Abstract: Routing of packets in a packet cross-connect switch is determined based on the particular type of packet, i.e., statistical or periodic, grade of service assigned to the packet, e.g., minimum delay, the actual queuing delay at output assigned to the particular packet destination and the status of the assigned output ports. Additionally, for periodic type packets the routing decision is also based on whether an interval is reserved for transmission of periodic packets at the assigned output ports. The routing decision is also based under certain conditions on whether or not the packet has been previously scheduled over an alternate route. The actual queuing delay at the assigned output ports is compared to predetermined delay threshold values in determining the packet route and/or whether it should be discarded.

Abstract: A unique packet transport word, i.e., header, format is employed which eliminates the possiblity of particular packet transport words being mistaken for other transport words used in a private network, public network or otherwise. This is realized by employing a unique network reference code word to compute one or more prescribed parity checks over bits in predetermined bit positions of the transport word. The network reference code word is used to specify the sense, i.e., odd or even, of predetermined ones of the parity check bits being computed which form the one or more prescribed parity checks. Individual ones of such network reference code words are assignable to specific private transport users and, thereby, provide transparency of their transport words in the public or other networks.

Abstract: A unique packet format is disclosed including a unique transport word, i.e, header, and a number M of relatively short-fixed length information words. The transport word includes a packet size field indicating the number M of information words in the packet and a field indicating the number of bytes of information in the last word of the packet. Additionally, the transport word includes a field which indicates whether the number M of information words in the packet is greater than zero. If the number of information words is not greater than zero, any user information being transported is in a predetermined field in the transport word. In one example, the size field in the transport word is used to transport the user information when the number of information words is indicated as being zero.

Abstract: Packet synchronization is obtained by employing a unique packet transport word including at least one prescribed parity check pattern in conjunction with a packet length indicator. An at least one prescribed parity check is computed over transport word length blocks of bits of an incoming packet and compared to an expected parity check pattern in predetermined bit positions in the incoming block of bits to identify possible transport word candidates. Once a transport word candidate is identified the packet length indicator is used to point to the next transport word candidate. Synchronization is declared upon obtaining a parity match for a subsequent transport word candidate pointed to by the packet length indicator. In a specific embodiment, at least two prescribed parity checks are employed to denote a possible transport word candidate.

Abstract: Improved throughput is realized in a packet cross-connect switch by including an addressable memory unit in each of a plurality of input ports for storing packets and by allowing each of a plurality of output ports to address directly any one of the input ports to obtain a particular packet stored therein, which is destined for the output port. To this end, the input ports supply the packet destination and starting address of the packet stored in their memory to a scheduler. The scheduler controllably selects an output port assigned to the packet destination and supplies packet output information to the selected output port including the packet starting address and the identity of the input port storing the packet. When a particular output port is ready to obtain a particular packet, it addresses the memory unit in the particular input port to read the first packet word. The addressed packet word is supplied via a data bus to the requesting output port.

Abstract: A multiple queue packet bandwidth reservation arrangement is disclosed in which statistical type packets are scheduled for transmission and a prescribed interval is reserved for transmission of periodic type packets for each scheduled statistical packet. Each arriving statistical packet is assigned a scheduled time of service based on the amount of packet information already queued to be supplied as an output and the duration of any intervals reserved for transmission of periodic packets at an assigned output port. Operation of the bandwidth reservation arrangement is such that normally a statistical packet is not delayed from being transmitted at its scheduled time of service for more than an interval needed to transmit a maximum length periodic packet.

Abstract: A unique packet transport word, i.e., header, format is disclosed which is advantageously employed to delimit the corresponding packet and to verify data fields in the transport word. An at least first parity check is employed in conjunction with a packet length indicator to delimit the corresponding packet. The at least first parity check is formed by computing a predetermined number of parity check bits from bits in predetermined bit positions of the transport word. These parity check bits are inserted into predetermined bit positions in the transport word. Similarly, bits representing the packet length indicator are also inserted into predetermined bit positions of the transport word. In a specific embodiment, a plurality of parity checks is employed to achieve increased robustness. The plurality of parity checks is formed such that each of the bits in predetermined bit positions of the transport word is used in computing at least two different parity check bits.

Abstract: Various implementations of a technique are presented for capitalizing on signal correlation in a manner for providing usable frequency information. In a specific embodiment, a filter (51) is adapted to a signal component of an input signal using a variable generated by an adapter 58. The variable has a prescribed relationship to the frequency of the signal component. The variable is used to weight a combination of signal values derived from past signal history to form a prediction of a future signal. An adder 56 combines the new signal value with the prediction to form an error signal which is used by the filter (51) and the adapter (58). When the filter converges, a frequency indicator (59) using the variable provides an output signal indicative of the frequency of the signal component.

Abstract: A speech detector uses a signal classifier (19) to identify portions of a representation of the average magnitude of a group of signal samples indicative of either speech or noise. A controller (33) in the signal classifier follows a four state sequence using appropriate time constants for signal measures in a variety of signal conditions in defining the speech and noise portions of the representation. A level estimator (21) uses selectively obtained signal measures from the defined portions of the representation to provide adaptively variable decision levels. A speech definer (16) compares the representation to a first decision level and the signal samples to a higher decision level to indicate the occurrence of speech signal activity when either decision level is exceeded. In a two way transmission arrangement, a receive trunk speech detector uses a stretcher (133) to prevent adaptation of the transmit speech detector thresholds when echo signals are present.

Abstract: A speech detector uses a signal classifier (19) to identify portions of a representation of the average magnitude of a group of signal samples indicative of either speech or noise. A controller (33) in the signal classifier follows a four state sequence using appropriate time constants for signal measures in a variety of signal conditions in defining the speech and noise portions of the representation. A level estimator (21) uses selectively obtained signal measures from the defined portions of the representation to provide adaptively variable decision levels. A speech definer (16) compares the representation to a first decision level and the signal samples to a higher decision level to indicate the occurrence of speech signal activity when either decision level is exceeded. In a two way transmission arrangement, a receive trunk speech detector uses a stretcher (133) to prevent adaptation of the transmit speech detector thresholds when echo signals are present.