Even it is not in the list of DBA's responsibilities essentially, time to time you may be asked for the required bandwidth value for your database. It could be for capacity planning of the WAN line between primary and disaster recovery sites or calculating traffic towards database by means of data streams etc.

Besides various networking tools, it is possible to calculate amount of data generated by monitoring usage of redo logs. Actually this is the suggested way to find out required bandwidth for Data Guard installations by Oracle.

The  metric to calculate bandwidth is "Redo Generated Per Sec". You can schedule a job that collects statistics regularly, say hourly. Script below inserts maximum and average values of the metric into a table with time stamp:

insert into bandwidth
     select sysdate, max(value) as max_val, avg(value) as avg_val
     from gv$sysmetric_history 
     where metric_id = 2016

The formulation to calculate bandwidth is:

Required bandwidth = ((Redo rate bytes per sec. /  0.7) * 8) / 1,000,000 = bandwidth in Mbps

Since you have collected enough data, you can figure out the peak and average bandwidth:

   ((max_val/0.7)*8)/1000000 as peak_mbps, 
   ((avg_val/0.7)*8)/1000000 as average_mbps
from bandwidth;