Network, Data communication, TOPOLGY, METHODs

What is SPIN:

2010-02-17T05:41:00.000-08:00

Spin is a set of tools used for analyzing the logical consistency of distributed systems. It is more specifically for the analyzing of data communication protocols used in different networks. This system for SPIN is described in a modeling language called "Promela" which is Process or Protocol Meta Language. The promela language allows the programmer or the user of SPIN for the dynamic creation of concurrent processes needed for the testing of communication protocols. Communication via message channels can be defined to be synchronous or in other words rendez-vous, and sometimes it is asynchronous or buffered. Xspin is a graphical front-end to drive Spin (written in Tcl/Tk).
How a MODEL SYSTEM OF SPIN WORKS?

A model system specified in Promela developed as a Spin can perform random or interactive simulations of the system's execution. It can also generate a C language program that performs a fast exhaustive verification of the system state space. During simulations and verifications Spin checks for the absence of
1. deadlocks,
2. unspecified receptions,
3. unexecutable code.
The verifier can also be used to prove the correctness of system invariants and it can find non-progress execution cycles.
Finally, it supports the verification of linear time temporal constraints; either with Promela never-claims or by directly formulating the constraints in temporal logic.
Promela
Promela programs consist of
1. processes, (Processes are global objects)
2. message channels, ( these can be declared either globally or locally within a process. )
3. variables. (these can also be declared either globally or locally within a process. )
All the three above mentioned parts , Processes specify behavior, channels and global variables define the environment in which the processes run. The syntax of Promela is C-like. Below.
Lexical conventions in Promela:
There are five classes of tokens:
1. identifiers,
2. keywords,
3. constants,
4. operators
5. statement separators.
But following also serve only to separate tokens.
Blanks, tabs, newlines, formfeeds and comments
If more than one interpretation is possible, a token is taken to be the longest string of characters that can constitute a token.
Comments in Promela
A comment starts with /* and terminates with */. Comments may not be nested.
Identifiers in Promela
An identifier is a single letter, period, or underscore followed by zero or more letters, digits, periods, or underscores.
Keywords in Promela
The following identifiers are reserved for use as keywords. active assert atomic bit bool break byte chan d_step Dproctype do else empty enabled fi full goto hidden if init int len mtype empty
never nfull od of pcvalue printf priority proctype provided run short skip timeout typedef unless unsigned xr xs
Labels in Promela
A label is an identifier followed by a colon (:). Any statement can be labeled. Labels that start with one of the sequences end, progress or accept have a special meaning.
Constants in Promela
A constant is a sequence of digits representing a decimal integer. There are no floating point numbers in Promela. Symbolic names for constants can be defined in two ways. The first method is to use a C-style macro definition
#define NAME 5
Structures in Promela
User-defined data types are supported through typedef definitions, typedef Msg {byte a[3], b;
chan p }
that can be used in variable declarations and, more generally, wherever a type definition is needed: Msg foo; chan stream =[0] of {mtype,Msg} Elements of structures are accessed as in C; e.g., foo.a[1]
Hidden variables in Promela
hidden int foo A hidden variable is not part of the system state and its value is always undefined, although it can be assigned to.

The Shielded twisted pair STP

2009-07-18T03:42:00.000-07:00

In Twisted pair cables two conductor wires are twisted together for the purposes of canceling out electromagnetic interference (EMI) from external sources AC DC motors, generators, electric main supply lines of one phase or three phase carrying high current and crosstalk between neighboring pairs. Two basic types of twisted-pair cable exist: unshielded twisted pair (UTP) and shielded twisted pair (STP). Shielded twisted-pair (STP) cable combines the techniques of shielding, cancellation, and wire twisting. Each pair of wires is wrapped in a metallic foil.They have usually 150-ohm impedance. The use of STP is in Ethernet network installations, because STP reduces electrical noise both within the cable which may be due topair-to-pair coupling, or crosstalk and from outside the cable for example EMI and RFI. STP is installed with STP data connector, which is created especially for the STP cable. The Speed and throughput of STP cables may ranges in 10 to 100 Mbps with Maximum cable length is 100 m. The construction of STP cables has following four layers,

