Final review of exchange principles

1. Three elements of communication network:

Exchange equipment, transmission equipment, user terminal equipment.

2. Synchronous time division multiplexing:

The basic principle of synchronous time division multiplexing is to divide time into basic units of equal length, which are generally called frames, and each frame is divided into smaller units called time slots. The time slots are numbered according to their positions in the frame. Assuming that a frame is divided into n time slots, the numbers can be written as 0, 1, 2..., n-1 in sequence.

3. There are two ways of packet switching:

One is the virtual circuit mode, and the other is the datagram mode.

1. The virtual circuit adopts a connection-oriented working mode;
   an end-to-end virtual connection is established before user data transmission;
   once the virtual connection is established, data packets belonging to the same call are transmitted along this required connection;
   the virtual connection is removed when the communication ends.
2. The datagram mode uses a connectionless working mode;
   there is no need to establish a connection before calling;
   each packet is independently routed according to the destination address in the packet header.

4. Four basic types of communication connection (P15):

Local office connection, outgoing connection, incoming connection, and transfer connection.
Outgoing connection: The caller of the communication is in this exchange, and the called is in another exchange.
Incoming connection: The called party of the communication is in this exchange, and the calling party is in another exchange.

6. 交换单元（SE）It is the most basic component of a switching network.
7. Space connector capacity = memory number, unit number, unit size = N * m * n.
   (P37 + P65)

Exercise 6 (P65)

9. The basic structure of digital program control exchange is

Consists of voice circuit subsystem and control subsystem

10. The interface equipment of digital program control exchange mainly includes

User circuit, relay circuit, signaling transceiver equipment

11. Audio signal type

Switch to user: single-frequency signal tone;
the signal sent from user to switch is mainly called number, including two forms: DC pulse and dual tone multi-frequency (DTMF).

12. Dual audio signal generation (PCM sampling frequency 8KHz, T=125us)
    (P81 + P127)

Exercise 8 (P 127) Five-step calculation and drawing

13. Calculate BHCA
    (P86 + P127)

The maximum number of busy-hour calls (BHCA) of the program-controlled exchange: t = a + b * N;
t is the system overhead of
the exchange control system ; a is the inherent overhead of
the exchange control system ; b is the exchange control system processing a call Extrinsic overhead (average value);
N is the total number of calls processed in a unit time (one hour), that is, the call processing capability value (BHCA);
b*N is the extrinsic overhead of the switch control system.
Problem 13 (P 127)

14. The working mode of multiprocessors-redundant mode

The dual-computer redundancy configuration can be divided into three types according to the specific working modes:
synchronization mode, mutual assistance mode, and main/standby mode

互助方式：

The load is shared equally between the main and standby machines, that is, when the main and standby machines are working normally, they respectively bear half of the traffic load. When one processor fails, the other processor has to undertake all the traffic processing work until the failed processor recovers: Return to the load sharing mode.

15. In the program-controlled switching system, tasks can be divided into the following according to the requirements of urgency and real-time:

Fault-level tasks, periodic-level tasks, and basic-level tasks (priority decreases in order).

16. China's telephone communication network adopts 5级结构its network topology as a hierarchical tree structure.

17. The main tandem methods that can be used in the tandem telephone network are

Outgoing tandem, incoming tandem, incoming and outgoing tandem, main and auxiliary tandem

18. User signaling and interoffice signaling

The signaling can be divided into the area in which the signaling works 用户信令和局间信令.
User signaling is 用户终端和交换节点the signaling transmitted on the subscriber line between.

19. Channel associated signaling and common channel signaling

Channel associated signaling is signaling that signaling and user information are transmitted on the same channel (China No. 1)
. The signaling channel and user information signaling of common channel signaling are separated, and signaling is transmitted on a dedicated signaling channel. . (No.7)

20. Features of end-to-end transmission:

High requirements for line transmission quality, fast signaling transmission speed, and short connection time require that the heart signaling transmitted on multiple sections of roads be of the same type.

21. Full mutual control mode:

In the signaling process, the sender sends signaling to receive control of the receiving segment, and the receiver sends signaling is also controlled by the sender.
Figure 4.9 Full mutual control mode (P 138)

22. No.7 signaling transmits various signaling through 信令的消息的最小单元----SUtransmission. The format of signaling unit:

1. Fill the signal unit FISU (LI = 0);
2. Link state signal unit LSSU (LI = 1, 2);
3. Message signal unit MSU (LI> 2).

23. Correspondence between my country's telephone network and signaling network

1. HSTP is located in the C1 and C2 switching centers. C1 and C2 long-distance offices are directly connected to HSTP. HSTP connects C1, C2 and the signaling of the LSTP.
2. LSTP is located in the C3 switching center. The long-distance offices in the same sub-signaling area should be connected to each pair of LSTPs in this office. LSTP connects the signaling of C3, C4, and C5 signaling points.

24. National signaling point codes using 24bita unified national numbering plan.
25. Reservation method (- flow control method)

Before sending packets to the receiving end, the sender first reserves a buffer storage area with the receiving end, and then the sender sends packets according to the number of packets allowed by the receiving end, thereby effectively avoiding deadlock at the receiving end.

26. Packet Exchange Protocol----X.25协议
27. In ATM, the transmission, multiplexing and exchange of various information are based on the cell as the basic unit.

The fixed length of an ATM cell is 53 bytes, the first 5 bytes are headers, and the last 48 bytes are information segments.

28. VP exchange and VC exchange

VP exchange: exchange that only changes the value of VPI without changing the VCI value;
VC exchange: exchange that both VPI value and VCI value must be changed.

30. Basic Principles of ATM Switching

Figure 7.15 Basic Principles of ATM Switching (P 287)

31. The existence of input buffer with FIFO rule排头阻塞现象(HOL)

（P291)