(t) -= B
a. Mark RED
b. Mark YELLOW
Tp(t) -= B
PBS
b. If Tc does NOT has enough token.
Mark YELLOW
Consume from Tp.
a. If Tp does NOT have
enough token.
Mark RED
CBS
c. Mark GREEN
Consume from Tp, Tc Packet arrives (B bytes)
trTCM
RFC2698
YES
NO
YES
NO
How Packets are Colored & Tokens are Consumed :
RFC 2698 (trTCM)

13. Intro to Single Rate / Two Rate Three Color Marker (srTCM/trTCM) | 2015/02/06 | @ebiken 14
Tc Tp
Tp(t) - B < 0
Tc(t) - B < 0
Packet Arrives
(Size B Bytes)
c. Mark GREEN
Tp(t) -= B
Tc(t) -= B
a. Mark RED
b. Mark YELLOW
Tp(t) -= B
2. Fill Token to Tc
(if Tc is not full)
1. Fill Token to Tp
(if Tp is not full)
PBS
b. If Tc does NOT has enough token.
Mark YELLOW
Consume from Tp.
a. If Tp does NOT have
enough token.
Mark RED
CBS
c. Mark GREEN
Consume from Tp, Tc Packet arrives (B bytes)
trTCM
RFC2698
1. Tp += PIR*Δt
if Tp(t) < PBS (not full)
Loop
Every Δt
2. Tc += CIR*Δt
if Tc(t) < CBS (not full)
YES
NO
YES
NO
Summary of RFC 2698 (trTCM)

14. RFC 4115 - trTCM with Efficient Handling of in-Profile Traffic
• Parameters
• EIR: Excess Information Rate … bits per second
• EBS: Excess Burst Size … Bytes (Burst size of EIR)
• CIR: Committed Information Rate … bits per second
• CBS: Committed Burst Size … Bytes (Burst size of CIR)
• Descriptions
• EIR/CIR defines how fast token will be refilled. (generated)
• EBS/CBS defines max size of token buckets named Te and Tc.
• Te(t) and Tc(t) stands for amount of tokens in the buckets at time “t”.
• EBS and CBS must be larger than MTU. (max expected length of incoming PDU)
• EIR and CIR can be set independently of each other, or, could be linked together by
defining a burst duration parameter, T, where T=EBS/EIR=CBS/CIR.
Intro to Single Rate / Two Rate Three Color Marker (srTCM/trTCM) | 2015/02/06 | @ebiken 15

15. Intro to Single Rate / Two Rate Three Color Marker (srTCM/trTCM) | 2015/02/06 | @ebiken 16
Tc Te
1. Fill Token to Tc
(if Tc is not full)
2. Fill Token to Te
(if Te is not full)
EBSCBS
trTCM
RFC4115
1. Tc += CIR*Δt
if Tc(t) < CBS (not full)
Loop
Every Δt
2. Te += EIR*Δt
if Te(t) < EBS (not full)
How Tokens are added : RFC 4115 (trTCM)

16. Intro to Single Rate / Two Rate Three Color Marker (srTCM/trTCM) | 2015/02/06 | @ebiken 17
Tc Te
B <= Tc(t)
B <= Te(t)
Packet Arrives
(Size B Bytes)
c. Mark RED
a. Mark GREEN
Tc(t) -= B
b. Mark YELLOW
Te(t) -= B
EBS
a. If Tc has enough token.
Mark GREEN
Consume from Tc.
b. If Te has enough token.
Mark YELLOW
Consume from Te
CBS
Packet arrives (B bytes) c. Mark RED
trTCM
RFC4115
YES
NO
YES
NO
How Packets are Colored & Tokens are Consumed :
RFC 4115 (trTCM)

17. Intro to Single Rate / Two Rate Three Color Marker (srTCM/trTCM) | 2015/02/06 | @ebiken 18
Tc Te
B <= Tc(t)
B <= Te(t)
Packet Arrives
(Size B Bytes)
c. Mark RED
a. Mark GREEN
Tc(t) -= B
b. Mark YELLOW
Te(t) -= B
1. Fill Token to Tc
(if Tc is not full)
2. Fill Token to Te
(if Te is not full)
EBS
a. If Tc has enough token.
Mark GREEN
Consume from Tc.
b. If Te has enough token.
Mark YELLOW
Consume from Te
CBS
Packet arrives (B bytes) c. Mark RED
trTCM
RFC4115
1. Tc += CIR*Δt
if Tc(t) < CBS (not full)
Loop
Every Δt
2. Te += EIR*Δt
if Te(t) < EBS (not full)
YES
NO
YES
NO
Summary of RFC 4115 (trTCM)

18. Comparison between RFC2698 and RFC4115
• Order of evaluating Buckets
• RFC2698 Tp (Peak) => Tc (Commit)
• RFC4115 Tc (Commit) => Te (Excess)
• GREEN packet will be evaluated only once using RFC4115.
• This will be much efficient if most of traffic fall into GREEN.
• RFC2698 will require GREEN packet to pass two conformance tests.
• This could make yellow traffic starve incoming in-profile green packets.
Intro to Single Rate / Two Rate Three Color Marker (srTCM/trTCM) | 2015/02/06 | @ebiken 19

19. Notes
• Which part of packet should be considered when calculating rate?
• RFC2697/2698 (srTCM/trTCM) mentions only size of IP packets will be
measured when calculating CIR. (i.e. Link layer headers are ignored.)
• The CIR is measured in bytes of IP packets per second, i.e., it includes the IP header,
but not link specific headers.
• However, some implementation will calculate rate including size of
MPLS/VLAN/Ethernet header.
• RFC4115 implies size of PDU (not necessary IP packet) to be used.
• Page 2: “The CBS and EBS are measured in bytes and must configure to be greater
than the expected maximum length of the incoming PDU.”
Intro to Single Rate / Two Rate Three Color Marker (srTCM/trTCM) | 2015/02/06 | @ebiken 20