Cisco CCIE Fundamentals Network Design

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.In pass-through mode, local acknowledgment is not used.Instead, the LLC2 session from the TokenRing-attached SNA device (the FEP) is terminated at the router connected to the X.25 network(Router A).QLLC conversion also supports a configuration in which SNA end stations (3174 or equivalent)that are connected to a Token Ring reach the FEP through an X.25 connection, as shown inFigure 5-22.In this case, IBM Network Packet Switching Interface (NPSI) software is installed onthe FEP.Figure 5-22 QLLC conversion supports SNA end-station connections over Token Ringand X.25 networks.TokenX.25 networkRingRouter3174 FEPSummaryThis chapter addresses some of the special requirements for implementing routing technology withinIBM System Network Architecture (SNA) environments.It describes the three techniques designedto enable internetworking capabilities for SNA-based network architectures, as follows:" SDLC via STUN" SDLLC Implementation" QLLC Conversion5-26 Cisco CCIE Fundamentals: Network DesignC H A P T E R 6Designing APPN InternetworksAdvanced peer-to-peer networking (APPN) is a second generation of the Systems NetworkArchitecture (SNA) from IBM.It moves SNA from a hierarchical, mainframe-centric environmentto a peer-to-peer environment.It provides capabilities similar to other LAN protocols, such asdynamic resource definition and route discovery.This chapter focuses on developing the network design and planning a successful migration toAPPN.It covers the following topics:" Evolution of SNA" When to Use APPN as Part of a Network Design" When to Use APPN Versus Alternative Methods of SNA Transport" Overview of APPN" Scalability Issues" Backup Techniques in an APPN Network" APPN in a Multiprotocol Environment" Network Management" Configuration ExamplesNote Although this chapter does discuss using APPN with DLSw+, for detailed information onusing DLSw+, refer to Chapter 7, Designing DLSw+ Internetworks.Evolution of SNAIntroduced in 1974, subarea SNA made the mainframe computer running AdvancedCommunications Function/Virtual Telecommunication Access Method (ACF/VTAM) the hub of thenetwork.The mainframe was responsible for establishing all sessions (a connection between tworesources over which data can be sent), activating resources, and deactivating resources.The designpoint of subarea SNA was reliable delivery of information across low-speed analog lines.Resourceswere explicitly predefined.This eliminated the need for broadcast traffic and minimized headeroverhead.Many enterprises today maintain two networks: a traditional, hierarchical SNA subarea network andan interconnected LAN network that is based on connectionless, dynamic protocols.The advantageof the subarea SNA network is that it is manageable and provides predictable response time.Thedisadvantages are that it requires extensive system definition and does not take advantage of thecapabilities of intelligent devices (for example, the PCs and workstations).Designing APPN Internetworks 6-1Evolution of SNARole of APPNWith APPN, you can consolidate the two networks (an SNA subarea network and an interconnectedLAN network) because APPN has many of the characteristics of the LAN networks and still offersthe advantages of an SNA network.The major benefits of using APPN include the following:" Connections are peer-to-peer, allowing any end user to initiate a connection with any other enduser without the mainframe (VTAM) involvement." APPN supports subarea applications as well as newer peer-to-peer applications over a singlenetwork." APPN provides an effective routing protocol to allow SNA traffic to flow natively andconcurrently with other protocols in a single network." Traditional SNA class of service (COS)/transmission priority can be maintained.As SNA has evolved, one feature has remained critical to many users: COS.This feature providestraffic prioritization on an SNA session basis on the backbone.This, in turn, allows a single user tohave sessions with multiple applications, each with a different COS.In APPN, this feature offersmore granularity and extends this capability all the way to the end node rather than just betweencommunication controllers.Types of APPN NodesAn APPN network has three types of nodes: LEN nodes, end nodes (EN), and network nodes (NN),as shown in Figure 6-1.Figure 6-1 Different types of APPN nodes.NNNN NNENAPPNENNN NNENCP-CP session pairLEN nodeEN = end nodeNN = network nodeNote Throughout the rest of this chapter, the abbreviations EN and NN are used in the illustrations.The full terms (end node and network node) are used within the text for clarity.Table 6-1 describes these different types of APPN nodes.The control point (CP), which isresponsible for managing a node s resources and adjacent node communication in APPN, is key toan APPN node.The APPN Control Point is the APPN equivalent of the SSCP.6-2 Cisco CCIE Fundamentals: Network DesignWhen to Use APPN as Part of a Network DesignTable 6-1 Different Types of APPN NodesType of APPN Node DescriptionLocal Entry Networking LEN nodes are pre-APPN, peer-to-peer nodes.They can participate in an APPN network(LEN) nodes by using the services provided by an adjacent network node.The CP of the LEN nodemanages the local resources but does not establish a CP-CP session with the adjacentnetwork node.Session partners must be predefined to the LEN node, and the LEN nodemust be predefined to the adjacent network node.LEN nodes are also referred to as SNAnode type 2.1, physical unit (PU) type 2.1, or PU2.1.End nodes End nodes contain a subset of full APPN functionality.They access the network throughan adjacent network node and use the adjacent network node s routing services [ Pobierz całość w formacie PDF ]

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