Types of Networks

Types of Networks

Below is a list of the most common types of computer networks in order of scale.

Personal Area Network

A personal area network (PAN) is a computer network used for communication among computer devices close to one person. Some examples of devices that are used in a PAN are printers, fax machines, telephones, PDAs and scanners. The reach of a PAN is typically about 20-30 feet (approximately 6-9 meters), but this is expected to increase with technology improvements.

Local Area Network

A local area network (LAN) is a computer network covering a small physical area, like a home, office, or small group of buildings, such as a school, or an airport. Current wired LANs are most likely to be based on Ethernet technology, although new standards like ITU-T also provide a way to create a wired LAN using existing home wires (coaxial cables, phone lines and power lines)

Campus Area Network

A campus area network (CAN) is a computer network made up of an interconnection of local area networks (LANs) within a limited geographical area. It can be considered one form of a metropolitan area network, specific to an academic setting.

In the case of a university campus-based campus area network, the network is likely to link a variety of campus buildings including; academic departments, the university library and student residence halls. A campus area network is larger than a local area network but smaller than a wide area network (WAN) (in some cases).

The main aim of a campus area network is to facilitate students accessing internet and university resources. This is a network that connects two or more LANs but that is limited to a specific and contiguous geographical area such as a college campus, industrial complex, office building, or a military base.

A CAN may be considered a type of MAN (metropolitan area network), but is generally limited to a smaller area than a typical MAN. This term is most often used to discuss the implementation of networks for a contiguous area. This should not be confused with a Controller Area Network. A LAN connects network devices over a relatively short distance. A networked office building, school, or home usually contains a single LAN, though sometimes one building will contain a few small LANs (perhaps one per room), and occasionally a LAN will span a group of nearby buildings. In TCP/IP networking, a LAN is often but not always implemented as a single IP subnet.

Metropolitan Area Network

A metropolitan area network (MAN) is a network that connects two or more local area networks or campus area networks together but does not extend beyond the boundaries of the immediate town/city. Routers, switches and hubs are connected to create a metropolitan area network.

Wide Area Network

A wide area network (WAN) is a computer network that covers a broad area (i.e. any network whose communications links cross metropolitan, regional, or national boundaries). Less formally, a WAN is a network that uses routers and public communications links.

Contrast with personal area networks (PANs), local area networks (LANs), campus area networks (CANs), or metropolitan area networks (MANs), which are usually limited to a room, building, campus or specific metropolitan area (e.g., a city) respectively. The largest and most well-known example of a WAN is the Internet.

A WAN is a data communications network that covers a relatively broad geographic area (i.e. one city to another and one country to another country) and that often uses transmission facilities provided by common carriers, such as telephone companies. WAN technologies generally function at the lower three layers of the OSI reference model the physical layer, the data link layer, and the network layer.

Global Area Network

A global area networks (GAN) specification is in development by several groups, and there is no common definition. In general, however, a GAN is a model for supporting mobile communications across an arbitrary number of wireless LANs, satellite coverage areas, etc. The key challenge in mobile communications is “handing off” the user communications from one local coverage area to the next. In IEEE Project 802, this involves a succession of terrestrial WIRELESS local area networks (WLAN).

Virtual Private Network

A virtual private network (VPN) is a computer network in which some of the links between nodes are carried by open connections or virtual circuits in some larger network (e.g., the Internet) instead of by physical wires. The link-layer protocols of the virtual network are said to be tunneled through the larger network when this is the case.

One common application is secure communications through the public Internet, but a VPN need not have explicit security features, such as authentication or content encryption. VPNs, for example, can be used to separate the traffic of different user communities over an underlying network with strong security features.

A VPN may have best-effort performance, or may have a defined service level agreement (SLA) between the VPN customer and the VPN service provider. Generally, a VPN has a topology more complex than point-to-point.

A VPN allows computer users to appear to be editing from an IP address location other than the one which connects the actual computer to the Internet.

Internetwork

Internetworking involves connecting two or more distinct computer networks or network segments via a common routing technology. The result is called an internetwork (often shortened to internet). Any interconnection among or between public, private, commercial, industrial, or governmental networks may also be defined as an internetwork.

