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NETWORK BASICS

Network A system of interconnected computers and computerized peripherals such as printers is called computer network. This interconnection among computers facilitates information sharing among them. Computers may connect to each other by either wired or wireless media. A computer network consists of a collection of computers, printers and other equipment that is connected together so that they can communicate with each other.  


Network application
A Network application is any application running on one host and provides a communication to another application running on a different host, the application may use an existing application layer protocols such as: HTTP(e.g. the Browser and web server), SMTP(e.g. the email-client). And may be the application does not use any existing protocols and depends on the socket programming to communicate to another application. So the web application is a type of the network applications. 
There are lots of advantages from build up a network, but the th…

CABILING & VARIOUS TRANSMISSION

CABILING & VARIOUS TRANSMISSIONNetwork cabling and wiring systems rely on a variety of structured cable system components working in harmony.  The weakest link in a cabling channel represents its highest performance. Some of the components of a cabling system include: patch panels for switching functions between router for incoming and outgoing lines, horizontal cables for in-wall installation, and patch cables to connect standalone computers to outlets and outlets to telecommunications closets. For housing and storage of network wiring systems, products such as cable troughs, wire ways, enclosure cables, rack accessories, and cabling cabinets are also installed. These components protect the wiring and equipment from dust, dirt, water, and oil while simplifying cable management. Building on our understanding of the different network topologies that connect computers, we focus next on the cables that connect them. In this lesson, we examine the construction, features, and operation of each type of cable, and the advantages and disadvantages of each. 


The vast majority of networks today are connected by some sort of wiring or cabling that acts as a network transmission medium that carries signals between computers. Many cable types are available to meet the varying needs and sizes of networks, from small to large. Cable types can be confusing. Belden, a leading cable manufacturer, publishes a catalog that lists more than 2200 types of cabling. Fortunately, only three major groups of cabling connect the majority of networks:  

  • Coaxial cable 
  • Twisted-pair (unshielded and shielded) cable 
  • Fiber-optic cable 
Coaxial Cable At one time, coaxial cable was the most widely used network cabling. There were a couple of reasons for coaxial cable's wide usage: it was relatively inexpensive, and it was light, flexible, and easy to work with. In its simplest form, coaxial cable consists of a core of copper wire surrounded by insulation, a braided metal shielding, and an outer cover. The term shielding refers to the woven or stranded metal mesh (or other material) that surrounds some types of cabling. Shielding protects transmitted data by absorbing stray electronic signals, called noise, so that they do not get onto the cable and distort the data. Cable that contains one layer of foil insulation and one layer of braided metal shielding is referred to as dual shielded. For environments that are subject to higher interference, quad shielding is available. Quad shielding consists of two layers of foil insulation and two layers of braided metal shielding. 

The core of a coaxial cable carries the electronic signals that make up the data. This wire core can be either solid or stranded. If the core is solid, it is usually copper. Surrounding the core is a dielectric insulating layer that separates it from the wire mesh. The braided wire mesh acts as a ground and protects the core from electrical noise and cross-talk. (Cross-talk is signal overflow from an adjacent wire. For a more detailed discussion of cross-talk, see the section Unshielded Twisted-Pair (UTP) Cable, later in this lesson.) The conducting core and the wire mesh must always be kept separate from each other. If they touch, the cable will experience a short, and noise or stray signals on the mesh will flow onto the copper wire. An electrical short occurs when any two conducting wires or a conducting wire and a ground come into contact with each other. This contact causes a direct flow of current (or data) in an unintended path. In the case of household electrical wiring, a short will cause sparking and the blowing of a fuse or circuit breaker. With electronic devices that use low voltages, the result is not as dramatic and is often undetectable. These low-voltage shorts generally cause the failure of a device; and the short, in turn, destroys the data. A no conducting outer shield—usually made of rubber, Teflon, or plastic—surrounds the entire cable. Coaxial cable is more resistant to interference and attenuation than twisted-pair cabling. As shown in Figure below attenuation is the loss of signal strength that begins to occur as the signal travels farther along a copper cable. The stranded, protective sleeve absorbs stray electronic signals so that they do not affect data being sent over the inner copper cable. For this reason, coaxial cabling is a good choice for longer distances and for reliably supporting higher data rates with less sophisticated equipment. 