Plastic cover - outer most layer
Metal shield or metal grid or mesh
Insulation of each individual copper wire
Cooper wire

what are the cables used in Networking

2009-07-17T21:51:00.000-07:00

THE Most of the Network are established with the use of UTP cables. UTP is the most common form of twisted pair wiring. It is less expensive and easier to work with than STP (Shielded Twisted Pair). UTP is used in Ethernet 10 Base-T and 100Base-T networks, as well as in home and office telephone wiring.The main advantage of use of UTP is that twist in UTP helps to reduce crosstalk interference between wire pairs.
Categories of UTP cables:
EIA has made some standards of UTP cables also. There are five major categories of UTP cables.
The categories of UTP cables is function of cable quantity with category 1 is less and category5 maximum quality.
Category 1 UTB cable (CAT 1) : It is suitable for voice communicatin thus mostly used in telephone line and less in data communication application, normally very low speed transmission is possible with CAT1 UTP.
Category 2 UTB cable (CAT 2) : This is of a little bit higher grad, but again recommended for voice communication and only for data transmission of equal or less than 4Mbps.
Category 3 UTB cable CAT 3) : The category3 or CAT3 UTP cables have at least 3 twist per foot in lenght. These can be used for data transmission of Up to 10MBps. Cat 3 UTP was the standard cable for use with Ethernet 10Base-T. But it is most standred cables used for Telephone industry.
Category 4 UTB cable CAT 4) : The category3 or CAT4 UTP cables must have at least 3 twist per foot in lenght. These can be used for data transmission of Up to 16MBps.
Category 5 UTB cable CAT 5) : The Cat5 UTP are used in data communication with speed of upto 100MBps and for ATM up to 155Mbit/s. Cat 5 UTP was the standard cable for use with Ethernet 100Base-TX.
Category 5e UTP cable (CAT 5e) : Category 5e UTP is an enhanced version of Cat 5 UTP. Cat 5e UTP is rated to carry data up to 1000Mbit/s. Cat 5e UTP is the standard cable for use with Ethernet 1000Base-T. Cat 5e can also be used to extend the distance of 100Base-TX cable runs up to 350 meters.

Modem standards

2009-07-02T10:35:00.000-07:00

There are many modem standards used in world, but some of them are briefely described here for just review purposes.

Bell Modem standards
ITU-T modem standards
Intelligent modems

Bell Modem standards:

In the early 1970s, Bell Labs created carrier standards for use with Bell equipment and lines, to accommodate the networks. Bell Standards include the following:

Bell 103 - Asynchronous data transmission, full-duplex operation over 2-wire dialup or leased lines; 300-bps data rate, work on barb wire.

Bell 212 A - Synchronous/ asynchronous data transmission, full-duplex operation over 2-wire leased or dialup lines; 1200-bps data rate. This versatile standard provides for efficient full-duplex operation over 2-wire dialup lines.

Bell 201 B, Bell 201 C - 201 B: Synchronous data transmission, full-duplex operation over 4-wire leased lines and half-duplex operation over 2-wire leased lines; 2400-bps data rate. 201 C: synchronous data transmission, half-duplex operation over 2-wire dialup lines; 2400-bps data rate. Both are comparable to ITU V.26. Bell 201 B compatible modems are the first of the fast modems.

Bell 208 A, Bell 208 B - 208 A: Synchronous data transmission, full-duplex operation over 4-wire leased lines, half-duplex operation over 2-wire leased lines; 4800-bps data rate. 208 B: same as 208 A, but over 2-wire dialup lines. Comparable to ITU V.27. The first standards to enable higher-speed data transmission (4800 bps) over leased lines for multipoint networks.

