Reference models - Model of an integrated service (ISDN and PTN) subscriber network

Block diagram of an integrated service subscriber network with two kinds of access (basic rate, primary rate) can be seen on the following figure:

          subscriber (user)             public provider (network)
  ------------------------------->|<------------------------------------------

               R        S         T        U          V  - reference points
               |        |         |        |          |
 +--------------------------------------------------------------------+
 | Basic Rate Interface (Access) BRI (BRA)  ((S0)) :
 |                                                                    |
 | TE2 - subscriber equipment (terminal)                           |
 |+----------+   +--+ 1                                               |
 ||xxxxxxxxxx+-R-+TA+--+                                              |
 |+----------+   +--+  |                                +--------+    |
 | TE2                 |                                | Local  |    |
 |+----------+   +--+ 2|    +---+   +---+        +--+   +--+     +--  |
 ||xxxxxxxxxx+-R-+TA+--+-S0-+NT2+-T-+NT1+---U----+LT+-V-+ET|     |    |
 |+----------+   +--+  |    +---+   +---+        +--+   +--+     +--  |
 | TE1                 |          |<--------------->|   | Local  |    |
 |+----------+        3|                 digital       |exchange|    |
 ||xxxxxxxxxx+---------+              line section      |        |    |
 |+----------+         |     +------------------------- |        | ---+
 | TE1                 |     |  +---------------------- |        | -------+
 |+----------+        4|     |  |                       +--+     |        |
 ||xxxxxxxxxx+---------+     |  |                   + V-+ET|     |        |
 |+----------+         |     |  |                   |   +--+     |        |
 |                           |  |                   |   |        |        |
 |                     |     |  |                   |   +--------+        |
 |                           |  |                   |                     |
 | TE1                 |     |  |                   |                     |
 |+----------+       8 |     |  |                   |                     |
 ||xxxxxxxxxx+---------+     |  |                   |                     |
 |+----------+               |  |                   |                     |
 +---------------------------+  |                   |                     |
 +------------------------------+                   |                     |
 |Primary Rate Interface (Access) PRI (PRA) (S2M):
 |                                                  |                     |
 |                           +---+              +--+|                     |
 |                       +---+NT1+-------U------+LT++                     |
 |                  S2M  T   +---+              +--+                      |
 |                       |                                                |
 |                   +---+---+                                +-------+   |
 | TE2               |  NT2  |                                |       |   |
 |+----------+  R    |       |     +----+            +----+   |       |   |
 ||xxxxxxxxxx+-------+       +--Q--| MP |--C- - - -C-| MP |-Q-+ társ  |   |
 |+----------+       | PABX  |     +----+     IVN    +----+   | PTNX  |   |
 |     .             |  v.   |              <----->           |       |   |
 |     .             | PTNX  |                                |       |   |
 |     .             |       |                                |       |   |
 | TE1               |       |                                |       |   |
 |+----------+  S    |       |                                |       |   |
 ||xxxxxxxxxx+-------+       |                                |       |   |
 |+----------+       +-------+                                +-------+   |
 +------------------------------------------------------------------------+
 

ISDN network can be accessed by subscribers through two kinds of access points:

• Basic Rate Interface (Access) BRI (BRA) access point providing connection (two information and data transmission channels with 64 kbit/s rate (Channel B), and one signalling channel with 16 kbit/s rate (2B+D).
• Primary Rate Interface (Access) PRI (PRA) access point providing connection (30 information and data transmission channels with 64 kbit/s rate (Channel B), and one signalling channel with 16 kbit/s rate (30B+D).

Elements of the network:

• TE - Terminal Equipment (subscriber equipment)
  • TE1 type :(ISDN terminal) it connects directly to the bus of the subscriber network (S-bus). (E.g. ISDN (digital) telephone, interface card accessible to a PC)
  • TE2 type :(non ISDN terminal) it connects to the bus of the subscriber network (S-bus) through a TA (Terminal Adapter. E.g. analogue telephone, modem with V interface.

• TA - Terminal Adapter It connects a TE2 type terminal to the S-bus
• NT1,NT2 - Network Termination
  An equipment connects the subscriber network to the provider.

Individual elements of the network connect to each other through standard, so called reference points (interface specifications are give to these points):

• R reference point
  It is the access point of not ISDN tools. (E.g. an RS-232 communication interface with asynchronous serial points.
• S reference point
  
  • S0 reference point It is the interface that connects the subscriber tools with each other. Max 8. TE can be accessed to it. Signal transmission rate: 192 kbit/s.

  • S2M reference point It is the boundary point between the subscriber network and the provider network, and the access point of the T reference point with a primer rate:

    

    Signal transmission rate: 2048 kbit/s. NT2 is an exchange in the case of primary rate access (PABX Private Automatic Branch Exchange). Note: TEs with a high rate can access to the provider with primary rate access, and NT2 exchanges can access with a connection of basic rate, too.

• T reference point
  It is the boundary point between the subscriber network and the provider network.

  

  NT1 and NT2 are closed up in individual ISDN applications, so the T point is a virtual point:

  

• U reference point
  This interface connects the subscriber network with the provider (ISDN exchange). U interface generates a digital line section with NT1 subscriber network adapter, and with LT exchange adapter. Digital line section is usually a duplex one, but there are four-wired solutions, too. At a duplex digital signal transmission we can apply either the time-compression technique, or the echo-deleting technique for transmitting the signals of the two direction at the same time.

• V reference point
  It is the access point of the exchange of provider.

• Q reference point
  It is the virtual connecting point with a primary rate of exchange pairs (PTNXs) in the applications of private networks.
  Signalling system: QSIG.

• C reference point
  It is the connecting point between the IVN interconnection network and the PTNXs in the applications of private networks.