See sections on "ITU-T I-Series Recommendations" and "ITU-T Q-Series
Recommendations" for ITU-T recommendations on frame relay, including:
I.122: Framework for frame mode bearer services
I.233: Frame mode bearer services
I.233.1: IDSDN frame relaying bearer service
I.233.2: ISDN frame switching bearer service
I.370: Congestion management for the ISDN FR bearer service
I.372: FR bearer service network-to-network interface requirements
I.620: Frame relay operation and maintenance principles & functions
Q.922: Data link layer spec for the frame mode bearer services
Q.933: Signalling spec for frame mode SVC and PVC control & status