Internet DRAFT - draft-feher-bmwg-benchres-term
draft-feher-bmwg-benchres-term
INTERNET-DRAFT <draft-feher-bmwg-benchres-term-00.txt> November 2000
Network Working Group Gabor Feher, BUTE
INTERNET-DRAFT Istvan Cselenyi, TRAB
Expiration Date: May 2001 Peter Vary, BUTE
Andras Korn, BUTE
November 2000
Benchmarking Terminology for Routers Supporting Resource Reservation
<draft-feher-bmwg-benchres-term-00.txt>
1. Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering
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The list of current Internet-Drafts can be accessed at
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This memo provides information for the Internet community. This memo
does not specify an Internet standard of any kind. Distribution of
this memo is unlimited.
2. Table of contents
1. Status of this Memo.............................................1
2. Table of contents...............................................1
3. Abstract........................................................2
4. Introduction....................................................2
5. Existing definitions............................................3
6. Definition of Terms.............................................3
6.1 Resource Reservation Protocol Basics........................3
6.1.1 Resource Reservation Session...........................3
6.1.2 Multicast Resource Reservation Session.................3
6.1.3 Reservation Capable Router.............................4
6.1.4 Signaling End-point....................................5
6.1.5 Reservation Initiator..................................5
6.1.6 Signaling Path.........................................6
6.2 Traffic Types...............................................7
6.2.1 Premium Traffic........................................7
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6.2.2 Best-Effort Traffic....................................8
6.3 Router Load Types...........................................8
6.3.1 Session Load...........................................8
6.3.2 Signaling Load.........................................9
6.3.3 Signaling Burst........................................9
6.4 Performance Metrics........................................10
6.4.1 Signaling Message Handling Time.......................10
6.4.2 Premium Traffic Delay.................................11
6.4.3 Best-effort Traffic Delay.............................11
6.4.4 Signaling Message Loss................................12
6.4.5 Scalability Limit.....................................12
7. Acknowledgement................................................13
8. References.....................................................13
9. Authors' Addresses:............................................14
3. Abstract
The purpose of this document is to define terminology specific to the
performance benchmarking of the resource reservation signaling of IP
routers. These terms are used in additional documents that define
benchmarking methodologies for routers supporting resource
reservation and define reporting formats for the benchmarking
measurements.
4. Introduction
The IntServ over DiffServ framework [3] outlines a heterogeneous
Quality of Service (QoS) architecture for multi domain Internet
services. Signaling based resource reservation (e.g. via RSVP [5]) is
an integral part of that model. While this significantly lightens the
load on most of the core routers, the performance of border routers
that handle the QoS signaling is still crucial. Therefore network
operators, who are planning to deploy this model, shall scrutinize
the scalability limitations in reservation capable routers and the
impact of signaling on the forwarding performance of the routers.
An objective way for quantifying the scalability constraints of QoS
signaling is to perform measurements on routers that are capable of
resource reservation. This document defines a specific set of tests
that vendors or network operators can use to measure and report the
signaling performance characteristics of router devices that support
resource reservation protocols. The results of these tests will
provide comparable data for different products supporting the
decision process before purchase. Moreover, these measurements
provide input characteristics for the dimensioning of a network in
which resources are provisioned dynamically by signaling. Finally,
these test are applicable for characterizing the impact of control
plane signaling on the forwarding performance of routers.
This benchmarking terminology document is based on the knowledge
gained by examination of (and experimentation with) several very
different resource reservation protocols: RSVP [5], Boomerang [6],
YESSIR [7], ST2+ [8], SDP [9], Ticket [10] and Load Control [11].
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Nevertheless, this document aspires to compose terms that are valid
in general and not restricted to these protocols.
5. Existing definitions
RFC 1242 [1] "Benchmarking Terminology for Network Interconnect
Devices" and RFC 2285 [2] "Benchmarking Terminology for LAN Switching
Devices" contains discussions and definitions for a number of terms
relevant to the benchmarking of signaling performance of reservation
capable routers and should be consulted before attempting to make use
of this document.
For the sake of clarity and continuity this document adopts the
template for definitions set out in Section 2 of RFC 1242.
Definitions are indexed and grouped together in sections for ease of
reference.