In modern practice, the interconnected networks use the Internet Protocol. There are at least three variants of internetwork, depending on who administers and who participates in them

Intranet

Extranet

Internet

Intranets and extranets may or may not have connections to the Internet. If connected to the Internet, the intranet or extranet is normally protected from being accessed from the Internet without proper authorization. The Internet is not considered to be a part of the intranet or extranet, although it may serve as a portal for access to portions of an extranet.

Intranet

An intranet is a set of networks, using the Internet Protocol and IP-based tools such as web browsers and file transfer applications, which are under the control of a single administrative entity. That administrative entity closes the intranet to all but specific, authorized users. Most commonly, an intranet is the internal network of an organization. A large intranet will typically have at least one web server to provide users with organizational information.

Extranet

An extranet is a network or internetwork that is limited in scope to a single organization or entity but which also has limited connections to the networks of one or more other usually, but not necessarily, trusted organizations or entities (e.g., a company’s customers may be given access to some part of its intranet creating in this way an extranet, while at the same time the customers may not be considered ‘trusted’ from a security standpoint).

Technically, an extranet may also be categorized as a CAN, MAN, WAN, or other type of network, although, by definition, an extranet cannot consist of a single LAN; it must have at least one connection with an external network.

Internet

The Internet is a specific internetwork. It consists of a worldwide interconnection of governmental, academic, public, and private networks based upon the networking technologies of the Internet Protocol Suite. It is the successor of the Advanced Research Projects Agency Network (ARPANET) developed by DARPA of the U.S. Department of

Defense. The Internet is also the communications backbone underlying the World Wide Web (WWW). The ‘Internet’ is most commonly spelled with a capital ‘I’ as a proper noun, for historical reasons and to distinguish it from other generic internetworks.

Participants in the Internet use a diverse array of methods of several hundred documented, and often standardized, protocols compatible with the Internet Protocol Suite and an addressing system (IP Addresses) administered by the Internet Assigned Numbers Authority and address registries. Service providers and large enterprises exchange information about the reachability of their address spaces through the Border Gateway Protocol (BGP), forming a redundant worldwide mesh of transmission paths.

Basic Hardware Components

All networks are made up of basic hardware building blocks to interconnect network nodes, such as Network Interface Cards (NICs), Bridges, Hubs, Switches, and Routers. In addition, some method of connecting these building blocks is required, usually in the form of galvanic cable (most commonly Category 5 cable). Less common are microwave links (as in IEEE 802.12) or optical cable (“optical fiber”).

Network Interface Cards

A network card, network adapter or NIC (network interface card) is a piece of computer hardware designed to allow computers to communicate over a computer network. It provides physical access to a networking medium and often provides a low-level addressing system through the use of MAC addresses.

Repeaters

A repeater is an electronic device that receives a signal and retransmits it at a higher power level, or to the other side of an obstruction, so that the signal can cover longer distances without degradation. In most twisted pair Ethernet configurations, repeaters are required for cable which runs longer than 100 meters.

Hubs

A hub contains multiple ports. When a packet arrives at one port, it is copied unmodified to all ports of the hub for transmission. The destination address in the frame is not changed to a broadcast address.

Bridges

A network bridge connects multiple network segments at the data link layer (layer ppp of the OSI model. Bridges do not promiscuously copy traffic to all ports, as hubs do, but learn which MAC addresses are reachable through specific ports. Once the bridge associates a port and an address, it will send traffic for that address only to that port. Bridges do send broadcasts to all ports except the one on which the broadcast was received.

Bridges learn the association of ports and addresses by examining the source address of frames that it sees on various ports. Once a frame arrives through a port, its source address is stored and the bridge assumes that MAC address is associated with that port. The first time that a previously unknown destination address is seen, the bridge will forward the frame to all ports other than the one on which the frame arrived.

Bridges come in three basic types

Local bridges Directly connect local area networks (LANs)

Remote bridges Can be used to create a wide area network (WAN) link between LANs. Remote bridges, where the connecting link is slower than the end networks, largely have been replaced by routers.

Wireless bridges Can be used to join LANs or connect remote stations to LANs.

Switches

A switch is a device that forwards and filters OSI layer 2 data grams (chunk of data communication) between ports (connected cables) based on the MAC addresses in the packets. This is distinct from a hub in that it only forwards the packets to the ports involved in the communications rather than all ports connected. Strictly speaking, a switch is not capable of routing traffic based on IP address (OSI Layer 3) which is necessary for communicating between network segments or within a large or complex LAN.