ITU-T modem standards:

The International Telephone and Telegraph Consultative Committee (CCITT), known since 1990 as the International Telecommunication Union (ITU).
The goal of the ITU is to define international communications standards. Modem standards can be divided into 3 categories:
Modulation standards (e.g. CCITT V.21)
Error correction standards (e.g. CCITT V.42)
Data compression standards (e.g. CCITT V.42bis)

V.22; 600 baud (Hz), 1200 Bits Per Second, The same as the Bell 212A standard but different handshaking.

CCITT V.21: 300 bps, Full duplex, An international standard similar to the Bell 103 standard.

ITU V.22bis: 2,400 bps, Full duplex, An international standard that is an improved version of the V.22 standard (thus the name V.22bis).

ITU V.23
1,200 bps
Half duplex
An international standard that transmits data in half-duplex mode, i.e. data is transmitted in just one direction at a time. Optional 75 baud reverse channel.
ITU V.23
1,200 bps/75 bps
Full duplex
An international standard giving asymmetrical full duplex, i.e. it allows data transmission in one direction at 1,200 bps and at 75 bps in the other direction.
ITU V.29: 9,600 bps, Half duplex, An international standard that transmits data in half-duplex mode, i.e. data is transmitted in just one direction at a time. This standard was developed especially for fax machines.
ITU V.32: 9,600 bps, Full duplex, An international standard that transmits in full-duplex mode and incorporates error correction standards. Data transmission takes place according to an error correction technique called quadrature amplitude trellis-coded modulation. This technique consists in sending an additional bit for each group of 4 bits that are sent on the transmission line.

ITU V.32bis: 14,400 bps, Full duplex, An international standard that improves on the v.32 standard by allowing 6 bits per baud to be sent and a transmission speed of up to 14,400 bps.
ITU V.32fast: 28,800 bps, Full duplex, An international standard sometimes called V.FC (Fast Class) that allows data transmission at a speed of 28,800 bps.
ITU V.34: 28,800 bps, Full duplex, An international standard that allows data transfer at 28,800 bps. Thanks to a DSP processor (Digital Signal Processor), modems using this standard can attain a speed of up to 33,600 bps.
ITU V.90: 56,000 bps, Full duplex, An international standard that allows transmission speeds of up to 56,000 bps.

Classification of network topologies

2009-03-31T01:33:00.000-07:00

There are also three basic categories of network topologies:

physical topologies

signal topologies

logical topologies

Physical topologies
The mapping of the nodes of a network and the physical connections between them, the layout of wiring, cables, the locations of nodes, and the interconnections between the nodes and the cabling or wiring system.

Classification of physical topologies

Point-to-point

Star

Ring

Mesh

Tree

Signal topology

The mapping of the actual connections between the nodes of a network, as evidenced by the path that the signals take when propagating between the nodes.

Logical topology

The mapping of the apparent connections between the nodes of a network, as evidenced by the path that data appears to take when traveling between the nodes.

What is topology?

2009-03-31T00:59:00.000-07:00

Topology:
(Greek : Τοπολογία, from τόπος, “place”, and λόγος, “study”)

The topology of a network refers to the configuration of cables, computers, and other peripherals used in network. Network topology is the study of the arrangement or mapping of the elements (nodes, etc.) of a network, especially the physical (real) and logical (virtual) interconnections between nodes. A local area network (LAN) is one example of a network that exhibits both a physical topology and a logical topology. Any given node in the LAN will have one or more links to one or more other nodes in the network and the mapping of these links and nodes onto a graph results in a geometrical shape that determines the physical topology of the network. Likewise, the mapping of the flow of data between the nodes in the network determines the logical topology of the network. The physical and logical topologies might be identical in any particular network but they also may be different.
Any particular network topology is determined only by the graphical mapping of the configuration of physical and/or logical connections between nodes. LAN Network Topology is, therefore, technically a part of graph theory. Distances between nodes, physical interconnections, transmission rates, and/or signal types may differ in two networks and yet their topologies may be identical. Flowing are some well known topologies used in networking:

