Subject: Re: ifSpeed on T1 and Frame Relay

From: [email-masked] (Art Berggreen)
Date: Fri, 3 Apr 98 14:14:50 PST

>
>The latest <draft-ietf-trunkmib-ds1-mib-08.txt> for the DS1-MIB is
>unambiguous on this point.  In section 3.1 it says to use 1544000
>for the ifSpeed for DS1 lines.
>
>> directions.  The same question holds for frame relay.  We are
>
>If a ds1(18) interface is used for Frame Relay, its ifSpeed will
>still always be 1544000.
>
>RFC 2115 says that the frameRelay(32) interface's ifSpeed is the
>"access rate for the frame relay interface" and then goes on to
>say that this "could be different from the speed of the underlying
>physical interface, e.g. in a fractional T1 case the access rate
>could be 384 kbits/s".  For a bundle of N DS0s, this would thus be
> N x 64000.

Interestingly, most T1s run channelized with a maximum user information
rate of 24X64000=1536000. Signalling and ones density often reduce this
to 24X56000=1344000.

The mib definition specifies the interface "bandwidth", which sure sounds
like user useable bandwidth to me.

But 1.544mb/s is probably too entrenched with the concept of T1s to
ever change this detail.

Art

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From: Gary Hanson <[email-masked]>
Date: Fri, 3 Apr 1998 15:57:15 -0800 (PST)

Hi Art,

On Fri, 3 Apr 1998, Art Berggreen wrote:

> [...]

This is certainly true.

> like user useable bandwidth to me.

I agree.  However, the bandwidth usable here is that usable by
the DS1 signal itself, which is 1544000.  The higher layers, of
course, cannot use all of this bandwidth, and thus they have a
lower ifSpeed value to report for themselves.

> But 1.544mb/s is probably too entrenched with the concept of T1s to

It certainly is an entrenched value, but that would not be a
detail that I would change.  Keeping it the way it is allows
the various levels of the stack to report the bandwidth that
they see "below" them (the bandwidth available to them, if
you will).  I would expect my DS1 physical links to report
its ds1 interface ifSpeed with the full DS1 bit rate.

> Art

Regards,
Gary

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From: Gary Hanson <[email-masked]>
Date: Fri, 3 Apr 1998 15:57:15 -0800 (PST)

Hi Art,

This is certainly true.

Regards,
Gary

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From: Gary Hanson <[email-masked]>
Date: Fri, 3 Apr 1998 15:57:15 -0800 (PST)

Hi Art,

This is certainly true.

Regards,
Gary