User manual

42 Publication 1783-UM003D-EN-E - December 2009
Chapter 2
Precision Time Protocol
(PTP)
The IEEE 1588 standard defines a protocol, called Precision Time Protocol,
or PTP, which enables precise synchronization of clocks in measurement and
control systems. The clocks communicate with each other over the
EtherNet/IP communication network. The PTP protocol enables
heterogeneous systems that include clocks of various inherent precision,
resolution and stability to synchronize. PTP generates a Master-Slave
relationship among the clocks in the system. All clocks ultimately derive their
time from a clock selected as the grandmaster clock.
Resilient Ethernet Protocol
(REP)
The Resilient Ethernet Protocol (REP) provides an alternative to Spanning
Tree Protocol (STP) to control network rings and loops, handle link failures,
and improve convergence time. REP controls a group of ports connected in a
segment, ensures that the segment does not create any bridging loops, and
responds to link failures within the segment. REP provides a basis for
constructing more complex networks and supports VLAN load balancing.
REP is a segment protocol. One REP segment is a chain of ports connected to
each other and configured with a segment ID. Each segment consists of
standard (transit) segment ports and two user-configured edge ports. A switch
can have no more than two ports that belong to the same segment, and each
segment port can have only one external neighbor. A segment can go through
a shared medium, but on any link only two ports can belong to the same
segment. REP is supported only on Layer 2 trunk interfaces. Selecting the
Switch for Automation Smartport enables Layer 2 trunking. REP is supported
on EtherChannels, but not on an individual port that belongs to an
EtherChannel.
You can construct almost any type of network based on REP segments. REP
also supports VLAN load-balancing, controlled by the primary edge port but
occurring at any port in the segment.
These types of REP ports are selectable in the Device Manager Web interface:
• Primary: This port is a primary edge port. This port always participates
in VLAN load balancing in the REP segment.
• Edge: This port is a secondary edge port. It also participates in VLAN
load balancing in the REP segment.
Edge ports are termination points of a REP segment. The user must
configure two edge ports, including one primary edge port, for each
REP segment. Entering edge without primary configures the port as a
secondary edge port. Primary and secondary edge ports must be
configured even if support of VLAN balancing is not required.