NEC SL1100 Issue 6.0
Networking Manual 6 - 5
using layer 2 classes of service (CoS) settings in the User Priority bits of
the 802.1Pq header. Refer to Program 84-09 : VLAN Setup on page
5-30 for information for VLAN configuration.
IP Precedence - Layer 3 QoS:
Allows you to specify the class of service for a packet. You use the three
precedence bits in the IPv4 header type of service (ToS) field for this
purpose. Using the ToS bits, you can define up to six classes of service.
Other devices configured throughout the network can then use these bits
to determine how to treat the packet in regard to the type of service to
grant it. These other QoS features can assign appropriate
traffic-handling policies including congestion management and
bandwidth allocation. By setting IP Precedence levels on incoming traffic
and using them in combination with QoS queuing features, you can
create differentiated service. (Refer to Program 84-10 : ToS Setup on
page 5-31 for detailed programming information.)
Differentiated service (Diffserv) - Layer 3 QoS:
Provides services differentiated on performance using weighted priority
queuing. DiffServ requires that edge routers classify traffic flows into a
member from a set of categories based on the TCP/IP header fields in
what is called a micro flow. Because the Diffserv is present in every
packet header, each node can provide differentiated services per-hop.
Refer to Program 84-10 : ToS Setup on page 5-31 for detailed
programming information.
Figure 6-1 Layer 2 Diagram (802.1Q)
PREAM SFD DA SA
Type
TAG
PT Data FCS
4 Bytes
PRI
CFI
VLAN ID
Layer 2
802.1Q/p
Three bits used for CoS
(user priority)
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