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Differentiate between HDLC and PPP encapsulation.

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HDLC (High-Level Data Link Control) and PPP (Point-to-Point Protocol) are two different data link layer protocols commonly used in networking to encapsulate and transmit data over communication links. Let's delve into the technical details of each to understand their differences:

  1. HDLC (High-Level Data Link Control):
    • Frame Format:
      • HDLC frames consist of a header and trailer. The basic frame format is:cssCopy codeFlag | Address | Control | Data | FCS | Flag
        • Flag: Delimiter indicating the start and end of the frame (01111110 in binary).
        • Address: Typically set to 11111111 for broadcast addresses in a LAN.
        • Control: Contains information about the frame type and sequence control.
        • Data: Payload of the frame.
        • FCS (Frame Check Sequence): Used for error detection using CRC (Cyclic Redundancy Check).
    • Address Field:
      • HDLC uses a destination address field but typically assigns the broadcast address for simplicity in point-to-point links.
    • Error Handling:
      • Uses FCS for error detection.
      • Frames with errors are usually discarded.
    • Usage:
      • Historically used in synchronous serial communication links.
  2. PPP (Point-to-Point Protocol):
    • Frame Format:
      • PPP frames are simpler than HDLC frames and consist of:cssCopy codeFlag | Address | Control | Protocol | Data | FCS | Flag
        • Flag: Same as in HDLC, indicating the start and end of the frame.
        • Address: Similar to HDLC but usually set to 11111111 for broadcast addresses in a LAN.
        • Control: Similar to HDLC but often set to a default value.
        • Protocol: Identifies the network layer protocol (e.g., IP, IPv6) being carried in the data field.
        • Data: Payload of the frame.
        • FCS (Frame Check Sequence): Similar to HDLC, used for error detection.
    • Address Field:
      • Although PPP includes an address field, it is often set to the default value (11111111) for simplicity in point-to-point links.
    • Error Handling:
      • Utilizes FCS for error detection, similar to HDLC.
    • Usage:
      • Commonly used for establishing and maintaining direct connections between network nodes, especially in dial-up connections and WAN links.

Differences:

  • Address Field:
    • HDLC uses a separate address field, while PPP has an address field but often uses a default value for simplicity in point-to-point links.
  • Frame Format:
    • PPP frames are more flexible due to the inclusion of the protocol field, allowing the encapsulation of different network layer protocols.
  • Usage:
    • HDLC was historically used in synchronous serial communication links, while PPP is more commonly used for point-to-point connections in WANs and dial-up scenarios.