Re: IP cameras on ring topology, not star

[Matt Ion <soundy@xxxxxxxxxxxxxxx>]

Pat Coghlan wrote:
> Matt Ion wrote:
>
>> Pat Coghlan wrote:
>>
>>> By hub on each pole I mean a device connected to the ring, with an
>>> ethernet port for 1 camera.
>>
>>
>> Umm, okay... what you're basically talking about then, is a three-port
>> hub on each pole: one port for the camera, one to uplink to the
>> previous pole, one to uplink to the next pole.  It's do-able (4-port
>> 10/100 ethernet switches are fairly cheap these days) but rather
>> convoluted.
>
>
> I'm not suggesting daisy-chaining up to a couple of hundred of these
> devices around 2 km ring.
>
> Let's get back to the main requirement: cameras must be connected in a
> ring rather than home-running (to borrow Morgan's description) each
> camera back to a switch.  I'd like to find out what the best way to do
> this would be.

That's just the point: I don't think there is one, short of a "faux"
ring as I desscibed above.  What you're basically looking for is some
way to "tee-splice" each camera into a single wiring ring... you can't
do that with video OR network, period.  The closest would be as I
desrcibed above, using a small switch at each pole as the "tee" connector.

The only type of network that would PHYSICALLY resemble this would be a
10base-2 setup (the old ethernet-over-coax), but then you'd have to find
IP cameras with a 10base-2 interface (non-existant, as 10base-2 is even
more obsolete than token-ring), and you'd also be limited to 10
megabits, which would not be nearly enough bandwidth.

The important question is, WHY *must* they be in a ring, rather than
home-run?  Perhaps the customer has unrealistic requirements or
expectations.

>>> IBM sells token ring routers, but they are physically wired as a star
>>> (every device has a physical connection back to the router), which
>>> does work for this application.
>>
>>
>> Token ring is an entirely different networking protocol from ethernet.
>> To use a token-ring hub, you have to have token-ring devices; you
>> can't just plug ethernet devices into a T-R hub.
>
>
> I kinda wondered if there might be adapter hubs that do this, especially
> whether they buffered traffic etc. until the token arrived.

You're talking about an ethernet to token-ring bridge, something like
this:
http://www.ringdale.com/products/st/asp/control.wizmoreinfo/id.227/po./en/default.html

However, token-ring wiring is STILL PHYSICALLY done as a home-run.

>> Token-ring being an essentially obsolete technology in a world of
>> dirt-cheap 10/100 switches (T-R data rates are 4 and 16 megabit), I
>> really doubt you'd ever find IP cameras that support it, and a
>> token-ring NIC for your DVR will be bloody expensive, as well as very
>> rare.  And despite the network's "ring" protocol design, 99.9% of
>> wiring designs use the same "star" topology as ethernet, which for
>> your purposes, completely eliminates any benefits there may be to T-R.
>
>
> The advantage of token ring would be that it resolves the collision
> issue that occurs with CSMACD.

That it does, but when you're talking 100 IP cameras, I don't think
you'll find it has enough bandwidth.  And again, it doesn't solve the
desire for a physical ring layout.

>> Again, your other option would be a low-cost 4- or 5-port switch
>> mounted with each camera, as described above - D-Link sells a 5-port
>> gigabit switch for around $60 - but in the long run you'll find that
>> an excessive cost-per-port figure (that's $6000 right there) and it
>> allows too many potential points of failure: one switch goes down, and
>> your whole camera network from that point outward goes down.
>
>
> Cost is not an object.

How about putting a little platform on each pole and just have a
security guard sit there with a handycam?

Again, I think you're looking at a small ethernet switch mounted on each
pole to act as a "tee" to a daisy-chained pole-to-pole ethernet run.  If
you're going gigabit, make sure to use AT LEAST Cat-5e cabling (Cat-6
preferable, since cost is not an object).


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