Switched channel-band network
View Patent ↗Rather than restricting a stream of data to a single channel within a multi-channel link between a source node and a core node, each channel is divided into time slots and the stream of data is distributed among these time slots in several channels. However, to ease the management of switching the stream of data at the core node, simultaneous time slots in each channel may be arranged into “stripes,” such that a particular stripe may only include data segments having a common destination. Switching these stripes of data at the core node requires that the source of such a stripe arrange the frame according to a frame structure provided by the core node. Advantageously, where the frame is striped across an entire link, the present invention provides for a variation on link switching that approaches the topological reach of TDM switching while maintaining relatively straightforward operation at the core node. As the switching scheme requires time-locking between the core node and the source node, methods are provided for initializing, maintaining and recovering this time-locking while offsetting the effect of optical signal dispersion in multi-wavelength fiber links.
1. A method of time-lock recovery at a core node in a composite-star network, said method comprising:
instructing a switch to connect a link from a source node to a selector;
instructing said selector to select input received from said switch;
sending instructions to a sink node associated with said source node, said instructions including a request to send a timing message;
continuously reading data received from said source node via said selector and said switch;
if said timing message is received, replying to said timing message with timing information;
repeating sending instructions at predefined intervals; and
discontinuing said repeating upon receipt of said timing message.
2. The method of claim 1 further comprising discontinuing said repeating upon expiry of a predefined time window.
3. The method of claim 2 further comprising, if said timing message is not received within said predefined time window, indicating that said source node is not functioning.
4. A core node in a composite-star network comprising:
a space switch having a plurality of input ports and a plurality of output ports;
a master controller having a master time indicator;
a selector having a plurality of selector inputs and a single selector output, said selector output communicatively connected to said master controller;
a plurality of 1:2 switches, each having a switch input, a first output communicatively connected to one of said input ports of said space switch, and a second output communicatively connected to one of said selector inputs;
where said master controller:
instructs one of said 1:2 switches to connect a link from a source node to said selector for time locking said source node to said master time indicator;
instructs said selector to direct input received from said one of said 1:2 switches to an input port of said master controller;
sends instructions to a sink node associated with said source node to transmit successive readings of a time indicator associated with said source node;
continuously reads said successive readings via said selector and said switch;
determines a time shift between one of said successive readings and a contemporaneous reading of said master time indicator; and
communicates said time shift to said sink node.
5. The core node of claim 4 wherein said master controller instructs said one of said 1:2 switches to connect said link to said space switch when said time shift reaches a negligible magnitude.
6. The core node of claim 4 wherein said master time indicator is a clock-driven cyclic time counter having a predefined period and said time indicator associated with said source node is a clock-driven time counter having a period equal to said predefined period.
7. The core node of claim 4 wherein said space switch is an optical switch.
8. The core node of claim 4 wherein said selector is an optical selector.
9. The core node of claim 4 wherein each of said 1:2 switches is an optical switch.
10. A network comprising:
a plurality of source nodes;
a plurality of upstream multi-channel links communicatively coupled to said plurality of source nodes;
a plurality of sink nodes;
a plurality of downstream multi-channel links communicatively coupled to said plurality of sink nodes;
a plurality of core nodes, each core node communicatively coupled to a subset of said plurality of upstream multi-channel links and a subset of said plurality of downstream multi-channel links;
a master controller associated with said each core node wherein said master controller:
receives control data from at least one of said plurality of source nodes;
generates a schedule for operation of a space switch associated with said each core node based on said control data, said schedule associating at least one of a plurality of time slots, within a multi-channel time division multiplexed frame, with a destination;
communicates said schedule to at least one of said plurality of sink nodes; and
maintains time-locking for individual channels in each upstream multi-channel link connecting to said space switch.
11. The network of claim 10 wherein each of said plurality of source nodes is paired with a corresponding one of said plurality of sink nodes to result in a plurality of network edge nodes.
12. A computer readable medium encoded with computer executable instructions which, when performed by a processor in a space switch master controller, cause the processor to:
receive from a multi-channel input link of a space switch a scheduling request specifying a multi-channel output link of said space switch and capacity allocation;
generate a schedule for operation of said space switch based on said scheduling request, said schedule associating at least one time slot of a plurality of time slots, within a time division multiplexed frame, with each channel of said multi-channel input link and each channel of said multi-channel output link of said space switch; communicate said schedule to a sink node; and
transmit instructions to a slave switch control unit for said space switch, where said instructions are based on said schedule.