1. Simplified X1 Protocol [1] X1 header always includes both MS/AT ID (RATI:ATI24 or UATI: ATI24) Target node ID (HRPD Sector ID) X1 header has Type indicator (T) T=0: Data  Only Data is included T=1: Control  Only Control messages are included SFF requirement Looks up IP address mapping table with MS/AT ID or Target Node ID in X1 header or A23 header, Forwards the packets with new source and destination IP address/port

2. Simplified X1 Protocol [2] X1 Header T( Type)  T=0: Data  T=1: Control MS/AT ID Type  ‘000’: Reserved  ‘001’: HRPD RATI  ’010’: HRPD UATI  ‘011’: (Reserved for WiMAX MS identifier)  ‘100’ - ‘111’: Reserved Target Node ID Type  ‘000’: Reserved  ‘001’: HRPD AN SectorID  ‘011’: (Reserved for WiMAX BS identifier)  ‘100’ - ‘111’: Reserved

3. Simplified X1 Protocol [3] X1 Control Messages X1 Control Message Types Error Notification Message Format  Error Cause Values