Synchronization is a procedure for establishing and maintaining certain time relationships between two or more processes.
There are element-by-element, group and cyclic synchronization.
With element-by-element synchronization, the required phase relationships between the significant moments of transmitted and received individual elements are established and maintained digital signals data. Element-by-element synchronization allows you to correctly separate one single element from another at reception and provide the best conditions for its registration.
Group synchronization - ensures correct division of the received sequence into code combinations.
Cycle synchronization - ensures proper separation of time combining cycles.
Timing devices with adding and subtracting pulses
The device belongs to the class without direct influence on the generator frequency and is 3-position.
When the synchronization system is running, three cases are possible:
The generator pulses pass unchanged to the input of the frequency divider.
1 pulse is added to the pulse sequence.
1 pulse is subtracted from the pulse sequence.
The master oscillator produces a relatively high-frequency pulse sequence. This sequence passes through a divider with a given division coefficient. Clock pulses from the output of the divider ensure the operation of the transmission system blocks and also enter the phase discriminator for setting.
The phase discriminator determines the sign of the phase discrepancy between the CM and TI of the master oscillator.
If the receiving frequency is greater, the PD generates a pulse subtraction signal for the UDVI, through which the passage of one pulse is prohibited.
If the receiving frequency is lower, then the pulse is added.
As a result, the clock sequence at the output D k is shifted by.
The following figure illustrates the change in clock position as a result of adding and subtracting pulses.
TI2 - as a result of addition, TI3 - as a result of subtraction.
Role of the up/down counter:
In a real situation, the received elements have edge distortions that vary randomly the position of significant moments in different directions from the ideal ZM. This may cause false timing adjustments.
Under the influence of CI, shifts of the CM both towards the advance and towards the lag are equally probable.
When the CM is displaced due to the fault of the synchronization device, the phase is stably shifted in one direction.
Therefore, to reduce the influence of CI on the synchronization error, set up/down counter capacity S. If S signals arrive in a row to add a pulse, indicating that the reception generator is lagging, then the pulse will be added and the next TI will appear earlier.
If the S-1 signal about advance comes first, then the S-1 signal about lag, then there will be no addition or subtraction.
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2.1. Course structure. Basic terms and definitions. Structure of the Unified Telecommunication Network (UTN) of the Russian Federation. Switching methods in data networks. Types of signals. Parameters of digital data signals.
2.2. Structural scheme discrete message transmission systems. Continuous channel and CBT. Edge distortion and fragmentation. Registration methods. Discrete channel. Channels with memory. Advanced discrete channel and its parameters. Characteristics of SPDS.
2.3. Principles of effective coding. Huffman method. Dictionary methods ZLW.
2.4. Noise-resistant coding. Linear codes. Generating and checking matrices of a linear Hamming code. Coder. Decoder. Cyclic codes. Construction of the encoder and its operation. Decoder with error detection.
Algorithm for determining an erroneous discharge. Decoders with error correction. Reed-Solomon codec. Iterative and cascade codes. Convolutional codes. Construction of the encoder and its operation. State diagram and trellis diagram. Decoding using the Viterbi algorithm.
2.5. Adaptive systems. Systems with iOS. Systems with ROS-OZH. Calculation of reliability and speed of information transfer.
2.6. Methods for pairing a source of discrete messages with a discrete channel. DTE/DCE, RS-232, etc.
2.7. Synchronization. Types of element-by-element synchronization. Technical implementation. Calculation of synchronization parameters. Group, cyclic synchronization.
2.8. OOPS. Classification. Recoding. AM, FM, FM. Modulators and demodulators. Relative phase modulation. Multi-position phase and amplitude-phase modulation. DMT, Trellis modulation. Review of xDSL technology. OFDM. Radio modems, satellite modems.
2.9. Computer networks PD. Principles of construction. Classification. Purpose of LAN. LAN types. Network topologies. Basic transmission media in a LAN. Data transmission network technologies in operator networks. Corporate PD networks, VPN. Model of interaction of open systems. OSI and IEEE network models. Interactions between levels. Examples of protocols at different levels. Protocol stacks. Methods of access to the transmission medium. Network architectures: Ethernet, Token Ring. LAN expansion devices. Repeater, bridge, switch, router, IP addressing.
Routing methods. Interaction of application processes via the TCP protocol. Gateways.
BASICS OF DISCRETE MESSAGES
Lecture No. 1.
Course structure. Basic terms and definitions.
Lectures 34 hours;
Practical classes 17 hours;
Laboratory work 17 hours.
