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Discussion Starter · #1 ·
This is a post from another web site from an expert about the myth of bandwidth problems. I was wondering if some other experts can comment on it. I believe it too be flawed. Thanks.

I don't know where this whole "stream bandwidth" myth started, but we're going to put it to rest right now.

There is NO issue with datastream bandwidth. DirecTV® can send pretty much as many CAM IDs on the blacklist as they want with no problem whatsoever. The control data for the sat receivers is insignificant compared to the MPEG2 video data.

To understand this, first let's look at some given data:

If you look up the specifications for the Link and Transport chips inside most IRDs you will find that they tune in one transponder at a time. The Link chip is responsible for demodulating the 1-2 GHz signal coming off the LNB, quantizing it back to digital form, and performing the error correction. The raw digital data stream is then fed to the Transport chip. The Transport chip is responsible for protocol conversion, which extracts control data from video/audio data, and is also responsible for decryption of the chosen video stream, using the decryption keys from the CAM. The transport chip sends the audio directly to the audio DAC, and sends the video to the MPEG2 chip for buffering and decompression. The MPEG2 chip sends the uncompressed digital data to the NTSC encoder for analog output to the television.

Now, the specifications on the Link chip says that the raw data output rate to the Transport chip is 60 Mbps. Think about that for a minute. That is a nearly fully saturated 100Base-T Ethernet connection. That is a boatload of data.

Now, let's do some calculations, shall we?

The control data consists of several components. But we will only look at the the components that use the most bandwidth.

Guide Data

Let's assume 250 channels of guide data, covering 8 hours of time, with an average of 1 program per hour, 1KB of data per program (covers program title, program description, PPV parameters, etc.), and that entire guide is sent to the IRD every 10 seconds = 1.638 Mbps.

Subscriber Tier Updates

Assume 16,000,000 subscriber cards, 256 cards per group, 3 tier updates every hour, using a 128 byte packet for each update = 0.071 Mbps.

Video Authorization Packets

250 channels, 1 authorization every 8 seconds, at 150 bytes per packet = 0.038 Mbps.

Blackouts/Locals/Time Zone

4 packets per second at 100 bytes per packet = 0.003 Mbps.

Subscriber Specific Packets

16,000,000 subscriber cards, averaging 1 update per day, at 128 bytes per packet = 0.190 Mbps.

Receiver Firmware

10 different types of Firmware, at 4MB per update, 1 update per day = 0.004 Mbps.

The 745 Blacklist

5,000,000 blacklisted IDs, 4 bytes per ID, repeating the entire list every 10 minutes = 0.267 Mbps.


Sum total bandwidth utilized by the control stream = 2.210 Mbps.

Percentage of the 60 Mbps of transponder bandwidth utilized by the control stream = 3.68 %

Typical "high quality picture" MPEG2 bandwidth = 6 Mbps.

Typical "low quality picture" MPEG2 bandwidth = 3 Mbps.

Number of channels available on the transponder in High quality = (60 - 2.21)/6 = 9 channels.

Number of channels available on the transponder in Low quality = (60 - 2.21)/3 = 19 channels.

There you have it. The control data is insignificant compared to video data. In fact, the bandwidth utilized by the 745 blacklist is tiny by comparison to other data, like the guide.

And this analysis doesn't include optimizations that can be made in the control stream, such as:

* Only sending VA packets for the channels contained in that transponder instead of all channels.

* Lossless compression format for the 745 blacklist, or a protocol that can describe ranges or groups of blacklisted IDs

* Lossless compression for the guide

So, the idea that DirecTV® needs to "clear bandwidth" in the datastream is a fallacy. If they wanted to send another 5,000,000 CAM IDs in the blacklist, they could do it by reducing the video bandwidth on the channels carried on that transponder by 0.02 Mbps per channel, which no one's eyes could even begin to perceive.

So why is the blacklist gone then? Hell if I know ...

LG 55" C9 OLED, Yamaha RX-A660, Monoprice 5.1.2 Speakers, WMC HTPC, TiVo Bolt, X1
45,616 Posts

You are talking about 2 different things. The comments above are not related to system capability in regards to carrying more HDTV channels.

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