Performance #3

NETWORK TOPOLOGIES

A network topology is the arrangement of a network, including its nodes and connecting lines. There are two ways of defining network geometry: the physical topology and the logical (or signal) topology.

The physical topology of a network is the actual geometric layout of workstations. There are several common physical topologies, as described below and as shown in the illustration.

In the bus network topology, every workstation is connected to a main cable called the bus. Therefore, in effect, each workstation is directly connected to every other workstation in the network.

In the star network topology, there is a central computer or server to which all the workstations are directly connected. Every workstation is indirectly connected to every other through the central computer.

In the ring network topology, the workstations are connected in a closed loop configuration. Adjacent pairs of workstations are directly connected. Other pairs of workstations are indirectly connected, the data passing through one or more intermediate nodes.

If a Token Ring protocol is used in a star or ring topology, the signal travels in only one direction, carried by a so-called token from node to node.

The mesh network topology employs either of two schemes, called full mesh and partial mesh. In the full mesh topology, each workstation is connected directly to each of the others. In the partial mesh topology, some workstations are connected to all the others, and some are connected only to those other nodes with which they exchange the most data.

The tree network topology uses two or more star networks connected together. The central computers of the star networks are connected to a main bus. Thus, a tree network is a bus network of star networks.

Logical (or signal) topology refers to the nature of the paths the signals follow from node to node. In many instances, the logical topology is the same as the physical topology. But this is not always the case. For example, some networks are physically laid out in a star configuration, but they operate logically as bus or ring networks.

Source: http://whatis.techtarget.com/definition/network-topology

NETWORK STANDARDS

There are two types of standards: formal and de facto. A formal standard is developed by an official industry or government body. For example, there are formal standards for applications such as Web browsers (e.g., HTTP, HTML), for network layer software (e.g., IP), data link layer software (e.g., Ethernet IEEE 802.3), and for physical hardware (e.g., V.90 modems). Formal standards typically take several years to develop, during which time technology changes, making them less useful.

De facto standards are those that emerge in the marketplace and are supported by several vendors but have no official standing. For example, Microsoft Windows is a product of one company and has not been formally recognized by any standards organization, yet it is a de facto standard. In the communications industry, de facto standards often become formal standards once they have been widely accepted.

The formal standardization process has three stages: specification, identification of choices, and acceptance. The specification stage consists of developing a nomenclature and identifying the problems to be addressed. In the identification of choices stage, those working on the standard identify the various solutions and choose the optimum solution from among the alternatives. Acceptance, which is the most difficult stage, consists of defining the solution and getting recognized industry leaders to agree on a single, uniform solution. As with many other organizational processes that have the potential to influence the sales of hardware and software, standards-making processes are not immune to corporate politics and the influence of national governments.

International Organization for Standardization One of the most important standards-making bodies is the International Organization for Standardization (ISO),2 which makes technical recommendations about data communication interfaces. ISO is based in Geneva, Switzerland. The membership is composed of the national standards organizations of each ISO member country.

International Telecommunications Union—Telecommunications Group The Telecommunications Group (ITU-T) is the technical standards-setting organization of the United Nations International Telecommunications Union, which is also based in Geneva (seewww.itu.int). ITU is composed of representatives from about 200 member countries. Membership was originally focused on just the public telephone companies in each country, but a major reorganization in 1993 changed this, and ITU now seeks members among public- and private-sector organizations who operate computer or communications networks (e.g., RBOCs) or build software and equipment for them (e.g., AT&T).

American National Standards Institute The American National Standards Institute (ANSI) is the coordinating organization for the U.S. national system of standards for both technology and nontechnology. ANSI has about 1,000 members from both public and private organizations in the United States. ANSI is a standardization organization, not a standards-making body, in that it accepts standards developed by other organizations and publishes them as American standards. Its role is to coordinate the development of voluntary national standards and to interact with ISO to develop national standards that comply with ISO’s international recommendations. ANSI is a voting participant in the ISO.

How Network Protocols Become Standards

There are many standards organizations around the world, but perhaps the best known is the Internet Engineering Task Force (IETF). IETF sets the standards that govern how much of the Internet operates.

The IETF, like all standards organizations, tries to seek consensus among those involved before issuing a standard. Usually, a standard begins as a protocol (i.e., a language or set of rules for operating) developed by a vendor (e.g., HTML [Hypertext Markup Language]). When a protocol is proposed for standardization, the IETF forms a working group of technical experts to study it. The working group examines the protocol to identify potential problems and possible extensions and improvements, then issues a report to the IETF.

If the report is favorable, the IETF issues a request for comment (RFC) that describes the proposed standard and solicits comments from the entire world. Most large software companies likely to be affected by the proposed standard prepare detailed responses. Many ”regular” Internet users also send their comments to the IETF.

The IETF reviews the comments and possibly issues a new and improved RFC, which again is posted for more comments. Once no additional changes have been identified, it becomes a proposed standard.

