The documentation set for this product strives to use bias-free language. For the purposes of this documentation set, bias-free is defined as language that does not imply discrimination based on age, disability, gender, racial identity, ethnic identity, sexual orientation, socioeconomic status, and intersectionality. Exceptions may be present in the documentation due to language that is hardcoded in the user interfaces of the product software, language used based on RFP documentation, or language that is used by a referenced third-party product. Learn more about how Cisco is using Inclusive Language.
This document provides information on the support for G.8275.2 telecom profile and how to configure Cisco cBR series routers
to avail the support.
Finding Feature Information
Your software release may not support all the features that are documented in this module. For the latest feature information
and caveats, see the release notes for your platform and software release. The Feature Information Table at the end of this
document provides information about the documented features and lists the releases in which each feature is supported.
G.8275.2 Telecom Profile
Information About G.8275.2 Telecom Profile
Precision Time Protocol (PTP) is a protocol for distributing precise time and frequency over packet networks. PTP is defined
in the IEEE Standard 1588. It defines an exchange of timed messages.
PTP allows for separate profiles to be defined in order to adapt PTP for use in different scenarios. A profile is a specific
selection of PTP configuration options that are selected to meet the requirements of a particular application.
Effective Cisco IOS XE Fuji 16.8.1, Cisco cBR Converged Broadband routers support the ITU- T G.8275.2 telecom profile (PTP
telecom profile for Phase/Time-of-day synchronization with partial timing support from the network).
The G.8275.2 is a PTP profile for use in telecom networks where phase or time-of-day synchronization is required. It differs
from G.8275.1 in that it is not required that each device in the network participates in the PTP protocol. Also, G.8275.2
uses PTP over IPv4 and IPv6 in unicast mode.
Why G.8275.2 Telecom Profile?
The G.8275.2 profile is based on the partial timing support from the network. Hence nodes using G.8275.2 are not required
to be directly connected.
The G.8275.2 profile is used in mobile cellular systems that require accurate synchronization of time and phase. For example,
the fourth generation (4G) of mobile telecommunications technology.
PTP Clocks
Two types of ordinary clocks are used in this profile:
Ordinary Clocks (OCs)
Telecom Grandmaster (T-GM)—A telecom grandmaster provides timing for other devices in the network, and is usually connected
to a primary reference time source, such as a GNSS receiver. It does not synchronize its local clock to other network elements.
Considerations for a T-GM:
Only one PTP port can be configured as a primary port.
One T-GM primary port can have multiple subordinates associated with it.
The T-GM OC primary port is a fixed port; that is, it always acts as a primary clock and its role does not change by negotiating
with its peer.
Partial-Support Telecom Time Subordinate Clocks (T-TSC-P and T-TSC-A)—A subordinate clock synchronizes its local clock to
another PTP clock (GM, T-GM or T-BC), and does not provide synchronization through PTP to any other device. Considerations
for a T-TSC-P:
An ordinary clock with single subordinate port can be configured.
Only one peer clock address can be configured as clock source.
Note
Ordinary clocks (OC) always have only one PTP port.
In G.8275.2 (02/2016), PTP transparent clocks are not permitted.
PTP Domain
A PTP domain is a logical grouping of clocks that communicate with each other using the PTP protocol.
A single computer network can have multiple PTP domains operating separately, for example, one set of clocks synchronized
to one time scale and another set of clocks synchronized to another time scale. PTP can run over either Ethernet or IP, so
a domain can correspond to a local area network or it can extend across a wide area network.
The allowed domain numbers of PTP domains within a G.8275.2 network are in the range of 44 and 63 (both inclusive). The default
domain number is 44.
PTP Messages and Transport
The following PTP transport parameters are defined:
In Cisco IOS XE Fuji 16.8.1, PTP over IPv4 in unicast mode must be used.
One-step clock mode must be used.
The G.8275.2 profile supports unicast message negotiation.
PTP Ports
A port can be configured to perform either fixed primary or subordinate role or can be configured to change its role dynamically.
If no role is assigned to a port, it can dynamically assume a primary, passive, or subordinate role based on the BMCA.
In G.8275.2, PTP ports are not tied to any specific physical interfaces, but are tied to a loopback (virtual) interface. Traffic
from a PTP port is routed through any physical interface based on the routing decision.
For a dynamic port, only one clock source can be configured.
