ENTERPRISE EXTENDER: A BETTER WAY TO USE IP NETWORKS

Size: px

Start display at page:

Download "ENTERPRISE EXTENDER: A BETTER WAY TO USE IP NETWORKS"

Brett Stafford
5 years ago
Views:

1 DATA COMMUNICATIONS MANAGEMENT ENTERPRISE EXTENDER: A BETTER WAY TO USE IP NETWORKS Richard J. Tobacco INSIDE Talking Transport; By Air, Land, or Sea: Link Selection; Taking Familiar Routes: Connection Oriented; First Class or Coach: Priority Queuing; Registered Shipments: Reliable Transport; Packaging: Encapsulation; What is Enterprise Extender? Larger Number of SNA Users; No Single Point of Failure; Traffic Priority; Efficient Message Sequencing; Choosing Between Enterprise Extender or DLSw INTRODUCTION Most businesses rely on legacy applications residing on mainframes. Access to these applications and databases were through networks based on Systems Network Architecture (SNA). Newer application development is often aimed at E-business, and these applications are generally based on TCP/IP networks. Initially, business created and supported these SNA and TCP/IP networks separately. Today s cost-conscious network managers are seeking ways to consolidate their SNA traffic onto the TCP/IP network. Rewrite of the estimated $3 billion dollar investment in legacy SNA-based applications is clearly not justified. Many businesses use TN3270e as their method of accessing those SNA applications. The TN3270e client communicates over a TCP/IP network to a TN3270e server that transforms the IP data-gram into an SNA data flow. The TN3270e server can be located within the application server, on a device channel attached to the application server, or on a branch office router. Unless the TN3270e server resides within the application server, there is a SNA data flow between the TN3270e and application servers. 1 This SNA data flow can be transported across an IP network. In 1992, IBM introduced Data Link Switching (DLSw) as a means for transporting Systems Network Architecture (SNA) data across a TCP/IP PAYOFF IDEA Data Link Switching is commonly used to transport SNA traffic over an IP network. Enterprise Extender is a newer alternative that offers some compelling advantages. This article compares and contrasts the two technologies, providing the network manager with assistance in deciding which is more appropriate for his or her environment.

2 DATA COMMUNICATIONS MANAGEMENT network. As the only nonproprietary TCP/IP encapsulation scheme, DLSw 2 gained widespread acceptance by all routing vendors, and many customers use this as their method for accessing SNA applications across a TCP/IP network. Five years later, IBM created Enterprise Extender as an open alternative way to integrate SNA applications onto an IP network. Recently, Cisco Systems, Inc., announced 3 that its routers will also provide the enterprise extender function called SNA Switching Services (SNASw). Enterprise Extender is a network integration technology that provides the flexibility to build the networks that cost-conscious network managers demand. It is a technology that extends the reach of SNA applications and data across IP networks to IP-attached clients, while providing users with the levels of reliability, scalability, and control they have come to expect from mission-critical SNA-based applications. Enterprise Extender provides this integration using standard IP technology and requires no new hardware or software in the IP backbone network. The following is a quick look at the nomenclature of protocol transport and some of the differences between DLSw and Enterprise Extender. TALKING TRANSPORT A few transport analogies may aid network managers trying to describe the transport differences to fellow workers. By Air, Land, or Sea: Link Selection Companies have long had the option of selecting the mode of product shipment. Perishable goods might go by air, normal deliveries by truck, and bulky products via barge or container ship. SNA provides a similar selection; part of class-of-service, where different types of data can be transported across different links, for example, satellite, modems, or fiber. The capability to select network links based on application-specified class-of-service is only provided by SNA networking. Recent Internet Engineering Task Force (IETF) work on Differential Services has improved the ability to affect the link selection; however, Enterprise Extender allows the link to be selected. Taking Familiar Routes: Connection Oriented One drives to a favorite vacation spot along familiar roads, not altering one s route unless an unexpected detour is encountered. One knows the travel time and progress toward the final destination is readily apparent. If delayed, concerned friends might be able to ascertain one s progress by checking at one s favorite stopping spots. In networking terms, one is connection oriented. 4 Had one been out joyriding and decided the route at each intersection, one would (in networking terms) be connection-less. Data path consistency, provided by a connection-oriented network, provides similar benefits to network managers. They can view data

