Данный материал содержит следующие 5 лекций:

Лекция 1: Архитектура протоколов абонентской сигнализации

Лекция 2: Протокол доступа к каналу D (LAPD-Q.921)

Лекция 3: Формат сообщений сигнализации DSS1

Лекция 4: Протокол абонентской сигнализации Q.931

Лекция 5: Процедуры управления вызовом

Лекция 3: Формат сообщений сигнализации DSS1

Вначале приведем пример реального сообщения сигнализации DSS1.  

Пример трассировки сообщений протокола DSS1

FROM USER SIDE  - Frame #0011   Time: 14:42:27.59 Length: 23 octets

SETUP, Calling # 23974

Hex Image:

00 CB 00 00 08 01 01 05 04 04 88 90 21 8F 6C 07 00 80 32 33 39 37 34

Layer 2 - Data Link Layer (протокол Q.921)                                                      

Address field                                                                  

   00    .......0   EA0                                                         

         ......0.   C/R = COMMAND                                              

         000000..   SAPI = 0 Call control procedures                           

   CB    .......1   EA1                                                         

         1100101.   TEI = 101 Automatic assignment                             

Control field                                                                  

   00    .......0   I Information                                               

         0000000.   N(S) = 0                                                   

   00    .......0   P                                                          

         0000000.   N(R) = 0                                                    

Layer 3 - Network Layer                                                        

   08               Protocol discriminator = Q.931                             

   01    ....0001   Call Reference Length = 1                                   

   01    0.......   Flag = ORIGINATOR                                          

         .0000001   Call Reference Value = 1                                   

   05    0.......   E – бит расширения                                                           

         .0000101   Message type = SETUP                                       

   04                  Info Element = BEARER CAPABILITY (описание свойств услуги)                        

   04                     Length = 4 octets                                     

   88          1.......   EXT                                                  

               .00.....   Coding standard = CCITT                              

               ...01000   Info transfer capability = Unrestricted digital info 

   90          1.......   EXT                                                  

               .00.....   Transfer mode = Circuit mode                         

               ...10000   Info transfer rate = 64 kbit/s                       

   21          0.......   EXT                                                  

               .01.....   Layer 1 ID                                           

               ...00001   User info layer 1 protocol = CCITT V.110 & X.30      

   8F          1.......   EXT                                                  

               .0......   Synchronous/Asynchronous = Synchronous data          

               ..0.....   Negotiation = In-band negotiation not possible       

               ...01111   User rate = 56 kbit/s V.6                            

   6C                  Info Element = CALLING PARTY NUMBER (№ абонента А)                     

   07                     Length = 7 octets                                    

   00          0.......   EXT                                                  

               .000....   Type of number = Unknown                             

               ....0000   Numbering plan = Unknown                             

   80          1.......   EXT                                                   

               .00.....   Presentation indicator = Presentation allowed        

               ...000..   Spare bit(s)                                         

               ......00   Screening indicator = User provided, not screened    

   32 33 39 37                                                                 

   34                     Number digits = 23974 - № абонента А                               

Для детальной разборки данного сообщения, рекомендуется следующий рисунок:

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