Questions about the Series 3

Discussion in 'TiVo Coffee House - TiVo Discussion' started by Justin Thyme, Jan 6, 2006.

  1. Jan 8, 2006 #81 of 167
    dt_dc

    dt_dc Mostly Harmless

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    Sounds good in theory ... but ...

    Anyway, yes ... you're starting to get at the heart of the cable view of two-way vs. the CEA view of two way ...

    However, the "open non proprietary technology" has it's problems too ...
     
  2. Jan 8, 2006 #82 of 167
    Justin Thyme

    Justin Thyme Contra sceleris

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    Right. Well I am going to have a go at "The OS War" in the living room, with a focus on OCAP v. Vista v. OSX vs. open standards.

    When Apple announces their bundle (last year's idea of Flat Panel + Tivo- apple is going to do an intel viiv inside a big screen), then we will know more details on if Apple went open, or did the same Fairplay lockout bit.

    All these vendor lock in schemes stink. But there aren't any rules to this game [referee can only make polite suggestions], so they do it.

    With a vengeance.
     
  3. Jan 8, 2006 #83 of 167
    DocNo

    DocNo Member

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    Ouch - my head hurts!

    Justin... you are confusing several technologies. Lets see if we can simply.

    In networking, you have the network itself and then devices on the networks. In internet parlance, any device on a network (server, PC, Tivo, etc.) are called hosts.

    A Local Area Network (LAN) is a piece of wire that has a common network address. In simplistic terms, if a device can talk to another device without having to cross a router, they are on the same network.

    Routers are used to route traffic between networks. Generally in a home, you have only one router - the device provided to you by your ISP. Often called a cable or DSL modem. It routes traffic between your ISP's wide area network, and your local home network.

    Once on your local home network, there are two devices that can enable you to have more than one device/host on your network. A hub, or a switch. A hub is just a dumb repeater. Whatever comes in on one port, gets broadcast out on all the other ports. A switch is more deterministic. If device A sends out a packet for Device B, the switch ensures that only port B gets the traffic. A device on port C or port D won't see that traffic.

    OK, that's nice, but why does it matter? Well, ethernet is CSMA/CD - Carrier Sense Multiple Access/Collision Detection. Basically, in ethernet, the "wire" is a shared medium. Think of it as a long hallway. Each device would be a door on that long hall way. If I want to talk to you, I lean out of my door, yell your name, you listen and then I talk to you. Works fine as long as it's just you and me talking, but more than one person trying to talk at once garbles everything up - in ethernet terms, a collision.

    Carrier sense - me leaning out the door to see if anyone is already talking
    Multiple access - all the devices sharing the same hallway
    Collision Detection - me talking, detecting someone else talking over me and backing off

    Collisions are really bad - because everyone on the network will stop what they are doing, back off a random amount of time before trying to talk again. These random amounts of time are much larger than normal communications times, so collisions really slow down a networks effective throughput. that's why hubs stink - every one (all devices on the network) are in the same collision domain.

    So, now we come to switches. Typically, there is one device per port on a switch so there is no possibility for collisions since there is no way for more than one device to be talking on that piece of wire. Instead of a long hallway, think more along the lines of the telephone network.

    So, switches can speed thing up two ways - one by preventing collisions due to their very nature, and two by restricting traffic between devices to just their wires. That way if Device A and B are talking, they don't take any bandwidth away from devices C and D that are talking.

    And that's also where Bus and Star come into play - a network setup with a hub is a bus - all the devices are peers. A network setup with a switch is a star network - the switch is the center of the star.

    As for speed - with ethernet it's 10Mbit, 100Mbit, or 1000Mbit (gige). There is some 10000Mbit out there (10gige) but it's pretty rare. That's maximum effective throughput, BTW - rarely realized due to collisions and overhead (packet headers, padding, etc.)

    So, each device will talk at the maxim effective rate of the network it is connected to. The only way to get around that is either via flow control tricks (i.e. telling the device the network is busy just to get the device to stop talking so the bandwidth on the network can be used by other devices) or by using Quality of Service (QOS). Tivo doesn't support QOS, so that's out, and flow control tricks really aren't needed on a home network.