Lecture topics:
1. Course structure. Basic terms and definitions;
2. Block diagram of the PDS system;
3. The principle of effective coding;
4. Noise-resistant coding;
5. Methods for pairing a source of discrete messages with a discrete channel;
6. Synchronization;
7. Signal conversion devices (SCD);
8. Adaptive systems;
9. Switching methods in the PDS network;
10. Computer data networks.
Documentary telecommunications– this is a type of telecommunication where a message can be displayed on any medium (paper, monitor screen).
Services:
Telegraph TGSOP;
Telephone;
Telex AT/Telex;
Facsimile SFS:
Fax server; networks
Datafax;
Transfer of newspaper strips to PGP;
Video text (email).
Telematic.
Methods for distributing information in PDS networks:
1. Channel switching;
2. Switching with accumulation:
Message switching;
Packet switching.
Circuit switching (CS) - establishing a connection, transmitting a message in both directions, destruction.
Channel switching:
Switching with accumulation. TFSOP:
УУ – Control device;
NU - Storage device;
OSD – External storage device.
The message is transmitted across sections of the network and stored in the management system. Consists of header and data. There is no establishment and release phase.
The title reads: The address of the management company is located. Recipient.
Message switching (MS) TSTN.
The header consists of seven levels. At each level, the message is processed and stored in external memory.
The main disadvantage of CS is that it is necessary to have a large memory, since messages of different lengths are transmitted.
Note: CKS on a computer (CKS - central com. message).
IN computer networks, telematic services (mail messages).
Packet switching:
The message is divided into packets. There is no NU. There is less message latency. High processing speed.
Applicable in:
Computer networks;
Ethernet: at layers 1 and 2 the header is saved, and then not;
TFSOP; SSPO
They use packet switching protocols.
NGN – Next Generation Network (packet network);
IP telephony.
The following protocols are used at the transport layer:
TCP (with the establishment of a virtual connection (virtual channel));
UDP – (connectionless (datagram mode)).
VVK – Temporary virtual switch (installed by the user).
PVC – Permanent temporary channel (set by the administrator).
In datagram mode, each packet is transmitted independently of each other. Used to transmit short messages.
The TCP protocol is more reliable.
Mixing bags– packets travel along different paths and appear at different times.
Lecture No. 2.
Block diagram of the PDS system.
Basically, the data transmission system uses packet switching.
All systems use discrete messages. For transmission of which discrete signals (two-level) are used.
e.e – single element.
Such a signal enters the communication channel; depending on the channel, conversion must be done. In the communication channel, the signal is affected by interference - external and internal. Therefore, noise-resistant coding is used.
Source DS (0:1) Communication channel (0:1) DS Receiver
In telegraph communications, noise-resistant coding is rarely used.
For telematic services and SPD – mandatory.
To transmit messages, in addition to noise-resistant coding, information compression methods are often used.
Block diagram of the diesel power station system:
IS – source of message, act. disc. communication, also called source encoder or data processing equipment.
RCD is an error protection device that adds check “r” bits to the “k” information bits, also called a channel encoder.
SCD - signal conversion device - converts the signal into a form suitable for transmission to the communication channel.
RCD and UPS are combined into APD - data transmission equipment.
PS – message receiver.
DC – discrete channel.
Efficiency – data transmission channel.
MKT-2 is used as the primary code (n=5, 
).
On long-distance communication – MKT-5 (SKPD) 
=128.
Primary codes cannot detect and correct errors.
In systems with OS, redundancy is introduced into the transmitted information taking into account the state of the discrete channel. As the channel condition deteriorates, the introduced redundancy increases, and vice versa, as the channel condition improves, it decreases.
Depending on the purpose of the OS, systems are distinguished:
with decisive feedback(ROS)
information feedback (IFE)
with combined feedback (COS)
Figure 21 – Scheme of the PDS system with ROS.
Figure 22 – Scheme of the PDS system with IOS.
In a system with POC, the receiver, having received a code combination and analyzed it for errors, makes the final decision to issue the combination to the information consumer or to erase it and send a signal through the reverse channel to retransmit this code combination. Therefore, systems with POC are often called systems with re-questioning, or systems with automatic error request (AEO). If a code combination is received without errors, the receiver generates and sends a confirmation signal to the OS channel, having received which, the PCper transmitter transmits the next code combination. Thus, in systems with DFB, the active role belongs to the receiver, and the decision signals generated by it are transmitted via the reverse channel.
