Deterministic Placement of Timestamp Packets Using a Periodic Gap

• US 20120008646A1
• Filed: 07/06/2011
• Published: 01/12/2012
• Est. Priority Date: 07/07/2010
• Status: Active Grant

• Current Assignee: Futurewei Technologies Incorporated (Huawei Investment & Holding Co., Ltd.)
• Original Assignee: Futurewei Technologies Incorporated (Huawei Investment & Holding Co., Ltd.)
• Inventors: Fourcand, Serge Francois
• Granted Patent: US 8,842,530 B2
• Time in Patent Office: Days
• US Class Current: 370/514
• CPC Class Codes: H04J 3/0667 Bidirectional timestamps, e.g. NTP or PTP for compensation of clock drift and for compensation of propagation delays arrangements for monitoring round trip delays in packet switching networks H04L43/0864
• CPC Class Codes: H04J 3/0673 using intermediate nodes, e.g. modification of a received timestamp before further transmission to the next packet node, e.g. including internal delay time or residence time into the packet

Abstract

An apparatus comprising a timestamp support logic component configured to identify a plurality of timestamps for a plurality of network nodes on a single link and align the timestamps in a plurality of corresponding time slots for the network nodes within a periodic transmission time window and a scheduler coupled to the timestamp support logic component and configured to align a plurality of packets that do not comprise timestamps in a corresponding time slot subsequent to the time slots for the timestamps in the periodic transmission time window.

Claims

1. An apparatus comprising:

a timestamp support logic component configured to identify a plurality of timestamps for a plurality of network nodes on a single link and align the timestamps in a plurality of corresponding time slots for the network nodes within a periodic transmission time window, wherein the timestamp for each node has a unique position for its corresponding time slot within the transmission time window; and

a scheduler coupled to the timestamp support logic component and configured to align a plurality of packets that do not comprise timestamps in a corresponding time slot subsequent to the time slots for the timestamps in the periodic transmission time window.

2. The apparatus of claim 1, further comprising:

a media access control (MAC) unit coupled to the timestamp support logic component;

a physical layer (PHY) unit coupled to the MAC unit or the timestamp support logic component; and

a switch fabric coupled to the scheduler.

3. The apparatus of claim 2, wherein both the scheduler and the timestamp support logic component are positioned between the switch fabric and the MAC unit.

4. The apparatus of claim 2, wherein both the scheduler and the timestamp support logic component are positioned between the MAC unit and the PHY unit.

5. The apparatus of claim 2, wherein the scheduler is coupled to the timestamp support logic component via the MAC.

6. The apparatus of claim 1, wherein the periodic transmission time window comprises the time slots for the timestamps at the start of the periodic transmission time window, the time slot for the packets that do not comprise timestamps, a packet guard-band where no transmission occurs subsequent to the time slot of the packets that do not comprise timestamps, and a physical layer (PHY) guard-band that comprises one or more idle symbols subsequent to the packet guard-band.

7. The apparatus of claim 6, wherein the periodic transmission time window further comprises an idle symbol between each two consecutive time slots for the timestamps, an idle symbol between the time slots for the timestamps and the time slot for the packets that do not comprise timestamps, and an idle symbol between the time slot for the packets that do not comprise timestamps and the packet guard-band.

8. The apparatus of claim 1, wherein the packets are Layer 2 Ethernet data or control packets, and wherein the egress link is a Layer 2 Ethernet link.

9. The apparatus of claim 1, wherein the packets correspond to a statistically-multiplexed packet-mode network.

10. A network component comprising:

a receiver configured to receive a plurality of timestamp packets and a plurality of non-timestamp packets;

a periodic timestamp transmission support logic unit configured to determine a buffer time for each of the timestamp packets in which to align each of the timestamp packets at a position in a periodic transmission time window designated for a corresponding network node on the same link;

a scheduler configured to determine a buffer time to hold the non-timestamp packets until all the timestamp packets are transmitted;

a buffer configured to hold each of the timestamp packets and the non-timestamp packets until the corresponding determined buffer time expires; and

a transmitter configured to transmit the timestamp packets and the non-timestamp packets after the corresponding buffer time expires on the same link.

11. The network component of claim 10, wherein the timestamp packets and the no-timestamp packets are Ethernet packets compliant with the Institute of Electrical and Electronics Engineers (IEEE) standard 802.3 and range from about 64 octets to about 2,000 octets in size.

12. The network component of claim 10, wherein the timestamp packets and the no-timestamp packets comprise Ethernet packets that have sizes greater than about 9,600 octets and Ethernet idle signaling units (SUs) that have sizes of about two octets.

13. The network component of claim 10, wherein timestamp packets and the no-timestamp packets are similarly transported in a forward direction in a periodic and determined manner along the network nodes on the same link according to the periodic transmission time window, and wherein the timestamps are used to adjust frequency timing between the network nodes.

14. The network component of claim 10, wherein timestamp packets and the no-timestamp packets are similarly transported in a forward direction and then in a reverse direction in a periodic and determined manner along the network nodes on the same link according to the periodic transmission time window, and wherein the timestamps are used to adjust phase timing between the network nodes.

15. A method comprising:

receiving a plurality of Ethernet packets comprising timestamp packets and other packets;

identifying and mapping each of the timestamp packets to a corresponding designated network node on the same egress link;

buffering each of the Ethernet packets for a determined time to align the Ethernet packets within a plurality of corresponding time slots in a virtual periodic time window for transmission; and

transmitting each of the Ethernet packets after the determined time expires.

16. The method of claim 15, wherein the timestamp packets are mapped to a plurality of corresponding designated network nodes by aligning the timestamp packets to a plurality of consecutive time slots that match in sequence the designated network nodes on the same egress link.

17. The method of claim 15, wherein the timestamp packets are mapped to a plurality of corresponding designated network nodes using a plurality of corresponding identities in the timestamp packets to identify the designated network nodes and the egress link.

18. The method of claim 15, wherein the Ethernet packets are buffered to allow a packet guard-band where no transmissions may occur, and wherein the packet guard-band has a time duration greater than or about equal to a largest network supported Ethernet packet or packet transmission including a minimum required inter-packet gap between packet transmissions.

19. The method of claim 18, wherein the minimum required inter-packet gap is equal to about 12 octets.

20. The method of claim 19, wherein the Ethernet packets are further buffered to allow a physical layer (PHY) guard-band that has a time duration greater than or about equal to the sum of the minimum required inter-packet gap and at least one maximum possible expected PHY adjustment.

21. The method of claim 15, wherein transmitting each of the Ethernet packets after the determined time expires improves packet contention handling by about 99 percent.