Most devices communicate in a raw telnet session without any
initial handshake involved. Other devices such as Cisco Codecs and BiAmp Tesira
require a handshake to open a telnet session. NetLinx controllers establish a
raw connection and therefore the telnet handshake must be handled in NetLinx
code. Most telnet clients quietly
perform a handshake in the background. With
Putty you can establish a raw connection as a test to determine if a handshake
is required.
In a handshake, there are all types of negotiation options
(i.e Echo, Binary Transmission, Reconnection). In most cases the client (in our
case a NetLinx Controller) needs to simply respond with either a
"DON'T" or "WON'T" based on each request. When a "WILL" ($FB) is received the
response would be "DON'T" ($FE).
When a "DO" ($FD) is received the response would be "WON'T"
($FC).
For example, the following is received upon the initial
telnet connection:
$FF$FD$18
$FF$FD$20 $FF$FD$23 $FF$FD$27
The response would be:
$FF$FC$18
$FF$FC$20 $FF$FC$23 $FF$FC$27
Byte 1: $FF is the IAC (Interpret as Command)
Byte 2: $FB (WILL), $FD (DO), $FE (DON’T), or $FC (WON’T)
Byte 3: is the option. (echo, binary, reconnect, etc.)
Here are some great resources:
support.biamp.com/Tesira/Control/Telnet_session_negotiation_in_Tesira
www.iana.org/assignments/telnet-options
Example Code to handle this:
DEFINE_DEVICE
dvDevice= 0:3:0
DEFINE_VARIABLE
volatile integer telnet_complete
volatile integer login_complete
DEFINE_EVENT
DATA_EVENT[dvDevice]
{
STRING:
{
STACK_VAR
CHAR sBuild[100]
STACK_VAR
INTEGER index
IF(!telnet_complete)
{
IF(FIND_STRING(data.text,"$FF",1))
{
sBuild =
data.text
index =
FIND_STRING(sBuild,"$FF",1)
WHILE(index)
{
IF(sBuild[index+1]
= "$FD") sBuild[index+1] =type_cast("$FC") //FD > FC (DO
> WON'T)
IF(sBuild[index+1]
= "$FB") sBuild[index+1] = type_cast("$FE") //FB > FE
(WILL > DON'T)
index =
FIND_STRING(sBuild,"$FF",index+1)
}
SEND_STRING
data.device,sBuild
}
ELSE ON[telnet_complete]
}
IF(telnet_complete AND !login_complete) //example login
{
IF(FIND_STRING(data.text,'ogin
successful',1)) ON[login_complete]
ELSE
IF(FIND_STRING(data.text,'ogin:',1)) SEND_STRING
data.device,"'admin',$0d"
ELSE
IF(FIND_STRING(data.text,'assword:',1)) SEND_STRING data.device,"'1988',$0d"
}}}
******
Be sure to manage "telnet_complete" and
"login_complete" full circle.
One Example:
{
IP_CLIENT_OPEN(dvDevice.Port,'10.35.93.102',23,IP_TCP)
OFF[telnet_complete]
OFF[login_complete]
}
