Data Communication
Fundamentals
The core components, flow, and physical structures of networks.
Components of Data Communication
Data communication is the exchange of data between two devices via some form of transmission medium. A system has 5 fundamental components:
Effectiveness of Data Communication
The effectiveness of a data communication system depends on four fundamental characteristics:
1. Delivery
System must deliver data to the correct destination. Data must be received by the intended device or user and only by that device or user.
2. Accuracy
System must deliver data accurately. Data that have been altered in transmission and left uncorrected are unusable.
3. Timeliness
System must deliver data in a timely manner. Data delivered late are useless. In video/audio, accurate delivery means delivering data as they are produced, without significant delay.
4. Jitter
Refers to the variation in packet arrival time. It is the uneven delay in the delivery of audio or video packets.
Transmission Modes
Transmission mode defines the direction of signal flow between two linked devices.
1. Simplex
Unidirectional. Only one device transmits, the other only receives.
Example: Keyboard to CPU, TV Broadcasting2. Half-Duplex
Bidirectional, but not simultaneously. Like a one-lane bridge with two-way traffic.
Example: Walkie-Talkie3. Full-Duplex
Bidirectional and simultaneous. Like a two-way street.
Example: Telephone Network, Mobile PhonesNetwork Criteria
Performance
Measured by Transit Time (time to travel) and Response Time (elapsed time between inquiry and response). Depends on # of users, medium type, and hardware.
Reliability
Measured by frequency of failure, recovery time after failure, and robustness during catastrophe.
Security
Protecting data from unauthorized access, damage, and development. Includes recovery policies.
Physical Structure & Topologies
Types of Connections
Point-to-Point
Dedicated link between two devices. The entire capacity is reserved for these two.
Multipoint (Multidrop)
More than two devices share a single link. Capacity is spatially shared.
Network Topologies
Mesh Topology
Every device has a dedicated point-to-point link to every other device.
- Pros: No traffic issues (dedicated links), Robust (one link fail doesn't stop others), Secure/Private, Easy fault identification.
- Cons: Difficult installation, Expensive (lots of cabling/ports), Bulk wiring.
- Formula:
n(n-1)/2cables for n devices.
Star Topology
Each device has a dedicated link only to a central controller (Hub/Switch).
- Pros: Easy to install/reconfigure, Robust (one link fail = only that device dead), Easy fault detection.
- Cons: If HUB fails, whole system fails. Requires more cable than Bus/Ring.
Bus Topology
One long cable (Backbone) connects all devices via drop lines and taps.
- Pros: Easy installation, Less cabling required (compared to Mesh/Star).
- Cons: Difficult reconnection/fault isolation. Signal reflection at taps causes degradation. Backbone break = System collapse.
Ring Topology
Each device has a dedicated point-to-point connection with only the two devices on either side of it. Signal is passed in one direction (Token Passing).
- Pros: Easy to install, minimal conflicts.
- Cons: Unidirectional traffic means slower data access. One break in the ring can disable the entire network.
Hybrid Topology
A combination of two or more different topologies (e.g., Star-Bus, Ring-Star). Used in large organizations to scale networks efficiently.
- Pros: Flexible, Scalable, Effective.
- Cons: Complex design, Expensive infrastructure.