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Network Protocols

Network protocols define the sets of rules governing communication between nodes on a network. Timing, format, sequencing, error control, routing, reliability, and security are all considerations that network protocols either have or will encompass. To cope with burgeoning network complexities, protocols are broken down into steps or layers, each with its own set of rules for operation and data organization. Each layer, in essence, is its own protocol.

Modern datacom is founded on the principles of Shannon's information theory, which consists of a set of elegant mathematical models for describing stochastic processes and ergodic systems made up of such processes. These models give rise to a probabilistic approach to data encoding and transmission characteristics. With Shannon, the ability to encode and effectively transmit binary codes in an environment that is always prone to noise (transmission errors) is made tractable. The stack approach to datacom is enabled at the lowest level by Shannon. The physical transmission of bits, which are transcribed and framed at the Data Link layer (OSI 7-layer model), relies almost completely on Shannon's information theory. Modern data transmission protocol inventions like DSL, 802.11, Bluetooth, are all founded on Shannon's work.[37]

There are a lot of datacom protocols. Novell offered a proprietary stack called internetworking packet exchange/sequenced packet exchange (IPX/SPX) for use with their NetWare operating system, one of the early players in the PC-networking space. Another is NetBIOS (network basic input/output system) from IBM, a now-standard interface that permits PC applications to communicate directly with other PCs at the transport layer. Which brings us to Transmission Control Protocol/Internet Protocol (TCP/IP), the standard that enables the internet. Loosely based on the ISO OSI 7-layer model,[38] TCP/IP provides basic networking capabilities for computing nodes that provide and consume Internet resources.

Myriad protocols building on top of TCP/IP give rise to other interesting applications. The now-indispensable browser relies on HyperText Transfer Protocol (HTTP), which operates above the transport layer, as do File Transfer Protocol (FTP), Simple Mail Transfer Protocol (SMTP), and Simple Network Management Protocol (SNMP). With the advent of Web Services, additional network protocols are being considered to enable a new generation of networked applications. Baked-in security and reliability, for example, are both required at the protocol level if the Web Services vision is to be realized. Indeed, additional protocols that build on top of the transport layer are becoming quite common and are likely being utilized as competitive differentiators in a business sense as much as they are standardized communication frameworks in a more secular NDC sense.

In NDC, communications protocols are of utmost importance. Indeed, many of the topics covered later in this volume contain discussion of the protocols germane to them. Suffice it to state here that network protocols are as abundant and complex as are the broad categories of NDC itself—that is, evolutionary forces will likely trim this fitscape too, given sufficient time, consumption, and investment.

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