Some switches are capable of routing based on IP addresses but are still called switches as a marketing term. A switch normally has numerous ports, with the intention being that most or all of the network is connected directly to the switch, or another switch that is in turn connected to a switch.

Switch is a marketing term that encompasses routers and bridges, as well as devices that may distribute traffic on load or by application content (e.g., a Web URL identifier). Switches may operate at one or more OSI model layers, including physical, data link, network, or transport (i.e., end-to-end). A device that operates simultaneously at more than one of these layers is called a multilayer switch.

Overemphasizing the ill-defined term “switch” often leads to confusion when first trying to understand networking. Many experienced network designers and operators recommend starting with the logic of devices dealing with only one protocol level, not all of which are covered by OSI. Multilayer device selection is an advanced topic that may lead to selecting particular implementations, but multilayer switching is simply not a real-world design concept.

Voice over Internet Protocol (VoIP) is a general term for a family of transmission technologies for delivery of voice communications over networks such as the Internet or other packet-switched networks. Other terms frequently encountered and synonymous with VoIP are IP telephony, Internet telephony, voice over broadband (VoBB), broadband telephony, and broadband phone.

Internet telephony refers to communications services - voice, facsimile, and/ or voice-messaging applications - that are transported via the Internet, rather than the public switched telephone network (PSTN).

The basic steps involved in originating an Internet telephone call are conversion of the analog voice signal to digital format and compression/translation of the signal into Internet protocol (IP) packets for transmission over the Internet; the process is reversed at the receiving end.

VoIP systems employ session control protocols to control the set-up and tear-down of calls as well as audio codecs which encode speech allowing transmission over an IP network as digital audio via an audio stream. Codec use is varied between different implementations of VoIP (and often a range of codecs are used); some implementations rely on narrowband and compressed speech, while others support fidelity stereo codecs.

Trends in Telecommunications

Over the past few years the landscape of the information and telecommunication industry has been subject to dramatic changes. The enormous growth of the Internet and the advances in both wired and wireless network technologies have boosted the emergence of advanced multimedia applications offered over distributed systems consisting of a heterogeneity of network technologies and information servers.

On the business side, the market share of e-business is increasing, the telco market is becoming more competitive and the unbundling of the telecommunications world has become reality. In this context, network and service providers experience that it is becoming crucial to be able to offer customers high and predictable end-to-end Quality of Service (QoS) in a cost- effective manner. These developments raise a number of new challenges for performance analysts.

Business Relies Increasingly on the Performance of ICT

Many companies in competitive markets are trying to become more cost- efficient by automating their business processes. One of the most prominent examples is the automation of sales by e-commerce applications. The doubling period is simply the time it takes to consume twice the server capacity that exists now. For some e-commerce sites, this period can be as short as six months, which is four times faster than Moore’s Law. Under these circumstances poor (network or IT) capacity planning will lead to major performance problems. And in the e-commerce context, customer dissatisfaction about overly long response times or unavailable servers will directly cause a decrease in revenues for e- commerce applications.

Other examples that illustrate that performance of information and communication infrastructures are becoming more business critical, are the use of Enterprise Resource Planning (ERP), supply chain management and billing tools. Those applications are used for increasing control over vital business processes and over the past decade their use has become increasingly popular, especially for larger companies.

Typically, these larger companies consist of several branch-stores that are geographically spread. And for this reason the enterprise applications are often implemented as distributed applications, which are connected by Virtual Private Network (VPN) communication technology. In practise, we see that unavailability of distributed enterprise applications for a few hours has negative consequences for customer care services, such as order intake and helpdesk facilities. Unavailability for a period of days makes management teams nervous, because they get the feeling of losing control over their business.

Unbundling

Unbundling of the telecom world is reality, separating functional roles in the telecom and information domain, such as access network providers, core network providers, service providers, portal providers and content providers.

This leads to a heterogeneous, multi-domain infrastructure over which new services and applications are supported, and consequently, an increasing business importance of Service Level Agreements (SLAs) between administrative domains.

A concrete example of unbundling can be found in the emerging market of mobile internet access services, such as i-mode and Vodafone-live. Fig shows a typical architecture for a mobile internet access service.