Bus Topology
Ring Topology
Star Topology
Tree Topology
Mess Topology

Disadvantages

2009-03-24T23:27:00.000-07:00

Disadvantages of Installing a Network:
Expensive to Install:
Although a network will generally save money over time, the initial costs of installation can be prohibitive. Cables, network cards, and software are expensive, and the installation may require the services of a technician.
Network Hardware, Software and Setup Costs:
Computers don't just magically network themselves, of course. Setting up a network requires an investment in hardware and software, as well as funds for planning, designing and implementing the network. For a home with a small network of two or three PCs, this is relatively inexpensive, possibly amounting to less than a hundred dollars with today's low prices for network hardware, and operating systems already designed for networks. For a large company, cost can easily run into tens of thousands of dollars or more.
Requires Administrative Time:
Proper maintenance of a network requires considerable time and expertise. Many schools have installed a network, only to find that they did not budget for the necessary administrative support.
Undesirable Sharing:
With the good comes the bad; while networking allows the easy sharing of useful information, it also allows the sharing of undesirable data. One significant “sharing problem” in this regard has to do with viruses, which are easily spread over networks and the Internet. Mitigating these effects costs more time, money and administrative effort.
File Server May Fail:
Although a file server is no more susceptible to failure than any other computer, when the files server "goes down," the entire network may come to a halt. When this happens, the entire school may lose access to necessary programs and files.
Illegal or Undesirable Behavior:
Similar to the point above, networking facilitates useful connectivity and communication, but also brings difficulties with it. Typical problems include abuse of company resources, distractions that reduce productivity, downloading of illegal or illicit materials, and even software piracy. In larger organizations, these issues must be managed through explicit policies and monitoring, which again, further increases management costs.
Cables May Break:
The Topology chapter presents information about the various configurations of cables. Some of the configurations are designed to minimize the inconvenience of a broken cable; with other configurations, one broken cable can stop the entire network.
Data Security Concerns:
If a network is implemented properly, it is possible to greatly improve the security of important data. In contrast, a poorly-secured network puts critical data at risk, exposing it to the potential problems associated with hackers, unauthorized access and even sabotage.

Advantages of Installing Network

2009-03-24T23:22:00.000-07:00

Advantages of Installing Network:
Speed:
Networks provide a very rapid method for sharing and transferring files. Without a network, files are shared by copying them to floppy disks, then carrying or sending the disks from one computer to another. This method of transferring files is very time-consuming.
Cost:
Networkable versions of many popular software programs are available at considerable savings when compared to buying individually licensed copies. Besides monetary savings, sharing a program on a network allows for easier upgrading of the program. The changes have to be done only once, on the file server, instead of on all the individual workstations.
Data Security and Management:
In a business environment, a network allows the administrators to much better manage the company's critical data. Instead of having this data spread over dozens or even hundreds of small computers in a haphazard fashion as their users create it, data can be centralized on shared servers. This makes it easy for everyone to find the data, makes it possible for the administrators to ensure that the data is regularly backed up, and also allows for the implementation of security measures to control who can read or change various pieces of critical information.
Centralized Software Management:
One of the greatest benefits of installing a network at a school is the fact that all of the software can be loaded on one computer (the file server). This eliminates that need to spend time and energy installing updates and tracking files on independent computers throughout the building.
Resource Sharing:
Sharing resources is another area in which a network exceeds stand-alone computers. Most schools cannot afford enough laser printers, fax machines, modems, scanners, and CD-ROM players for each computer. However, if these or similar peripherals are added to a network, they can be shared by many users.
Internet Access:
The Internet is itself an enormous network, so whenever you access the Internet, you are using a network. The significance of the Internet on modern society is hard to exaggerate, especially for those of us in technical fields.
Electronic Mail:
The presence of a network provides the hardware necessary to install an e-mail system. E-mail aids in personal and professional communication for all school personnel, and it facilitates the dissemination of general information to the entire school staff. Electronic mail on a LAN can enable students to communicate with teachers and peers at their own school. If the LAN is connected to the Internet, students can communicate with others throughout the world.
Flexible Access:
School networks allow students to access their files from computers throughout the school. Students can begin an assignment in their classroom, save part of it on a public access area of the network, then go to the media center after school to finish their work. Students can also work cooperatively through the network.
Workgroup Computing:
workgroup software allows many users to work on a document or project concurrently. For example, educators located at various schools within a county could simultaneously contribute their ideas about new curriculum standards to the same document and spreadsheets.
Connectivity and Communication:
Networks connect computers and the users of those computers. Individuals within a building or work group can be connected into local area networks (LANs); LANs in distant locations can be interconnected into larger wide area networks (WANs). Once connected, it is possible for network users to communicate with each other using technologies such as electronic mail. This makes the transmission of business (or non-business) information easier, more efficient and less expensive than it would be without the network.
Entertainment:
Networks facilitate many types of games and entertainment. The Internet itself offers many sources of entertainment, of course. In addition, many multi-player games exist that operate over a local area network. Many home networks are set up for this reason, and gaming across wide area networks (including the Internet) has also become quite popular. Of course, if you are running a business and have easily-amused employees, you might insist that this is really a disadvantage of networking and not an advantage.