1) Thin (thinnet) cable 
2) Thick (thicknet) cable 

Thinnet Cable: Thinnet cable is a flexible coaxial cable about 0.64 centimeters (0.25 inches) thick. Because this type of coaxial cable is flexible and easy to work with, it can be used in almost any type of network installation. Thinnet cable connected directly to a computer's network interface card (NIC). Thinnet coaxial cable can carry a signal for a distance of up to approximately 185 meters (about 607 feet) before the signal starts to suffer from attenuation. Cable manufacturers have agreed upon specific designations for different types of cable. Thinnet is included in a group referred to as the RG-58 family and has 50ohm impedance. (Impedance is the resistance, measured in ohms, to the alternating current that flows in a wire.) The principal distinguishing feature of the RG-58 family is the center core of copper 


RG-58/U
Solid copper core
RG-58 A/U
Stranded wire core
RG-58 C/U
Military specification of RG-58 A/U
RG-59
Broadband transmission, such as cable television
RG-6
Larger in diameter and rated for higher frequencies than RG-59, but also used for broadband transmissions
RG-62
Arc Net networks

Thicknet Cable: Thicknet cable is a relatively rigid coaxial cable about 1.27 centimeters (0.5 inches) in diameter. Thicknet cable is sometimes referred to as Standard Ethernet because it was the first type of cable used with the popular network architecture Ethernet. Thicknet cable's copper core is thicker than a thinnet cable core.  The thicker the copper core, the farther the cable can carry signals. This means that thicknet can carry signals farther than thinnet cable. Thicknet cable can carry a signal for 500 meters (about 1640 feet). Therefore, because of thick-net's ability to support data transfer over longer distances, it is sometimes used as a backbone to connect several smaller thinnet-based networks. 

Transceiver: A transceiver connects the thinnet coaxial cable to the larger thicknet coaxial cable. A transceiver designed for thicket Ethernet includes a connector known as a vampire tap, or a piercing tap, to make the actual physical connection to the thicknet core. This connector is pierced through the insulating layer and makes direct contact with the conducting core. Connection from the transceiver to the NIC is made using a transceiver cable (drop cable) to connect to the attachment unit interface (AUI) port connector on the card. An AUI port connector for thicknet is also known as a Digital Intel Xerox (DIX) connector (named for the three companies that developed it and its related standards) or as a DB-15 connector.  


Data Transmission Rate of 10Mbps
it has a maximum transmission speed of  up to 10Mbps
Uses base-band transmission
"BASE" is shorthand for "base-band transmission" or "base-band Ethernet," meaning that the medium only transmits Ethernet signals;
Used in Ethernet networks it has a maximum cable length of 500 meters
maximum network segment length of 185 meters


Both thinnet and thicknet cable use a connection component, known as a BNC connector, to make the connections between the cable and the computers. There are several important components in the BNC family, including the following: 


The BNC cable connector is either soldered or crimped to the end of a cable. 
The BNC T connector: This connector joins the network interface card (NIC) in the computer to the network cable. 
The BNC barrel connector:  connector is used to join two lengths of thinnet cable to make one longer length. 
The BNC terminator: A BNC terminator closes each end of the bus cable to absorb stray signals. 


The type of cable grade that you should use depends on where the cables will be laid in your office. Coaxial cables come in two grades: 
  • Polyvinyl chloride (PVC) grade 
  • Plenum grade 
Polyvinyl chloride (PVC) is a type of plastic used to construct the insulation and cable jacket for most types of coaxial cable. PVC coaxial cable is flexible and can be easily routed through the exposed areas of an office. However, when it burns, it gives off poisonous gases. A plenum is the shallow space in many buildings between the false ceiling and the floor above; it is used to circulate warm and cold air through the building. 
Fire codes give very specific instructions about the type of wiring that can be routed through this area, because any smoke or gas in the plenum will eventually blend with the air breathed by everyone in the building. Plenum-grade cabling contains special materials in its insulation and cable jacket. These materials are certified to be fire resistant and produce a minimum amount of smoke; this reduces poisonous chemical fumes. Plenum cable can be used in the plenum area and in vertical runs (for example, in a wall) without conduit. However, plenum cabling is more expensive and less flexible than PVC cable. 


Consider the following coaxial capabilities when making a decision about which type of cabling to use.  
Use coaxial cable if you need a medium that can:  
  • Transmit voice, video, and data. 
  • Transmit data for greater distances than is possible with less expensive cabling. 
  • Offer a familiar technology with reasonable data security. 

In its simplest form, twisted-pair cable consists of two insulated strands of copper wire twisted around each other.  
A number of twisted-pair wires are often grouped together and enclosed in a protective sheath to form a cable. The total number of pairs in a cable varies. The twisting cancels out electrical noise from adjacent pairs and from other sources such as motors, relays, and transformers. 

  
UTP, using the 10BaseT specification, is the most popular type of twisted-pair cable and is fast becoming the most popular LAN cabling. The maximum cable length segment is 100 meters, about 328 feet. Traditional UTP cable consists of two insulated copper wires. UTP specifications govern how many twists are permitted per foot of cable; the number of twists allowed depends on the purpose to which the cable will be put. In North America, UTP cable is the most commonly used cable for existing telephone systems and is already installed in many office buildings.

