Flexible mapping of circuits into packets

• US 20030091052A1
• Filed: 07/26/2002
• Published: 05/15/2003
• Est. Priority Date: 07/30/2001
• Status: Active Grant

• Current Assignee: Adtran Networks SE (ADTRAN Holdings, Inc.)
• Original Assignee: Overture Networks, Inc. (ADTRAN Holdings, Inc.)
• Inventors: Skinner, Emily Jean, Lynch, Robert Leroy, Griswold, David Stephen, Pate, Prayson Will, Poupard, Michael Joseph
• Granted Patent: US 6,768,748 B2
• Time in Patent Office: Days
• US Class Current: 370/395.1
• CPC Class Codes: H04L 1/0007 by modifying the frame length
• CPC Class Codes: H04L 12/6418 Hybrid transport
• CPC Class Codes: H04L 41/5009 Determining service level performance parameters or violations of service level contracts, e.g. violations of agreed response time or mean time between failures [MTBF]
• CPC Class Codes: H04L 43/0864 Round trip delays
• CPC Class Codes: H04L 43/10 Active monitoring, e.g. heartbeat, ping or trace-route
• CPC Class Codes: H04L 43/106 using time related information in packets, e.g. by adding timestamps
• CPC Class Codes: H04L 43/16 Threshold monitoring
• CPC Class Codes: H04L 43/50 Testing arrangements
• CPC Class Codes: H04L 47/10 Flow control; Congestion control
• CPC Class Codes: H04L 47/18 End to end
• CPC Class Codes: H04L 47/2416 Real-time traffic
• CPC Class Codes: H04L 47/283 in response to processing delays, e.g. caused by jitter or round trip time [RTT]
• CPC Class Codes: H04L 47/35 by embedding flow control information in regular packets, e.g. piggybacking
• CPC Class Codes: H04L 47/365 Dynamic adaptation of the packet size

Abstract

A system for optimally mapping circuits into packets based on round trip delay (RTD), and a system for measuring RTD for use in packet communications systems such as circuit emulation (CEM) systems is disclosed. The measured RTD value can be used in a system that adjusts packet size to reduce capture delay to partially offset an increase in RTD. As the use of smaller packets increases the overhead burden on the packet communication system, the packet size can be increased to reduce the overhead burden when the size of the current RTD becomes appropriately short. The disclosure also teaches the placement of data from two or more circuits destined for the same emulation endpoint into the same transmission packet in order to improve system performance. The abstract is a tool for finding relevant disclosures and not a limitation on the scope of the claims.

Claims

1. A method for measuring round trip delay in a packet transmission network for the roundtrip delay for the transmission of a particular packet transmitted from a Device A to a Device B and for the transmission of a return packet back to the Device A, the method comprising:

A. transmitting from the device a to the device b the particular packet comprising;

a TxTime field representative of the time of packet transmission from Device A; and

at least one payload;

B. receiving the transmitted particular packet at the Device B;

C. transmitting from the Device B to the Device A, a return packet comprising;

the TxTime received from the particular packet from the Device A;

an indication of the interval between the receipt of the particular packet at the Device B and the transmission of the return packet; and

at least one payload;

.

D. receiving the return packet at the Device A; and

E. calculating round trip delay for the transmissions of the particular packet and the transmission of the return packet.

2. The method of claim 1 wherein the step of receiving the particular packet at Device B includes the sub-step of starting a timer to measure the delay between receipt of the particular packet and the transmission of the return packet and wherein the indication of the interval between the receipt of the particular packet at the Device B and the transmission of the return packet is based upon the timed value obtained from the timer.

3. The method of claim 1 wherein calculating the round trip delay for the transmission of the particular packet and the return packet is achieved through a calculation mathematically equal to:

subtracting the TxTime of the particular packet conveyed by the return packet from the time of receipt of the return packet; and

then

subtracting the indicated interval between the receipt of the particular packet at the Device B and the transmission of the return packet.

4. The method of claim 1 further comprising the measurement of round trip delay in the packet transmission network for the roundtrip delay of the return packet transmitted from the Device B to the Device A and a transmission of a subsequent packet from the Device A to the Device B, wherein:

the return packet transmitted from the Device B to the Device A further comprises a TxTimeB field with a TxTimeB value representative of the time of packet transmission from the Device B;

after the return packet is received at the Device A;

transmitting the subsequent packet from the Device A to the Device B, the subsequent packet comprising;

the TxTimeB value received from the return packet from the Device B;

an indication of the interval between the receipt of the return packet and the transmission of the subsequent packet; and

at least one payload;

receiving the subsequent packet at Device B;

calculating round trip delay for the transmission of the return packet and the transmission of the subsequent packet.

