Re: IP cameras on ring topology, not star

[Pat Coghlan <info@xxxxxxxxxx>]

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.

A couple of people mentioned wireless, but the customer does not feel
that wireless is secure enough.

>
>> 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.

>
> 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.

> Frankly, I think you've been misled by the "ring" designation - it
> refers to the way packets are distributed around the network, rather
> than the physical cabling of the network.

I haven't been misled by anything.  The "ring" designation is a hard
requirement.  200 cameras can't be wired back to a common switch/panel.
  They must operate as drops on a ring/loop and be wired to two other poles.

>
>> I've seen some gigabit LAN gear which supports a ring topology, but
>> I'm curious to hear if anyone has actually done this.
>
> Given the other considerations you'll have with 100 cameras - most
> notably, processing power and storage issues with the DVRs themselves -
> you need to go back to the beginning in your design concept.
> Particularly: you're almost certainly going to need multiple DVRs to
> handle the amount of data 100 cameras are going to be outputting.  That
> alone means breaking the network up into segments.  At that point, you
> can segment groups of cameras, each to a switch central to that group,
> with that switch feeding back to a main switch with the DVRs.

...as long as they go back to the main switch via the ring they are
physically wired to.

>
> Example: break camera locations down into seven groups of 14-15 cameras
> that are nearest each other.  Locate a 16-port switch near the center of
> each group.  Run a network feed from each camera to its assinged switch.
>    Then locate a 16-or-more port switch in your "server room" (or
> wherever your DVRs are located).  Run a network line from each of the
> outlying switches back to the central room.

No can do.  In addition to this being a wide perimiter configuration,
it's also a temporary project.  Everything needs to go in with pre-cut
cables etc.  You're pretty much looking at going pole-to-pole to set up
and take down.

> 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.

>
>
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--

-Pat