Local Area Network Operating Systems and Remote Access

CHAPTER 9 LOCAL AREA NETWORK OPERATING SYSTEMS AND REMOTE ACCESS Concepts Reinforced OSI model Top-down model Protocols and standards Hardware/software compatibility Network architectures Concepts Introduced Network operating system Functional network analysis functionality Client/server network operating Peer-to-peer network operating systems systems Network operating systems Network technology analysis architectures Client network operating systems Server network operating systems Remote access Remote control Mobile computing Remote access security OBJECTIVES After mastering the material in this chapter you should: 1. Understand the compatibility issues involved with implementing LAN software. 2. Understand the basics of network operating system functionality. 3. Understand the important differences between peer-to-peer and client/ server network operating systems architectures. 4. Understand the emerging role of the client network operating system and the universal client. 5. Understand how to analyze functional networking requirements and match those requirements to available technology. Network Operating Systems Overview 337 ■ INTRODUCTION Network operating systems, like most other aspects of data communications, are undergoing tremendous change. As a result, before examining the operational characteristics of a particular network operating system, it is important to gain an overall perspective of network operating systems in general. In particular, network operating systems architectures are in a state of transition from closed environments in which only clients and servers running the same network operating system could interact, to open environments in which universal clients are able to inter-operate with servers running any network operating system. In this chapter network operating system functionality is examined for both client and server network operating systems. This functionality is representative of current network operating systems in general rather than any particular product. With the evolution of portable computers and the Internet users need to gain access to an organization’s data from a variety of locations other than the traditional office setting. One of the most important things to understand about such remote access is the relatively limited bandwidth of the wide area network links that individ- uals will use to connect to the main office information resources. Although the goal of remote access may be to offer transparent remote connectivity, decreases in bandwidth by a factor of 100 on WAN links as compared to LAN links cannot be ignored. The overall goal of the second half of this chapter is to outline a methodology for the proper design of remote access solutions based on a thorough understanding of user needs, network architecture alternatives, and available technology. ■ NETWORK OPERATING SYSTEMS OVERVIEW Traditionally, there were two major product categories of network operating systems: peer-to-peer and client/server. In a peer-to-peer network operating system, individual workstations can be configured as a service requester (client), a service provider (server), or both. The terms client and server in this case describe the workstation’s functional role in the network. The installed network operating system is still considered a peer-to-peer network operating system, because all workstations in the network use the same networking software. Designed as a low cost, workgroup solution, peer-to-peer network operating systems lacked the ability to offer central- ized authentication and authorization and suffered from exponential performance decreases as the number of users increased. As a result, peer-to-peer network operating systems were often characterized as lacking scalability. In contrast to the homogeneous, peer-to-peer software environment, traditional client/server network operating systems require two distinct software products for client and server computers. The specialized client software required less memory and disk space, and was less expensive than the more complicated and expensive server software. The client software was made to interact with the corresponding server software. As a result, although traditional client/server network operating systems over- came the scalability limitation of peer-to-peer network operating systems, they did not necessarily overcome the interoperability limitation. Functionally, client/server network operating systems offered faster, more reliable performance than peer-to-peer LANs and well as improved administration, scalability, and security. 338 Chapter Nine/Local Area Network Operating Systems and Remote Access Functional Requirements of Today’s Network Operating Systems Although traditional peer-to-peer and client/server network operating systems successfully met the functional requirements for workgroup and departmental computing, as these departmental LANs needed to be integrated into a single, cohesive, interoperable, enterprise-wide information system, the limitations of these traditional NOS (network operating system) architectures became evident. In order to understand the architectural specifications of today’s network operating systems, it is first necessary to understand the functional requirements that these network operating systems must deliver. In taking a top-down approach to network operating system requirements analysis, one might ask, “What are users of an enterprise-wide information system demanding of a network operating system in terms of services?” The answer to this question lies in the application layer of the top-down model. Given that it is distributed applications that will enable enterprise- wide productivity and decision making, the underlying network operating systems must support these distributed applications by supplying the message services and global directory services required to execute these applications in an enterprise- wide, multiple server environment. Figure 9-1 illustrates these functional requirements and contrasts them with the requirements traditionally demanded of client/server and peer-to-peer network operating systems. As illustrated in Figure 9-1, the new or emerging demands being put on network operating systems are application services, directory services, and integration and migration services. In order to successfully meet these functional requirements, network operating system architectures have shifted from integrated, single-vendor client/server network operating systems to independent, distinct, multivendor, client and server network operating systems. The functional characteristics of these distinct client and server network operating systems are described in detail later in this chapter. Figure 9-2 illustrates this architectural shift in network operating system development. All services delivered seamlessly across multiple server platforms regardless of installed network operating system Traditional Requirements Emerging Requirements FILE PRINTER APPLICATION DIRECTORY INTEGRATION/MIGRATION SERVICES SERVICES SERVICES SERVICES SERVICES Database back-end Global directory or Allow multiple different client engines naming services network operating systems to Messaging and All network objects transparently interoperate with communication defined in single multiple, different server back-end engines location and shared network operating systems by all applications Provide easy-to-implement SUPPORT FOR: Directory information paths for upgrades to more 32 bit symmetrical is stored in replicated, recent versions or migration to multi-processing distributed databases different network operating Pre-emptive multi- for reliability, systems tasking redundancy, fault Applications run in tolerance protected memory mode Multithreading Figure 9-1 Required Network Operating System Services: Traditional vs. Current Network Operating Systems Overview 339 Client/Server Network Operating System NOS-specific communication servers. workstations. server software installed on client software installed on Network operating system specific Network operating system specific Client-portion, Departmental solution Server-portion, same NOS same NOS Clients and servers of same network operating system are able to easily communicate Client Network Operating System —and— Server Network Operating System NOS-independent communication network operating system operating system desired. install whatever client network Client workstations are able to client software or other server’s Network operating system server software can vary independently of Client NOS Enterprise solution Server NOS Independently installed client Universal and server network operating Multi-Protocol systems provide enterprise- Clients wide transparent client-to- Servers server interoperability Figure 9-2 Client/Server NOS vs. Client and Server NOS Client Network Operating Systems: The Universal Client Client network operating systems, as illustrated in Figure 9-2, integrate traditional operating system functionality with highly configurable networking features to enable communication with a variety of network operating system servers. The client workstation’s ability to interoperate transparently with a number of different network operating system servers without the need for additional products or configurations breaks the traditional hard linkage between client and server NOS. This ability is commonly referred to as universal client capability. Server Network Operating Systems Because the client and server platforms

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