1 / 12

HDLC

HDLC. High-Level Data Link Control ( HDLC ) is a bit-oriented code-transparent synchronous data link layer protocol developed by the International Organization for Standardization (ISO). Most important data link control protocol. From where it started???.

melodie-norman
Download Presentation

HDLC

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. HDLC • High-Level Data Link Control (HDLC) is a bit-oriented code-transparent synchronous data link layer protocol developed by the International Organization for Standardization (ISO). • Most important data link control protocol.

  2. From where it started??? • Synchronous Data Link Control (SDLC) by IBM • Advanced Data Communication Control Procedure (ADCCP) by ANSI

  3. Basic Characteristics • Primary station • Responsible for controlling the operation of the link. • Handles error recovery • Frames issued by the primary station are called commands. • Secondary station • Operates under the control of the primary station. • Frames issued by a secondary station are called responses. • The primary station maintains a separate logical link with each secondary station. • Combined station • Combine the features of both primary and secondary station.

  4. Two Link Configurations Unbalanced Mode Commands Primary Responses Secondary Secondary Balanced mode Combined Combined commands/Responses

  5. Three Data Transfer Modes • Normal Response Mode (NRM) • Used with an unbalanced configuration. • Primary may initiate data transfer to secondary. • But secondary may only transmit data in response to a command from a primary. • NRM is used on multidrop lines. • Asynchronous Balanced Mode(ABM) • Used with balanced configuration. • Either combined station may initiate transmission without receiving permission from the other combined station. • Widely used, efficient used to connect from one device from one another. • Asynchronous Response Mode(ARM) • Used with an unbalanced configuration. • The secondary may initiate transmission without permission of the primary.

  6. Frame Structure of HDLC

  7. FLAG FIELD: -Frame contains unique pattern at both ends. -No assurance of occurrence of same bit pattern somewhere inside the frame. -Bit Stuffing is used. Original Pattern: 111111111111011111101111110 After bit-stuffing: 1111101111101101111101011111010 • ADDRESS FIELD: -Identify the secondary station that transmitted or is to received the frame.

  8. CONTROL FIELD: The first one or two bits are used to identify the type of frame. Defines three types of frames:- -INFORMATION FRAME(I-FRAME) -Carry data to be transmitted for the user. -Flow and error control data, using the ARQ mechanism, are piggybacked on an I-Frame. -SUPERVISORY FRAME(S-FRAME) -Used for flow and error control whenever piggybacking is impossible -UNNNUMBERED FRAME(U-FRAME) -Used for link management, and can also be used to transfer user data. -They exchange session management and control information between connected devices.

  9. All of the control field contain poll/final (P/F) bit. • It is called Poll when set by the primary station to obtain a response from a secondary station. • Final when set by the secondary station to indicate a response or the end of transmission. In all other cases, the bit is clear.

  10. There are four different supervisory frames: • Receive Ready (RR) Bit Value = 00 Indicate that the sender is ready to receive more data. • Receive Not Ready (RNR) Bit value = 01 Acknowledge some packets and request no more be sent until further notice. • Reject (REJ) Bit value = 10 Requests immediate retransmission starting with N(R). • Selective Reject (SREJ) Bit value = 11 Requests retransmission of only the frame N(R). • FRAME CHECK SEQUENCE FIELD: -Error detecting code calculated from the remaining bits of the frame and exclusive of flags.

  11. THANK YOU.. MY BLOG ID: Anamikasirohi89.wordpress.com

More Related