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Versions: (draft-feher-bmwg-benchres-term) 00 01 02 03 04 05 06 07 08 RFC 4883

Benchmarking Working Group                             Gabor Feher, BUTE
INTERNET-DRAFT                                     Istvan Cselenyi, TRAB
Expiration Date: May 2003                              Andras Korn, BUTE

                                                           November 2002

  Benchmarking Terminology for Routers Supporting Resource Reservation
                 <draft-ietf-bmwg-benchres-term-02.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
   Task Force (IETF), its areas, and its working groups. Note that other
   groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time. It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt

   The list of Internet-Draft shadow directories can be accessed at
   http://www.ietf.org/shadow.html

   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 Unicast Resource Reservation Session...................3
         6.1.2 Multicast Resource Reservation Session.................4
         6.1.3 Resource Reservation Capable Router....................4
         6.1.4 Signaling End-point....................................5
         6.1.5 Reservation Orientation................................5
         6.1.6 Reservation Session State..............................6
         6.1.7 Signaling Path.........................................7
      6.2 Traffic Types...............................................8
         6.2.1 Best-Effort Data Packets...............................8

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         6.2.2 Premium Data Packets...................................8
      6.3 Router Load Types...........................................9
         6.3.1 Traffic Load...........................................9
         6.3.2 Session Load...........................................9
         6.3.3 Signaling Load........................................10
         6.3.4 Signaling Burst.......................................11
      6.4 Performance Metrics........................................11
         6.4.1 Signaling Message Handling Time.......................11
         6.4.2 Premium Traffic Delay.................................12
         6.4.3 Best-effort Traffic Delay.............................12
         6.4.4 Signaling Message Loss................................13
         6.4.5 Session Refreshing Capacity...........................13
         6.4.6 Scalability Limit.....................................14
   7. Security Considerations........................................14
   8. Acknowledgement................................................15
   9. References.....................................................15
   10. Authors' Addresses............................................16

3. Abstract

   The purpose of this document is to define terminology specific to the
   benchmarking of the resource reservation signaling of IP routers.
   These terms can be 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 [1] outlines a heterogeneous
   Quality of Service (QoS) architecture for multi domain Internet
   services. Signaling based resource reservation (e.g. via RSVP [2]) is
   an integral part of that model. While this approach significantly
   lightens the load on most of the core routers, the performance of
   border routers that handle QoS signaling is still crucial. Therefore
   network operators, who are planning to deploy this model, shall
   scrutinize the scalability limitations of 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 terminology for 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 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,
   the tests are applicable for characterizing the impact of the
   resource reservation signaling on the forwarding performance of the
   routers.

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   This benchmarking terminology document is based on the knowledge
   gained by examination of (and experimentation with) several very
   different resource reservation protocols: RSVP [2], Boomerang [5],
   YESSIR [6], ST2+ [7], SDP [8] and Ticket [9]. Nevertheless, this
   document defines terms that are valid in general and not restricted
   to these protocols.

5. Existing definitions

   RFC 1242 [3] "Benchmarking Terminology for Network Interconnect
   Devices" and RFC 2285 [4] "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 into different 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 Unicast Resource Reservation Session

   Definition:
      The term unicast resource reservation session (or shortly
      reservation session) expresses that two end-nodes explicitly
      request the network nodes, which forward their data flow, to
      assign special QoS treatment for data packets belonging to the
      flow.

   Discussion:
      The QoS treatment is defined by specifying the amount of
      networking resources that should be dedicated to the data flow
      during the length of the reservation session. There are different
      approaches, how to specify the network resource requirement of a
      data flow. It can be described by high-level parameters, like the
      required bandwidth or the maximum data delay; or it can be low-
      level information, such as the parameters of a leaky-bucket model
      describing the data flow [10].

      Reservation sessions must be uniquely registered in network nodes
      assuring the QoS treatments. Practically, the transport address of
      the destination end-node and the transport protocol of the
      communication are sufficient to distinguish the reservations,


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      however in extreme cases the transport address of the source
      should be included as well.

