EXAMPLE DATA LINK PROTOCOLS - HDLC

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HDLC - HIGH-LEVEL DATA LINK CONTROL

• High-Level Data Link Control (HDLC) is a bit-oriented data link layer protocol
• It is a standard protocol defined by the International Organization for Standardization (ISO) and is widely used in various communication systems
• HDLC is designed to ensure reliable and efficient communication over point-to-point and multipoint links.
• It supports both half-duplex and full-duplex communication and can operate in various modes, including Normal Response Mode (NRM), Asynchronous Response Mode (ARM), and Asynchronous Balanced Mode (ABM).

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HDLC - HIGH-LEVEL DATA LINK CONTROL

• HDLC operates at the bit level, meaning it treats the data as a stream of bits rather than bytes or characters.
• First used in the IBM mainframe world: SDLC (Synchronous Data Link Control) protocol
• Later, it became ADCCP (Advanced Data Communication Control Procedure)
• ISO modified it to become HDLC (High-level Data Link Control).
• It is often used in WANs (Wide Area Networks).

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HDLC - HIGH-LEVEL DATA LINK CONTROL

• Frame Format:

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• Flag: Marks the beginning and end of a frame (typically 01111110).
• Address: Identifies the secondary station involved in the communication.
• Control: Contains control information, such as frame type (information, supervisory, or unnumbered) and sequence numbers.
• Data: The actual payload being transmitted.
• Checksum: Used for error detection (typically a CRC).

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HDLC - HIGH-LEVEL DATA LINK CONTROL

Frames Format:

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• Error Detection and Recovery: HDLC uses the Checksum field to detect errors. If an error is detected, the frame is retransmitted. It also supports sliding window protocols for flow control and error recovery.
• Transparency: HDLC ensures data transparency by using bit stuffing. If the flag sequence (01111110) appears in the data, an extra 0 is inserted after five consecutive 1s to distinguish it from the flag. The receiver removes the extra 0 during decoding.

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HDLC - HIGH-LEVEL DATA LINK CONTROL

Three types of Frames:

1. Information Frames (I-frames): Carry user data and control information (e.g., sequence numbers for flow control and error detection).
2. Supervisory Frames (S-frames): Used for flow control and error recovery (e.g., ACK, NAK).
3. Unnumbered Frames (U-frames): Used for link management (e.g., establishing and terminating connections).

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HDLC - HIGH-LEVEL DATA LINK CONTROL

Applications of HDLC:

1. Information Point-to-Point Protocol (PPP), which is derived from HDLC.
2. X.25 packet-switched networks.
3. Frame Relay networks.
4. ISDN (Integrated Services Digital Network).

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HDLC - HIGH-LEVEL DATA LINK CONTROL

Advantages of HDLC:

1. Information Efficiency: HDLC is efficient due to its bit-oriented nature and support for sliding window protocols.

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• Flexibility: It supports multiple modes of operation and can be used in various network configurations.

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• Reliability: Error detection and recovery mechanisms ensure reliable data transmission.

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THE DATA LINK LAYER ON THE INTERNET

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THE DATA LINK LAYER ON THE INTERNET

PPP (Point-to-Point Protocol):

• The Internet needs a point-to-point protocol for a variety of purposes, including router-to-router traffic and home user-to-ISP traffic.
• PPP handles error detection, supports multiple protocols, permits authentication, and has many other features.

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PPP (POINT-TO-POINT PROTOCOL):�

PPP (Point-to-Point Protocol) - Features:

1. Multi-Protocol Support:

PPP can carry packets from multiple network layer protocols (e.g., IP, IPX, AppleTalk) over the same link.

• Error Detection:

PPP includes a frame check sequence (FCS) field for error detection.

• Link Control:

PPP has a Link Control Protocol (LCP) for establishing, configuring, testing, and terminating the link.

• Authentication:

PPP supports authentication protocols like Password Authentication Protocol (PAP) and Challenge Handshake Authentication Protocol (CHAP).

• Compression:

PPP can compress data to improve efficiency over low-bandwidth links.

• Dynamic IP Address Assignment:

PPP can assign IP addresses dynamically using the IP Control Protocol (IPCP).

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PPP (POINT-TO-POINT PROTOCOL):�

PPP (Point-to-Point Protocol) – Frame Format:

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PPP (POINT-TO-POINT PROTOCOL):FRAME FORMAT�

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PPP-PHASES OF OPERATION�

PPP (Point-to-Point Protocol) – Phases of operation:

1. Link Dead:

The link is not in use (e.g., the modem is disconnected).

• Link Establishment:

The Link Control Protocol (LCP) is used to negotiate link parameters (e.g., maximum frame size, authentication protocol).

If negotiation is successful, the link transitions to the Authenticated or Network Layer Protocol phase.

• Authentication (Optional):

If authentication is required, PPP uses protocols like PAP or CHAP to verify the identity of the peer.

• Network Layer Protocol:

PPP uses Network Control Protocols (NCPs) to configure network layer protocols (e.g., IPCP for IP).

Once configured, data packets can be transmitted.

• Link Termination:

The link is terminated using LCP, and the connection returns to the Link Dead phase.

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PPP - ADVANTAGES

PPP (Point-to-Point Protocol) – Advantages:

1. Flexibility:

Supports multiple network layer protocols and can be used over various physical links.

• Error Detection:

Includes a frame check sequence (FCS) for reliable data transmission.

• Authentication:

Provides secure authentication mechanisms (e.g., CHAP).

• Compression:

Improves efficiency over low-bandwidth links.

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PPP - PROTOCOLS

PPP (Point-to-Point Protocol) – Protocols:

1. Link Control Protocol (LCP):

Used to establish, configure, and test the data link connection.

• Network Control Protocols (NCPs):
• Used to configure and manage network layer protocols.
• Examples:
• IPCP (IP Control Protocol): Configures IP addresses and other IP-related parameters.
• IPXCP (IPX Control Protocol): Configures IPX parameters.
• Authentication Protocols:
• PAP (Password Authentication Protocol):
• Sends the username and password in plaintext.
• Less secure than CHAP.
• CHAP (Challenge Handshake Authentication Protocol):
• Uses a three-way handshake and cryptographic hashing for secure authentication.

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THANK YOU

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