The 568A Commercial Building Wiring Standard of the Electronic Industries Association and the Telecommunications Industries Association (EIA/TIA) specifies the type of UTP cable that is to be used in a variety of building and wiring situations. The objective is to ensure consistency of products for customers. These standards include five categories of UTP:  
  • Category 1 This refers to traditional UTP telephone cable that can carry voice but not data transmissions. Most telephone cable prior to 1983 was Category 1 cable. 
  • Category 2 This category certifies UTP cable for data transmissions up to 4 megabits per second (Mbps). It consists of four twisted pairs of copper wire. 
  • Category 3 This category certifies UTP cable for data transmissions up to 16 Mbps. It consists of four twisted pairs of copper wire with three twists per foot. 
  • Category 4 This category certifies UTP cable for data transmissions up to 20 Mbps. It consists of four twisted pairs of copper wire. 
  • Category 5 This category certifies UTP cable for data transmissions up to 100 Mbps. It consists of four twisted pairs of copper wire. 
Most telephone systems use a type of UTP. In fact, one reason why UTP is so popular is because many buildings are prewired for twisted-pair telephone systems. As part of the prewiring process, extra UTP is often installed to meet future cabling needs. If preinstalled twisted-pair cable is of sufficient grade to support data transmission, it can be used in a computer network. Caution is required, however, because common telephone wire might not have the twisting and other electrical characteristics required for clean, secure, computer data transmission.  One potential problem with all types of cabling is cross-talk (As discussed earlier in this lesson, cross-talk is defined as signals from one line interfering with signals from another line.) UTP is particularly susceptible to cross-talk, but the greater the number of twists per foot of cable, the more effective the protection against cross-talk.  


STP cable uses a woven copper-braid jacket that is more protective and of a higher quality than the jacket used by UTP. STP also uses a foil wrap around each of the wire pairs. This gives STP excellent shielding to protect the transmitted data from outside interference, which in turn allows it to support higher transmission rates over longer distances than UTP.          

While we have defined twisted-pair cabling by the number of twists and its ability to transmit data, additional components are necessary to complete an installation. As it is with telephone cabling, a twisted-pair cable network requires connectors and other hardware to ensure proper installation.  


Twisted-pair cabling uses RJ-45 telephone connectors to connect to a computer. These are similar to RJ-11 telephone connectors. Although RJ-11 and RJ-45 connectors look alike at first glance, there are crucial differences between them. The RJ-45 connector is slightly larger and will not fit into the RJ-11 telephone jack. The RJ-45 connector houses eight cable connections, while the RJ-11 houses only four. Several components are available to help organize large UTP installations and make them easier to work with.  


Distribution racks and rack shelves can create more room for cables where there isn't much floor space. Using them is a good way to organize a network that has a lot of connections.  


These come in various versions that support up to 96 ports and transmission speeds of up to 100 Mbps.  


These single or double RJ-45 jacks snap into patch panels and wall plates and support data rates of up to 100 Mbps.  

Wall plates: These support two or more couplers.   

Various twisted-pair cabling components  

Twisted-Pair Cabling Considerations  

  • Your LAN is under budget constraints. 
  • You want a relatively easy installation in which computer connections are simple. 
Do not use twisted-pair cable if?  
  • Your LAN requires a high level of security and you must be absolutely sure of data integrity.
  • You must transmit data over long distances at high speeds

In fiber-optic cable, optical fibers carry digital data signals in the form of modulated pulses of light. This is a relatively safe way to send data because, unlike copper-based cables that carry data in the form of electronic signals, no electrical impulses are carried over the fiber-optic cable. This means that fiber optic cable cannot be tapped, and its data cannot be stolen.  

Fiber-optic cable is good for very high-speed, high-capacity data transmission because of the purity of the signal and lack of signal attenuation.  


An optical fiber consists of an extremely thin cylinder of glass, called the core, surrounded by a concentric layer of glass, known as the cladding. The fibers are sometimes made of plastic. Plastic is easier to install, but cannot carry the light pulses for as long a distance as glass. Fiber Optics is sending signals down hair-thin strands of glass or plastic fiber. The light is “guided” down the center of the fiber called the “core”. The core is surrounded by a optical material called the “cladding” that traps the light in the core using an optical technique called “total internal reflection. The core and cladding are usually made of ultra-pure glass. The fiber is coated with a protective plastic covering called the “primary buffer coating” that protects it from moisture and other damage. More protection is provided by the “cable” which has the fibers and strength members inside an outer covering called a “jacket”.  
Because each glass strand passes signals in only one direction, a cable includes two strands in separate jackets. One strand transmits and one receives. A reinforcing layer of plastic surrounds each glass strand, and Kevlar fibers provide strength. The Kevlar fibers in the fiber-optic connector are placed between the two cables. Just as their counterparts (twisted-pair and coaxial) are, fiber-optic cables are encased in a plastic coating for protection.  


