With the increased exchange of multiple information and data units across distinct network modules, the need for HDLC protocols arises in the network channel. These protocols are used by the data link layer to apply an efficient and secure channel between multiple network devices. Hi guys and welcome to yet another interesting video by SimpliLan. But before we begin, if you love watching tech videos, subscribe to our channel and hit the bell icon to never miss an update from us.
Now without further ado, let's take a look at the agenda for today's session. To begin with, we will look into what is HDLC. Moving on with different HDLC stations available. different HDLC transfer models and then looking into HDLC frame model and types. Now let's move on to the first heading that is what is HDLC.
Let's take a look. The HDLC stands for high level data link control. It refers to the bit oriented network protocol design to connect multiple network system according to the communication requirement. The HDLC model applies the ARQ protocol for application and establishes a full duplex communication channel between the network devices.
Moving on we have the different types of HDLC stations available. HDLC stations can efficiently be differentiated into three different types where the first type is primary station. In this station it handles the establishing and destablishing of the primary data channel to share different frames in the network channel known as commands. It also performs the data management for the network.
Moving on we have the secondary station. This station work under the command of the primary station and the frames issued by the stations are known as responses. As for the last station we have combined station.
As the name suggests, this type of station is available for both commands and response value. Next, we will look into HDLC transfer models. The HDLC protocol supports two types of transfer models which are applied according to the need of communication channel, where the first type is known as Normal Response Model or in short NRM.
This transfer model combines the primary station and the secondary station in a point to point or multipoint configuration to exchange commands from primary station and responses from the secondary station and response to the multi connection. Moving on we have the second type of transfer model which is asynchronous balanced model. In this transfer model, the combined stations are installed in a point-to-point configuration for exchange of command or responses from either of the node.
Moving on, let's take a look at the HDLC frame model and types. The data unit for sharing information in the HDLC protocol is known as frames. The HDLC frame consists of multiple frame fields which may vary according to the frame type.
In general, the HDLC frame consists of five different frame fields where the first field is flag field. In HDLC, each frame starts with the flag field in the configuration and is defined by an 8-bit octet sequence which is 0 1 1 1 1 1 0. In the flag field. Moving on we have the address field. It encapsulates the receiver's address in the field. For example, if the frame is sent from the primary station, it contains the secondary station's address and vice versa.
Next we have the control field. This field contains the flow and error control information in byte format. Next we have payload or the information field.
It carries the actual information from the upper layer of the OSI module. And the last field is known as FCS field. This field stands for frame sequence check and acts as an error detection field in the HDLC protocol, which includes a 6-bit CRC check given is a frame format for an HDLC protocol with flag in the both ending and the starting point, followed by address field, control field, information field, and FCS field. Now let's take up a quiz to understand all the things we have learned so far. The question is the HDLC protocol functions under which network layer in the OSI model and the options are application layer, data link layer, physical layer and the network layer.
You can give your answers in the comment section. Now let's move on to different types of frame models available in HDLC. The frame models in HDLC can be classified of following three types depending upon the control field value of the frame. Where the first frame is known as I-frame. The I-frame stands for information frame and is applied to encapsulate the user information from the upper layer in the model and then transmitted to the network channel.
Note, the first bit of the control field in this frame is always 0 which also acts as an identification point for iframe. Moving on we have the S frame. The S frame stands for supervisory frame and is used for error and data flow control and does not contain any information regarding the information field in the format.
Note for the S frame is. The first two bits of the control field is 1 and 0 which acts as an identification point for S-frame. As for the last type of frame model we have U-frame. The U-frame stands for unnumbered frame used for system management and exchanging information between connected network devices. With this we have covered all the relevant information regarding the HDLC protocol.
If you have any questions regarding the topic, you can ask them in the comment section. Thank you for watching.