US 5,467,342 A · Methods and apparatus for time stamp correction in an asynchronous transfer mode network

Abstract

Packets of data, some of which may carry a timestamp value, are transmitted through an Asynchronous Transfer Mode (ATM) network. Prior to transmission, each packet of data is encapsulated in a respective convergence sublayer protocol data unit (CS-PDU) having a header portion and a payload portion. The header portion of each CS-PDU contains a time correction indicator (TCI), which indicates whether the CS-PDU carries a packet of data having a timestamp value that may require correction after the CS-PDU passes through the network, and a time reference correction (TRC) field. Each CS-PDU is then segmented into a plurality of successive segments; a first one of the segments of each CS-PDU contains the CS-PDU header. Each segment is then inserted into the payload section of a respective ATM cell for transmission through the network. At each node in the network, cells are examined to determine if they contain a CS-PDU header. If a cell contains a CS-PDU header, any variable delays imposed upon that cell as it passed through the node are measured and added to the TRC field in the CS-PDU header prior to sending the cell to the next node. At a destination node, the accumulated TRC value may be added to the time stamp value of the packet carried in the CS-PDU in order to compensate for the variable delays imposed upon that packet as the cells carrying the packet traversed the network.

Claims13

Dependent claims

A method of transmitting a packet of data through an Asynchronous Transfer Mode (ATM) network wherein the packet of data contains a timestamp value, said method comprising the steps of:

(a) encapsulating the packet of data in a convergence sublayer protocol data unit (CS-PDU) having a header and a payload, the payload comprising the packet of data;
(b) segmenting the CS-PDU and inserting successive segments of the CS-PDU into a plurality of ATM cells, one of said ATM cells carrying the CS-PDU header;
(c) maintaining, in a field of the CS-PDU header carried in said one ATM cell, a value indicative of the accumulated variable delay imposed upon said one ATM cell as the plurality of ATM cells are transmitted through switching nodes of the network;
(d) receiving said plurality of ATM cells at a destination node of the network, and reassembling the CS-PDU therefrom;
and
(e) adjusting the timestamp value of the packet of data based on the accumulated delay value in said field of the CS-PDU header.

3 more elements

A method of transmitting packets of data through an Asynchronous Transfer Mode (ATM) network wherein selected ones of the packets of data contain timestamp values, said method comprising the steps of:

(a) encapsulating each packet of data in a respective convergence sublayer protocol data unit (CS-PDU) having a header and a payload, the payload comprising the respective packet of data, the header comprising a time reference correction (TRC) field;
(b) segmenting each CS-PDU and inserting successive segments of each CS-PDU into a respective plurality of ATM cells, one of the respective plurality of ATM cells containing the header of the CS-PDU, each ATM cell having a header comprising an indicator that indicates whether the ATM cell carries the header of a CS-PDU;
(c) transmitting each ATM cell into the network and performing the following additional steps at each of a plurality of switching nodes in the network:
(i) receiving an ATM cell at the switching node and determining, based on the indicator in the header of the received ATM cell, whether the received ATM cell carries the header of a CS-PDU;
(ii) if the received ATM cell carries the header of a CS-PDU, then determining the amount of variable delay imposed by the switching node on the received ATM cell;
and
(iii) adding a value indicative of the amount of variable delay to the TRC field of the CS-PDU header carried in the ATM cell prior to transmitting the ATM cell to a next switching node;
(d) receiving a plurality of ATM cells containing the respective segments of one of said CS-PDUs and reassembling the CS-PDU therefrom;
and
(e) if the packet of data carried in the payload of the CD-PDU contains a timestamp value, adjusting the timestamp value based on the accumulated delay value in the TRC field of the CS-PDU header.

7 more elements

(a) encapsulating each packet of data in a respective convergence sublayer protocol data unit (CS-PDU) having a header and a payload, the payload comprising the respective packet of data, the header comprising a time reference correction (TRC) field and a time correction indicator (TCI) that indicates whether the packet of data in the payload of the CS-PDU contains a timestamp value;
(b) segmenting each CS-PDU and inserting successive segments of each CS-PDU into a respective plurality of ATM cells, one of the respective plurality of ATM cells containing the header of the CS-PDU, each ATM cell having a header comprising an indicator that indicates whether the ATM cell carries the header of a CS-PDU;
(c) transmitting each ATM cell into the network and performing the following additional steps at each of a plurality of switching nodes in the network:
(i) receiving an ATM cell at the switching node and determining, based on the indicator in the header of the received ATM cell, whether the received ATM cell carries the header of a CS-PDU;
(ii) if the received ATM cell carries the header of a CS-PDU, then examining the TCI in the CS-PDU header and determining therefrom whether packet of data carried in the payload of that CS-PDU contains a timestamp value;
(iii) if the TCI indicates that the packet of data contains a timestamp value, then determining the amount of variable delay imposed by the switching node on the received ATM cell;
and
(iv) adding a value indicative of the amount of variable delay to the TRC field of the CS-PDU header carried in the received ATM cell prior to transmitting that ATM cell to a next switching node.

5 more elements

Dependencies are inferred from the claim text.

Methods and apparatus for time stamp correction in an asynchronous transfer mode network

Life of this patent

Methods and apparatus for time stamp correction in an asynchronous transfer mode network

Life of this patent

Abstract

Claims13