Subject: ifSpeed on T1 and Frame Relay

From: Rob Steinberger <[email-masked]>
Date: Fri, 03 Apr 1998 14:38:10 -0500

All,

Sorry if this has been discussed in the IETF before, but it has become
a hot topic locally.

Should the ifSpeed for a T1 interface be 1.54Mb or should it be 3.08Mb
in that it can sustain 1.54Mb in both the transmit and receive
directions.  The same question holds for frame relay.  We are
currently reporting the number of DS0s times the rate of each DS0.
Should this be twice this number to account for its full duplex
nature?

Thanks for any responses.

Rob Steinberger
Paradyne Corporation

---

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.
>
>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

---

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

Art