3 ENTERPRISE EXTENDER: A BETTER WAY TO USE IP NETWORKS EXHIBIT 1 SNA and TCP/IP Transport First versions of SNA, designed to support networks with unreliable links, were very tightly coupled with data integrity checked at each path step. Improved link quality enabled SNA to be restructured with data verification only at the endpoints. This advanced SNA High Performance Routing (HPR) separates transport functions from data integrity functions. The similarity of HPR an improved Advanced Peer-to-Peer Networking (APPN) SNA routing protocol with TCP/IP may be apparent; end stations ensure data integrity and intermediate devices forward traffic. The intermediate Automatic Network Routing (ANR) nodes forward packets, have no session awareness, and rely on the endpoints for error recovery. The endpoint Rapid Transport Protocol (RTP) nodes provide end-to-end error recovery, nondisruptive rerouting, and selective retransmission of lost packets. People familiar with TCP/IP networks will relate RTP to the TCP portion and ANR to IP part of the TCP/IP stack. Both transports are valid and leading networking products will continue to support TCP/IP and SNA. A key difference between SNA and TCP/IP transport is that HPR sessions use the same path as long as it is available, whereas TCP/IP sessions may often change paths. Because the HPR endpoints establish a path and maintain it until a failure occurs, the intermediate routing devices use routing information contained within the transmitted packets. This eliminates the need for the routing devices to make routing decisions. If there is a path change, the packet labels are changed by the RTP endpoints. Separating transport and integrity functions also means that SNA messaging characteristics can be applied to SNA applications crossing an IP network. Enterprise Extender code provides priority queuing for SNA sessions, making IP transport appropriate for business-critical applications. progress, check for congestion roadblocks, and monitor and plan for increases in traffic. High performance routing (HPR), a lower-overhead less-complex SNA, creates connection-oriented networks by providing the data path information to the routers and virtually eliminating router overhead for the SNA sessions. With Enterprise Extender, HPR-capable endpoints provide connection-oriented routes for the UDP/IP datagrams forwarded by the intermediate network routers (see Exhibit 1). First Class or Coach: Priority Queuing We have become accustomed to priorities in business. CEO air-travel arrangements are made first; they travel first class and avoid having to wait in long lines boarding or exiting the aircraft. Likewise, some data transmissions are more important to a business than others. Being able to assign priority based on the data type (e.g., interactive or batch) can mean business-critical data gets transmitted first. Access devices such as routers often create queues for data placed on the network. And IP networks can provide Type of Service (TOS) or port prioritization such that both SNA networks and the new application transport, Enterprise Extender, can provide priority transmission throughout the entire network. Registered Shipments: Reliable Transport Many have sent or received registered mail. At transfer points, the mail (or contents of a shipment) is accounted for prior to being forwarded. This additional effort of accounting for shipment integrity often results in

