RE: ipoib-cm multiple connection model

Hi Vandana,

I too agree there is no problem here.

I think you are right if the left peer accepts the connection. However,
if the reverse was the case, that is the left peer rejected the connection
since it is found that the local address is numerically larger. It will
do this comparison since its REQ is also outstanding.  The right peer will
not receive any REQ  (it is delayed or yet to be retransmitted). If it
receives the reject it will cancel its request. At a later time it will
receive the delayed/retransmitted request and one connection will be 
established.

Dror, do these two scenarios look right to you?

Vivek

On Thu, 20 Oct 2005, Vandana Rao wrote:

> Hi Dror,
> I think you are confusing the 2 IDs that come into play in this setup. The 
> communication ID is something that the CM entity on a node understands but 
> the transaction ID is something that the MAD handling entity uses (for 
> retransmission, req/resp matchup etc.).
> So, in the second slide, there should not be a retransmission of the left 
> peer REQ MAD since when the left peer accepts the connection, it will cancel 
> its outstanding REQ request and hence the retransmission should not take 
> place.
> -Vandana
>
> At 12:39 AM 10/20/2005, Dror Goldenberg wrote:
>> After giving it some more thought, I think that there is still a problem. 
>> Please look at the attached pdf.
>> 
>> In the first slide, everything happens smoothly, the left peer knows that 
>> it has to accept the connection and the right peer knows that it has to 
>> decline.
>> On the 2nd slide, the left peer REQ transmission is dropped in the fabric. 
>> It is retransmitted independently by the CM way after a channel has already 
>> been established. Now the right side can not really tell whether this is a 
>> new channel request or an old "simultaneous connection channel". This may 
>> lead to two channels being opened mistakenly.
>> 
>> I don't believe it can be solved by looking at the communication ID. This 
>> number is just being fabricated by the sender of the REQ and is just a 
>> "random number" with respect to what we're trying to determine.
>> 
>> -Dror
>> 
>> -----Original Message-----
>> From: Dror Goldenberg
>> Sent: Wednesday, October 19, 2005 9:37 PM
>> To: 'Vandana Rao'; Dror Goldenberg; [email protected]
>> Subject: RE: [Ipoverib] ipoib-cm multiple connection model
>> 
>> Hi Vandana,
>> 
>> Thanks for clarifying this. I agree that if IPoiB-CM implementation looks 
>> at the Communication ID it can make those decisions correctly. The question 
>> is whether this value is exposed through common CM APIs. For all other 
>> purposes, the CM doesn't need to expose the Communication ID to the ULP. 
>> However, seems like it's not a big deal to expose this value to the ULP.
>> Anyway, it worth noting this explanation in the RFC so that it's clear that 
>> a proper implementation of IPoIB-CM should monitor Communication ID as part 
>> of the simultaneous connection decision.
>> 
>> -Dror
>> -----Original Message-----
>> From: Vandana Rao [mailto:[email protected]]
>> Sent: Wednesday, October 19, 2005 6:40 PM
>> To: Dror Goldenberg; [email protected]
>> Subject: Re: [Ipoverib] ipoib-cm multiple connection model
>> 
>> Hi Dror,
>> The purpose of the MAD transaction ID is to allow one to do what you say 
>> below, i.e. have multiple connection establishment MADs between 2 peers. It 
>> is essentially the same as the "channel ID" that you talk about below. Its 
>> just that it is a generic channel ID for any MAD transactions, not just CM 
>> MADs.
>> I do not believe there is any issue with existing IB CM in this regard.
>> -Vandana
>> 
>> At 03:11 AM 10/19/2005, Dror Goldenberg wrote:
>>> I think that the current model for multiple connections establishment 
>>> between
>>> two peers works well for 1 connection but is broken for more than one 
>>> connection.
>>> Because of cases where CM packets are dropped or travel on different VLs, 
>>> they
>>> might get reordered on the way and observed in a different order than were 
>>> originally
>>> sent. This breaks the current model which assumes that the REQs are sent 
>>> and
>>> processed in order.
>>> 
>>> I think that we need to think of a model which is robust to CM packets 
>>> reordering
>>> which can be one of:
>>> - Adding a "channel ID" in the private data. The field goes 0,1,2 and on. 
>>> It helps
>>>    synchronizing both peers on which is the channel at question now. The 
>>> rest
>>>    of the decision (per channel) of whether to accept or reject can be the 
>>> same
>>>    as defined in the draft.
>>> - Not supporting multiple connections between the same peers.
>>> 
>>> -Dror
>>> _______________________________________________
>>> IPoverIB mailing list
>>> [email protected]
>>> https://www1.ietf.org/mailman/listinfo/ipoverib
>> 
>