| The MIB module for PTPv2 (IEEE1588 - 2008)
Overview of PTPv2 (IEEE 1588-2008)
This IEEE standard defines a protocol enabling precise
synchronization of clocks in measurement and control systems
implemented with packet-based networks, the IEEE Standard PTPv2
1588 (2008). This MIB does not address the standard IEEE
1588 (2002). The protocol is applicable to network elements
communicating using IP. The protocol enables heterogeneous
systems that include clocks of various inherent precision,
resolution, and stability to synchronize to a grandmaster
clock.
The protocol supports system-wide synchronization accuracy in
the sub-microsecond range with minimal network and local clock
computing resources. The standard uses UDP/IP. It includes
formal mechanisms for message extensions, higher sampling
rates, correction for asymmetry, a clock type to reduce error
accumulation in large topologies, and specifications on how to
incorporate the resulting additional data into the
synchronization protocol. The standard defines conformance and
management capability also.
MIB description
This MIB is to support the Precision Timing Protocol (PTP)
feature of Cisco System devices.
Acronyms:
ARB arbitrary
BMC best master clock
CAN Controller Area Network
CP Communication Profile
[according to IEC 61784-1:200710]
CPF Communication Profile Family
[according to IEC 61784-1:2007]
DS Differentiated Service
E2E End-to-End
E2ETC End-to-End Transparent Clock
EUI Extended Unique Identifier.
FFO Fractional Frequency Offset
GPS Global Positioning System
IANA Internet Assigned Numbers Authority
ICV Integrity Check Value
ID Identification
IPv4 Internet Protocol version 4
IPv6 Internet Protocol version 6
JD Julian Date
JDN Julian Day Number
MAC Media Access Control
[according to IEEE Std 802.3-2005]
MJD Modified Julian Day
NIST National Institute of Standards and
Technology (see www.nist.gov)
NTP Network Time Protocol (see IETF RFC 1305
[B7])
OUI Organizational Unique Identifier(allocated
by
the IEEE)
P2P Peer-to-Peer
P2PTC Peer-To-Peer Transparent Clock
PHY physical layer [according to IEEE Std
802.3-2005]
POSIX Portable Operating System Interface
(see ISO/IEC 9945:2003)
PPS Pulse per Second
PTP Precision Time Protocol
SA Security Associations
SNTP Simple Network Time Protocol
SOF Start of Frame
TAI International Atomic Time
TC Traffic Class
TC Transparent Clock
TLV Type, Length, Value [according to IEEE Std
802.1AB]
ToD Time of Day Synchronization
ToS Type of Service
UCMM UnConnect Message Manager
UDP/IP User Datagram Protocol
UTC Coordinated Universal Time
References:
[1] Precision clock synchronization protocol for networked
measurement and control systems - IEC 61588 IEEE 1588(tm)
Edition 2.0 2009-02
Definitions from [1] section 3.1
Accuracy:
The mean of the time or frequency error between the clock under
test and a perfect reference clock, over an ensemble of
measurements. Stability is a measure of how the mean varies
with respect to variables such as time, temperature, and so on.
The precision is a measure of the deviation of the error from
the mean.
Atomic process:
A process is atomic if the values of all inputs to the process
are not permitted to change until all of the results of the
process are instantiated, and the outputs of the process are
not visible to other processes until the processing of each
output is complete.
Boundary clock:
A clock that has multiple Precision Time Protocol(PTP) ports in
a domain and maintains the timescale used in the domain. It
may serve as the source of time, i.e., be a master clock, and
may synchronize to another clock, i.e., be a slave clock.
Boundary node clock:
A clock that has multiple Precision Time Protocol(PTP) ports in
a domain and maintains the timescale used in the domain. It
differs from the boundary clock in that the clock roles can
change.
Clock:
A node participating in the Precision Time Protocol (PTP) that
is capable of providing a measurement of the passage of time
since a defined epoch.
Domain:
A logical grouping of clocks that synchronize to each other
using the protocol, but that are not necessarily synchronized
to clocks in another domain.
End-to-end transparent clock:
A transparent clock that supports the use of the end-to-end
delay measurement mechanism between slave clocks and the master
clock. Each node must measure the residence time of PTP event
messages and accumulate it in Correction Field.
Epoch:
The origin of a timescale.
Event:
An abstraction of the mechanism by which signals or conditions
are generated and represented.
Foreign master:
An ordinary or boundary clock sending Announce messages to
another clock that is not the current master recognized by the
other clock.
Grandmaster clock:
Within a domain, a clock that is the ultimate source of time
for clock synchronization using the protocol.
Holdover:
A clock previously synchronized/syntonized to another clock
(normally a primary reference or a master clock) but now
free-running based on its own internal oscillator, whose
frequency is being adjusted using data acquired while it had
been synchronized/syntonized to the other clock. It is said to
be in holdover or in the holdover mode, as long as it is within
its accuracy requirements.
Link:
A network segment between two Precision Time Protocol ports
supporting the peer delay mechanism of this standard. The peer
delay mechanism is designed to measure the propagation time
over such a link.
Management node:
A device that configures and monitors clocks.
Master clock:
In the context of a single Precision Time Protocol
communication path, a clock that is the source of time to which
all other clocks on that path synchronize.
Message timestamp point:
A point within a Precision Time Protocol event message serving
as a reference point in the message. A timestamp is defined by
the instant a message timestamp point passes the reference
plane of a clock.
Multicast communication:
A communication model in which each Precision Time Protocol
message sent from any PTP port is capable of being received and
processed by all PTP ports on the same PTP communication path.
Node:
A device that can issue or receive Precision Time Protocol
communications on a network.
