|
David, I would contend that without wrapping or
steering, the formula for A should be (N-2)*MTU, since there is no jitter
associated with the sending or receiving station. However, the more
important case may be wrapping, rather than steering. Consider the ring of
stations A B C D E F with A sending to F the long way, and a break occurring
between E and F so that E wraps. The message goes from A via the path A-B,
B-C, C-D, D-E, E-D, D-C, C-B, B-A, A-F. In general the maximum jitter can
be (2N-3)*MTU.
In general, we need to make sure that we look at
the worst case conditions which are often not the normal ring operating
conditions.
Best regards,
Robert D. Love Chair, Resilient Packet Ring Alliance President, LAN
Connect Consultants 7105 Leveret Circle Raleigh, NC
27615 Phone: 919 848-6773 Mobile: 919
810-7816 email: rdlove@xxxxxxxx
Fax: 208 978-1187
----- Original Message -----
Sent: Thursday, March 28, 2002 12:35
PM
Subject: RE: [RPRWG] RAH: Re: Minutes of
Rate Ad Hoc meeting
All,
Sorry for being a bit quiet recently, had a few
internal
tasks that popped up (I too have another
job!).
I think we have agreement on functionality but
some
conflicting visions of implementation
feasibility.
Let me try to summarize.
As to the desired client-visible classes, these
are
listed below:
Class
Jitter
Bandwidth
------- -------------
-----------
class-A ~N*MTU jitter
provisioned (up to 100%)
class-B
~RCT
provisioned (up to 100% minus class-A)
class-C
(unspecified) residual BW with
weighted fairness
Note:
N is the number of
stations
MTU is the maximum packet
size
RCT is the ringlet-circulation
time
Some folks have argued for a few more classes,
such
as A- and B+, or barely passing D
grades,
but these discussions should probably be
skipped
until we conclude on the basic definitions of
A,B,C.
The implementation concern is the techniques for
supporting
class-A traffic. Two techniques are
possible:
subclass-A0 - upstream
stations ensure provisioned rate
of idles for downstream station at all times
subclass-A1 - upstream stations ensure
provisioned rate
of idles for downstream stations, when
throttling is requested via flow-control signal
The key observations are that:
a) the subclass-A1 traffic is more
efficient, because
temporal as well as spatial
reuse is possible.
b) the subclass-A1 traffic is more costly,
because
larger 2nd transit queue
sizes are needed.
c) the levels of supportable class-A1 traffic
are dependent
on the ratio
of:
secondQueueDepth/linkLength
although the equation is a
bit more complex if the
queue depths
and link lengths are not all
the same.
What happens if
our station has a second transit queue,
that queue can only sustain 5% of subclass-A1
traffic, and
10% of class-A traffic is requested by the
client?
This is what happens when a MAC designed for Palo
Alto is
overextended to the Bay Area, for
example.
The answer is simple: the MAC provisions 5% of
subclass-A1
and 5% of subclass-A0 traffic, to meet the cumulative
10%
class-A requirement. Thus, any second transit queue
design
can support 100% of class-A traffic, its just that
larger
amounts of less-efficient subclass-A0
provisioning are used
when the queue-size is small and/or the link-length
is large.
There is also a secondary concern with regards to
management
of the secondary transit queue to sustain
downstream
demands for class-A traffic. I believe the basic
concept
in the current draft is OK, but refinements are
needed to
ensure successful operation. But, that's a topic for
another
day.
Again, I would like to emphasize deferral (not
cancellation)
of intermediate A- or B+ grades until convergence on
the
behavior and implementation of A0/1,B,C classes. At
that
time, their relative impact and benefits can be
better
evaluated.
DVJ
David V. James, PhD
Chief Architect
Network Processing
Solutions
Data Communications Division
Cypress Semiconductor
110
Nortech Parkway
San Jose, CA 95134
Work: +1.408.942.2010
Cell:
+1.650.954.6906
Fax: +1.408.942.2099
Work:
djz@xxxxxxxxxxx
Base: dvj@xxxxxxxxxxxx
Raj,
>>So, the corollary, that if the
LPTB size is fixed on the ring than for a
given
>>ring
circumference only a certain level of HP traffic, with
absolute guarantees
>>on
jitter, can be provided. This implies that carriers would have to
predict
>>the
levels of HP traffic in the network before they procure their
equipment.
