Difference between HDLC and SDLC

SDLC is a character-oriented protocol and HDLC is bit-oriented; this is where the two protocols diverge the most. The fault detection capability, dependability, and speed of HDLC and SDLC are different.

The data is divided into bits in HDLC before being sent over the network, whereas characters are divided into bits in SDLC. Another difference between the two standards is the use of an escape character by HDLC, as opposed to SDLC, to indicate when the bit stuffing method should be used.

HDLC is thought to be a suitable superset of SDLC. HDLC and SDLC share the same frame format. Fields in HDLC are functionally equivalent to those in SDLC. Like SDLC, HDLC is capable of synchronous, full-duplex operation.

There are two distinct minor variations between HDLC and SDLC: HDLC offers a 32-bit checksum option, and HDLC doesn't really enable the Loop nor Hub go-ahead settings. However, the primary distinction between HDLC and SDLC is that HDLC allows three transfer modes, while SDLC supports only one.

Read this article to find out more about HDLC and SDLC and how they are different from each other.

What is HDLC?

A data link layer protocol known as HDLC is employed for both synchronous and asynchronous circuits. High-level Data Link Control is its full name, and it was created by the International Organization for Standardization (ISO). On a variety of physical media, including twisted pair, optical fibre, and radio frequency (RF) carriers, HDLC can be utilised as a bit-oriented, point-to-point protocol. After IBM presented SDLC to multiple standards groups, one of which (ISO) changed SDLC and produced the HDLC protocol, HDLC came into being.

Asynchronous Transfer Mode (ATM) networks are the setting where HDLC is most frequently used because they benefit from its dependable connections and low overhead. Due to its ability to reach higher data rates with lower overhead, HDLC is more effective than SDLC. For reliable communication to be possible, HDLC also allows error detection and correction.

What is SDLC?

An outline of the procedures necessary to create a system is provided by the systems development life cycle (SDLC). Another name for it is the software development life cycle(SDLC). IBM created the System Development Lifecycle (SDLC) in 1975 for use in SNA environments.

The software is maintained from the time of release until it is discontinued. There are typically five to seven steps, though there is a chance for more. The documentation phase is usually carried out in tandem with the development process for any given application, regardless of the SDLC model used.

In order to decide what needs to be developed, you must collect requirements from stakeholders and analyses them during the analysis phase. In the design stage, you will also need to develop comprehensive designs for the system's construction. SDLC is simpler to construct than HDLC since it is less complicated. Additionally, it operates better in networks that have a lot of noise or interference.

Difference between HDLC and SDLC

The following table highlights the major differences between High-Level Data Link Control and System Development Lifecycle −




Stands for

High-Level Data Link Control

System Development Lifecycle


A data link layer protocol known as HDLC is employed for both synchronous and asynchronous circuits.

An outline of the procedures necessary to create a system is provided by the systems development life cycle (SDLC).


It is a standard protocol

It is not a standard protocol


It is developed by the ISO

It is developed by IBM


The HDLC follows the ISO/IEC 13229 standard

The SDLC follows the ISO/IEC 12207 standard

Size of packet

It supports the multiple bits of octets

It is compatible with the 8, 16, and 32 bit systems


It uses the frames to encapsulate the data

It uses the SDLC packets


It supports asynchronous and synchronous transmission

It only supports synchronous transmission


In conclusion, HDLC and SDLC are both significant communications protocols with unique benefits and drawbacks. HDLC involves additional overhead because it is a little more sophisticated than SDLC. While SDLC is better suited for big data transfers since it can support numerous stations, HDLC is a reliable protocol that offers greater performance in terms of speed.

Depending on the demands of the application, either protocol can be utilised, together or individually. However, knowing the difference between HDLC and SDLC will help you choose the right protocol for your particular requirements.