Fiber-optic cable transmissions are not subject to electrical interference and are extremely fast, currently transmitting about 100 Mbps with demonstrated rates of up to 1 gigabit per second (Gbps). They can carry a signal the light pulse for many miles.  
Single Mode fiber optic cable has a small diametric core that allows only one mode of light to propagate. Because of this, the number of light reflections created as the light passes through the core decreases, lowering attenuation and creating the ability for the signal to travel faster, further. This application is typically used in long distance, higher bandwidth runs by Telco’s, CATV companies, and Colleges and Universities. 
Multi-mode fiber optic cable has a large diametric core that allows multiple modes of light to propagate. Because of this, the number of light reflections created as the light passes through the core increases, creating the ability for more data to pass through at a given time. Because of the high dispersion and attenuation rate with this type of fiber, the quality of the signal is reduced over long distances. This application is typically used for short distance, data and audio/video applications in LANs. RF broadband signals, such as what cable companies commonly use, cannot be transmitted over multi-mode fiber. 


Use fiber-optic cable if you:  
  • Need to transmit data at very high speeds over long distances in very secure media. Do not use fiber-optic cable if you:  
  • Are under a tight budget. 
  • Do not have the expertise available to properly install it and connect devices to it. 
ST
Twist on
Single mode /Multimode
PC, UPC
1
LANs
Keyed
FC
Screw on
Single mode /Multimode
PC, UPC, APC 
1
Datacom, Telecommuni- cations 
Keyed
SC
Snap on
Single mode /Multimode
PC, UPC, APC
1
CATV, Test Equipment
Keyed
LC
Snap on RJ45 style
Single mode /Multimode
PC, UPC, APC
1
Gigabit Ethernet, Video Multimedia
Small Form Factor (SFF)
MU
Snap on RJ45 style
Single mode /Multimode
N/A
1
Medical, Military 
Small Form Factor (SFF)
MT-RJ
Snap on RJ45 style
Single mode /Multimode
N/A
2
Gigabit Ethernet, Asynchronous Transmission Mode (ATM)
One of Mating Connectors must have Alignment Pins
MPO  (MTP) 
Push/Pull
Single mode /Multimode
N/A
4, 8,  12, 16, 24 
Active Device Transceiver, Interconnec tions for O/E Modules
One of Mating Connectors must have Alignment Pins


Two techniques can be used to transmit the encoded signals over cable: base-band and broadband transmission.  


Base-band systems use digital signaling over a single channel. Signals flow in the form of discrete pulses of electricity or light. With base-band transmission, the entire communication channel capacity is used to transmit a single data signal. The digital signal uses the complete bandwidth of the cable, which constitutes a single channel. The term bandwidth refers to the data transfer capacity, or speed of transmission, of a digital communications system as measured in bits per second (bps).  
As the signal travels along the network cable, it gradually decreases in strength and can become distorted. If the cable length is too long, the received signal can be unrecognizable or misinterpreted.  

As a safeguard, base-band systems sometimes use repeaters to receive incoming signals and re-transmit them at their original strength and definition. This increases the practical length of a cable.  


Broadband systems. With analog transmission, the signals are continuous and no discrete. Signals flow across the physical medium in the form of electromagnetic or optical waves. With broadband transmission, signal flow is unidirectional.  
If sufficient total bandwidth is available, multiple analog transmission systems, such as cable television and network transmissions, can be supported simultaneously on the same cable.  

Each transmission system is allocated a part of the total bandwidth. All devices associated with a given transmission system, such as all computers using a LAN cable, must then be tuned so that they use only the frequencies that are within the allocated range.  

While base-band systems use repeaters, broadband systems use amplifiers to regenerate analog signals at their original strength.  

In broadband transmission, signals flow in one direction only, so there must be two paths for data flow in order for a signal to reach all devices. There are two common ways to do this:  
  • Through mid-split broadband configuration, the bandwidth is divided into two channels, each using a different frequency or range of frequencies. One channel transmits signals; the other receives signals. 
  • In dual-cable broadband configuration, each device is attached to two cables. One cable is used to send, and the other is used to receive. 

Increasing the speed of data transmission is a priority as network sizes and data traffic increase. By maximizing the use of the data channel, we can exchange more data in less time. The most basic form of data or information transmission is called simplex. This means that data is sent in one direction only, from sender to receiver. Examples of simplex transmission are radio and television. With simplex transmission, problems encountered during the transmission are not detected and corrected. Senders cannot even be sure that the data is received.  


