Short Tutorial on Networks and the Internet

 

Overview of Network Services 

Network services provide a transport mechanism that is at the bottom of the IT infrastructure. Network services are provided through communication networks that are a collection of equipment and physical media, viewed as one autonomous whole, that interconnect two or more stations. A station is an end-point (source/sink) in a communication network and can be a terminal, computer, telephone, sensor or a TV. A network can be configured as a wide area network (WAN) for long distance communications, a local area network (LAN) for short-haul communications within a building, or a metropolitan area network (MAN) for communications within a city. Most enterprise networks are a combination of LANs, MANs, and WANs. Physically speaking, the communication between stations on a network can use analog or digital transmission facilities over copper, wireless or fiber optic media.

The major growth in networking is interconnection and integration of LANs, MANs and WANs into large and high data rate (known as "broadband") networks. Network interconnections are based on network architectures that describe the physical components, the functions performed by the components and the interfaces between the components of a network. Network architecture standards are needed to interconnect different networks from different vendors with different capabilities.

The Open System Interconnection (OSI) Reference Model, shown in Figure 1 specifies standards for networks from different vendors to exchange information with each other. The model describes network services in terms of 7 layers, but the lowest 4 layers are devoted to network services. These services are responsible for routing and transporting your messages in an error-free manner across a network. A common example of layered network protocols is the TCP/IP (Transmission Control Protocol/Internet Protocol) that is at the foundation of the Internet.   

Figure 1: Conceptual View of OSI Network Model

Network Interconnectivity

Network interconnectivity is needed in large networks to provide interfaces and transport of messages between remotely located users, applications, databases, and devices. For example, if you access the Paris University Web site from Chicago, then many interconnectivity devices are used to get you from Chicago to Paris. The two principal network interconnectivity devices are:

Many routers and gateways are used commonly in enterprise networks and the general Public Internet. For example, if a salesman in Detroit needs to access a customer database in New York, then a series of routers and gateways would be needed to find the path between the two cities. Figure 2 shows a realistic enterprise network that uses TCP/IP very heavily, except the IBM SNA network (an old network technology) at the mainframe. The routers are used between all TCP/IP network segments and gateways are used to convert the TCP/IP messages to SNA and the Novell protocol.

Figure 2: Network Interconnectivity in an Enterprise Environment

Broadband and Wireless Networks

The advancements in network transmission technologies have resulted in high data rate local and wide area transmissions, typically in the range of 100 million bits per second (Mbps) or higher (Gigabit networks). Examples of the evolving network communication technologies are Asynchronous Transfer Mode (ATM), Frame Relay, Fiber Distributed Data Interface (FDDI), and wireless networks. In general, networks are becoming faster, ubiquitous and more reliable. Another area of advancement is the integration of voice, data and video images for multimedia applications such as teleconferencing and group problem solving, among others. In particular, Next Generation Networks (NGNs) combine the voice and data networks into an integrated high speed network.

Wireless networks, as the name implies, interconnect devices without using wires -- instead they use the air as the main transmission medium. Wireless networks are enjoying widespread public approval with a rapidly increasing demand. The increase in the number of cellular phones, palm pilots, laptops, notebooks, and other handheld devices is phenomenal. To meet this demand, mobile communications technologies are emerging with digital speech transmission and the ability to integrate cordless systems into other networks. In the meantime, researchers are developing the next generation of technologies for several years to come.

The unique features of the wireless networks are:

A very large body of work on wireless networks exists with emphasis on different aspects such as radio transmission technologies, standards, protocols, systems engineering, and carriers. For our purpose, wireless networks can be broadly classified in terms of wireless local area networks, wide area networks and metropolitan area networks (see Figure 3).

Figure 3: A View of Wireless Network Landscape

IP Networks and the Internet

Internet is of particular interest to e-business, since more than 80% of the e-business activities are expected to be conducted over the Internet. The origin of Internet is the ARPANET (Advanced Research Projects Agency Network) that was initiated in 1969 to support researchers on DOD (Department of Defense) projects. For many years, Internet was used mainly by scientists and programmers to transfer files and send/receive electronic mail. The users of Internet relied on text-based user interfaces and tedious commands to access remote computing resources. In 1989, this changed with the introduction of World Wide Web (WWW), commonly referred to as the Web. Technically speaking, Internet is a large collection of IP (Internet Protocol)-based networks that are interconnected through a wide range of interconnection devices. IP networks reside on a variety of physical network elements (e.g ., ATMs, DSL, wireless networks) to support Web technologies. The Web has been a major contributor in turning the Internet, once an obscure tool, into a household word. The Web allows users to access, navigate and share information around the globe through GUI clients ("Web browsers") that are available on almost all computing platforms. The Web browsers allow users to access information that is linked through hypermedia links. Thus a user transparently browses around, or "surfs" around, different pieces of information that is located on different computers in different cities and even in different countries. In addition to Web, the IP-based networks are being used for a wide range of applications such as Internet Telephony, video conferencing, and corporate computing.

