Internet Engineering Task Force Longsong Lin
INTERNET DRAFT Jeffrey Lo
Expires February 2000 NEC USA Inc.
Fang-Ching Ou
National Yunlin University
August,1999
A Generic Traffic Conditioner
<draft-lin-diffserv-gtc-01.txt>
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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Distribution of this memo is unlimited.
Abstract
This document defines a Generic Traffic Conditioner (GTC) for
Diffserv-capable nodes [RFC2475, RFC2474]. The GTC employs a token
bucket to meter the traffic stream, and a shaping buffer to store
out-of-profile packets of a behavior aggregate in order to enforce
conformance to the traffic profile. The GTC employs a policer to
decide whether to shape, drop, or re-mark the out-of-profile packets.
The GTC marks each outgoing packet with a Diffserv codepoint (DSCP)
according to the traffic conditioning result in accordance with the
Traffic Conditioning Specification. By enabling the components and
configuring them with associated traffic parameters, the GTC can be
used to condition the traffics for EF PHB [Jacobson], AF PHBs
[Heinanen], as well as Class Selector PHBs [RFC 2474].
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1. Introduction
The Generic Traffic Conditioner (GTC) consists of five functional
elements: meter, policer, dropper, marker, and shaper as shown in
Figure 1. The meter measures an IP packet stream and recognizes the
packets as either in-profile or out-of-profile according to the
traffic profile in the Traffic Conditioning Specification (TCS). The
result of metering is reflected in the marker where the in-profile
packets are marked with a corresponding DSCP. Usually, marking takes
place at DS boundary node that connects one DS domain to another.
However, the in-profile packets could bypass the marker to a
fowarding PHB if marking is not necessary. The meter then hands over
the out-of-profile packets to the policer where the decision is made
as to shape, drop or re-mark the packets in accordance with the
provisioning policy in the TCS. The shaper could delay the out-of-
profile packets which will be fedback as an input to the meter for
re-metering against the same traffic profile. The dropper discards
out-of-profile packets. The marker could re-mark the out-of-profile
packets with a different corresponding DSCP according to the result
of policing.
bypass
+---------------+
| |
TR | +-------+ v
| +--->|Marker |-----DP-> Marked Packet
v | +-------+ Stream
+-------+ | ^
| |---IN----+ |
| Meter | RM
| | +--------+ |
Packet --AR-->| (TBS) |--OUT->|Policer |-+
Stream +-------+ +--------+
^ | |
| | DR +-------+
| SI +-->|Dropper|
| | +-------+
| +--------+ | |
SBO | | |<--+ v
+--| Shaper | +----------+
| (SBS) |----OF--> \ Discard/
+--------+ \Packet/
\____/
Figure 1. Generic Traffic Conditioner (GTC)
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2. Configuration and Monitoring
The GTC is configured by enabling the selected components and by
assigning values to three traffic parameters: Token Rate(TR), Token
Bucket Size (TBS), and an Shaping Buffer Size (SBS).
The GTC MAY be configured to serve traffic contracted at different
PHBs. For example, it may function as a TC for EF PHB by enabling a
meter, a policer, a shaper, a dropper, and a marker, i.e., with all
components enabled. Next, it may function as a TC for AF PHB by
enabling a meter, a policer, dropper, and a marker.
It MUST be possible to monitor over certain time interval the current
Token Bucket Occupancy (TBO), Shaping Buffer Occupancy (SBO), the
number of bytes that have arrived at the shaper (SI), the in-profile
packets in bytes (IN), the out-of-profile packets in bytes (OUT), the
number of bytes of out-of-profile packets that are dropped (DR), the
number of bytes that have been re-marked (RM) and the number of bytes
that overflow the shaping buffer (OF).
The token rate (TR) is measured in bytes of IP packets per unit time.
It is assumed for simplicity that the unit time be one second and
that all corresponding operations of the components in GTC MUST be
completed within unit time. The TBS, TBO, SBS and SBO are measured
in bytes. Each packet includes the IP header, but not link specific
headers.
