WO2000072469A1

WO2000072469A1 - Packet based telephony over satellite links

Info

Publication number: WO2000072469A1
Application number: PCT/IL1999/000278
Authority: WO
Inventors: Jacob Tirosh
Original assignee: Comgates Communications, Ltd.
Priority date: 1999-05-25
Filing date: 1999-05-25
Publication date: 2000-11-30
Also published as: AU4161599A

Abstract

A method of transmitting data between a plurality of sites (22). The method includes providing in a first site at least one stream of interactive data, transmitting the at least one stream of data to a satellite (24), retransmitting the data from the satellite (24) to the plurality of sites (22) and receiving the retransmitted data in substantially all the other sites. The receiving sites utilize only received data directed to the site.

Description

PACKET BASED TELEPHONY OVER SATELLITE LINKS

FIELD OF THE INVENTION

The present invention relates generally to real time communications, and in particular, to two-way satellite communication systems. BACKGROUND OF THE INVENTION

Satellites are used to transmit information between sites without use of communication cables. For example, television broadcasts are transmitted from a single point to a satellite which retransmits the television broadcasts over a large area in which receiving stations may receive the broadcasts. Such broadcasting is also used to pass Internet packets in one-way, non-real-time, Internet on demand, applications.

Satellites are also used for two-way point-to-point real-time communication, to replace telephone cables. For example, an existing regional telephone system connects local telephone networks of a plurality of sites using a satellite-based wide area network. Satellite based networks are used, for example, in areas in which it is not feasible and/or there is not enough time to lay telephone cables, and/or when existing cables do not provide sufficient bandwidth.

In such a regional telephone system, as is common in regional cable networks, all the telephone messages sent out concurrently from each site may be compressed and synchronized together, for example, using a time domain multiplexing (TDM) method, and are sent via the satellite to an intermediate switching station. In the switching station, the messages are decompressed and are re-grouped according to their destination sites. The messages to each site are again compressed and synchronized together and are sent again via the satellite to their destination sites.

Thus, most messages are sent twice via the satellite, substantially doubling the delay of the telephone messages. Furthermore, this setup is wasteful on bandwidth. Each switching station site is assigned a pair of channels for transmitting data to and from the satellite. An additional pair of channels are assigned to each site for receiving messages from the switching station. In

* - addition, the double compression and decompression operations are time-consuming and reduce the quality of the telephone data.

Sending the messages directly from source sites to destination sites may be performed by assigning each pair of source and destination a pair of channels. Assuming each site may send messages to any other site, the number of channels required increases exponentially with the number of sites. SUMMARY OF THE INVENTION

It is an object of some aspects of the present invention to provide a method of transmitting with a relatively small delay, real-time telephony between a plurality of sites, using a satellite.

One aspect of some preferred embodiments of the present invention relates to a protocol for transmitting telephony data including fragments directed to a plurality of respective sites, via a satellite. The protocol allows sites receiving the data to easily determine for each fragment whether the data is directed to the receiving site.

Preferably, the data is transmitted in packets, such as IP packets. At each of the plurality of sites the data being transmitted is parsed into packets with a destination site address put in a header of each packet. The transmitted packets are sent to the satellite which transmits the packets to substantially all the other sites. Each of the sites receives the packets, and forwards to local subscribers only those packets which are addressed to the receiving site.

One aspect of some preferred embodiments of the present invention relates to a method of transmitting telephony data between a plurality of sites via a satellite, in which each of the sites receives substantially all the data from all the other sites. The received data is preferably decoded and each of a plurality of fragments forming the received data are checked to determine whether the fragment is destined to the receiving site. Preferably, each fragment is accompanied by a destination address and fragments not addressed to the receiving site are discarded. Preferably, each site is assigned a separate channel for transmitting its data to all the other sites, and each site listens concurrently to the channels of all the other sites.

In a preferred embodiment of the present invention, the destination addresses of the fragments are not encoded with the fragments before transmission, so that the receiving sites do not need to encode the data in order to determine which fragments are to be discarded.

It is noted that the term telephony data is taken to include, in addition to voice telephone conversations, other forms of interactive point-to-point data transmitted as telephony data. For example, the telephony data may include facsimile messages and/or video conferencing data.

Furthermore, various types of interactive and non-interactive data may be transmitted simultaneously, using preferred embodiments of the present invention.

There is therefore provided in accordance with a preferred embodiment of the present invention, a method of transmitting data between a plurality of sites, the method including providing in a first site at least one stream of interactive data, transmitting the at least one stream of data to a satellite, retransmitting the data from the satellite to the plurality of sites, receiving the retransmitted data in substantially all the other sites, and utilizing in each site, only received data directed to the site.