   See Also:
      Reservation Session State

6.1.2 Multicast Resource Reservation Session

   Definition:
      A multicast resource reservation session (or, in short, multicast
      reservation session) denotes that end-nodes forming a multicast
      group ask the network nodes, which forward the data packets of the
      multicast group, to assign a certain QoS treatment to their data
      traffic.

   Discussion:
      In a multicast group there can be several data traffic sources and
      destinations. The required QoS treatment is specified the same way
      as in the case of the unicast resource reservation sessions. In
      the case of multicast reservations, however, unlike in the case of
      unicast reservations, the amount of reserved network resources
      does not have to be the same on each network node forwarding the
      multicast data traffic. Multicast reservations must be registered
      in network nodes forwarding the associated data traffic similarly
      as it happens in the unicast case.

      Generally, there are two types of multicast resource reservations:
      many-to-many and one-to-many. Those of the first type allow
      multicast data traffic to be originated from several sources,
      while those of the second type permit only one fix data traffic
      source in the whole multicast group that must not change during
      the lifetime of the session.

6.1.3 Resource Reservation Capable Router

   Definition:
      A router is resource reservation capable -- supports resource
      reservation -- if it understands a resource reservation protocol
      that signals the set-up, tear-down and modification of resource
      reservation sessions.

   Discussion:
      Resource reservation protocols define signaling messages that are
      interpreted by resource reservation capable routers. The router
      captures the signaling message and manipulates the resource
      reservation sessions and/or the reserved network resources
      according to the content of the message.

   Issues:
      Despite that resource reservation sessions are considered to be
      unique, resource reservation capable routers might aggregate them
      and allocate network resources to these aggregated sessions at
      once. The aggregation can be based on similar flow attributes

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      (e.g. aggregation using DiffServ code-points [11]) or it can
      combine arbitrary sessions as well. While reservation aggregation
      significantly lightens the signaling processing task of a resource
      reservation capable router, it also requires the administration of
      the aggregated flows and might also lead to the violation of the
      quality guaranties of individual reservations within an
      aggregation.

6.1.4 Signaling End-point

   Definition:
      A signaling end-point is a network node capable of initiating and
      terminating resource reservation sessions.

   Discussion:
      Besides traditional end-systems, there is also another type of
      signaling end-point: the reservation gateways. Reservation
      gateways 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.

   Issues:
      Typically, signaling end-points have a dedicated protocol stack,
      which interprets and generates the signaling messages. However, in
      some special cases, the resource reservation initiation is carried
      out without the notice of the signaling terminating node. For
      example, the Boomerang resource reservation protocol encapsulates
      the reservation requests in an ICMP Echo message. This message is
      bounced back from the signaling terminating network node ("Far-End
      Node") and as a result the node becomes a signaling end-point
      without understanding the reservation protocol.

6.1.5 Reservation Orientation

   Definition:
      The reservation orientation tells which signaling end-point(s)
      initiates the network resources allocation to obtain special QoS
      treatment for the data traffic of the reservation session.

   Discussion:
      Resource reservation protocols can be classified into two groups
      depending on the relationship between the reservation initiators
      and their role in the data traffic flow. First, there are sender-
      oriented protocols, where the source(s) of the reservation
      sessionÆs data traffic initiates the network resource allocation
      message. Second, in the case of the receiver-oriented protocols,
      the receiver(s) of the reservation sessionÆs data traffic
      initiates the resource allocation messages. Due to the asymmetric
      routing nature of the Internet, in the latter case, the
      receiver(s) should know the route(s) of the desired data traffic
      before it would be able to send the resource allocation

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      message(s). For this reason, even in the second case, the first
      signaling message(s) establishing the reservation session comes
      from the source(s) of the data traffic marking the route(s) on
      which the resource allocation message(s) might travel backward.

