Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1999-12-16
2004-06-01
Pham, Chi (Department: 2667)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
Reexamination Certificate
active
06744764
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not Applicable
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
Not Applicable
REFERENCE TO MICROFICHE APPENDIX
Not Applicable
BACKGROUND OF THE INVENTION
The present invention relates to the transmission of encoded speech over packet-switched data networks that provide connectionless, best-effort (non-guaranteed) delivery, such as Internet Protocol (hereinafter “IP”) networks. More particularly, the invention relates to the recovery of a relative alignment in time of separately transmitted segments of speech so as to best approximate the user experience of conversing over the connection-oriented, circuit-switched infrastructure of the Public Switched Telephone. Network (hereinafter “PSTN”).
The development of far-reaching data networks initially sponsored by corporate, education and governmental needs has in recent years exploded due to the interest in the Internet shown by the general public. As access to such networks becomes more widespread and the carrying capacity increases, new uses for them are being continually devised. A significant emerging use is the transport of real-time speech between users who would otherwise place telephone calls on the conventional PSTN.
The factors motivating the transmission of speech over data networks as opposed to the PSTN are economic and logistical:
1. incumbent local exchange and long distance telephone carriers are proving difficult to displace from traditional services such as PSTN telephony and therefore maintain fee levels consistent with captive consumers;
2. the provision of Internet access is highly competitive and fees are either flat or based only on time, never on the geographical span of communication;
3. corporate information services managers have significant investment in data networks and are motivated to make use of spare capacity;
4. the management of a single corporate network for data and voice is attractive as compared to separate networks;
5. the PSTN is itself slowly migrating to packet-based technology where speech is considered one among many sources of data for transport.
Using data networks for speech can thus be expected to begin with Internet telephony for long distance charge avoidance and migrate through unconventional access such as wireless and cable modem to fully integrated data/telephony networks.
Significant problems that need to be overcome in the use of data networks to carry real-time, two-way speech relate to the fundamental properties of packet-switched data networks as opposed to circuit-switched networks such as the PSTN. These properties derive from the same differences in operation that make packet-switched networks more efficient and flexible than circuit-switched networks:
1. continuous information, such as speech, must be divided into blocks (packets) at the transmitter, each of which is conveyed over the network separately and must be reassembled at the receiver into the original form;
2. the multiplexing of information packets across network links is performed in a statistical fashion rather than by assignment to pre-allocated transmission slots as in circuit-switched networks;
3. due to statistical multiplexing, packets must be queued for entry to the network and at switching points within the network, both of which introduce significant transfer delay as compared to circuit-switched networks;
4. as packets contend with other packets for transmission capacity, they experience variable transfer delays, particularly during periods of network congestion (load approaching the upper limit);
5. severe network congestion and transmission errors can both cause packets to be dropped and therefore not reach their destination.
In addition, connectionless, best-effort data networks, such as IP networks, have the following properties:
6. both transfer delay and the variation of transfer delay from packet to packet can be many tens of milliseconds;
7. large changes in transfer delay can occur as the network resolves the route that packets should take over the network;
8. changes in route can cause packets to arrive at the destination in a different order to that in which they were transmitted;
9. packets may occasionally take multiple routes, resulting in duplicates of the same packet arriving at the destination;
10. severe congestion is quite common since, in a connectionless network, the network switching/routing elements cannot (without pseudo-connection-oriented reservation protocols, such as RSVP, yet to be widely deployed) predict or control the load offered for transport;
11. accepted congestion alleviation strategies include discarding (dropping) groups of consecutive packets from a source (transmitter).
It is an object of the present invention to reassemble packetized, encoded speech information transmitted over an IP or similar network with the above characteristics so as to offer to the users an experience as close as possible to the use of the traditional, circuit-switched telephony network.
SUMMARY OF THE INVENTION
The foregoing and other objects are achieved by the invention, a system for recovering the temporal alignment of digitally encoded speech information transmitted over connectionless, best-effort delivery, packet-switched data networks. In general, the system operates on a plurality of digital data chunks that are sequentially generated by a data transmitter according to a natural temporal order and time alignment, and are transmitted across a digital data network to a receiver, such that the digital data chunks arrive at the receiver in a received temporal order substantially independent of the natural temporal order, and a received time alignment substantially independent of the natural time alignment. The system re-sequences and re-aligns the plurality of digital data chunks at the receiver so as to transform the received temporal order into the natural temporal order and the received time alignment into the natural time alignment. In one aspect, the system comprises a chunk sorter for storing the digital data chunks in a data buffer and thereafter sequentially transferring, at a chunk transfer rate compatible with a playout rate, the digital data chunks to a playout destination according to the natural temporal order. The system further includes a chunk sequence analyzer for measuring an average time that the digital data chunks remain in the data buffer. The chunk sequence analyzer also adjusts the playout rate so as to balance an increase in the average time, with an amount of data chunks lost due to arriving late and missing a playout deadline.
In one embodiment of the invention, the digital data network includes a best effort delivery, packet-switched network.
In another embodiment of the invention, the chunk sorter further includes a packet unassembly buffer for receiving a plurality of packets of the digital data chunks, a jitter buffer having a plurality of storage slots for storing the data chunks, and a digital signal processor for receiving the data chunks from the jitter buffer and sequentially playing out the data chunks in the natural temporal order at the playout rate.
In another embodiment of the invention, the chunk sorter transfers each of the digital data chunks from the packet unassembly buffer to the jitter buffer in an order corresponding to a relative sample time associated with each of the data chunks.
In another embodiment of the invention, the relative sample time is a predetermined function of a timestamp associated with each of the plurality of packets.
In another embodiment of the invention, the chunk sorter zero-fills the storage slots so as to accommodate data chunks having a data width less than a width of the storage slots.
In another embodiment of the invention, the chunk sequence analyzer further includes a chunk holding time calculator for determining a chunk holding time for each of the data chunks in the data buffer. The chunk sequence analyzer also includes a mean holding time calculator for receiving the chunk holding time corresponding to each of the data chunks, and averaging a predetermined
Bigdeliazari Ali
Davies Graham
Matias John P.
Smith Steve B.
Boakye Alexander O.
Mapletree Networks, Inc.
McDermott & Will & Emery
Pham Chi
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