6. Definition of Terms
6.1 Resource Reservation Protocol Basics
This group of definitions applies to various signaling based resource
reservation protocols implemented on IP router devices.
6.1.1 Resource Reservation Session
Definition:
A resource reservation session (or shortly reservation) expresses
that routers along the data path between two hosts apply special
QoS treatment to a certain traffic flow.
Discussion:
The QoS treatment is specified by giving the amount of networking
resources that are dedicated to the traffic flow during the length
of the reservation session. Depending on the protocol, there are
different approaches to define the network resource requirement of
a traffic flow. It can be described by high-level parameters, like
the required bandwidth, or the maximum traffic delay; or it can be
low-level information, like the parameters of a leaky-bucket model
of the traffic flow [12].
Each resource reservation session has a unique flow descriptor
that identifies the associated traffic flow to the router. In
order to obtain unique flow descriptors, typically traffic flow
parameters, such as the protocol number and the IP address and
port of the source and the destination are used to generate them.
See Also:
Signaling Path
6.1.2 Multicast Resource Reservation Session
Definition:
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A multicast resource reservation session (or, in short, multicast
reservation) denotes that certain QoS treatment is applied to the
packets of every traffic flow related to a multicast group.
Discussion:
Usually, there are several traffic sources and destinations in a
multicast group. In order to be able to guarantee the QoS
parameters for each packet of the multicast flow, every router
that forwards the multicast traffic must dedicate resources to the
flow.
Generally, there are two types of multicast resource reservation
protocol: many-to-many multicast and one-to-many multicast
protocols. Those of the first type allow reservations for traffic
flows that originate from several traffic sources, while those of
the second type allow only one traffic source in the whole group.
In the case the many-to-many multicast protocols, the amount of
resources dedicated to the reservation session does not have to be
the same for every involved router. Depending on the capabilities
of the resource reservation protocol, the traffic destinations in
the multicast group may request different QoS parameters. In
addition to the different QoS requirements for the destinations,
the protocols may have more than one reservation models that
express the resource requirement distribution among the involved
routers. (e.g. RSVP SE/WF/FF [5])
Issues:
Naturally, many-to-many multicast protocols are bound to be more
complex than one-to-many or non-multicast protocols. In the many-
to-many case, each router has to calculate the resource
requirements of the multicast reservation session based on the
reservation model, the distribution of the traffic sources and
destinations on its network interfaces. Either the router has to
know all the resource requirements of the destinations at the time
the reservation is made or it has to adjust the resource
reservation of the multicast reservation session according to
newly appearing traffic destination requirements. Both methods
cause delays in the multicast reservation session setup.
Also:
Signaling Path
6.1.3 Reservation Capable Router
Definition:
By definition, a router is reservation capable if it understands a
resource reservation protocol that signals the set-up or tear-down
of resource reservation sessions or changes in an existing
reservation session.
Discussion:
Reservation capable routers always maintain states for each
reserved flow expressing the current condition of the reservation.
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Based on the way these states are handled, resource reservation
protocols are divided into two categories: soft-state protocols
and hard-state protocols.
In the case of hard-state protocols, the resource reservation
session established by a set-up signaling primitive is permanent
and is cancelled only when the corresponding tear-down signaling
primitive arrives to the router. In the case of the soft-state
protocols there are no permanent resource reservations, rather the
resource reservation state must be regularly refreshed by
appropriate signaling primitives. If no refresh signaling
primitives arrives, this is assumed to indicate that the resource
reservation session is not maintained any longer; and therefore,
the router tears it down without waiting for any explicit request.
For this reason, soft-state protocols exhibit more robust behavior
than hard-state protocols, since failures in the participants of a
reservation session does not cause resource stuck in the routers.
Issues:
Although soft-state protocols are more robust than hard-state
protocols, they require that reservation sessions be maintained by
regularly sending appropriate signals. These refresh signaling
messages may cause a serious increase in router load. To decrease
this kind of load, the resource reservation protocol may support
various mechanisms to aggregate the refresh signaling messages.
6.1.4 Signaling End-point
Definition:
A signaling end-point is a network node capable of initiating and
terminating resource reservation sessions.