5. The method of claim 4 wherein the particular packet, the return packet and the subsequent packet share a common format comprising:

a particular field for a transmit time that carries the TxTime for the particular packet and the TxTimeB for the return packet;

a field for the echoed transmit time that carries the TxTime for the particular packet in the return packet and carries the TxTimeB for the return packet in the subsequent packet; and

a field for a delay indication containing the indication of the interval between the receipt of the particular packet and the transmission of the return packet in the return packet and containing the indication of the interval between the receipt of the return packet and the transmission of the subsequent packet in the subsequent packet.

6. The method of claim 1 wherein the transmitted packet transmitted from Device A to Device B comprises a set of at least two data units with each data unit comprising:

A. a TxTimeDU field representative of the time of packet transmission from Device A such that the TxTime field reference in claim 1 appears in at least two TxTimeDU fields;

B. an EchoTxTimeDU representative of an earlier transmission time of a particular data unit from Device B to Device A;

C. a TxTimeDU delay representative of the interval between the receipt of the particular data unit from Device B and the transmission of this data unit from Device A to Device B; and

D. a data unit payload.

7. The method of claim 6 wherein each data unit further comprises a control field indicating whether another data unit follows this data unit in the transmitted packet.

8. A method of dynamically altering the number of frames in a first circuit emulation packet in a network transmitting circuit emulation packets from a Device A to a Device B, the method comprising:

A. measuring RTD-AB which is a round trip delay for a circuit emulation packet transmitted from the Device A to the Device B and for a circuit emulation packet transmitted from the Device B to the Device A;

B. selecting a number of frames per circuit emulation packet for the next circuit emulation packet to be transmitted from the Device A to the Device B based on the measured round trip delay; and

C. transmitting a next circuit emulation packet from Device A to Device B containing the selected number of frames.

9. The method of claim 8 wherein the selection of frames per circuit emulation packet for the next circuit emulation packet to be transmitted from the Device A to the Device B is based on a smoothed value of recent measurements of RTD-AB.

10. The method of claim 8 wherein:

The first circuit emulation packet and a second circuit emulation packet destined for transmission from Device A to Device B are placed in a single transmission packet and a control flag is set in the first circuit emulation packet to indicate that another circuit emulation packet follows within the transmission packet.

11. A method of dynamically altering the number of frames per packet in a network transmitting packets from a Device A to a Device B, the method comprising:

A. measuring RTD-AB that is a round trip delay for a packet transmitted from the Device A to the Device B and for a packet transmitted from the Device B to the Device A;

B. determining the number of frames to place in a new packet to be transmitted to from the Device A to the Device B using the measured RTD-AB value as an input until a new measurement is obtained for RTD-AB; and

C. transmitting the new packet from Device A to Device B containing the selected number of frames.

12. The method of claim 11 wherein the step of determining the number of frames sets the number of frames to a first value if RTD-AB is less than a first RTD parameter, sets the number of frames to a second value, higher than the first value, if RTD-AB exceeds the first RTD parameter but is less than a second RTD parameter, and sets the number of frames to a value higher than the second value if RTD-AB exceeds the second RTD parameter.

13. The method of claim 11 wherein the step of determining the number of frames to place in a new packet is biased against reversing a recent switch to a particular number of frames per packet.

14. The method of claim 11 wherein the transmitted new packet transmitted from Device A to Device B comprises a set of at least two data units with each data unit comprising:

A. a TxTimeDU field representative of the time of packet transmission from Device A such that the TxTime field reference in claim D-1 appears in at least two TxTimeDU fields;

B. an EchoTxTimeDU representative of an earlier transmission time of a particular data unit from Device B to Device A;

C. a TxTimeDU delay representative of the interval between the receipt of the particular data unit from Device B and the transmission of this data unit from Device A to Device B; and

D. a data unit payload.

15. The method of claim 14 wherein each data unit further comprises a control field indicating whether another data unit follows this data unit in the transmitted new packet.