Communications system including synchronization information for timing upstream transmission of data and ability to vary slot duration

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG.
1 is an illustration of a neighborhood cable tv system 100 adapted according to the present invention to provide data-communication between Signal Conversion System (SCS) 101 located at a head-end 103 and client stations 105a-j located at subscriber locations.
Each SCS 101 is connected to a packet router 117 that routes data packets to and from remote server stations.
In an alternative connection scheme, an SCS 101, e.
g.
, 101", interfaces locally or remotely to a circuit switcher 119 for circuit switched constant bit rate services.
The latter may be used to provide a digitized voice connection to a telephone network.
In many cable tv systems about 500 to 2000 subscribers are attached to the same headend 103.
The headend 103 communicates with the various subscriber locations 105 via optic fibre cables 107a and 107b connected to a fibre node 109.
The fibre node 109 is further attached via coaxial cables 111a and 111b.
The fibre node 109 contains a mechanism for converting between optical and electrical signals.
The communication between a router 117 and an SCSs 101 is digital.
However, the communication between the headend 103 and the subscriber locations is in an analog form.
The SCS 101 converts the digital communications signals between routers 117 and the analog communications that occur on the optic fibre and coaxial cables of a Cable TV system.
Each client station 105 contains a Cable modem 113 connected to a computer 115.
In alternative embodiments the computer 115 is substituted with other devices that would benefit from data communication with the headend 103 over the cable 111.
Examples, of such alternatives include set-top boxes for making requests for particular cable tv operations, e.
g.
, video-on-demand type services, and interactive television.
FIG.
2 is a block diagram of the Signal Conversion System (SCS) 101.
The Signal Conversion System (SCS) 101 is attached to the fibre cables 107a and 107b.
Using a transmitter 205 the SCS 101 transmits data using 64-QAM (64 bit Quadrature Amplitude Modulation) or 256-QAM (256 bit QAM) transmission format onto the fibre cable 107a