Coraid Ethernet Console (cec) Abstract The Coraid Ethernet Console (cec) implements a bidirectional conversationover raw ethernet frames with provisions for retransmission and discovery.  Like serial consoles, each machine has a single shared interface per servicetype,  but any number connections can be made from any machine connected to the same physical network.  The communications from the various connectionswill be interleaved.  The first implementation of cec is for console communicationsto Coraid appliances. Outline 1. Packet format2. The Tdiscover packet and Toffer reply.3.  Initializing a connection. Tinit[abc]4.  The connection.  Tdata and Tack5.  Closing the connection.  Treset 1. Packet Format All cec packets are follow the layout implied by the following structure 	struct Pkt {		uchar	dst[6];		// destination ethernet address		uchar	src[6];		// source ethernet address		uchar	etype[2];		// service type		uchar	type;		// type of packet.		uchar	conn;		// unique connection id.		uchar	seq;		// packet sequence number		uchar	len;		// data length.		uchar	data[1500];	}; The packet types are as follows: 	enum {		Tinita,		Tinitb,		Tinitc,		Tdata,		Tack,		Tdiscover,		Toffer,		Treset,	}; 2. The Tdiscover packet and Toffer reply. The Tdiscover packet is used to discover the avaliable cec devices on the localnetwork.  The packet sent is of the form 	Tdiscover = {	[dest]	0xffffffff,	[src]	mac of local interface,	[etype]	service type,	[type]	Tdiscover,	[seq]	0,	[len]	0,	[data]	0,	} The reply to the Tdiscover packet is of type Toffer which differes fromTdiscover in that data and len may be set.  The contents of data is applicationspecific. 3.  Initializing a connection. Tinit[abc] A connection is initialized by the following conversation: In additionto the fields set for the Tdiscover packet, the client sends a packetof type Tinita with the conntag of its choice.  The server responds toTinita with a packet of type Tinitb.  And finally the client sents aTinitc packet back to the server, completing the connection. 4.  The connection.  Tdata and Tack Data is sent from the client to the console server with the Tdata packet.The seq field is incremented for each data packet sent.  Thus data packetsmay be transmitted if lost.  The data is whatever data the client has tosend to the server, up to 255 bytes.  Typically, however, each keystrokeis sent in a seperate packet.  The len field is the length of thedata. The server responds to a Tdata message with a Tack message with the same seq sequence number. 5.  Closing the connection.  Treset Either the server of the client may send a Treset message to close the connection.  There is no response to a Treset message, however anyinformation associated with that connection (conntag) is discarded when the Treset message is recieved.