3. Minimum Functionality
The TBS MUST be configured to be larger than 0 and the SBS MAY be
configured larger than or equal to 0. It is RECOMMENDED that the
value of the TBS or the SBS, if larger than 0, be larger than or
equal to the size of the largest possible IP packet in the stream.
The SBS, if larger than 0, and TBS MUST be configured at least larger
than maximum transimssion unit (MTU).
The TBS SHOULD be configured with respect to the requirements of the
service and the jitter and delay due to the configuration should not
cause any violation of these requirements. The SBS SHOULD be
configured with respect to the TBS and TR. It is possible to
configure the SBS as up to two bandwidth-delay products. However,
since shaping often introduces jitter and delay for packets being
shaped, it is RECOMMENDED that the SBS be configured according to the
requirements of the service and the jitter and delay incurred due to
shaping should not result in any violation of these requirements.
The output of the GTC SHOULD average TR and MUST not exceed TBS+TR*t
when measured over certain time interval t equal to or longer than
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INTERNET-DRAFT A Generic Traffic Conditioner August 1999
the time it takes to send an output link MTU sized packet at TR.
4. Algorithm
The behavior of the GTC is specified in terms of two decision
elements (metering and policing) and three respective action elements
(marking, shaping, and dropping).
The meter measures the incoming packets against the measurement
specified in the TCS, e.g., the inter-arrival rate, to determine
whether the packets conform to the profiled measurement (in-profile)
or otherwise (out-of-profile). The meter SHOULD not change the
behavior of a packet stream but only identify the conformance
characteristics of each packet. While the in-profile packets will be
marked with a corresponding DSCP, the out-of-profile packets are
subjected to policing.
The policer controls the subsequent treatment of each out-of-profile
packet, subject it to shaping, re-marking, or dropping. The decision
as to which action to take should consider the delay, jitter or loss
requirement of the packet stream.
An out-of-profile packet may be enqueued to a shaper which can
regulate the packet to conform to the traffic profile via re-
measuring. The size of shaping buffer is constrained by the delay
requirement of the packet stream and shaping is possible only if the
buffer is not overflowed. An out-of-profile packet may be transformed
to other classes of service by re-marking it with a different DSCP;
otherwise, it may be silently discarded by a dropper. The decision as
to re-marking or dropping depends on the provisioning policy at the
node.
The marker marks (re-marks) packets according to the results of
metering (policing). A diagrammatic representation of the algorithm
is given in Figure 2.
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+----------------------------------+
| +-------+
| | Init |
| +-------+
| + - - - - - - - - - - - - - - -|- - - - - - - - - - - - - - - - +
| | V |
| | +---------------------------+ |
| | | PTM(t) = SBO(t-1) + AR(t) | |
| | +---------------------------+ |
| | V |
| | +---------------------------+ |
| | | TBO(t) = TBO(t-1) + TR(t) | |
| | +---------------------------+ |
| | V |
| | +===========================+ |
| | | If TBO(t) > TBS | ---+ |
| | +===========================+ | |
| | V Yes | No |
| | +---------------------+ | |
| | | TBO(t) = TBS | | |
| | +---------------------+ | |
| | |----------------- + |
| | V |
| | No +====================+ Yes |
| | +---------| TBO(t) >= PTM(t) ? |---------+ |
| | V +====================+ V |
| | +------------------------------+ +---------------------+ |
| | | IN(t) <= TBO(t) | | IN(t) = PTM(t) | |
| | |TBO(t) < IN(t)+OUT(t) = PTM(t)| | OUT(t) = 0 | |
| | +------------------------------+ +---------------------+ |
| | | | | |
| + - - - - - | - - - - - | - - - - - - - - - - - - - | - - - - - +
| OUT(t) +------IN(t)--------+ IN(t)
| | | |
| V V V
| +---------+ +----------------------+
| +-DR(t)-| Policer |-----+ | TBO(t)= PTM(t)-IN(t) |
| | +---------+ | +----------------------+
| | | | |
| | | RM(t) IN(t)
| | SI(t) | |
| | | | V
| | | +--------------->+-------------------+
| | V | DP(t)=IN(t)+RM(t) |
| | +--------------------------+ +-------------------+
| | | SI(t)=OUT(t)-RM(t)-DR(t) | |
| | | SBO(t)=SBO(t)+SI(t) | |
| | +--------------------------+ |
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| | | |
| | | |
| | | +----------+ |
| +-----------+------------>| t = t+1 |------------+
| +----|-----+
+---------------------------------+
Figure 2. GTC Algorithm
The token bucket is initially (at time 0) full, i.e., the token
bucket occupancy TBO(0) = TBS, while the shaping buffer is initially
empty, i.e., the shaping buffer occupancy SBO(0) = 0.