In the next level of data transmission, called half-duplex transmission, data is sent in both directions, but in only one direction at a time. xamples of technology that uses half-duplex communication are shortwave radio and walkie-talkies. With half-duplex transmission, you can incorporate error detection and request that any bad data be resent. Surfing the World Wide Web is a form of half-duplex data transmission. You send a request for a Web page and then wait while it is being sent back to you. Most modem connections use half-duplex data transmission. 


The most efficient method of transmitting data is to use a full-duplex transmission, in which data can be transmitted and received at the same time. A good example is a cable connection that not only allows you to receive TV channels, but also supports telephone and Internet connection. A telephone is a full-duplex device because it allows both parties to talk at the same time. Modems, by design, are half-duplex devices. They either send or receive data, switching between transmission modes and receiving mode. You can create a full-duplex modem channel by using two modems and two telephone lines. The only requirement is that both computers be connected and configured to support this type of communication. 


When we enter data into the computer via keyboard, each keyed element is encoded by the electronics within the keyboard into an equivalent binary coded pattern, using one of the standard coding schemes that are used for the interchange of information. To represent all characters of the keyboard, a unique pattern of 7 or 8 bits in size is used. The use of 7 bits means that 128 different elements can be represented, while 8 bits can represent 256 elements. A similar procedure is followed at the receiver that decodes every received binary pattern into the corresponding character. The most widely used codes that have been adopted for this function are the Extended Binary Coded Decimal (EBCDIC) and the American Standard Code for Information Interchange codes (ASCII). Both coding schemes cater to all the normal alphabetic, numeric, and punctuation characters, collectively referred to as printable characters and a range of additional control characters, known as non-printable characters.   Data transmission refers to the movement of data in form of bits between two or more digital devices. This transfer of data takes place via some form of transmission media (for example, coaxial cable, fiber optics etc.) Types of Data Transmission 


Definition: Within a computing or communication device, the distances between different sub-units are too short. Thus, it is normal practice to transfer data between sub-units using a separate wire to carry each bit of data. There are multiple wires connecting each sub-unit and data is exchanged using a parallel transfer mode. This mode of operation results in minimal delays in transferring each word.   
In parallel transmission, all the bits of data are transmitted simultaneously on separate communication lines. 
• In order to transmit n bits, n wires or lines are used. Thus each bit has its own line. 
• All n bits of one group are transmitted with each clock pulse from one device to another i.e. multiple bits are sent with each clock pulse. 
• Parallel transmission is used for short distance communication. As shown in the fig, eight separate wires are used to transmit 8 bit data from sender to receiver.


 It is speedy way of transmitting data as multiple bits are transmitted simultaneously with a single clock pulse. 


It is costly method of data transmission as it requires n lines to transmit n bits at the same time.   


Defination: When transferring data between two physically separate devices, especially if the separation is more than a few kilometers, for reasons of cost, it is more economical to use a single pair of lines. Data is transmitted as a single bit at a time using a fixed time interval for each bit. This mode of transmission is known as bit-serial transmission.   

In serial transmission, the various bits of data are transmitted serially one after the other. 
• It requires only one communication line rather than n lines to transmit data from sender to receiver. 
Thus all the bits of data are transmitted on single line in serial fashion. 
• In serial transmission, only single bit is sent with each clock pulse. 
• As shown in fig., suppose an 8-bit data 11001010 is to be sent from source to destination. Then least significant bit (LSB) i,e. 0 will be transmitted first followed by other bits. The most significant bit (MSB) i.e. 1 will be transmitted in the end via single communication line. 
• The internal circuitry of computer transmits data in parallel fashion. So in order to change this parallel data into serial data, conversion devices are used. 
These conversion devices convert the parallel data into serial data at the sender side so that it can be transmitted over single line. 
On receiver side, serial data received is again converted to parallel form so that the interval circuitry of computer can accept it 
• Serial transmission is used for long distance communication. 


Use of single communication line reduces the transmission line cost by the factor of n as compared to parallel transmission.  


1. Use of conversion devices at source and destination end may lead to increase in overall transmission cost. 

2. This method is slower as compared to parallel transmission as bits are transmitted serially one after the other.  


There are two types of serial transmission-synchronous and asynchronous both these transmissions use 'Bit synchronization' 

Bit Synchronization is a function that is required to determine when the beginning and end of the data transmission occurs. 

Bit synchronization helps the receiving computer to know when data begin and end during a transmission. Therefore bit synchronization provides timing control.  


