Digital Data Communications Message Protocol (DDCMP) is a byte-oriented communication protocol and a synchronous data link layer protocol, devised by digital equipment corporation. A byte oriented protocol views the frames as a collection of bytes/characters.
Some of the popular byte oriented protocols are –
- BISYNC (Binary synchronous communications protocol)
- PPP (Point to point protocol)
- DDCMP (Digital data communications message protocol)
Digital data communications message protocol (DDCMP) differs from BISYNC and PPP protocols, as it employs byte counting approach. Counting, here, refers to the number of bytes in the count field of the frame format.
DDCMP : Frame Format –
- In the frame format, there are two synchronous fields(SYN) of 8 bits each (similar to synchronous fields in BISYNC protocol).
- A class field of 8 bits(similar to class field in PPP protocol).
- A header field of 42 bits.
- A count field of 14 bits, to count the number of bytes in the frame body.
- The body field is of variable length.
- The CRC (cyclic redundancy check) field of 16 bits, performs error detection, on the data.
DDCMP Drawback : Transmission error –
A Transmission error can affect any bit pattern in the frame. If it corrupts the count field, then the end of frame would not be correctly detected by the receiver. The frame structure can get cluttered.
Consider, we have three frames.
- The count field is in every frame.
- Let us consider the frame, drawn green in the above figure be F3[Frame-3]. This is the frame created by the sender.
- Let us consider the frame, drawn red in the above figure be F2[Frame-2].
- Let us consider the frame, drawn blue in the above figure be F1[Frame-1].
- The sender, sends the information to the receiver, and the receiver reads the count field ‘5’ first and understands that, the next 5 bytes belong to one frame i.e., F1[Frame-1].
- Similarly. it reads the count field ‘4’ and ‘6’ respectively and understands that the next 4 and 6 bytes belong to two frames respectively.
- Unfortunately, when the transmission error occurs and say, affects F2[Frame-2]. The count field of F2 gets modified into ‘7’ from ‘4’. Hence, the receiver understands that the next 7 bytes after ‘7’ belongs to one frame i.e F2[Frame-2], but it is not the frame created by sender. When the receiver identifies this as F2[Frame-2], framing error occurs.
In above figure, Transmission error depicted in an example for DDCMP frame format.
Attention reader! Don’t stop learning now. Get hold of all the important CS Theory concepts for SDE interviews with the CS Theory Course at a student-friendly price and become industry ready.
- Networks and Process of Network Communications
- Network Protocols and Communications
- Internet Control Message Protocol (ICMP)
- Introduction of Message Queue Telemetry Transport Protocol (MQTT)
- Syslog Message Logging Protocol
- Cisco Discovery Protocol (CDP) and Link Layer Discovery Protocol (LLDP) in Data Link Layer
- Hot Standby Router Protocol (HSRP) and Virtual Router Redundancy Protocol (VRRP)
- Difference between Stop and Wait protocol and Sliding Window protocol
- Difference between File Transfer Protocol (FTP) and Secure File Transfer Protocol (SFTP)
- Difference between Serial Line Internet Protocol (SLIP) and Point-to-Point Protocol (PPP)
- Difference between Border Gateway Protocol (BGP) and Routing Information Protocol (RIP)
- Message Authentication Codes
- How message authentication code works?
- Message switching techniques
- Transforming a Plain Text message to Cipher Text
- Difference between Circuit switching and Message switching
- Message Digest in Information security
- What is HMAC(Hash based Message Authentication Code)?
- Difference between Message and Packet Switching
- Difference Between High-level Data Link Control (HDLC) and Point-to-Point Protocol (PPP)
If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to firstname.lastname@example.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.
Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.