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User Guide
70
The second port-wide setting to be configured is the Maximum Transmission Unit
(MTU). This setting is relevant for the analyser only and it configures the largest frame
S-VLAN TPID Ethertype to be associated to the S-VLAN tag in Q-in-Q
frames. Four different values are possible: 0x8100, 0x9100,
0x9200 and 0x9300.
It the encapsulation is set to IEEE 802.1ad, the S-VLAN Eth-
ertype is automatically set to 0x88a8 and this field is not
available for configuration.
S-VID VLAN identifier assigned to the S-tag in double tagged
frames (IEEE 802.1ad, Q-in-Q). In frames with two VLAN
tags, the S-VID usually accounts for the VLAN structure cor-
responding to the service provider network.
Any value within 0 to 4095 is allowed for this field.
S-VLAN priority 3-bit class of service (CoS) field defined to set frame groups
with different priorities or to provide specific treatments to
special frames within a network or an administrative domain.
This field is carried by the S-tag (service provider tag) of
Ethernet frames with two tags.
Any value from 0 to 7 is allowed for this field. Specific actions
to be carried out on frames with different CoS labels depend
on the network and the service provider.
Drop-eligible indica-
tor
This is a single bit field that is used to mark drop eligible
frames. These frames are usually dropped first when con-
gestion is detected in a network node.
The Drop eligible operator is carried within the S-tag of IEEE
802.1ad frames.
Frame size Ethernet MAC frame size including the destination MAC
address, source MAC address, type / length field, payload,
FCS and any VLAN tag carried by the frame.
Anything between 64 B and 10000 B is allowed but frames
longer than 1518 B (without VLAN tags and MPLS labels) are
out of the IEEE 802.3 standard.
It is possible to generate frames longer than the port Maxi-
mum Transmission Unit (MTU) but these frames are consid-
ered oversized frames when they are analysed by the tester.
To avoid an OverS anomaly in this case, increase the value
of the port MTU.
Table 4.1: Ethernet Frame Settings
Setting Description
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