   Issues:
      The orientation of the reservation initiator affects the basics of
      the resource reservation protocols and therefore it is an
      important design decision. In the case of multicast reservation
      sessions, the sender-oriented protocols require the traffic
      sources to maintain a list of receivers and send their allocation
      messages considering the requirements of the receivers. A less
      polite, but less demanding solution is when the sources ignore the
      QoS requirements of the receivers and send the allocation requests
      at will. Using multicast reservation sessions, the receiver-
      oriented protocols give the chance to the receivers to place their
      own resource allocation requests and thus ease the task of the
      sources. However, in this case the resource allocations must be
      preceded by the marking of the data routes of the reservation
      session (c.f. RSVP PATH message [2]). In case of large multicast
      groups, enabling the receivers to specify their QoS requirements,
      the receiver-oriented approach seems to be a better choice,
      however in other cases the sender-oriented protocols promise less
      complexity.

6.1.6 Reservation Session State

   Definition:
      A reservation session state is a holder for all the relevant
      information about the corresponding reservation session registered
      in the resource reservation capable router.

   Discussion:
      Resource reservation capable routers maintain reservation session
      states to store information about the reservation session. This
      information might include the QoS treatment that the reservation
      session requires; the description of how and where to forward the
      incoming signaling messages; policies regarding the QoS treatment
      or the reservation session; timing information about the
      reservation session; etc.

      Based on how reservation session states are stored in a
      reservation capable router, the routers can be categorized into
      three classes:

      Hard-state resource reservation capable routers (e.g. ST2 capable
      routers [7]) store the reservation session states permanently,
      established by a set-up signaling primitive, until a corresponding
      tear-down signaling primitive arrives or until the router is
      informed that the reservation session canceled.

      There are also soft-state resource reservation capable routers,
      where there are no permanent reservation session states, but each

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      state have to be regularly refreshed by appropriate refresh
      signaling messages. If no refresh signaling message arrives during
      a certain period then the router cancels the reservation session
      assuming that the signaling end-points do not intend to keep up
      the reservation session any longer or the communication lines are
      broken somewhere along the data path. This feature makes soft-
      state resource reservation capable routers more robust than hard-
      state routers, since no failures can cause permanent resource
      stuck in the routers.

      Finally, there are stateless resource reservation capable routers
      storing no information about the individual reservation sessions.
      Without reservation session states the resource reservation
      capabilities of such routers are limited, e.g. there is no support
      for many-to-many multicast resource reservation sessions; and the
      reservation session must be sender oriented.

   Issues:
      Although soft-state reservation capable routers are more robust
      than hard-state ones, the frequent processing of refresh signaling
      messages or the detection of the missing reservation session state
      refreshes might cause serious increase in the router load, which
      can be a base of the scalability problems. In order to decrease
      the number of refresh signaling messages, the resource reservation
      capable router might support various mechanisms to pack several
      refresh signaling messages into one larger message.

6.1.7 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:
      Resource reservation capable routers must assure that all other
      router, which is responsible for handling the actual signaling
      message, really receives that message. Therefore, routers forward
      the signaling messages along the signaling path and each router,
      affected by the message, processes it.

      Usually signaling messages are immediately forwarded by resource
      reservation capable routers towards the destination(s), spreading
      the information as fast as possible. However, there might be
      protocol messages that do not affect all the routers along the
      signaling path, but only a subset of it (e.g. refresh messages in
      RSVP). These kinds of signaling messages are terminated by routers
      when they are not necessary anymore.

   Issues:
      Resource reservation capable routers must be prepared that there
      are other routers along the signaling path unable to interpret the
      actual resource reservation protocol. Even in this case the

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      signaling messages must be delivered to all corresponding resource
      reservation capable routers (usually using some kind of
      tunneling).

6.2 Traffic Types

   This group of definitions defines traffic types forwarded by resource
   reservation capable routers.

6.2.1 Best-Effort Data Packets

   Definition:
      Best-effort data packet is a packet that has no associated
      resource reservation session in the routers and thus it is served
      in the "default" way.

