Page 4: Fundamental Concepts

Analog vs. Digital

In the realm of signal processing and communication, data can be represented in two fundamental ways: analog and digital. Each has its own distinct characteristics and advantages, depending on the context of its use.

Analog

Communications: Occur via a continuous signal. This varies in elements like frequency, amplitude, phase, and voltage.
- This continuous variation creates a wave shape.
Issues:
- Analog signals can get corrupted due to attenuation over long distances and interference.

Digital

Communications: Employ a discontinuous electrical signal. This is characterized by state changes or on-off pulses. This leads to more reliability over extreme distances and amid interference.
Binary Representation: Digital signals use voltage states.
- Voltage "on" signifies a binary '1'.
- Voltage "off" signifies a binary '0'.
- These on-off pulses result in a stream of binary data.

Synchronous vs Asynchronous

Synchronous Communication:

Relies on a timing or clocking mechanism.
Can be based on either an independent clock or a time stamp embedded in the data stream.
Typically supports very high rates of data transfer, e.g., networking.

Example: Online Gaming: Multiplayer online games, especially fast-paced ones, rely on synchronous communication to maintain game state across players.

Asynchronous Communication:

Uses a stop and start delimiter bit to manage data transmission.
Ideally suited for transmitting smaller amounts of data.

Example: sending an email. Even though underlying protocols might use synchronization for secure transport, the act of email exchange between sender and receiver is asynchronous. The sender decides when to send, and the receiver checks and responds based on their availability.

Baseband vs Broadband

while baseband focuses on transmitting a single signal over the entire bandwidth of its medium, broadband divides the available bandwidth into multiple channels, allowing for simultaneous transmissions.

Baseband

Definition: Baseband refers to the transmission of a digital or analog signal over a communication channel without changing its original frequencies. It uses the entire bandwidth of the medium to transmit a single signal.
Characteristics:
- Single Channel: As mentioned, it supports only one communication channel at a time.
- Signal Representation: A high level of direct current represents a binary signal of 1, and a low level represents a binary signal of 0.
- Range: Typically used for short-distance transmissions due to signal attenuation over longer distances.
Example:
- Ethernet Cables (e.g., Cat 5, Cat 6): When you connect devices in a local area network (LAN) using Ethernet cables, the data transmission is baseband. The entire bandwidth of the cable is used for a single digital signal.

Broadband

Definition: Broadband refers to the transmission method that allows multiple signals to share the same communication medium by allocating each signal to a different frequency channel.
Characteristics:
- Multiple Channels: Can support multiple signals or channels simultaneously.
- Frequency Modulation: Uses modulation techniques to allow multiple signals on the same medium. These signals are separated by assigning them to different frequency ranges.
- High Throughput: Suitable for transmitting a large amount of data, especially when signals are multiplexed.
- Analog Nature: While broadband can carry digital signals, the underlying transmission is often analog in nature.
Examples:
- Cable Television: Many channels are delivered over a single coaxial cable to homes, with each TV channel assigned to a specific frequency.
- DSL (Digital Subscriber Line): Uses existing telephone lines to deliver high-speed internet by separating the voice and data signals into different frequency bands.
- Cable Internet: Provides internet service over the same infrastructure as cable television. Different data streams (e.g., internet data, TV channels) are assigned distinct frequency ranges.

Broadcast, Multicast, and Unicast

Broadcast, Multicast, and Unicast
These terms determine how many destinations a single transmission can reach:
1. Broadcast
  Broadcast technology supports communication to all possible recipients.
  Example: DHCP requests. When a device joins a network and needs an IP address, it will send a DHCP broadcast request to all devices on the local network segment, asking for an available IP address.
2. Multicast
  Multicast technology supports communication to multiple specific recipients.
  Example needed
3. Unicast
  Unicast technology supports communication to just one specific recipient.
  Example: SSH (Secure Shell) sessions between a user's computer and a server. When you connect to a server using software like PuTTY or OpenSSH, you're establishing a unicast connection to that specific server.

Carrier Sense Multiple Access (CSMA)

Carrier sense multiple access (CSMA) is a technology incorporated into networking to handle data collisions at the datalink layer.

It aims to minimize collisions when multiple stations attempt to transmit signals simultaneously.
Stations must first assess the medium's condition before transmitting.

While CSMA doesn't prevent collisions outright, it plays a role in decreasing their likelihood.

CSMA/CA (Collision Avoidance)

CSMA/CA focuses on preventing collisions by allowing only one transmission at a time.

Often likened to a discussion where only the individual with the ball speaks.
Primarily used in wireless networks.
First communicates its intent to send before actual data transmission.
Adheres to the 802.11 standard.
Example: Token Ring

CSMA/CA is effective before a collision and nearly matches simple CSMA in efficiency.

CSMA/CD (Collision Detection)

CSMA/CD responds to collisions, making adjustments after they occur.

If a collision is detected, each node in the domain waits for a random period before retrying.
Primarily utilized in wired networks.
Focuses on swift recovery post-collision.
Automatically resends data if a collision is noted.
Adheres to the 802.3 standard.
Example: Ethernet

CSMA/CD is effective post-collision and boasts higher efficiency than regular CSMA.

Token Passing

Imagine a group of people sitting in a circle. They can only speak if they have a special item (let's say a "talking stick"). Once a person finishes speaking, they pass the "talking stick" to the next person in the circle. This ensures only one person speaks at a time, preventing everyone from talking (or transmitting data) all at once.

That's how Token Passing works in networks:

Token Passing is a communication method using a digital "talking stick" (token).
Devices in a network can only transmit data when they have this token.
Once data transmission is finished, the device passes the token to the next device.

Token Passing is great for preventing "overlapping conversations" (collisions) in ring networks.

Polling

Consider a teacher in a classroom. Before any student speaks or answers a question, they wait for the teacher to ask or "poll" them. This way, only the student being asked (polled) will respond.

This is similar to Polling in networks:

Polling uses a "master-slave" configuration. Think of the master as the teacher and the slaves as the students.
The "master" device asks (or polls) each "slave" device one by one if they have data to transmit.
Only when "polled" by the master, the slave device can send its data.

The concept behind Polling is ensuring orderly communication by having one device control who speaks next.

Master-Slave Configuration: In the context of networking and computing, a master-slave configuration means one device (master) controls one or more other devices (slaves). Just like the teacher (master) controls which student (slave) gets to speak in the class example.

SDLC (Synchronous Data Link Control) is a protocol that uses polling. Imagine it's a specific set of classroom rules the teacher uses to ensure students speak in a synchronized and orderly fashion.