Ascend Archive
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: (ASCEND) Suggested LQM settings?

> I've been playing with this, and I KNOW I'm shooting in the dark
> with the settings. What do all you folks use for LQM settings?
> And why?

There are three paramters for LQM in the Answer profile: "LQM", "LQM Min",
and "LQM Max".  You should set "LQM" to "Yes.  You should set "LQM Min" to
"500".  You should set "LQM Max" to be "1500".

The reason for the values is so that the average value, which is the value
that the MAX will request, is exactly 10 seconds (e.g., 1000).  The average
value should be 10 seconds so that it agrees with the majority of other PPP
implementations (Cisco, Morning Star, etc.)  The minimum value should be
picked so that LQM will not be allowed to consume a significant portion of
the bandwidth.  The "LQM Max" value should be calculated based on the Min
and average values desired.

The size of an LQR packet is 52 bytes (48 bytes data, 4 bytes header).
Each packet will need a response of equal size.

Assuming a 9600 bps link and a 5 second interval, the Link Quality Reports
will not consume a significant portion of the bandwidth.

  (52 bytes * 2) * 10 bits per byte * 100 / 9600 bits per second * 5 seconds

Only 2.2% of the total bandwidth will be used for LQM, which is quite
reasonable for the benefit.

> Along the same lines, feedback on where to use it would be great too.
> Is it appropriate for modem, ISDN, T1 links?

Yes, it is appropriate for modem, ISDN, and T1 links.

LQM is very useful in detecting Data Link Layer problems.  The Internet
standards (RFC 1662 "Recommended LCP Options") recommend the use of Link
Quality Monitoring.  It is appropriate for modem, ISDN, or T1 links.

> Is it helpful/harmful for all link types?
> Or only specific situations?

It is helpful for all links, in all situations.  It is able to detect
problems such as line loops (which can occur on T1 lines) and misconfigured
modems (where the link has failed but carrier has not dropped or the
flow control between the serial port and the modem are mismatched) and
bad cables (DCD or RTS not connected).

> What about client platform, in the case of modem/ISDN TAs?
> Should/must it also be enabled on the remote device?

It is best enabled on both sides of the link using the same values.

> > 2. You should specify a minimum and maximum LQM range including 10
> > seconds - this is required by Cisco's PPP implemention for instance.
> 
> Yeah, but WHAT? 600 and 100? My question was- it don't seem to matter 
> WHAT you set it to. So WHAT should you set it to? I know all about
> Cisco's brain-damaged 10-second thingie and could care less- like most 
> of the list, we have MAINLY dialup>consumer>genericmodem issues here.
> 
> SO. What do we set LQM to? or does NOBODY know?

I would recommend reading over the appropriate PPP documents.  For information
on the recommended options, see RFC 1662.  For information on using the Quality
Protocol, check RFC 1989.  For more information on using LCP Echo Requests for
quality monitoring when the quality protocol is refused, see RFC 1172.
++ Ascend Users Mailing List ++
To unsubscribe:	send unsubscribe to ascend-users-request@bungi.com
To get FAQ'd:	<http://www.nealis.net/ascend/faq>