Telecommunications and Networking Notes

Intro to Telecommunication and Networks

• Instructor: Jiang Lu
• Department: Computer Engineering, University of Houston Clear Lake

Review

• Flow and Error Control
  • Stop and Wait
  • Sliding Window
  • Three ARQs

Outlines

• Data Link Control Protocols (7.3)
  • High Level Data Link Control (HDLC)
• Multiplexing (8.1, 8.2)
  • Frequency-Division Multiplexing
  • Synchronous Time-Division Multiplexing
• Multiple Channel Access (8.6, 17.5)
  • FDMA
  • TDMA
  • CDMA

Data Link Control Protocols (7.3)

High Level Data Link Control (HDLC)

• Importance: Most widely used data link control protocol.
• Standards: ISO 3309, ISO 4335.
• Types of Stations:
  • Primary: Controls link operation.
  • Secondary: Controlled by the primary.
  • Combination: Features of both primary and secondary.
• Link Configurations:
  • Unbalanced: (One Primary, multiple Secondaries) - used in point and multipoint operations.
  • Balanced: (Combinations) - used only in point-to-point operations.

Data Transfer Modes

• Normal Response Mode (NRM): Unbalanced, uses polling and selection on multidrop lines.
• Asynchronous Balanced Mode (ABM): Balanced; either station can initiate transmission (point-to-point).
• Asynchronous Response Mode (ARM): Unbalanced; secondary may initiate transmission (rarely used).

Frame Structure

• Components:
  • Flags: Start and end.
  • Address: Identifies secondary stations.
  • Control: ACKs, sync, supplementary control.
  • Information: Transmitted data.
  • Frame Check Sequence: 16- or 32-bit CRC for error checking.

Multiplexing (8.1 - 8.2)

Definition

• Multiplexing: Technique to allow simultaneous processing of different analog and digital transmission streams over a shared link by dividing high capacity into low capacity logical mediums.
• Types of Multiplexing:
  • Frequency-Division Multiplexing
  • Synchronous Time-Division Multiplexing
  • Wavelength-Division Multiplexing

Frequency-Division Multiplexing (FDM)

• Definition: Splits a transmission facility into multiple channels by dividing the frequency bandwidth.
• Characteristics:
  • Used with analog signals.
  • Channels separated by guard bands.
• Problems:
  • Crosstalk and intermodulation noise.
  • Requires demodulation of all signals.
  • Narrow sub-bandwidth and inflexible.

Time-Division Multiplexing (TDM)

• Definition: Shares a channel by dividing the available time into time slots designated for each user.
• Characteristics:
  • Primarily used for digital signals but can also be used for analog signals.
  • Synchronous TDM: fixed time slots assigned.
  • Adaptive time slot assignment can help with channel capacity waste.
• Flow Control and Error Control:
  • No flow control; error control per channel.
• Example Scenario:
  • Multiplexing 11 sources with various frequencies and its impact on data rates and usage of time slots.

Wavelength Division Multiplexing

• Definition: Transmits multiple beams of light at different frequencies on a single optical fiber.
• Application: Each wavelength can implement time division multiplexing to accommodate additional data signals.

Multiple Channel Access

General Concept

• Frequency Division Duplex: Two stations with full duplex connection transmitting on different bands.
• Time Division Duplex: Data transmitted in one direction at a time, utilizing time-compression multiplexing.

Frequency Division Multiple Access (FDMA)

• Definition: Each user allocated a unique frequency channel during a call duration.
• Usage: Found in first generation systems.

Time Division Multiple Access (TDMA)

• Definition: Divides channel time into time slots; each user transmits in their assigned slot.
• Usage: Common in second generation systems.

Code Division Multiple Access (CDMA)

• Definition: Users share bandwidth using orthogonal code sequences.
• Example: Illustration of how spreading codes work; orthogonal codes defined such that their inner product equals zero (e.g., Walsh codes).