Today in "IP Over Avian Carriers" news:


I think every day about how cable internet is IP over MPEG. this is a literal fact. DOCSIS sends downstream data in MPEG frames because that's what the cable networks are optimized for and what all the switching equipment understood when cable broadband took off. "Instead of using Ethernet-based formatting, the downstream packets are formatted as a continuous stream of 188-octet MPEG packets, each packet comprising a four-octet header followed by 184 octets of data."

So Netflix on Comcast is MPEG over IP over MPEG.

You would be forgiven for assuming that RFC 4259 is an April Fool's joke, with this diagram in it:

|T|V|A|O|  O   |            | O |S |O |         |
|e|i|u|t|  t   |            | t |I |t |         |
|l|d|d|h|  h   |     IP     | h |  |h | Other   |
|e|e|i|e|  e   |            | e |T |e |protocols|
|t|o|o|r|  r   |            | r |a |r | native  |
|e| | | |      |            |   |b |  |  over   |
|x| | | |      |   +---+----+-+ |l |  |MPEG-2 TS|
|t| | | |      |   |   | MPE  | |e |  |         |
| | | | |   +--+---+   +------+ |  |  |         |
| | | | |   | AAL5 |ULE|Priv. | |  |  |         |
+-+-+-+-+---+------+   |      +-+--+--+         |
|  PES  |   ATM    |   |Sect. |Section|         |
|                  MPEG-2 TS                    |
|Satellite| Cable | Terrestrial TV | Other PHY  |

Figure 1: Overview of the MPEG-2 protocol stack


The 44,100 Hz sampling rate for CDs came about because there was no digital storage medium capable of holding the 650 MB of a compact disc and so analog video cassette tapes were used. These had 245 field lines 3 sound samples each line 60 frames per second. 245x3x60 = 44100.

BTW here is a screengrab of 245 x 3 = 735 samples for 1/60 second of music.

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13 Responses:

  1. Jbillings says:

    Can anyone model “DOCSIS Escape Velocity”

  2. Nathan Roberts says:

    I'm reminded of the abomination that was PPPoE. PPP over Ethernet. Used as a ghetto authentication method for DSL connections.

    My Unix professor described it thusly: "The point of PPP is to emulate ethernet over serial lines. So, that means that PPPoE emulates ethernet over ethernet."

  3. I think I'm just as glad I got out of the video industry before I learned how DOCSIS worked. That might have broken me.

  4. Kyle Huff says:

    It's emulations all the way down.

  5. jwz says:

    Now that I think about it, I wonder if Netflix is actually MPEG over TCP over MPEG, which is possibly even nuttier.

    • Nick Lamb says:

      Yes, but not for long?

      Netflix uses HTTPS, so today that's TLS, which runs on top of TCP. But tomorrow (for some value of tomorrow) it will be QUIC instead which uses UDP because they weren't able to encrypt enough of TCP.

      The truly compelling thing about End to End Encryption turns out not to be protection from snooping or anything noble like that, it's that Middleboxes are built by incompetent morons so the more you take them out of the equation the better everything works. Not having Network neutrality laws doesn't cause you any worries when the ISP can't tell a blog page from a VoIP call or a movie from a firmware upgrade.

  6. Louis says:

    I remember some stupid organization requiring some document via fax. So I added an image of my signature to a Word document and sent it from Word to my fax-capable printer over WiFi. The fax in turn was attached to the RJ45 port of my DSL modem. (I guess fax doesn't use the V of VoIP?) On the other end that org probably has an incoming-fax-to-pdf-as-email-attachment converter...

    • ssl-3 says:

      In the gap between ubiquitous Internet and smartphones, I had a prescription that I needed refilled every month.

      Because the pharmacy couldn't be trusted to actually get this done without prompting, I had re-order it myself.

      The first time, I went to the pharmacy, asked for a refill, and waited for that to get done.

      That got really old.

      So I tried ordering with a web browser, and it was a pain in the ass: Verification upon verification, email confirmations that barely worked, endless torturous stuff.

      And even when jumping through those hoops, it didn't believe that I was me.

      So I called the pharmacy and a computer answered. It offered to issue a refill, all it wanted was a prescription number and a date of birth. Not so bad.

      So I plugged that into a dialing sequence on my dumb phone: It called, paused, pressed 1 for a refill, entered the RX and DOB, and entered an exit code to hang up.

      At first I had pauses between these things, but it turned out that the IVR was perfectly content with all of the digits being sent in rapid-fire. So it went something like 12024346558,127433443537080319891112

      In this way, I dialed one contact, heard an interrupted "Thank y--" and a rapid succession of DTMF interspersed with occasional consonant speech glitches followed immediately by "Goodbye." I didn't even have to end the call myself.

      Refills became easy. But I wasn't done yet -- there were still snags.

      This pharmacy computer would call back when my refill was ready, and that was pretty annoying. So I set those calls to be silently routed to voicemail and it was actually proficient at leaving that voicemail.

      This was working really well at this point. It was almost totally convenient.

      I set up Google Voice to transcribe those voicemails to text, and then forward that text via SMS to my cell phone.

      This was fantastic: Push a couple of buttons to get a refill and wait for a text to let me know it was ready to it up. It was like living in the fucking future, but without all of the nonsense involved with the overbearing website. It was all so backwards that it made me laugh every time it worked.

      And it did work. Flawlessly. Every single time.

  7. Pierre B. says:

    If you think this is an abomination, then I recommend you do not interest yourself in how wifi really works under the hood. At least IP-over-MPEG had the excuse of a big installed base.

    • Doctor Memory says:

      Is there any wireless data protocol that isn't a crawling Lovecraftian horror under the hood? I've occasionally edged up against various permutations of this dating back to the early satellite era and every single time it's ended with me nursing a large drink and a larger headache.

  8. Tinus says:

    If I counted correctly ethernet has 38 octets of overhead for a frame that has up to 1500 octets of data, so 4 octets of overhead for 184 octets of data isn’t too poor.

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