module inserts sequence numbers into outgoing frames replicates the outgoing frames for forwarding to each of said switch modules and monitors incoming frames from each of the switch modules to select frames for forwarding to an application based on the sequence numbers in this way redundancy is maintained at all times while duplicate frames are eliminated at the receiving module application_number US 66830907 A description fig1 depicts a chassis based data communication device the system consists of a series of modular components the chassis 100 the backplane 107 add in cards 101 104 and switch cards 105 106 more or less add in cards 101 104 can be utilized without affecting the invention described the chassis 100 is typically a metal enclosure suitable to be rack mounted in a data center or central office it houses the backplane 107 and provides mechanical alignment power cooling and other basic services to the cards 101 106 the backplane 107 is a circuit card different from other common circuit cards it has very few if any active components the primary components of the backplane 107 are connectors the connectors are arranged in slots or banks each slot would typically be used to house a single add in card or switch card 101 106 the backplane 107 provides a series of communication links 108 between the slots a communication link 108 typically consists of one or more electrical connections but optical variants are also possible it may be unidirectional or bidirectional the topology of these communication links 108 on.