US 5,740,164 A · Traffic routing for satellite communication system

Abstract

Methods and apparatus which route, control and manage traffic throughout a Satellite Communication System operating in low Earth orbit are disclosed. Voice, video and data traffic from terrestrial gateways (G) and from portable (P), mobile (M) or fixed (F) terminals are directed up through the constellation of satellites (S) and back down to destinations on Earth. The satellites provide continuous worldwide communication services while insuring uniform end-to-end transmission delays. The satellite network is highly adaptive to the constantly changing network topology, and will offer a synchronous circuit switched communication service that provides sequential delivery of user data, regardless of the type of the data transmitted. The network employs datagram switching, as opposed to conventional virtual circuit switching techniques. Packets associated with a single phone call do not necessarily travel along the same route, and consequently arrive at their common destinations at different times with a variable transmission delay. Packets (26) received from a portable (P), mobile (M) or fixed (F) terminal, from a satellite (S), or from a stationary gateway (G) are dispatched from an origin node (OUR.sub.-- NODE) to a destination node (DEST.sub.-- NODE) according to address instructions carried in the packet header (28). At each node, propagation delay vectors OUR.sub.-- DELAY.sub.-- EST DEST.sub.-- NODE, ! are calculated using local computers. These delay vectors estimate a time delay which the packet (26) encounters in traveling from the origin node (OUR.sub.-- NODE) to the destination node (DEST.sub.-- NODE). An optimal route (opt.sub.-- link) is then selected from the set of calculated delay vectors, and the packet (26) is routed to the destination node (DEST.sub.-- NODE) via the pathway (opt.sub.-- link) that insures both the lowest end-to-end delay and the best overall traffic management of the network.

A method of transporting each packet (26) of a message which includes a plurality of packets (26) from an origin node (OUR-NODE) to a destination node (DEST-NODE);

said origin node (OUR-NODE) and said destination node (DEST-NODE) being located among a plurality of satellites (S) and among a plurality of stationary gateways (G) on the Earth;
said method comprising the steps of:
(A.) receiving each said packet (26) at said origin node (OUR-NODE) synchronously transmitted from one of
a plurality of portable terminals (P),
a plurality of mobile terminals (M),
a plurality of fixed terminals (F),
said plurality of stationary gateways (G) and
said plurality of satellites (S);
each of said plurality of satellites (S) having aboard a fast packet switch (22);
each one of said plurality of packets (26) including a header (28) containing an address and a payload (30);
(B.) calculating a plurality of propagation delay vectors which estimate a time delay which said packet (26) would encounter in traveling from said origin node (OUR-NODE) to said destination node (DEST-NODE) over a plurality of links () using orbit position information about each node;
said orbit position information being generated onboard each of said plurality of satellites (S);
each of said plurality of satellites (S) traveling in low Earth orbits and constantly moving with respect to the Earth;
said vectors using an algorithm in which
one of said plurality of propagation delay vectors in one of said plurality of links () between said origin node (OUR-NODE) and said destination node (DEST-NODE) is represented by a variable "OUR-DELAY-EST (DEST-NODE, )",
a current propagation time delay in one of said plurality of links () connecting said origin node (OUR-NODE) to a neighboring node (OUR-NEIGHBOR ()) is represented by a variable "LINK-PROP-DELAY ()",
a current link time delay for packet queuing, including time to be spent by said packet (26) in a link buffer awaiting transmission (Twait-in-q) and time for transmission (Ttx), is represented by a variable "LINK-Q-DELAY ()";
a least time delay for transmission of said packet (26) from a neighboring node (OUR-NEIGHBOR ()) to said destination node (DEST-NODE) determined by said neighboring node calculating a time delay of packet transmission over each link () from said neighboring node (OUR-NEIGHBOR ()) to said destination node (DEST-NODE), is represented by a variable "OUR-NEIGHBOR-DELAY-EST (DEST-NODE, OUR-NEIGHBOR ())";
said algorithm having the form
______________________________________ OUR-DELAY-EST (DEST-NODE, ) = LINK-PROP-DELAY () + LINK-Q-DELAY()+OUR-NEIGHBOR-DELAY-EST(DEST-NODE, OUR-NEIGHBOR());
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(C.) selecting one of said plurality of propagation delay vectors (OUR-DELAY-EST (DEST-NODE, ) which constitutes a minimum time delay for forwarding said packet (26) from said origin node (OUR-NODE) to said destination node (DEST-NODE) and designating that selected propagation delay vector as an optimal link (opt-link);
said optimal link having at least one next-node-in-path-to-destination;
(D.) selecting for said packet (26), at each said next-node-in-path-to-destination of said optimal link (opt-link), one of said plurality of propagation delay vectors (OUR-DELAY-EST (DEST-NODE, ) which constitutes a minimum time delay for forwarding said packet (26) from said next-node-in-path to said destination node (DEST-NODE) and designating that selected propagation delay vector as a next optimal link (opt-link);
(E.) routing said packet (26) from said origin node (OUR-NODE) asynchronously through said fast packet switch (22) aboard one of said plurality of satellites (S) to said destination node (DEST-NODE) via said optimal links (opt-link) between said fast packet switch (22) and said destination node (DEST-NODE);
said fast packet switch (22) being capable of functioning as a sovereign, autonomous and independent switching node among said plurality of satellites (S) traveling in low Earth orbit;
(F.) repeating steps (A.) through (E.) for each one of said plurality of packets (26) until each said packet (26) reaches said destination node (DEST-NODE);
and
(G.) sorting said plurality of packets (26) in said fast packet switch (22) at said destination node (DEST-NODE) to account for out-of sequence arrival and transmitting said packets (26) in a restored sequence to one of said portable terminals (P), mobile terminals (M) and fixed terminals (F).

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Traffic routing for satellite communication system

Life of this patent

Traffic routing for satellite communication system

Life of this patent

Abstract

Claims11