Discussion:
Typically, signaling end-points have a separate protocol stack
that is capable of generating and understanding the signaling
messages. However, in some special cases, the resource reservation
initiation is carried out without the notice of the network node.
For example, the Boomerang resource reservation protocol
encapsulates the reservation requests in an ICMP Echo message.
This message is bounced back from the destination network node and
as a result the node becomes a signaling end-point without
understanding the reservation protocol.
Reservation gateways are protocol translators that translate the
signaling messages of one resource reservation protocol into
messages of another resource reservation protocol. Thus the
reservation gateway represents two signaling end-points in one, as
it is both a signaling terminator and a signaling initiator.
6.1.5 Reservation Initiator
Definition:
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The reservation initiator is the signaling end-point that
initiates the resource reservation session setup.
Discussion:
Resource reservation protocols can be classified depending on the
relationship between the reservation initiators and their role in
the traffic flow.
In the case of receiver-oriented protocols, the traffic
destinations, which are the receivers of the data traffic,
initiate the reservation session setup, unlike the sender-oriented
protocols where this is done by traffic sources. There also are
protocols where both the traffic source and destination can act as
the reservation initiator.
The importance of the reservation initiator orientation is only
dominant in case of multicast reservation sessions. Generally, in
multicast groups the number of traffic destinations changes more
frequently than the number of traffic sources. The receiver-
oriented protocols do not require the traffic sources to change
their state and generate signaling messages when a new traffic
destination joins or an existing one leaves the group, it is
enough that the traffic destination node sends its reservation or
tear-down request.
See Also:
Signaling end-point
Signaling path
6.1.6 Signaling Path
Definition:
A signaling path is a sequence of network nodes and links along
which signaling messages travel from one signaling end-point to
the other.
Discussion:
In the case of sender-oriented protocols, the data traffic and the
signaling messages are addressed to the IP address of the
destination and therefore routed on the same path. Thus the
signaling messages are delivered to every router that handles the
traffic flow to which the reservation session refers. No more and
no fewer routers are affected. However, in the case of receiver-
oriented protocols, the reservation request and the data traffic
are forwarded in opposite directions. And since Internet routing
is asymmetric, it is not mandatory that they go through the same
routers. To assure that the signaling messages reach every router
that handles the traffic flow from the source to the destination,
the traffic source issues a special message addressed to the
destination marking the path for the reservation. This message is
called PATH message in the RSVP protocol. Each router that
receives a PATH message remembers the address of the node where
the message came from, and when a signaling message arrives
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carrying reservation information it is forwarded to the stored
address, which is the address of the previous node. Thus the PATH
message marks out a path along which the reservation message
travels backward.
In the case of a multicast reservation session, the situation is
slightly more complicated. The signaling path is rather a
signaling mesh where the signaling messages travel from the
sources to the destinations.
Issues:
It is not unusual for routers to change their routing from time to
time. The reason for the change can be a failure of a neighboring
router; the router may also choose an alternative route because of
changed traffic conditions. When the routes change, the data
traffic will be forwarded along a different path than the
signaling messages used in establishing the resource dedications
for the reservation session. In order to properly handle this
situation, hard-state protocols have to be extremely sophisticated
in order to detect the route change and to re-reserve the
resources on the new path. However, soft-state protocols do not
have to worry about this situation, since the refresh messages can
be used to set up the reservation on the new path and the
dedicated resources will eventually disappear from routers of the
obsoleted path.
Nowadays, routers capable of load balancing are emerging. This
means that when there is more than one route to the destination,
the router can share the packets of the traffic flow among the
alternative routes. In this case the unaware resource reservation
protocols are helpless, since the mechanism allows making a
reservation setup along one of the paths only. Additionally, the
refresh messages of a soft-state protocol might be shared among
the paths, making it impossible to refresh the existing
reservation.
6.2 Traffic Types
This group of definitions defines traffic types forwarded by resource
reservation capable routers.
6.2.1 Premium Traffic
Definition:
Premium traffic is a traffic type that the router distinguishes
from best-effort traffic (to be defined later) and forwards its
packets according to a QoS agreement.
Discussion:
Traffic that corresponds to a resource reservation session in the
router is premium traffic. The QoS treatment is defined in the
associated flow descriptor that is established by the signaling
messages during the reservation session setup.
