Cobweb Optic Cabling

Fast and Gigabit Ethernet Media and Standards

Jan L. Harrington , in Ethernet Networking for the Small-scale Office and Professional person Home Role, 2007

Single versus Multimode Cobweb Optics

There are two types of fiber optic cabling, single mode and multimode. Single mode, which can transmit a unmarried wavelength of light long distances, is used primarily for WAN connections. Multimode tin transmit multiple signals at 1 tim, but is more than limited in length and typically used in LANs.

When light is introduced into an optical fiber, it can either become direct downwardly the middle of the optical tube or information technology can travel at an angle, reflecting off the side of the tube every bit it travels. Each signal traveling down the tube at a time is known equally a mode.

The diameter of the core of a unmarried-mode cobweb is very small (for example, ix microns). A single ray of light is transmitted down the core, and information technology travels without reflection straight to its destination. In theory, 1 single-mode fiber link tin can exist as long equally 10 kilometers.

Multimode fiber has a larger core bore and supports the transmission of multiple signals. Each ray of light has a dissimilar angle of reflection, making it possible for the receiving device to separate the individual signals. (See Figure iii-6.) However, the reflection angles disperse over distances (modal dispersion), spreading the signals and ultimately making it incommunicable to tell the signals apart. This limits the distance of multimode fiber. If the core is 62.5 microns in bore, the maximum length is approximately 275 meters; 50 micron fiber can go every bit far equally 550 meters.

Figure 3-6. Multiple signals traveling down multimode fiber

Multimode fiber is by and large easier to work with than single mode. Because fiber optic cabling cannot be spliced, the ends of two pieces of unmarried manner fiber must the aligned precisely when they are to be used as a single run of cable. Multimode fiber, because of its shorter runs, often doesn't need to be assembled out of multiple pieces of cabling; it can employ a single unbroken piece of cobweb.

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Network Media

Naomi J. Alpern , Robert J. Shimonski , in Eleventh Hr Network+, 2010

Interference

Interference is an issue affecting media that transmit electrical signals such as UTP and coaxial cable. Fiber-optic cabling is non susceptible to interference since it is not a copper-based media and it uses light rather than electronic signals to transmit data. At that place are three main types of interference:

■

Electromagnetic interference (EMI) It is a depression voltage, low current, high frequency point that comes from an outside source, which can interfere with the electronic signals transmitted over cabling. UTP is vulnerable, STP is less vulnerable, and fiber optic is immune to EMI.

■

Radio frequency interference (RFI) It is caused past electromagnetic radiation in the radio frequency range generated by radio and television broadcast towers, microwave satellite dishes, appliances, and furnaces. UTP is vulnerable, STP is less vulnerable, and fiber optic is immune to RFI.

■

Crosstalk The electromagnetic field of i wire interferes with the manual of information along another wire. This type of interference tin cause a loss or abuse of information. UTP is vulnerable, STP is less vulnerable, and fiber optic is immune to crosstalk.

EXAM WARNING

Don't get crosstalk confused with EMI. Retrieve that when one cablevision has its information communications bleed onto another cable, it is crosstalk. EMI tin come from any number of sources, including florescent lights or mechanism.

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It Systems Infrastructure∗

Thomas Norman CPP , in Effective Physical Security (5th Edition), 2017

Cabling

Network cabling tin be wired or cobweb optic. Fiber optic cabling types include unmarried mode and multimode.

Wired Cabling

Category 5e and half-dozen cables are used for network cabling. Both have a native distance limit of 300   ft. Cat5e and Cat6 cables can support 10Base-T, 100Base-T, and 1000Base-T connections, with distance decreasing equally the speed increases.

Fiber Optic

Cobweb optic cabling can support faster speeds, longer distances, and simultaneous communications. Unlike wired cable, cobweb only supports a unmarried communication on a unmarried frequency at one time.

Multimode

Multimode fiber uses cheap LEDs operating at 850 or 1500   nm to transmit data. Multimode cobweb is made of cheap plastic. In multimode fiber, the light propagates through the cobweb core, bouncing off its edges (thus multimode). Multimode fiber can support only one communication at a time on each frequency. Typically, 2 fibers are used together, one to transmit and one to receive.

