Next Generation EPICS

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24 Οκτ 2013 (πριν από 4 χρόνια και 8 μήνες)

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Next Generation EPICS
Communications Protocols

Jeffrey O. Hill



EPICS protocols essentially unchanged
since 1993

expanding EPICS user community

new supporting role: dissimilar system

substantial improvements are possible

Expanding EPICS

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

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

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

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


Quality of

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

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
service in IP kernel

adjustment of dispatch priority in the server

embed time stamp in server state

Improved Client Side API

simplified C++ client side API is easier to

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

initial minor version number exchange
between client and server

replaceable protocol dispatch table



proposed changes are crucial facilitators for certain

they are not trivial optimizations

EPICS is increasingly used to integrate dissimilar

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