As far as the ISDN connectivity is required from MTNL, its not proven with best performance. The total bandwidth available with MTNL which is procured from the principle VSNL. This total bandwidth is shared over a larger ratio.
Normally the ratio of sharing the bandwidth among the users needs to be 1:4. In case of MTNL the sharing ratio is more than 1:8.
NOrmally all the users do not use the bandwidth at a one time. One can see the effect of bandwidth at peak hours when large number of users are logged in whether it is Dial up ISDN or any.
Hope the information is clear. If more info required pls write to me without hesitation
mapfin