Single Fashion

Single-mode fiber uses more expensive lasers and optical glass. Unmarried-mode communication is correct downwards the eye of the drinking glass fiber, never bouncing (thus unmarried mode). Single-mode fiber can stand higher power and thus yields longer distances.

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MCSA/MCSE 70-291: Reviewing TCP/IP Basics

Deborah Littlejohn Shinder , ... Laura Hunter , in MCSA/MCSE (Examination seventy-291) Study Guide, 2003

Layer One: Network Interface

The Network Interface layer of the DoD model corresponds to the lowest level of the TCP/IP protocol architecture and correlates to Layers 1 and 2 in the OSI model. The Network Interface layer provides most of the capabilities provided for in the Physical and Information Link layers of the OSI model.

Let's begin with a brief overview of the hardware involved in the network at this level. We have the network medium, typically coaxial or twisted pair cabling (although wireless networking is increasing in popularity); and nosotros have the network interface carte (NIC) that has both a physical MAC address and a logical IP address (nosotros'll talk over the IP address a bit later on).The NIC has logic (a circuit board and fries) congenital into it that gives information technology bones functionality. It uses a driver, which is a minor software program that interfaces between the hard-ware and the operating system, to provide additional functionality. The NIC typically is involved at Layers ane and 2 of the OSI model, thus it operates at Layer 1 in the TCP/IP model.

The specifications related to how the network engineering science is implemented are defined by an international association of engineers called the Plant of Electrical and Electronics Engineers (IEEE, called the "Middle-triple E" past industry members). The IEEE helps define common standards for use in a diverseness of technical fields, including computing. Ane such standard is the 802 standard, then named because the initial committee coming together was in 1980, in February (the second month). This standard defines specifications for the lower level networking technologies; that is, those at the concrete level (NIC, connectors, and cables) and at the information link level (access methods).

As you'll see, the standards vary, depending on the network technology (Ethernet, Token Ring, ATM, Frame Relay, and so forth). Because TCP/IP works independently of network technology, information technology can be used with each of these types of networks, and tin can exist used to send information betwixt two dissimilar networks as well. For more data on the IEEE, yous can visit their Web site at world wide web.ieee.org.

The standards prepare by the 802 committee pertaining to networking are equally follows:

▪

802.1 Internetworking standards that bargain with the direction of local area networks (LANs) and metropolitan area networks (MANs), including bridges and the spanning tree algorithm used past bridges to prevent looping

▪

802.2 Logical link control, and the division of OSI Layer 2 into two sublayers, LLC and MAC

▪

802.iii CSMA/C, the media access control method used on Ethernet networks, and frame formats for Ethernet

▪

802.4 Token Bus networks that use 75ohm coaxial or cobweb optic cabling and the token passing access method

▪

802.5 Token Ring, the technology adult by IBM that uses a physical star and logical ring topology with twisted pair cabling (shielded or unshielded) and the token passing access method

▪

802.6 MANs, networks of a size and scope that falls between that of the LAN and the WAN

▪

802.vii Broadband transmissions that use Frequency Division Multiplexing (FDM), including CATV

▪

802.viii Fiber eyes networks, including Fiber Distributed Information Interface (FDDI) using the token passing access method

▪

802.9 Integrated services (voice and data) over ISDN

▪

802.10 Virtual private networking to create a secure connection to a individual network over the public Cyberspace

▪

802.11 Wireless networking technologies, including the near common 802.11b, faster 802.11a, and newest 802.11   g wireless communications methods

▪

802.12 The 100VG AnyLAN applied science developed by Hewlett Packard, which uses the demand priority access method

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Customized fashion: finding the right fit

Anthony S. Chow , Timothy Bucknall , in Library Engineering science and User Services, 2012

Networking profiles of our case studies

Both the public and school libraries in our case study apply bandwidth shaping, which provides more bandwidth to users, or limits bandwidth usage, based on whether or not a given task requires it (e.g. video or music streaming). This minimizes the likelihood of slow downloads thereby reducing user frustration. Network speed is controlled primarily by the amount of bandwidth purchased through the organization's Isp, by the blazon of cabling that connects the organization to the ISP and also by the individual computer's connections to the organization's servers. The academic library, with more resources, has i Gbps to the desktop through fiber optic cabling and a larger bandwidth agreement with its ISP. The public and school libraries accept xx–50 Mbps to the desktop, considerably slower, but nevertheless more than than sufficient to back up the needs of its users (public and employees). All iii have costless wireless services, which take become an expectation for library users as buying of laptops and other wireless devices (i.e. smart phones, iPods, tablets, etc.) has risen.

