Next Generation EPICS

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24 Οκτ 2013 (πριν από 3 χρόνια και 5 μήνες)

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Next Generation EPICS
Communications Protocols

Jeffrey O. Hill

LANL

Motivation


EPICS protocols essentially unchanged
since 1993


expanding EPICS user community


new supporting role: dissimilar system
integration


substantial improvements are possible

Expanding EPICS
Community


over 100 sites in collaboration


since Jan 1st 1998


20 sites added to the collaboration


> 75 new users have received EPICS training


large new projects based on multi
-
laboratory collaborations have complex
new requirements

Significant Improvements
Possible


comprehensive process entity paradigm


better support for data acquisition


wide area network transparency


protocol compression


controlled degradation under load


client side API upgrade

Comprehensive Process
Entity Paradigm


Extensible Attribute Set


application expands set of named attributes


units, limits, process
-
passive, mesons per sec, etc


application defined container types


message passing to “process entities”


command completion


Generalized Matrix Data


client discovers N dimensional bounds of data


client addresses any hyper cube within bounds


eliminate string and vector size limits

Better Support for Data
Acquisition


application defined event types


servers post RF arch down events


clients subscribe for RF arch down events
when POWER>10KW


clients subscribe for periodic updates


consistent sample rate compared with periodic
queries originating from client


clients adjust server’s event queue length

WAN Transparency


plug
-
compatible directory service interfaces


wildcard queries


resource location monitoring


detection of name space collisions during resource installation


simplified configuration


strengthened security


kerberos, SSH tunnel etc


replace IP broadcast with IP multicast

WAN
Guaranteed

Quality of
Service


from the EPICS server


from next generation Internet protocols


of particular interest to projects on large
geographic scale


complex and expensive WAN


desire to route feedback control and process control
messages on the same network

Protocol Compression


increase information density of protocol


level 1


simply reorganize the protocol


level 2


adaptive Huffman coding of resource identifiers


fidelity controls for analog data streams (lossy
compression)


client side “plug
-
ins” for compressed analog data


possible symbioses with EPICS archiving tools

Controlled Degradation
Under Load


clients specify quality of service


adjustment of network data stream’s quality
-
of
-
service in IP kernel


adjustment of dispatch priority in the server


embed time stamp in server state
-
of
-
health
-
beacon

Improved Client Side API


simplified C++ client side API is easier to
extend

and use


client API exports full functionality
currently in the server API


support multiple threads without requiring
vxWorks “task variables”

Uneventful Upgrade


large installed base of EPICS users


Simultaneous upgrade to a new version
results in too much risk


Backward compatibility must be
maintained


initial minor version number exchange
between client and server


replaceable protocol dispatch table

Benefits


Conclusions


proposed changes are crucial facilitators for certain
applications


they are not trivial optimizations


EPICS is increasingly used to integrate dissimilar
systems


careful attention to process entity paradigm is warranted


proposed changes can be accomplished without
impacting backward compatibility


increasing size of the EPICS user community increases
the practicality of devoting resource to this effort