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[EFM] RE: [EFM-OAM] Performance monitoring, installation, trouble shoot ing.


Thanks for your feedback.

I think I did not make it clear in my e-mail as to what the support of
802.1D user_priority really meant. In deed, I was thinking about the
priority queuing mechanism as you mentioned in your e-mail. An example will
be for Ethernet packets with different user_priority bits be stored in
queues with different priority for transmission. Yes, it can be an
implementation issue. But, without providing guarantee on delay and delay
variation for the EFM-cu link, EFM-cu will not be acceptable to support
certain applications.

Currently, DSL uses ATM QoS on a per VC basis to prioritize data traffic
from multiple applications. As a result, the quality of VoAAL2 is comparable
to toll quality. It is my understanding that EFM-cu is intended to eliminate
the overhead and complexity of ATM, but we should not compromise on QoS.

I agree with you that higher speed can alleviate the problems, but priority
queuing and data fragmentation are still required, because vocie packets
can't wait during the DVD downloading.

Joey Chou

-----Original Message-----
From: carlosal@xxxxxxxxxxxxxxxxxx [mailto:carlosal@xxxxxxxxxxxxxxxxxx]
Sent: Wednesday, January 23, 2002 6:45 PM
To: Chou, Joey
Cc: Geoff Thompson; bob.barrett@xxxxxxxxxxxxxxx; mattsquire@xxxxxxx;;
Subject: RE: [EFM-OAM] Performance monitoring, installation, trouble
shoot ing.


As you said:

> I thought there should be a need for an OAM requirement to support
> 802.1D user_priority bits to prevent voice packets from blocking
> by huge Ethernet data packets.

Assuming that the typical speed of the EFM link is going to be very high,
this blocking effect is not really an issue, as it can be solved with good
queue management. That's an implementation issue. For low speed links, this
is a serious problem, because it takes a long time to transmit a big frame.
The Frame Relay Forum took specific measures to avoid this situation; for
examplo, big frames may be fragmented before transmission. It's better to
avoid fragmentation, though, as it's a complex implementation that presents
its own set of issues to be solved.

That said, it's important to state that this is not enough to solve all
issues related to the support of TDM emulation services over EFM. Speed is
good, and may help a lot by avoiding the need for complex mechanisms such
as fragmentation, but there are other issues to watch out, specially in the
case of the P2MP implementation.

Carlos Ribeiro
CTBC Telecom