Shared communication channel that interleaves 1 PPS signals and messaging
A shared bus time interleaves 1 PPS signal and control and coordination information between a primary timing source and line cards that need to be synchronized using the 1 PPS signals. The shared bus utilizes 1 second frames divided into time slots. The 1 PPS signals are interleaved at predetermined locations in the frame so the delays introduced by interleaving the 1 PPS data in time can be precisely removed. While the bus is not being used for 1 PPS signals, the bus is available to send control and coordination information between the line cards and the primary timing source, avoiding the use of another system and increasing utilization of an available communication path.
1. An information transmission apparatus comprising:
a first line card;
a second line card;
a third line card; and
a bus connected to a first bidirectional buffer of the first line card, a second bidirectional buffer of the second line card, and a third bidirectional buffer of the third line card, the first bidirectional buffer, the second bidirectional buffer, and the third bidirectional buffer each configured to limit asymmetry in communication over the bus the third line card configured to send a first pulse per time interval signal over the bus to the first line card during a first time slot of a plurality of time slots that form a frame on the bus and to send a second pulse per time interval signal over the bus to the second line card during a second time slot of the plurality of time slots, the first pulse per time interval signal being a timing signal that is interleaved with control data, the first line card configured to send first information to the third line card over the bus during a third time slot of the plurality of time slots, the second line card configured to send second information to the third line card over the bus during a fourth time slot of the plurality of time slots, the third time slot assigned to a first location in the frame based on a first line card identification associated with the first line card and the fourth time slot assigned to a second location in the frame based on a second line card identification associated with the second line card.
2. The information transmission apparatus of claim 1 wherein the first pulse per time interval signal is a one pulse per second signal.
3. The information transmission apparatus of claim 1 wherein the first pulse per time interval signal is received from a satellite system.
4. The information transmission apparatus of claim 1 wherein the first line card is configured to send first time stamp information to the third line card over the bus during the third time slot, the first time stamp information indicative of a first time that a first timing message from the third line card is received.
5. The information transmission apparatus of claim 4 wherein the second line card is configured to send second time stamp information to the third line card over the bus during the fourth time slot, the second time stamp information indicative of a second time that a second timing message from the third line card is received by the second line card.
6. The information transmission apparatus of claim 1 wherein the third line card is configured as a timing source.
7. The information transmission apparatus of claim 1 wherein the bus is a bidirectional bus.
8. The information transmission apparatus of claim 1 wherein the third line card supplies a clock signal to the first line card and the second line card over a clock signal line, the clock signal synchronized with the first pulse per time interval signal.
9. The information transmission apparatus of claim 1 wherein the third line card is configured to send the first pulse per time interval signal at a first particular location with respect to a beginning of the first time slot and to send the second pulse per time interval signal at a second particular location with respect to the beginning of the second time slot.
10. A distributed system comprising:
a first line card;
a second line card;
a third line card; and
a bus connected to a first bidirectional buffer of the first line card, a second bidirectional buffer of the second line card, and a third bidirectional buffer of the third line card, the first bidirectional buffer, the second bidirectional buffer, and the third bidirectional buffer each configured to limit asymmetry in communication over the bus, the third line card configured to send a first pulse per time interval signal over the bus to the first line card during a first time slot of a plurality of time slots that form a frame on the bus and to send a second pulse per time interval signal over the bus to the second line card during a second time slot of the plurality of time slots, the first pulse per time interval signal being a timing signal that is interleaved with control data the first line card configured to send first information to the third line card over the bus during a third time slot of the plurality of time slots, the second line card configured to send second information to the third line card over the bus during a fourth time slot of the plurality of time slots, the third line card configured to send the first pulse per time interval signal at a first location with respect to a beginning of the first time slot and to send the second pulse per time period signal at a second location with respect to a beginning of the second time slot.
11. The distributed system of claim 10 wherein the first line card is configured to send first time stamp information to the third line card over the bus during the third time slot, the first time stamp information indicative of a first time that a first timing message from the third line card is received.
12. The distributed system of claim 10 wherein the second line card is configured to send second time stamp information to the third line card over the bus during the fourth time slot, the second time stamp information indicative of a second time that a second timing message from the third line card is received by the second line card.
13. The distributed system of claim 10 wherein the third line card receives the first pulse per time interval signal from a satellite system.
14. The distributed system of claim 10 wherein the third time slot is assigned to a location in the frame based on a first line card identification associated with the first line card and the fourth time slot is assigned to another location in the frame based on a second line card identification associated with the second line card.
15. The distributed system of claim 10 wherein the third line card supplies a clock signal to the first line card and the second line card over a clock signal line, the clock signal synchronized with the first pulse per time interval signal.
16. The distributed system of claim 10 wherein the bus is a bidirectional time information bus.
17. A method for transmitting information over a bidirectional bus comprising:
dividing a time interval into a plurality of time slots;
sending a first pulse per time interval signal over the bidirectional bus from a third line card to a first bidirectional buffer of a first line card during a first time slot of the plurality of time slots, the first pulse per time interval signal being a timing signal that is interleaved with control data;
sending first information from the first line card over the bidirectional bus to a third bidirectional buffer of the third line card during a second time slot of the plurality of time slots, the second time slot assigned to a location in the time interval based on a first line card identification associated with the first line card;
sending a second one pulse per time interval signal over the bidirectional bus from the third line card to a second bidirectional buffer of a second line card during a third time slot of the plurality of time slots; and
sending second information from the second line card to the third bidirectional buffer of the third line card over the bidirectional bus during a fourth time slot of the plurality of time slots, the first bidirectional buffer, the second bidirectional buffer, and the third bidirectional buffer each configured to limit asymmetry in communication over the bidirectional bus.
18. The method of claim 17 wherein the first time slot and the second time slot are even time slots and the third time slot and the fourth time slot are odd time slots or the first time slot and the second time slot are odd time slots and the third time slot and the fourth time slot are even time slots.
19. The method of claim 17 wherein at least one of the plurality of time slots is encoded with time slot identifying information.
20. The method of claim 17 wherein the first pulse per time interval signal is a one pulse per second signal.