SyncE: Major Changes for Clock Distribution

CD.

SyncE (Synchronous Ethernet) is a network synchronization technology that is used to distribute frequency and time information across Ethernet networks. It offers several significant changes over traditional Ethernet that make it suitable for clock distribution.

The two major changes SyncE offers over traditional Ethernet to make it suitable for clock distribution are:

1. Introduction of Boundary Clocks and Transparent Clocks:

Boundary clocks and transparent clocks are two essential concepts introduced by SyncE that improve network scalability and accuracy of clock synchronization. Boundary clocks act as a synchronization endpoint for a group of slave clocks, and they buffer and timestamp the synchronization messages. They also provide isolation between synchronization domains, which helps prevent synchronization loops. Transparent clocks, on the other hand, timestamp synchronization messages as they pass through the device, and they adjust the timestamp value to compensate for any delay introduced by the device. This allows for more accurate synchronization across the network, even in the presence of network delays and asymmetries.

2. High-Priority Synchronization Packets:

SyncE uses high-priority synchronization packets to continually adjust its own oscillator. These packets are sent at a fixed rate, and the receiving device measures the difference between the expected arrival time and the actual arrival time to adjust its oscillator. This helps maintain accurate synchronization across the network, even in the presence of network delays and asymmetries.

The other options given in the question are incorrect:

B. Industry standards that guarantee interoperability:

Industry standards for SyncE do exist, but they do not guarantee interoperability. Specific field values and behaviors are specified, but there are still variations in implementation that can cause interoperability issues.

C. A mandated clock accuracy of 4.6 ppm:

There is no mandated clock accuracy for SyncE. However, SyncE aims to achieve a clock accuracy of better than 4.6 ppm (parts per million) in the presence of network delays and asymmetries.

D. ESMC Protocol for clock selection, distribution, management, traceability, and failover:

ESMC (Ethernet Synchronization Message Channel) is a protocol used by SyncE to distribute synchronization messages and manage clock selection and failover. It is not a major change offered by SyncE over traditional Ethernet.

Therefore, the correct answers to the question are A and E.