Networking protocol??

[billy]

Hi,

I'm building a network over cable and also a wireless network that would consist of about 4 nodes and 1 controller. The data being transmitted would be power measurements from a power distributor (these would be the nodes) and these would be sent to the controller which then sends it to a device that is readable by humans.

Would anyone have any suggestions as to what type of network protocol would be suitable for a system like this.? It's basically data from the nodes being sent to a controller and I want there to be an addressing scheme so the controller knows who to send requests to and knows who's data is being received.

I've bought an AVR STK500 development board and am thinking of using AVR Atmega16 microcontrollers for the networking. The data will probably be serial data and this would be transmitted over Cat5 cable.

I've considered using a protocol similar to Token Ring or Modbus, but would like to know if there are any other suggestions or if I could get some help on where to start.

thanks

 

[HoLoCroN]

Is there a way to find out what the native protocols that are currently in use by the equipment?

 

[billy]

Do u mean what is currently available in the market? Or what protocols the equipment is currently using?

there is a company that make a similar system using a protocol developed by Echelon, it's based on Differential Manchester Encoding which can be used on Token Ring networks. But their system is much more advanced and what I need is something relatively simple.

If your'e talking about the equipment's protocols, it doesn't have any. The units I'm monitoring are power distributors and they aren't networked, they are just powered up independently, no software involved.

I'm thinking I might write my own protocol, because it is a relatively simple design, but I would like to base it on something existing or maybe even use that protocol. I'm an amateur at this so I need a bit of guidance

 

[Rachit]

Star Topolopy is best i guess!

hi billy, what i can perceive is that you have a small network
and have a fast Controller too, what you can do is go for a
star topology as that is the easiest to implement.

And if you have star topology you neednt worry
weather data communicaiton protocol is connectionless or connection oriented. I mean that you can use protocols like UDP for your data transfer.

Diagramatically it is something like below:

o------[]------o
/ | \
/ | \
0 0 0


0 are your nodes
[] is the controller sitting at the center acting as a hub/switch

Regards,
Rachit

 

[Rachit]

Some more here on the same!

the txt image i wanted to draw is distorted.
please let me know if it is unclear.

<marquee>rachit</marquee>

 

[TheMajor]

do a google for "echelon watch"

 

[mdshort]

TCP
or
UDP

 

[billy]

Rachit, when you're talking about the star topology, do u mean logically? or physically? Physically, it would be a ring topology, but i'm not sure how this ends up electrically being a star, but i think it can be done.

I'm thinking of using only UDP, to keep it simple, as this isn't going to be an overly complex system.

thanks for your help everyone - at the moment my plan is to use Modbus. I'm reading up on it now so i'll probably have questions specifically on Modbus from now on...

billy

 

[Rachit]

I meant physically STAR

Billy,

I meant a physical and logical Star. I literally meant star.
You can connect the nodes physically to the controller. But I assume you have
a Switch (H/W) or a soft switch with MUX at the controller end.

Rachit

 

[billy]

is it possible at all to have the network set up physically as a ring? I would prefer to have the cables connecting each node rather than each node having a cable going to a centralised controller. i'd like to minimise the amount of cable as much as I can.

I get a bit confused with the difference between physical and logical topologies, esp when I found out that a bus topology like Ethernet is physically wired as a star. now i think with other topologies - is the physical layout always different to the logical layout?

I'm thinking the master can send a message around to a slave with an address assigned to it. if the address matches the slave then the slave performs the action. if not, it passes it to the next slave and so on. does this make it a ring topology - physically and logically?