[18278] in North American Network Operators' Group
Re: T1 Circuit actual throughput 1290Kbps
daemon@ATHENA.MIT.EDU (Lincoln Dale)
Thu Jul 9 00:55:18 1998
To: tonyh@noc.cbn.net.id
cc: nanog@merit.edu
In-reply-to: Your message of "Thu, 09 Jul 1998 10:44:26 +0700."
<19980709034534.AAA1627@wolfpack>
From: Lincoln Dale <ltd@interlink.com.au>
Reply-To: Lincoln Dale <ltd@interlink.com.au>
Date: Thu, 09 Jul 1998 15:37:49 +1000
In message <19980709034534.AAA1627@wolfpack>, Tony S. Hariman writes:
>Does anybody have experience having a T1 circuit with PPP
>encapsulation getting only 1290 Kbps maximum throughput looking
>at "sh int" result from cisco router or MRTG ?
A T1 is capable of achieving 1536 kbps maximum (24 x 64 kbps).
typically, the output shown both via snmp interface-counters
and from a cisco "show int" includes all of the associated
PPP framing.
bear in mind that the output of a "show int" by default
shows a 5-minute-exponentially-decayed average of the throughput.
this will 'smooth' out instantaneous traffic bursts and troughs.
the figure reported as a 'kbps' figure is most likely bursting
much higher than this.
>This is the explanation our upstream provider gave us:
>
>You have a 1.536Mbps port. However, there is the overhead from
>PPP and the translation overhead which takes place in all circuits.
>Judging by your settings that limit ends up somewhere between
>1.3 and 1.4. This overhead would be the non-data portion of cells
>or frames for example. For example, you might have 1.3 Mbps of
>data which gets framing or cell information appended onto it before
>sending taking up additional bandwidth. It is to be expected in all
>circuits.
PPP doesn't have much of the overhead of IP-in-ATM-cells
(fixed-cell-size, very-badly-chosen-prime-number-cell-size, ..)
that the discussion given to you by your upstream is talking
about.
what kind of traffic are you sending over the link ?
perhaps there isn't enough traffic / the traffic isn't of the
variety to actually fill the link capacity.
if its mostly TCP traffic, don't expect it to fill the whole
pipe all the time.
cheers,
lincoln.
