The advantages and disdvantages of Forward error correction (FEC) are( ). (Select 2 answers)

A. it has high requirements for latency, which makes it difficult to use in live networks, it is effective only in slight packet loss. In addition, it results in more video jitter

B. it occupies little bandwidth and slightly impacts the video quality

C. The video quality is affected because the redundant data occupies some bandwidth. In addition, it cannot handle burst packet loss, and a certain delay is introduced

D. it can restore the lost data with a certain probability and it is applicable to common packet loss scenarios

NAT works at the ( ).

A. Data link layer

B. Network layer

C. Application layer

D. Transport layer

After the conference ends, the recording server sends a recording address to the SMC who will then send emails to relevant users, notifying them of the on-demand playback.( )

A. TRUE

B. FALSE

A transaction only can be identified by a unique branch.( )

A. TRUE

B. FALSE

The SIP works on the basis of messages which are the base units for the interaction between the SIP client and server( ).

A. TRUE

B. FALSE

The Content header field contains the attributes of message bodies/'Content-Length" specifies the length of the message body, which is optional for the TCP packets and mandatory for UDP packets. ( )

A. TRUE

B. FALSE

Humans obtain more than 20% information through hearing. Sound perceptible to human ears is a mechanical wave with frequencies within the range ( )of Hz.

A. 50-20000

B. 30-30000

C. 20-20000

D. 20-40000

Forward error correction uses an algorithm where the transmitting device sends redundant data and the decoding device restores the data streams using the redundant data;( )

A. TRUE

B. FALSE

Which does not belong to six major request messages of SIP protocol.( )

A. ACK

B. CANCEL

C. SETUP

D. BYE

Of the messages between GKs, a/an ( ) message is sent by the called terminal to the calling terminal to indicate that the called terminal is off-hook.

A. alerting

B. proceeding

C. setup

D. connect