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444 Chapter 12: SNA Technology
-- Element number--The element component identifies the particular NAU
within the subarea, similar to a host in IP. See Figure 12-9.
Figure 12-9
Network Address
Boundary nodes communicate with peripheral nodes with FID2 PIU packets.
·
FID2 are the frame types used to communicate between a cluster controller and a FEP.
In Figure 12-10, the boundary node segments the large Token Ring frames into small SDLC
frames.
Figure 12-10
Path Information Units
Some SNA networks might have a number of FEPs connected, with Token Ring between the
mainframe and the cluster controllers. The boundary device is the last subarea node (FEP)
where the node type 2 (cluster controller) is attached. The main function of this device is to
convert a local address into a full network address when a message unit passes from a peripheral
node to a subarea node. Figure 12-11 depicts the boundary node concept. In Figure 12-11, the
16-bit network
address
Subarea address
Element address
Bit 0
Floating boundary
Bit 15
IBM 3745
(FEP)
IBM S/370
IBM 3174
Cluster controller PU 2
Token
Ring
IBM 3745
(FEP)
Token
Ring
IBM 3745
IBM 3174
IBM 3174
Channel - bus and tag or
ESCON
NCP software
Cluster controller PU 2
Cluster controller
PU 2
SDLC
FID 2 PIU
SDLC
FID 2
<---Boundary node
SDLC
FID 4 PIU
FID 4 PIU
FID 2 PIU
87200333.book Page 444 Wednesday, August 22, 2001 2:53 PM