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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.
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.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature
Navigator, go to
http://tools.cisco.com/ITDIT/CFN/.
An account on http://www.cisco.com/ is not required.
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 1.1.1.1
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:
Effective Cisco IOS XE Fuji 16.12.1y, Cisco cBR Converged Broadband router provides support for Digital Physical Interface
Card (DPIC) Precision Time Protocol (PTP) Primary. With the DPIC PTP Primary feature, RPD will sync to the PTP primary with
some switch between them.
Note
The DPIC PTP Primary feature is only supported on DPIC40, and not supported on DPIC100.
The DPIC PTP Primary feature has the following capabilities:
PTP primary works as ordinary clock (OC mode) when using default profile.
PTP primary works as Boundary clock (BC mode limited) only when using G8275.2 Profile.
Supports PTP One-step mode
Supports IPv4/IPv6 UDP PTP packets
Supports up to 200 RPDs, 100 RPDs when ptp redundancy is configured
Supports G8275.2 Profile
Supports SUPHA and LCHA configurations
Note
The following scenarios are not supported:
PTP packets that are sent and received through SUPPIC or DPIC100
Boundary clock mode with both primary and subordinate clock port
Two step mode
Dual Stack (IPv4/v6)
Configuring DPIC PTP Primary
The DPIC PTP Primary configuration involves the following steps in sequence:
Basic setup
Configure cBR as PTP Primary with its loopback interface.
Ensure that the IP address of cBR loopback interface and RPD core interface should be in global or same VPN Routing/Forwarding
(VRF).
In RPD, configure cBR loopback as its PTP Primary IP.
Ensure that the RPD uses its core interface IP as its PTP Gateway.
Note
The PTP traffic between cBR loopback interface and RPD are routed through the RPD core interface. Therefore, IP address of
the cBR loopback interface and RPD core interface should be in global or same VRF.
PTP setup redundancy
If Line Card High Availability (LCHA) is configured, RPD uses the corresponding DPIC interface on standby LC as it is an alternate
clock source and gateway. Use the following snippet to configure the LCHA for PTP redundancy:
By the ITU G8275.2 Profile specification, the ordinary clock supports only one clock-port with G8275.2 Profile. You need to
use the boundary clock if you have scenarios where multiple clock-ports are required.
To check the PTP Primary state, you can use the show ptp clock running domain <id> command. See the following example:
Router# show ptp clock running domain 55
Load for five secs: 4%/0%; one minute: 4%; five minutes: 4%
Time source is NTP, 04:34:17.164 CST Tue Dec 19 2017
PTP Boundary Clock [Domain 55]
State Ports Pkts sent Pkts rcvd Redundancy Mode
FREQ_LOCKED 2 2005322 971815 Hot standby
PORT SUMMARY
PTP Master
Name Tx Mode Role Transport State Sessions Port Addr
22 unicast master Lo1588 Master 2 -
33 unicast master Lo1589 Master 2 -
SESSION INFORMATION
22 [Lo1588] [Sessions 2]
Peer addr Pkts in Pkts out In Errs Out Errs
2001:120:101:16:A94F:61DB:D324:76B4 240839 497336 0 0
2001:120:101:16:2827:F9A6:4332:81AF 245193 505541 0 0
33 [Lo1589] [Sessions 2]
Peer addr Pkts in Pkts out In Errs Out Errs
2001:120:101:16:A94F:61DB:D324:76B4 240582 496880 0 0
2001:120:101:16:2827:F9A6:4332:81AF 245201 505565 0 0
Router#
To check detailed stream statistics, use the show platform software ptpd stat stream <id|ip> command. For example:
Router# show platform software ptpd stat stream 2001:120:101:16:A94F:61DB:D324:76B4
Load for five secs: 5%/0%; one minute: 4%; five minutes: 4%
Time source is NTP, 04:40:43.466 CST Tue Dec 19 2017
IP-Address : 2001:120:101:16:a94f:61db:d324:76b4 Stream-Number: 0
SYNC Contract
Remaining Duration : 105 (secs), State : ACTIVE
Tx packets : 247592, Rx Packets : 0 Error Packets : 0
Announce Contract
Remaining Duration : 105 (secs), State : ACTIVE
Tx packets : 15490, Rx Packets : 0 Error Packets : 0
Delay-Response Contract
Remaining Duration : 101 (secs), State : ACTIVE
Tx packets : 246878, Rx Packets : 0 Error Packets : 0
Router# show platform software ptpd stat stream 0
Load for five secs: 3%/0%; one minute: 4%; five minutes: 4%
Time source is NTP, 04:40:26.810 CST Tue Dec 19 2017
LOCK STATUS : FREERUN
SYNC Packet Stats
Time elapsed since last packet: 0.0
Configured Interval : -4, Acting Interval -4
Tx packets : 247325, Rx Packets : 0
Last Seq Number : 0, Error Packets : 0
Delay Req Packet Stats
Time elapsed since last packet: 0.0
Configured Interval : 0, Acting Interval : -4
Tx packets : 0, Rx Packets : 246612
Last Seq Number : 26116, Error Packets : 0
Delay Response Packet Stats
Time elapsed since last packet: 0.0
Configured Interval : -4, Acting Interval : -4
Tx packets : 246612, Rx Packets : 0
Last Seq Number : 0, Error Packets : 0
Announce Packet Stats
Time elapsed since last packet: 0.0
Configured Interval : 0, Acting Interval : 0
Tx packets : 15474, Rx Packets : 0
Last Seq Number 0 Error Packets 0
Signalling Packet Stats
Time elapsed since last packet: 0.0
Configured Interval : 0, Acting Interval : 0
Tx packets : 162, Rx Packets : 162
Last Seq Number : 0, Error Packets : 0
Current Data Set
Offset from master : +0.000000000
Mean Path Delay : +0.000000000
Forward Path Delay : +0.000000000
Reverse Path Delay : +0.000000000
Steps Removed 0
General Stats about this stream
Packet rate : 0, Packet Delta (ns) : 0
Clock Stream handle : 0, Index : 0
Oper State : 3, Sub oper State : 6
Log mean sync Interval : 0, log mean delay req int : 0
To check the RPD PTP state, you can use the following commands:
show ptp clock 0 state command is used to check the PTP state on RPD. For example:
Router# show ptp clock 0 state
apr state : PHASE_LOCK
clock state : SUB_SYNC
current tod : 1423125872 Thu Feb 5 08:44:32 2015
active stream : 0
==stream 0 :
port id : 0
master ip : 2001:158:158:158::158
stream state : PHASE_LOCK
Master offset : -110
Path delay : 957
Forward delay : 888
Reverse delay : 1026
Freq offset : -418299
1Hz offset : 40
==stream 1 :
port id : 0
master ip : 2001:158:158:158::159
stream state : PHASE_LOCK
Master offset : -15
Path delay : 969
Forward delay : 916
Reverse delay : 1023
Freq offset : -418526
1Hz offset : 47
Router#
The show ptp clock 0 statistics command is used to check PTP packets statistics on RPD. See the following example usage:
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 Fuji 16.8.1
This feature was introduced in Cisco IOS XE Fuji 16.8.1 on Cisco cBR Series Converged Broadband Router.
DPIC PTP Primary
Cisco IOS XE Gibraltar 16.12.1y
This feature was introduced in Cisco IOS XE Gibraltar 16.12.1y on Cisco cBR Series Converged Broadband Router.