Browse Prior Art Database

NON-DISRUPTIVE BUFFER RECLAIMATION ON FIBRE CHANNEL

IP.com Disclosure Number: IPCOM000014601D
Original Publication Date: 2000-Mar-01
Included in the Prior Art Database: 2003-Jun-19
Document File: 3 page(s) / 81K

Publishing Venue

IBM

Abstract

There are several parts to this proposal:

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 52% of the total text.

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NON-DISRUPTIVE BUFFER RECLAIMATION ON FIBRE CHANNEL

There are several parts to this proposal:
1. Detection that BB credit is below some threshold and needs to be recovered
2. Short term solution to recovering BB credit using FC-4
3. Long term solution using FC-2 layer

Detection

The detection part of this proposal has not yet been addressed. There are several possibilities, but hardware changes in the Emulex ENDEC may be necessary, hence it doesn't make sense to spend a lot of time right now discussing it. Instead of an explicit detection mechanism, the current direction is to perform the BB credit reclaimation proccess on a periodic basis.

Short Term Solution

The main problem to solve in the short term is how to recover the BB credit without causing frames/sequences to be dropped. This proposal lowers the probability that that any frames in flight get clobbered, but does not eliminate the possibility.

The following description is not "architecture-eze". I'll leave that up to Giles and Joe, but you should be able to understand the intent:

When either a channel or control unit determine that BB credit has reached a point where it needs to be recovered, it sends a Quiesce FC-4 Link Service to all N_Ports that it has logical paths established with, and starts a timer, Qu_TIV (quiesce time interval). When either all Quiese responses have been received or Qu_TIV has expired the sender of the Quiesce issues a Link Reset. At the conclusion of the LR/LRR process it sends a Resume.

When either a channel or control unit receives a Quiesce, it sends a Quiese_Response FC-4 Link Service frame, and then stops sending sequences to the N_Port that originated the Quiesce until either it receives a Resume, or Re_TIV (Resume time interval) has expired. Any sequences that have been queued but not transmitted prior to sending the Quiese Response are allowed to complete.

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If a "ship pass" condition occurs where two or more N_Ports send a Quiesce to each other, then each side proceeds with it's BB credit reclamation as if the incoming Quiesce was not received. After LR/LRR completes with it's nearest neighbor, then it sends a Resume as in the non-ship pass case. It does not send anything else to that N_Port until it receives a Resume or until Re_TIV expires.

The net result is that a reasonable effort has been made to allow the incoming (from the point of view of the N_Port with the BB credit "problem") pipe to drain.

The receiver of a Quiesce must be able to tollerate a loss of light condition at the sender without loosing the Quiesced state. Editor's note: There may be a need to quiesce for a longer duration that the proposed 20...