   Discussion:
      Data packets that do not require QoS guarantees along their path
      are considered to be best-effort packets. "Best-effort" means that
      the router makes its best effort to forward the data packet
      quickly and safely, but does not guarantee anything (e.g. delay or
      loss probability). This type of traffic is the most common type in
      today's Internet. (There may be scenarios where resource
      reservation is done even for best-effort traffic too, but those
      are outside of the focus of this memo.) We will refer to the
      traffic of the best-effort data packets shortly as best-effort
      traffic.

6.2.2 Premium Data Packets

   Definition:
      Premium data packets are the packets that the resource reservation
      capable router distinguishes from best-effort packets and forwards
      them according to a QoS agreement.

   Discussion:
      Data packets that correspond to a resource reservation session in
      the router are premium data packets. The QoS treatment is defined
      in the associated resource reservation state (e.g. flow
      descriptor) that is established by signaling messages during the
      reservation session setup.

      The router may distinguish several types of premium. Data packets
      belonging to different types of premium traffic may receive
      different QoS treatment. We will refer to the traffic of the
      premium data packets shortly as premium traffic.

   Issues:
      The router has to identify every packet whether it belongs to any
      resource reservation session or not. This can be done by either
      multi-field classification [11] using the IP 5-tuple or the ToS
      field in the header of the IP packet. However, if a packet has an
      associated resource reservation session in the router, then the

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      corresponding resource reservation states describing the QoS
      treatment has to be looked up. This look up procedure might be
      quite time consuming in routers with vast amounts of resource
      reservation sessions.

6.3 Router Load Types

   This group of definitions describes different load component types
   that impact only a specific part of the resource reservation capable
   router. Categorizing the router load is crucial, since the
   conventional router load metric expressing the processing power
   utilization of the router does not characterize precisely enough a
   the resource reservation capable router. In the case of routers
   supporting resource reservations it is also important to know the
   source of the processing power utilization.

6.3.1 Traffic Load

   Definition:
      Usually traffic load means the load that is raised by the data
      traffic forwarding task of the router. However, we define the
      traffic load as the volume of the input data traffic that causes
      the router to be loaded.

   Discussion:
      It is obvious that forwarding the data packets, which requires
      obtaining the routing information and transferring the data packet
      between network interfaces, requires processing power. In general
      router benchmarking measurements only this type of load is
      considered as the source of the processing power utilization.
      Although the traffic load is the dominant load component,
      benchmarking routers supporting resource reservations must
      consider other load components also in line with the resource
      reservation handling.

   Measurement unit:
      The amount of the traffic load is represented by the volume of the
      data traffic. The volume is measured by the transferred bits
      during a second, i.e. the measurement unit is bit per seconds
      (bps).

6.3.2 Session Load

   Definition:
      Similar to the traffic load, we define the session load as the
      number of reservation sessions in the router.

   Discussion:
      Each resource reservation capable router that employs a packet
      classifier algorithm distinguishing the flows referring to
      reservation sessions maintains resource reservation session states
      keeping track of the resource reservation dedication. Obviously,
      the more reservation session states are set up on the router, the

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      more complex the traffic classification becomes, and the longer
      time it takes to look up the corresponding resource reservation
      session sate.

      Moreover, in most protocols, not only the traffic flows, but also
      the signaling messages that manipulate resource reservation
      sessions on the router have to identify themselves first, before
      taking any other actions. This kind of classification also gives
      extra work to the router.

   Issues:
      In the case of soft-state resource reservation capable routers,
      the session load also affects reservation session maintenance. The
      maintenance of timers that watchdog the reservation session
      refreshes and the refresh signaling messages may cause severe load
      on the router. Based on the initiating point of the refresh
      messages, resource reservation protocols can be divided into two
      groups. First, there are protocols where it is the responsibility
      of the signaling end-points to initiate refresh messages and these
      messages are forwarded along the whole signaling path refreshing
      the corresponding resource reservation session. Second, there are
      other protocols, where the reservation session refresh happens
      only between the two peering network nodes of the signaling path.
      In this latter case, the routers and signaling end-points have
      their own schedule for the refresh message initiation. The first
      approach lightens the load of the session maintenance task;
      however, the second approach bears the ability to adjust the
      signaling intensity along the signaling path.