Asynchronous transmission sends only one character at a time where a character is either a letter of the alphabet or number or control character i.e. it sends one byte of data at a time. 
• Bit synchronization between two devices is made possible using start bit and stop bit. 
• Start bit indicates the beginning of data i.e. alerts the receiver to the arrival of new group of bits. A start bit usually 0 is added to the beginning of each byte. 
• Stop bit indicates the end of data i.e. to let the receiver know that byte is finished, one or more additional bits are appended to the end of the byte. These bits, usually 1s are called stop bits.              
Addition of start and stop increase the number of data bits. Hence more bandwidth is consumed in asynchronous transmission. 
• There is idle time between the transmissions of different data bytes. This idle time is also known as Gap 
• The gap or idle time can be of varying intervals. This mechanism is called Asynchronous, because at byte level sender and receiver need not to be synchronized. But within each byte, receiver must be synchronized with the incoming bit stream. 


1. Asynchronous transmission is well suited for keyboard type-terminals and paper tape devices. The advantage of this method is that it does not require any local storage at the terminal or the computer as transmission takes place character by character.                       
2. Asynchronous transmission is best suited to Internet traffic in which information is transmitted in short bursts. This type of transmission is used by modems.   


1. This method of data transmission is cheaper in cost as compared to synchronous e.g. If lines are short, asynchronous transmission is better, because line cost would be low and idle time will not be expensive. 
2. In this approach each individual character is complete in itself, therefore if character is corrupted during transmission, its successor and predecessor character will not be affected. 
3. It is possible to transmit signals from sources having different bit rates. 
4. The transmission can start as soon as data byte to be transmitted becomes available. 
5. Moreover, this mode of data transmission in easy to implement. 


1. This method is less efficient and slower than synchronous transmission due to the overhead of extra bits and insertion of gaps into bit stream. 
2. Successful transmission inevitably depends on the recognition of the start bits. These bits can be missed or corrupted.   Synchronous Transmission  
• Synchronous transmission does not use start and stop bits. 
In this method bit stream is combined into longer frames that may contain multiple bytes. 
• There is no gap between the various bytes in the data stream. 
• In the absence of start & stop bits, bit synchronization is established between sender & receiver by 'timing' the transmission of each bit. 
Since the various bytes are placed on the link without any gap, it is the responsibility of receiver to separate the bit stream into bytes so as to reconstruct the original information. 
• In order to receive the data error free, the receiver and sender operates at the same clock frequency.   Application of Synchronous transmission   
• Synchronous transmission is used for high speed communication between computers.   Advantage of Synchronous transmission   
1. This method is faster as compared to asynchronous as there are no extra bits (start bit & stop bit) and also there is no gap between the individual data bytes.   


1. It is costly as compared to asynchronous method. It requires local buffer storage at the two ends of line to assemble blocks and it also requires accurately synchronized clocks at both ends. This lead to increase in the cost. 

2. The sender and receiver have to operate at the same clock frequency. This requires proper synchronization which makes the system complicated. 

1
Number of bits transmitted at one clock pulse
One bit
n bits
2
No. of lines required to transmit n bits
One line
n lines
3
Speed of data transfer
Slow
Fast
4
Cost of transmission
Low as one line is required
Higher as n lines are required
5
Application
Long distance communication between two computers
Short distance communication like computer to printer


Sr.No.
Factor
Asynchronous
Synchronus
1
Data send at one time
Usually 1 byte
Multiple bytes
2
Start and stop bit
Used
Not used
3
Gap between Data units
Present
Not present
4
Data transmission
Slow
Fast
5
Cost
Low
High


IBM has developed its own cabling system, complete with its own numbers, standards, specifications, and designations. Many of these parameters, however, are similar to non-IBM specifications.  

IBM introduced its cabling system in 1984. The purpose of this system was to ensure that the cabling and connectors would meet the specifications of their equipment. The IBM specification includes the following components: 
  • Cable connectors 
  • Face plates 
  • Distribution panels 
  • Cable types
The one IBM cabling component that is unique is the IBM connector, which is different from standard BNC or other connectors. These are IBM Type A connectors, known elsewhere as universal data connectors. They are neither male nor female; you can connect one to another by flipping either one over. These IBM connectors require special face-plates and distribution panels to accommodate their unique shape.  

The IBM cabling system classifies cable into types. For example, in the IBM system, Category 3 cable (voice-grade UTP cable) is referred to as Type 3. The cable definitions specify which cable is appropriate for a given application or environment. The wire indicated in the system conforms to American Wire Gauge (AWG) standards.  

AWG: The Standard Cable Measurement: Cable measurements are often expressed as numbers, followed by the initials AWG. (AWG is a measurement system for wire that specifies its thickness.) As the thickness of the wire increases, the AWG number decreases. Telephone wire is often used as a reference point; it has a thickness of 22 AWG. A wire of 14 AWG is thicker than telephone wire, and wire of 26 AWG is thinner than telephone wire.