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The router may distinguish several types of premium traffic (e.g.
delay sensitive traffic, loss sensitive traffic, etc.). Different
types of premium traffic may receive different QoS treatment.
Issues:
The router has to identify every packet whether it belongs to a
resource reservation session or not. This is usually not
complicated, as usually packets that are part of a premium traffic
flow are often marked in a way that is detected easily (e.g. IP
TOS field). However, if a packet claims that it has an associated
resource reservation session in the router, the router has to find
the flow descriptor, which might be time consuming in routers with
vast amounts of resource reservation sessions.
6.2.2 Best-Effort Traffic
Definition:
Best-effort traffic is a traffic type that has no reservation
entry in the router.
Discussion:
Traffic flows that do not require QoS guarantees along their path
are considered to be best-effort traffic. "Best–effort" means that
the router makes its best effort to forward every data packet, but
does not guarantee anything. This is the most common type of
traffic on today’s Internet.
6.3 Router Load Types
This group of definitions describes different load component types
that are independent of each other and impact only a specific part of
the resource reservation capable router's control plane. A
combination of such independent load types is used to generate
arbitrary load distribution on the router, forming the input function
during the benchmarking
6.3.1 Session Load
Definition:
Session load is the load that manifests itself as the excess
processing power required to keep track of many reservation
session.
Discussion:
All signaling based resource reservation protocol implementation
employ a packet classifier algorithm that distinguishes the flows
having reservations in the router from the others that do not.
Therefore each implementation maintains a list of flow descriptors
that is instrumental in keeping track of the resource reservation
sessions. Obviously, the more reservation sessions are set up on
the router, the more complex traffic classification becomes, and
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the more time it takes for the classification algorithm to
identify a flow.
Moreover, in most protocols, not only the traffic flows, but also
signaling messages that manipulate resource reservations on the
router have to identify themselves first, before taking any other
actions. This kind of classification gives extra work for the
router.
Measurement unit:
The session load is represented by the number of reservation
sessions in the router.
6.3.2 Signaling Load
Definition:
Signaling load is the load that manifests itself as the time
required to process the incoming signaling messages.
Discussion:
The processing of signaling messages requires processing power
that raises load on the control plane of the router. In the case
of routers where the control plane and the data plane are not
totally independent (for example, certain parts of them are served
by the same processor) the signaling load can have an impact on
the router's packet forwarding performance as well.
Most of the resource reservation protocols have several protocol
primitives realized by different signaling message types. Each of
these message types may require a different amount of processing
power from the router.
Measurement unit:
The signaling load is characterized by the signaling intensity,
which expresses how many signaling messages arrive to the router
within a time unit. The typical unit of the signaling intensity is
[1/s], which is the number of signaling messages that arrive
within one second.
6.3.3 Signaling Burst
Definition:
The signaling burst denotes a certain number of signaling messages
that arrive to the input port(s) of the router without
interruption, causing persistent load on the signaling message
handler.
Discussion:
Back-to-back signaling messages on one port of the router form a
typical signaling burst. However, other cases are imaginable, for
example when signaling messages arrive on different ports
simultaneously or with an overlap in time (i.e. when the tail of
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one signaling message is behind the head of another one arriving
on another port).
Measurement unit:
The signaling burst is characterized by its length, which is the
number of messages that have arrived during the burst.
6.4 Performance Metrics
This group of definitions is a collection of the measurable effects
of the impact a resource reservation protocol has on the router
device it is running on.
6.4.1 Signaling Message Handling Time
Definition:
The signaling message handling time (or, in short, signal handling
time) is the time that a signaling message spends inside the
router before it is forwarded to the next node on the path.
Discussion:
Usually, signaling messages are issued by a signaling end-point
and forwarded along the signaling path by the routers. However, in
addition to the usual message forwarding, the router also
interprets the messages and acts on them. Thus the message
handling time is longer than forwarding time of data packets of
the same size. Moreover, there are signaling message primitives
that are altered during the processing and there may also be
messages that are drained by the router or ones that are generated
by the router. Thus, the signal message handling time is the time
difference between the time when a signaling message is received
and the time the corresponding processed signaling message is
transmitted. If a message is not forwarded on the router, the
signal handling time is immeasurable; therefore it is not defined
for such messages.
