P1525's approach is to define an ASN.1 framework for all data objects to be exchanged between IEDs. Then, when the data object details are defined by others, using this framework, they must be registered in the public domain.

A different approach, taken in UCA™ 2.0 is to define the data structure of all (or nearly all) data objects to be exchanged. Their approach does not formally define ASN.1 structures, but lists the attributes of the data object in a table. These data objects are complete and their semantics are well defined. They use a hierarchical-name structure so that the semantics of the composite data structure is understood by parsing the name. These data objects are defined in GOMSFE - Generic Object Model for Substation and Feeder Equipment. This same approach has been adopted with minor modification for IEC 61850.

Interoperability is a highly desired goal, but it must be affordable. Either approach is acceptable.

Graceful integration of the substation communication system into the communication with both the Energy Management System (EMS) and Distribution Management System (DMS) is required to prevent the development of another island of automation. Each utility must determine which approach is best by comparing the overall cost/benefits, and considering the  constraints imposed by their enterprise communication architecture and operating procedures.

Risk management is a major cost driver. Whichever approach is taken, there must be a cost-effective risk management plan to migrate existing substations to these highly-automated substations.

Many vendors participating in the UCA™ Users Group, and those that are closely aligned with 61850, prefer the approach taken by 61850 because they have in place a vendors agreement, which will be codified in a standard.

Although 61850 defines the data objects, it leaves open (as it should) the ability to add vendor specific extensions and tailoring. Thus, interoperability is not guaranteed - but a well defined framework is in place to negotiate the differences between vendor implementation.

One disadvantage of 61850, or the UCA™ GOMSFE approach is that the development of new data objects must work their way through IEC or UCA™ Users Group to get approval. This can be a long arduous process.

Many vendors that are not closely aligned with 61850 prefer P1525 because it permits them to continually add to the object definitions as long as they publish these definitions. Any vendor can then write the applications to use these published objects.

P1525 is designed to use only the Internet Protocol specifications. 

	P1525 does not require special shims in the communication stack to force the use of an Application Service Element (ASE) such as ISO 9406 (Manufacturing Messaging Specification - MMS). MMS was selected for UCA™ and has been adopted as the initial ASE for 61850 (see part 8.1). P1525 allows the vendor to write an application, open a communication socket, and go, no ASE is required.
	P1525 specifies IP version 6, and 61850 specifies IP version 4 - the two are not interoperable, but an IED vendor can provide both in the communication stack.
	Given the events of 9/11, security against cyber-attack is a must. P1525 specifies IPSec for security. 61850 does not use IPSec, but it does have in Part 8.1 a mechanism for strong authentication.
	P1525 specifies the User Datagram Protocol (UDP) for multicasting messages, which can bridge across multiple LAN segments. 61850 does not use UDP; it does provide for multicast, but it is limited to one logical LAN segment.