    Anyway, hopefully that helped make it as clear as mud :) If not, you can try this writeup. Feel free to ask any further questions if things are still muddy ;)
     
  4. Jan 8, 2006 #84 of 167
    classicsat

    classicsat Astute User

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    As in non-bradcast? That would be defined as "Cable". You could narrow that down to "Pay Cable", or "Controlled Cable"
     
  5. Jan 8, 2006 #85 of 167
    Justin Thyme

    Justin Thyme Contra sceleris

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    DrNo- I hope I'm not that far off in the weeds. The picture I was attempting to convey is the following.

    The switch in what consumers call routers (which is actually a router and a smart hub) isolates segments.

    What I was saying was that segments ("spokes") TivoA-> Router, and Router ->TivoB could be running at 70Mbits, and segments TivoC-> Router and Router->TivoD could be running at 70Mbits. Because they were isolated segments, and there were no collisions, 140Mbits/sec of data would be flowing on a 100Mbit LAN.

    Seems like I got this right in your discussion of switch capability, ending with:
    So my statement about the data rates of those segments through the "router" was correct, right?
     
  6. Jan 8, 2006 #86 of 167
    Justin Thyme

    Justin Thyme Contra sceleris

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    You are not following my question.
    1) On a Pay cable system, I have the local OTA stations listed. This is Set 1 of channels.
    2) all other channels not in Set 1 are called what? The term used in FCC documents is "Premium Channels". Are you aware of an alternate term less liable to cause confusion to readers of this forum?
     
  7. Jan 9, 2006 #87 of 167
    krypdo

    krypdo Not Majority

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    My situation exactly. Almost exactly. I'm actually holding off upgrading my main living room rear projection to HDTV until the S3 comes out. Been tempted a few times to just use Comcast's DVR but I know anything less than a TiVo UI won't survive "the wife's test". HDTV is meaningless without TiVo in my house.

    However, MRV between S3 and S2 is critical, even if it means only SD contents. Got kids who want to have every show accessable at every TV in the house.

    I actually have no question. Just want it to work as described.
     
  8. Jan 9, 2006 #88 of 167
    DocNo

    DocNo Member

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    In the scenario you outlined, and assuming the switch is an efficient one and has the internal bandwidth to handle it, then yes - you can get greater than 100Mb throughput.

    Again, there are all kinds of things that conspire to keep you from seeing anywhere near that real throughput, but you are essentially on the right track :)
     
  9. Jan 9, 2006 #89 of 167
    Justin Thyme

    Justin Thyme Contra sceleris

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    So ITV- it looks like the concensus answer has been formed. For typical home set ups where the lines for the home all go into a modern router, then you should assume that T3 to T3 communication will go at near the maximum real life limits of 100BaseT lines- which Dan mentioned as being max 70Mbits/sec. You could have any number of pairs of T3's talking to each other, and they would still be talking at 70Mbits/sec.

    This condition does not apply when you have one T3 interacting with two Tivos, or when the topology of the network is different- like you have a double star where there is a shared backbone that must carry mixed traffic.

    Okay?
     
  10. Jan 9, 2006 #90 of 167
    nhaigh

    nhaigh Member

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    Lawrencevill...
    Sorry is this is repeating the question. Does this mean that the T3 must be hard wired, i.e. no wireless networks or powerline adaptors becuase the required throughput will be to high?
     
  11. Jan 9, 2006 #91 of 167
    DocNo

    DocNo Member

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    Your always going to get better performance with a wired solution vs. a wireless solution.

    While I'm currently using wireless now, and pretty happy with it, I will definitely be running cat5 throughout the house - and heck, I may even pull some fiber (probably plastic, no need for glass) from the basement to the attic while I'm at it just in case I want to play with something beyond 100Mb in the future.
     
  12. Jan 9, 2006 #92 of 167
    segaily

    segaily Member

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    Just as a comment most ethernet now supports what is called full duplex ethernet meaning no more collisions. This allows you to get full bandwidth 100Mbits/sec going in both directions at the same time on a full duplex fast ethernet port. You do still have some overhead from packet headers etc, so you are not moving 100Mbits/sec of data, but you are moving 100Mbits/sec.

