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MRV with DECA verses hardwired ethernet?

Discussion in 'DIRECTV Connected Home' started by JRThiele, Apr 7, 2010.

  1. veryoldschool

    veryoldschool Lifetime Achiever Staff Member Super Moderator DBSTalk Club

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    DECA's "single pipe" is a spread spectrum modulated RF signal, which can't really be compared to twisted pairs directly, at the level you're trying to I don't think.
    The cloud is "Hub-like", since all DECAs receive the same signal, while the DECA outputs are "filtered", so they're more like a switch, and only output what the device connected wants/needs.

    Maybe it's just where this is viewed from:
    Inside the cloud is a hub function.
    Inside a switch isn't.
    Outside of the cloud is like a switch, not hub like.
     
  2. wavemaster

    wavemaster Godfather

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    It would be nice if the term "cloud" wasn't used. It isn't applicable here. There is no distributed load, data store, redundancy etc. It is nothing more than a LAN over D*'s wiring.
     
  3. veryoldschool

    veryoldschool Lifetime Achiever Staff Member Super Moderator DBSTalk Club

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    I just received a message reaffirming this and a "whole bunch" more about DECA verses IP traffic over ethernet.

    The short breakdown in "blonde speak":

    With two devices on the network, there is little difference between any of these, DECA, switched, or Hub.
    The more devices on the network, the more each "fights to talk/listen". Switches are better than hubs here.

    DECA is the "FedEx" of networking video streams, since it prioritizes the package/commands and will "bump" high priority commands above lower packages.
    Ethernet doesn't/can't do this. Everything is sent via ground service by simply being loaded on the truck when the truck is there and routed to its destination.[/blonde speak]

    While this may be a crude attempt to explain, I hope some will understand.

    I'll leave the networking gurus to fight between themselves.
     
  4. harsh

    harsh Beware the Attack Basset

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    It probably isn't appropriate to introduce the concepts of Frame Relay into this discussion. Cloud in the sense of a network segment where everybody gets rained on fits pretty well.
     
  5. veryoldschool

    veryoldschool Lifetime Achiever Staff Member Super Moderator DBSTalk Club

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    Cloud in the sense of an electron cloud, where you don't really know where it is at any one time. There is such a multitude of RF signal paths, that it's hard to know which one is being used and by tapping in to monitor them, you've changed them.
     
  6. wavemaster

    wavemaster Godfather

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    Look up the practice - THIS has nothing to do with cloud/cloud applications/cloud computing. It is a LAN over coax. Nothing more.

    Saying cloud or using the term cloud just confuses the subject.
     
  7. wavemaster

    wavemaster Godfather

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    In my network, DECA is ground service for only a few users.

    Ethernet is Express Overnight for everyone.
     
  8. BudShark

    BudShark New Member

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    DECA has a mechanism to prioritize packets, bypassing FIFO queues (windows and app buffers)

    Ethernet doesn't (at least not without application/specific hardware).

    Thats all he's saying. Utilizing the current analogy:

    I need 3 day delivery all the time, and I have critical items I need in 8 hours sometimes (trickplay commands):
    DECA is 2 day delivery with option of 4 hour delivery.
    Ethernet is 1 day delivery.

    So Ethernet affords me no advantage over DECA because, although its faster in general, both meet my minimum need.
    DECA affords me an advantage because it has a priority delivery when I need it. Ethernet simply has the "always faster" option that isn't fast enough for my priority.
     
  9. veryoldschool

    veryoldschool Lifetime Achiever Staff Member Super Moderator DBSTalk Club

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    While I understand your network is fast, does it change priority "on demand"?
    This was the point I was trying to make. DECA does. Everything can be moving along fine and then "This has to get there right now" overrides everything else.
    I think yours is simply so fast/free of load that, for you, it doesn't matter.
     
  10. BudShark

    BudShark New Member

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    In MoCA/DECA speak, cloud refers to the network created by joining 2 or more clients to the physically connected MoCA/DECA rhealm. It is 100% correct, and logical, to call a DECA network a cloud.

    You are confusing it with another use of cloud in computer speak.
     
  11. harsh

    harsh Beware the Attack Basset

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    In the context of MRV, switches are nothing like hubs. Switches offer bidirectional communications between two nodes that only risk collision when other nodes try to "horn in" on existing sessions or there is a broadcast packet. Most of the time, the traffic flows up to the rated capacity in both directions entirely without concern for (nor awareness of) what is going on in the rest of the network.

    In contrast, hubs send everything from each node to every other node in relay fashion kind of like a distribution amplifier. If there is a collision, both packets are lost and each must be retransmitted after a random delay interval.

    DECA's closest analog is probably along the lines of an administered Token Ring setup where the token is handed out by the Network Controller as opposed to being passed on to the next node. While a node has been given the nod by the NC, it broadcasts its packet and waits for another nod.
     
