Hi There!
My name is Bernardo and recently have implemented MikroTik in all my network they have near 150 ADSL simultaneous connection on a level 5 running in a Pentium 4 based PC with 1Gb DDR. So really works fine, but got a little problemā¦ 
in some cases (very aleatory) some users (that have connected to a different DSLAM and different location) have this problem:
The connection bandwidth is go to zero, still there a few seconds (usually 10 or 20) and goes to the profile limit again (it happens in every profile, default, 512, 256, 1Mb, etc).
I have implemented PPPoE for connections, have path ping carefully implemented, queues for bandwidth managementā¦ and so much other beatiful mikrotikās tools.
Any one can help me with this problem?.. If need some details, please feel free to request me
Thanks in advance 
IĀ“m from La Plata too! 
In Spanish
Creo que puedo escribir en espaƱol ya que nos entendemosā¦
Yo empezaria por lo facil, tirale ping al cliente continuamente y fijate que pasa cuando no tiene transferencia, o sea, ver si en ese momento se pierden paquetes.
Otra cosa, revisa el CCQ de la seƱal del AP, por lo menos debe ser mayor a 40 y el signal strength de -40 para arriba como para decir que es un enlace acetable. Aca en La Plata es un asco la banda de 2.4ghz, yo tengo -84 de noise floor, eso tambien puede influir, dependiendo del tipo de placa que usesā¦
Te dejo mi MSN por si queres que nos pongamos en contacto: viroslash@hotmail.com
In English:
Make ping continuously to the client and see what happened when youĀ“re experimenting the problem.
If in this moment the link have a massive data lost, your problem should be in the wireless configuration.
Take a look at the data rates, TX Power (set it according to your minipci card), CCQ and Signal Strength
i think you missunderstood the question, coz he is not using wireless, but ADSL for last mile .