| From: | 4DTVENG-GI -(4DTVENG) | TO: | ALL |
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| Date Posted: | 201999-24-11 7:02:00 |
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| Message: Body: |
11/24/99 4Dtv Operation and Design FAQ Okay, here goes . . . This is an attempt to create a FAQ for some of the many questions regarding 4Dtv that arise here. ============================= Section 2. Maps What are maps? Section 3. Guide ------------------------------ Subject: Section 1. General FAQ and Information ------------------------------ Subject: What is this? This is a work in progress. However, note that the time I have to spend on 4Dtv is limited. And any time I spend composing this FAQ is likely my own time. You can help with this FAQ by asking questions, but be aware that there are many questions I will not answer. I'll start the FAQ off with a few of those. ------------------------------ Subject: What features will the next code release have? And when will it be out? When will the next generation 4Dtv be out? I can't answer these questions. These decisions are left to product management. I have virtually no control what happens here. Besides, due to our "dynamic" market, schedules and features routinely change. What was on the drawing board today could be in the wastebasket tomorrow. Or it could be on the assembly line (probably not tomorrow though). ------------------------------ Subject: How come the XYZ channel is no longer available? I can't answer this either. I don't keep up with the comings and goings of program providers. The questions answered here will cover more of the design and operations aspects of the system. However, you can email IPG@gi.com with these issues. ------------------------------ Subject: Section 2. Maps ------------------------------ Subject: What are maps? "Maps" are the information that the box needs to navigate. The maps are comprised of CDT (Carrier Definition Table) Other map tables also exist, but are not necessary for 4Dtv (e.g., Transponder Name Tables). For more detail, see the "A/56 System Information for Digital
Television 3 Jan 96" which can be found at http://www.atsc.org/Standards/stan_rps.html
. ------------------------------ Subject: Where do the 4Dtv Maps come from? The 4Dtv NITs originate from the SAC (Subscriber Authorization Computer) in San Diego, at the GI ACC (Access Control Center). They are then transmitted to each DCII uplink that allows 4Dtv access. The SAC stream is then input to the DCII encoder and multiplexed with the video and audio data. ------------------------------ Subject: How much storage does the 4Dtv IRD have for the maps? Each map (a.k.a. "table") is comprised of a number of records. The 0x6D code allows for the following record storage: CDT 256 ------------------------------ Subject: Since each SIT record equals one satellite, is 80 Satellites enough? What's gonna happen when there are more than 80 satellites? First of all, C/Ku combos count for two satellites in this system. So actually, worst case (all sats are C/Ku), there is only room for 40 satellites. But this probably more than covers the foreseeable future. ------------------------------ Subject: Only 1920 TDT records? Is that enough? It should be. But, this will take some careful management on GI's part. ------------------------------ Subject: Why is TDT record space running out? Simply answer: generic satellites. 1920 TDT records is more than enough TDT records for the "real" satellites. However, since the current code offers no manual tuning capability, "generic" satellites were created at the GI ACC. In order to offer as much generic capability as possible, generic satellites and their transponders were added until the network storage space was full or nearly full. The first record space to reach its limit was the TDT record space. The result is that now every time we have to add a real satellite (and its associated transponders), we must delete another satellite to make room. ------------------------------ Subject: What data is saved and what data is deleted when I unplug my 4Dtv? Generally speaking, all user settings and Maps are saved when the 4Dtv is unplugged. However, IPG data is not saved when the 4Dtv is unplugged. Maps and user settings are saved Flash RAM. IPG is saved in DRAM. Maps are the CDT, MMT, SIT, STT, TDT, VCT, and RTTs. IPG data includes guide data as well as the SNT (Source Name Table). Source Names are the names of the various channels. ------------------------------ Subject: How is the IPG data associated with the MAP data? The source ID. Within each VCT record is the Satellite ID, the transponder number, and the source ID. Within each SNT record is the source name and the source ID. Guide data is also referenced by source ID. Thus, the source ID is the link between the relatively static MAP data and the dynamic IPG data. ------------------------------ Subject: How come I can tune to satellite, but I can't change channels correctly? The 4Dtv has the SIT record, but not the TDT record. This usually happens when the TDT space is getting maxed out. If the 4Dtv receives a TDT that is does not have room for, the 4Dtv will flush out the TDT of the last satellites that was stored. So the 4Dtv will flip flop between storing the last two received satellite's transponders. The satellite without the transponder records cannot be navigated correctly. The GI ACC will have to delete a satellite to correct the situation. (note: there is also a question of why channel surfing doesn't work past a certain channel. I'm still looking into this one.) ------------------------------ Subject: How come when I tune to X7 and A2, the number of channels changes? Starchoice broadcasts its own map on A2. This map covers just the channels on A2. When the 4Dtv tunes to A2, it updates its A2 map with the changes. Then when 4Dtv tunes back to normal DCII satellite, the 4Dtv updates the map with the 4Dtv A2 map. This does not really hamper the operation of the 4Dtv, but does lead to questions like this one. To eliminate the questions, the 4Dtv A2 map will be made the same as the Starchoice map. When? I don't know. X7 (HITS) presents a similar situation, except that the way that the HITS system is setup, the 4Dtv should not be receiving any maps from the HITS feed. However, it looks like we are receiving one HITS virtual channel definition. I don't know why. Once again, this does not hamper the operation of the 4Dtv. This is a low priority problem. ------------------------------ Section 3. Guide ------------------------------ Subject: Does adding or removing a satellite affect the guide data? No. In reality, all removing/adding a satellite does it to set a bit in the SIT record as "show"/"don't show." All satellite information is always in the 4Dtv. Additionally, the 4Dtv downloads as much IPG data as it can fit its DRAM. IPG data is not filtered by satellite. In fact, the IPG data contains no satellite information. Generally speaking, IPG data is just source IDs that point to program names that point to program information. ------------------------------ Subject: A channel is missing. Unplugging it brought it back. What happened? Most likely, our guide data provider dropped it. Our guide data provider provides us with hundreds of channels of data. They do the same service for many other customers. Occasionally (or maybe not so occasionally), a channel gets lost. Our customers complain. We call the guide data provider. They fix the problem. Unfortunately, the 4Dtv does not know that the problem is fixed until it gets the next update (likely that night). However, if the problem is fixed, unplugging the 4Dtv will cause the 4Dtv to lose its IPG data. Then when you plug the 4Dtv back in and get new data, the problem will be fixed. <end> |