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Section 3 LAN Interconnectivity Basics
Mainstream networks in the late 1990s no longer consist of standalone LANs. Rather, networks are constructed from a close alliance of traditional LAN technologies and LAN interconnection technologies. A mastery of both is essential for the network designer tasked with providing high-performance LANs in support of value-added business solutions.
Throughout the 1980s and well into this decade, considerable attention was given to the Holy Grail of interconnectivity known as the OSI reference model. It was believed by many that when OSI arrived, diverse, but OSI-compliant systems would simply plug and play, resulting in universal connectivity. More recently, it appears that OSI has either simply disappeared or has been replaced by TCP/IP. In fact, no network or IS manager should be without at least a basic knowledge of TCP/IP. Chapter 3-1, TCP/IP Essentials, provides a good primer for those not well versed in this critical technology, and can serve as a good refresher for those with some TCP/IP experience.
Just as other technologies refuse to stand still, the same can be said for TCP/IP. Chapter 3-2, Practices for IP Addressing and Routing, describes the latest developments in IP addressing and how they affect the all-important routing function. The chapter emphasizes recent advances designed to improve the efficiency of both routing and IP address utilization.
With all the emphasis on TCP/IP, many readers are probably wondering, What really happened to OSI? The fact of the matter is that OSI has neither gone away nor will it ever arrive in a readily identifiable fashion. Instead, OSI principles and concepts have found their way into the design of many networking components and specifications in use today. The most important of these concepts is that of layer independence, and no matter what name is attached to the means of achieving it, the most important objective of OSI is interconnectivity. Chapter 3-3, Internetworking at the Physical and Data Link Layers, describes in substantial detail, the state of the practice in providing the functions defined for OSI Layers 1 and 2.
Despite the attention devoted to global interconnectivity via the Internet, interoffice connectivity remains of paramount importance, both for networking managers and business managers, especially those advocating the virtual organization concept. The need to remain cost-effective while delivering service to end users who have ever-higher expectations has become a difficult balancing act, indeed. Chapter 3-4, A Frame Relay Primer, takes a close look at the role this Layer 2 (data link layer) technology can play in solving the paradox through the combined effect of frame relays service stability and its economic advantages compared with dedicated leased line networks.
In the not-so-distant past, it was easy to distinguish between LAN technologies and interconnection technologies. Put simply, a hub was a hub and a router was a router. As indicated in the previous section of this Handbook, the line between the two is rapidly blurring with the advent of hubs that also perform switching and routing functions. Having looked at some pure interconnectivity technology, we are now positioned to resume our discussion on the merger of LAN and LAN interconnection technologies by taking a look at the reasons for this trend as well as a closer look at the technology itself, starting with Chapter 3-5, Desktop Evolution Driving Connectivity Technologies.
Chapter 3-6, Tutorial on LAN Switching, continues the discussion on switching by taking a more in-depth look at the technology behind the switch. The chapter compares and contrasts different switch designs, such as store-and-forward, cut-through, and adaptive-cut-through, and discusses other factors of importance to the network designer.
Chapter 3-7, Implementing Routing, Switching, and VLANs in Modern Corporate Networks, wraps up our discussion of switching technologies. This chapter considers three focal points for network design performance, management, and redundancy and provides a comparative assessment of routing, switching, and VLANs as alternative network designs. The chapter concludes with the observation that despite (or perhaps because of) its unprecedented complexity, network design technology of the late 1990s offers choices that allow designers to build networks around real-life functional requirements, rather than technology-bound constraints.
3-1 TCP/IP Essentials
SMOOT CARL-MITCHELL
The Transmission Control Protocol/Internet Protocol(TCP/IP) suite of networking protocols is currently the most widely used set of protocols for internetwork communication. The name TCP/IP is derived from the most widely used protocols in the suite: TCP is a byte stream protocol that provides reliable end-to-end communication between two processes running on the same or different host systems; IP is a simple best-effort packet switching protocol that allows many different interconnected networks to share the same virtual address space and form a single internetwork. From the hosts point of view, IP makes the underlying internet appear as a single virtual network.
The worlds largest computer network, the Internet, uses TCP/IP as its dominant protocol suite. The Internet today is a worldwide internet. It connects over 1.7 million hosts and has a user community estimated at approximately 30 million people. TCP/IP is also used on many corporate networks and is particularly popular with UNIX workstations. However, TCP/IP implementations can be found for almost any class of machine from PCs to supercomputers.
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