Hi Don, for now don't worry about
the timeslot maps. I'm sure other folk will bring this up. I want an efficient method to send update
changes in to circuit switched bandwidth.
For example my OC-192 has just gone from having 49 STS-1 equivalent
bandwidth available to 47 STS-1 bandwidth available. It seems like a single byte can convey
this. While at the same time I may
also want to convey the fact that one or more of the already uses STS-1s are
being "sub-multiplexed" and have space for say 36 VT1.5s. However this VT1.5 bandwidth isn't
equivalent to STS-1 bandwidth.
(Similar issues apply up and down the multiplex hierarchy). I don't know why you say integers
aren't "dynamic" enough.
They are very easy to change rapidly and book keep
accurately for TDM purposes.
From: Don Fedyk
Sent: Tuesday, February 26, 2002
To: Bernstein, Greg; Kireeti
Subject: RE: Routing drafts
Yes I recall the discussions on this. The bandwidth
the minimal amount of information
to make a routing decision. They
do not cover all of the detail that
could be in a timeslot map.
Integers are definitely not dynamic
enough. The issue is that even
if you have this detailed
information you still have to augment
signaling with the capability to
deal with glare conditions. So
our strategy was not to overburden
routing with this information
but to put the capability in
>From: Bernstein, Greg [mailto:GregB@ciena.com]
>Sent: Monday, February 25, 2002
>To: Fedyk, Don
[BL60:1A00:EXCH]; Kireeti Kompella; email@example.com
>Subject: RE: Routing drafts.
>Actually floating point is
overkill for TDM. We'd like to use small
>integers to describe and update
them more frequently.
>The TDM multiplexing is
straight forward but unforgiving.
>We had this same discussion
when we decided to breakout the labels
>for SONET/SDH GMPLS
signaling. I want to know that I've got 14
>STS-1 of capacity, XX unused
VT1.5, etc... For those SONET/SDH
>systems that have to deal with
timeslot inflexibility (i.e.,
>fragementations issues) more
complete information on time slot
>usage is advantageous.
For example with rings that don't
>have Time Slot Interchange, a
map of the timeslots could
>be helpful. Eric and I
had a bunch of stuff about this in
>our earlier routing drafts.
>Dr. Greg M. Bernstein, Sr.
Director Technology, Ciena Corp.
>From: Don Fedyk [mailto:firstname.lastname@example.org]
>Sent: Monday, February 25, 2002
>To: Bernstein, Greg; Kireeti
>Subject: RE: Routing drafts
>Greg you wrote:
>> (b) Big issue -- The
parameters for representing bandwidth on
>> a link are not
>> very appropriate for TDM
signals or WDM signals. I've
>> included below some
>> more explanation taken
from the IPO working group draft.
>> However, this is
>> the same thing that led to
us breaking out the traffic
>> descriptor stuff in
>> GMPLS signaling for the
SONET/SDH case. This is really
>> needed here too.
>These bandwidths in our draft
are exact floating point numbers.
>Are you saying that the
resolution of the floating point is an issue
>with optical? Or are you
implying that bandwidths are percentages ?
>The text below is implying that
statistical multiplexing can use
>inexact bandwidth but optical
can (and should) use exact bandwidths.
>I did not see problems with the
floating point range or our draft.
>> (From IPO working group
draft on Inter-domain optical routing)
Differences between MPLS and Optical Circuit routing
>> The bandwidth accounting
needed in optical circuit-switched
>> networks is also
>> different than in packet
networks. In packet networks using
>> either ATM QoS
>> or MPLS-TE, complex
statistical measures are used to
>> characterize the load
>> on a link, often with
varying degrees of accuracy. The
>> inexactness of such
>> measures and the
"compressibility" of statistically
>> multiplexed traffic
>> imply that a small
percentage change in link utilization can
>> usually be
>> absorbed by the network.
>> By contrast, if an OC-192
link has just one STS-1 path
>> occupied (less than
>> 1% of the link bandwidth),
it cannot accommodate an STS-192c
>> path. Due to
>> the relatively simple
finite multiplex structures currently
>> use in optical
>> networks tracking
bandwidth resources is much easier than
>> packet switched
>> networks, however much
stricter bandwidth accounting is
>> required on circuit
>> switched links. In
particular, it is expected that an
>> individual optical
>> circuit switched link can
be fully utilized, while due to
>> queuing effects a
>> packet switched link on
average can never be run at full
>> capacity and is
>> typically run at less then
80% of capacity.
>> Greg B.