Alternate BPCA
The BPCA (Best Primary Clock Algorithm, which is also known as Best Master Clock Algorithm (BMCA [RFCÂ 7273]) implementation
in G.8275.2 is different from that in the default PTP profile. The G.8275.2 implementation specifies an alternate best primary
clock algorithm (ABPCA), which is used by each device to select a clock to synchronize to, and to decide the port states of
its local ports.
The following consideration apply to the G.8275.2 implementation of the BPCA:
PrimaryOnly—A per port attribute, PrimaryOnly defines the state of the port. If this attribute is true, the port is never
placed in the subordinate state.
Priority 1—Priority 1 is always static in this profile and is set to 128. Priority 1 is not used in BPCA.
Priority 2—Priority 2 is a configurable value and its range if from 0 to 255.
Local Priority—Local priority is configured locally on clock ports to set the priority on nominated clocks. The default value
is 128 and valid range is from 1 to 255.
Benefits
With upcoming technologies like LTE-TDD, LTE-A CoMP, LTE MBSFN and Location-based services, eNodeBs (base station devices)
are required to be accurately synchronized in phase and time. Having GNSS systems at each node is not only expensive, but
also introduces vulnerabilities. The G.8275.2 profile meets the synchronization requirements of these new technologies.
Restrictions for Using the G.8275.2 Profile
In G.8275.2, PTP can be used in both hybrid mode and non-hybrid mode. In hybrid mode, PTP is used to provide phase and time-of-day
throughout the network synchronization along with PHY layer frequency support (SyncE). In non hybrid mode, PTP is used without
PHY layer frequency support (SyncE).
A G.8275.2 PTP clock can have redundant clock sources configured (through multiple PTP ports). However, at any given time,
a G.8275.2 PTP clock synchronizes to only one clock source, which is selected by BMCA.
The G.8275.2 does not provide any recommendations for performance analysis and network limits for the clocks.
How to Configure the G.8275.2 Profile
Creating an Ordinary Subordinate (T-TSC-P)
Cisco cBR-8 supports PTP ordinary clock subordinate mode with G8275.2 profile. In this mode, PTP ports are either on the Supervisor
PIC cards or on the 10GE Ethernet ports on the DPIC cards.
To create an ordinary subordinate, run the following steps:
ptp clock Ordinary domain 44
clock-port slave-port slave profile G.8275.2
transport ipv4 unicast interface lo 0 negotiation
clock source 10.1.1.1
Configuring Dual PTP Primary Clocks
Dual PTP primary clocks must connect to the same grandmaster. Both PTP primary clocks and the grandmaster must be set to Priority
2 configuration. You must set the minimum Priority 2 value for the grandmaster to keep the highest priority. The PTP primary
clocks connected to the grandmaster must have a Priority 2 value.
The following example shows a grandmaster in the Dual PTP primary clocks configuration:
Router# show run | se ptp
license feature ptp
ptp clock ordinary domain 44
priority2 2
clock-port master-to-two903 master profile g8275.2
sync interval -5
sync one-step
transport ipv4 unicast interface Lo1588 negotiation
Configuring the G.8275.2 Profiles
To configure G.8275.2 Profiles, run the following steps:
Router# config terminal
Enter configuration commands, one per line. End with CNTL/Z.
Router(config)# ptp clock ordinary domain 55
Router(config-ptp-clk)#servo tracking-type R-DTI
Router(config-ptp-clk)#clock-port slave-port slave profile g8275.2
Router(config-ptp-port)# delay-req interval -4
Router(config-ptp-port)# sync interval -4
Router(config-ptp-port)# sync one-step
Router(config-ptp-port)# transport ipv6 unicast interface Lo1588 negotiation
Router(config-ptp-port)# clock source ipv6 2001:158:158:158::158
Configuring an IPv4 Single Clock Source
To configure IPv4 single clock source, run the following steps:
Use Cisco Feature Navigator to find information about the platform support and software image support. Cisco Feature Navigator
enables you to determine which software images support a specific software release, feature set, or platform. To access Cisco Feature
Navigator, go to the https://cfnng.cisco.com/ link. An account on the Cisco.com page is not required.
Note
The following table lists the software release in which a given feature is introduced. Unless noted otherwise, subsequent
releases of that software release train also support that feature.
Table 1. Feature Information for G.8275.2 Profile
Feature Name
Releases
Feature Information
G.8275.2 Profile
Cisco IOS XE Everest 16.8.1
This feature was introduced in Cisco IOS XE Everest 16.8.1 on Cisco cBR Series Converged Broadband Router.