TYPES OF SYNCHRONIZATION Flashcards
is crucial in data communications to ensure
that data is transmitted and received accurately. It also
allows for the efficient use of communication channels by
preventing devices from transmitting or receiving data
simultaneously, which could cause collisions or data loss.
Synchronization
is a process that involves coordinating
the execution of multiple threads to ensure a desired outcome without
corrupting the shared data and preventing any occurrence of deadlocks and
race conditions
Synchronization
also occurs between network nodes to ensure that data streams
are received and transmitted correctly, and to prevent data collision. It usually
uses a clock signal transmitted in sequence with a data stream to maintain
proper signal timing
Synchronization
refers to the method used by the data communication system so
that the destination station recognizes the start of a data stream and
reliably reads the information sent
Timing
Two major timing schemes
- Asynchronous Transmission
- Synchronous Transmission.
sends data from the source to the destination without
synchronizing the two clock systems
Asynchronous communications or transmission
The source and destination clocks are free running and not locked to each other. Short characters of
7 to 8 bit data are sent one at a time framed by a start bit and 1 or 2 stop bits.
Asynchronous communications or transmission
is used for low data transfer rates usually 128 kbps or less and short
bursts of data. Faster data rates and longer data lengths cause the data errors at the receiver
Asynchronous communications or transmission
Conventional representation has asynchronous data flowing left to right and synchronous data
flowing right to left.
Indicate the end of a character’s transmission.
Typically 1 stop bit is used (sometimes 2)
Stop Bits
Characters are sent individually.
A quiet period (idle state at 0 bit level) exists between characters.
Character Transmission
Transmitter and receiver each have their own internal clocks.
Clocks are not locked together but operate at the same frequency
Free-Running Clocks
The start bit acts as a “wake-up call” for the receiver.
Data bits are sampled in the middle of each bit period.
Evenly spaced sampling ensures accurate data reception
Receiver Operation
is a method of data communication that requires the
source and destination to synchronize their clocks together.
Synchronous Transmission
This synchronization of the clocks can occur externally to the data information or be incorporated with the data information
Synchronous Transmission
two types of synchronous data transmission
- Externally clocked synchronous transmission
- Internally encoded synchronous transmission
The advantage to having the clocks synchronized is that longer blocks of data can be sent without loss of synchronization.
Less overhead is required for the amount of data sent. In asynchronous transmission,
there are 3 to 4 bits of overhead (start, stop, parity bits) sent with each character of data (7 to 8 bits). The start and stop bits were used to identify the beginning and end of transmission.
blocks of data up to 64Kbytes in size can be sent without loss or corruption of data. A start field and end field indicate the beginning and end of transmission. Smaller overhead results in a more efficient delivery of data.
synchronous transmission
has separate lines from the data
lines for synchronizing the clock.
Externally clocked synchronous transmission
used to send out a timing clock to the
destination
Transmit Timing balanced pair
separate clock timing received from the
destination
Receive Timing balanced pair
Special sequence of bits called
__________ are required at the beginning and end of the block of data to inform the destination that new data is arriving.
fields
sends blocks of characters at a time. Each block of data is preceded by a Start Field which is used to tell the receiving station that a new packet of characters is arriving. The blocks of data also have End Fields to indicate the end of the data
block.
Synchronous Transmission
has two pairs of wires used for synchronizing the source
and destination clocks
V.35 physical layer standard
The packet can contain up to ______ bytes depending on the protocol.
64,000
Both Start and End
Fields have a special bit sequence that the receiving station recognizes to indicate the start and end of a data block. The Start and End Fields may be only _____ bytes each.
2
is more efficient than asynchronous (character transmission) as little as only
4 bytes (2 Start Framing Bytes and 2 Stop Framing bytes) are required to transmit up to 8K bytes
Synchronous transmission
Extra bytes, like the Start and Stop Frame, that are not part of the data are called
Overhead
consists of control information used to control the communication
Overhead
EFFICIENCY FORMULA
of data bytes / total # of bytes transmitted
is more difficult and expensive to implement than externally clocked synchronous transmission.
Internally clocked synchronous transmission
The timing signal for synchronization between the source and destination is encoded within the
data stream
is an example of an internally clocked synchronous transmission code.
Manchester encoding
It is used with all higher transfer rates of communication: Ethernet, ArcNet, Token Ring etc…
Internally Clocked Synchronous Transmission
is often called self clocking as no external timing lines are required.
Internally Clocked Synchronous Transmission
Internally clocked synchronous transmission is used in fast transfer rates ranging from
100 Kbps to 100 Mbps
In the _______, there is a transition at the middle of each bit period. The mid-bit transition serves as a clocking mechanism and also as data: a low to high transition represents a 1 and a high to low transition represents a 0.
Manchester Code
also called a self-clocking code and has no direct current (DC) component
Manchester Encoding
There is always a transition in each bit period, these transitions synchronize the transmit and receive clock
Manchester Encoding
It has the added benefit of requiring the least amount of bandwidth compared to the other Line Codes (Unipolar, Polar, etc..)
