I think i'm gonna try build a network using rs232 as the physical layer - but not p2p or master/slave etc :) It'll be shared medium! (ring toplogy for physical layer is nice, but means i have to write more code for layer2 processing.. i'll do this another time) Silvio Cesare -- PHYSICAL NETWORK TOPOLOGY RING TOPOLOGY SHARED MEDIUM STAR TOPOLOGY VIRTUAL RING NETWORK TOPOLOGY HOST CONFIGURATION RING TOPOLOGY STAR TOPOLOGY NETWORK PROTOCOL SHARED MEDIUM STAR TOPOLOGY PHYSICAL NETWORK TOPOLOGY ------------------------- For each node on the RS232 network, they require one RS232 port. In a Collision Detection Multiple Access (CDMA) network such as ethernet, every node is able to transmit and received data at approximately the same time without prior consultation or network management. If a collision is detected on the network, then the data is retransmitted with a random pause for each node trasmitting data. For RS232, it seems harder to detect collisions since a signal is rated between +- 3-25V. If two nodes transmit at the same time using 4V, then you still fall well within the normal range. RING TOPLOGY ------------ In the ring topology for the physical layer, more processing is required for the layer2 protocols. This is due to the fact that nodes are no longer in the same broadcast domain. The RD and TD will be chained in a ring to each node cycling back to the first at the last node. All nodes will have GRND connected in a ring. CTS and RTS will not be used. DTS and CD will be looped back to the DTR pin on each port as in a NULL modem cable. [For a 3 node network] NODE1 will have TD to RD on NODE2 NODE1 will have RD to TD on NODE3 NODE2 will have TD to RD on NODE3 NODE2 will have RD to TD on NODE1 NODE3 will have TD to RD on NODE1 NODE3 will have RD to TD on NODE2 SHARED MEDIUM ------------- STAR TOPLOGY ------------ This will be established as a star style network. The TD pin on each port connected to the network, will cross over to the RD pin on every other node. The RD pin on each port connected to the network, will cross over to the TD pin on every other node. DTS and CD will be looped back to the DTR pin on each port as in a NULL modem cable. VIRTUAL RING NETWORK TOPOLOGY ----------------------------- To avoid collisions, a virtual ring network toplogy may be established. +-------------------------------------+ | | +-> NODE1 -> NODE2 -> NODE3 -> NODE4 -+ Through the use of a token travelling around the network, nodes may be allowed to transmit data. This will now act much like a Time Division Multiple Access (TDMA) network. A Token indicates that a node may transmit a limited amout of data on the network. All nodes on the network will passively sniff traffic and wait for packets destined to them. They may receive packets at any time, except when in control of the token. After completion of a node's time slice, the token is passed to the next node, by transmission of a TOKEN packet. HOST CONFIGURATION ------------------ RING TOPOLOGY ------------- No configuration is required on the network in this physical network toplogy. STAR TOPOLOGY ------------- Each node on the network will have configured locally the virtual network toplogy. NETWORK PROTOCOL ---------------- RING TOPOLOGY ------------- SHARED MEDIUM ------------- STAR TOPOLOGY ------------- A packet looks like this --> u8[16] marker; [0xff] u8 type; [TOKEN | TRANSMIT] u8 next_node; [only valid for TRANSMIT] u8 node; u8 size; [maybe u16?] u8 data[]; For token passing, a TOKEN packet is sent to the next_node in the virtual ring topology. If a TRANSMIT packet is used, then the node indicates the destination, and the next_node indicates the next node controlling the token. The marker is used, in case one of the nodes loses timing and is unable to determine the start of a frame through normal means. [ yes.. i realize this network is weak, and has no error recovery! ] -- Silvio