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.