understanding the data tables in the DCT

[usbbdm]

By tiredofbeing moved here.

I was going through the patents that motorola has on digital cable boxes... thought this might be of some use in determining how channels are either on or off... its patent number 4908859 the portion of interest is follows:


The service definition message (MS systems only) is configured as shown in Table 1. The message is used to determine generic features of services offered on different channels. The message contains definitions for 20 services.

TABLE 1
______________________________________
Service Definition Message Format
BYTE DEFINITION
______________________________________
1 FLAG CHARACTER
2 MESSAGE TYPE BYTE 94H [BROADCAST]
3 SUPPLIER ID
4 SERVICE ID RANGE
5-6 SERVICE DEFINITION 1
.
.
.
43-44 SERVICE DEFINITION 20
45-48 CRC
______________________________________



The supplier ID identifies the supplier of the service definition message. It is the low byte of the category address.

The category address is a 16-bit number representing the category into which a decoder 10 has been placed.

The service ID range byte identifies the first of 20 consecutive services being described. The value of this byte shall not exceed 80.

The remainder of the message consists of 20 service definitions. The format of a service definition is defined in Table 2.

TABLE 2
__________________________________________________________________________
Service Definition Format
BYTE BITS DEFINITION
__________________________________________________________________________
0[LSB]
7 STABLE [0 = UNSTABLE/ 1 = STABLE]
6 ACTIVE [0 = INACTIVE/1 = ACTIVE]
5-0 SERVICE TYPE
1[MSB]
7 UNIVERSAL [0 = TIED/1 = UNIVERSAL]
5-0 CHANNEL NUMBER
__________________________________________________________________________



Bit 7 of byte 0, if set to 1, indicates that the definition is stable, and can be used without questions for transitions from non-MULTIPLE-SERVICE-COMPONENT waveform channels. If set to 0, these transitions require acquisition of a current value for the entry when making transitions from a non-MS waveform channel.

Bit 6 of byte 0, if set to 1, indicates that the service is currently active on the associated channel. If set to 0, the service is not currently active on the associated channel. The setting of bit 6 is ignored if bit 7 is set to 1 or if bit 6 is overridden by the scrambler in the frame count message.

The defined service types for the preferred embodiment are shown in Table 3.

TABLE 3
______________________________________
Service Types
BITS DEFINITION
______________________________________
543210
000000
NULL
000001
VIDEO (NO AUDIO)
000010
PASSIVE TEXT (NO AUDIO)
000100
INFORMATION SERVICE (NO AUDIO)
000100
HBI AUDIO LEFT
000101
PASSIVE TEXT + HBI AUDIO LEFT
000111
INFORMATION SERVICE + HBI AUDIO LEFT
001000
HBI AUDIO RIGHT
001001
PASSIVE TEXT + HBI AUDIO RIGHT
001011
INFORMATION SERVICE + HBI AUDIO RIGHT
001100
COMBINED HBI AUDIO
001101
VIDEO + COMBINED HBI AUDIO
001110
PASSIVE TEXT + COMBINED HBI AUDIO
001111
INFORMATION SERVICE + COMBINED HBI
AUDIO
010000
SUBCARRIER AUDIO
010001
NTSC VIDEO + SUBCARRIER AUDIO (UNCON-
TROLLED)
010010
PASSIVE TEXT + SUBCARRIER AUDIO
010011
INFORMATION SERVICE + SUBCARRIER
AUDIO
010100
VIDEO + SUBCARRIER AUDIO
010101
VIDEO + SUBCARRIER AUDIO + HBI AUDIO
LEFT
010110
VIDEO + SUBCARRIER AUDIO + COMBINED
HBI AUDIO
010111
PERSONAL MESSAGE SERVICE (UNIVERSAL,
NO AUDIO)
011000
UNCONTROLLED SUBCARRIER AUDIO
011001
UNCONTROLLED VIDEO (NO AUDIO)
011010
UNCONTROLLED INFORMATION SERVICE (NO
AUDIO)
011011
UNCONTROLLED INFORMATION SERVICE +
SUBCARRIER AUDIO
011100
UNCONTROLLED VIDEO + SUBCARRIER
AUDIO
011101
VBI, LINE 10, PART 1
011110
VBI, LINE 10, PART 2
011111
VBI, LINE 11, PART 1
100000
VBI, LINE 11, PART 2
. .
. .
. .
111111
[RESERVED]
______________________________________



The "VIDEO" service component identified in Table 3 is non-NTSC video, such as scrambled video.

