Date: Thu, 9 Jul 1998 10:18:51 -0400 (EDT) From: "Robert E. Seastrom" <rs@bifrost.seastrom.com> To: dorian@blackrose.org CC: ltd@interlink.com.au, tonyh@noc.cbn.net.id, nanog@merit.edu Subject: Re: T1 Circuit actual throughput 1290Kbps

From: Dorian Kim <dorian@blackrose.org>

...

A T1 is capable of achieving 1536 kbps maximum (24 x 64 kbps).

While this doesn't seem to apply to Tony's case, I wouldn't make a blanket statements like that. If the T1 is provisioned ESF, yes you can get 1536 kbps, but there are places where you still can only get SF/D4 framing.

Precisely. The most likely explanation is that the T1 is actually D4 framed, which gives it a throughput of (24 * 56kbps) == 1344k. Or the T1 may be properly provisioned but the CSU/DSUs incorrectly configured for the old-fashioned framing (I think I saw this working at one point, can't remember for sure). The PPP is hardly eating anything at all in the grand scheme of things.

---Rob

It isn't D4 or ESF framing that causes a loss in usable bandwidth on a T1, but AMI line coding. As stated above, when using AMI line coding, the T1 will not be provisioned for clear channel (64k) DS0s, but will be provisioned for 56k DS0s, thus providing an aggregate bandwidth of 1344 kbps. The least significant zero of each DS0 is forced to a 'one', thus insuring correct ones density on the line. The better solution is B8ZS coding, which allows full use of each DS0's bandwidth. Inverting the data on the router won't give you back the "lost" 192 kbps of bandwidth, since you're still limited to using 56kb/s of each DS0. -rb Ron Buchalski SE, Cisco Systems ______________________________________________________ Get Your Private, Free Email at http://www.hotmail.com