    A max size ethernet packet is 1518 bytes. You probably have about 32 bytes of header and a 4 byte checksum. Not every packet is max size, but when you are doing a large file copy hopefully most of your packets are near max size. Hopefully we will be able to copy shows at about 95Mbits/sec from one s3 to another.

    As far as the wireless network goes. They are still giving us usb ports so I expect they will still support it. With a good wireless network you will get about half the speed you would on a wired network. It will not be as good but hopefully that will be good enough.
     
  13. Jan 9, 2006 #93 of 167
    nhaigh

    nhaigh Member

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    Lawrencevill...
    But how many Mbits/sec need to be transfered to be able to watch an HD program using MRV in real time i.e. so that it transfers at least as fast as it plays back?
     
  14. Jan 9, 2006 #94 of 167
    Justin Thyme

    Justin Thyme Contra sceleris

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    I think Tivo is very big on wireless but think you are right- they will focus on peripherals, not integrated in the box solutions.

    But I suppose wireless integrated is still concievable, though Megazone's CES2006 box photos give no indication and I wouldn't bet on it for this time around. Still, they could have stuck a Yagi antenna in the front panel, but a natural thing to expect would be a connector on the rear for an external.
    [​IMG]
    Tivo has been heavily into Broadcom chips, and Broadcom is pushing the envelope with pre-N chips since 2003. N theoretically goes up to what- 500mbits but people only seem to believe 100Mbits, with greater range and use of 5ghz spectrum. My understanding is that the cablecard 1.0 spec has support for doing a cablemodem- so a cablecard box could be constructed to compete with triple play devices from the carrier.

    The idea here is that the Tivo 3.x architecture might at some time make Tivo the gateway to the internet for many homes. Cable in, Wireless-N out to VOIP phones etc. But that would mean they would be integrating a lot of network technology in the box, and I am a little skeptical they want to bite all this off, or place any bets on where that market is going. But you see why Cisco is interested- and bought Kiss, Sci-Atl and NetLink who make a dvr and an various STBs.
     
  15. Jan 9, 2006 #95 of 167
    Justin Thyme

    Justin Thyme Contra sceleris

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    Dan covered this question. 17-20Mbits. Although Dan is not ALWAYS right, he nearly always is when he makes a definitive statement of fact, and I have battle scars to prove it. You can take Dan's numbers to the bank.
     
  16. Jan 9, 2006 #96 of 167
    nhaigh

    nhaigh Member

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    Lawrencevill...
    Thanks. I did read Dan's post back then but didn't assimilate the information. I think I'm going to run some cat 5 around the house anyway seeing as this will be the third device in the Den that "requires" a network and none of them are PC's :)
     
  17. Jan 9, 2006 #97 of 167
    Dan203

    Dan203 Super Moderator Staff Member TCF Club

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    I usually do some fact checking on Google before I post definitive numbers like that, so it's more of a case of thoroughness then being right or wrong. :)

    Dan
     
  18. Jan 9, 2006 #98 of 167
    Dan203

    Dan203 Super Moderator Staff Member TCF Club

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    Why would they do that when they can leave it out and sell you a USB wireless adapter for an extra $50? :)

    Dan
     
  19. Jan 11, 2006 #99 of 167
    megazone

    megazone Hardcore TiVo Geek

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    That makes it sound sinister. You could also say - why include it and raise the price of every unit? ;-)

    Wired Ethernet components are very inexpensive now, but WiFi components still cost enough to impact product pricing. Also, wired technology is fairly stable and slow changing, while WiFi is still changing rapidly. 11g is it today, but 11n will be coming before long. Anything they build into the unit will be obsolete before too long. Making new adapters is easier.

    It also makes a performance difference. Putting my adapter up on the corner of the entertainment center cause a big jump in connection quality compared to having it down by the TiVo.
     
  20. interactiveTV

    interactiveTV New Member

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    I guess we're also assuming the Tivo won't be a bandwidth constraint as in S2. The encrypted stream should be written to disk and thus, I guess, there is less for the Tivo CPU to do when sending across the network, yes?

    Or does the 100baseT adapter in the S3-- assuming we know who makes it -- handle some of the communication tasks and thus free up CPU cycles (which, as I understand it, is what the Tivo branded USB adapter does in a minor way)?

    Perhaps I should put all Tivos on their own switch apart from the rest of the network?

    _ITV
     

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