4 DATA COMMUNICATIONS MANAGEMENT slower and more costly delivery. If one generally finds that normal shipments reach their destination, one will rely on the final recipient to verify shipment integrity, thus reducing the cost of shipment. In TCP/IP networks, registered shipments are analogous to reliable transport and normal shipments are comparable to unreliable transport. 5 Network links have become more reliable and transmission error rates have declined significantly. Although it was more efficient, if not necessary, for SNA to verify message integrity at each transfer node in the 1960s, it is now possible to avoid the cost of additional processing overhead. Enterprise Extender uses unreliable UDP transport for forwarding SNA application data across a TCP/IP network. Message integrity is guaranteed by the session endpoints instead of each intermediate router within the network. Packaging: Encapsulation In networking parlance, placing a letter in an envelope is encapsulation. The envelope has an external address that is used by a carrier to route the letter to its destination. Once received, the envelope is discarded and the contents distributed as appropriate. DLSw is the encapsulation of SNA protocols within a TCP/IP package. The package is a usable TCP/IP address that has been discovered by the DLSw-capable routers. Likewise, Enterprise Extender is the transport of SNA protocols within a lighter UDP package. WHAT IS ENTERPRISE EXTENDER? Enterprise Extender is an extension to HPR technology that provides efficient encapsulation of SNA application traffic within UDP frames by HPR-capable devices at the edges of an IP network. To the IP network, the SNA traffic is UDP datagrams that get routed without hardware or software changes to the IP backbone. The Enterprise Extender session is normal SNA with predictable performance and high availability. Unlike gateways, there is no protocol transformation and, unlike most common tunneling mechanisms, the encapsulation is performed at the routing layers without the overhead of additional transport functions. Enterprise Extender enables efficient use of the IP infrastructure for support of IP-based clients accessing SNAbased data. Enterprise Extender is currently supported on all IBM Communication Servers and routers, on IBM Personal Communications products (TN3270e client), on Cisco routers (as SNASw), and within the operating system of System/390 servers. 6 Enterprise Extender can be implemented in traffic consolidating communications servers or remote routers or within a single end user s Personal Communications product. Terminat-

5 ENTERPRISE EXTENDER: A BETTER WAY TO USE IP NETWORKS ing this traffic within a System/390 enables pure IP transport by existing routers and eliminates many shortcomings of DLSw TCP encapsulation. Larger Number of SNA Users At both the sending and receiving locations, DLSw-capable routers terminate the SNA connection and locally acknowledge transmissions. Connection setup and maintenance is process intensive, involving link-level acknowledgment, TCP retransmit, congestion control, protocol translation, and data store-and-forward. This is a significant router burden even to the more powerful routers. Very often, the expensive data center DLSw router is incapable of supporting more than a few hundred SNA users. Enterprise Extender eliminates the termination and acknowledgment workload, thereby enabling the routers to handle a much larger number of users. Because Enterprise Extender uses end-system to end-system congestion control and connectionless UDP, there are no TCP retransmit buffers, no timers, and no congestion control logic in the router. Because of these savings, the edge routers can concentrate on the job they do best forwarding packets rather than providing protocol translation and maintaining many TCP connections. Enterprise Extender allows the existing data center routing platforms to handle larger networks and larger volumes of network traffic. In similar network configurations, the same router has been measured to be up to ten times faster when using Enterprise Extender rather than DLSw. No Single Point of Failure Enterprise Extender leverages the inherent availability features of IP to provide failure-resistant SNA application access. With DLSw, the data center router, where termination and acknowledgment occurs, is a single point of failure. Should this router fail, although an alternate path may exist, all SNA connections would be disrupted and would have to be reestablished. Because Enterprise Extender does not terminate the session flow, it can support the IP reroute capability, maintain the connection, and switch to an alternate path without session disruption. When Enterprise Extender is operating within S/390 Parallel Enterprise Servers (Parallel Sysplex), 7 the UDP/IP flow extends into the sysplex. The HPR-controlled session over an IP network is from the end user all the way to the application on the server. This provides applications full parallel sysplex support in the event the original application processor fails, it can move to another processor without terminating the original session. This results in five nines availability of the legacy SNA application ( percent availability) running on OS/390 with no changes to the SNA applications.

