Network Synchronization Support
Network Synchronization Overview
2
Cisco ASR 1000 Series Aggregation Services Routers Software Configuration Guide
Network Synchronization Overview
The following goals must be taken into account while designing the synchronization plan for a network:
•
Synchronize the greatest number of network elements to the smallest number of independent clock
sources. Ideally, all network elements are synchronized to a single clock source.
•
Use clock sources of the highest quality (in terms of stability and long-term accuracy).
•
To ensure resiliency of the synchronization, plan for possible failure of the clock sources, network
elements, and network trunks.
Synchronous Ethernet (SyncE) defined by the Telecommunication Standardization Sector (ITU-T)
standards, such as G.8261 and G.8262, leverages the PHY layer of the Ethernet to transmit clock
information to the remote sites.
SyncE provides a cost-effective alternative to the Synchronous Optical Networking (SONET) networks.
For SyncE to work, each network element along the synchronization path must support SyncE. To
implement SyncE, the bit clock of the Ethernet is aligned to a reliable clock that is traceable to the
Primary Reference Clock (PRC).
Cisco ASR 1000 Series Aggregation Services Routers have a dedicated external interface known as BITs
interface to recover clocking information from a Synchronization Supply Unit (SSU). The router uses
this clock for SyncE. The BITS interface supports E1(European SSUs) and T1 (American BITS)
framing.
Table 1
lists the framing modes for a BITS port on the Cisco ASR 1002-X Router.
Table 2
lists the framing modes for a BITS port on the other Cisco ASR 1000 Series Aggregation
Services Routers.
Table 1
Framing Modes for a BITS Port on the Cisco ASR 1002-X Router
BITS or SSU Port Support
Matrix
Framing Modes
Supported
SSM or QL
Support
Tx Port
Rx Port
T1
T1 ESF
Yes
Yes
Yes
T1
T1 SF
Yes
Yes
Yes
T1
T1 D4
Yes
Yes
Yes
E1
E1 CRC4
Yes
Yes
Yes
E1
E1 FAS
Yes
Yes
Yes
E1
E1 CAS
Yes
Yes
Yes
E1
E1 CAS CRC4
Yes
Yes
Yes
2048 kHz
2048 kHz
Yes
Yes
Yes
Table 2
Framing Modes for a BITS Port on the Other Cisco ASR 1000 Series Aggregation
Services Routers
BITS or SSU Port Support
Matrix
Framing Modes
Supported
SSM or QL
Support
Tx Port
Rx Port
T1
T1 ESF
No
No
Yes
T1
T1 SF
No
No
Yes
E1
E1 CRC4
No
No
Yes