In the case of signaling messages that carry information
pertaining to multicast flows, the router might issue multiple
signaling messages after processing. In this case, by definition,
the signal handling time is the time interval elapsed between the
arrival of the incoming signaling message and the departure of the
last related signaling message.
Signal handling time is an important characteristic as it directly
affects the setup time of a session. It is also an indication of
the signal processing capacity of the router as it is correlated
to the maximum number of signaling messages that can be processed
within a time unit.
This metric depends on the load on the router, as other tasks may
limit the processing power available to signaling message
handling. In addition to the router load, the signal handling time
may also be dependent on the type of the signaling message. For
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example, it usually takes a shorter time to tear down a resource
reservation session within a router node than to set it up.
Issues:
In the case of soft-state protocols, the refresh messages are
usually generated automatically by the protocol stack and
propagated along the signaling path based on internal timers
without user interaction. Moreover, each network node along the
signaling path might have an individual agreement on the refresh
time interval with its neighboring nodes. Thus, the incoming
refresh message is not forwarded on; instead, a new message is
generated when the internal timer expires. Other soft-state
protocols do not stop the refresh messages, rather let them
refresh the whole signaling path. In the former case it is
impossible to measure the signaling message handling time of a
refresh message.
Measurement unit:
The typical unit of the signaling message handling time is
microseconds.
6.4.2 Premium Traffic Delay
Definition:
Premium traffic delay is the forwarding time of a packet that
belongs to a premium traffic flow passing through a resource
reservation capable router.
Discussion:
Premium traffic packets must be classified first in order to find
the resources dedicated to the flow. The time of the
classification is added to the usual forwarding time that a router
would spend on the packet without any resource reservation
capability.
There are routers where the processing power is shared between the
control plane and the data plane. This means that the processing
of signaling messages may have an impact on the data forwarding
performance of the router. In this case the premium traffic delay
metric reflects the influence the two planes have on each other.
Measurement unit:
The typical unit of the premium traffic delay is the microsecond.
6.4.3 Best-effort Traffic Delay
Definition:
Best-effort traffic delay is the forwarding time of a packet that
does not belong to any premium traffic flow passing through a
resource reservation capable router.
Discussion:
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It is obvious that the classification algorithms do not have any
influence on the best-effort traffic. However, the processing
power sharing between the control and data plane may cause delays
in the forwarding procedure of each packet.
Measurement unit:
The typical unit of the best-effort traffic delay is the
microsecond.
6.4.4 Signaling Message Loss
Definition:
Signaling message loss is the ratio of the expected and the actual
number of signaling messages leaving a resource reservation
capable router.
Discussion:
Signaling messages are generally generated at signaling end-points
and forwarded through routers. However, traffic congestion can
arise in heavily loaded routers, and, as a result, signaling
messages might be lost. This metric is therefore suitable for
sounding out the scalability limits of a resource reservation
capable router.
However, in the case of soft-state protocols where the refresh
messages generated individually, it may be difficult to detect
lost signaling messages. Thus, signaling loss only considers
signaling messages that leave the router as a consequence of
processing an entering signaling message. Note that signaling
messages in a multicast reservation session might trigger several
signaling messages.
Issues:
In the case of routers where network packets are queued in several
places, we have to be aware that a signaling message may be
delayed seriously. Therefore, it may be hard or impossible to
determine whether the signaling message is still in the queues or
whether it was dropped due to the congestion. By definition we say
that a signaling message is lost in either of the following cases:
when a signaling message of the same type that arrived later than
the investigated signaling message leaves the router; when the
signaling message handling time would exceed the triple of the
signaling message handling time measured on other signaling
messages under same conditions.
Measurement unit:
Usually, we measure the signaling loss over a longer period of
time and then we express it as a percentage value of packet lost.
However, in many cases it is enough to know that there was
signaling loss.
6.4.5 Scalability Limit
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Definition:
The scalability limit is the threshold between the steady state
and the overloaded state of the tested equipment.
