The station that provides or transmits data is the primary station. HDLC protocol in computer networks has mainly three stations defined. The Synchronous Data Link Control Protocol (SDLC) protocol was first developed by IBM and later standardized by ISO (International Organization for Standardization) as High-Level Data Link Control protocol. Some frequently asked questions on HDLC are as follow -Īfter reading this HDLC Protocol Tutorial students can answer the all above questions. The control field is different for different types of frames in HDLC protocol.Bit oriented protocol means, here the data collected from the network layer are actually tackling in the form of sequence of bits in the frame. HDLC generally uses this field to determine how to control process of communication. A primary address can either be a source of communication or a destination that eliminates requirement of including address of primary. This address might include a particular address, a group address, or a broadcast address. Each byte can identify up to 128 stations. This field can be of 1 byte or several bytes long, it depends upon requirements of network. This field also generally consists of 8 bits therefore it is capable of addressing 256 addresses. It helps to identify secondary station will sent or receive data frame. The address field generally includes HDLC address of secondary station. This bit pattern is also not allowed to occur anywhere else inside a complete frame. This bit pattern also serves as a synchronization pattern for receiver. It is an 8-bit sequence with a bit pattern 01111110 that basically helps in identifying both starting and end of a frame. So, the flag field is basically using delimiter 0x7e to simply indicate beginning and end of frame. In HDLC protocol, there is no start and stop bits. The flag field is generally responsible for initiation and termination of error checking. Let us understand these fields in details : Variable (not used in some type of HDLC frames)
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