Hello Seema kumar,
Please, see the inline below.
Whatever the reason is for a 3-step transaction model, I foresee the problem I
mentioned in my previous email (Point 3 of my previous mail). Do you have any
comments on it?
3) In the 3-step transaction, I foresee a problem when there are concurrent
requests from different neighbours. Regarding concurrent requests, the
draft-wang-6tisch-6top-protocol-00 says “A node MAY support concurrent 6P
Transactions from different neighbors” in Section 4.3.3. A node would reply
BUSY to requester only when it does not have enough resources.
Problem: In the topology specified in the draft, consider node B and C requires
2 cells each from node A. Node A has 4 or more cells. The SF chooses 3-step
transaction.
NumCells = 2,[]
Step 1: B -------------------------> A
[(1,2),(2,2),(3,5),(4,6)]
Step 2: B <------------------------- A
NumCells = 2, []
Step 3: A <------------------ C
At this step, if Node A specifies [(1,2),(2,2),(3,5),(4,6)] as candidate list,
there will be problem if both Node B and C choose same cells. What should Node
A do at this point ? This problem would not arise in 2-step transaction.
Currently, if SF0 is used, node A would specify [(1,2),(2,2),(3,5),(4,6)] as
candidate list. Am I right? Then the problem mentioned above would occur.
As of my understanding, “ node A(Parent/Neighbor node)” can have multiple
interfaces where node-B (Child-1/Requestor) and node-C (Child-2/Requestor)
would send the 6P ADDRequest with “NumCells” field to node-A at same time in
different interfaces. Once, the Candidate cells are send by node-A to node-B in
Step-2 of 3-step transaction then node-A can’t assign the same cells to node-C
concurrently. The reason behind this is node-A will mark the candidate cells as
“Temporary reserved” in its Chunk. If node-A has some other free cells
available in its chunk then step-2 operation to node-C is performed as “6P
Response”, otherwise it should be as “BUSY” message.
If 6P ADDRequest from node-B and node-C reach to node-A at exactly same time
then node-A should allow only one request at a time to access the chunk
information.
Hope my explanation make sense for your Step 3.
With Regards,
Satish.
From: 6tisch [mailto:[email protected]] On Behalf Of Seema Kumar
Sent: 2016年4月27日 18:16
To: Satish Anamalamudi (Satish Anamalamudi); [email protected]
Subject: Re: [6tisch] Doubts in 3-step transactions mentioned in
draft-wang-6tisch-6top-protocol-00
Hello Satish,
I agree with the example you have given, both the nodes get equal opportunity.
But, I don't think there is a provision in the current draft to propose the
candidate list in the first step of a 3-step transaction.
With my understanding, the only differentiation between 2-steps and 3-steps
model is who proposes the candidate list.
Whatever the reason is for a 3-step transaction model, I foresee the problem I
mentioned in my previous email (Point 3 of my previous mail). Do you have any
comments on it?
Thanks,
Seema
On Wed, Apr 27, 2016 at 8:05 AM, Satish Anamalamudi (Satish Anamalamudi)
<[email protected]<mailto:[email protected]>> wrote:
Hello Seema Kumar,
I would like to express my idea for 3-step 6P transaction :
Let us consider a case when requester send candidate list along with NumCells
to neighboring node during 6P ADDRequest.
1. node A (Requester) in Step.2 send the candidate list to Node B(Neighbor
node).
2. If Node B has not all the cells available from candidate list of Node A
then Node B can add some cells in Candidate cells during 6P response to node
A(step .3).
3. In step.4, Node A can send the 6P confirmation to node B with scheduled
cells.
With this operation, both node A and node B will have equal opportunity to
suggest their best available channels.
What do you think ?
With Regards,
Satish.
From: 6tisch [mailto:[email protected]<mailto:[email protected]>]
On Behalf Of Seema Kumar
Sent: 2016年4月26日 18:39
To: [email protected]<mailto:[email protected]>
Subject: [6tisch] Doubts in 3-step transactions mentioned in
draft-wang-6tisch-6top-protocol-00
Dear All,
I have few comments with respect to the draft-wang-6tisch-6top-protocol-00.
1) The draft includes 3-step transaction described in Section. 4.1.1, for
negotiation of cells between two neighbours. In step 4 of 3-step transaction,
there is a mistake. “The SF running on node B selects 2 cells” is written. It
should have been “The SF running on node A selects 2 cells".
2) In 3-step transaction, the requester only specifies number of cells, and the
candidate list is not specified by the requester. I assume, the neighbouring
node is free to choose the candidate list.
When requester sends empty list, what is the motivation behind the neighbouring
node sending the candidate list in second step of 3-step transaction ? Is it
because the requester has better knowledge about the cell quality, and
therefore can pick the right ones ?
3) In the 3-step transaction, I foresee a problem when there are concurrent
requests from different neighbours. Regarding concurrent requests, the
draft-wang-6tisch-6top-protocol-00 says “A node MAY support concurrent 6P
Transactions from different neighbors” in Section 4.3.3. A node would reply
BUSY to requester only when it does not have enough resources.
Problem: In the topology specified in the draft, consider node B and C requires
2 cells each from node A. Node A has 4 or more cells. The SF chooses 3-step
transaction.
NumCells = 2,[]
Step 1: B -------------------------> A
[(1,2),(2,2),(3,5),(4,6)]
Step 2: B <------------------------- A
NumCells = 2, []
Step 3: A <------------------ C
At this step, if Node A specifies [(1,2),(2,2),(3,5),(4,6)] as candidate list,
there will be problem if both Node B and C choose same cells. What should Node
A do at this point ? This problem would not arise in 2-step transaction.
Currently, if SF0 is used, node A would specify [(1,2),(2,2),(3,5),(4,6)] as
candidate list. Am I right? Then the problem mentioned above would occur.
In my opinion, there is no need for specifying the candidate list in step 2 of
3-step transaction. When requester is not particular about cells, the
neighbouring node can give any 2 cells instead of again asking the requester to
choose.
Regards,
Seema Kumar
_______________________________________________
6tisch mailing list
[email protected]
https://www.ietf.org/mailman/listinfo/6tisch
