RE: [EFM] Necessity of DBA mechanisms ...
Roy,
QoS implementation typically relies on layer 2 mechanisms - RSVP is the
signaling protocol that is layer 2 independent. The actual scheduling part
of QoS relies on Layer 2 specific implementation. With shared access
networks such as ePON there has to be a way to schedule transmissions for
competing traffic flows. As such, QoS cannot be implemented at Layer 3
alone.
QoS allows precise differentiation among these competing traffic flows down
to the application flow level, if needed. Without this differentiation, all
application flows get the same (i.e. best effort) treatment. Hence the low
margin service common denominator.
You can certainly throw additional bandwidth to resolve the QoS issues.
However, this does not scale, especially on subscriber access networks which
typically see substantial oversubscription to be economical.
Harry
-----Original Message-----
From: Roy Bynum [mailto:rabynum@xxxxxxxxxxxxxx]
Sent: Wednesday, July 18, 2001 7:47 AM
To: Harry Hvostov; Harry Hvostov; Harry Hvostov; Harry Hvostov; 'Menard,
Francois'; Ajay Gummalla
Cc: stds-802-3-efm@ieee.org
Subject: RE: [EFM] Necessity of DBA mechanisms ...
Harry,
I think that you have just validated my argument. You are looking at a
higher layer protocol, not Ethernet. In the RFC that you reference, the
timing is about how a RSVP message functions and times out. It has
absolutely nothing to do with the reliability or stability of a customer's
data inside of a subscription service network.
Over the last two years, several companies, referred to as "legacy free
service providers", that have started to provide services over GbE as the
service infrastructure. There are more than one. Each uses a different
vendor's data switches for equipment. The only common denominator is that
they use dark fiber access to by-pass the ILEC. They provide Ethernet VPNs
using VLAN tags to transport IP protocol traffic. Their infrastructure
costs are very close to what any CLEC would have to do a dark fiber by-pass
of an ILEC copper facility. This is a low cost, low margin service. Over
the existing legacy free service providers' infrastructure, a customer can
receive service that has a very low data loss, as little as 10-8 data
frames lost per second. Over the existing legacy free service providers'
infrastructure, a customer can receive a service that has a very low data
in-stability, as low as 500us of latency variance end to end over the
service provider network. This is achieved without the need for QOS.
QOS should not be part of the discussion of the technology requirements for
EFM. QOS, if it is implemented should be done at a higher layer in the
service stack. I believe that, like the GbE service infrastructures, if
EFM technology is done correctly, then QOS will not even be needed at the
higher service layers.
Thank you,
Roy Bynum
At 10:35 AM 7/17/01 -0700, Harry Hvostov wrote:
>Roy,
>
>Check out the IETF RFC-2205 RSVP Flow/TSpecs for definition of data
>latency/jitter bounds for traffic flows over IP networks.
>
>I am not sure what you mean by unstable infrastructure. DOCSIS transports
>Ethernet transparently with up to 2,000 subs per downstream channel -
rather
>stably.
>
>Harry
>
>
>-----Original Message-----
>From: Roy Bynum [mailto:rabynum@xxxxxxxxxxxxxx]
>Sent: Tuesday, July 17, 2001 10:26 AM
>To: Harry Hvostov; Harry Hvostov; Harry Hvostov; 'Menard, Francois';
>Ajay Gummalla
>Cc: stds-802-3-efm@ieee.org
>Subject: RE: [EFM] Necessity of DBA mechanisms ...
>
>
>Harry,
>
>The only reason that unsolicited grant service is used for VoIP today is
>that it is running over an infrastructure that does not have any inherent
>stability. I could be wrong, but as far as I know, none of the IETF
>standards have specifications for data jitter(data latency variance), or
>data loss. The Internet today can have a data latency variance as great as
>200ms. GbE has an inherent data latency of 12us. TDM latency variance is
>measured in ps. If this group was only going to produce another Internet
>quality infrastructure, then they are wasting their time.
