I have a remote site customer with a Cisco 2620XM router with a NM-16 network module and they are testing it out to do some IP to serial port conversion. They are polling a device called an RTU (remote terminal unit) which is connected via the async cable. RTU is used by all utility companies everywhere to calculate voltage and other information.
They are polling that RTU by using socket (IP of the router and the raw TCP port). They tested this functionality using a Dymec Dynastar 1500 hardened router. They ran into a problem where Dymec router was truncating the data into 129 bytes. There was a configuration option under the serial line where we were able to change it to 500 bytes and it worked. According to Dymec's definition of that parameter, it is called "Max port forward limit" Indicates when packets will be forwarded: either every x bytes (1-1024) or according to X.3 values.
So, when they tested this witch Cisco router they ran into the same problem, here Ci
sco is truncating the message to 2 bytes only.
We need to know what the equivalent parameter is in Cisco's line (line 33 in our case) or global command where we can achieve the same result.
exec-timeout 0 0
transport input all
Here is a more descriptive definition of the problem as seen by their RTU engineers:
The message coming back is being broken up into two byte messages which cause the message being rejected by the master.
They had similar problems with the Dymec DynaStar 1500 terminal server that was breaking the serial messages up into 129 bytes. In that case, they were able to change the parameter (MAX port forward limit ). They set it higher than the max serial messages that are sent by the RTU, which did fix the problem.
The question is whether or not the CISCO router has a parameter that can be changed to force it to send the complete serial messages as one packet.