draft-ietf-ippm-bw-capacity-02.txt   draft-ietf-ippm-bw-capacity-03.txt 
IP Performance Metrics Working P. Chimento IP Performance Metrics Working P. Chimento
Group JHU Applied Physics Lab Group JHU Applied Physics Lab
Internet-Draft J. Ishac Internet-Draft J. Ishac
Expires: November 18, 2006 NASA Glenn Research Center Expires: December 23, 2006 NASA Glenn Research Center
May 17, 2006 June 21, 2006
Defining Network Capacity Defining Network Capacity
draft-ietf-ippm-bw-capacity-02 draft-ietf-ippm-bw-capacity-03
Status of this Memo Status of this Memo
By submitting this Internet-Draft, each author represents that any By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79. aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that
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and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
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This Internet-Draft will expire on November 18, 2006. This Internet-Draft will expire on December 23, 2006.
Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2006). Copyright (C) The Internet Society (2006).
Abstract Abstract
Measuring capacity is a task that sounds simple, but in reality can Measuring capacity is a task that sounds simple, but in reality can
be quite complex. In addition, the lack of a unified nomenclature on be quite complex. In addition, the lack of a unified nomenclature on
this subject makes it increasingly difficult to properly build, test, this subject makes it increasingly difficult to properly build, test,
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The previous definitions specify a link's capacity, namely the IP The previous definitions specify a link's capacity, namely the IP
information bits that can be transmitted across a link or path should information bits that can be transmitted across a link or path should
the resource be free of any congestion. Determining how much the resource be free of any congestion. Determining how much
capacity is available for use on a congested link is potentially much capacity is available for use on a congested link is potentially much
more useful. However, in order to define the available capacity we more useful. However, in order to define the available capacity we
must first specify how much is being used. must first specify how much is being used.
IP Layer Link Usage: IP Layer Link Usage:
The average usage of a link L, Used(L,T,I), is the actual number The average usage of a link L, Used(L,T,I), is the actual number
of IP layer bits correctly transmitted from any source over link L of IP layer bits from any source, correctly received over link L
during the interval [T, T+I], divided by I. during the interval [T, T+I], divided by I.
An important distinction between usage and capacity is that An important distinction between usage and capacity is that
Used(L,T,I) is not the maximum amount, but rather, the actual amount Used(L,T,I) is not the maximum amount, but rather, the actual amount
of IP bits that are sent. The information transmitted across the of IP bits that are correctly received. The information transmitted
link can be generated by any source, including those who may not be across the link can be generated by any source, including those who
directly attached to either side of the link. In addition, each may not be directly attached to either side of the link. In
information flow from these sources may share any number (from one to addition, each information flow from these sources may share any
n) of links in the overall path between S and D. Next, we express number (from one to n) of links in the overall path between S and D.
usage as a fraction of the overall IP layer link capacity. Next, we express usage as a fraction of the overall IP layer link
capacity.
Average IP Layer Link Utilization: Average IP Layer Link Utilization:
Util(L,T,I) = ( Used(L,T,I) / C(L,T,I) ) Util(L,T,I) = ( Used(L,T,I) / C(L,T,I) )
Thus, the utilization now represents the fraction of the capacity Thus, the utilization now represents the fraction of the capacity
that is being used and is a value between zero, meaning nothing is that is being used and is a value between zero, meaning nothing is
used, and one, meaning the link is fully saturated. Multiplying the used, and one, meaning the link is fully saturated. Multiplying the
utilization by 100 yields the percent utilization of the link. By utilization by 100 yields the percent utilization of the link. By
using the above, we can now define the capacity available over the using the above, we can now define the capacity available over the
link as well as the path between S and D. Note that this is link as well as the path between S and D. Note that this is
essentially the definition in [PDM]. essentially the definition in [PDM].
IP Layer Available Link Capacity IP Layer Available Link Capacity
AvailCap(L,T,I) = C(L,T,I) * ( 1 - Util(L,T,I) ) AvailCap(L,T,I) = C(L,T,I) * ( 1 - Util(L,T,I) )
IP Layer Available Path Capacity IP Layer Available Path Capacity
AvailCap(P,T,I) = min {1..n} {AvailCap(Ln,T,I)} AvailCap(P,T,I) = min {1..n} {AvailCap(Ln,T,I)}
Since measurements of available capacity are more volatile that that Since measurements of available capacity are more volatile than that
of capacity, it is important that both the time and interval be of capacity, it is important that both the time and interval be
specified as their values have a great deal of influence on the specified as their values have a great deal of influence on the
results. In addition, a sequence of measurements may be beneficial results. In addition, a sequence of measurements may be beneficial
in offsetting the volatility when attempting to characterize in offsetting the volatility when attempting to characterize
available capacity. available capacity.
3. Discussion 3. Discussion
3.1 Standard or Correctly Formed Packets 3.1 Standard or Correctly Formed Packets
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