[Karighattam, Vasan] If
you say that carriers will not like this, I think the correct solution would
be to ignore the reclaimability issue completely. So your reclaimable
HP bandwidth is set ~0 (implies small or non existent 2nd TB). Then
reserve required bandwidth around each segment. With the shapers at
the output of each MAC, you will never need to suffer from priority
inversion. It also solves the scalability issue you have raised for
10G rings. If not, the only useful size for the 2nd TB would be
2RTT!!
Vasan
-----Original Message-----
From: Raj
Sharma [mailto:raj@xxxxxxxxxxxx]
Sent: Wednesday, March 27, 2002
4:43 PM
To: 'Harry Peng'; Raj Sharma
Cc:
stds-802-17@xxxxxxxx
Subject: RE: [RPRWG] RAH: Re: Minutes of Rate
Ad Hoc meeting
Harry,
I am not suggesting a lossy ring. I requested
one, but most of you convinced
me that will never happen in RPR. So, I am moving
on with an assumption of
a loss less RPR ring and I request you do
too.
However, if I were to uphold the argument
for a loss less ring while absolutely
guaranteeing no priority inversion
than
a certain size of LPTB buffer must designed
in. Obviously the size of this
LPTB depends on the levels of HP traffic and the
RTT. Everything has a
consequence - there is no freee lunch
!
So, the corollary, that if the
LPTB size is fixed on the ring than for a given
ring circumference only a certain level
of HP traffic, with absolute guarantees
on jitter, can be provided. This implies that
carriers would have to predict
the levels of HP traffic in the network before
they procure their equipment.
The one way to resolve this problem is to be able
to "add" more LPTB
to the RPR MAC to sustain higher levels of HP
traffic on the ring. Unfortunately,
at 10 gbps speeds off-chip TB schemes will have
significant penalties.
Anyway, you missed my statement I made in the
original email.
I said that if one were to prevent packet loss
and avoid priority inversion
than one must AVOID situations that creates a
scenario to pick one
over the other. Somehow, that seems like a simple
logic to me. So,
my argument was not for supporting a lossy ring
but what you need to
in order to have a loss less ring and avoid
priority inversion.
In fact, I wonder why you don't think similar
since your requirement is to
have a loss less ring, no priority inversion and
a single 2 MTU TB. I would think
the a single TB with ability to buffer 2 packets
cries out for some method
to AVOID a situation that will force priority
inversion to honor a loss less ring
requirement. I must be missing something
!
The real issue is that I am not fixated on
preserving any implementation at
the cost of having an absurd standard. On the
other hand, I am tolerant to the
big guns who want to do this I think we need to
ensure that the RPR WG
do diligence.
raj
Raj:
There are really two issues
one
is vendor box issues when interworking:
1)
utilization versus implementation to achieve the desired packet delivery
behavior.
The 1 TB and 2 TB
design fall with in this category
Once reserved BW is allocated globally or at link level, you think your
box provide
better ring BW
utilization. All the power to you.
2) Lossy ring
This
is an 802.17 issue.
Lossless
behavior is a must. You are arguing for lossy.
Regards,
Harry
-----Original Message-----
From:
Leon Bruckman [mailto:leonb@xxxxxxxxxxxxx]
Sent: Tuesday, March 26, 2002 1:59 AM
To: 'Raj Sharma'
Cc:
stds-802-17@xxxxxxxx
Subject: RE: [RPRWG] RAH:
Re: Minutes of Rate Ad Hoc meeting
For the 2 transit buffer scheme there is another
way:
Have a LPTB that is deep enough. The LPTB
depth to avoid both: "on transit"
LP traffic
discard and reduced HP priority, can be calculated using the
formula in:
http://grouper.ieee.org/groups/802/17/documents/presentations/jan2002/vk_dwd
el_02.pdf
This formula can be
modified for the case of links with different reserved
rates also.
Leon
-----Original Message-----
From:
Raj Sharma [mailto:raj@xxxxxxxxxxxx]
Sent: Tuesday, March 26, 2002 3:43 AM
To: 'Sanjay K. Agrawal'; Li Mo; stds-802-17@xxxxxxxx; Nader
Vijeh
Subject: RE: [RPRWG] RAH: Re: Minutes of
Rate Ad Hoc meeting
The only way to guarantee HP traffic and have no packet
loss
is to be able to AVOID situations that will
reduce the priority
of HP traffic to satisfy a
loss less ring.
There are two ways to avoid:
1.
Provision the low priority to ramp-up very slowly - this
will result in low link utilization.
