Regarding data link protocols, what is the main difference between DDCMP (Digital Data Communications Message Protocol) and SDLC (Synchronous Data Link Control) as implied by their framing and synchronization methods?

Introduction:
DDCMP (from DEC) and SDLC (from IBM) are classic data link protocols that solved framing and reliability differently. Understanding their synchronization/framing approach clarifies hardware requirements and historical deployment choices on synchronous lines.

Given Data / Assumptions:

• DDCMP is a byte-count, message-oriented protocol that embeds length information in its header.
• SDLC is a bit-oriented protocol that uses flag sequences and bit-stuffing for frame delimitation.
• We focus on the implication for recognizing the start of a frame and hardware needs.

Concept / Approach:
Because DDCMP includes an explicit length field in the header and relies on character-oriented framing, it can identify message boundaries without specialized bit-level hardware for continuous flag detection. In contrast, SDLC frames begin and end with the 01111110 flag and use bit-stuffing: hardware or tightly timed logic typically monitors the bit stream to locate flags and remove stuffed bits. Hence, the practical takeaway is that DDCMP’s design reduces the need for specialized flag-detection hardware to find message starts, whereas SDLC’s bit-oriented method traditionally benefits from such support.

Step-by-Step Solution:
1) Note DDCMP header includes a count/length field that defines frame size.2) DDCMP parsing can proceed after header recognition without flag-scanning the entire stream.3) SDLC requires continuous monitoring for flag patterns and bit-stuff handling to detect frame boundaries.4) Conclude the key practical difference: DDCMP avoids special flag-detect hardware for frame starts, aligning with option A.

Verification / Alternative check:
Protocol descriptions show DDCMP’s count-based framing and SDLC’s flag/bit-stuff scheme; equipment from the era often implemented SDLC with hardware assist for reliable, high-speed flag detection.

Why Other Options Are Wrong:

• DDCMP has a message header (B): true but not distinctive; SDLC also has header/control fields.
• SDLC has an IP address (C): IP addressing belongs to the network layer, not the data link layer framing.
• SDLC does not use CRC (D): incorrect; SDLC uses a Frame Check Sequence based on CRC.
• None of the above (E): invalid because option A captures the salient difference.

Common Pitfalls:
Conflating “character-oriented” vs. “bit-oriented” with the presence of headers; both have headers, but the framing method—and hardware implications—differs markedly.

Final Answer:
DDCMP does not need special hardware to find the beginning of a message