Preferably, providing the data includes providing data directed to a plurality of sites. Preferably, providing the data includes parsing the data into packets. Further preferably, parsing the data includes parsing the data into IP packets. Preferably, the method includes encrypting the data using a code known to substantially all of the plurality of sites. Preferably, transmitting the data includes transmitting the data on a channel assigned to the transmitting site.

Preferably, the method includes transmitting data from each of the sites on respective channels. Preferably, the method includes listening to substantially all the channels by each of the sites. Preferably, the method includes determining by a receiving site a destination address of the received data and discarding by the receiving site of data which has an address other than of the receiving site.

Preferably, providing the data includes providing telephony data. Preferably, retransmitting the data includes receiving data on a plurality of channels by the satelhte and combining the data to one or more combined channels prior to refr-msmitting. Preferably, utilizing only data directed to the site includes decrypting only data directed to the site. Alternatively or additionally, utilizing only data directed to the site includes transmitting the data to a subscriber connected to the site.

There is further provided in accordance with a preferred embodiment of the present invention, a method of transmitting and receiving data between a plurality of sites via a satellite, including transmitting concurrently at least two streams of telephony data from at least two of the sites to the satellite, retransmitting the at least two streams from the satellite, receiving the retransmitted streams in substantially all the sites, and discarding in each of the sites data not directed to the particular receiving site. Preferably, transmitting the data includes transmitting data which requires a short delay.

Further preferably, transmitting the data includes transmitting the data in packets.

Preferably, receiving the retransmitted streams in substantially all the sites includes receiving the streams in all the sites except the respective transmitting sites.

There is further provided in accordance with a preferred embodiment of the present invention, a method of transmitting data between a plurality of sites via a satelhte, including providing at a first site a plurality of streams of point to point data, combining packets from the plurality of streams in a manner which allows simple access to a destination field in substantially each packet, transmitting the combined packets to the satellite, receiving the combined packets by the satellite and retransmitting the data from the satellite, receiving the combined packets in substantially all of the sites from the satellite, and reading an address field in the received packets at the sites.

Preferably, the method includes discarding at a receiving site packets in which the address read is different than an address of the receiving site.

Preferably, combining packets includes forming IP packets.

Preferably, receiving the combined packets in substantially all the sites includes receiving the streams in all the sites except the respective transmitting sites.

There is further provided in accordance with a preferred embodiment of the present invention, a ground station for receiving data from a satellite, including a receiver which receives a stream of telephony data from the satellite, and a gateway which retrieves packets from the stream of data and discards packets not addressed to the receiving ground station.

There is further provided in accordance with a preferred embodiment of the present invention, a ground station for transmitting data via a satellite, including a gateway which receives at least one stream of telephony data, and parses the data into packets, and a transmitter which transmits the packets to the satellite. Preferably, the at least one stream received by the gateway includes a plurality of point to point data streams.

There is further provided in accordance with a preferred embodiment of the present invention, a satellite system for transmitting telephony data, including a satellite, and a plurality of ground stations, each of which receives at least one stream of telephony data, parses the data into packets and transmits the packets to the satelhte.

Preferably, the satelhte retransmits the packets to substantially all the ground stations, and the ground stations receive the retransmitted packets and discard packets not addressed to the particular receiving ground station. Preferably, each of the plurality of ground stations includes a plurality of receivers for receiving from the satellite packets originating from substantially all the other ground stations. Preferably, each of the plurality of ground stations includes a multi channel receiver for receiving from the satelhte packets originating from a plurality of other ground stations. Preferably, the satelhte receives the transmitted packets on a plurality of channels and combines the packets to one or more combined channels.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be understood and appreciated more fully from the following detailed description taken in conjunction with the accompanying drawings in which: Fig. 1 is a schematic overview of a satellite real time communication system, in accordance with a preferred embodiment of the present invention;

Fig. 2 is a schematic block diagram of an exemplary set-up of apparatus within a ground site of the system of Fig. 1, in accordance with a preferred embodiment of the present invention; Fig. 3 is a flow chart of the actions performed by a gateway in preparing data for transmission, in accordance with a preferred embodiment of the present invention; and

Fig. 4 is a flow chart of the actions performed by a gateway in interpreting received data, in accordance with a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT Fig. 1 is a schematic overview of a satellite telephony system 20, in accordance with a preferred embodiment of the present invention. System 20 comprises a plurality of ground sites 22 which communicate with each other through a satelhte 24. Ground sites 22 comprise cities, villages, offices, private houses and/or any other sites which include one or more end-sets 26 which generate and/or receive data streams compatible with telephony systems. Preferably, end- sets 26 comprise telephones, video conferencing apparatus, computers and/or facsimile machines which generate and receive real time, interactive point-to-point data. Additionally or alternatively, end-sets 26 generate off-line data. Optionally, satellite 24 provides connections to other satellites as indicated by an arrow 28.