2. Constantly, provide each node the ability to determine
what conditions would lead to congestion.
raj
> -----Original Message-----
> From: Sanjay K. Agrawal [mailto:sagrawal@xxxxxxxxxxxxxxxxxx]
> Sent: Monday, March 25, 2002 5:03 PM
> To: Li Mo; stds-802-17@xxxxxxxx; Nader
Vijeh
> Subject: Re: [RPRWG] RAH: Re: Minutes
of Rate Ad Hoc meeting
>
>
>
>
For me 2 is very important otherwise I have very limited
> spatial reuse . On
> the other hand, allowing the packet loss on the ring, will
> limit the scope
> of this technology to TCP/IP networks. I think somehow we
have to
> accommodate both.
>
> -Sanjay K. Agrawal
>
>
> ----- Original Message -----
>
From: "Li Mo" <limo01@xxxxxxxxx>
> To:
<stds-802-17@xxxxxxxx>; "Nader Vijeh"
<nader@xxxxxxxxxxxxxx>
> Sent: Friday,
March 22, 2002 11:04 AM
> Subject: RE:
[RPRWG] RAH: Re: Minutes of Rate Ad Hoc meeting
>
>
>
>
> I agree with
the comments made by previous authers. I used to
> think one of
> the key
characteristics of RPR is "no packet loss" once it is
> in transport.
> But, with the
different reservation rate possible on
>
different spans (unless
> a very
sophasticated fairness algorithm has been used which
> is unknow at
> this time, this
characteristics may be unattendable. Hence
> we have a choice
> to be
made:
>
> 1. allow
the packet loss on the ring
> 2. allow
different reserved rate on different span
>
> For those, I would like to see the first
one unless somebody
> developed a
> fairness algorithm which achieves both.
>
> Li...
>
> -----Original
Message-----
> From:
owner-stds-802-17@xxxxxxxxxxxxxxxxxx
> [mailto:owner-stds-802-17@xxxxxxxxxxxxxxxxxx]On
Behalf Of Nader Vijeh
> Sent: Friday, March
22, 2002 12:12 PM
> To:
stds-802-17@xxxxxxxx
> Subject: RE: [RPRWG]
RAH: Re: Minutes of Rate Ad Hoc meeting
>
>
>
> We have customers that find loosing packets
in the transport
> side of the
> network unacceptable. One of the reasons we hear
is the "multi-tier"
> environment, where the
transport and the service side may be
>
"logically"
> separate and belong to
different business entities. Another item to
> consider is that RPR is competing with SONET for the data
transport
> infrastructure and SONET does not
loose packets in transit.
>
> Nader
>
> -----Original Message-----
>
From: Mike Takefman [mailto:tak@xxxxxxxxx]
> Sent: Friday, March 22, 2002 7:44 AM
> To: Italo.Busi@xxxxxxxxxx
> Cc:
jalemon@xxxxxxxxx; pazy@xxxxxxxxxxxx; stds-802-17@xxxxxxxx
> Subject: Re: [RPRWG] RAH: Re: Minutes of Rate Ad
Hoc meeting
>
>
>
> I beg to
differ. We had presentations by Sprint at the working
> group that it is really important where packets get
lost.
>
> Losing
packet on the media is not acceptable to them.
>
> As I said previously, routers
or switches tend to have
> buffers that are
orders of magnitude larger than any
> buffer
we are considering for the MAC. Therefore,
>
loss probability is low at that level and they can engineer
> their network, (just like they would engineer the
media)
> to get the loss statistics where
they want them.
>
> cheers,
>
> mike
>
> Italo.Busi@xxxxxxxxxx wrote:
>
>
> > See my comment in line
> >
> >
Italo
> >
>
> > -----Original Message-----
> >
> From: pazy@xxxxxxxxxxxx [mailto:pazy@xxxxxxxxxxxx]
> > > Sent: Tuesday, March 19, 2002 3:55
PM
> > > To: jalemon@xxxxxxxxx
> > > Cc: pazy@xxxxxxxxxxxx;
stds-802-17@xxxxxxxx
> > > Subject: RE:
[RPRWG] RAH: Re: Minutes of Rate Ad Hoc meeting
> > >
> > >
> >
> > ...
> >
> > >
> > > Furthermore, if a user traffic is
rejected at the ingress
> point, the
> > > user gets an immediate feedback.
Assuming such a feedback is
> > >
useful, how
> > > would a network do it
if a given packet was dropped not
> at the
ingress
> > > but rather somewhere on
the ring, say on the 5th node in a
> >
> 10-node path.
