User's Manual Part 1

Chapter 1: Product description Ethernet bridging
Quality of service for bridged Ethernet traffic
The PTP 650 Series supports eight traffic queues for Ethernet frames waiting for transmission over
the wireless link. 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,
or the Traffic Class in an MPLS header.
PTP 650 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 650 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.
Wireless link down alert
The PTP 650 Series provides an optional indication of failure of the wireless link by means of a
brief disconnection of the copper data port or the 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.
Lowest Ethernet Modulation Mode
The PTP 650 ODU can be configured to discard Ethernet frames when the modulation mode is
lower than the configured Lowest Ethernet 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 Ethernet
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 Ethernet 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.
Page
1-17