what all threads are created when we add a database to replication server system ?

Hi,
I have read the manuals of replication server ....not fully but to good extent. I have following questions/doubts related to queues and threads :

what all threads are created when we add a database to replication server system ? Lets say i create a database test1 on primary and replicate site. I added these databases to rep server REP_TEST1 ,now i see many threads. This is one way replication primary to secondary.

Now i see following threads ...can someone please explain me each with few lines please:


  107 DSI EXEC   Awaiting Command     103(1) SYB_PRIMARY.test1
   55 DSI        Awaiting Message     103 SYB_PRIMARY.test1
   70 DIST       Awaiting Wakeup      103 SYB_PRIMARY.test1
   84 SQT        Awaiting Wakeup      103:1  DIST SYB_PRIMARY.test1
   32 SQM        Awaiting Message     103:1 SYB_PRIMARY.test1
   31 SQM        Awaiting Message     103:0 SYB_PRIMARY.test1
   97 REP AGENT  Awaiting Command     SYB_PRIMARY.test1

  104 DSI EXEC   Awaiting Command     104(1) SYB_DR.test1
   62 DSI        Awaiting Message     104 SYB_DR.test1
   33 SQM        Awaiting Message     104:0 SYB_DR.test1

Also My doubt is which one are inbound queues and outbound queues and why ? Why we have DSI for primary when nothing will be written into primary by replication server?