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All TV channels missing, but radio is fine - any ideas?
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That's what I thought - channel numbers are just allocated by the IDTV or STB. However, some additional research has thrown up the e-book from the IEC which throws up a definition of LCN (logical channel numbers) (which I last came up against in X.25 packet switching - showing my age -eh:D).
Anyhow - there would seem to be recommendations for receivers where they encounter LCNs in the data stream - read and enjoy, questions will be asked later:
9.4.4.2 Receiver rules
It is a manufacturer option to provide an automatic service numbering facility on the basis of
logical channel numbers. However, when the manufacturer supports logical channel numbers
for automatic service numbering, he shall comply to the rules set out below.
NOTE Receivers are recommended to support logical channel numbering, as they aid communication between the
broadcaster and the consumer. For example, they provide a concise method for one service to describe viewing
options on another service. In addition, they provide a convenient method for providing references from other
media – such as printed event listings.
9.4.4.2.1 Logical channel number zero
Services associated to logical channel number 0 should be disregarded as part of the process
below (irrespective of the value of the visible_service_flag). These services are not intended
to be presented as part of the viewer’s service list. These services are not intended to be
selectable by viewers.
9.4.4.2.2 Invisible services
• Receivers shall support a “default” mode in which they will not show services marked
“invisible” in their user service list or selectable in normal P+/P- browsing. The receiver
may ignore the presence of “invisible” services when (re-)allocating services to service
numbers requested by “invisible” services.
• Receivers shall support a mode (for example as a service mode or as an installation
option) in which it will allow direct selection of all services (irrespective of being marked
invisible) by the user. It may display all services also as part of the user service list in this
mode.
• It is a manufacturers option to combine the two modes mentioned above, by allowing
direct selection of “invisible” services while not showing them as part of the service list.
9.4.4.2.3 First initialisation
When a receiver service list is first initialised, the receiver shall perform in accordance with
the following rules:
a) It shall attempt to allocate the services to a service number equal to the logical_ channel_
number for that service. This rule implies that if there is only one service with a particular
logical_channel_number available it shall (initially) be allocated to this service number.
b) It shall resolve any conflict between services that use the same logical channel number.
– National preference: it is recommended to give preference to services of one
original_network_id when allocating service numbers in case of a conflict (effectively
implementing a country preference).
– Regional preference: since networks shall broadcast non-conflicting logical channel
numbers, the receiver may choose to give preference of one network over the other
(effectively implementing a certain regional preference) in assigning services to
service numbers. It may also assume that services with the same logical_channel_
number are regional variants as long as they have the same original_network_id.
c) It is recommended to keep services from the same network that cannot be assigned to
their logical_channel_number grouped together in the service list. It is recommended to
preserve any ordering information among such services. In particular, in countries that
plan appropriate gaps in the logical channel numbering, it is appropriate to allocate
regional variants of services to the next “gap” in the service list.
If some services do not have an associated logical_channel_number, they shall get the lowest
priority in the assignment of a service number. The only exception is an original_ network_id
preference, which allows a receiver to first allocate service numbers to all services of an
original_network_id before allocating service numbers of any other original_network_id.
9.4.4.2.4 Adding a new service
If a receiver decides to add a new service to the service list, it shall first try to allocate a
service number according to the successor service rules (see 9.4.4.2.6) and secondly,
according to its logical channel number. In case of a conflict, it should try to allocate a free
service number.
9.4.4.2.5 Removing a service
If the receiver decides a service can be removed from the service list, it will visibly delete the
service and its service number from the service list. It shall preserve the information about the
removed service in case a successor service is found later (see below) to allow such a
successor service to take the place of the removed service in the service list. This retention
mechanism also improves the robustness of the receiver against network SI errors (wrongfully
signalled deletion of a service) or otherwise unintentionally removed services.
It should be noted that the (temporary) inability to receive a service as such should not be the
sole reason for a receiver to delete a service from the service list: in general, additional user
intervention is recommended in such a case. However, deletion of a service from the NITactual
and SDTactual
shall be considered positive confirmation of the deletion of a service by a
receiver.
9.4.4.2.6 Network re-configuration
When the receiver detects a service offer change including the addition and deletion of
multiple services and/or networks it shall first remove all services which it can (positively)
determine to be permanently removed from the service list and then add the new services.
Where possible, the receiver shall attempt to find suitable successor services for those
services (previously) removed from the service list applying the following successor service
rules:
a) The receiver shall first try match to a new service (successor service) to a
logical_channel_number and network_id and original_network_id from a service previously
removed from the service list.
Any remaining new services shall be allowed to replace services of other networks no
longer available (match only on logical_channel_number and original_network_ id), taking
into account rule b) under 9.4.4.2.3 (use national and regional preference) to select the
most suitable candidate.
Any new services that remain after successor service rules have been applied shall be
assigned in accordance with the service number allocation rules as mentioned under
9.4.4.2.3, but shall not change already existing service number allocation. Such services may
take any free position in the service list, thereby potentially using the service number of a
removed service that might be replaced later and thus blocking such a future successor.
Receiver manufacturers should attempt to minimise such events.
It is suggested to mark (for example using an alternate colour or an icon) those services with
changed status (added, deleted, or changed) in order to indicate the changes to the user.
9.4.4.2.7 Change of LCN numbering scheme
Any re-arrangement by the broadcaster of LCN numbering of services will be treated as above
under network re-configuration. This implies that user changes and non-default allocation of
services to service numbers by the receiver will be preserved as much as possible unless a
reinstallation is done.0 -
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