   Measurement unit:
      The session load is measured by the number of reservation sessions
      in the router.

6.3.3 Signaling Load

   Definition:
      Similarly to the previous load types, the signaling load is
      determined by the incoming signaling message intensity.

   Discussion:
      The processing of signaling messages requires processor power that
      raises the load on the control plane of the router. In routers
      where the control plane and the data plane are not totally
      independent (e.g. certain parts of the tasks are served by the
      same processor; or the architecture has common memory buffers or
      transfer buses) 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.


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   Measurement unit:
      The signaling load is characterized by the signaling intensity,
      which expresses how many signaling messages arrive to the router
      within a second. Thus the unit of the signaling intensity is
      [1/s].

6.3.4 Signaling Burst

   Definition:
      The signaling burst denotes a certain number of signaling messages
      that arrive to the input port(s) of the router back-to-back,
      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
      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 within the burst.

6.4 Performance Metrics

   This group of definitions is the collection of the measurable impacts
   that a resource reservation protocol has over the tested 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 signaling
      path.

   Discussion:
      Depending on the type of the signaling message, the router also
      interprets the signaling messages, acts on them and usually
      forwards a modified signaling message. Thus the message handling
      time is usually longer than forwarding time of data packets of the
      same size. In addition, there might be also signaling message
      primitives that are drained or generated by the router. Thus, the
      signal handling time is defined as the time difference between the
      time when a signaling message is received and the time the
      corresponding processed signaling message is transmitted. If a
      signaling message is not forwarded on the router (see Signaling
      Path), the signal handling time is immeasurable; therefore it is
      not defined for such messages.


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      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 signaling message related to the received one.

      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
      example, it usually takes a shorter time for the router to tear
      down a resource reservation session than to set it up.

      The signal handling time is an important characteristic as it
      directly affects the setup time of a session.

   Measurement unit:
      The unit of the signaling message handling time is the second.

6.4.2 Premium Traffic Delay

   Definition:
      Premium traffic delay is the forwarding time of a premium data
      packet passing through a resource reservation capable router.

   Discussion:
      Premium traffic packets must be classified first in order to
      assign the network resources dedicated to the flow. The time of
      the classification is added to the usual forwarding time
      (including the queuing) 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 unit of the premium traffic delay is the second.

6.4.3 Best-effort Traffic Delay

   Definition:
      Best-effort traffic delay is the forwarding time of a best-effort
      packet passing through a resource reservation capable router.

   Discussion:
      Marking the premium traffic packets also marks the best-effort
      traffic packets via the lack of marking. In this case the
      detection of the best-effort packets is straightforward, so the
      classification algorithms do not have any influence on the best-

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      effort traffic. However, the processing power sharing between the
      control and data plane might still cause delays in the forwarding
      procedure of each packet.

   Measurement unit:
      The unit of the best-effort traffic delay is the second.

6.4.4 Signaling Message Loss

   Definition:
      Signaling message loss is the ratio of the actual and the expected
      number of signaling messages leaving a resource reservation
      capable router subtracted from one.

   Discussion:
      There are certain types of signaling messages required to be
      forwarded by the resource reservation capable router immediately
      when their processing is finished. However, due to the high router
      load or for other reasons, the forwarding or even the processing
      of these signaling messages might be canceled. To characterize
      such situations we introduce the signaling message loss metric
      expressing the ratio of the signaling messages that actually have
      left the router and those ones that were expected to leave the
      router as a result of the incoming sequence of signaling messages.

      Since the most frequent reason for the signaling message loss is
      the high router load, therefore this metric is suitable for
      sounding out the scalability limits of resource reservation
      capable routers.

   Issues:
      Sometimes it may be hard to determine whether a signaling message
      is still in the queues of the router or whether it has already
      been dropped. For this reason we define that a signaling message
      is lost if there is no appearing forwarded signaling message
      within a reasonable long time period. This time period should be
      adjusted to the actual resource reservation protocol and might
      also depend on the type of the message, too. For example, in the
      case of soft-state resource reservation capable routers the
      measurer may wait as much as the refresh period to detect the loss
      of a signaling message.

