Technical Summary
Pseudowires (PWs) have become a common mechanism for tunneling
traffic, and may be found in unmanaged scenarios competing for network
resources both with other PWs and with non-PW traffic, such as TCP/IP
flows. It is thus worthwhile specifying under what conditions such
competition is acceptable, i.e., the PW traffic does not significantly
harm other traffic or contribute more than it should to congestion. We
conclude that PWs transporting responsive traffic behave as desired
without the need for additional mechanisms. For inelastic PWs (such as
TDM PWs) we derive a bound under which such PWs consume no more
network capacity than a TCP flow. For TDM PWs, we find that the level
of congestion at which the PW can no longer deliver acceptable TDM
service is never significantly greater than this bound, and typically
much lower. Therefore, as long as the PW is shut down when it can no
longer deliver acceptable TDM service, it will never do significantly
more harm than even a single TCP flow. We propose employing a
transport circuit breaker to shut down a TDM PW that persistently
fails to comply with acceptable TDM service criteria.
Working Group Summary
This draft was the result of one of the chartered work items in the
PWE3 WG, "Publish document outlining PW-specific congestion avoidance
and response guidelines." The process has been slow due to the
challenge of finding a set of authors that were both qualified and
willing to undertake the work in a thorough manner, and once they
volunteered, competing demands for their time and changes in thei
employment. The great majority of the work was done during the
lifetime of the PWE3 WG. It received a good set of comments during WG
LC, which have been included in the draft, and it is now ready for
publication.
Note that due to the use of modeling, simulations, and resulting color
graphs, the PDF version of this draft is the canonical version.
Document Quality
This is informational, so there are no implementations. The draft
received a thorough set of reviews from both WG chairs during WG LC,
and I did another shepherd's review following WG LC comment resolution.
Personnel
Who is the Document Shepherd for this document? Who is the
Responsible Area Director? If the document requires IANA
experts(s), insert 'The IANA Expert(s) for the registries
in this document are <TO BE ADDED BY THE AD>.'
Andy Malis, Deborah Brungard