Blindsided by the Flash!

[k0mbachi]

For those interested, it seem most of the questions in the Cisco ESIM and Odom books are repeated in the Cisco Flash Card product. However, not all. Two questions that are interesting (format is an adaptation from the original macromedia (yuk) format):

1. This is from the former:

Sequencing, acknowledgements and flow control are characteristic of which OSI layer?
A. Layer 4 (Transport)
B. Layer 3 (Network)
C. Layer 5 (Session)
D. Layer 2 (Data Link)

Answer: A

2. This is from the latter:

Which of the following ways define how TCP achieves reliability?
A. Sequencing
B. Flow Control
C. Segmentation
D. Acknowledgements

Silly me. I enthusiastically check off A, B and D. However, the answer is:

Answer: A, D

I'm starting to suspect QoS from CiscoPress is not consistent with Cisco's usual standards.

 

[ecafracs]

The answer is right. To achieve reliability, the transport layer uses Sequencing and Acknowledgements. Flow Control is also in the transport layer, but this is used to control the flow of data. If the receiving end has its buffers full, it will indicate or send a not ready indicator. And will send a ready indicator, if it is again ready to receive data. The transport layer's function is to segment the data, as in the normal process in the OSI layer. Data, Segment,Packets,Frames,Bits.
Any data not acknowledge will be resent by the sender,and the data is sequenced back to its original sequence on the receiving end.

 

[k0mbachi]

OK, the acknowledgements of sequenced packets are the key to reliability. I can see how handshaking, flow control could be allocated to the performance realm. Without flow control, there would be a need for many more packets to be resent.

ecafracs, I appreciate your assistance with the fine tuning process I'm currently experiencing.