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Chapter 3: System planning
An advantage of Ethernet priority is that any VLAN-tagged frame can be marked with a priority,
regardless of the higher-layer protocols contained within the frame. A disadvantage of Ethernet
priority is that the priority in the frame must be regenerated whenever traffic passes through a
router.
IP/MPLS priority scheme
IP priority is encoded in the DSCP value encoded in the ToS field in IPv4 and Traffic Class in IPv6.
The DSCP field provides 64 levels of priority. Determine the DSCP values used in the network and
select a suitable mapping from these DSCP values to the eight PTP 650 queues.
The advantages of IP priority are that priority in the IP header is normally propagated transparently
through a router, also the DSCP field supports a large number of distinct priority code points. A
disadvantage of DSCP is that frames receive a single default classification if they contain a network
layer protocol other than IPv4 or IPv6. This is controlled by the user setting the Unknown Network
Layer Protocol queue value in the same QoS Configuration page under IP/MPLS QoS.
MPLS priority is encoded in the traffic class (TC) field in the outermost MPLS label. Select a
suitable mapping from MPLS TC to the eight PTP 650 queues.
"Daisy-chaining" PTP 650 links
When connecting two or more PTP 650 links together in a network (daisy-chaining), do not install
direct copper Cat5e connections between the PSUs. Each PSU must be connected to the network
terminating equipment using the LAN port. To daisy-chain PTP 650 links, install each ODU-to-ODU
link using one of the following solutions:
•
A copper Cat5e connection between the Aux ports of two ODUs. For details of the Ethernet
standards supported and maximum permitted cable lengths, see
lengths
on page 2-20.
•
A copper Cat5e connection between the Aux port of one ODU and the SFP port of the next
ODU (using a copper SFP module). For details of the Ethernet standards supported and
maximum permitted cable lengths, see
•
Optical connections between the ODUs (SFP ports) using optical SFP modules at each ODU.
For details of the Ethernet standards supported and maximum permitted cable lengths, see
SFP module kits
on page 2-27.
Green Ethernet switches
Do not connect PTP 650 units to Ethernet networking products that control the level of the
transmitted Ethernet signal based on the measured length of the Ethernet link, for example Green
Ethernet products manufactured by D-Link Corporation. The Ethernet interfaces in these
networking products do not work correctly when connected directly to the PTP 650 PSU.
Ethernet standards and cable lengths
Page
3-30
Data network planning
Ethernet standards and cable
on page 2-20.
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