Discussion:
All existing routers have finite buffer memory and finite
processing power. In the steady state of the router, the memory
buffers are not fully utilized and the processing power is enough
to cope with all tasks running on the router. As the router load
increases the router has to postpone more and more task. These
tasks (e.g. forwarding certain packets) are stored into the
buffers, and processed later. However, there is a certain point
where no more buffer memory is available; thus, the router becomes
overloaded and is unable to store any more tasks for future
processing, so it is forced to drop them. Therefore the overloaded
state of the router can be recognized by the fact that some kind
of data loss occurs. A resource reservation capable router may
drop signaling messages, data packets or entire resource
reservation sessions.
The critical load condition when the router is still in the steady
state but the smallest amount of constant load increase would
drive it to the overloaded state is the scalability limit of the
router.
7. Acknowledgement
We would like to thank the following individuals for their help in
forming this document: Joakim Bergkvist and Norbert Vegh from Telia
Research AB, Sweden, Balazs Szabo, Gabor Kovacs from High Speed
Networks Laboratory of BUTE.
8. References
[1] S. Bradner, "Benchmarking Terminology for Network
Interconnection Devices", RFC 1242, July 1991
[2] R. Mandeville, "Benchmarking Terminology for LAN Switching
Devices", RFC 2285, February 1998
[3] Y. Bernet, et. al., "A Framework For Integrated Services
Operation Over Diffserv Networks", Internet Draft, May 2000,
<draft-ietf-issll-diffserv-rsvp-05.txt>
[4] S. Bradner, J. McQuaid, "Benchmarking Methodology for Network
Interconnect Devices", RFC 2544, March 1999
[5] B. Braden, Ed., et. al., "Resource Reservation Protocol (RSVP) -
Version 1 Functional Specification", RFC 2205, September 1997.
[6] J. Bergkvist, I. Cselenyi, "Boomerang Protocol Specification",
Internet Draft, June 1999, <draft-bergkvist-boomerang-spec-
00.txt>
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[7] P. Pan, H. Schulzrinne, "YESSIR: A Simple Reservation Mechanism
for the Internet", Computer Communication Review, on-line
version, volume 29, number 2, April 1999
[8] L. Delgrossi, L. Berger, "Internet Stream Protocol Version 2
(ST2) Protocol Specification - Version ST2+", RFC 1819, August
1995
[9] P. White, J. Crowcroft, "A Case for Dynamic Sender-Initiated
Reservation in the Internet", Journal on High Speed Networks,
Special Issue on QoS Routing and Signaling, Vol 7 No 2, 1998
[10] A. Eriksson, C. Gehrmann, "Robust and Secure Light-weight
Resource Reservation for Unicast IP Traffic", International WS
on QoS'98, IWQoS'98, May 18-20, 1998
[11] L. Westberg, Z. R. Turanyi, D. Partain, Load Control of Real-
Time Traffic, A Two-bit Resource Allocation Scheme, Internet
Draft, <draft-westberg-loadcntr-03.txt>, April 2000
[12] J. Wroclawski, "The Use of RSVP with IETF Integrated Services",
RFC 2210, September 1997
9. Authors' Addresses:
Gabor Feher
Budapest University of Technology and Economics (BUTE)
Department of Telecommunications and Telematics
Pazmany Peter Setany 1/D, H-1117, Budapest, Hungary
Phone: +36 1 463-3110
Email: feher@ttt-atm.ttt.bme.hu
Istvan Cselenyi
Telia Research AB
Vitsandsgatan 9B
SE 12386, Farsta
SWEDEN,
Phone: +46 8 713-8173
Email: istvan.i.cselenyi@telia.se
Andras Korn
Budapest University of Technology and Economics (BUTE)
Institute of Mathematics, Department of Analysis
Egry Jozsef u. 2, H-1111 Budapest, Hungary
Phone: +36 1 463-2475
Email: korn@math.bme.hu
Peter Vary
Budapest University of Technology and Economics (BUTE)
Department of Telecommunications and Telematics
Pazmany Peter Setany 1/D, H-1117, Budapest, Hungary
Phone: +36 1 463-3110
Email: kanya@iq.sch.bme.hu
Feher, Cselenyi, Vary, Korn Expires May 2001 [Page 14]