>
>Thank you,
>Roy Bynum
>
>At 12:13 PM 7/16/01 -0700, Harry Hvostov wrote:
>
> >Roy,
> >
> >By definition, unsolicited grant service is used to enforce stringent
>packet
> >jitter and delay constraints for isochronous traffic flows such as VoIP.
>The
> >requests are implicit, resulting in additional b/w conservation.
> >
> >Fundamental to this is the process of traffic flow admission, based on
the
> >parameter set which specifies concrete inter-packet jitter and delay
> >constraints. In other words, two or more active traffic flows on the
shared
> >link imply that the jitter and delay bounds are met for all of them
> >simultaneously.
> >
> >Harry
> >
> >-----Original Message-----
> >From: Roy Bynum [mailto:rabynum@xxxxxxxxxxxxxx]
> >Sent: Monday, July 16, 2001 10:54 AM
> >To: Harry Hvostov; Harry Hvostov; 'Menard, Francois'; Ajay Gummalla
> >Cc: stds-802-3-efm@ieee.org
> >Subject: RE: [EFM] Necessity of DBA mechanisms ...
> >
> >
> >Harry,
> >
> >Actually, I have exactly the opposite point. I am less concerned about
> >overall latency than I am latency variance. Unsolicited grant service
will
> >vary the latency based on the grant requests from the other UNIs as
> >well. This causes an overall lack of predictability and
pre-determination
> >that can not be defined very well in a high margin service SLA.
> >
> >Thank you,
> >Roy Bynum
> >
> >At 10:48 AM 7/16/01 -0700, Harry Hvostov wrote:
> > >Roy,
> > >
> > >Precisely my point. Interpacket jitter is hard to control if ONUs are
> > >allocated time slots based on the network split ratio rather than the
> >period
> > >that the G.7xx vocoder requires. An example of dealing with this is
>DOCSIS
> > >unsolicited grant service that places strict bounds on packet delay and
> > >jitter by enforcing slot allocations of appropriate size and period.
> > >
> > >Harry
> > >
> > >
> > >
> > >-----Original Message-----
> > >From: Roy Bynum [mailto:rabynum@xxxxxxxxxxxxxx]
> > >Sent: Monday, July 16, 2001 10:20 AM
> > >To: Harry Hvostov; 'Menard, Francois'; Ajay Gummalla
> > >Cc: stds-802-3-efm@ieee.org
> > >Subject: RE: [EFM] Necessity of DBA mechanisms ...
> > >
> > >
> > >Harry,
> > >
> > >VoIP, uncompressed, uses less than 1 Mbps of bandwidth. The real
problem
> > >with VoIP is latency variance. More often than not, IP vendor throw
> > >excessive bandwidth into the mix to provide low utilization and that
have
> > >low base latency and hopefully reduce latency variance to address this
> > >issue. Having as much as 50Mbps with the low latency variance that
> > >Ethernet traditionally has will provide more than bandwidth for even
> > >broadcast quality interactive video applications that are even more
> > >sensitive than voice.
> > >
> > >Thank you,
> > >Roy Bynum
> > >At 09:49 AM 7/16/01 -0700, Harry Hvostov wrote:
> > >
> > > >Francois,
> > > >
> > > >I agree that P2P topologies may not present the DBA challenge.
> > > >
> > > >However, wasting 20% on a Gigabit link represents 200 Mbps - compared
>to
> >2
> > > >Mbps on HFC. Hence the need to use intelligent b/w allocation on ePON
> > > >remains.
> > > >
> > > >VoIP will require the use of various compression algorithms, not just
> > >G.711.
> > > >Hence, the ePON link will need to support isochronous traffic with
> > >arbitrary
> > > >periods. This requires dynamic b/w allocation, not a rigid TDM
scheme.
> >The
> > > >same applies to IP video with its periodic variable size grant needs.