Preferably, the number of sites 22 ranges between 3 and about 100. Nonetheless, by using channel sharing protocols, such as the ALOHA protocol, many thousands of sites 22 may be accommodated by system 20.

Reference is also made to Fig. 2 which is an exemplary set-up of apparatus within a ground site 22, in accordance with a preferred embodiment of the present invention. Ground site 22 comprises a public switch 30 which routes telephone calls within the site. Calls directed out of the site 22 are passed from public switch 30 to a gateway 32 which compresses the data and parses it as described hereinbelow with reference to Fig. 3. Thereafter, the data is passed to a router 34 which prepares the data for transmission in a physical layer, as is known in the art. For example, router 34 translates the data from a local area network (LAN) protocol used by public switch 30 to a wide area network (WAN) protocol. The data from router 34 is then passed to a transceiver 36 which transmits the data to satellite 24 using a satellite-dish 38. Preferably, transceiver 36 encrypts and modulates the data before it is transmitted, as is known in the art. Transceiver 36 preferably comprises a transmitter which transmits the data received from router 34 on an up-going channel assigned to the site 22. Transceiver 36 preferably further comprises a plurality of receivers, one for each site 22 except the receiving site itself, which receive signals on down-going channels of the other sites. Alternatively or additionally, transceiver 36 comprises one or more multi-channel receivers instead of or in addition to one or more of the plurality of receivers. It is noted that the channels may be differentiated using different methods, such as based on frequencies, time slots, and/or coding (for example CDMA).

Alternatively or additionally, satellite 24 (or sites 22 based on a predetermined scheme) combines data from one or more up-going channels into a single down going channel. Thus, sites 22 need listen to fewer channels than the number of sites 22. In a preferred embodiment of the present invention, satelhte 24 combines the data from substantially all the up-going channels to a single down going common channel. Preferably, sites 22 control the amount of data they transmit according to characteristics of data flow on the down-going common channel. For example, when the common channel is full, sites 22 preferably slow the rate at which they transmit data, for example by replacing the compression algorithm used or by refusing connections. Alternatively or additionally, sites 22 monitor the transmission of data based on a jitter and/or a delay of the transmitted data.

Further alternatively or additionally, some of sites 22 may use a common up-going channel for example using the ALOHA protocol.

Returning to Fig. 2, the received signals are passed from transceiver 36 to router 34 which reverses the operations performed in preparing the data for transmission. Thereafter, the data is passed to gateway 32 which decompresses the data and reverses the operations performed in the gateways 32 of the transmitting sites in preparing the data for transmission. Gateway 32 preferably also determines which data is destined to the receiving site 22 and passes that data to public switch 30 for distribution to end-sets 26. Preferably, gateway 32 discards data not destined to the receiving site 22 as described further herein below with reference to Fig. 4.

Fig. 3 is a flow chart of the actions performed by gateway 32 in preparing data for transmission, in accordance with a preferred embodiment of the present invention. Preferably, the data is compressed (52) using a standard compression algorithm, such as, G723 or G729. The compressed data is preferably parsed (54) into IP packets. Alternatively, the data is parsed into other types of packets, such as ATM packets. A header is annexed (56) to each packet stating an IP address of the destination site of the packet. Preferably, the IP packets are grouped (58) together according to the IP address destinations of the packets. Optionally, the grouped packets are encrypted (60) such that unauthorized sites not belonging to system 20 cannot decipher the information passing between sites 22.

In a preferred embodiment of the present invention, the contents of the packets are encrypted (preferably in addition to the encryption of step 60) in accordance with a predetermined code common to a sub-group of sites 22, in order to prevent other sites 22 from deciphering messages not addressed to them. Preferably, this encryption is not applied to the headers of the packets, so that the sites 22 to which the messages are not destined understand the address in the header although they do not have the code. Optionally, each pair of sites 22 share a different predetermined code.

Fig. 4 is a flow chart of the actions performed by gateway 32 in interpreting received data, in accordance with a preferred embodiment of the present invention. The data received by gateway 32 from router 34 is preferably decrypted (70). The headers of the packets of the decrypted data are checked to determine (72) the destination addresses of the packets. Packets with addresses different from the address of the receiving site are preferably discarded (76). Those packets which are destined to the receiving site are decompressed (78) and passed (80) to public switch 30 for distribution to end-sets 26.

It is noted that although the above description of Figs. 1 and 2 was written as relating mainly to a telephone service provider, the present invention is not limited to such usage. Specifically, preferred embodiments of the present invention may be used by other service providers such as providers of video teleconferencing. Furthermore, some preferred embodiments of the present invention may be used for inter-corporate communications.

