Internet DRAFT - draft-aboulmagd-trTCM-inprofile
draft-aboulmagd-trTCM-inprofile
Network Working Group Osama Aboul-Magd
Internet Draft Sameh Rabie
Document: draft-aboulmagd-trTCM-inprofile-00.txt
Category: Informational Nortel Networks
September, 2003
Two Rate Three Color Marker for Efficient Handling of
In-Profile Packets
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026 [1].
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1. Abstract
This document describes a two rate three color marker that has been
in use for data services including Frame Relay services. This marker
can be used for metering per-flow traffic in the emerging IP and L2
VPN services. The marker defined here is different from previously
defined markers in the handling and guarantee afforded to the in-
profile traffic. Furthermore this marker doesnÆt impose peak rate
shaping requirements on customer edge (CE) devices.
2. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
this document are to be interpreted as described in RFC-2119 [2].
3. Introduction
The differentiated service defines a quality of service (QoS)
architecture for the Internet [3]. Integral component of this
architecture are traffic metering and marking. This document
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describes a two rate three color metering/marker algorithm that is
suitable for the differentiated service applications such as IP and
L2 VPNs. This algorithm has been in use for data services including
Frame Relay Service.
The metering/marker defined here is different from those in [4] and
[5]. It is different from [4] in that it is a two-rate, three-color
marker. In contrast [4] is a single rate marker. It is different
from [5] in the way its parameters are defined which allows a better
handling of in-profile traffic for predominant service scenarios
over a wider range of traffic parameters.
Furthermore the algorithm described here eliminates the need for the
CE to shape its traffic to a certain peak information rate (PIR) as
might be the case for the marker defined in [5] when the value for
the peak burst size (PBS) is smaller than that for the committed
burst size (CBS).
The marker described here operates for both color-blind and color-
aware modes as defined in [5]
4. Configuration
The operation of the marker is described by two rate values, those
are the committed information rate (CIR) and the excess information
rate (EIR). Each of CIR and EIR defines the token generation rate of
a token bucket with size that is equal to committed burst size (CBS)
and excess burst size (EBS) respectively.
The CBS and EBS are measured in bytes and must configure to be
greater than the expected maximum length of incoming PDU. Both CIR
and EIR are measured in bits/s. The CIR and EIR can be set
independent of each other. Alternatively CIR and EIR can be linked
together by defining a burst duration parameter T, where
T=CBS/CIR=EBS/EIR.
5. Metering and Marking
The behavior of the meter is defined in terms of its mode and two
token buckets, C and E, with rate CIR and EIR respectively and
maximum size CBS and EBS.
The token buckets C and E are initially (at time 0) full, i.e. the
token count Tc(0) = CBS and Te(0) = EBS. Thereafter the token counts
Tc is incremented by one CIR times per second up to CBS and the
token count Te is incremented by one EIR times per second up to CBS.
In the color aware operation it is assumed that the algorithm can
recognize the color of the incoming packet (Green, yellow, or red).
The color-aware operation of the metering is:
When a green packet of size B arrives at time t, then
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o if Tc(t)- B > 0, the packet is green and Tc(t) is decremented by
B, else
o if Te(t)- B > 0, the packet is yellow and Te(t) is decremented by
B, else
o the packet is red
When a yellow packet of size B arrives at time t, then
o if Te(t)- B > 0, the packet is yellow and Te(t) is decremented by
B, else
o the packet is red
Incoming red packets are not tested against any of the two token
buckets and remain red.
In the color blind operation 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.
The salient feature of the algorithm described above is that traffic
that is within the defined CIR is colored green directly without the
need to pass additional conformance tests. This feature is the main
differentiator of this algorithm compared to that described in [5]
where traffic is marked green after it passes two conformance tests
(those for PIR and CIR). In either color blind or color aware modes
the need to pass two conformance tests could result in packets
being dropped at the PIR token bucket even though they are perfectly
within their CIR (in-profile traffic). Furthermore, in the color
aware mode of operation, the need to pass two conformance tests
could result in yellow traffic starving incoming in-profile green
packets.
The operation of the algorithm is illustrated in the flow chart
below:
+---------------------------------+
|periodically every T sec. |
| Tc(t+)=MIN(CBS, Tc(t-)+CIR*T) |
| Te(t+)=MIN(EBS, Te(t-)+EIR*T) |
+---------------------------------+
Packet of size
B arrives /----------------\
---------------->|color-blind mode|
| OR |YES +---------------+
| green packet |---->|packet is green|
| AND | |Tc(t+)=Tc(t-)-B|
| B <= Tc(t-) | +---------------+
\----------------/
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|
| NO
v
/----------------\
|color-blind mode|
| OR |YES +----------------+
| NOT red packet |---->|packet is yellow|
| AND | |Te(t+)=Te(t-)-B |
| B <= Te(t-) | +----------------+
\----------------/
|
| NO
v
+---------------+
|packet is red |
+---------------+
Figure 1: Traffic Metering/Marking Algorithm
In Figure 1, we have X(t-) and X(t+) to indicate the value of a
parameter X right before and right after time t.
6. Service Scenarios
The described marker can be used to mark an IP packet stream in a
service, where different, decreasing levels of assurances (either
absolute or relative) are given to packets which are green, yellow,
or red. For example, a service may discard all red packets, because
they exceeded the peak rate, forward yellow packets as best effort,
and forward green packets with low drop probability. The marker
could also be used for metering L2 VPN services such as the emerging
Ethernet transport over IP networks.
7. Security Considerations
The marker/metering algorithm described here has no known security
concerns.
8. References
1 Bradner, S., æThe Internet Standards Process -- Revision 3Æ, BCP
9, RFC 2026, October 1996.
2 Bradner, S., æKey words for use in RFCs to Indicate Requirement
LevelsÆ, BCP 14, RFC 2119, March 1997
3 Blake, S., et. al., æAn Architecture for Differentiated
ServicesÆ, RFC 2475, December 1998.
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4 Heinanen, J., and Guerin, R., æA Single Rate Three Color MarkerÆ,
RFC 2697, September 1999.
5 Heinanen, J., and Guerin, R., æA Two Rate Three Color MarkerÆ,
RFC 2698, September 1999.
9. Author's Addresses
Osama Aboul-Magd
Nortel Networks
P.O. Box 3511, Station C
Ottawa, ONT, Canada
K1Y-4H7
Phone: +1 613 763 5827
E.mail : osama@nortelnetworks.com
Sameh Rabie
Nortel Networks
P.O. Box 3511, Station C
Ottawa, ONT, Canada
K1Y-4H7
Phone: +1 613 765 2587
E.mail : rabie@nortelnetworks.com
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Full Copyright Statement
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or assist in its implmentation may be prepared, copied, published
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the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
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followed, or as required to translate it into.
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