Type 1
Shielded twisted-pair
Two pairs of 22 AWG wires surrounded (STP) cable by an outer braided shield; used for computers and multi-station access units (MAUs)
Type 2
Voice and data cable
A voice and data shielded cable with two twisted pairs of 22 AWG wires for data, an outer braided shield, and four twisted pairs of 26 AWG wires for voice
Type 3
Voice-grade cable
Consists of four solid, unshielded twisted-pair, 22 or 24 AWG cables
Type 4
Undefined

Type 5
Fiber-optic cable
Two 62.5/125-micron multi-mode optical fibers—the industry standard
Type 6
Data patch cable
Two 26 AWG twisted-pair stranded cables with a dual foil and braided shield
Type 7
Undefined

Type 8
Carpet cable
Housed in a flat jacket for use under carpets; two shielded twisted-pair 26 AWG cables; limited to one half the distance of Type 1 cable
Type 9
Plenum-grade cable
Fire safe  Two shielded twisted-pair cables


To determine which cabling is the best for a particular site you need to answer the following questions: 
  • How heavy will the network traffic be? 
  • What level of security does the network require? 
  • What distances must the cable cover? 
  • What are the cable options? 
  • What is the budget for cabling? 
The better the cable protects against internal and external electrical noise, the farther and faster the cable will carry a clear signal. However, the better the speed, clarity, and security of the cable, the higher the cabling cost.  


As with most network components, there are trade-offs with the type of cable you purchase. If you work for a large organization and choose the least expensive cable, the accountants might initially be pleased, but you might soon notice that the LAN is inadequate in both transmission speed and data security.  

Which cabling you select will depend on the needs of a particular site. The cabling you purchase to set up a LAN for a small business has different requirements from those of a larger organization, such as a major banking institution.  

In the rest of this section, we examine some of the considerations that affect cabling price and performance.  


How easy is the cable to install and work with? In a small installation where distances are short and security isn't a major issue, it does not make sense to choose thick, cumbersome, and expensive cable.  


The level of shielding required will affect cable cost. Almost every network uses some form of shielded cable. The noisier the area in which the cable is run, the more shielding will be required. The same shielding in a plenum-grade cable will be more expensive as well.  


Cross-talk and noise can cause serious problems in large networks where data integrity is crucial. Inexpensive cabling has low resistance to outside electrical fields generated by power lines, motors, relays, and radio transmitters. This makes it susceptible to both noise and cross-talk. 


Transmission rates are measured in megabits per second. A standard reference point for current LAN transmission over copper cable is 100 Mbps. Fiber-optic cable transmits at more than 1 Gbps.  


Higher grades of cables can carry data securely over long distances, but they are relatively expensive; lower-grade cables, which provide less data security over shorter distances, are relatively inexpensive.  


Different cable types have different rates of attenuation; therefore, cable specifications recommend specific length limits for the different types. If a signal suffers too much attenuation, the receiving computer will be unable to interpret it. Most networks have error-checking systems that will generate a re-transmission if the signal is too weak to be understood. However, re-transmission takes time and slows down the network



Unroll the required length of network cable and add a little extra wire, just in case. 


Carefully remove the outer jacket of the cable. Be careful when stripping the jacket as to not nick or cut the internal wiring. One good way to do this is to cut lengthwise with snips or a knife along the side of the cable, away from yourself, about an inch toward the open end. This reduces the risk of nicking the wires' insulation. Locate the string inside with the wires, or if no string is found, use the wires themselves to unzip the sheath of the cable by holding the sheath in one hand and pulling sideways with the string or wire. Cut away the unzipped sheath and cut the twisted pairs about 1 1/4" (30 mm). You will notice 8 wires twisted in 4 pairs. Each pair will have one wire of a certain color and another wire that is white with a colored stripe matching its partner (this wire is called a tracer). 


Inspect the newly revealed wires for any cuts or scrapes that expose the copper wire inside. If you have breached the protective sheath of any wire, you will need to cut the entire segment of wires off and start over at step one. Exposed copper wire will lead to cross-talk, poor performance or no connectivity at all. It is important that the jacket for all network cables remains intact. 


Untwist the pairs so they will lay flat between your fingers. The white piece of thread can be cut off even with the jacket and disposed .For easier handling, cut the wires so that they are 3/4" (19 mm) long from the base of the jacket and even in length. 

