HDLC is a bit-oriented protocol. It was generated by the International Organization for Standardization (ISO). It can decrease under the ISO standards ISO 3309 and ISO 4335. It is used to define a packetization standard for serial connections. It has discovered itself being used throughout the world.
It has been broadly executed because it provides both half-duplex and full-duplex connection lines, point-to-point (peer-to-peer) and multi-point networks, and switched or unswitched medium.
HDLC provides different modes of operation, such as a simple sliding window mode for dependable delivery. This is because the internet supports retransmission at larger levels (i.e., TCP). Some Internet applications use HDLC's unreliable delivery mode, unnumbered data.
There are various types of stations which are as follows −
Within a network using HDLC as its data link protocol, if a structure is used in which there is a primary station, it is used as the ruling station on the connection. It has the authority of controlling all several stations on the link (generally secondary stations).
A primary issues commands and secondary issues feedback. Despite this essential element of being on the connection, the primary station is also answerable for the organization of the data stream on the link. It can also take responsibility for error recovery at the data link level (layer 2 of the OSI model).
If the data link protocol being used is HDLC, and a primary station is present, a secondary station should also be present on the data link. The secondary station is under the control of the primary station. It has no capacity or direct authority for controlling the connection.
It is only stimulated when requested by the primary station. It is used to only acknowledge the primary station. The secondary station's frames are known as responses.
It is used to deliver response frames when requested by the primary station. A primary station provides an independent logical connection with each secondary station.
A combined station is a set of primary and secondary stations. On the link, all combined stations can send and receive commands and feedback without any permission from multiple stations on the link.
Each combined station is in complete control of itself and does not depend on some other stations on the link. There are no other stations that can control any combined station. It can issue both commands and responses.
HDLC also represents three types of configurations for the three types of stations. The word configuration defines the relationship between the hardware devices on a connection.