> > >
> >
> > As far as I
know, metro netwoks are tipically made by many
> > interconnected rings (SBC made a good presentation in
> September about
> > this assumption).
> >
This implies that you are loosing packets in the metro
> network so the
> > issue is
not completely solved.
> > From the
customer point of view there is no difference
> between loosing
> > packets on
the ring or in the routers/bridges interconnecting rings.
> > The big difference is made by the amount of
packets that
> the customer
> > sees as lost at end-to-end perspective ...
> >
> > > Again,
I hope that I've managed to clarify my views, but
> I am not sure
> > > if we
"violently agree" or still have some differences.
> > >
> > > Offer
Pazy
> > >
>
> > Burlington, MA
> > > Tel:
(781)359-9099 x1907
> > >
> > >
> > >
-----Original Message-----
> > > From:
John Lemon [mailto:jalemon@xxxxxxxxx]
> > > Sent: Monday, March 18, 2002 8:43
PM
> > > To: pazy@xxxxxxxxxxxx
> > > Cc: stds-802-17@xxxxxxxx
> > > Subject: Re: [RPRWG] RAH: Re: Minutes of
Rate Ad Hoc meeting
> > >
> > > Offer,
> >
>
> > > As I mentioned in the Ad
Hoc, and as Harry and Yiming
> have
reiterated,
> > > there
> > > are trade offs between utilization,
delay/jitter, and
> loss. You can
> > > choose
> >
> at most 2 of the 3. I believe there is a general clear
> preference for
>
> > lowest
> > > loss most, then
for lowest delay/jitter next, and then for highest
> > > utilization of the available bandwidth
last.
> > >
> > > But Yiming's suggestion of allowing this to be
configurable is
> > >
intriguing.
> > > While I believe we
would always have the order I list above as the
> > > default,
> > > I
could imagine a customer wanting to change it away from
> the default.
> > > If
it
> > > were an option that they
didn't have to configure, those that
> >
> wanted to
> > > change from the
default would be accommodated; and those
>
that didn't
> > > want to
> > > be bothered with configing yet another
parameter could safely
> > > ignore
it.
> > >
>
> > John Lemon
> > > -----
Original Message -----
> > > From:
"Offer pazy" <pazy@xxxxxxxxxxxx>
> >
> To: "'Mike Takefman'" <tak@xxxxxxxxx>; "'Yiming Yao'"
> > > <YYao@xxxxxxxxxxxx>
> > > Cc:
<hans-j.reumerman@xxxxxxxxxxx>;
<stds-802-17@xxxxxxxx>
> > >
Sent: Monday, March 18, 2002 2:44 PM
> >
> Subject: RE: [RPRWG] RAH: Re: Minutes of Rate Ad Hoc meeting
> > >
> >
>
> > >
>
> > I fully concur with Mike's response. We have to be
> extremely careful
> > > about adding optional behavior (and variety) to
the
> standard. In my
> > > opinion, we already have far too many options (for
this
> early stage of
> > > the standard development). Options are a nightmare
(and
> if someone can
> > > help me with a stronger word, please do :-) for
users (carriers),
> > > testers,
general audience, and finally to ourselves as we
> will have to
> > > work
much harder to make all these options work together, are
> > > consistent, and that all combinations
are covered.
> Additionally, there
> > > is the important issue of
interoperability which is made
>
exponentially
> > > more complex with
each additional option.
> > >
> > > >From my experience, developers often
tend to "be nice to
> users" by
> > > offering every options possible, just to
later be
> rejected by the end
> > > users who don't have the infrastructure,
the personnel, and the
> > > knowledge
to sort out the options, to decide, to manage and
> > > to maintain
> > >
their many network nodes.
> > >
> > >
> > >
Specifically, please note that the packet loss we are
> considering here
> > > (or
considering not allowing) is at the very low level of
> the physical
> > > level.
Look at it as the property of the wire. And at some
> > > point we must
> >
> establish a common model for this "wire" to be able to
> build the upper
> > > layers. This has nothing to do with the legitimate
topic
> that is being
> > > discussed of policing traffic on the ingress
points to
> the network.
> > > There of course, there are many tradeoffs that are
better
> > > left of to the
> > > operators, and these tradeoffs are much
more relevant to
> > > jitter,
latency
> > > and the such.
