Which Layer 2 protocol encapsulation type supports synchronous and asynchronous circuis and has built-in security mechanisms?

IT Questions Bank › Which Layer 2 protocol encapsulation type supports synchronous and asynchronous circuis and has built-in security mechanisms?

Question:
Which Layer 2 protocol encapsulation type supports synchronous and asynchronous circuis and has built-in security mechanisms?

HDLC
PPP
X.25
Frame Relay

Explanation: PPP supports both synchronous (like analog phone lines) and asynchronous circuits (such as ISDN or digital links). With synchronous circuits we need to use clock rate.

Note: Serial links can be synchronous or asynchronous. Asynchronous connections used to be only available on low-speed (<2MB) serial interfaces, but now, there are the new HWICs (High-Speed WAN Interface Cards) which also support asynchronous mode. To learn more about them please visit

http://www.cisco.com/en/US/prod/collateral/modules/ps5949/ps6182/prod_qas0900aecd80274424.html.

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