Networking

2009-03-24T23:19:00.000-07:00

Introduction:

A network consists of two or more computers that are linked in order to share resources (such as printers and CD-ROMs,etc), exchange files, or allow electronic communications. The computers on a network may be linked through cables, telephone lines, radio waves, satellites, or infrared light beams.In the world of computers, networking is the practice of linking two or more computing devices together for the purpose of sharing data. Networks are built with a mix of computer hardware and computer software.
Local Area Network:
A Local Area Network (LAN) is a network that is confined to a relatively small area. It is generally limited to a geographic area such as a writing lab, school, or building. Rarely are LAN computers more than a mile apart. In a typical LAN configuration, one computer is designated as the file server. It stores all of the software that controls the network, as well as the software that can be shared by the computers attached to the network. Computers connected to the file server are called workstations. The workstations can be less powerful than the file server, and they may have additional software on their hard drives. On most LANs, cables are used to connect the network interface cards in each computer. A local area network (LAN) is a group of computers and associated devices that share a common communications line or wireless link. Typically, connected devices share the resources of a single processor or server within a small geographic area (for example, within an office building). Usually, the server has applications and data storage that are shared in common by multiple computer users. A local area network may serve as few as two or three users (for example, in a home network) or as many as thousands of users (for example, in an FDDI network). Major local area network technologies are:

Ethernet
Token
FDDI

Ethernet is by far the most commonly used LAN technology. A number of corporations use the Token Ring technology. FDDI is sometimes used as a backbone LAN interconnecting Ethernet or Token Ring LANs. Another LAN technology, ARCNET, once the most commonly installed LAN technology, is still used in the industrial automation industry. Typically, a suite of application programs can be kept on the LAN server. Users who need an application frequently can download it once and then run it from their local hard disk. Users can order printing and other services as needed through applications run on the LAN server. A user can share files with others at the LAN server; read and write access is maintained by a LAN administrator. A LAN server may also be used as a Web server if safeguards are taken to secure internal applications and data from outside access.Wide Area Network:Wide Area Networks (WANs) connect larger geographic areas, such as Florida, the United States, or the world. Dedicated transoceanic cabling or satellite uplinks may be used to connect this type of network. Using a WAN, schools in Florida can communicate with places like Tokyo in a matter of minutes, without paying enormous phone bills. A WAN is complicated. It uses multiplexers to connect local and metropolitan networks to global communications networks like the Internet. To users, however, a WAN will not appear to be much different than a LAN or a MAN.