GE T1000, Техническое руководство

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Chapter 4
– Functions
GE Reason Switches
88 REASON SWITCHES-TM-EN-3
Ingress filtering and acceptance can be configured by user, when the port selected
permits. If port ingress filtering is used, port can select if it will accept tagged or
untagged frames. If not used, the switch will perform its function in promiscuous
mode, that is, all incoming data will be received.
Egress filtering and acceptance can be configured by user, when the port selected
permits. When used, the switch can be configured to untag all egressing frames, tag
all egressing frames and untag (cut VLAN information of the frame) PVID frames. If
untag all is used, then frames will always egress the switch without VLAN
information, including the ones which have come with VLAN information. If tag all is
used, then frames will always egress the switch with VLAN information, including
these ones which have come without VLAN information. In that case, untagged
incoming frames will be encapsulated in an 802.1Q frame with PVID identification.
Finally, if untag PVID is used, than only frames with PVID identifier will have their
VLAN information discarded, and all of the others VLAN identifiers will be maintained.
Attention is required when using meshed VLAN and VLAN-unaware equipment in the same port. If the application imposes this,
use different VLAN identifiers in VLAN-aware equipment from PVID number, which will be used only for VLAN-unaware
equipment, and then choose untag PVID at the egress tagging. If the same identifier is used on both VLAN-aware and unaware
equipment, all frames with PVID (send to the VLAN-aware and unaware hosts) will have its 802.1Q information discarded.
Allowed and forbidden VLAN are concepts used to define which VLAN (or which VLAN
ID range) the port will be a member of. Trunk and Hybrid ports can be members of as
many VLAN as it is possible. Thus, such ports can receive data from all of the allowed
VLAN configured. Besides, as it is desirable to explicitly define of which VLAN the port
must not be a member, there is the forbidden concept. In this concept, the port will
allow any VLAN to be a member, except for the forbidden ones. This last concept is
particularly useful if there are too many VLAN whose port should be a member and a
few that should not be member. Thus, all of the VLAN accepted and a short list of the
ones that are not accepted can be configured. In power system applications, for
instance, such a concept can be used to guarantee that Sampled Values data do not
leave the process bus, thus increasing station bus bandwidth security.