Now add the classes

 # tc class add dev ppp0           \ 
   parent 1:1 classid 1:10 htb     \ 
   rate 10kbps ceil 50kbps burst 2k

 # tc class add dev ppp0           \ 
   parent 1:1 classid 1:11 htb     \ 
   rate 90kbps burst 2k          

The first class is guaranteed 10kbps of the 100kbps, but can grow to 50, if available. The second class however can take up to 90kbits.