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Subject |
Re: [GLIF controlplane] RE: Network Control Architecture |
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From |
Harvey Newman <Harvey.Newman@xxxxxxx> |
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Date |
Thu, 19 Apr 2007 10:39:05 -0700 |
This is a limited view that will run into the same problems as are
well-known
from RSVP. One will never get to reserve a multi-domain path this way.
Operational steps in a services-oriented architecture:
(reservations are stateful, time-dependent, and responsive to
capability to use the allocated resource):
(1) AAA, with priority schemes and policy expressed by each VO.
(2) Inter-VO allocations according to quotas; coupled to tracking of
what has been used during a specified time period
(3) Service to verify end-system capability and load as being
consistent with the request
(4) Agents to build the path and verify its state (up, down,
which segment(s) are down or impaired) also agents to
verify end-system capability (hardware, system and kernel
config., network interface and settings); verification
of end-to-end capability with an active probe (viz.
FDT); build or tear down circuits in parallel in a
time < the TCP timeout.
(5) Tracking of capability (if relevant, as in large scale data
transfer)
(6) Adjustment of channel capability if allowed, according to
performance end-to-end. For example with LCAS
[allocation of a non-adjustable channel takes longer,
and becomes an economic question.]
(7) Adjustments driven by (a) entry of higher priority
allocation-requests; these could affect many or even
all channels or (b) re-routing of certain flows if better
paths become available (c) optimization of workflow according
to deadline scheduling for certain flows
Except for the higher-level "strategic" parts above (policy and
quotas; which need to come from the VOs), many of the technical pieces
above exist, and will be hard to match.
Harvey
Steve Thorpe wrote:
Hello Bert, everyone,
The point Bert made "...if the pre-reservation of resources is not an
atomic action..." is very important.
My belief is the pre-reservation of resources, or Phase 1 of a 2-phase
commit protocol, *must* be atomic. That is, there must be a guarantee
that at most one requestor will ever be granted a pre-reservation of a
given resource. Then, the requestor should come back with a
subsequent "Yes, commit the pre-reservation", or "No, I release the
pre-reservation". In the case where the requestor does not come back
within a certain amount of time, then the pre-reservation could expire
and some other requestor could then begin the 2-phase commit process
on the given resource.
There may be situations where a resource broker can not get the
desired resource reservation(s) booked. But, I don't see deadlocking
here - where both resources can *never* be booked. Unless of course,
a resource broker books them once and is allowed on to them forever.
The atomicity of the pre-reservation (phase 1) stage of the 2-phase
commit process is a very critical part for this to work.
Steve
PS I have also added Jon MacLaren to this thread, as I'm not sure he's
on the GLIF email list(s).
Bert Andree wrote:
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
