Definition: Bandwidth is the maximum amount of data that can be transmitted over a communication channel per unit time. It represents the capacity of the channel.
Measured in: bits per second (bps), kilobits (Kbps), megabits (Mbps), or gigabits (Gbps)
Example: A 100 Mbps Ethernet connection can transfer 100 million bits per second.
Key Points:
- Higher bandwidth → faster data transfer.
- Limited by medium type (fiber optic > copper > wireless).
Definition: Bit rate is the actual number of bits transmitted per second over a network.
Measured in: bits per second (bps)
Formula:
Bit Rate = Number of bits transmitted / Time taken
Relation to Bandwidth:
- Bandwidth = Theoretical limit
- Bit Rate = Actual data transfer achieved (depends on noise, congestion, interference)
Example: If 10 MB of data is sent in 8 seconds → Bit rate = (10 × 8 × 10⁶ bits) / 8 = 10 Mbps
Definition: Throughput is the actual rate of successful data delivery over a network channel.
Measured in: bits per second (bps)
Key Difference from Bit Rate:
- Bit rate includes all transmitted bits, including overhead and retransmissions.
- Throughput considers only successfully delivered bits.
Factors Affecting Throughput:
- Network congestion
- Protocol overhead
- Retransmissions due to errors
- Network device performance
Example: A 100 Mbps network may only achieve 80 Mbps throughput due to traffic and overhead.
Definition: Propagation delay is the time taken by a signal to travel from sender to receiver through the transmission medium.
Formula:
Propagation Delay = Distance / Propagation Speed
Units: seconds (s)
Example: If the distance = 3000 km and propagation speed = 2 × 10⁸ m/s → Delay = 0.015 seconds (15 ms)
Note: Propagation speed ≈ speed of light in the medium (e.g., fiber ≈ 2/3 * c)
Definition: Noise refers to unwanted electrical signals that interfere with data transmission and distort the original signal.
Types of Noise:
- Thermal Noise: Random motion of electrons due to heat.
- Crosstalk: Interference between adjacent channels.
- Impulse Noise: Sudden spikes due to power surges or lightning.
- Intermodulation Noise: Mixing of multiple frequencies.
Effect:
- Causes data errors, retransmissions, and reduced bit rate.
Definition: Distortion occurs when the shape or form of a signal changes during transmission.
Causes:
- Different frequency components travel at different speeds.
- Medium imperfections or mismatched impedance.
Example: In analog systems, high frequencies may lag or lead lower ones, altering waveform shape.
Effect:
- Leads to corrupted or unreadable data at the receiver.
Definition: Attenuation is the gradual loss of signal strength as it travels through a medium.
Measured in: decibels (dB)
Formula:
Attenuation (dB) = 10 × log10(Ptransmitted / Preceived)
Example: A signal transmitted at 100 mW and received at 10 mW → Attenuation = 10 log(100/10) = 10 dB.
Solution: Use amplifiers (analog) or repeaters (digital) to regenerate signal strength.
Definition: A Frame is a data link layer (Layer 2) unit of data that includes:
- Source & destination MAC addresses
- Error detection bits (CRC)
- Actual payload data
Function: Used for node-to-node delivery within a local network (e.g., Ethernet).
Example: Ethernet frame = 1500 bytes payload + header + trailer.
Analogy: A frame is like an envelope that contains your data along with sender and receiver info.
Definition: A Packet is a network layer (Layer 3) data unit containing:
- Source and destination IP addresses
- Payload (user data)
- Control info (TTL, checksum)
Function: Used for end-to-end communication across networks.
Frame vs Packet:
| Feature | Frame | Packet |
|---|---|---|
| OSI Layer | Data Link (L2) | Network (L3) |
| Addressing | MAC addresses | IP addresses |
| Delivery | Hop-by-hop | End-to-end |
| Example | Ethernet frame | IP packet |
Definition: A Host is any device assigned an IP address that can send or receive data over a network.
Examples: Computers, servers, mobile phones, IoT devices.
Identifiers:
- IP Address (logical)
- MAC Address (physical)
Definition: The Local Host refers to the current computer you are using.
IP Address: 127.0.0.1
Domain Name: localhost
Use Case: Used to test applications locally without internet access.
Example:
Running a local server and accessing it via http://localhost:8080
Definition: A Peer is a device that participates in a peer-to-peer (P2P) network, where all nodes share equal authority.
Example:
- File sharing via BitTorrent
- Two devices directly exchanging data
Peer-to-Peer vs Client-Server:
| Feature | Peer-to-Peer | Client-Server |
|---|---|---|
| Control | Decentralized | Centralized |
| Communication | Direct | Through server |
| Example | Torrent | Email server |
Definition: A Client is a device or software that requests services or resources from another device (server).
Examples:
- Browser → Web server
- Email app → Mail server
Function: Initiates requests and processes responses for the user.
Definition: A Server is a powerful system that provides data, services, or resources to clients over a network.
Examples:
- Web Server: Hosts websites (Apache, Nginx)
- Database Server: Manages databases (MySQL, PostgreSQL)
- Mail Server: Sends/receives emails
Characteristics:
- Always running
- Handles multiple requests concurrently
- Centralized data management
| Term | OSI Layer / Concept | Description | Example |
|---|---|---|---|
| Bandwidth | Physical | Theoretical capacity of data transfer | 100 Mbps Ethernet |
| Bit Rate | Physical | Actual data rate achieved | 10 Mbps |
| Throughput | Physical | Actual successful data delivery rate | 80 Mbps effective |
| Propagation Delay | Physical | Time for signal to travel through medium | 15 ms across fiber |
| Noise | Physical | Unwanted interference | Crosstalk |
| Distortion | Physical | Alteration of signal shape | Frequency delay |
| Attenuation | Physical | Loss of signal strength | Long cable loss |
| Frame | Data Link (L2) | Data unit with MAC addresses | Ethernet frame |
| Packet | Network (L3) | Data unit with IP addresses | IP packet |
| Host | Network Concept | Any networked device | Computer |
| Local Host | Network Concept | Your own device (127.0.0.1) | Local testing |
| Peer | Network Concept | Equal participant node | Torrent node |
| Client | Application Concept | Requests service | Browser |
| Server | Application Concept | Provides service | Web server |