Technically speaking, Internet is a network based on the TCP/IP protocol stack. At present, the term Internet is used to refer to a large collection of TCP/IP networks that are tied together through network interconnectivity devices such as routers and gateways . The TCP/IP (Transmission Control Protocol/Internet Protocol) was developed in the late 1960s and early 1970s by the Defense Advanced Research Projects Agency (DARPA). TCP/IP was developed for interconnecting many computers in the ARPANET (Advanced Research Projects Agency Network). ARPANET initially consisted of five protocols (indicated with * in the following list) that have been augmented with other key protocols (see Figure 4):

Figure 4 The IP Stack – Foundation of Internet

Although, the Internet at present uses TCP (i.e., higher level protocols and applications are based on TCP), this may not be true in the future since some future (especially real time) applications may be built directly on IP or newer alternatives to TCP. The main strength of IP is that it runs on top of a very diverse array of physical networks (wide area, local area, wireless) . In fact, IP supports almost all current physical network technologies and is expected to support most of the future high speed networks. We thus will use the following simple definition of the Internet:

Definition: Internet is a network of networks that is supported by the Internet Protocol (IP).

What does this mean? Basically it says that you need to have an IP network (or a gateway that translates to IP) to join the Internet. Once you have an IP network, then you can run almost any physical network under it and take advantage of voice, data, or video applications for your e-business that run on top of IP. At present, the term Internet is used to symbolize a Public Internet that is not owned by any single entity -- it consists of many independent IP networks that are tied together loosely.

Initially, the public Internet was used to tie different university networks together. With time, several commercial and private networks have joined the public Internet. The computers on the public Internet have publicly known Internet Protocol (IP) addresses that are used to exchange information over the public Internet (we will discuss IP addresses later). The public Internet at present consists of millions of computers (PCs, Macs, Sun workstations, HP systems, IBM mainframes) that are interconnected through thousands of networks that use different underlying network technologies (ATMs, frame relays, Ethernet LANs, and wireless networks) in different parts of the world. All these computers and networks are tied together through a global IP network (see Figure 5).

Figure 5: Public Internet – A Global IP Network

Private Value Added Networks (VANs)

E-commerce (EC) requires network services, of course, but also additional “value added” services such as purchasing and billing.  Similarly, telephone network users also typically need value added services such as voice mail, call forwarding, and caller ID. Some networks, known as value added networks (VANs) bundle the value added services in addition to network transport services.  Many VAN vendors such as GEIS, AT&T, and Harbinger support EC activities through very reliable, secure and well managed private data networks and proprietary technologies. In particular, these networks support purchasing and billing quite well (i.e., purchasing by sending purchase orders and billing by supporting invoices). The well known EDI standards X850 (for purchase orders) and X810 (for invoices) are examples of VAN services for EC. However, these networks were never designed for general public advertising and browsing. In addition, VANs for EC are too expensive and require too many proprietary interfaces and software modules to support advertising and browsing services for a large number of trading partners. In many cases, the traditional proprietary VANs for EC are finding  it tough to compete with the Internet-based value added services.

Extranets and Virtual Private Networks (VPNs)

"Extra-net" or "enterprise intra-nets" are semi-private IP networks which are used to communicate within a group of interdependent communities of enterprises or trading partners. Examples of such a group of interdependent community would be the automotive industry (including parts suppliers, manufacturers, retailers, and insurers), the health care industry (including physicians, pharmacists, hospitals, labs, and health insurers), or the real estate industry (including brokers, lending agencies, insurers, lawyers, and inspectors). To succeed, Extranets need to support high quality EC services (e.g., advertising, browsing/selection, purchasing, billing, and payments) coupled with security and management considerations.

An Extranet consists of a collection of Internet segments (intranets), each protected by firewalls, which are interconnected using secure leased lines across the remote locations. This solution provides security and guaranteed bandwidth, at the cost of leasing lines from telecomm providers. In contrast, Virtual Private Networks (VPNs) achieve a similar goal (that is, securely connecting remote locations, branch offices, field workers, telecommuters, vendors, customers, and suppliers) using the public Internet instead of leased lines. Specifically, VPNs encrypt the messages to provide security.