Manchester Encoding
Manchester coding requires 2 frequencies: the ___________________. All other types of Line Coding require a range from 0 hertz to the maximum transfer rate frequency. In other words, Manchester Encoding requires a Narrow Bandwidth.
base carrier and 2 x the carrier frequency
is used as an introduction to Synchronous Data Transmission. As we
explore more standards and protocols, we find that we can expand the frame structure
(packet) into better defined sections that will allow easier understanding of different
frame types
Generic Packet X
Appears at the very start of each frame (or packet).
It is used to:
a. Alert the Receiver: Tells the receiving device that a new packet is on its way.
b. Synchronize the Receive Clock: Helps the receiver’s clock line up with the sender’s
clock
Preamble: Starting Delimiter/Alert Burst/Start of Header
Used to indicate the Type of Information being sent as Data
Its purpose is to identify whether the packet or frame is meant
for Control or Data.
It can also be used to indicate the size of the packet and Data.
Control Field
consists of a Source Address and/or a Destination Address.
These addresses are hexadecimal numbers that identify:
Source Address: Identifies who is sending the data (the sender).
Destination Address: Identifies who should receive the data (the receiver).
These addresses usually come from the Network Interface Card (NIC).
They can be:
Built into the NIC’s firmware.
Assigned during the NIC’s initialization.
Under some protocols, there may not be both Source and Destination Addresses; only one address may be present.
Address Field(s): Source and/or Destination
Used when establishing a connection
(handshaking)
Control Information
Such as file transfers between clients and servers
Data
It is the actual information being transmitted.
It can contain:
Control Information: Used for handshaking.
Data: Actual content used by applications
Data/Message
indicates the size of the Data Field
Control Field
is also called the Info field by some protocols
Data field
used to pad the data field when the protocol has a fixed Data Field size.
Example: If the Data Field size is fixed at 1200 bytes but only 300 bytes of information
are available, the Pad fills the remaining 900 bytes (e.g., 900 bytes of 00h).
It may also ensure a minimum Data Field size.
Optional Pad
Contains an error-checking number that the Destination uses to verify that the
packet is okay and error-free
Checksums work similarly but use a different algorithm
CRC/ Frame Check Sequence
CRC is an abbreviation for
Cyclic Redundancy Checking
The FCS typically incorporates a ____ CRC check
32-bit
As each packet is sent, the Source calculates a check number from the data
using a predetermined algorithm (formula).
The result of this calculation is appended to the packet in the FCS field.
At the Destination, the same calculation is performed and the result is
compared to the transmitted FCS.
If the result generated at the Destination is identical to the FCS, then it is
assumed that the packet is error-free at the bit level
CRC/ Frame Check Sequence
A series of bytes with a specific bit pattern that marks the end of the packet for the
Destination.
Not all protocols include an End Frame Delimiter.
In protocols with fixed packet sizes, the Destination may simply count the number of bytes received instead of relying on an End Frame Delimiter.
End Frame Delimiter
is simple and inexpensive to implement
Asynchronous transmission
It is used mainly with Serial
Ports and dialup connections
Asynchronous transmission
Requires start and stop bits for each character - this adds a high
overhead to transmission
Asynchronous transmission
is more efficient as little as only 4 bytes (3 Start Framing bytes and 1 Stop Framing byte) are required to transmit up to 64 kbits
Synchronous transmission
is more difficult and expensive to implement
Synchronous transmission
It is used with all higher communication transfer rates: Ethernet, Token Ring etc… Synchronous is used in fast transfer rates typically 56 kbps to 100 Mbps.
Synchronous transmission
ASYNCHRONOUS A & D
Simple and Inexpensive / High Overhead
SYNCHRONOUS A & D
Efficient / Complex and Expensive
Types of Synchronization
- Bit-Level Synchronization
- Byte-Level Synchronization
- Block-Level Synchronization
Ensures that the sender and receiver are
synchronized at the bit level, allowing the
receiver to correctly interpret the timing and value of each bit
Bit-Level Synchronization
Bit-Level Synchronization Example
Ethernet
Ensures that the sender and receiver are
synchronized at the byte level, allowing the
receiver to correctly interpret the start and
end of each byte.
Byte-Level Synchronization
Byte-Level Synchronization Example
USB, Serial Communication
Ensures that the sender and receiver are synchronized at the block level, allowing the receiver to correctly interpret the start and end of larger data units
Block-Level Synchronization
Block-Level Synchronization Example
Bluetooth & Wi-Fi, GSM
Bit-Level Synchronization Mechanism
Clock signals & encoding
Byte-Level Synchronization Mechanism
Start and stop bits
Block-Level Synchronization Mechanism
Synchronization patterns
The simultaneous execution of multiple threads or processes to reach a handshake
such that they commit a certain sequence of actions.
Process Synchronization
Process Synchronization Examples
Locks, Mutexes, and Semaphores.
is an abstraction that allows at most one thread to own it at a time
Locks
Typically an integer variable.
Allows multiple program threads to access a finite instance of resources
Semaphores
is an object.
Allows multiple program threads to access a single shared resource, but one at a
time
Mutexes
Involves the maintenance of data to keep multiple copies of data
coherent with each other, or to maintain data integrity.
Data Synchronization
