DMX cable by the foot?

[PilotLight]

Thanks guys,
What a great thread!! I feel well advised now.
Mike

 

[bdesmond]

What makes cat 5 usable for DMX is that it is a twisted media, 802.3 (the ethernet standard) is a much higher data rate then DMX, and therefore DMX can run on the media just as well as 802.3 data. Ethernet is the protocol, Cat 5 is what the protocol runs on (and it runs the same on fiber as it does on copper). The DMX512 protocol however is not a routable protocol like 802.3 is. DMX aquates to more of a serial protocol (think old modems) then the ethernet protocol. You can get DMX to ethernet nodes (artnet, shownet, etcnet2) that will convert your DMX signal to ethernet so you can run multiple universes accross one wire, and manage where your data goes. ACN which just got standardized is what is going to replace DMX eventualy, and that protocol is a routable protocol so you will be able to use off the shelf switches and routers to run with. This is the reason that is is sudgested to pull cat5 in renovations so that when the day comes that ACN will be usable its a simple matter of changing connectors, not pulling new wire.

Almost, but not quite. We need to look at the first three layers of the OSI Model here to understand this:

Layer 1 is your physical layer, contrary to popular opinion, this is not actually the wiring, but rather how the data is transmitted over the wire - be it electrically over some CAT5 cable or optically over fiber. Even then so, Layer 1 is different for different types of fiber optic and copper connections. A hub operates at layer 1 - it simply repeats each signal it receives out every port.

Layer 2 is Ethernet and the 802.3 standards. This is where you have your Layer 2 address, the MAC Address. Layer 2 traffic is non routeable here. There are some goofy things you can do to span subnets and routed links, but as a rule of thumb consider Layer 2 (Ethernet) non routeable. A switch is a layer 2 device - it maintains a table mapping layer 2 addresses (MAC Addresses) to port numbers and only forwards the data to the port where the destination is.

Layer 3 is IP. This is where you have your Layer 3 address, the IP address. Layer 3 traffic is routeable. A router is a layer 3 device - it moves traffic between subnets.

The rule of thumb here is that to cross layer 2 domains, you need a layer 3 device. This is where the concepts of subnets, vlans, and wans really comes into play, but that's out of scope here. There are other protocols that run at these two layers (for example Token Ring and IPX), but this discussion is centered around Ethernet/IP.

To get DMX running on your IP network, you need to encapsulate the DMX data in Ethernet packets, and likely in IP and TCP or UDP headers as well. This will allow your hubs/switches to process the data. If you chose to only do DMX over Ethernet (but not IP), you would have to hard code the MAC Address of each DMX device in your system as there is no name resolution at this layer (like DNS). Moving to IP allows you to have routed traffic (for example your control room could be on the third floor and your auditorum on the second which are on different subnets). Another example is a console which controls devices in another building. Buildings are often seperate subnets (aka layer 3 domains).

TCP/IP is actually not layer 3. It's a combination of Layer 4 and 3. TCP is layer 4, and IP is layer 3. UDP is the other Layer 4 protocol you'll usually hear about.

There are seven layers in the OSI Model:

1 - Physical
2 - Data Link
3 - Network
4 - Transport
5 - Session
6 - Presentation
7 - Application

The way I remember this when I forget is: All People Seem To Need Data Protection.

 

[Pie4Weebl]

bdesmond, I know understand why the company Level 3 is named as such.

 

[bdesmond]

bdesmond, I know understand why the company Level 3 is named as such.

Yup. Do a bit of research and InterNAP and Equinix are two more that will be pretty obvious.