GSM Layer3 in Atu

third (Layer 3) signaling

The third layer of signaling is to look at the network operation of the information layer, from the third layer can see the various actions of the network: such as: Call flow, congestion, user busy, location update, System Information total of 8 types, type1-4 only appear in the standby state, type5-8 only appear in the call State:

1. System Information Type1

Cell broadcast information, there is the cell's own frequency point, rach some parameters set, Xiang see above.

2. System Information Type2

The measurement frequency of the cell in the standby mode, (the same frequency band, the mobile network has two bands, GSM900 and DCS1800),

In the call mode has another defined measurement frequency point, that is, a cell can be in standby to do the measurement frequency, while the call does not do measurement frequency, allowing the cell to re-election and not allow the switch, the other hand can only allow the switch does not allow cell re-election can also, but usually standby and call the measurement frequency is consistent.

3. System Information Type2ter

The measurement frequency of the cell in the standby mode, (different frequency band, the mobile network has two bands, GSM900 and DCS1800),

4. System Information Type 3

Cell broadcast information, you can see ATT, T3212, ACC, CRO, CRH and accmin, etc., Cheung see above

5. System Information Type 4

Cell broadcast information, here you can see the CRH, CRO, Accmin, Maxret, CB, CBQ, PT and other parameters set values, see above.

6. System Information Type 5

Service cell measurement frequency point in active mode (same frequency band, mobile network with two bands, GSM900 and DCS1800)

Only the service community has to do the measurement of the cell frequency points, will be measured to the cell signal, otherwise in the list of adjacent areas will not see the cell, will not switch. In our usual road test, often encountered strong signal does not switch, if done a measurement frequency point, you can see very clearly there is a strong adjacent area signal, but if not to do the measurement frequency point is more recessive.

7. System Information Type 5ter

The measurement frequency of the service cell in the active mode (different frequency bands, the mobile network has two bands, GSM900 and DCS1800).

8. System Information Type 6

Call status under the service community some information, he and Type1 a bit like, also can see NCC permitted;

9. System Information Type 7

Not seen for the moment.

10. System Information Type 8

Not seen for the moment.

11, Paging Requst type1

It can be seen that in the signaling, paging signaling is particularly numerous, because the network to the mobile phone paging is a location in the area of paging, only when the phone to unlock this information will respond.

12. Synch Channel Information

Synchronization information, in the standby state and call status will appear, digital communications, synchronization is the most basic and most important, and adjacent areas need to be synchronized.

13. Other:

① dropped words;

② Location Update

③ switching

④ Measurement Report

Here to talk about the principle of lock frequency and forced switching, usually we test often use the lock frequency and forced switching, these operations are not required network action, just by the mobile phone to complete, and how the phone is done. is by changing the measurement report. When the tester clicks the lock frequency or the forced switch command, the phone will stop the measurement of other frequency points, just upload the test personnel locked the measurement report, the other frequency points do not upload, as shown above, so the network will think that the cell phone only receive the signal and if the service cell will be locked, if the neighborhood network will be switched.

⑤channel release signaling inside the cause (event number) corresponding to the network of things, here we can see a lot of reasons for the network release, such as: we usually test, in the case of the call Phone no one to answer or is talking, it will be counted as a connection failure, If we only use words in the report, the persuasion is not strong, but if in the report can explain that cause is 17, 19 is easy to persuade others, and congestion can also be seen in the signaling cause is 34, in addition to the times there are many cause, you can see the following table:

Number	Reason
1	unassiagned number (empty number)
3	No route to destination (no routes to destination)
6	Channel unacceptable (unacceptable channels)
16	Normal clearing (normally cleared)
17	User busy (Users busy)
18	No user responding (no users response)
19	User Alerting,no Answer (users are reminded, but no answer is available)