6 DATA COMMUNICATIONS MANAGEMENT Enterprise Extender eliminates a TCP/IP network connection into the server with a stub SNA session between the gateway routing device and the server. Extending the UDP/IP flow into the S/390 server also eliminates the complexity of multiple gateways each supporting several hundred TN3270 sessions. 8 The data center router or switch can be ES- CON channel attached or use the recently available gigabit Ethernet adapter for high-speed IP attachment 9 to the S/390 server. And, recent S/390 operating system enhancements have eliminated the single access and further improved TCP/IP stack availability. Traffic Priority Most routers provide some form of prioritized queuing; however, the difficulty has been to properly identify the priority at which an SNA packet should be sent. With DLSw, for example, where traffic prioritization is handled on a link basis, multiple links must be defined to the same SNA device. Other traffic prioritization techniques either have no capability to provide SNA priority, require guesswork, or adherence to addressing conventions. Enterprise Extender ends this guesswork and configuration overhead and provides real priority by mapping the priority of SNA packets to UDP port numbers that routers within the IP network can easily use to properly handle the traffic. 10 Efficient Message Sequencing DLSw uses TCP/IP reliable transport to avoid messages arriving at their destination scrambled or out of sequence. This is because although higher layers of SNA could correct scrambled messages, correction can require significant retransmission that would severely impact response times. Enterprise Extender employs congestion avoidance (Adaptive Rate-Based) and selective retransmission of lost packets. When only an occasionally missing message part has to be selectively retransmitted, instead of the missing segment and all segments following it, the HPR-capable endpoints manage the retransmission with little effect on response times. Choosing Between Enterprise Extender or DLSw Today there are no ubiquitous network solutions. Thousands of native SNA transport networks have provided unsurpassed reliability and predictability. Emerging E-business opportunities rely on the Internet, intranets, and internal TCP/IP networks. Companies deciding how to merge these SNA and TCP/IP networks should consider both Data Link Switching and Enterprise Extender. Consider the total cost of ownership. Are the routers currently in the network capable of supporting DLSw? Do existing routers have the capacity to handle the increased DLSw workload? Are the current network

7 ENTERPRISE EXTENDER: A BETTER WAY TO USE IP NETWORKS devices capable of providing HPR support to Enterprise Extender? What is the skill set of the people within the organization? Will education offset any savings in initial purchase prices? How much will it cost to maintain the solution? Consider implementation implications. Are skills currently available or will they have to be recruited? How long will it take to redesign and upgrade the current network? Does one want to maintain the current IP network without change? Does one want gigabit Ethernet attachment into the S/390 server? Does one want to use TN3270 servers to transform from IP-based to SNA-based data flows? Where will one locate and how will one maintain any TN3270e servers? How will current decisions affect future network plans? How one consolidates the networking will affect future growth and acquisition plans. External E-business customers, business partners, as well as internal executives may see one s network performance. Therefore, choose wisely network consolidation decisions will impact business. Notes 1. Enterprise Extender also supports communication between a DLUR and S/390, between APPC applications or between S/390 servers. 2. Although DLSw is nonproprietary (RFC 1795), implementations (such as Cisco Systems Inc. DLSw+) are proprietary. The additional features provided by proprietary extensions are only useable in a single vendor implementation. Multi-vendor DLSw implementations will revert to a restricted base-set of functions. 3. September 7, 1999, News Release: Cisco Introduces an Easier, More Scalable SNA Solution for IP Infrastructures. 4. Technically, the connection-oriented and connection-less definitions depend on the presence of session set-up/tear-down protocol and control blocks within the routing device. The less common descriptor pinned-route may be a more acceptable answer. 5. This is TCP/IP network nomenclature only and hopefully the U.S. Post Office will not take offense with the analogy. 6. Enterprise Extender is available on Communications Server for OS/390 V2R6 (or later) as a base component of OS/ IBM, Parallel Sysplex, and S/390 are trademarks of the IBM Corporation. 8. Communications Server for OS/390 has tested support of 64,000 TN3270 sessions. Continuing the DLSw flow to the S/390 also eliminates the complexity of multiple TN3270-capable routers. 9. The gigabit Ethernet adapter on S/390 servers only supports IP flows. Enterprise Extender is the recommended method of high-speed access to SNA applications. 10. The routers must support TOS or port prioritization. Because segmented packets lose port number prioritization, TOS is preferred. Richard J. Tobacco has more than 15 years of experience in sales support and marketing of networking products. He currently works for the Network Computing Software Division of IBM as the Brand Manager for Communications Server for OS/390.

SNIA Discussion on iscsi, FCIP, and IFCP Page 1 of 7. IP storage: A review of iscsi, FCIP, ifcp

SNIA Discussion on iscsi, FCIP, and IFCP Page 1 of 7 IP storage: A review of iscsi, FCIP, ifcp SNIA IP Storage Forum With the advent of new IP storage products and transport protocol standards iscsi, FCIP,