February 15, 2020
Amitraj
High-level Data Link Control (HDLC) -
HDLC (High-level Data Link Control) is a WAN protocol intended to perform the encapsulation of the data in the data link layer. The encapsulation of the data means to change the format of the of the data. SDLC is the predecessor of the HDLC which stands for the Synchronous Data Link Control protocol. Both SDLC and HDLC protocol are developed by IBM and submitted to the ANSI and ISO for the acceptance as the international standards.
The HDLC protocol follows the bit-oriented concept and uses bit stuffing for achieving data transparency. Here bit oriented approach signifies that the single bit is used to present the control information. The frame structure of HDLC contains the address, control, data, checksum and flag fields. The default encapsulation protocol in the Cisco devices is the HDLC. The Cisco proprietary HDLC only works when the devices in both of the ends of the link are of cisco. Standard HDLC can have different devices in the ends.
Frame format for the bit-oriented protocols-
Point-to-Point Protocol (PPP) -
PPP (Point-to-Point Protocol) is also a WAN protocol, but there are several enhancements made in the PPP protocol after HDLC. Priorly, the PPP protocol is not proprietary, which means that it can be used with two different type of devices without committing changes over the format of the data.
There are several features of PPP, which are discussed below.
1. To clearly identify the start and end of the frame, the framing method is used on the asynchronous data. It is also beneficial in the detection of the errors.
2. A link control protocol is used for enabling the network lines, testing them, terminate them when no longer used. This link control protocol is basically helpful in handling the synchronous and asynchronous circuits, and byte and bit-oriented encodings.
3 .It can select the NCP (Network Control Protocol) for each supported network layer.
Frame format for the PPP -
The PPP frame contains two flag fields, a protocol filed to determine the type of packet residing in the payload, and a payload field which can variate. However, the rest of the fields are the same as the HDLC protocol.
Differences Between HDLC and PPP
1. The HDLC is a bit-oriented protocol while PPP is byte-oriented as well as bit oriented because it can be sent over the dial-up modem lines and also true bit-oriented HDLC.
2. Only synchronous media can be used in HDLC. In contrast, PPP can work with synchronous and asynchronous media.
3. No link authentication is provided in HDLC, whereas it is provided in PPP.
4. PPP can dynamically assign and frees up the IP address according to the use. As against, this not the case in HDLC.
5. Interoperability between the non-cisco devices in HDLC is not achievable. However, this limitation of HDLC is eliminated from the PPP protocol.
Conclusion
Between HDLC and PPP, the PPP protocol performs better than HDLC because there is no compulsion of using the Cisco devices in both the ends, which means these are interoperable. PPP also supports multiple protocols and support authentication.
HDLC (High-level Data Link Control) is a WAN protocol intended to perform the encapsulation of the data in the data link layer. The encapsulation of the data means to change the format of the of the data. SDLC is the predecessor of the HDLC which stands for the Synchronous Data Link Control protocol. Both SDLC and HDLC protocol are developed by IBM and submitted to the ANSI and ISO for the acceptance as the international standards.
The HDLC protocol follows the bit-oriented concept and uses bit stuffing for achieving data transparency. Here bit oriented approach signifies that the single bit is used to present the control information. The frame structure of HDLC contains the address, control, data, checksum and flag fields. The default encapsulation protocol in the Cisco devices is the HDLC. The Cisco proprietary HDLC only works when the devices in both of the ends of the link are of cisco. Standard HDLC can have different devices in the ends.
Frame format for the bit-oriented protocols-
Point-to-Point Protocol (PPP) -
PPP (Point-to-Point Protocol) is also a WAN protocol, but there are several enhancements made in the PPP protocol after HDLC. Priorly, the PPP protocol is not proprietary, which means that it can be used with two different type of devices without committing changes over the format of the data.
There are several features of PPP, which are discussed below.
1. To clearly identify the start and end of the frame, the framing method is used on the asynchronous data. It is also beneficial in the detection of the errors.
2. A link control protocol is used for enabling the network lines, testing them, terminate them when no longer used. This link control protocol is basically helpful in handling the synchronous and asynchronous circuits, and byte and bit-oriented encodings.
3 .It can select the NCP (Network Control Protocol) for each supported network layer.
Frame format for the PPP -
The PPP frame contains two flag fields, a protocol filed to determine the type of packet residing in the payload, and a payload field which can variate. However, the rest of the fields are the same as the HDLC protocol.
Differences Between HDLC and PPP
1. The HDLC is a bit-oriented protocol while PPP is byte-oriented as well as bit oriented because it can be sent over the dial-up modem lines and also true bit-oriented HDLC.
2. Only synchronous media can be used in HDLC. In contrast, PPP can work with synchronous and asynchronous media.
3. No link authentication is provided in HDLC, whereas it is provided in PPP.
4. PPP can dynamically assign and frees up the IP address according to the use. As against, this not the case in HDLC.
5. Interoperability between the non-cisco devices in HDLC is not achievable. However, this limitation of HDLC is eliminated from the PPP protocol.
Conclusion
Between HDLC and PPP, the PPP protocol performs better than HDLC because there is no compulsion of using the Cisco devices in both the ends, which means these are interoperable. PPP also supports multiple protocols and support authentication.