It will be appreciated that the above described apparatus and methods may be varied in many ways. In addition, a multiplicity of various features have been described. It should be appreciated that different features from different embodiments may be combined in different ways. In particular, not all the features shown above in a particular embodiment are necessary in every similar preferred embodiment of the invention. Further, combinations of the above features are also considered to be within the scope of some preferred embodiments of the invention. It should also be appreciated that although some of the preferred embodiments were described only as methods, apparatus for carrying out the methods are within the scope of the invention. It is noted that the above described embodiments are given by way of example only, and the scope of the invention is limited only by the claims. When used in the following claims, the terms "comprise", "include", "have" or their conjugates mean "including but not limited to".

Claims

1. A method of transmitting data between a plurality of sites, comprising: providing in a first site at least one stream of interactive data; transmitting the at least one stream of data to a satellite; retransmitting the data from the satelhte to the plurality of sites; receiving the retransmitted data in substantially all the other sites; and utilizing in each site, only received data directed to the site.

2. A method as in claim 1, wherein providing the data comprises providing data directed to a plurality of sites.

3. A method as in claim 1 or claim 2, wherein providing the data comprises parsing the data into packets.

4. A method as in claim 3, wherein parsing the data comprises parsing the data into IP packets.

5. A method as in any of the preceding claims, comprising encrypting the data using a code known to substantially all of the plurality of sites.

6. A method as in any of the preceding claims, wherein transmitting the data comprises transmitting the data on a channel assigned to the transmitting site.

7. A method as in any of the preceding claims, comprising transmitting data from each of the sites on respective channels.

8. A method as in claim 7, comprising listening to substantially all the channels by each of the sites.

9. A method as in any of the preceding claims, comprising deteirnining by a receiving site a destination address of the received data and discarding by the receiving site of data which has an address other than of the receiving site.

10. A method as in any of the preceding claims, wherein providing the data comprises providing telephony data.

11. A method as in any of the preceding claims, wherein retransmitting the data comprises receiving data on a plurality of channels by the satellite and combining the data to one or more combined channels prior to retransmitting.

12. A method as in any of the preceding claims, wherein utilizing only data directed to the site comprises decrypting only data directed to the site.

13. A method as in any of the preceding claims, wherein utilizing only data directed to the site comprises transmitting the data to a subscriber connected to the site.

14. A method of transmitting and receiving data between a plurality of sites via a satellite, comprising: transmitting concurrently at least two streams of telephony data from at least two of the sites to the satellite; retransmitting the at least two streams from the satellite; receiving the retransmitted streams in substantially all the sites; and discarding in each of the sites data not directed to the particular receiving site.

15. A method as in claim 14, wherein transmitting the data comprises transmitting data which requires a short delay.

16. A method as in claim 14 or claim 15, wherein transmitting the data comprises transmitting the data in packets.

17. A method as in any of claims 14-16, wherein receiving the retransmitted streams in substantially all the sites comprises receiving the streams in all the sites except the respective transmitting sites.

18. A method of transmitting data between a plurality of sites via a satellite, comprising: providing at a first site a plurality of streams of point to point data; combining packets from the plurality of streams in a manner which allows simple access to a destination field in substantially each packet; transmitting the combined packets to the satelhte; receiving the combined packets by the satellite and retransmitting the data from the satelhte; receiving the combined packets in substantially all of the sites from the satelhte; and reading an address field in the received packets at the sites.

19. A method as in claim 18, comprising discarding at a receiving site packets in which the address read is different than an address of the receiving site.

20. A method as in claim 18 or 19, wherein combining packets comprises forming IP packets.

21. A method as in any of claims 18-20, wherein receiving the combined packets in substantially all the sites comprises receiving the streams in all the sites except the respective transmitting sites.

22. A ground station for receiving data from a satelhte, comprising: a receiver which receives a stream of telephony data from the satellite; and a gateway which retrieves packets from the stream of data and discards packets not addressed to the receiving ground station.

23. A ground station for transmitting data via a satelhte, comprising: a gateway which receives at least one stieam of telephony data, and parses the data into packets; and a transmitter which transmits the packets to the satelhte.

24. A station as in claim 23, wherein the at least one stream received by the gateway comprises a plurality of point to point data streams.

25. A satellite system for transmitting telephony data, comprising: a satellite; and a plurality of ground stations, each of which receives at least one stream of telephony data, parses the data into packets and transmits the packets to the satellite.

26. A system as in claim 25, wherein the satellite retransmits the packets to substantially all the ground stations, and the ground stations receive the retransmitted packets and discard packets not addressed to the particular receiving ground station.

27. A system as in claim 25 or 26, wherein each of the plurality of ground stations comprises a plurality of receivers for receiving from the satelhte packets originating from substantially all the other ground stations.

28. A system as in claim 25 or 26, wherein each of the plurality of ground stations comprises a multi channel receiver for receiving from the satelhte packets originating from a plurality of other ground stations .

29. A system as in claim 25 or 26, wherein the satellite receives the transmitted packets on a plurality of channels and combines the packets to one or more combined channels.