  12. veryoldschool

    veryoldschool Lifetime Achiever Staff Member Super Moderator DBSTalk Club

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    Yes they are [in the context used by me] since they'll sending the MRV stream.
    Don't "cherry pick" my posts to further your nonsense please.
    If you follow what I posted and you'll see where I distinguished between the two and further how DECA is different.
     
  13. LameLefty

    LameLefty I used to be a rocket scientist

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    Here's a suggestion for Harsh -

    Why don't you install a DECA-based network for your own DVRs and do some real-world comparisons so you can post with some first-hand experience, like those of the rest of us who've actually used it for awhile? It's hitting the mainstream in a couple of weeks so you won't have any excuses. ;)
     
  14. BudShark

    BudShark New Member

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    :)

    There's a lot of fact and theory. The facts are:

    - half-duplex networks bad
    - switched networks good, but no priority for command/control packets
    - DECA networks good, but no priority for command/control packets

    Both Ethernet and DECA have the bandwidth and ability to support streaming. As long as you avoid half-duplex, collision prone networks you are fine from a data transmission standpoint.

    DECA provides an advantage only because I have a mechanism for priority. And that priority is more of an advantage NOT because its faster on the wire (which it isn't and can't be), not because I knock something off the wire (which I don't), but solely because I can bypass the FIFO queues on both sides of the equation - affording me a more "local" trickplay experience.

    There's nothing you can do with an Ethernet network that overcomes that entirely. I can speed things up, I can go enterprise class, I can do all that. I can eliminate all my ethernet bottlenecks. But my trickplay packet will still be queued up in the network stack window and buffers behind video packets... and in this case DECA, in its cloud based, shared bandwidth, scheduled data delivery - will be faster, everytime.

    There's lots of reasons why DECA makes sense for DirecTV to make it the preferred option.
    There's also reasons why DECA is preferred even if you have a great Ethernet network.
    Some people just don't want to hear that, and for them, there is the option of self-supporting it on Ethernet and being happy with what they have. Just, please, stop mischaracterizing it unless you understand it (or at least have used it, unlike some little basset hounds I know.. ;) )
     
  15. harsh

    harsh Beware the Attack Basset

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    The aspect that seems to be eluding you is that switched Ethernet doesn't need to be prioritized because the MRV traffic is routed exclusively between the client and server involved in the MRV session. Similar traffic between other nodes is of absolutely no concern as those conversations are traveling on their own TX and RX current loops connected by the switch relay "fabric". Broadcast traffic comes through occasionally (as it does with DECA), but the packets are few and the sizes are relatively small.

    If "lag" is an issue and connecting the "client" and "server" via a direct cable doesn't fix it, the problem isn't with the communications medium. The reports that I've seen from those who tried a direct CAT5 connection was that the lag was not appreciably improved.
     
  16. wavemaster

    wavemaster Godfather

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    Well you have the whole shop laughing today (a shop full of network engineers). So you will confuse some and totally entertain others. Whatever blows your hair back.
     
  17. BudShark

    BudShark New Member

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    You haven forgotten about your buffers and queues that exist along the way, primarily in the network stack.

    Its just like driving a car. The slowest part of the trip isn't the highway... its the off ramps and the traffic control at the end of the ramp. Now imagine you had the ability to bypass everyone sitting behind the red light and go to the front of the off-ramp.

    Thats the difference. Not this other stuff you keep dragging in. People want to mischaracterize the data flows and rates and mechanisms. There are lots of variables, but the fact remains, a correctly setup DECA and Ethernet both have the ability to move MRV data without lag or bandwidth being an issue.
     
  18. LameLefty

    LameLefty I used to be a rocket scientist

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    Congratulations. You've missed the entire point. Again. :lol:
     
  19. wavemaster

    wavemaster Godfather

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    This is funny stuff here today.

    If you have 10,000 cars a day on your dirt road, you will need to prioritize traffic with a traffic cop. Or limit the traffic to 10 cars. This is what you have with DECA and if it works for you great!

    If you have a 6 lane freeway with 10,000 cars a day on it, A. everyone is screaming along, and B. you can handle a lot more cars.

    Oh, and not JUST ONE BRAND OF CAR (like DECA with D*'s STB) but all makes and models.
     
  20. BudShark

    BudShark New Member

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    Cloud: A network cloud exists because when data is transmitted across a packet-switched network in a packet, no two packets will necessarily follow the same physical path. The unpredictable area that the data enters before it is received is the cloud.

    In an RF based network with splitters, no signal travels the same path. Hence, MoCA physical networks are referred to clouds, because the path is unpredictable. But I'm glad I was able to give you guys a laugh. ;)
     

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