Abstract: TDM (time division multiplexed) traffic is transported together with a TDM performance monitoring channel over a ATM (asynchronous transfer mode) network. The TDM traffic is segmented at ingress to the ATM network and is packed as payload data into ATM cells. Each cell payload is provided with an AAL1 segmentation and reassembly protocol data unit (SAR-PDU) containing a channel state information (CIS) field, a sequence number field, and a sequence number protection field. A performance monitoring channel is provided by utilising spare bits in the CIS field in alternate cells. On egress from the ATM network, the sequence number protection and performance monitoring data provide a means of identifying both missing and corrupted cells so as to determine a measure of the quality of transport of the TDM traffic over the ATM network. The measured transmission quality may be compared with service levels defined in a service level agreement.

Abstract: A method and apparatus is disclosed for providing an interworking function to interface a frame relay LAN to an ATM network. Data from a broadband packet switched data data communications network which uses data packets of a fixed size is transferred to a narrow-band packet switched network which uses data packets of variable size by queuing input fixed length data packets data packets of variable size; processing the data payloads of said input data packets received from said queue to line-encode said data so it may be transmitted in said data packets of variable size; and generating output fixed length data packets of the same size as the input fixed-length data packets for transmitting said processed data payloads to a fixed-length to variable lengh data packets conversion device.