The TBO is increased by TR bytes per unit time. Hence the total
available token for the data stream at time t is
o TBO(t) = TBS, for t=0.
o TBO(t) = TBO(t-1)+TR(t), for t>0.
o If TBO(t) > TBS, then TBO(t) =TBS.
The packets to be measured (PTM) by token bucket come from two
sources: one from the input arrival at the traffic conditioner (AR)
and the other from the feedback from the output of shaping buffer
(SBO), i.e.,
o PTM(t) = SBO(t-1)+AR(t).
To prevent packet reordering, the packets in the shaping buffer MUST
be measured before any new packet arriving at the GTC.
If TBO(t) < PTM(t), then the total number of bytes in the packets
that are in-profile (IN) will be IN(t) <= TBO(t), and the total
number of bytes in the packets that are out-of-profile (OUT) should
satisfy TBO(t) < IN(t)+OUT(t) = PTM(t).
If TBO(t) >= PTM(t), then all the packets are in-profile, i.e.
IN(t)= PTM(t) and OUT(t)=0.
The OUT(t) in any unit time may be made up of multiple packets. The
policer operates on each of these packets in turn. It decides how
each of the out-of-profile packets is treated depending on the
present occupancy of the shaping buffer as well as service policy.
Packets whose addition will not results in violation of expected
per-hop behavior may be submitted to the shaping buffer for re-
measuring; otherwise, they should be dropped. Packets not dropped
will be enqueued for shaping or remarked depending on the service
policy. For each out-of- profile packet i with length Pi,
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INTERNET-DRAFT A Generic Traffic Conditioner August 1999
o If SBO(t)+Pi > SBS, then
drop the packet, DR(t) += Pi,
o Else
shape the packet, SI(t) += Pi, Or
remark the packet, RM(t) += Pi.
+====================+
| |
--- OUT(t)---->| SBO(t)+Pi>SBS |------+
| | |No
+====================+ |
| V
Drop | +=================+ Remark
| | |-------+
| | Policy Dependent| |
|Yes | | |
| +=================+ | No
| | |
| Shape |Yes |
V V V
+-----------------++---------------++---------------+
| DR(t) += Pi || SI(t) += Pi || RM(t) += Pi |
+-----------------++---------------++---------------+
| | |
V V V
DR(t) SI(t) RM(t)
Figure 3. Policer
Thereafter, the token bucket and shaping buffer will be updated as
follows.
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For packets in IN(t),
o TBO(t) = TBO(t)-IN(t).
For packets in OUT(t),
o SBO(t) = SBO(t-1) + SI(t), where SI(t)=OUT(t)-RM(t)-DR(t).
o If SBO(t) > SBS, then
discard the overflow packets (OF) and
SBO(t) = SBO(t)- OF(t).
5. Re-marking
The marker marks the in-profile packets according to traffic profile
defined in the Traffic Conditioning Specification (TCS). The marker
will distinguish whether or not the current boundary node is a first-
hop router [RFC2475] or an interior node. If it is a first-hop router
, it may mark the unmarked packets or re-mark previously marked
packets to an effective codepoint.
The marker also re-marks packets that are out-of-profile subject to
the service policy. Re-marking may result in either change of PHB
group or change of drop preference in a service class. For example,
re-marking could demote a packet from an AF PHB to the Default best-
effort PHB. As another example, re-marking may change the drop
precedence of the packet in AF PHB class [Heinanen]. Re-marking MUST
not cause packet reordering.
