The Convergence Sublayer (CS) is a sublayer of the ATM adaptation layer. The CS sublayer supports procedures and functions for converting ATM to non-ATM formats, such as converting ATM protocols to Frame Relay or Switched Multimegabit Data Service (SMDS).
The CS sublayer receives a Service Data Unit (SDU) and extends it with a header and a trailer according to the protocol. The resulting Protocol Data Unit (PDU) is passed to the Segmentation Sublayer (SAR). The CS sublayer has been further subdivided for ATMAdaptationLayer (AAL) 3/4 and AAL -5 into a part containing common functions for a group of services, the Common Part Convergence Sublayer (CPCS), and an application-dependent part, the Service Specific Convergence Sublayer (SSCS).depacketization effects as well as transmission errors in the form of incorrectly inserted or lost ATM cells.