Abstract: A timing source is provided for sending timing information via a packet network. The source comprises a first clock for generating the timing information and a packet forming section for forming a sequence of packets. An output section in the form of a packet launch control section transmits the packets via the network as packet bursts, each of which comprises a plurality of packets with the intervals between consecutive packets of each burst being less than the intervals between consecutive packets. A time-stamping section inserts into each packet a transmission time derived from the timing information generated by the clock.

Abstract: A timing source is provided for sending timing information via a packet network. The source comprises a clock for generating the timing information and a packet-forming section for forming a sequence of packets for transporting the timing information to a destination node. A time-stamping section inserts into each packet of the sequence a transmission time derived from the clock and acts as an output section for forwarding the packets to the network at the respective transmission times. In one mode, the packet forming section forms all of the packets of the sequence with the largest size which the packet network is capable of transporting. In another mode, the packets of the sequence have a distribution of sizes which may be fixed or which may vary in response to traffic conditions.

Abstract: A method of synchronising first and second clocks coupled respectively to ingress and egress interfaces 6,7 of a packet network 1, the method comprising calculating a minimum packet Transit Time over the network 1 in each of successive time intervals, and varying the frequency of the second clock so as to track variations in the minimum packet Transit Time.

Abstract: A method for distributing timing information across a packet network includes generating timing signals at a master clock at predictable intervals using a clock reference of a given frequency. The timing signals are broadcast or multicast to a plurality of slave clocks over the packet network, preserving the timing signal intervals. At each slave clock, the intervals between successively received timing signals are determined. A clock recovery algorithm is applied to the determined intervals to recover in substantially real time the original clock frequency. The local clock frequency of the slave clock is synchronized to the recovered frequency.

Abstract: A method of synchronising first and second clocks coupled respectively to ingress and egress interfaces 6,7 of a packet network 1, the method comprising calculating a minimum packet Transit Time over the network 1 in each of successive time intervals, and varying the frequency of the second clock so as to track variations in the minimum packet Transit Time.

Abstract: A method of recovering a clock signal for a TDM output from packets of TDM data which have been transmitted over a packet network, from a source having a source TDM clock to a destination having a destination TDM clock. The method includes providing at least some packets with a Remote Time stamp representing the state of the source TDM clock when the packet is created; providing said at least some packets with a Local Timestamp representing the state of the destination TDM clock when the packet is received; determining a Transit Time value representing the difference between said Local and Remote Timestamps; and controlling the clock frequency of the TDM output on the basis of said Transit Time as determined above.

Abstract: A method of updating a lookup table associated with a TDM transmit unit which is coupled to a packet network to receive data therefrom, the lookup table mapping packet network contexts to TDM channels. The method includes priming a controller with data for updating the lookup table in advance of the receipt of packets containing data to which the update relates, incorporating a flag in each packet sent over the packet network to the TDM transmit unit, the flag being set to indicate whether or not a packet is the first packet to which the update relates, and detecting the setting of the flag in a first packet and in response updating the lookup table with the update data.

Abstract: A method of mapping between contexts of a packet network and TDM channels and streams. The method comprises constructing a lookup table defining the sequence in which data is to be mapped between contexts and TDM channels and streams, and including for each row of the table a flag which indicates whether or not that entry is the first entry in the table for the corresponding context. As the TDM receive or transmit entity cycles through the lookup table, use is made of the flags to synchronize the start of each packet with the first entry of a TDM frame for each context.

Abstract: A method of synchronising first and second clocks coupled respectively to ingress and egress interfaces 6,7 of a packet network 1, the method comprising calculating a minimum packet Transit Time over the network 1 in each of successive time intervals, and varying the frequency of the second clock so as to track variations in the minimum packet Transit Time.

Abstract: A method of distributing timing information across a packet network 7. The method comprises generating timing signals at a master clock 8 at predictable intervals using a clock reference of a given frequency. The timing signals are broadcast or multicast to a plurality of slave clocks 9 over said packet network 7, preserving the timing signal intervals. At each said slave clock 9, the intervals between successively received timing signals are determined. A clock recovery algorithm is applied to said determined intervals to recover in substantially real time the original clock frequency. The local clock frequency of the slave clock is synchronised to the recovered frequency.

Abstract: A system is provided for processing requests for service from a plurality of modules, the system including a processor arranged to process the requests a FIFO queue means providing a FIFO queue for storing the identities of the modules, and control means for placing in the FIFO queue the identities of modules requiring service by the processor. When the processor is ready to service another module the processor reads the identity of the module at the head of the FIFO queue, and services that module.

Abstract: A method of updating a lookup table associated with a TDM transmit unit which is coupled to a packet network to receive data therefrom, the lookup table mapping packet network contexts to TDM channels. The method includes priming a controller with data for updating the lookup table in advance of the receipt of packets containing data to which the update relates, incorporating a flag in each packet sent over the packet network to the TDM transmit unit, the flag being set to indicate whether or not a packet is the first packet to which the update relates, and detecting the setting of the flag in a first packet and in response updating the lookup table with the update data.

Abstract: A method of mapping between contexts of a packet network and TDM channels and streams. The method comprises constructing a lookup table defining the sequence in which data is to be mapped between contexts and TDM channels and streams, and including for each row of the table a flag which indicates whether or not that entry is the first entry in the table for the corresponding context. As the TDM receive or transmit entity cycles through the lookup table, use is made of the flags to synchronize the start of each packet with the first entry of a TDM frame for each context.

Abstract: A TDM transmitter system for receiving packets of TDM data from a packet network and transmitting these on a TDM network. The TDM transmitter system includes a packet receiver arranged to receive the packets from the packet network, a buffer memory for storing packets received by the receiver, and a TDM transmitter arranged to receive the packets from the memory buffer, convert these to TDM data for transmission on a TDM network, and transmit said TDM data on a TDM network. The TDM transmitter of the TDM data corresponding to the first packet is delayed for a programmable number of TDM frame periods.