Step 5:  

Arrange the wires based on the wiring specifications you are following. There are two methods set by the TIA, 568A and 568B. Which one you use will depend on what is being connected. A straight-through cable is used to connect two different-layer devices (e.g. a hub and a PC). Two like devices normally require a cross-over cable. The difference between the two is that a straight-through cable has both ends wired identically with 568B, while a cross-over cable has one end wired 568A and the other end wired 568B. For our demonstration in the following steps, we will use 568B, but the instructions can easily be adapted to 568A.  
o orange 
o white green 
o blue 
o white blu
o green 
o white brown o brown 
o orange 
o white green 
o blue 
o white blue 
o green 
o white brown 
o brown 
o orange 
o white green 
o blue 
o white blue 
o green 
o white brown 
o brown 
o white/green 
o green 
o white/orange 
o blue 
o white/blue 
o orange 
o white/brown 
o brown 


Press all the wires flat and parallel between your thumb and forefinger. Verify the colors have remained in the correct order. Cut the top of the wires even with one another so that they are 1/2" (12.5 mm) long from the base of the jacket, as the jacket needs to go into the 8P8C connector by about 1/8", meaning that you only have a 1/2" of room for the individual cables. Leaving more than 1/2" untwisted can jeopardize connectivity and quality. Ensure that the cut leaves the wires even and clean; failure to do so may cause the wire not to make contact inside the jack and could lead to wrongly guided cores inside the plug. 


Keep the wires flat and in order as you push them into the RJ-45 plug with the flat surface of the plug on top. The white/orange wire should be on the left if you're looking down at the jack. You can tell if all the wires made it into the jack and maintain their positions by looking head-on at the plug. You should be able to see a wire located in each hole, as seen at the bottom right. You may have to use a little effort to push the pairs firmly into the plug. The cabling jacket should also enter the rear of the jack about 1/4" (6 mm) to help secure the cable once the plug is crimped. You may need to stretch the sleeve to the proper length. Verify that the sequence is still correct before crimping.  
 

Place the wired plug into the crimping tool. Give the handle a firm squeeze. You should hear a ratcheting noise as you continue. Once you have completed the crimp, the handle will reset to the open position. To ensure all pins are set, some prefer to double-crimp by repeating this step. 
  

Test the cable to ensure that it will function in the field. Mis-wired and incomplete network cables could lead to headaches down the road. In addition, with power-over-Ethernet (PoE) making its way into the marketplace, crossed wire pairs could lead to physical damage of computers or phone system equipment, making it even more crucial that the pairs are in the correct order. A simple cable tester can quickly verify that information for you. Should you not have a network cable tester on hand, simply test connectivity pin to pin. 


Below are the steps involved in configuring your computer to connect them on a LAN using Ethernet cable. 


In order to start the connection, you’ll have to assign different IP address for both computers. To change the IP address of your computers for the LAN connection, you should make changes in the LAN adapter settings. 
  • Open Control panel from the start menu and click on Network and Internet and click on Network and Sharing center. 
  • From the left sidebar, click on Change adapter settings. 
  • Under the Network connections window select the appropriate icon for your LAN  
  • Adapter and right-click on it, then choose Properties. 
  • Under the Network tab select Internet Protocol Version 4 (TCP/IPv4) and click on the Properties button. 
  • Now set the addresses as mentioned below in each computer and click OK. 

IP address:       192.168.0.1 

Subnet mask:  255.255.255.0 


IP address:       192.168.0.2 

Subnet mask:  255.255.255.0 


Now, connect one end of the cable into the Ethernet port of Computer 1 and the other end with the same of the Computer 2 and apply the following steps in both the computers. 
  • Right-click on Computer from the start menu and select Properties. 
  • The system properties Control Panel window opens as shown below. 
  • Click on Change settings and the System properties dialog box appears. Under the Computer Name tab, click on the Change button to assign a WORK-GROUP. Assign the same work-group name for both computers otherwise it won’t work. 
Restart each computer. It does not matter which computer you restart first. After starting both the computer, double-click on the Computer icon at the start menu and then click on Network from the left side of the explorer window. 

In the computer 1, you should see an icon denoting your second computer’s name under the Network window. Similarly, you can see that the first computer has been appeared under the Network window of your second computer. 

If they do not appear, you should get a message prompting to turn on Network Discovery and file Sharing. Click that security pop-up and select “make the network a private network”. In case, you may have to restart your computers. 
Once you see the other computer in your Network computer window, just double click on it. If the other computer is password protected, you will have to enter the exact user name and password of that computer to get access of the shared folder. 
If you want to share some files or folder of a computer with the other computer on the network, right-click on that and select Share with > Home group. Even you can share a total drive by right-clicking on it. 


1) Ping two computer after using straight through cable. 

2) Ping tow computer using cross over cable. 

3) Share files in between two computers those who are connected through the straight through cable. 
  


a) Equal resistance 
b) The same diameter 
c) Both A & B 
d) A common axis 


a) Inner conductor 
b) Outer conductor 
c) Diameter of cable 
d) Insulating Material 


a) Pure Ethernet 
b) Ethernet Over SDH 
c) Ethernet over MPLS 
d) All of the mentioned 


a) Coaxial Cable 
b) Twisted pair Cable
c) Optical fiber 
d) None of the Above 


a) Coaxial Cable 
b) Twisted pair Cable 
c) Optical fiber 
d) None of the Above 

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