51-20-02 Enterprise Networks—The Challenges Previous Screen Keith G
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51-20-02 Enterprise Networks—The Challenges Previous screen Keith G. Knightson Payoff Establishing an enterprise network is a difficult and complex task. This article recommends that time and effort be spent in thoroughly analyzing the networking options and vendor offerings. Such investment and the production of a blueprint for the enterprise network architecture will prevent expensive surprises and disruptions in communications within the enterprise. Introduction “Enterprise networks” and “entrprise networking” are buzz buzz phrases of the 1990s. They are on every salesperson's lips, together of course with “open” and “open systems.” Many products are glowingly described with these phrases. Creating an enterprise network, however, requires more than just a knowledge of buzzwords. This article explains the basic subtleties of an enterprise network and the challenges of establishing one. The Next Generation of Enterprises There is nothing particularly mysterious about the word enterpriseor its intent. This is nothing more than a fancy name for a given company or organization. It conveys, however, the notion of a geographically dispersed, multifaceted organization, an organization comprising many branches, departments, and disciplines (e.g.,marketing, manufacturing, finance, administration). It represents an organization with some overall business objective—making automobiles or banking, for example. So, the word enterprise really represents the totality of an organization. In the past, the networking and information technologies deployed in an enterprise were many and various. In some cases, this occurred because of local departmental or work group autonomy, or simply because of accidental ignorance among different parts of the enterprise as to what information systems were being used, or it was an artifact of historical equipment acquisition procedures. The allegiance of specific departments to particular vendors, either because of previous successful projects, political decisions, or better local salesmanship by a particular vendor, was also a factor. The simple passing of time causes different parts of an organization to be playing leap-frog in terms of product life cycles and acquisition financing. Because acquisition of capital equipment usually is performed gradually rather than implemented all at once, across the board, so it has been difficult to make sure that all equipment is mutually compatible. Finally, the lack of an enterprisewide view, strategy, or policy with respect to networking and information technology, and unawareness of the possible convergence solutions, are contributing considerations. What IS an Enterprise Network? In the same sense that the word enterprise conveys the totality of an organization's operations, the phrase enterprise network means combining all the networking and information technology and applications within a given enterprise into a single, seamless, consolidated, integrated network. The degree of integration and consolidation may vary; total integration and Previous screen consolidation may not be always achievable, as this article will show. The first example is an organization that has an System Network Architecture network from IBM Corp. and a DECnet from Digital Equipment Corp. In all probability, these two networks have their own communications components; there might be one set of leased lines serving the SNA network and another completely independent set of leased lines serving the DECnet. It would be useful if all the IBM users could intercommunicate with all Digital Equipment Corporation users, but a first and evolutionary step might be to have both the SNA network and DECnet share the same leased lines. Now, only one physical network has to be managed instead of two separate ones, and more efficient and cost-effective sharing of the physical communications plant can be achieved. A second step might be to interconnect the mail systems of the two networks to achieve at least the appearance of a single enterprisewide electronic mail system. A third step might be to unify the data and information and its representation as used within the organization. This would enable basic forms of data to be operated on by many applications. The challenges of building an enterprise network fall into two distinct categories: getting the data (i.e., information) from A to B; and enabling B to understand the data when it receives it from A. These two categories are referred to in this article as the“networking challenge,” and the “beyond the networking challenge.” In this context, network is used as it is in the Open Systems Interconnection (OSI) reference model, that is, layer 3 and below. The Networking Challenge The networking part of the problem has three major components: · Choosing from and integrating the many network technologies. · Selecting from the many vendor solutions. · Moving information from a local to a global environment. Network Technologies The first basic problem with networks is that there are so many of them. In this context, networks are taken to mean the raw network technologies—leased lines (i.e., T1 and T3), X.25, Integrated Services Digital Network, frame relay, Asynchronous Transfer Mode, and t he many and various LAN access methods. If all the users in an enterprise are connected to the same network technology, there is no problem. Unfortunately, this is never likely to be the case, and communication between users on dissimilar networks (e.g., two different LANs) is where the problem occurs. Each network technology has its own characteristics and inherent protocols. From an enterprise viewpoint, this is very bad news. For example, users connected to an X.25 network cannot easily be connected to those already connected to a LAN. How, for example, would the X.25 user indicate the destination's Media Access Control address, and vice-versa? X.25 networks understand only X.25 addresses, and LANs understand only MAC addresses. The differences between network technologies and native protocols almost invariably prevent their direct interconnection. Differences in addressing schemes present another difficulty. Addressing considerations alone will typically dictate the use of a Previous screen Network Interconnection Device at the point at which two network technologies come together. Exhibit 1 illustrates several network technologies, represented by N1,N2, N3,N4. Each of these technologies has its own native protocol (i.e., P1, P2,P3,P4). The Interoperability Problem A way must be found to integrate all these disparate technologies into a single supernetwork, with globally uniform and globally understood characteristics and a single addressing scheme. This is achieved by operating an integrating, unifying protocol(shown in Exhibit 2 as Px), sometimes known as an internet protocol, over the top of all the possible basic communications networks. The Internet Protocol (IP) of TCP/IP is one such protocol. The Connectionless Network Layer Protocol (CNLP)specified in the Open Systems Interconnection International Standard (IS) 8473 is another. Proprietary systems have their own internet protocols (e.g., Novell uses its Internetwork Packet eXchange and Banyan uses Vines). The Interoperability Solution From the architectural standpoint, the technical term for such an internet protocol is subnetwork independent convergence protocol(SNICP). The protocols used on real-world communications networks (e.g., leased lines, X.25, frame relay, LANs) are known as subnetwork access control protocols (SNACP). Readers interested in obtaining a more detailed technical understanding about the network layer architecture and principles of internetworking should consult IS 8648,Internal Organization of the Network Layer. The basic internetworking architecture is shown in Exhibit 3. Network Layer Architecture Unification does not mean simplification. Two protocols operating over a given subnetwork still require two address schemes. Routing tables are then needed in the Network Interconnection Device to map the global enterprise address to the address to be used by the network interconnection device (NID) for the next link in the composite path. Exhibit 4 is a simplification of how the two addresses are used. In practice, the “next” address may be more complex, depending on the internetworking protocols under consideration. A network interconnection device (NID) of this type is called a router. Simplified View of Addressing Vendor Solutions The second basic problem is that each system vendor has a vendor-specific idea of how to build the supernetwork—the type of supernetwork protocol, theglobal addressing scheme, and the internal routing protocols to be used. At worst, this leads to a multiprotocol network, which amounts to several separate internets operating in parallel over the same physical communications plant. Previous screen Previous screen Previous screen Previous screen An alternative to the multiprotocol network is to choose a single protocol for the Previous screen entire enterprise supernetwork. This inevitably requires finding techniques to accommodate the systems that do not inherently operate this chosen protocol. Such techniques include encapsulation (sometimes called tunneling) at the edges of the single-protocol network, or other techniques (e.g., transport service interfaces and application gateways). However, even with a single protocol, tunneling permits only the coexistence of incompatible systems; there can be little or no interaction between each of the tunneled applications.