Benefits Of Out-Of-Bank Clocking - Cisco ASR 1000 Series Software Configuration Manual

Configuring the Circuit Emulation over Packet Shared Port Adapter
Out-of-band clocking provides a way to deliver a clock signal between two SPAs. This allows TDM devices
connected to the SPAs to communicate with each other. Dedicated pseudowires (called out-of-band clock
channels) carry the timing signal between the sending and the receiving SPAs. When a TDM device sends
data to a destination TDM device, the receiving SPA uses the out-of-band clock channel to recover the clock
signal that was used to send the data.
By keeping the timing packets separate from data packets, out-of-band clocking delivers an extremely accurate
timing signal. This timing accuracy is important for mobile wireless applications and other specialized
applications that have very low tolerances for such things as packet delay variation (PDV), jitter, and latency
in the network. In-band clocking (where timing information is derived from the data stream) does not provide
a clock that is accurate enough for these applications.
To set up out-of-band clock channels, you must configure a master clock interface and a slave clock interface
on the SPAs and configure pseudowires to connect the master and slave clocks. Instructions for performing
these steps are provided later in this section.
The SPA-2CHT3-CE-ATM does not support Out-of-Band (OOB) clocking in the CEM mode due to lack
Note
of hardware support.

Benefits of Out-Of-Bank Clocking

Out-of-band clocking provides the following benefits:
• Enables mobile wireless providers to migrate from TDM networks to PSNs in order to save on costs
and improve scalability.
• CEM SPA equipment can ignore the contents of the timing packets that are sent over the out-of-band
clock channel because the packets do not contain data.
• Uses the CEM SPA for applications that use something other than constant bit rate (CBR) data. For
example, out-of-band clocking uses the SPA for 3G (data) wireless applications, which use AAL2 in
variable bit rate (VBR) mode. In addition, out-of-band clocking uses the SPA for 2G (voice) applications.
• Provides recovered clock accuracy that complies with ITU-T G.823 and G.824 specifications, which
enables the CEM SPA to be used in mobile and wireless applications (including voice) that require
extreme synchronization accuracy.
• Provides an alternative clock-recovery mechanism when adaptive clocking cannot be deployed.
• Enables the CEM SPA to be the master clock in a PSN.
• Makes it possible to have two master clocks. Previously, only one master clock was possible.
Guidelines for Configuring Out-Of-Band Clocking
The following guidelines apply to out-of-band clocking on CEM SPA:
• The default packet size for out-of-band clock channels (CEM circuits) is 910 bytes.
• Out-of-band clocking can co-exist with Stateful SwitchOver (SSO), but it is not SSO compliant. Therefore,
if a switchover occurs, the out-of-band clocking functionality is not available for a brief period of time
while the feature is brought back online.
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Cisco ASR 1000 Series Aggregation Services Routers SIP and SPA Software Configuration Guide, Cisco IOS XE
Configuring Out-of-Band Clocking
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