RE: [EFM] RE: EPON TDMA
Glen,
As a real world service provider that looks at a lot of different
technology issues I would like to wade in here. There is a growing concern
that the cost of deploying best effort services such as IP and fixed
bandwidth services such as Private Line. True, customers are wanting to
only pay best effort prices. More and more are recognizing that the
reliability and data stability are not good enough with the best effort
services to provide support for things like voice, or interactive
video. This is the reason that things like QoS are being attempted by IP
services. There is also the issue that services that statistical multiplex
at the customer data level, such as IP, simply can not provide the security
that are non-statistically multiplexed services do.
I think that the group would be good to pay attention to the fact that
several, if not all, of the legacy free vendors that are providing Ethernet
infrastructure based services are not "over subscribing" their service
bandwidth. In other words, to provide services to customer expectations,
bandwidth allocation is at a one for one ratio. In this case, there is no
benefit from statistical multiplexing other than slightly lower costs based
on commodity products used for data switching. The cost of the fiber and
other facilities remain the same, regardless of the service. The ability to
provide lower cost services is more in by-passing the ILEC than it is in
reduced equipment costs. The real cost savings to customers is more in the
reduced cost of their equipment to make use of Ethernet infrastructure
based services.
Having fixed time slots gives the service provider the ability to have
equipment vendors that provide technology for fully segregated customer
traffic similar to the traditional TDM service, or provide other, less
profitable services such as access to the Internet. If any of the EFM
technologies is to get wide deployment, they must be able to support the
high margin services as well as the low margin services.
Ethernet based infrastructure services have an inherent data stability that
is only exceeded by traditional TDM infrastructure services. I have had
conversations with several costumers of the current "legacy free" services
providers. They find that they do not need such things as QoS to support
voice applications. One customer stated that the cost of the level of
effort to implement QoS exceeded the benefits. This may be counter to what
is being pushed by some groups of people, but if you look at the low
"quality" of their protocols, I think you can understand.
As a service provider, I can support fixed time slots that are variable in
provisionable in quantity assigned to each customer. What the size of the
time slots are, how they much they can vary in quantity, and how is a
management channel provided in each time slot that does not use the
customers data traffic are issues that do need to be discussed.
Thank you,
Roy Bynum
At 05:20 PM 7/14/01 -0400, Ajay Gummalla wrote:
>Glen:
> I would not agree with your description that Stat Muxing and
>DBA are two different things.
>
>Stat Muxing can happen at different levels.
>The traffic from the behind the ONU (could be a LAN) is
>Stat Muxed in the ONU. This level of stat Muxing is obtained
>both by SBA (static bandwidth allocation) and DBA.
>The next level of possible Stat Muxing is between traffic from
>different ONUs. This can be obtained only by DBA. Our presentation
>and our traffic studies show that Stat Muxing between ONUs is
>important because even the data traffic after the first level of stat
>muxing is very bursty. As you can see in our presentation, simple DBA
>can provide 20-30% improvement (based
>on traffic type) over SBA schemes. I would further like to note that
>the efficiency numbers you show in your presentation can only
>be achieved only theoritically at infinite delay. It will be useful
>to the group show the delay of a TDMA based scheme as a function of
>efficiency.
>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.
>
>I also heard a comment in this thread that QoS is not within the
>scope of the project. Subscriber access is a new space for Ethernet.
>Ethernet never tried to support voice, video and data. It is necessary
>provide mechanisms in the EFM standard to provide some level of
>QoS support. I will try to make the case with an example. If a
>Voice packet arrives behind a large data packets, mechanisms to transmit
>voice packet ahead of the data packet will be useful. The arguement
>presented in this thread is that this should be performed above the
>MAC. How will a higher layer entity know the size and interval of the
>time slot for this ONU? How can one control the timing between a
>physical layer running at Gbps and a high layer running on a different
>clocks? These interfaces are important if different vendors are to
>implement different parts of the overall system and they are expected
>to interoperate. While we do not want to burden the standard with
>ATM like QoS we need some "lite" mechanisms to differentiate service.
>
>
>regards,
>Ajay