In the i-mode case illustrated in Fig the mobile access network and the service platform are both in the mobile operator domain. The gateway mainly supports authentication functionality and the service platform supports functionality such as, the start page for the service (i-menu), subscription to content provider sites and e-mail distribution (i-mail). Content such as local weather forecasts, traffic information, etc., is delivered by several contentproviders. For some cases the inter-connectivity between the mobile operator and the content provider is realised by yet another network provider.

The business success of previous mobile data services, such as WAP, was disappointing. In general, the reasons for this lack of success are due to (amongst others) the limited type and range of the offered content, the text- based presentation of information and the long browsing response times. For the commercial success of mobile internet services the gap between mobile internet access and wired internet access will have to be filled, for each of the mentioned criteria. With the breakthrough of the next generation mobile internet access services most of the obstacles for success are eliminated. For example, the latest terminals feature glossy displays and sounds, and much attention is paid to make sure that a wide range of content is provided to the users. The requirement of good browsing performance remains quite a challenge, in particular because end-to-end performance is no longer an issue of one single provider.

Increasing Heterogeneity of Services

Demand for device- and location-independent access to information and services that are presented according to user specified preferences, is still growing. In conjunction with this growing demand and boosted by the opportunities enabled by the Internet, the variety of offered services and user-devices has grown tremendously. Typically, in order to stay in business service providers have to offer a wide range of these services, such as e-mail, information downloading, on-line banking, ticketing, remote access to a company intranet and streaming services.

For these applications, the end users typically have access to information servers via a heterogeneous mix of wired and wireless access networks and backbone infrastructures. We observe that new user demands emerge with the technological advances in distributed system architectures. Each of these services has its own traffic characteristics and performance requirements, depending for example on the type of content and the level of user interaction.

Emergence of Distributed Applications and Middleware Architectures

Besides the increasing heterogeneity of user demands and offered services, network providers see new business opportunities in terms of so-called third party service provisioning (3PSP). 3PSP is the concept where network providers provide ‘open interfaces’ for ‘third party’ service providers to build services on top of communication networks. Note, that the 3PSP concept is partly a result of the unbundling trend and its growing popularity emphasises the increasing ICT dependency of modern industry.

To support applications with that cover a wide range of features, functionalities and open interfaces in multi-domain environments, software infrastructures have become increasingly complex. This has led to the development of so-called middleware architectures. Middleware technology enables to manage this heterogeneity by abstracting details of lower-layer communication protocols for application programmers.

Middleware is software that resides between the application and operating system, as illustrated in Figure. The most popular middleware architectures are the Common Object Request Broker Architecture (CORBA), a product of the Object Management Group (OMG), Microsoft’s proprietary middleware called Distributed Component Object Model (DCOM), and Sun’s increasingly popular Enterprise Java Beans (EJB). For implementation of open network interfaces much work is being done on the Open Service Architecture (OSA, recently called Open Service Access), Parlay and Simple Object Access Protocol (SOAP).

In an environment where services are created on top of middleware, much of the service control functionality is performed by the middleware layer. As a consequence, the middleware performance will have strong impact on service performance, making it important to control middleware performance.

Paradigm Shift in Performance Bottlenecks

In the context of the increasing complexity of software architectures, we observe

Pp growing impact of server and software performance on the end-to-end performance observed by the end user. During a study of i-mode page download times, we encountered an interesting effect. It appeared that the average response time was dominated by the throughput of radio links. However, the variability of response times was dominated by the service platform and content providers.

Since the 95%- percentiles of response times, which was regarded as key performance indicator, depend both on the average and the variability of response times the performance model had to include both network and server performance. In general, we experience that the assumption network performance dominates end-to-end performance will not hold.

When reviewing approaches to performance analyse, we observe a typical difference. Opposite to the communication community the emphasis in the information technology community is much more on performance monitoring and testing than on performance modelling.

This difference in approach to performance analysis seems to be an obstacle for joining communication and IT expertise in performance analysis.

This addresses a fundamental paradigm shift that has received relatively little attention in the performance modelling community, which traditionally has focused on performance aspects of communication networks, rather than servers and software architectures. Realistic modelling of end-to-end performance requires combined knowledge of performance modelling of communication and information technology.

