Re: [RE] Grand master identifier
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
>
>
>