[afnog] Channelising E1s

Mark Tinka mtinka at globaltransit.net
Tue Jul 8 09:19:06 UTC 2008

On Tuesday 08 July 2008 14:55:31 muhump at mtn.co.ug wrote:

> Hi good people,
> I would like some help, when provisioning a customer who
> has requested for 512Kpbs i.e. 256K Up/256 Down, I
> allocate 4 timeslots i.e. 64k * 4 = 256K knowing this is
> full duplex so it becomes 256k * 2 = 512K. But my problem
> is; the customer doesn't seem to reach the whole 512K
> total Up and Down. My question is; should I be allocating
> 8 timeslots for a 256K UP / 256K DOWN customer to make
> sure there is a guaranteed 512K pipe? Or there is another
> problem I should investigate.

The time slot assignment is on a full duplex basis. If you 
assign a single TDM time slot, e.g., 64Kbps, it is both in 
and out. You cannot define total bandwidth by the sum of 
its symmetry (or asymmetry, for that matter) - which is to 
say, 64Kbps (in and out) doesn't mean 128Kbps because it's 
64Kbps up and 64Kbps down. It's just 64Kbps.

If you assign 8 time slots, you are effectively providing 
512Kbps, in either direction (not 1.024Mbps).

The question to ask is why the customer is unable to reach 
their full 256Kbps in either direction (assuming they are 
trying to).

Applications like Iperf, or a simple FTP session, 
end-to-end, will give you an idea of whether the full 
bandwidth utilization can be achieved or not.

Check that the line is clean, the customer routers (and your 
transit routers) are not dropping any packets on any 
interfaces, and that the routers are not busy doing 
something else that they can't focus on routing 256Kbps, 
full duplex.

Hope this helps.


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