Chapter 1: Product description
Ethernet bridging
Page 1-33
Ethernet frames are classified by inspection of the Ethernet priority code point in the outermost
VLAN tag, the Differentiated Services Code Point (DSCP) in an IPv4 or IPv6 header including
DSCP in an IPv4 or IPv6 datagrams encapsulated in PPP and PPPoE headers,
or the Traffic
Class in an MPLS header.
PTP 670 provides a configurable mapping between Ethernet, IP or MPLS priority and
transmission queue, together with a simple way to restore a default mapping based on the
recommended default in IEEE 802.1Q-2005. Untagged frames, or frames with an unknown
network layer protocol, can be separately classified.
Scheduling for transmission over the wireless link is by strict priority. In other words, a frame
at the head of a given queue is transmitted only when all higher priority queues are empty.
Fragmentation
The PTP 670 Series minimizes latency and jitter for high-priority Ethernet traffic by fragmenting
Ethernet frames before transmission over the wireless link. The fragment size is selected
automatically according to channel bandwidth and modulation mode of the wireless link.
Fragments are reassembled on reception, and incomplete Ethernet frames are discarded.
Data port wireless link down alert
The PTP 670 Series provides an optional indication of failure of the wireless link by means of a
brief disconnection of the copper or optical data port allocated to the customer data network.
The Wireless link down alert can be used to trigger protection switching by Spanning Tree
Protocol (STP) or Ethernet Automatic Protection Switching (EAPS) and other higher layer
protocols in a redundant network.
Note
PTP 670 does not support Data port wireless link down alert in the HCMP topology.
Lowest Data Modulation Mode
The PTP 670 ODU can be configured to discard Ethernet frames in the Data Service when the
modulation mode is lower than the configured Lowest Data Modulation Mode.
This feature is likely to be useful in networks that have alternate routes, for example in a ring or
mesh topology where EAPS or RSTP is used to resolve loops. In this application, Lowest Data
Modulation Mode should be set to ensure that an active link will provide at least the minimum
necessary capacity for high-priority constant bit rate traffic such as voice over IP or TDM
pseudo wire. An active link will be blocked when the capacity falls below the minimum
required, triggering a routing change in associated Ethernet switches to bring alternate links
into use.
Lowest Data Modulation Mode should normally be set to BPSK 0.63 Single in simply connected
tree networks or other topologies that do not have alternative routes.
