Re: IP cameras on ring topology, not star

[Matt Ion <soundy@xxxxxxxxxxxxxxx>]

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.

> 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.

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.

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'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.

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.

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.


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