3.4 PTPv2 IEEE 1588-2008 Conguration Guide Page 7
3.4 PTPv2 IEEE 1588-2008 Configuration Guide
Setting up all devices in a PTP synchronization infrastructure is one of the most important parts in a network
time synchronization project. The settings of the involved Grandmaster clocks as the source of time and the end
devices (Slaves) have to match in order to allow them to synchronize and avoid problems later, when the PTP
infrastructure is deployed to production environments. In addition to that, the use of PTP aware network infras-
tructure components, namely network switches, introduces another set of parameters that have to be harmonized
with the masters and slaves in a PTP setup.
It is therefore very important to start with making decisions how the to-be-installed PTP synchronization so-
lution should operate, e.g. should the communication between the devices be based on multicast or unicast
network trac or how often should the masters send SYNC messages to the slaves.
This chapter lists the most important options and their implications on a synchronization environment in general.
A detailed explanation of the conguration settings within the LANTIME conguration interfaces can be found
later within this documentation.
3.4.1 General Options
The following general mode options have to be decided before deploying the infrastructure:
1) Layer 2 (Ethernet) or Layer 3 (UDP/IPv4) connections
2) Multicast or Unicast
3) Two-Step or One-Step Operation
4) End-to-End or Peer-to-Peer Delay Mechanism
The above options need to be dened for the whole setup, if devices do not stick to the same settings, they will
not be able to establish a working synchronization link.
3.4.2 Network Layer 2 or Layer 3
PTP/IEEE 1588-2008 oers a number of so-called mappings on dierent network communication layers. For
Meinberg products you can choose between running PTP over IEEE 802.3 Ethernet connections (network Layer
2) or UDP/IPv4 connections (Layer 3).
Layer 3 is the recommended mode, because it works in most environments. For Layer 2 mode the network
needs to be able to provide Ethernet connections between master and slave devices, which is often not the case
when your network is divided into dierent network segments and you have no layer 2 routing capabilities in your
network infrastructure.
The only benet of using Layer 2 mode would be a reduced trac load, because the transmitted network frames
do not need to include the IP and UDP header, saving 28 bytes per PTP packet/frame. Due to the fact that PTP
is a low trac protocol (when compared to other protocols), the reduced bandwidth consumption only plays a
role when low-bandwidth network links (e.g. 2Mbit/s) have to be used or in pay-per-trac scenarios, for example
over leased-line connections.
3.4.3 Multicast or Unicast
The initial version of PTP (IEEE 1588-2002 also known as PTPv1) was a multicast-only protocol. Multicast
mode has the great advantage that the master clock needs to send only one SYNC packet to a Multicast address
and it is received by all slave devices that listen to that multicast address.
In version 2 of the protocol (IEEE 1588-2008) the unicast mode was introduced in addition to the multicast
mode. In unicast mode, the master has to send one packet each to every slave device, requiring much more CPU
performance on the master and producing orders of magnitudes more trac.
On the other hand, some switches might block multicast trac, so that in certain environments, Unicast mode
has to be used.
PTP270PEX Date: 22nd November 2012
7