The null type may be stable (indicating that the service is never defined) or unstable (indicating that the service may occasionally be defined, e.g., a one-time pay-per-view service). It is always inactive.

The definition of a service normally on an MS waveform is not changed if the headend supporting that service goes into bypass mode. This is how the decoder differentiates bypass from an NTSC-format service.

HBI audio may be protected via an encryption keystream. Services using HBI audio must all use the same associated program encryption key. This is obtained through the program rekey message. If HBI audio on a channel is shared between more than one service, separate program rekey messages must be distributed for each service.

All audio channels associated with a service type carry the same audio (or possible stereo L and R if both HBI channels are used) unless the program rekey message for the service marks the current program as being bilingual. In that case, the different channels carry primary and alternate languages.

Services are access-controlled unless otherwise specified. A preferred technique of access control is described in U.S. Pat. No. 4,712,238, issued Dec. 8, 1987. Access control is exercised through the program rekey message, except for passive text services which use the tier fields of the tier-addressed screen message. Passive text services associated with HBI audio require both forms of control: the tier masks must agree.

Impulse purchase may only be offered on video and audio services which use the HBI audio channels. If the left and right HBI channels on a given frequency band are used by different services, only one of these services may offer impulse purchase.

Certain service IDs may be reserved. For example, service 0 may only be assigned to an uncontrolled information service with no audio and must be stable; service 1 is the only service that may carry the personal message service; and services 2-13 must be NTSC video services and a service that is protected through the tier mechanism must have an ID in the range 14-70. If these assignments are not made, the service must be assigned to a stable null service.

The universal bit indicates whether the service is tied to the channel named in the channel number field, or whether if may be found on any channel carrying an MS waveform.

The channel number field determines which channel the service may be found on. If the service is defined as universal, the channel number defines one channel where the service may be found. The channel number is always defined unless the service is a null service, in which case the value is ignored.

The interface channels 18 carrying the MDS services may be found in the IF spectrum between 150 MHz and 404 MHz. Each channel has a 6 MHz bandwidth, and channel boundaries may occur anywhere in the range at 250 KHz increments. The exact channel allocations may differ between systems due to local noise conditions etc., and channel allocations may occasionally be changed. For this reason, channel configuration is also downloaded to the decoder 10.

Each interface channel 18 is identified by a one-byte channel number. This is an index for the service definition table 14. The headend downloads a channel configuration map 20 which maps the channel number to the actual frequency. The frequency is given as a 16 bit number in units of 250 KHz, allowing for frequencies up to 16 GHz to be specified. The decoder 10 will pass this number to the receiver 12 which is responsible for synthesizing the receive frequency format required by that receiver 12.

As well as providing flexible system configuration, this interface between the decoder 10 and the receiver 12 has the advantage of being able to specify non-MDS frequencies. VHF channel definitions can be downloaded this way, and tied into the service definition table. Future generations of receivers, which do not downconvert the MDS/ITFS signals, can also be accommodated under this scheme.

An important part of the decoder 10 intallation procedure consists of acquiring the channel configuration map 20 and service definition tables 14. For this purpose, one channel is identified as an installation channel, which should be available 24 hours a day. The service definition table 14 for stable services and the channel configuration map 20 is broadcast more frequently on the installation channel than on other channels. The installer will manually select the installation channel frequency to acquire these tables. Manual frequency selection will also be available as a backup procedure for reacquiring service configuration information.

As with service redefinition, channel reconfiguration takes effect immediately. Channels are reconfigured one at a time using a spare encoder. During the transition period, the spare encoder is tuned to the old frequency and is continuously broadcasting channel configuration information for the new frequency. Channel reconfiguration is expected to be an extremely rare event, so configuration information is broadcast at a very low rate on most channels.