DIM

1
DIM

• A Portable, Light Weight Package for Information
  Publishing, Data Transfer and Inter-process
  Communication

2
DIM Design Requirements

• Efficient Communication Mechanism
• Asynchronous Communications
• One to Many Communications
• Uniformity
• The same mechanism for all types of
  communications
• Transparency
• Reliability and Robusteness
• Wide-Area Availablility

3
Communication mechanism
RPC CORBA
DIM

• Synchronous
• One-to-one

• Asynchronous
• One-to-many

4
Design Philosophy

• Client/Server (Publish/Subscribe)
• Services
• Set of data (any type or size)
• Free name space
• Servers publish Services.
• Clients subscribe to Services.
• ONCE ? TIMED ? MONITORED
• Clients can also send Commands to Servers
• Name Server
• Keeps the coordinates of available Services

5
DIM Dataflow

• Internal mechanism

6
DIM transparency

• DIM clients do not know where their interlocutors
  are.
• Servers can move from one machine to another, all
  connections are transparently re-established.
• The Name Server can also migrate.
• All platform differences are handled internally
  (byte swapping, structure alignment, floating
  point representation)

7
DIM Monitoring

• Large distributed systems are normally difficult
  to Test, Debug and Monitor
• Due to the DIM publishing mechanism
• DIM components (the Name Server and the Servers)
  publish a set of standard Services used for
  monitoring
• A tool - DID - (using the standard DIM client
  API) allows access to all information

8
DIM Monitoring - DID
9
DIM Performance

• Comparison DIM - Raw TCP-IP
• Ethernet 1.05x slower, 900KB/s max.
• FDDI 1.04x slower, 9.5 MB/s max.
• Loopback 1.4x slower, 23 MB/s max.

10
DIM Availability

• DIM is available
• As Server and Client libraries
• Interface API C, C and Java (client only)
• For the platforms
• VMS (VAX and APHA)
• UNIX flavours (HP-UX, Sun-OS, Sun-Solaris,
  IBM-AIX, DEC-OSF, Linux)
• Windows NT
• Real-time OSs (OS9, LynxOS, VxWorks)

11
DIM example
12
DIM in Delphi

• DIM is used by all the 500 processes in Delphis
  Online System for
• Control
• Read Out
• Data Monitoring and Processing
• User Interfacing
• It makes available more than 35000 services from
  450 servers in more than 60 machines

13
Delphis Control System

• Homogeneous
• Same tools and methods used for all control areas
• Finite State Machines
• All devices and Sub-systems are modeled as
  objects behaving as finite state machines using a
  tool - SMI.
• Complete Automation
• The Experiment runs without operator intervention

• 1000 FSM Objects, 200 processes in 40 machines
• All communications via DIM

14
Delphis Read-Out Monitoring

• Delphi Events are read-out via DIM.
• Sub-detector data is also published by DIM for
  monitoring and stand-alone operation
• Monitors produce histograms that are again
  published via DIM
• Histogram Consumers (presenters) get them via DIM

15
Delphi User Interface
16
DIM outside DELPHI

• DIM is used in L3 and L3 Cosmics for
• Database Server
• Read Out
• Monitoring
• Job Control
• In general for data exchanges between
• UNIX (hp-ux, solaris, linux)
• VMS (vax and alpha)
• LynxOS
• OS9
• Dim is used in BaBar
• As the communication layer for SMI
• Hundreds of SMI domains running on SUN Solaris
  machines

17
Conclusions

• Online applications (control, monitoring) have
  particular needs in terms of communications
• Asynchronous Response
• Multiple destination updates
• Multiple platforms
• Efficiency and Reliability
• DIMs publish/subscribe mechanism is well suited
  for such applications

18
DIM example
19
DIM - WWW