Data Transmission and Packets

Data Transmission

• Data transmission has three key factors, those being direction, method, and synchronization between devices.

Data Packets

• Data is broken into packets, usually 64 KiB in size, to be transmitted.
• A packet contains a header, payload, and a trailer.
• The header includes the destination address, packet number, and originator’s address.
• The payload contains the actual data, usually about 64 KiB.
• The trailer identifies the packet's end and checks for transmission errors using cyclic redundancy checks (CRCs).
• The packet header stores routing information and ensures correct message reconstruction.

Cyclic Redundancy Checks (CRCs)

• This is an error-checking method for data packets.
• The sending computer adds all 1-bits in the payload, storing it as a hex value in the trailer.
• The receiving computer recalculates the number of 1-bits in the payload.
• If the values match, no errors occurred, otherwise, the packet is re-sent.

Packet Switching

• Data splits into packets, each with its own route, routing depends on congestion.
• Packets do not always arrive in the order they were sent.

Process of Packet Switching

• A message is broken down into smaller, same-sized packets.
• Each packet travels independently along varying routes/paths.
• A router selects the most efficient path.
• Packets may arrive out of order and are reassembled at the destination using header information.
• Re-transmission requests are sent if packets are missing/corrupted.

Function of a Router in Packet Switching

• Routers examine packet headers, reads the destination IP address, accesses a routing table, and decides on the next hop/best route.

Advantages of Packet Switching

• Optimizes channel capacity using alternative routes.
• Accurate message delivery is ensured.
• The use of alternative routes increases security and makes interception difficult.
• Provides better security as packets are hashed and sent via different routes.
• Alternative routes offer robustness, with paths available to others.
• Enables easy detection of missing packets; a re-sent request ensures complete message arrival.
• Routers can detect network changes, sending data alternatively to ensure its arrival.
• It does not use complete bandwidth, and allows simultaneous use of channels by multiple users.

Disadvantages of Packet Switching

• Time delays occur while reassembling packets and correcting errors at the destination.
• Packets may be lost, requiring re-transmission.
• Delivery requires complex protocols.
• Real-time transmission applications, such as live sporting events, are unsuitable.

Uses of Packet Switching

• Sending email messages and voice Over Internet Protocol(VoIP).

Hopping

• Packets can get lost. To prevent this, hopping is used .
• A hop number is added to each packet header, with a limited number of hops allowed.
• The hop number decreases by one each time the packet passes through a router.
• Packets are deleted if they don't reach their destination when the hop number reaches zero.
• The receiving computer flags the missing packets and requests that they be re-sent.

Direction of Data Transmission

• Data transmission can be simplex, in one direction only. An Example is data sent from a computer to a printer.
• Half-duplex is in both directions, but not simultaneously, like a phone conversation
• Full-duplex, also called "Duplex data transmission", happens in both directions simultaneously. An Example is broadband connection.

Serial Data Transmission

• Data is sent one bit at a time over a single wire or channel, arriving in sequence, and can be synchronous or asynchronous.
• It can be simplex, half-duplex, or full-duplex.

Advantages of Serial Transmission

• More reliable over longer distances.
• Less expensive wiring is needed.
• There is less chance of interference/data corruption.
• Data is sent more accurately over longer distances with less chance of it being skewed.

Disadvantages of Serial Transmission

• Slower data transmission rate.

Applications of Serial Transmission

• Computer to modem, Universal Serial Bus (USB), Wi-Fi, It is also used for transmission over long distances (100+ meters).

Parallel Data Transmission

• Multiple bits of data(usually 1 byte) are sent simultaneously through several wires/channels.
• Bits might arrive out of order,
• It can only be synchronous.
• It can be simplex, half-duplex or full-duplex.

Advantages of Parallel Transmission

• Faster data transmission rate.

Disadvantages of Parallel Transmission

• Less reliable over longer distances.
• More expensive wiring.
• Greater chance of interference/data corruption.
• Data is sent less accurately over longer distances, and it has more chance of the data being skewed.

Applications of Parallel Transmission

• Computer to printer.
• Internal electronics inside the computer.
• CPU and memory pathways.
• Integrated circuits, buses, and other internal components.
• Shorter distances (10 meters and less).

Asynchronous Data Transmission

• Transmission occurs per arranged bit patterns, with data bits (1s/0s) grouped with control bits.
• It prevents data being mixed up or skewed
• It is a slower process of date transfer.

Synchronous Data Transmission

• A continuous data stream paired with timing signals from an internal clock.
• The receiver counts bits and reassembles them into bytes.
• It is a faster method of data transfer, often network communications.
• Precise timing is crucial.

Universal Serial Bus (USB)

• It is an asynchronous serial data transmission method.
• Data bits are sent one at a time.
• It's a universal standard for data transfer between computers and devices, allowing both half-duplex and full-duplex transmissions.