In systems with IOS, information about code combinations arriving at the receiver is transmitted via the reverse channel before their final processing and final decisions are made. A special case of IOS is the complete retransmission of CCs or their elements arriving at the receiving line. These systems are called relay systems. If the amount of information transmitted over the OS channel is equal to the amount of information in the message transmitted over the forward channel, then the IOS is called complete. If the information contained in the receipt reflects only some of the characteristics of the message, then the IOS is called shortened. Thus, either the entire helpful information, or information about its distinctive features, therefore such an OS is called informational.
The information received via the OS channel is analyzed by the transmitter, and based on the results of the analysis, the transmitter makes a decision on transmitting the next CC or repeating previously transmitted ones. After this, the transmitter transmits service signals about the decisions made, and then the corresponding CC. The PKpr receiver either gives the accumulated code combination to the recipient, or erases it and remembers the newly transmitted one. Systems with a shortened IOS have less load return channel, but there is a greater likelihood of errors compared to the full IOS.
In systems with CBS, the decision to issue a CC to the recipient of information or to retransmit it can be made both in the receiver and in the transmitter of the PDS system, and the OS channel is used to transmit both receipts and decisions.
OS systems:
with a limited number of repetitions (CC is repeated no more than L times)
with an unlimited number of repetitions (QC is repeated until the receiver or transmitter decides to issue this combination to the consumer).
OS systems can discard or use the information contained in rejected QCs in order to make a more correct decision. The first type of system is called a system without memory, and the second type is called a system with memory.
OS systems are adaptive: the rate of information transfer through communication channels is automatically adjusted to the specific conditions of signal transmission.
Research has shown that, for a given transmission fidelity, the optimal code length in systems with IOS is somewhat smaller than in systems with POS, which reduces the cost of implementing encoding and decoding devices. However, the overall complexity of implementing systems with IOS is greater than systems with DOS. Therefore, systems with POC have found wider application. Systems with IOS are used in cases where the return channel can be effectively used for transmitting receipts without prejudice to other purposes.
IS – message source;
N 1 – transmitter storage;
УУ 1 – transmitter control device;
UAS – solution signal analysis device;
PDK – direct discrete channel;
RDC – reverse discrete channel;
N 2 – receiver storage;
УУ 2 – receiver control device;
UFS – decision signal generation device;
PS – message recipient.
IS N 1 Encoder PDK Decoder N 2 PS
UU 1 UAS ODK UFS UU 2
Transmitter discrete receiver
Rice. 5.5 Block diagram of the system with ROS - coolant.
The circuit works as follows. Upon command from the transmitter control device (TC), the message source (IS) issues code combinations that are recorded in the transmitter storage (H 1), where a block for transmission is formed. Next, the block enters the encoder, where redundancy is introduced, i.e. coding with a code that allows errors to be detected. The encoded block is then fed into the forward discrete channel. At the receiver, the decoder determines whether an error occurred when transmitting a block over the forward channel. In addition, the received block is written to the receiver's storage (H 2). If no error is detected in the block, then the receiver control device issues a command to the decision signal generation device (DSG) to generate a “confirmation” command. The UFS generates a command and sends it via a reverse discrete channel. In addition, CU 2 issues a command to H 2, and the received block is transmitted to the message recipient. If an error is detected in the received block, then CU 2 issues a command to H 2 to erase the received block, as well as a command to the UFS to generate a “request” command. The transmitter, having received the feedback signal via the return discrete channel, analyzes the signal in the decision signal analysis unit. If a confirmation signal is received, then CU 1 sends a command to the message source to issue the following code combinations and the transmission cycle is repeated. If the UAS decrypts the “request” signal, then the UAS 1 issues a command to H 1 to repeat the previous block. This is repeated until the block is correctly received by the receiver.
Let us depict a time diagram of the operation of the system with ROS - coolant.
nτ 0 t p t ab t c t p t p
in maximum permissible concentration 1 2 2 3 t
t p t p t ac t ac
PRM 1 2 2 3 t
from PDK t ab t ab t ab
PRD P 3 P t
τ with ROS – coolant τ with τ with
Rice. 5.6 Time diagram of ROS - coolant
The timing diagram shows:
t r – signal propagation time over a discrete communication channel
t ab – time of block analysis in the receiver (decoding)
t s – duration of the signal in the reverse discrete channel
t ac – time of signal-decision analysis from the ODK
t cool – waiting time, i.e. idle time of direct discrete channel
C – cycle time of the PDS system
The following relationship can be written directly from the timing diagram:
t cool = t r + t ab + t c + t r + t ac =2 t r + t c + t ab + t ac
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