If a SIP Message includes two a=crypto attributes, how do SIP devices handle them?

If a SIP Message includes two a=crypto attributes, how do SIP devices handle them?

• A. They ignore both attributes
• B. They use the last attribute for audio and video
• C. They use the 1st valid attribute for both streams
• D. They alternate between the attributes for each stream

Answer: (C)

When a SIP message includes multiple `a=crypto` attributes, SIP devices follow a defined behavior regarding the selection of cryptographic attributes for secure communications. The specified handling of such multiple attributes is to utilize the first valid attribute found. This means that when a SIP participant receives a message with more than one `a=crypto` line, it scans through the options provided and selects the first one that is deemed valid for both audio and video streams. This behavior is based on the assumption that if multiple attributes are offered, the initiating party has a reason for ordering them the way they did, with the first one generally being preferred due to its position. This approach helps avoid confusion and ensures that a consistent method of encryption is used across media streams, enhancing interoperability among different SIP user agents or endpoints. Thus, when managing multiple `a=crypto` attributes in a SIP message, relying on the first valid attribute for both media streams is the accepted practice, which is why this response is correct.

When a SIP message includes multiple a=crypto attributes, SIP devices follow a defined behavior regarding the selection of cryptographic attributes for secure communications. The specified handling of such multiple attributes is to utilize the first valid attribute found.

This means that when a SIP participant receives a message with more than one a=crypto line, it scans through the options provided and selects the first one that is deemed valid for both audio and video streams. This behavior is based on the assumption that if multiple attributes are offered, the initiating party has a reason for ordering them the way they did, with the first one generally being preferred due to its position.

This approach helps avoid confusion and ensures that a consistent method of encryption is used across media streams, enhancing interoperability among different SIP user agents or endpoints. Thus, when managing multiple a=crypto attributes in a SIP message, relying on the first valid attribute for both media streams is the accepted practice, which is why this response is correct.