Re: [RE] Grand master identifier
Hi Hugh:
I am not aware of any low cost standardized methods for provisioning,
admission control, policing and QoS which work together to satisfy
the requirements of RE. The consumer electronics definition of low
cost is NO INCREMENTAL COST.
My understanding of the 2 most basic RE requirements:
1. We need a low cost way to ensure that the traffic for one
application does not interfere with the timely delivery of all
traffic for another application.
2. We need a low cost way to ensure a very low max latency (250 usec
per hop) for all traffic of a specific application.
My comments on current mechanisms for this in 802.3:
A. There is no mechanism in 802.3 to ensure requirement #2 will be
met in every case, across various implementations.
-Overprovisioning cannot provide such a guarantee as more
applications are added to the network.
-There is no admission control system for 802.1D priorities.
Of course, higher layer protocols (Layer 3+) could be used for
admission control, but at considerable cost and added risk to
interoperability.
B. There is no mechanism in 802.3 to ensure requirement #2 will be
met in every case, across various implementations.
John Gildred
Pioneer Electronics
On May 5, 2005, at 2:53 PM, Hugh Barrass wrote:
> Arthur,
>
> It is definitely the case that many things become easy with over
> provisioning and simple QOS. However, the term "over provisioning"
> has two key elements: "over" implies that you must set a level of
> usage that is not exceeded. This may be 75% of link b/w as has been
> suggested, it may be lower to enable better statistical behavior.
> In any case, there is a level at which "over" is no longer
> satisfied. Secondly there is "provisioning." There needs to be a
> mechanism to guarantee that the QOS will work as required. This
> generally takes the form of admission control and/or policing.
>
> Personally, I believe that the existing standards for provisioning,
> admission control, policing and QOS could be implemented easily and
> cheaply in a residential environment. If this is not the case, then
> proof should be presented to make a case for new standards. Either
> way, I think there is a need for some architectural specification
> to ensure that RE products have appropriate capabilities to allow
> plug in and go operation.
>
> Hugh. < speaking strictly for myself >
>
> Arthur Marris wrote:
>
>
>> David,
>> I am not an STP expert but my understanding is that spanning
>> tree is
>> used by bridges to find out which of their ports are connected to
>> other
>> bridges. The protocol then determines a root bridge and shuts down
>> redundant links to make sure there are no network loops. As I
>> understand
>> it the MAC address is for the bridge rather than the end station. I
>> don't think the end stations are involved in STP.
>>
>> I am not sure whether you are inviting general feedback on your
>> working paper but I have some concerns. It assumes that there will be
>> access control, bandwidth allocation and time slots for transmission.
>>
>> Is bandwidth allocation really necessary to meet RE requirements?
>> Over-provisioning and best-effort (with class of service) may be
>> adequate. You can get a lot of data through a conventional gigabit
>> switch with very low latencies. The RE traffic can be given a higher
>> priority and so not be held up by less urgent traffic.
>>
>> With access control what happens if access is denied? My assumption
>> is that a user connecting to a RE network would prefer best-effort
>> service to no service at all if there is no spare bandwidth to be
>> allocated. If you decide you need to support best-effort as a
>> fallback
>> then you need buffers in your end stations and the reason for
>> using time
>> slots goes away.
>>
>> Arthur.
>>
>> -----Original Message-----
>> From: owner-stds-802-3-re@IEEE.ORG [mailto:owner-stds-802-3-
>> re@IEEE.ORG]
>> On Behalf Of David V James
>> Sent: 29 April 2005 22:20
>> To: STDS-802-3-RE@LISTSERV.IEEE.ORG
>> Subject: [RE] Grand master identifier
>>
>> All,
>>
>> I was starting to update a group-contribution working paper,
>> when a couple of questions arose. For reference, these questions
>> are with respect to:
>> http://www.ieee802.org/3/re_study/material/index.html
>> Subclause 5.2.
>>
>> We assume that the grand master is selected by picking one
>> of the clock-master capable stations. To do this, IDs need
>> to be distributed externally (between bridges and stations)
>> as well as internally (between bridge ports).
>>
>> To avoid invention, we assume the existing STP identifier
>> format should be used (why be different?). The format, not
>> the actual values; an grand master could be different from
>> the STP root.
>>
>> My original assumption was that the precedence value,
>> transmitted between stations, consists of:
>> 16 bits -- system
>> 48 bits -- MAC address
>> 16 bits -- port
>>
>> Having started to write things in more detail, it seems
>> like the port information need only be used within a
>> bridge, and need never appear on Ethernet.
>>
>> Pardon my asking, but the appropriate 802.1 documents are
>> not that easy for me to read. Am I correct in my recent
>> thoughts, that the port portion of this identifier is
>> only used within the bridge, and never appears on the outside?
>>
>> DVJ
>>
>>
>