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Steve McQuerry. Interconnecting Cisco Network Devices. (Cisco Press: 2000) page 22.
Q. 223
Which two statements about a reliable connection oriented data transfer are true? (Choose two)
A. Recipients acknowledge receipt of data.
B. When buffers are filled to capacity, datagrams are discarded and not re transmitted.
C. Windows are used to control the amount in outstanding acknowledged data segments.
D. If the segments timer expires between receipt of an acknowledgement the sender drops the connection.
E. The receiving device waits for acknowledgements from the sending device before accepting more data
segments.
Answer: A, C.
Explanation:
Connection orientated protocols, such as TCP, communication use acknowledgement of packets. This is how
error control is possible. To govern the flow of data between devices, TCP uses a flow control mechanism.
The receiving TCP reports a “window” to the sending TCP. This window specifies the number of octets,
starting with the acknowledgment number, that a receiving TCP is currently prepare to receive.
TCP windows sizes are variable during the lifetime of the connection. Each acknowledgment contains a
window advertisement that indicates how many bytes the receiver can accept. TCP also maintains a congestion
control window that is normally the size as the receiver’s window but is cut in half when a segment is lost (for
example, there is congestion). This approach permits the window to be expanded or contracted as necessary to
manage buffer space and processing.
Incorrect Answers:
B is incorrect; with connection orientate protocols packet delivery is guaranteed. Packet will not be dropped.
Flow control (windowing) addresses the buffer issue.
D is incorrect; if the sending system does not receive an acknowledgement from the receiving system then the
packet will be resent.
E is incorrect; the receiving device sends the acknowledgement of packets and this states how much data the
receiving device can receive.
Steve McQuerry. Interconnecting Cisco Network Devices
. (Cisco Press: 2000) pages 213-4.
Q. 224
Which three functions are supported by connection oriented services? (Choose three)
A. Connection parameters are synchronized
B. Any loss or duplication of packets can be corrected