[Sis-csi] Green book thoughts

[Dai Stanton]

Re: Chris Taylor's comments on retransmission

Agreed. The operators do not believe in the reliability of comms links
and don't need to because reliability of just the comms isn't enough for
them, stuff could go wrong between the reliable reception of a packet
and the firing of the actuator it demands, so they have their own checks
at application layer. 

So they send a command to open a valve, check the valve is open and then
do their next thing. This process doesn't need reliable, in sequence
underlying service. It's why SNMP can use UDP. Every Set is always
followed by a Get to check that the parameter has actually been changed.

Fire up the Cisco MMI to see this in action.

Dai