6. Example Services
The GTC can be used to serve EF PHB and AF PHB. The GTC conditions
packet aggregate via policing and shaping so that its arrival rate to
a PHB at any node is always less than that node's configured minimum
departure rate for the PHB. This property ensures the traffic
conditioning requirement for EF PHB. EF flow packets see sufficient
tokens present will have their EF codepoints marked. When tokens are
not sufficient, EF packets will be held in the shaping buffer until
tokens arrive. If an EF flow bursts enough to overflow the shapping
buffer, its packet will be dropped.
For an AF PHB class, in-profile packets and out-of-profile packets
are distinguished by marking them with different AF codepoints. For
examples, the in-profile packet can be marked as AFx1 and the out-
of-profile packets can be policed to be marked as AFx(2,3), omitting
shaping and dropping. The GTC may also shape the out-of-profile AF
packets if necessary.
The GTC can support CS DSCP with preferential forwarding marking. The
relative order of the CS DSCPs can be implemented by using the
policer and remarker to transform from one CS DSCP to another. The
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probability of timely forwarding can be enforced by GTC token bucket
mechanism as well as by the CS-compliant PHB mechanisms. As an
extreme case, packet dropped by a GTC policer is considered to be
untimely forwarding. A GTC meter should be configured with a minimum
rate for the CS DSCP behavior agregates in accordance with the CS-
compliant PBH and the default PHB.
7. Assumptions
The GTC has no known security concerns and no a priori information
for input traffic.
8. Discussion
The arrangement of the components of the GTC in this document is by
no means the only solution to provide conditioning for diffserv
traffic. A simple configuration for providing a particular service is
possible. For example, a cascaded configuration of a meter with a
marker is sufficient for supporting AF PHB.
The components in the GTC is a generic representation of
funcationality; each component can be extended to cover more complex
functions. For example, the meter could output multiple levels of
conformance information, instead of two levels of IN or OUT of
profile information. A multi-color marker is an example of the
extension.
It is noted that any other components which offer new functionality
for out-of-profile packets can easily be embedded in the GTC as long
as it is configured appropriately. For instance, a spacer can be
employed on non-conforming traffic to reduce the delay variation.
Finally, it is noted that the GTC can operate in accordance to the
periodical sampling times or to the events by packet arrivals.
9. References
[Heinanen] J. Heinanen, et al., Assured Forwarding PHB Group.
Internet draft draft-ietf-diffserv-af-06.txt, February 1999.
[Nichols] K. Nichols and B. Carpenter, Format for Diffserv Working
Group Traffic Conditioner Drafts. Internet draft draft-ietf-diffserv-
traffcon-format-00.txt, February 1999.
[RFC2474] K. Nichols, et al., Definition of the Differentiated
Services Field (DS Field) in the IPv4 and IPv6 Headers. RFC 2474,
December 1998.
[RFC2475] S. Blake, et al., An Architecture for Differentiated
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Services. RFC 2475, December 1998.
[Heinanen1] J. Heinanen, et al. A Three Color Marker. Internet draft
draft-heinanen-diffserv-tcm-01.txt, February 1999.
[Jacobson] V.Jacobson, et al., Expedited Forwarding Per Hop Behavior
Internet Draft draft-ietf-diffserv-phb-ef-02.txt, February 1999.
10. Author Address
Longsong Lin
NEC USA, Inc.
110 RIO ROBLES
SAN JOSE, CA 95134, USA
Email : lin@ccrl.sj.nec.com
Tel : (408) 943 3032
Fang-Ching Ou
Dept. of Electronic and Information Engineering
National Yunlin University of Science and Technology
123 University Rd. Section 3, Touliu City, Yunlin, Taiwan
Email : ofcaltos@ms14.hinet.net
Jeffrey Lo
NEC USA, Inc.
110 RIO ROBLES
SAN JOSE, CA 95134, USA
Email : jlo@ccrl.sj.nec.com
Tel : (408) 943 3033
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