Re: [RE] Grand master identifier
Arthur,
Thanks for the timely response and inquisitive comments.
A few responses follow...
>> I don't think the end stations are involved in STP.
For selecting the grand master, the desire is to use the same
unique-number format as used in STP.
I think that would be the systemID concatenated with the
macAddress (when messages go between bridges). One would postfix
the portID also, when resolved within the bridge.
However, this part isn't all that readable, so a sanity check
on this perception would be helpful.
>> I am not sure whether you are inviting general feedback on your
>> working paper but I have some concerns.
Any comments from anyone are always welcome; that's why a contact
point is listed. Also, this typically decrease time-to-consensus.
>> You can get a lot of data through a conventional gigabit
>> switch with very low latencies.
An objective is to facilitate 75% time-sensitive utilization
on 100Mb/s links.
>> The RE traffic can be given a higher
>> priority and so not be held up by less urgent traffic.
If there is nothing preventing the cumulative time-sensitive
traffic from exceeding 75%, the problems remain.
Also, the annexes show how bursting and bunching still cause
problems, unless all ingress sources (and 100Mb bridges)
are well behaved.
>> With access control what happens if access is denied?
This one is more of a marketing question, so opinions
may vary. IMHO, the following.
If one is listening to high-fidelity music, the most likely
answer is to identify & stiffle you child's net-party
video games activities for the evening. Its a bit like
removing you teenager from the telephone, when you have
someone important to call...
That is better than having highFidelty==>lowFidelty.
Otherwise, apparently "defective" products are returned,
resulting in damaged product reputations and higher
distribution costs.
DVJ
>> -----Original Message-----
>> From: owner-stds-802-3-re@IEEE.ORG
>> [mailto:owner-stds-802-3-re@IEEE.ORG]On Behalf Of Arthur Marris
>> Sent: Monday, May 02, 2005 2:37 AM
>> To: STDS-802-3-RE@LISTSERV.IEEE.ORG
>> Subject: Re: [RE] Grand master identifier
>>
>>
>> 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
>>