Method and apparatus for measuring quality of service parameters of networks delivering real time MPEG video
View Patent ↗Variation in delay in transmission of data from a transmitting station to a receiving station is measured by encapsulating a portion of the data and an outgoing time stamp in a packet, the outgoing time stamp substantially representing the degree of progression of a periodic process at the time of including the outgoing time stamp in the packet. The packet is transmitted from the transmitting station and is received at the receiving station. At the receiving station, an incoming time stamp is added to the packet. The incoming time stamp substantially represents the degree of progression of a periodic process at the time of adding the incoming time stamp to the packet. The incoming time stamp is compared to the outgoing time stamp.
1. A method of measuring variation in propagation delay for network packets transmitted from a transmitting station to a receiving station, wherein a first periodic process at the transmitting station progresses at substantially the same frequency as a second periodic process at the receiving station, said method comprising the steps:
a) generating a network packet,
b) encapsulating a plurality of data packets in the network packet,
c) generating an outgoing time stamp and inserting the outgoing time stamp into the network packet, said outgoing time stamp substantially representing a degree of progression of the first periodic process at the time of including the outgoing time stamp in the network packet,
d) transmitting the network packet from the transmitting station to the receiving station,
e) receiving said network packet at the receiving station,
f) generating an incoming time stamp and adding said incoming time stamp to the network packet, said incoming time stamp substantially representing a degree of progression of the second periodic process at the time of receiving said network packet,
g) comparing the incoming time stamp to the outgoing time stamp to obtain a first delay measurement for the network packet,
h) repeating steps a–g at least twice to obtain at least second and third delay measurements, and
i) comparing the first, second and third delay measurements to obtain maximum and minimum delay measurements and comparing the maximum and minimum delay measurements.
2. A method according to claim 1 , wherein the method comprises the step of, prior to step b, creating a reserved space in one of the plurality of data packets and step c comprises inserting the outgoing time stamp into said reserved space.
3. A method according to claim 1 , wherein the plurality of data packets are MTS packets and step b comprises encapsulating MTS packets in an IP packet.
4. A method according to claim 1 , wherein the first periodic process is evolution of a first clock reference, the second periodic process is generation of a second clock reference, the data packets include a synchronizing component, and the method includes synchronizing generation of the second clock reference with evolution of the first clock reference.
5. A method according to claim 4 , wherein the method further comprises, in parallel with steps a through i, counting the first and second clock references, step c comprises including a first count value of the first clock reference in the network packet transmitted from the transmitting station, step f comprises including a second count value of the second clock reference in the network packet received at the receiving station, and step g comprises comparing the first and second count values.
6. A method according to claim 1 , wherein the network packets are IP packets, the data packets comprise packetized elementary stream data and step b comprises encapsulating PES data in MTS packets and encapsulating a plurality of MTS packets in an IP packet.
7. A method according to claim 6 , wherein step b comprises encapsulating the outgoing time stamp in one of said plurality of MTS packets.
8. A method according to claim 6 , comprising employing an encoder to encapsulate the PES data in the MTS packets and employing a network interface driver to encapsulate said plurality of MTS packets in the IP packet, and the method further comprises employing the network interface driver to insert the outgoing time stamp into said one MTS packet.
9. A method according to claim 8 , comprising employing a second network interface driver at the receiving station to insert the incoming time stamp into the IP packet.