HP 600 Series, Services And Applications

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Encapsulation Bridging
There are many protocols that are non-routable and therefore must be
bridged. These non-routable protocols must be encapsulated in an FDDI
frame in order to be transported across the ring. Encapsulation is the
bridge’s implementation that enables interconnection of similar networks
over an FDDI network. Figure 7 shows how non-routable protocols might be
encapsulated across an FDDI network. Within such a topology, a bridge
encapsulates the original Ethernet/IEEE 802.3 frame into a new message
type (in this case, an FDDI-specific packet) for travel across the FDDI ring.
At the destination, the message is removed from the FDDI packet and
transmitted in its original form.
Figure 7. Encapsulation Bridging
It is important to note that encapsulation is not the preferred method of
transporting data across an FDDI network. In addition, no standard method
of encapsulation exists, preventing multivendor interoperability.
FDDI Ring
LAN 1 LAN 2
DA SA
type
data FCS
DA SA LLC
Ethernet
data FCS
DA SA type data
FCS
LAN 1 Frame
FDDI
Encapsulated
Frame
LAN 2 Frame
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Shining a Light on FDDI
Internetworking with HP Routers
3-53