The formula N(N-1)/2 calculates the number of connections needed for a full mesh.
5 routers for example need 10 pvc’s for the full mesh. 5*4/2=10.
It’s easier to make a table and write down the connections first before configuering frame-relay.
For example here are the serial interfaces with the dlci.
S1 Â Â Â S2Â Â Â Â Â S3 Â Â Â S4Â Â Â Â Â S5
101—201
102 ———-301
103 ——————-401
104 —————————501
——–202–302
——–203———-402
——–204——————-502
—————-303–403
—————-304———–503
———————-404—–504
So if you have configured Router1 with
int s0
encap frame
frame-relay interface-dlci 101
frame-relay interface-dlci 102
frame-relay interface-dlci 103
frame-relay interface-dlci 104
and so on with the other routers r2,r3,r4
your have to configure the siwtch like this:
frame-relay switching
conf t
int s1
encap frame
frame-relay intf-type dce
frame-relay route 101 serial 2 201
frame-relay route 102 serial 3 301
frame-relay route 103 serial 4 401
frame-rleay route 104 serial 5 501
and so on with the other router, like in the table configured before.