Network I/O Protocols
The OSI Network Reference Layers,
The difference between a "serial bus" and a "serial interface" and a "network
protocol" is blurring -- see busses (Modbus,
X10, USB, MIDI, etc.), serial IO (RS485,
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YASP: A simple and open protocol for building networks with small
* Adresses length: 1 to n bytes
* Medium access: CDMA/CS/NDA (Carrier Sense Multiple Access / Collision Detection
/ Non-Destructive Arbitration)
* Addressing modes: unicast, broadcast and multicast
* Smallest frame: 6 bytes
* Error detection: CRC16
* Physical layer: 1-wire "open collector" or 2-wire diferential (CAN
* Current PIC implementation: about 480 words of code and 25 bytes of RAM
* License: LGPL
The Network Administrators
Guide by Olaf Kirch
"Practically Networked has provided practical, easy-to-understand help for
small network builders since early 1998"
Selecting A Home Network Kit - Choose The Right Tools For Putting PCs In
Tiny Embedded Network
LON - http://www.lonmark.org
peer-to-peer serial protocol. It supports heirarchical addressing (scalable
up to 32K nodes in a logical network), multi-drop, multiple media - twisted
pair, RF, Fiber, powerline (or a mix of media in a logical network). Since
it is peer-to-peer, every node can act as a master or you can implement a
mult-master architecture. The protocol is done and implemented in silicon
available from multiple sources. Echelon wants to charge $5 per node (!)
for use and restricts doc's/changes spec to enforce this.
The powerline version of the physical layer is starting to exceed 10Mbit/s,
blowing away the 120 bit/s of X10, and there are physical layer specs for
RS485, RF, IR, etc. The problem of custom chips is still there, but the price
is reasonable, and there are at least a couple sources. Also, there is huge
buy in as this is supposed to be the new home automation standard. Lucent,
Cutler Hammer, and Microsoft, to name a few.
CEBUS packets allow the addressing of 0xFFFF homes with 0xFFFF nodes, sending
256 bytes data per packet. Data is context sensitive. ie. A TV will have
volume up/down power on/off channel up/down pip on/off etc. A light switch
will have power on/off dim up/down. Thus your packetization is as simple
as your device and doesn't require a big micro implementing 17 software layers
to turn on a light bulb!
For an example product, see
http://www.intelogis.com They make
a powerline peer to peer networking solution for sharing data between 2 computers
and sharing a printer. 10Mbit over power line, $99 for the package. And they
now have an open source
SNAP - http://www.hth.com/snap/ free
and open , easy to learn and light weighted network protocol
HDLC - Very mature.
FLAG ADDRESS Payload CRC FLAG
(8bits) (0-16Bits) (8 * N Bits) (16 Bits) (8Bits)
The flag is a fixed byte (often 0b01111110 or 0x7E)
The flag must be escaped if it appears in the data stream.
Ken Websters PIC16C74 serial port
multiplexer. This includes a packet system with addressing, control,
checksums, etc... Actually almost a network (OSI 3) system.
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