The Precision Time Protocol (PTP) is a timing-over-packet protocol defined in the IEEE 1588v2 standard 1588 PTP 2008.
PTP may be deployed as an alternative timing-over-packet option to ACR. PTP provides the capability to synchronize network elements to a Stratum-1 clock or primary reference clock (PRC) traceable source over a network that may or may not be PTP-aware. PTP has several advantages over ACR. It is a standards-based protocol, has lower bandwidth requirements, can transport both frequency and time, and can potentially provide better performance.
The basic types of PTP devices are the following:
ordinary clock
boundary clock
end-to-end transparent clock
peer-to-peer transparent clock
Table: Synchronization options for 7210 SAS platforms lists the 7210 SAS platform support for the different types of PTP devices.
The 7210 SAS communicates with peer 1588v2 clocks, as shown in the following figure. These peers can be ordinary clock timeReceivers or boundary clocks. The communication can be based on either unicast IPv4 sessions transported through IP interfaces or Ethernet multicast PTP packets transported through an Ethernet port.
IP/UDP unicast and Ethernet multicast support for the 7210 SAS platforms is listed in the following table.
PTP is supported on all 7210 SAS platforms as described in this document, except the 7210 SAS-Sx 10/100GE and 7210 SAS-Sx/S 1/10GE operating in standalone-VC mode. See Configuration guidelines and restrictions for PTP for a list of PTP profiles, and the configuration guidelines and restrictions.
Platform |
IP/UDP Unicast |
Ethernet Multicast |
|---|---|---|
7210 SAS-T |
Yes |
Yes |
7210 SAS-Mxp |
Yes |
Yes |
7210 SAS-Sx 1/10GE |
Yes |
Yes1 |
7210 SAS-S 1/10GE |
No |
No |
7210 SAS-Sx 10/100GE2 |
No |
Yes1 |
7210 SAS-R6 |
Yes |
Yes3 |
7210 SAS-R12 |
Yes |
Yes3 |
Unicast IP sessions support two types of peers: configured and discovered. The 7210 SAS operating as an ordinary clock timeReceiver or as a boundary clock must have configured peers for each PTP neighbor clock from which it might accept synchronization information. The 7210 SAS initiates unicast sessions with all configured peers. A 7210 SAS operating as a boundary clock accepts unicast session requests from external peers. If the peer is not configured, it is considered a discovered peer. The 7210 SAS can deliver synchronization information toward discovered peers (that is, timeReceivers).
For Ethernet multicast operation, the node listens for and transmits PTP messages using the configured multicast MAC address. Neighbor clocks are discovered via messages received through an enabled Ethernet port. The 7210 SAS supports only one neighbor PTP clock connecting into a single port (see Figure: Ethernet multicast ports); multiple PTP clocks connecting through a single port are not supported. This might be encountered with the deployment of an Ethernet multicast LAN segment between the 7210 SAS and the neighbor PTP ports using an end-to-end transparent clock or an Ethernet switch. The use of an Ethernet switch is not recommended because of PDV and potential performance degradation, but it can be used if appropriate for the application.
The 7210 SAS does not allow simultaneous PTP operations using both unicast IPv4 and Ethernet multicast. A change of profile to G.8275.1 or from G.8275.1 to another profile requires a reboot of the node.
The following figure shows one neighbor PTP clock connecting into a single port.
7210 SAS platforms do not support ordinary clock timeTransmitter configuration.
The IEEE 1588v2 standard includes the concept of PTP profiles. These profiles are defined by industry groups or standards bodies that define the use of IEEE 1588v2 for specific applications.
The following profiles are supported for 7210 SAS platforms (as described in Table: IP/UDP unicast and Ethernet multicast support):
IEEE 1588v2 (default profile)
ITU-T Telecom profile (G.8265.1)
ITU-T Telecom profile for time with full timing support (G.8275.1)
The following caveats apply to G.8275.1 support. See sectionConfiguration guidelines and restrictions for PTP for configuration guidelines and restrictions.
PTP with Ethernet encapsulation is only supported with G.8275.1 profiles.
