Specifications

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Cisco MWR 2941 Mobile Wireless Edge Router Release 3.5 Software Configuration Guide, Cisco IOS Release 15.1(3)MR
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Chapter 17 Configuring Synchronous Ethernet ESMC and SSM
Restrictions for Synchronous Ethernet (SyncE): ESMC and SSM
Restrictions for Synchronous Ethernet (SyncE): ESMC and SSM
• To use the network-clock synchronization ssm option command, the following conditions are
required:
– No input source is in the configuration.
– No network clock quality level is in the configuration.
– No network clock source quality source is set under any synchronous Ethernet interface.
• The network-clock synchronization ssm option command must be compatible with the
network-clock eec command in the configuration.
• The esmc process and synchronous mode commands can be used only if the SyncE capable
interface is installed on the router.
Information About Synchronous Ethernet (SyncE): ESMC and
SSM
• Synchronous Ethernet (SyncE): ESMC and SSM, page 17-2
Synchronous Ethernet (SyncE): ESMC and SSM
Customers using a packet network find it difficult to provide timing to multiple remote network elements
(NEs) through an external time division multiplexed (TDM) circuit. The SyncE feature helps to
overcome this problem by providing effective timing to the remote NEs through a packet network.
SyncE leverages the physical layer of Ethernet to transmit frequency to the remote sites. SyncE’s
functionality and accuracy resemble the SONET/SDH network because of its physical layer
characteristic. SyncE uses ESMC to allow the best clock source traceability, to correctly define the
timing source, and to help prevent a timing loop.
SONET/SDH use 4 bits from the two S bytes in the SONET/SDH overhead frame for message
transmission. Ethernet relies on ESMC that is based on an IEEE 802.3 organization-specific slow
protocol for message transmission. Each NE along the synchronization path supports SyncE, and SyncE
effectively delivers frequency in the path. SyncE do not support relative time (for example, phase
alignment) or absolute time (Time of Day).
SyncE provides the Ethernet physical layer network (ETY) level frequency distribution of known
common precision frequency references. Clocks for use in SyncE are compatible with the clocks used
in the SONET/SDH synchronization network. To achieve network synchronization, synchronization
information is transmitted through the network via synchronous network connections with performance
of egress clock. In SONET/SDH the communication channel for conveying clock information is
Synchronization Status Message (SSM), and in SyncE it the Ethernet Synchronization Message Channel
(ESMC).
ESMC carries a Quality Level (QL) identifier that identifies the timing quality of the synchronization
trail. QL values in QL-TLV are the same as QL values defined for SONET and SDH SSM. Information
provided by SSM QLs during the network transmission helps a node derive timing from the most reliable
source and prevents timing loops. ESMC is used with the synchronization selection algorithms. Because
Ethernet networks are not required to be synchronous on all links or in all locations, the ESMC channel
provides this service. ESMC is composed of the standard Ethernet header for an organization-specific