Question 1.
If an X.25 host's T2 timer expires, and it has no data to send, what frame should it send?
| a) |
RR |
| b) |
ACK |
| c) |
UA |
| d) |
Last transmitted Info frame |
Answer
Question 2.
Using X.25 terminology, what is the sequence of packets that starts a call from the perspective of the calling and called hosts?
| a) |
Call Request, Call Indication |
| b) |
Call Request, Call Request |
| c) |
Call Request, Call Confirmation |
| d) |
Call Request, Incoming call |
Answer
Question 3.
In X.25, what is the packet sequence in Fast Select?
| a) |
The caller sends a Call Request immediately followed by a Data packet; the called host returns Data followed by Call Clear. |
| b) |
The caller sends a Call Request immediately followed by a Data packet; the called host returns Call Clear with a code indicating that a Data packet will follow. |
| c) |
The caller sends a Call Request with a Data field; the called host returns Data followed by Call Clear. |
| d) |
The caller sends a Call Request with a Data field; the called host returns a Call Clear with a data field. |
Answer
Answers
Question 1.
If an X.25 host's T2 timer expires, and it has no data to send, what frame should it send?
| a) |
RR |
| b) |
ACK |
| c) |
UA |
| d) |
Last transmitted Info frame |
Answer
Explanation
If the T2 timer expires without any data to send, and the receiving host is capable of accepting more data, it sends a Receiver Ready (RR) frame.
[4492]
Question 2.
Using X.25 terminology, what is the sequence of packets that starts a call from the perspective of the calling and called hosts?
| a) |
Call Request, Call Indication |
| b) |
Call Request, Call Request |
| c) |
Call Request, Call Confirmation |
| d) |
Call Request, Incoming call |
Answer
| d) |
Call Request, Incoming call |
Explanation
To create an X.25 virtual circuit, the originating host sends a Call Request packet to the destination. When the packet arrives at the destination, even though it is unchanged from the Call Request (except that it will use a locally significant LCN probably different from the caller's), it is called an Incoming Call packet. This illustrates a practice that is unfortunately common in the X.25 documentation: using different names for exactly the same information depending on whether it is incoming or outgoing.
[4502]
Question 3.
In X.25, what is the packet sequence in Fast Select?
| a) |
The caller sends a Call Request immediately followed by a Data packet; the called host returns Data followed by Call Clear. |
| b) |
The caller sends a Call Request immediately followed by a Data packet; the called host returns Call Clear with a code indicating that a Data packet will follow. |
| c) |
The caller sends a Call Request with a Data field; the called host returns Data followed by Call Clear. |
| d) |
The caller sends a Call Request with a Data field; the called host returns a Call Clear with a data field. |
Answer
| d) |
The caller sends a Call Request with a Data field; the called host returns a Call Clear with a data field. |
Explanation
An X.25 optional capability, frequently used in credit authorization and other point of sales applications, is called Fast Select. Fast Select lends itself to transaction-based processing, consisting of a paired query and response. The query is attached to the Connect Request packet that indicates Fast Select, and the response is attached to the Clear Confirmation.
[4506]
[IE-X25-SQ1-F03]
[2002-01-28-01]
|
|
|
Copyright © 2002 Genium
Publishing
Corporation