which is important in high-speed environments.
on the same LAN. In Figure 13-16, if PC1 wants to send information to the printer on the Token
Ring LAN, a feature is needed that permits that to happen without disturbing the router. This is
where virtual nodes come in.
Every end node still has a CP-CP session with the network node, but sessions with another
resource on the LAN do not pass through the network node. Each network node defines two
connections--one to the network node and one to the virtual node.
same medium and selects a route that directly connects the two through the virtual node rather
than through the network node.
most applications were 3270 applications, the corporate world did not embrace it right away.
However, in VTAM release 4.2, a feature known as dependent LUs was introduced. This feature
allowed the use of APPN for any application in the network.
upstream or downstream devices. Primary and secondary roles are negotiated by the nodes.
Dependent Logical Units (DLUs) are legacy LUs--types 0, 1, 2, 3, and so on. They cannot
initiate sessions without the intervention of VTAM, and they lack the ability to actively
participate in a peer-to-peer session initiation.
initiate a session and become the primary; the primary then sends the BIND to set up the
session. In APPN, there is no concept of a node that cannot send a BIND. Special support has
been added to APPN to permit legacy LUs to participate. This support is called Dependent
Logical Unit Requester/Server (DLUR/DLUS), where the server is implemented in VTAM 4.2
and the requester can be in a network node or end node in the network. DLUR is implemented
in the Cisco router.
available in Cisco release 11.0. Features included ISR routing, support for nodes on a LAN, DLU
support, and APPN routing across the channel using the CIP card. A Cisco router can support
LENs as well as DLUs. Because the LENs do not establish CP-CP sessions with their adjacent