Re: [RE] Proposal from Jose Morales
I can attest that the proposed scheme will work on wired networks. We use
essentially the same technique in our CobraNet real-time audio over Ethernet
technology.
-----Original Message-----
From: owner-stds-802-3-re@IEEE.ORG [mailto:owner-stds-802-3-re@IEEE.ORG] On
Behalf Of Jose Morales
Sent: Friday, November 12, 2004 3:38 AM
To: STDS-802-3-RE@listserv.ieee.org
Subject: [RE] Proposal from Jose Morales
All,
Dear friends, I would like to propose the following solution:
In order to obtain an isochronous network, we can use the following
strategies:
- Synchronize at physical/802.3 level.
This implies to modify all the network elements (switches), and to
use
new equipment in all the network.
- Synchronize at MAC/802.3 level. It can be origin of
incompatibilities.
- Synchronize in LLC/802.3 level .
The perfect place to do this, because it is is transparent to all
802.3
network,
and will work also over 802.11, 802.15, 802.16, etc.
For the synchronization of the network, could be used a technique
equivalent to
the one employed in 802.5, where all the stations have capacity to do the
synch
master, but only the active monitor does it, and all the others synchronize
with
him. Also I suppose that you know the mechanism which guarantees that there
is
always only one master synch, that would be the station with the lower value
in
the MAC address.
The system that I propose is very simple: The synch master station sends
periodically (for example each 20 or 100 milliseconds) a broadcast or
multicast
802.3 frame, containing one 802.2 that transports the time stamp (the value
of
the real time clock). All the isochronous stations can synchronize their
clock,
compensating the very small jitter that it would take place in the
transmission
of the consecutive frames.
The frame will look like this:
(The SAP=27 and 28, as far as I know, are not used in any other application)
|DA=Broad/Multicast | SA | LENGTH |
|DSAP=27|SSAP=27|UI(03)| TIMESTAMP|
|PAD|FCS|
Once synchronized all the stations, the isochronous traffic could be sent in
multicast with LLC type 1 protocol or in unicast with LLC type 2 protocol,
including in each frame the time stamp.
LLC2 protocol has many advantages, like the error and flow control
(end-to-end),
the identification of streams by means of P/F bit and that it would make
possible the congestion management. Remember that TCP protocol also have the
timestamp option, with 4 octes. It will be very useful to define the same
size
here.
The frame LLC2 will look like this:
|DA| SA | LENGTH |
|DSAP=28|SSAP=28| INFO|N(R)|P/F|N(S)|TIMESTAMP (4 octets)|DATA|FCS|
With the system I propose, we have "High quality synchronization services
that
provides all stations with a low jitter house clock". Now it is only
necessary a
802.3 switch that guarantees that "isochronous services can use up to 75% of
the
link bandwidth, while the remaining is always available to best-effort
traffic"
and "assign resources for isochronous services".
This system is exactly the one that I propose in the manuscript "Universal
Ethernet Telecommunications Service: The Convergence of Internet, Broadband
and
Telephone networks on the IEEE 802 standards". I have sent it to the IEEE
Communications Magazine and now is "Under Review", reason why I cannot pass
it
to the reflector.
Comments?
Jose Morales Barroso, Ph.D.
jmb@ieee.org