> > >
> > >
Offer Pazy
> > >
> > > Burlington, MA
> >
> Tel: (781)359-9099 x1907
> >
>
> > >
>
> > -----Original Message-----
> >
> From: owner-stds-802-17@xxxxxxxxxxxxxxxxxx
> > > [mailto:owner-stds-802-17@xxxxxxxxxxxxxxxxxx]
On Behalf Of
> > > Mike Takefman
> > > Sent: Monday, March 18, 2002 3:37
PM
> > > To: Yiming Yao
> > > Cc: 'hans-j.reumerman@xxxxxxxxxxx';
stds-802-17@xxxxxxxx
> > > Subject: Re:
[RPRWG] RAH: Re: Minutes of Rate Ad Hoc meeting
> > >
> > >
> > > Yiming,
>
> >
> > > speaking as a technical
expert,
> > >
> > > while I understand your desire to have LP packets
> dropped, be aware
> > > that 802 has never had a MAC that drops packets
from the medium
> > > except due to a
CRC errors.
> > >
> > > >From a compliance testing perspective, the
issue of packet drops
> > > would make
it difficult (if not impossible) to provide a test
> > > that proved compliance if packet drops were
allowed. Remember,
> > > if you can't
test for compliance, it is not a standard.
>
> >
> > > I believe that proper
use of reserved BW will remove any need to
>
> > drop packets. I look forward to seeing the simulation
results
> > > that show problems as a
part of the RAH.
> > >
> > >
> > > mike
> > >
> >
>
> > > > Yiming Yao
wrote:
> > > >
> > > > Hans,
> > >
>
> > > > The current draft of
the RPR standard tries to achieve several
>
> > objectives: high link utilization,
> > > > guaranteed minimum jitter for reserved HP
traffic, no
> packet loss on
> > > the ring, etc, and these
> > > > objectives are conflicting to each other
sometimes. One
> customer may
> > > want to disallow any LP
> > > > packet drop on the ring even this means high
jitter for the HP
> > > traffic;
another may want to
> > > >
guarantee minimum jitter to HP traffic (carrying TDM) at risk of
> > > occasionally dropping some LP
> > > > packets.
> > > >
> > > >
My suggestion is that RPR provide a choice for the
> customer to make
> > >
his/her decision in conflict
> > > >
resolution.
> > > >
> > > > I didn't assume the operator wants to adjust
the total
> > > load/throughput. Maybe
this can be done
> > > > more easily
if the above choice is provided.
> > >
>
> > > > Regards,
> > > >
> >
> > Yiming
> > > >
> > > >
-----Original Message-----
> > >
> From:
hans-j.reumerman@xxxxxxxxxxx
> > > [mailto:hans-j.reumerman@xxxxxxxxxxx]
> > > > Sent:
Friday, March 15, 2002 1:35 AM
> > >
> To: stds-802-17@xxxxxxxx
> > > >
Subject: [RPRWG] RAH: Re: Minutes of Rate Ad Hoc meeting
> > > >
> >
> > > Yiming Yao: allow customer
to choose between loss,
> > > jitter,
and
> > > utilization
> > > >
> > >
> Is the underlying assumption that the
operator of the ring
> > > (=customer?)
wants to
> > >
> adjust the total
load/throughput? Would this be for
>
> > loadbalancing purposes?
> > >
>
> > >
> regards,
>
> > > Hans
> > > >
> > >
>
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > > >
Hans-Jürgen Reumerman
> > >
>
Hans-J.Reumerman@xxxxxxxxxxx
> > >
> Digital Communications &
networking
> > >
pww.pfa.research.philips.com/dc/
> > >
> Philips Research Laboratories
> > > Phone: +49 241 6003 629
> > > > Weisshausstr.2,
52066 Aachen,
Germany
> Fax: +49 241
> > > 6003 519
> > >
>
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > >
> > >
--
> > > Michael
Takefman
tak@xxxxxxxxx
> > > Manager of
Engineering, Cisco Systems
> > > Chair IEEE 802.17 Stds WG
> > > 2000 Innovation Dr, Ottawa, Canada, K2K
3E8
> > > voice:
613-254-3399 fax:
613-254-4867
> > >
> > >
> > >
> > >
> >
> >
>
--------------------------------------------------------------
> --------------
>
------------------------
>
>
Name: WINMAIL.DAT
> >
WINMAIL.DAT Type: application/ms-tnef
>
>
Encoding: base64
>
> --
> Michael
Takefman
tak@xxxxxxxxx
> Manager of
Engineering, Cisco Systems
> Chair IEEE 802.17 Stds WG
> 2000 Innovation Dr, Ottawa, Canada, K2K 3E8
> voice: 613-254-3399 fax:
613-254-4867
>
>
>
_________________________________________________________
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