What is Diameter ? how it is better than Radius

Diameter is Advanced protocol than Radius
*  Its More Reliable uses TCP or SCTP               
*  Larger address space for attribute-value pairs (AVPs) and identifiers is 4 Bytes (32 bits instead of 8 bits)

Radius
*  uses UDP
*  identifiers is 1 Byte only 256 Attributes supported

---Remote Authentication Dial In User Service (RADIUS)
RADIUS server checks that the information is correct using authentication schemes like PAP, CHAP or EAP
NAS (Network Access Server (ASNGW) ) sends Access request to AAA

RADIUS -UDP ports
1812 for RADIUS Authentication and
1813 for RADIUS Accounting