SSCA SDP Protocol 2 — Questions and Answers
Question 1: Which SDP field specifies the network type and address type for the connection?
- c= field (Correct answer)
- o= field
- m= field
- t= field
Correct answer: c= field
The c= (connection) field specifies the network type (e.g., IN), address type (e.g., IP4 or IP6), and connection address.
Question 2: In SDP, what does the 'a=sendonly' attribute indicate?
- The endpoint will only send media and not receive (Correct answer)
- The endpoint will only receive media
- The endpoint will send and receive media
- The media session is inactive
Correct answer: The endpoint will only send media and not receive
The 'a=sendonly' attribute indicates the endpoint intends to send media but not receive it in that direction.
Question 3: Which SDP line is mandatory in every SDP session description?
- v= (protocol version) (Correct answer)
- b= (bandwidth)
- k= (encryption key)
- r= (repeat times)
Correct answer: v= (protocol version)
The v= line indicating the SDP protocol version (always '0') is mandatory in every SDP session description.
Question 4: In SDP, what is the purpose of the 'a=rtpmap' attribute?
- Maps RTP payload type numbers to codec names and clock rates (Correct answer)
- Specifies the RTCP port for a media stream
- Defines the maximum bandwidth for RTP
- Lists supported DTMF tones
Correct answer: Maps RTP payload type numbers to codec names and clock rates
The a=rtpmap attribute maps dynamic RTP payload type numbers to encoding names, clock rates, and optional encoding parameters.
Question 5: What SDP attribute is used to indicate support for DTMF telephone events over RTP?
- a=rtpmap with telephone-event (Correct answer)
- a=fmtp:telephone
- a=dtmf
- a=rfc2833
Correct answer: a=rtpmap with telephone-event
DTMF events are carried using RTP payload type 101 (or another dynamic type) with 'a=rtpmap:101 telephone-event/8000'.
Question 6: Which SDP field identifies the originator of the session and the session ID?
- o= field (Correct answer)
- s= field
- i= field
- u= field
Correct answer: o= field
The o= (origin) field contains the username, session ID, session version, network type, address type, and unicast address of the session creator.
Question 7: In an SDP offer, if no 'a=sendrecv', 'a=sendonly', 'a=recvonly', or 'a=inactive' attribute is present, what is the default direction?
- sendrecv (Correct answer)
- sendonly
- recvonly
- inactive
Correct answer: sendrecv
Per RFC 4566, the default directionality for a media stream when no direction attribute is specified is sendrecv.
SSCA SDP Protocol 2
Which SDP field specifies the network type and address type for the connection?