Usually, several vendors adopt the proposed standard and develop products based on it. Once at least two vendors have developed hardware or software based on it and it has proven successful in operation, the proposed standard is changed to a draft standard. This is usually the final specification, although some protocols have been elevated to Internet standards, which usually signifies mature standards not likely to change.

The process does not focus solely on technical issues; almost 90 percent of the IETF’s participants work for manufacturers and vendors, so market forces and politics often complicate matters. One former IETF chairperson who worked for a hardware manufacturer has been accused of trying to delay the standards process until his company had a product ready, although he and other IETF members deny this. Likewise, former IETF directors have complained that members try to standardize every product their firms produce, leading to a proliferation of standards, only a few of which are truly useful.

Institute of Electrical and Electronics Engineers The Institute of Electrical and Electronics Engineers (IEEE) is a professional society in the United States whose Standards Association (IEEE-SA) develops standards. The IEEE-SA is probably most known for its standards for LANs. Other countries have similar groups; for example, the British counterpart of IEEE is the Institution of Electrical Engineers (IEE).

Internet Engineering Task Force The IETF sets the standards that govern how much of the Internet will operate. The IETF is unique in that it doesn’t really have official memberships. Quite literally anyone is welcome to join its mailing lists, attend its meetings, and comment on developing standards.

Keeping Up with Technology

The data communications and networking arena changes rapidly. Significant new technologies are introduced and new concepts are developed almost every year. It is therefore important for network managers to keep up with these changes.

There are at least three useful ways to keep up with change. First and foremost for users of this topic is the Web site for this topic, which contains updates to the topic, additional sections, teaching materials, and links to useful Web sites.

Second, there are literally hundreds of thousands of Web sites with data communications and networking information. Search engines can help you find them. A good initial starting point is the telecom glossary at www.atis.org. Two other useful sites are networkcomputing.com and zdnet.com.

Third, there are many useful magazines that discuss computer technology in general and networking technology in particular, including Network Computing, Data Communications, Info World, Info Week, and CIO Magazine.

Common Standards

There are many different standards used in networking today. Each standard usually covers one layer in a network. Figure 1.5 outlines some of the most commonly used standards. At this point, these models are probably just a maze of strange names and acronyms to you, but by the end of the topic, you will have a good understanding of each of these. Figure 1.5 provides a brief road map for some of the important communication technologies we discuss in this topic.

For now, there is one important message you should understand from Figure 1.5: For a network to operate, many different standards must be used simultaneously. The sender of a message must use one standard at the application layer, another one at the transport layer, another one at the network layer, another one at the data link layer, and another one at the physical layer. Each layer and each standard is different, but all must work together to send and receive messages.

Layer	Common Standards
5. Application layer	HTTP, HTML (Web) MPEG, H.323 (audio/video) SMTP, IMAP, POP (e-mail)
4. Transport layer	TCP (Internet and LANs) SPX (Novell LANs)
3. Network layer	IP (Internet and LANs) IPX (Novell LANs)
2. Data link layer	Ethernet (LAN) Frame relay (WAN) T1 (MAN and WAN)
1. Physical layer	RS-232C cable (LAN) Category 5 cable (LAN) V.92 (56 Kbps modem)

Figure 1.5 Some common data communications standards. HTML = Hypertext Markup Language; HTTP = Hypertext Transfer Protocol; IMAP = Internet Message Access Protocol; IP = Internet Protocol; IPX = internetwork package exchange; LAN = local area network; MPEG = Motion Picture Experts Group; POP = Post Office Protocol; SPX = sequenced packet exchange; TCP = Transmission Control Protocol

Either the sender and receiver of a message must use the same standards or, more likely, there are devices between the two that translate from one standard into another. Because different networks often use software and hardware designed for different standards, there is often a lot of translation between different standards.

Source: http://what-when-how.com/data-communications-and-networking/network-standards-data-communications-and-networking/

COMMUNICATION DEVICES

A communication device is a hardware device capable of transmitting an analog or digital signal over the telephone, other communication wire, or wirelessly. The best example of a communication device is a computer Modem, which is capable of sending and receiving a signal to allow computers to talk to other computers over the telephone. Other examples of communication devices include a network interface card (NIC), Wi-Fi devices, and an access point. Below is a picture of some of the different types of Wi-Fi devices that are all examples of a communication device.

Communication device errors

Any time a communication device encounters problems communicating with another device you may encounter a communication error. Below are a listing of general steps that can be verified when this error is encountered.

• If your communication device is using a wire, make sure it is firmly connected.

• Make sure the proper drivers are installed and that no errors or conflicts are occurring with the driver and that the device is being detected.

• If your communication device requires settings, make sure they're correct. For example, a network card will require the proper IP, DNS, and Subnet settings to establish a connection with the network and be able to find its route to other network devices.

Communication device examples

• Bluetooth devices

• Infrared devices

• Modem (over phone line)

• Network card (using Ethernet)

• Smartphone

• Wi-Fi devices (using a router)

Source: http://www.computerhope.com/jargon/c/communication-devices.htm