2.8.11 Performance Implications of Link Characteristics (pilc)

NOTE: This charter is a snapshot of the 51st IETF Meeting in London, England. It may now be out-of-date. Last Modified: 31-Jul-01


Spencer Dawkins <spencer.dawkins@fnc.fujitsu.com>
Aaron Falk <a.falk@ieee.org>

Transport Area Director(s):

Scott Bradner <sob@harvard.edu>
Allison Mankin <mankin@isi.edu>

Transport Area Advisor:

Allison Mankin <mankin@isi.edu>

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Description of Working Group:

Erik Nordmark (nordmark@eng.sun.com) is the Technical Advisor.

The Internet network-layer and transport-layer protocols are designed to accommodate a very wide range of networking technologies and characteristics. Nevertheless, experience has shown that the particular properties of different network links can have a significant impact on the performance of Internet protocols operating over those links, and on the performance of connections along paths that include such links. This is especially of concern to the wireless networking community.

The PILC working group will produce several BCP/Informational documents. The first document will discuss considerations for link-layer designers from the perspective of best supporting existing IETF protocols will be produced. The next document will discuss the capabilities, limitations and pitfalls of 'performance enhancing proxies' (PEPs), that is, active network elements that modify or splice end-to-end flows in an attempt to enhance the performance they attain in the face of particular link characteristics. The remaining documents will either discuss the impact and mitigations for a problematic link-layer characteristic (or group of closely related characteristics), or provide overviews of which other PILC documents apply to particular problem domains.

As one of its first work items, the WG will review an existing I-D on considerations for "long, thin" networks (one of the salient characteristics of terrestrial wireless links). This will be published as a preliminary assessment of the problem domain, to be refined by later PILC documents.

All documents will identify which of their considerations remain research topics versus which are established as advanced development. Research topics will be explicitly flagged as not part of any recommendations. All documents will also identify any security implications associated with their considerations.

The working group will also serve as a forum for discussing possible modifications to IETF protocols to improve performance in environments with problematic link characteristics - however, not to the detriment of performance and stability in the general Internet, nor to undermine existing security models.

It is incumbent upon the chairs to ensure that the WG maintains good communications with other groups interested in related technology issues, such as wireless forums.

Goals and Milestones:



Submit Internet-Draft on significantly low bandwidth links.



Submit Internet-Draft on significantly lossy links.



Submit Internet-Draft on long-thin networks (based on draft-montenegro-pilc-ltn-01.txt) submitted to the IESG for publication.



Draft of link-layer design considerations document.



Draft of PEP capabilities and limitations document.



Draft on asymmetric network paths.



Document on lossy links to IESG for publication as BCP.



Document on PEP capabilities and limitations submitted for publication as Informational.

Apr 01


Document on low bandwidth links to IESG for publication as BCP.

Aug 01


Draft of TCP Over Wireless document to the IESG as BCP

Aug 01


Document on link-layer design considerations submitted for publication as BCP.

Aug 01


Document on asymmetric network paths submitted to the IESG for publication as BCP.

Aug 01


Possible rechartering of WG to address modifications to IETF protocols.

Request For Comments:






Performance Enhancing Proxies Intended to Mitigate Link-Related Degradations

Current Meeting Report

Meeting Date: Tuesday, August 6, 2001
Meeting Time: 1415 - 1515 (one hour)
Meeting Location:
Hilton London Metropole
225 Edgware Road
London, United Kingdom W2 1JU

Working group chairs:
Spencer Dawkins (mailto:spencer.dawkins@fnc.fujitsu.com) and Aaron Falk (mailto:a.falk@ieee.org)

Notes taken by:
Spencer Dawkins (mailto:spencer.dawkins@fnc.fujitsu.com)
Gab Montenegro (mailto:gab@sun.com)
Rod Ragland (mailto:rragland@hns.com)


0. Agenda bashing

Agenda slides are available at http://pilc.grc.nasa.gov/meetings/ietf51/pilc-status.pdf.

1. Working group status

PEP (RFC 3135, INFO), SLOW (RFC 3150, BCP 48), and ERROR (RFC 3155, BCP 50) have been approved as RFCs (ERROR was still in the RFC editor queue, but has been published since the London meeting). We're close on LINK (BCP), ARQ (INFO), and ASYM (INFO). We have more work to do on 2.5G3G (BCP), but should be able to finish this document before the next IETF. PILC may not meet at IETF 52 (Salt Lake City).

2. Discussion of docs in progress

- ARQ:

Gorry presented draft-ietf-pilc-link-arq-issues-02.txt

ARQ was "hummed" for working group last call, after minor editorial updates (version 03).

Slides are available at http://pilc.grc.nasa.gov/meetings/ietf51/pilc-arq-02-pres-51.pdf.


Gorry presented draft-ietf-pilc-asym-05.txt.

We discussed making this document Experimental track, but decided that the mitigations aren't described in enough detail to allow experimentation.

Comment: this document needs to be less prescriptive, if it's going to be Informational.

ASYM was "hummed" for working group last call, after minor editorial updates (version 06).

Slides are available at http://pilc.grc.nasa.gov/meetings/ietf51/pilc-asym-05-pres-51.pdf.

- 2.5G3G:

Hiroshi presented draft-ietf-pilc-2.5g3g-03.txt.

This document didn't get a lot of discussion until it was last-called in the working group, but we did get last-call comments, involving bandwidth-delay product, connection splitting, applications section (which has been removed), etc. The chairs' opinion is that we're a couple of revisions away from an RFC.

"Careful TCP splitting" is not being recommended in a BCP-targeted document.

If one-percent error rates are possible with 3GPP, this needs to be pointed out in the document, probably in Section 2, because error rates this high will definitely affect performance.

Reiner Ludwig put in a plea for a longer initial RTO value, because the current 3-second maximum is too close to the 1.5 seconds it takes for a maximum-length packet to clear an 8000-bps link. This is a tradeoff, because a longer timer value is the obvious right answer for slow links, but penalizes fast links.

Slides are available at http://pilc.grc.nasa.gov/meetings/ietf51/pilc-ietf51-presen.pdf.


Phil presented draft-ietf-pilc-link-design-06.txt.

This document is essentially complete, except for discussions we're having about the Security Considerations section.

The basic question is what we say about subnetwork-level security.

We have agreement that there's no substitute for end-to-end security, and that subnetwork infrastructure needs to be protected. Our remaining issue is what we say about encryption of user data at the subnetwork level, and our concern is whether recommending bulk encryption will make IPSEC more or less likely to be deployed. We agreed not to DIScourage subnetwork encryption.

This discussion needs to be completed on the mailing list (in September!).


Advice to link designers on link Automatic Repeat reQuest (ARQ)
TCP Performance Implications of Network Asymmetry
Status: TCP over 2.5G and 3G Wireless Networks