New challenges for performance analysts

Increased importance of performance monitoring capabilities

New concepts for modelling ICT performance

Analysis techniques for performance models of servers and software architectures

Development and analysis of end-to-end multi-domain performance models

Implementing integrated performance and capacity management

Business Value of Telecommunications Network

The International Telecommunication Union (ITU) estimates the number of mobile subscribers worldwide at 4.01 billion at the end of 2008, up from 1.41 billion in 2003. This is a compound annual growth rate of 23.2%, and represents 59.3% of world population.

Global wireless subscribers will grow to over 5.5 billion by 2011 to 2012, as low-cost providers are making service prices low enough to be affordable for vast numbers of people in Third World nations. Inexpensive cell phones are now indispensable to consumers from Haiti to Africa to New Guinea. Telecommunications remains one of the largest providers of employment in the world, with over 1 million employees in the U.S. alone.

Several major factors are creating changes in the telecommunications sector today, including

Budgetary pressures and slower growth due to the global recession,

A shift in residential and personal use from wired services to wireless,

Intense competition between cable and wired services providers and

Rapid advances in Internet and wireless technologies, including more advanced cellular handsets and wider availability of 3G services.

No other industry touches as many technology-related business sectors as telecommunications, which, by definition, encompasses not only the traditional areas of local and long-distance telephone service, but also advanced technology-based services including wireless communications, the Internet, fiber-optics and satellites.

Telecom is also deeply intertwined with entertainment of all types, including cable TV systems, since cable companies are now aggressively offering local exchange service and high-speed Internet access. The relationship between the telecom and cable sectors has become even more complex as telcos are now selling TV via IP (Internet protocol) services, competing directly against cable for consumers’ entertainment dollars.

Ingenuity, innovation, cost control and a reasonable approach to spending and investment will help to move the industry ahead. New cellular, cable telephony, VOIP (Voice Over Internet Protocol) and wireless technologies promise continuous rapid evolution of this sector and pose a massive threat to traditional landlines. The cost of a cell phone call has become a bargain worldwide, and cell phone manufacturers are adding advanced new features to their phones on a regular basis.

Improved cell phone service has prompted tens of millions of consumers to cancel their landlines altogether, eating into traditional revenue streams at AT&T, Verizon and Qwest, among others. Meanwhile, wireless access to the Internet threatens traditional broadband suppliers. WiMAX, an advanced wireless technology with a range of up to 30 miles, has the potential to disrupt traditional broadband, cell phone, landline and Wi-Fi systems.

As more consumers recognize the promise, and good value, of phone service using VOIP, the number of companies offering this service has increased dramatically and millions of households and businesses worldwide have signed up for less-expensive VOIP service as an alternative to landlines, often through their cable providers as part of a bundle of services. Several heavy hitters, such as Comcast, have jumped on the VOIP bandwagon, along with startups like Skype and Vonage.

At the same time, local phone companies, led by Verizon and AT&T, are laying fiber-optic cable directly to the neighborhood and even into the home and office in order to retain customers with promises of ultra-high-speed Internet connections and enhanced entertainment offerings online.

This is the big telcos’ way of fighting back. If cell phone owners are dropping their landlines, while VOIP over cable takes even more landline customers away, then the best weapon that traditional telcos can use in their battle for market share is the Internet.

AT&T and its peers are focusing on bundled service packages (combining wireless accounts, very high-speed Internet access and entertainment such as video on demand and TV via IP, in addition to VOIP or landlines).

Next, the traditional telcos need to create innovative new value-added services that are accessed online. For example, consumers might respond well to online services that monitor home security or adjust home energy usage, or services that monitor the movements and needs of elderly family members at home. The right value-added services, controlled via cellphones and/or the Internet, could get consumers hooked, with the potential to build new revenues and stop customer turnover.

In the U.S., cellular phone companies have upgraded many of their networks to 3G. In addition, they are adding new towers in large numbers to better handle traffic volume. In developing nations, wireless service providers such as India’s Bharti Airtel have become extremely innovative and cost-effective, providing basic cellular service for very modest amounts of money.

Mergers, acquisitions and other industry changes redefined telecom. AT&T and SBC merged (changing the name of the merged company to AT&T, Inc.), and MCI merged into Verizon. Sprint and Nextel have combined to create wireless giant Sprint Nextel. The competitive landscape is shifting dramatically due to these mergers.

In addition, government regulations are evolving quickly, which will bring even bigger changes to business strategies. Overall, the telecommunications industry is in a state of continuous technological and economic flux driven by intense competition and new technologies.