PTP over IP encapsulation is only with the IEEE 1588v2 and G.8265.1 profiles; it is not supported for G.8275.1 profiles.
When a 7210 SAS receives Announce messages from one or more configured peers or multicast neighbors, it executes a Best timeTransmitter Clock Algorithm (BTCA) to determine the state of communication between itself and the peers. The system uses the BTCA to create a hierarchical topology, allowing the flow of synchronization information from the best source (the grandmaster clock) out through the network to all boundary and timeReceiver clocks. Each profile has a dedicated BTCA.
If the profile setting for the clock is "ieee1588-2008", the precedence order for the BTCA is as follows:
priority1
clock class
clock accuracy
PTP variance (offsetScaledLogVariance)
priority2
clock identity
steps removed from the grandmaster
The 7210 SAS sets its local parameters as described in the following table.
Parameter |
Value |
|---|---|
clockClass |
248 – the 7210 SAS is configured as a boundary clock 255 – the 7210 SAS is configured as an ordinary clock timeReceiver |
clockAccuracy |
FE - unknown |
offsetScaledLogVariance |
FFFF – not computed |
clockIdentity |
Chassis MAC address following the guidelines of section 7.5.2.2.2 of IEEE 1588-2008 |
If the profile setting for the clock is "itu-telecom-freq" (ITU G.8265.1 profile), the precedence order for the best timeTransmitter selection algorithm is:
clock class
PTSF (Packet Timing Signal Fail) - Announce Loss (miss 3 Announce messages or do not get an Announce message for 6 seconds)
priority
The 7210 SAS sets its local parameters as described in the following table.
Parameter |
Value |
|---|---|
clockClass |
80-110 – value corresponding to the QL out of the central clock of the 7210 SAS as per Table 1/G.8265.1 255 – the 7210 SAS is configured as an ordinary clock timeReceiver |
The ITU-T profile is for use in environments with only ordinary clock timeTransmitters and timeReceivers for frequency distribution.
If the profile setting for the clock is "g8275dot1-2014", the precedence order for the best timeTransmitter selection algorithm is very similar to that used with the default profile. It ignores the priority1 parameter, includes a localPriority parameter, and includes the ability to force a port to never enter the timeReceiver state (master-only). The precedence is as follows:
clock class
clock accuracy
PTP variance (offsetScaledLogVariance)
priority2
localPriority
clock identity
steps removed from the grandmaster
The 7210 SAS sets its local parameters as described in the following table.
Parameter |
Value |
|---|---|
clockClass |
165 – the 7210 SAS is configured as a boundary clock and the boundary clock was previously locked to a grandmaster with clock class of 6 248 – the 7210 SAS is configured as a boundary clock 255 – the 7210 SAS is configured as an ordinary clock timeReceiver |
clockAccuracy |
FE – unknown |
offsetScaledLogVariance |
FFFF – not computed |
clockIdentity |
Chassis MAC address following the guidelines of section 7.5.2.2.2 of IEEE 1588-2008 |
The 7210 SAS supports a limited number of configured (possible timeTransmitter or neighbor boundary clocks) and a discovered peers (timeReceivers).These peers use the unicast negotiation procedures to request service from the 7210 SAS clock. A neighbor boundary clock counts as two peers (both a configured and a discovered peer) toward the maximum limit.
The number of configured Ethernet ports is not restricted.
On the 7210 SAS-Mxp, 7210 SAS-R6, 7210 SAS-R12, 7210 SAS-Sx 1/10GE, 7210 SAS-Sx 10/100GE 64SFP+ 4QSFP28, and 7210 SAS-T, there are limits on the number of timeReceivers enforced in the implementation for unicast and multicast timeReceivers.
Contact a Nokia technical support representative for scaling information about specific unicast message limits related to PTP.
The following figure shows the unicast negotiation procedure performed between a timeReceiver and a timeTransmitter clock that is selected to be the timeReceiver clock. The timeReceiver clock requests Announce messages from all peer clocks, but only requests Sync and Delay_Resp messages from the clock selected to be the timeTransmitter clock.