Structure of a USB cable

• Four-wire shielded cable with two wires for power/earth and two for data transmission.

USB Port Usage

• A computer automatically detects a device's presence via voltage-level changes.
• The device is automatically recognized, and the appropriate device driver is loaded.
• If a new device is detected, the computer prompts the user to download appropriate software if no driver matches.

Advantages of USB Systems

• Devices are automatically detected and configured due to voltage level changes.
• Connector design prevents incorrect insertion.
• High-speed connectivity means faster data-transfer.
• Cheaper to manufacture.
• Compatible with earlier USB versions.
• Can power devices.
• Drivers are automatically downloaded.

Disadvantages of USB Systems

• The maximum cable length is currently around 5 meters (or more).
• Transmission rate is less than 500 megabits per second maximum.

USB-C System

• It is a new USB connector type common in laptops and tablets/phones.
• A symmetrical 24-pin connector fits either way.
• It is expected to become the new industry standard format.
• Smaller and thinner than older connectors.
• It offers 100 watt (20 volt) power connectivity and supports 4K video delivery.
• It is backward-compatible (to USB 2.0/3.0).

Errors During Data Transmission

• Errors in transmission are commonly the result of interference, packet switching problems, or data skewing.
• Error detection methods include parity checks, checksums, and echo checks.

Parity Checks

• A parity bit indicates the number of 1s in the data.
• Set to odd or even, agreed upon by sender/receiver.
• It is transmitted together with the individual chunks of data.
• In block checks, error locations can be identified.
• Undetected errors occur with multiple errors producing the same parity, even/odd digit changes, or transposition errors.

Checksum

• Before sending the data, an algorithm generates an additional checksum value.
• The receiver recalculates this value and compares it to the original.
• If the checksums differ, an this means an error has occurred.
• A retransmission request is then sent.

Echo Check

• Data is copied and sent back to the sender for comparison.
• Differences indicate errors during transmission, although it is not able to reveal whether the original transmission was corrupted

Check Digits

• Check digits identify errors in data entry.
• It is used for barcodes, ISBNs, and VINs
• Digits being omitted or extra digits may make this technique unable to be used

Common Types of Errors Check Digits Can Detect

• It can detect an incorrect entry of digits.
• It can also detect the transposing or omitting of digits.

Process of Check Digit

• It is calculated and appended to the data.
• The receiving system recalculates the check digit.
• Error is detected if the digits are different. However, no error is detected if the digits match.

ISBN 13

• In ISBN 13, the check digit is the 13th digit.

Automatic Repeat Query (ARQ)

• Used to ensure data is received without errors.
• It uses acknowledgement and timeout.
• The sender starts a timer, sending a request requiring acknowledgment.
• Positive acknowledgement indicates the data is correctly received.
• Negative acknowledgement indicates that an error was detected.

Encryption

• Protects data transmitted over networks from interception.
• It renders data unintelligible without a decryption key.
• Encryption involves scrambling data to make it meaningless, using encryption algorithms and keys.
• Plaintext is the original data prior to encryption.
• Ciphertext is the encrypted version created after encryption.

General Encryption Procedure

• The text before encryption is known as plain text
• Plain text is rendered unreadable using an encryption algorithm and key. The result is known as cypher text.
• Keys are used to decrypt the cypher text after transmission.

Types of Encryption

• Encryption commonly happens using two methods symmetric encryption and assymetric encryption.

Symmetric Encryption

• The same key is used for encryption/decryption.
• It is a security system with a secret key.

Encryption Using Symmetric Encryption

• Plaintext is scrambled using an encryption key and algorithm, converting it into ciphertext.
• it prevents unauthorized data access, requires decrypting the key

Symmetric Key Risks

• Keys can be cracked quiclky.
• Key interception is possible if the key is intercepted.
• The Modulo-11 is used to solve this challenge.

Ways to Increase Security with Encryption

• Increase key length.
• Use a more complex/algorithm.

Drawbacks of Symmetric Key Encryption

• Key exchange challenges involve a hack.
• Compromised keys can decrypt sent and received messages.
• No way is known to make encryption secure.

Asymmetric Encryption

• Asymmetric encryption overcomes some of the problems that stem from symetric encryptiomn
• Uses public and private keys – the public key is available to everyone, while each user has a private key only they know.

Asymmetric Keys

• Symmetric encryption is a security system and uses a secret key which can be a combination of characters.

Asymmetric Encryption Data Procedure

• It uses different keys for encryption and decryption.
• Sender uses receiver’s public key to encrypt the message.
• The receiver decrypts it using a private key.

benefits of Asymmetric Key Encryption

• Greater security as the single key is private.
• It is hard to be intercepted
• Allows message authentication and tampering is detected.