Abstract: Round trip travel time of cells in an asynchronous transfer mode (ATM) communication network is measured by injecting a time stamp into test cells in a first test instrument, transmitting these test cells to a remote node in the network, looping the test cells back from the remote node to an originating node, and detecting their arrival. Preferably the time stamps are injected into test cells configured as OAM-PM (operation, administration, and maintenance performance management) cells. A time-of-departure stamp is injected into the payload of the test cell on transmission, and a time-of-arrival time stamp is appended upon its receipt. The time-of-arrival and time of departure time stamps are compared to determine the actual round trip travel time of the cell within the network. This information can then be used to optimize network traffic flow, especially for available bit rate virtual connections.

Abstract: A test instrument for monitoring operation of ATM communication networks is capable of identifying individual cells passing through a node to which the instrument is connected as belonging to a particular virtual connection, and transmitting test cells replacing the identified cells, transmitting modified identified cells, or augmenting cells transmitted over the identified virtual connection with operations, administration, and maintenance cells. Specific test cells can be detected by a second test instrument connected to a node elsewhere in the network for accurately monitoring specific network operating characteristics. Cell delay, cell delay variation, cell error rates, and the like may all be monitored by the test instrument according to the invention.

Abstract: An instrument for identifying the types of individual cells in a stream of ATM cells by individually examining the cell header and cell payload information of each cell. A microprogram within a microsequencer is vectored responsive to each cell type for updating appropriate statistical counters. Identification of individual cell types by examination of their cell headers on networks operating at speeds of up to 622 Mbps allows numerous network utilization statistics of interest to be gathered.

Abstract: A test instrument for measuring the rate and size of bursts of cells received at a given node of an ATM network with respect to a particular virtual connection includes a cell filter for identifying cells belonging to the virtual connection. The "leaky bucket" algorithm is implemented for determining conformity with contractual performance standards, and for delineating the bursts.