> > > >
> > > >B/w overhead associated with dynamic requests can be further reduced
if
>a
> > > >traffic flow parameters are described a priori. An example is an
> > >isochronous
> > > >traffic flow which requires
> > > >grants of fixed size at periodic intervals - without explicit
requests
> >sent
> > > >by ONUs.
> > > >
> > > >In addition, the request/grant scheme offers direct feedback of ONU
> >state,
> > > >including such critical measurements as queue occupancy.
> > > >
> > > >In general, I have a feeling that those of us familiar with DOCSIS
tend
> >to
> > > >favor the dynamic request/grant protocol approach, while those that
are
> > >not,
> > > >favor reinventing the wheel.
> > > >
> > > >Harry
> > > >
> > > >
> > > >-----Original Message-----
> > > >From: Menard, Francois [mailto:f.menard@xxxxxxxxxxxxxx]
> > > >Sent: Monday, July 16, 2001 7:24 AM
> > > >To: Ajay Gummalla
> > > >Cc: stds-802-3-efm@ieee.org
> > > >Subject: RE: [EFM] Necessity of DBA mechanisms ...
> > > >Importance: High
> > > >
> > > >
> > > >
> > > >Ajay wrote: > It seems to me that there is a consensus in this group
>that
> > > >dynamic adaptation is required though there are differences on how
> > > >exactly and on what time scale the adaptation is done.
> > > >
> > > >Ajay,
> > > >
> > > >In EFM, there are 3 issues, and DBA may only apply to only one of the
> > >three:
> > > >
> > > >Issue #1) For P2P EFM, DBA is clearly not an issue.
> > > >Issue #2) For P2P EPON, DBA is clearly not an issue
> > > >Issue #3) For P2MP EPON, DBA may be an issue,
> > > >
> > > >For those of us not seeking that IEEE wastes time delaying issues 1
and
>2
> > >in
> > > >order to develop products surrounding issue #3, saying that there is
> > > >consensus in this group that DBA is required is not accurate. Saving
>20%
> > >of
> > > >bandwidth at Gigabit speeds is not as crucial as saving 20% of
>bandwidth
> > > >over bandwidth-limited HFC systems. The complexity and costs
>associated
> > > >with shielding DBA head-end grants with security mechanisms
protecting
> > >them,
> > > >do not represent, in my view, an effort that is worth the costs of
more
> > > >expensive CPE and head-end equipment for EFM.
> > > >
> > > >My personal agenda with EFM is being distracted by those seeking DSL
>EFM
> > >and
> > > >those seeking the development of P2MP EPON. I do not claim however
>that
> > >one
> > > >of my specific issues represent "consensus in this group". One of
the
> > >merit
> > > >of dealing with all EFM issues as a whole right now is that we can
> >discern
> > > >what constitutes consensus from what does not. We agree that minimal
> > > >modifications to the MAC for O&M to indicate link failures and signal
> > >levels
> > > >are a good idea. We also agree that single-strand tranceivers are
>worth
> > > >standardizing. While we have discussed this, little discussions
>surround
> > > >how 802.1s/w/x will integrate to EFM. We need to look at this from a
> > > >systemic point of view. While mine surrounds FTTx P2P EFM, others
may
> >have
> > > >different priorities for different markets. I am willing to consider
> >that
> > > >issue #1 is being delayed, but not at the expense of seeing claims of
> > > >consensus being reached on issues which I think have nothing to do
with
> > > >ensuring the development of cost-effective FTTx P2P EFM products.
> > > >
> > > > > If a Voice packet arrives behind a large data packets, mechanisms
to
> > > >transmit
> > > >voice packet ahead of the data packet will be useful.
> > > >
> > > >A G.711 packet arriving behind a 1500 bytes data at one megabit per
> >second
> > > >is clealy not the same than a G.711 packet arriving behind a 1500
bytes
> > > >packet at one gigabit per second.
> > > >
> > > >-=Francois=-