________________________________________
From: goutam kumar [[email protected]]
Say Alice and Bob are in a call. Now,
STEP I
Alice puts Bob on hold. i.e.
INVITE (RTP-sendonly)
Alice -------------------------------------> Bob
200 OK (RTP-recvonly)
<------------------------------------
ACK
------------------------------------->
STEP II
After this Bob puts Alice on hold. i.e.
INVITE(RTP-inactive)
Alice <-------------------------------------- Bob
200 OK (RTP-inactive)
---------------------------------------->
ACK
<----------------------------------------
( If Alice has already put the call on hold, then is Step II possible?? )
After this sequence of signaling, say Alice takes the call off hold i.e.
INVITTE(RTP-sendonly)
Alice -------------------------------------------> Bob
200 OK (RTP ?????)
<--------------------------------------------
My Question is:What should bob send as a reply now?
_______________________________________________
Step II is possible -- After all, Bob can press the Hold button on his
phone! But Bob sends "sendonly", since the mode he sends in offer SDP
is independent of Alice's state. (His SDP *queries* Alice's state!)
INVITE(RTP-sendonly)
Alice <-------------------------------------- Bob
200 OK (RTP-inactive)
---------------------------------------->
ACK
<----------------------------------------
Step III is when Alice takes the call off hold. Since Alice wants to
communicate, her UA sends SDP "sendrecv". But Bob's UA responds
"sendonly", because Bob's UA is still in Hold state:
INVITTE(RTP-sendrecv)
Alice -------------------------------------------> Bob
200 OK (RTP-sendonly)
<--------------------------------------------
ACK
------------------------------------->
Step IV is when Bob takes the call off hold (that is, hold for his end):
INVITE(RTP-sendrecv)
Alice <-------------------------------------- Bob
200 OK (RTP-sendrecv)
---------------------------------------->
ACK
<----------------------------------------
Dale
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