I have not work experience over the diameter protocol but as per my knowledge there are mainly two types of AVPs known as IETF defined AVP and another one vendor specific.
Session Id AVP is defined by IETF and its command code value is 263.
Current-Location AVP is defined by 3GPP which is nothing but one of vendor and its command code value is 707.
There may be some other types of AVPs for diameter. Looking for other professionals to respond.