   Measurement unit:
      This measure has no unit; it is expressed by a real number, which
      is between zero and one (including the limits).

6.4.5 Session Refreshing Capacity

   Definition:
      The session refreshing capacity metric is applied for soft-state
      resource reservation capable routers only and tells the ratio of
      the truly refreshed reservation sessions and the number of
      sessions that should be refreshed during one refresh period.

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   Discussion:
      When a soft-state resource reservation capable router is
      overloaded, it may happen that the router is not able to refresh
      all the registered reservation sessions having no time to run the
      session refresh task. In this case sooner or later the resource
      reservation sessions over the session refresh capacity are dropped
      even if the resource reservation end-points are still refreshing
      them.

      The session refreshing capacity sounds out the limit of the
      resource reservation session number that the router is capable to
      maintain.

   Measurement unit:
      This measure has no unit; it is expressed by a real number, which
      is between zero and one (including the limits).

6.4.6 Scalability Limit

   Definition:
      The scalability limit is the threshold between the steady state
      and the overloaded state of the device under test.

   Discussion:
      All existing routers have finite buffer memory and finite
      processing power. In the steady state of the router, the buffer
      memories 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 tasks. These
      tasks (e.g. forwarding certain packets) are queued in the buffers,
      and processed later. However, there is a certain point where no
      more buffer memory is available or a task cannot be postponed any
      longer; thus, the router is forced to drop the packet or the
      activity. This way the overloaded state of the resource
      reservation capable router can be recognized by the fact that some
      kind of data (signaling or packet) or task (e.g. refreshing) loss
      occurs.

      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. Security Considerations

   As this document is solely for providing terminology and describes
   neither a protocol nor an implementation, there are no security
   considerations associated with this document.





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8. 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, Krisztian Nemeth, Balazs Szabo, Gabor Kovacs and
   Peter Vary from the High Speed Networks Laboratory, Budapest
   University of Technology and Economics, Hungary.

9. References

   [1]  Y. Bernet, et. al., "A Framework for Integrated Services
        Operation over Diffserv Networks", RFC 2998, November 2000

   [2]  B. Braden, Ed., et. al., "Resource Reservation Protocol (RSVP) -
        Version 1 Functional Specification", RFC 2205, September 1997.

   [3]  S. Bradner, "Benchmarking Terminology for Network
        Interconnection Devices", RFC 1242, July 1991

   [4]  R. Mandeville, "Benchmarking Terminology for LAN Switching
        Devices", RFC 2285, February 1998

   [5]  G. Feher, K. Nemeth, M. Maliosz, "Boomerang : A Simple Protocol
        for Resource Reservation in IP Networks," Vancouver, IEEE Real-
        Time Technology and Applications Symposium, June 1999

   [6]  P. Pan, H. Schulzrinne, "YESSIR: A Simple Reservation Mechanism
        for the Internet", Computer Communication Review, on-line
        version, volume 29, number 2, April 1999

   [7]  L. Delgrossi, L. Berger, "Internet Stream Protocol Version 2
        (ST2) Protocol Specification - Version ST2+", RFC 1819, August
        1995

   [8]  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

   [9]  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

   [10] J. Wroclawski, "The Use of RSVP with IETF Integrated Services",
        RFC 2210, September 1997

   [11] K. Nichols et al., "Definition of the Differentiated Services
        Field (DS Field) in the IPv4 and IPv6 Headers", RFC 2474

   [12] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6)
        Specification", RFC 2460, December 1998

   [13] Postel, J., Editor, "Internet Protocol", STD 5, RFC 791,
        September 1981

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10. Authors' Addresses

   Gabor Feher
   Budapest University of Technology and Economics (BUTE)
   Department of Telecommunications and Telematics
   Magyar Tudosok krt. 2, H-1117, Budapest, Hungary
   Phone: +36 1 463-1538
   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































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