The Cisco MGX Service Resource Module-Enhanced Model B provides three major functions for service modules: bulk distribution of T1 and E1 traffic, bit error rate testing (BERT) of T1 and E1 lines and ports, and 1: N redundancy.The Cisco MGX SRME/B is an enhanced version of the existing Cisco MGX SRM, operating at line speeds of OC-3 or T3. The Cisco MGX SRME/B provides the existing functions of the Cisco MGX SRM 3T3/C, such as bulk distribution, 1: N redundancy, and BERT. It supports either one SONET or SDH interface using SMFIR-155 (optical) and SMB-155 (electrical) back cards or three T3 interfaces using SMB back cards.