Re: [GLIF controlplane] RE: Network Control Architecture

[Bert Andree <handree@xxxxxxxxxxxxxx>]

Hi Gigi,

What exactly dou you mean with one RB per request.
Suppose there are two independant RB's,RB-A and RB-B and two resources, 
RS-1 and RS-2.
Suppose that there is a request to RB-A to book both resources and a 
request to RB-B to do the same. Now, if the pre-reservation of resources 
is not an atomic action, two different strategies may introduce specific 
problems.

Stategy 1: an availibility request does not reserve the resource:
RB-A asks for RS-1 (available)
RB-B asks for RS-2 (available)
RB-A asks for RS-2 (available)
RB-B asks for RS-1 (available)

RB-A confirms RS-1 (success)
RB-B confirms RS-2 (success)
RB-A confirms RS-2 (fail)
RB-B confirms RS-1 (fail)

The obvious solution would be to free all resources and try again. In 
complex systems there is a fair chance that both resources can never be 
booked (deadlock).


Stategy 2: an availibility request reserves the resource:
RB-A asks for RS-1 (available)
RB-B asks for RS-2 (available)
RB-A asks for RS-2 (not available)
RB-B asks for RS-1 (not available)

RB-A and RB-B free all resources and try again. In complex systems there 
is a fair chance that both resources can never be booked (deadlock).

The only way to prevent is, is to have some queing of requests and even 
then "individual starvation", e.g. RB-A can never book any resources is 
possible in complex systems.

Best regards,
Bert

Gigi Karmous-Edwards wrote:

> Hi Admela,
>
> I agree, there are two phases, 1) check availability from xRM, and 2) If 
> all xRMs give an ack. then go th second phase of commit, 2') if one or 
> more xRM gives a nack, then do not proceed to the phase two commit. In 
> the architecture sent out, the responsibility of coordinating and 
> administering the two phases is in ONE RB per request. Each xRM will 
> rely on the RB to tell them  whether to proceed to a commit or not. If 
> they get a commit from an RB, it then becomes the xRM's responsibility 
> to make the reservation and allocation in the actual resources. I think 
> if  for example RB-A talks to an xRM in domain "B", then it may be the 
> responsibility of the xRM-B to tell its own  RB-B of its interaction 
> with RB-A. Is this in line with your thoughts?
>
> Gigi