Which user agent has the recipient role in this SIP REFER call transfer?

Refer to the exhibit.

Which user agent has the recipient role in this SIP REFER call transfer?
A . user agent A
B . user agent B
C . user agent C
D . user agent B and C
E . user agent A and B

Answer: B

Explanation:

The Refer method has three main roles:

• Originator―User agent that initiates the transfer or Refer request.

• Recipient―User agent that receives the Refer request and is transferred to the final-recipient.

• Final-Recipient―User agent introduced into a call with the recipient.

Reference: http://www.cisco.com/c/en/us/td/docs/ios_xr_sw/iosxr_r3-4/sbc/configuration/guide/sbc_c34/sbc34stx.pdf