The IEC Technical Committee 57 (Working Group 03) have developed a protocol standard for telecontrol, teleprotection, and associated telecommunications for electric power systems.
The details of variable length frame is given below -- IEC 60870-5-103 [IEC103] is a standard for power system control and associated communications.
It defines a companion standard that enables interoperability between protection equipment and devices of a control system in a substation.
There are two separate link layers defined in the standard, which is suitable for data transfer over Ethernet & serial line (PPP - Point-to-Point Protocol).
The security of IEC 104, by design has been proven to be problematic,[2] as many of the other SCADA protocols developed around the same time.
Due to the increase in complexity and cost, system owners are reluctant to roll this out on their networks.