Madge Networks Token Ring Switch - Manual (Page 42)

42
Smart DeskStream Technical Presentation 42
Source Route Switching
‘Annex K’
n Components of Annex K ?
n Concentrator Relay Function (CRF)
l Handles switching process
l All ports access the network using the same ring
number (source routing)
l Includes all ports (by default) within a stack of
DeskStreams
n Bridge Relay Function (BRF)
l Allows bridging between CRF and ports on different
ring numbers
l Equivalent to an IEEE SRT switch
The CRF manages all the basic ports including a ‘virtual’ port which
gives a link to the BRF interface and any ports which have been
transferred to that interface.
Ports within the CRF all use the same ring number (although they are
not in a ring - this is a switched environment). This allows an SR
frame (in an SR network) to find the correct DeskStream stack; the
CRF will sort out, from its Address/Descriptor table, which port to
pass the frame to.
The BRF allows us to take some ports out of the CRF and assign a
different ring number to each. The BRF manages the switching
between these ports and - via the CRF - to the basic ports.