Relationships between application layer protocols in softswitch are explored . Two concepts, i .e ., protocol relationship and protocol grouping , are proposed .On the basis of a well-known protocol relationship named protocol conversion , three novel protocol relationships including protocol collabo ration relationship , protocol cooperation relationship and protocol independency relationship are presented , so that protocol relationships are classified into four t pes .According to the functionality and purpose of each protocol , main protocols related to softswitch are divided into five groups.A theorem of protocol relationships in softswitch is induced from all kinds of service scenarios of softswitch .This theorem summarizes protocol relationships within each protocol group or between each two protocol groups .A merit of protocol grouping together with classification of protocol relationship is also presented .

protocol engineering , softswitch , protocol relationship , protocol grouping ,