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Overview of IBM Networking
STUN and BSTUN
BC-213
Cisco IOS Bridging and IBM Networking Configuration Guide
78-11737-02
• Allows networks with IBM mainframes and communications controllers to share data using Cisco
routers and existing network links. As an SDLC function, STUN fully supports the IBM SNA and
allows IBM SDLC frames to be sent across the network media and shared serial links. illustrates a
typical network configuration without STUN and the same network configured with STUN.
• Encapsulates SDLC frame traffic packets and routes them over any of the supported network media
(serial, FDDI, Ethernet, and Token Ring, X.25, SMDS, and T1/T3) using TCP/IP encapsulation.
Because TCP/IP encapsulation is used, you can use any of the Cisco routing protocols to route the
packets.
• Copies frames to destinations based on address. STUN in passthrough mode does not modify the
frames in any way or participate in SDLC windowing or resending; these functions are left to the
communicating hosts. However, STUN in local acknowledgment mode does participate in SDLC
windowing and resending through local termination of the SDLC session.
• Ensures reliable sending of data across serial media having minimal or predictable time delays. With
the advent of STUN and WAN backbones, serial links now can be separated by wide geographic
distances spanning countries and continents. As a result, these serial links have time delays that are
longer than SDLC allows for bidirectional communication between hosts. The STUN local
acknowledgment feature addresses the problems of unpredictable time delays, multiple resending,
or loss of sessions.
• Allows for configuration of redundant links to provide transport paths if part of the network goes
down.