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ME60 V800R010C10SPC500 Feature Description - System Management 01

This is ME60 V800R010C10SPC500 Feature Description - System Management
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Basic Concepts

Basic Concepts

Clock Domain

Logically, a physical network can be divided into multiple clock domains. Each clock domain has a reference time with which all devices in the domain are synchronized. Each clock domain has its own reference time and these times are independent of one another.

A device can transparently transmit time signals from multiple clock domains over a bearer network to provide specific reference times for multiple mobile operator networks. The device, however, can join only one clock domain and can synchronize only with the synchronization time of that clock domain.

Clock Node

Each node on a time synchronization network is a clock. The 1588v2 protocol defines the following types of clocks:

  • Ordinary clock

    An ordinary clock (OC) has only one 1588v2 clock interface (a clock interface enabled with 1588v2) through which the OC synchronizes with an upstream node or distributes time signals to downstream nodes.

  • Boundary clock

    A boundary clock (BC) has multiple 1588v2 clock interfaces, one of which is used to synchronize with an upstream node. The other interfaces are used to distribute time signals to downstream nodes.

    The following is an example of a special case: If a device obtains the standard time from a BITS through an external time interface (which is not enabled with 1588v2) and then distributes time signals through two 1588v2 enabled clock interfaces to downstream nodes, this device is a BC node, as it has more than one 1588v2 clock interface.

  • Transparent clock

    A transparent clock (TC) does not synchronize the time with other devices (unlike BCs and OCs) but has multiple 1588v2 clock interfaces through which it transmits 1588v2 messages and corrects message transmission delays.

    TCs are classified into end-to-end (E2E) TCs and peer-to-peer (P2P) TCs.

  • TC+OC

    A TC+OC is a special TC, which has the functions of both the TC and OC. On interfaces having TC attributes, the TC+OC can transparently transmit 1588v2 messages and correct message transmission delays. On interfaces having OC attributes, the TC+OC performs frequency synchronization, but does not implement time synchronization.

    As mentioned before, the TC corrects for transmission delays of its 1588v2 messages. If the times on the inbound and outbound interfaces of the TC are synchronous, the message transmission delay is determined by subtracting the time of the 1588v2 message's arrival at the inbound interface from the time of departure at the outbound interface. If the clocks of the TC and the BC or OC with which the TC synchronizes are asynchronous, the obtained message transmission delay is inaccurate, causing a time offset in the BC or OC time synchronization. As a result, the time synchronization's accuracy may be degraded.

    To ensure accuracy, it is recommended that frequency synchronization between the TC and the BC or OC be implemented through a physical clock, such as a WAN clock or synchronous Ethernet clock. If no such physical clock is available, the TC needs to use 1588v2 Sync messages sent periodically to restore frequency and to realize time synchronization with an upstream device.

    TC+OCs are classified into E2E TC+OCs and P2P TC+OCs.

Figure 14-2 shows the location of the TC, OC, and TC+OC on a time synchronization network.

Figure 14-2 Location of the TC, OC, and TC+OC on a time synchronization network

Time Source Selection

On a 1588v2 time synchronization network, all clocks are organized into a master-slave synchronization hierarchy with the Grandmaster (GM) clock at the top. This topology can be statically configured or automatically generated by 1588v2 using the Best Master Clock (BMC) algorithm.

1588v2 Announce messages are used to exchange time source information, including information about the priority level of the GM, time strata, time accuracy, distance, and hops to the GM between clocks. After this information has been gathered, one of the clock nodes is selected to be the GM, the interface to be used for transmitting clock signals issued by the GM is selected, and master and slave relationships between nodes are specified. A loop-free and full-meshed GM-rooted spanning tree is established after completion of the process.

If a master-slave relationship has been set up between two nodes, the master node periodically sends Announce messages to the slave node. If the slave node does not receive an Announce message from the master node within a specified period of time, it terminates the current master-slave relationship and finds another interface with which to establish a new master-slave relationship.

Clock Modes of a 1588v2-enabled Device

  • OC
  • BC
  • TC
  • E2ETC
  • P2PTC
  • TCandBC

Encapsulation Modes of a 1588v2 Packet

A 1588v2 packet can be encapsulated in either MAC or UDP mode:

  • In MAC encapsulation, VLAN IDs and 802.1p priorities are carried in 1588v2 packets. MAC encapsulation is classified into two types:
    • Unicast encapsulation
    • Multicast encapsulation
  • In UDP encapsulation, Differentiated Service CodePoint (DSCP) values are carried in 1588v2 packets. UDP encapsulation is classified into two types:
    • Unicast encapsulation
    • Multicast encapsulation

Supported Link Types

Theoretically, 1588v2 supports all types of links, but at present it has only been defined for encapsulation and implementation on Ethernet links and thus the ME60 supports only Ethernet links.


A time synchronization network is like a GM-rooted spanning tree. All other nodes synchronize with the GM.


When a pair of nodes performs time synchronization, the upstream node distributing the reference time signals is the master node and the downstream node receiving the reference time signals is the slave node.

Updated: 2019-01-04

Document ID: EDOC1100059466

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