Experimental Physics and
Industrial Control System

Dear,

 

After reading some documentation and presentations I came across the fact that Channel Access will send out UDP search packets at a 30 ms initial interval then doubling until some limit. However I could not find an equivalent algorithm for PVA.

 

I did some basic tests comparing caget with pvget for an invalid PV name to listen to the UDP search packets and indeed witnessed CA as described in the documentation (first dump), but for PVA it seems somewhat different, starting with a 200 ms interval and then roughly doubling until 60 seconds and then having an interval of 30/31 seconds thereafter (second dump).

 

Are my tests correct?

 

If so, can anyone please help me understand why PVA follows a different search pattern?

Is it more efficient, or is it primarily done to not conflict with CA search requests?

 

CA

"No.","Time","Source","Destination","Protocol","Length","Info"

1,0.000000000,"10.0.2.15","10.0.2.255","UDP","92","53434  >  5064 Len=48"

2,0.031722001,"10.0.2.15","10.0.2.255","UDP","92","53434  >  5064 Len=48"

3,0.095184894,"10.0.2.15","10.0.2.255","UDP","92","53434  >  5064 Len=48"

4,0.223854894,"10.0.2.15","10.0.2.255","UDP","92","53434  >  5064 Len=48"

5,0.479483401,"10.0.2.15","10.0.2.255","UDP","92","53434  >  5064 Len=48"

6,0.991141127,"10.0.2.15","10.0.2.255","UDP","92","53434  >  5064 Len=48"

7,2.015237229,"10.0.2.15","10.0.2.255","UDP","92","53434  >  5064 Len=48"

8,4.063262008,"10.0.2.15","10.0.2.255","UDP","92","53434  >  5064 Len=48"

9,8.159122093,"10.0.2.15","10.0.2.255","UDP","92","53434  >  5064 Len=48"

10,16.352008891,"10.0.2.15","10.0.2.255","UDP","92","53434  >  5064 Len=48"

11,32.737132230,"10.0.2.15","10.0.2.255","UDP","92","53434  >  5064 Len=48"

12,65.503686690,"10.0.2.15","10.0.2.255","UDP","92","53434  >  5064 Len=48"

 

PVA

"No.","Time","Source","Destination","Protocol","Length","Info"

1,0.000000000,"10.0.2.15","10.0.2.255","UDP","102","39160  >  5076 Len=58"

2,0.238798042,"10.0.2.15","10.0.2.255","UDP","102","39160  >  5076 Len=58"

3,0.719405981,"10.0.2.15","10.0.2.255","UDP","102","39160  >  5076 Len=58"

4,1.671395331,"10.0.2.15","10.0.2.255","UDP","102","39160  >  5076 Len=58"

5,3.572739798,"10.0.2.15","10.0.2.255","UDP","102","39160  >  5076 Len=58"

6,7.381955685,"10.0.2.15","10.0.2.255","UDP","102","39160  >  5076 Len=58"

7,15.002222834,"10.0.2.15","10.0.2.255","UDP","102","39160  >  5076 Len=58"

8,30.242905754,"10.0.2.15","10.0.2.255","UDP","102","39160  >  5076 Len=58"

9,60.723217274,"10.0.2.15","10.0.2.255","UDP","102","39160  >  5076 Len=58"

10,91.441239917,"10.0.2.15","10.0.2.255","UDP","102","39160  >  5076 Len=58"

11,121.923730892,"10.0.2.15","10.0.2.255","UDP","102","39160  >  5076 Len=58"

12,152.401489023,"10.0.2.15","10.0.2.255","UDP","102","39160  >  5076 Len=58"

13,182.881808983,"10.0.2.15","10.0.2.255","UDP","102","39160  >  5076 Len=58"

14,213.362068330,"10.0.2.15","10.0.2.255","UDP","102","39160  >  5076 Len=58"

15,243.843906293,"10.0.2.15","10.0.2.255","UDP","102","39160  >  5076 Len=58"

16,274.323287000,"10.0.2.15","10.0.2.255","UDP","102","39160  >  5076 Len=58"

 

Apologies if this is already documented somewhere, but I have been unable to find information on this.

 

Kind regards,

Tom