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.

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.

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.

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.

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.

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.

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.

• 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.

The DPIC PTP Primary configuration involves the following steps in sequence:

1. Basic setup

   1. 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).

   2. In RPD, configure cBR loopback as its PTP Primary IP.

   3. 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.

2. 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:

   
   ptp r-dti <id>
   ptp-domain <domain id>
    clock-port <port id>
      clock source <ip address> gateway ip <ip address >
      clock source <ip address> gateway ip <ip address >alternate
   

3. Configure using either of the following formats:

   • With Default Profile

     • For cBR PTP configuration:

       
       ptp clock ordinary domain <domain id>
        servo tracking-type R-DTI
        clock-port <port_name0> master 
         sync interval <interval>
         sync one-step
         transport <ipv4/ipv6> unicast interface <loopback0> negotiation
        clock-port <port_name1> master
         sync interval <interval>
         sync one-step
         transport <ipv4/ipv6> unicast interface <loopback1> negotiation
         clock-port <port_name2> master
         sync interval <interval>
         sync one-step
         transport <ipv4/ipv6> unicast interface <loopback2> negotiation
       .
       .
       .
        clock-port <port_name63> master
         sync interval <interval>
         sync one-step
         transport <ipv4/ipv6> unicast interface <loopback63> negotiation
       

       Note	cBR supports up to 64 clock-ports.

     • For RPD PTP configuration:

       
       ptp r-dti <id>
        ptp-domain <domain id>
        clock-port <port id>
          ethernet x
          [transport ipv6]
          clock source [ipv6] <ip address> gateway ip <ip address >
          clock source [ipv6] <ip address> gateway ip <ip address >alternate
       

       Note	The gateway ip is the active and standby core interface

   • With G8275.2 Profile

     • For cBR PTP configuration:

       
       ptp clock boundary domain <domain id>
        servo tracking-type R-DTI
        clock-port <port_name0> master  profile G8275.2
         sync interval <interval>
         sync one-step
         transport <ipv4/ipv6> unicast interface <loopback0> negotiation
        clock-port <port_name1> master  profile G8275.2
         sync interval <interval>
         sync one-step
         transport <ipv4/ipv6> unicast interface <loopback1> negotiation
         clock-port <port_name2> master profile G8275.2
         sync interval <interval>
         sync one-step
         transport <ipv4/ipv6> unicast interface <loopback2> negotiation
       .
       .
       .
        clock-port <port_name63> master profile G8275.2
         sync interval <interval>
         sync one-step
         transport <ipv4/ipv6> unicast interface <loopback63> negotiation
       

       Note	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.

     • For RPD PTP configuration:

       
       ptp r-dti <id>
        profile G.8275.2
        ptp-domain <domain id>
        clock-port <port id>
          ethernet x
          [transport ipv6]
          clock source [ipv6]  <ip address> gateway ip <ip address >
          clock source [ipv6]  <ip address> gateway ip <ip address >alternate
       

       Note	The gateway IP is the active and standby core interface.

Use the following options to verify your DPIC PTP Primary configuration:

• To check the cBR and RPD PTP configuration, use the show run | se ptp command. The syntax is as follows:

  
  show run | se ptp
  
  ptp clock boundary domain <domain id>
   servo tracking-type R-DTI
   clock-port <port_name0> master  profile G8275.2
    sync interval <interval>
    sync one-step
    transport <ipv4/ipv6> unicast interface <loopback0> negotiation
   clock-port <port_name1> master  profile G8275.2
    sync interval <interval>
    sync one-step
    transport <ipv4/ipv6> unicast interface <loopback1> negotiation
    clock-port <port_name2> master profile G8275.2
    sync interval <interval>
    sync one-step
    transport <ipv4/ipv6> unicast interface <loopback2> negotiation
  .
  .
  .
   clock-port <port_name63> master profile G8275.2
    sync interval <interval>
    sync one-step
    transport <ipv4/ipv6> unicast interface <loopback63> negotiation
  
   

• 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:

    
    Router# show ptp clock 0 statistics
    AprState    4  :
               2@0-00:11:41.897          1@0-00:11:32.266          0@0-00:09:37.062
               4@0-00:09:17.861
    ClockState  5  :
               5@0-00:12:02.947          4@0-00:11:59.305          3@0-00:11:55.663
               2@0-00:11:42.664          1@0-00:11:41.866
    BstPktStrm  1  :
               0@0-00:09:10.010
    StepTime    1  :
       773016962@0-00:11:01.145
    AdjustTime  3  :
              12@0-00:13:57.520       -280@0-00:13:33.895      -1137@0-00:11:27.895
    fwdFltr     0  :
               Total: 4828                        Drop: 513
                MEAN: 973                       stdDev: 974
           Threshold:     -299027 ~ 300973      shrink: 85714
    revFltr     0  :
               Total: 4827                        Drop: 513
                MEAN: 950                       stdDev: 951
           Threshold:     -299050 ~ 300950      shrink: 85714
    fwdFltr     1  :
               Total: 1507                        Drop: 256
                MEAN: 974                       stdDev: 975
           Threshold:     -299026 ~ 1373        shrink: 42914
    revFltr     1  :
               Total: 1505                        Drop: 257
                MEAN: 947                       stdDev: 947
           Threshold:         619 ~ 300947      shrink: 42904
    streamId  msgType           rx          rxProcessed     lost        tx
    0        SYNC              4828        4828            0           0
    0        DELAY REQUEST     0           0               0           4827
    0        P-DELAY REQUEST   0           0               0           0
    0        P-DELAY RESPONSE  0           0               0           0
    0        FOLLOW UP         0           0               0           0
    0        DELAY RESPONSE    4827        4827            3           0
    0        P-DELAY FOLLOWUP  0           0               0           0
    0        ANNOUNCE          314         314             0           0
    0        SIGNALING         5           5               0           5
    0        MANAGEMENT        0           0               0           0
       TOTAL                    9974        9974            3           4832
    1        SYNC              1507        1507            0           0
    1        DELAY REQUEST     0           0               0           1505
    1        P-DELAY REQUEST   0           0               0           0
    1        P-DELAY RESPONSE  0           0               0           0
    1        FOLLOW UP         0           0               0           0
    1        DELAY RESPONSE    1505        1505            2           0
    1        P-DELAY FOLLOWUP  0           0               0           0
    1        ANNOUNCE          103         103             0           0
    1        SIGNALING         2           2               0           7
    1        MANAGEMENT        0           0               0           0
       TOTAL                    3117        3117            2           1512
    Router#