One-step clock:
A clock that provides time information using a single event
message.
On-pass support:
Indicates that each node in the synchronization chain from
master to slave can support IEEE-1588.
Ordinary clock:
A clock that has a single Precision Time Protocol port in a
domain and maintains the timescale used in the domain. It may
serve as a source of time, i.e., be a master clock, or may
synchronize to another clock, i.e., be a slave clock.
Parent clock:
The master clock to which a clock is synchronized.
Peer-to-peer transparent clock:
A transparent clock that, in addition to providing Precision
Time Protocol event transit time information, also provides
corrections for the propagation delay of the link connected to
the port receiving the PTP event message. In the presence of
peer-to-peer transparent clocks, delay measurements between
slave clocks and the master clock are performed using the
peer-to-peer delay measurement mechanism.
Phase change rate:
The observed rate of change in the measured time with respect
to the reference time. The phase change rate is equal to the
fractional frequency offset between the measured frequency and
the reference frequency.
PortNumber:
An index identifying a specific Precision Time Protocol port on
a PTP node.
Primary reference:
A source of time and or frequency that is traceable to
international standards.
Profile:
The set of allowed Precision Time Protocol features applicable
to a device.
Precision Time Protocol communication:
Information used in the operation of the protocol, transmitted
in a PTP message over a PTP communication path.
Precision Time Protocol communication path: The signaling path
portion of a particular network enabling direct communication
among ordinary and boundary clocks.
Precision Time Protocol node:
PTP ordinary, boundary, or transparent clock or a device that
generates or parses PTP messages.
Precision Time Protocol port:
A logical access point of a clock for PTP communications to the
communications network.
Recognized standard time source:
A recognized standard time source is a source external to
Precision Time Protocol that provides time and/or frequency as
appropriate that is traceable to the international standards
laboratories maintaining clocks that form the basis for the
International Atomic Time and Universal Coordinated Time
timescales. Examples of these are Global Positioning System,
NTP, and National Institute of Standards and Technology (NIST)
timeservers.
Requestor:
The port implementing the peer-to-peer delay mechanism that
initiates the mechanism by sending a Pdelay_Req message.
Responder:
The port responding to the receipt of a Pdelay_Req message as
part of the operation of the peer-to-peer delay mechanism.
Synchronized clocks:
Two clocks are synchronized to a specified uncertainty if they
have the same epoch and their measurements of the time of a
single event at an arbitrary time differ by no more than that
uncertainty.
Syntonized clocks:
Two clocks are syntonized if the duration of the second is the
same on both, which means the time as measured by each advances
at the same rate. They may or may not share the same epoch.
Time of Day:
Timeout:
A mechanism for terminating requested activity that, at least
from the requester's perspective, does not complete within the
specified time.
Timescale:
A linear measure of time from an epoch.
Traceability:
A property of the result of a measurement or the value of a
standard whereby it can be related to stated references,
usually national or international standards, through an unbroken
chain of comparisons all having stated uncertainties.
Translation device:
A boundary clock or, in some cases, a transparent clock that
translates the protocol messages between regions implementing
different transport and messaging protocols, between different
versions of IEEE Std 1588-2008/IEC 61588:2009, or different
Precision Time Protocol profiles.
transparent clock:
A device that measures the time taken for a Precision Time
Protocol event message to transit the device and provides this
information to clocks receiving this PTP event message.
Two-step clock:
A clock that provides time information using the combination of
an event message and a subsequent general message.
The below table specifies the object formats of the various
textual conventions used.
Data type mapping Textual Convention SYNTAX
-------------------- ------------------ ---------------------
5.3.2 TimeInterval ClockTimeInterval OCTET
STRING(SIZE(1..255))
5.3.3 Timestamp ClockTimestamp OCTET STRING(SIZE(6))
5.3.4 ClockIdentity ClockIdentity OCTET
STRING(SIZE(1..255))
5.3.5 PortIdentity ClockPortNumber INTEGER(1..65535)
5.3.7 ClockQuality ClockQualityClassType
Simple master-slave hierarchy [1] section 6.6.2.4
---------------
- Ordinary -
- Clock(1) -
- GrandMaster -
-------M-------
|
1
|
-------S-------------------------------
- Boundary -
- Clock(1) -
--------------M------------------M-----
| |
2 3
| |
-----S------ -------S------------------
- Ordinary - - Boundary -
- Clock(2) - - Clock(2) -
------------ -----M-------------M------
| |
4 5
| |
-----S------ -----S------
- Ordinary - - Ordinary -
- Clock(3) - - Clock(4) -
------------ ------------
Grandmaster
Boundary Clock(0-N) Ordinary Clocks(0-N)
Ordinary Clocks(0-N)
Relationship cardinality
PTP system 1 : N PTP Clock
PTP Clock 1 : 1 Domain
PTP Clock 1 : N PTP Ports
PTP Port N : N Physical Port (interface in IF-MIB)
Transparent clock diagram from section 6.7.1.3 of [1]
+----------------------------+
| Boundary clock - 1 |
+----------------------------+
| |
| |
+-- A --+ B
| |
+---------------------+ |
| Ordinary clock - 1| |
+---------------------+ |
+----------------------+
+--------------+ | End-to-end |
| Ordinary |------------------| transparent clock- |
| clock 1-1 | | 1 - 1 |
+--------------+ +----------------------+
|
|
C
|
|
+----------------------+
+--------------+ | End-to-end |
| Ordinary |------------------| transparent clock- |
| clock 1-2 | | 1 - 2 |
+--------------+ +----------------------+
The MIB refers to the sections of the IEEE 1588 standard for
reference. Throughout the MIB various secions from the standard
are referenced |
