A. FramingB. De-encapsulationC. EncapsulationD. De-fram……

多项选择题Regarding PAR (Positive Acknowledgement and Re-transmission), which of the answer choices below are correct?（）

A. The source device will only retransmit lost packets on the request of the destination device.
B. The source device starts a timer when it sends a segment and retransmits if an acknowledgment is not received before the timer expires.
C. The destination device acknowledges receipt of a segment by sending a packet with a new sequence number and the ACK bit sent.
D. The destination device acknowledges receipt of a segment by sending a packet that indicates the next sequence number it expects.
E. If the destination device does not receive a segment, all segments are retransmitted.
F. The source device keeps a record of all segments sent and expects and acknowledgment of each.

单项选择题Error detection schemes check errors in the data packets by reading which field frame IDs?（）

A.MTU
B.PDU
C.FCS
D.Flag
E.MAC
F.BRI

单项选择题Which frame field do error detection schemes view to perform their function?（）

A. ERR
B. Flag
C. FCS
D. MTU
E. MAC
F. PDU

单项选择题Which of one the following fields is contained within an IEEE Ethernet frame header?（）

A. source and destination MAC address
B. source MAC address and destination network address only
C. source and destination network address only
D. source network address and destination MAC address
E. source and destination MAC address and source and destination network address

单项选择题Which device enables a router serial interface to connect to the ISDN BRI?（）

A.NT2
B.NT1
C.TE
D.TA
E.TE1