Networking back up FAQs

ane.

How tin can I tell if it is the estimator, browser, network or ISP that is having connectivity problems?

When a computer cannot connect there are many things to endeavor to decide where exactly the problem lies. First is to open another browser every bit the browser may have just frozen. Another quick option is to check another website to make sure the problem does not rest specifically with the website that the user is trying to admission. Certainly another selection is to cheque another computer within that network segment as a network outage would hateful all computers would be cutting off from the network. Besides, ever check the cables at the dorsum of the reckoner. Lastly, for Windows machines, you can utilise the 'cmd' and 'ping' [insert website address] pick to 'ping' the server of a website yous are trying to access to ensure that website's server is receiving and sending out packets of information. Just go to Start and and so type in cmd.

2.

How do I determine a calculator's IP address?

Again, for Windows machines type in 'cmd' to get to your computer's control prompt and then enter in 'ipconfig' to see your computer's IP accost and to brand sure it is active and able to send and receive network information.

3.

What is an IP address and how is it related to a web address?

Net Protocol (IP) is based on iv sets of numbers called octets (each of the four sets of numbers tin actually have 8 distinct numbers). So if you ping www.google.com , you will find their IP accost to be: 74.125.47.106. The commencement octet, 74, designates Google'southward network ID while the remaining three octets identify the specific host and node identification of the web server hosting Google's website. Web addresses but add a text descriptor and organizer to otherwise intimidating and difficult to remember numerical IP addresses.

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Storage Networks

Gary Lee , in Cloud Networking, 2014

Fibre Channel

Different SCSI, which was first adult within a unmarried company before information technology was standardized, FC was developed by an industry group and eventually approved as an ANSI standard in 1994. Information technology initially competed with IBM'southward proprietary series storage compages standard, but it eventually became the dominant standard in SANs. It'southward interesting that the development group decided to use the British spelling of the discussion fiber. They did this because FC was extended to include copper wire implementations equally well as fiber optic cabling and they idea this change in spelling would make that situation less confusing (since so, all the copper implementations have disappeared). Although FC was developed to transport a variety of upper layer protocols, such as IP and ATM, today it is primarily used to ship SCSI.

Like SATA and SAS, FC is a serial protocol. Early FC-based products connected an array of disk drives at 1G bit per second in an arbitrated loop, basically a ring architecture like nosotros described in Chapter 3. Because an arbitrated loop must share bandwidth, it has a limited port count and loop failure tin can be acquired by a single device failure. Because of this, SAS expanders take replaced FC for connecting drives within storage arrays today. But FC has found good success in switch fabric topologies used in SANs and provides serial data rates of 1G, 2G, 4G, 8G, and 16G flake per second using optical cabling. The FC frame format is shown in Effigy viii.ix. The FC header supports a 24-bit address that tin can access over 16M ports. The payload can range from 0 bytes to over 2K bytes and the entire frame is protected with a CRC field. Because frame commitment order cannot be guaranteed, a sequence control and sequence ID field is used along with an exchange ID.

Figure 8.9. The Fibre Channel frame format.

In that location are more often than not iv component types in a FC SAN. HBAs are used in the servers, providing a connection to the FC network. Like the SCSI protocol, the hosts are chosen initiators. FC switches are similar to the Ethernet superlative of rack switches we described before and make connections to multiple servers and storage arrays within the rack. Directors are big modular switches similar to the end of row switches used in Ethernet networks and can connect to a large number of servers and storage arrays. Finally, the storage arrays themselves look something similar the block diagram Figure eight.8 and utilize a SAS expander to connect the disc drives while the CPU on the storage controller board provides FC target port functionality.

FC supports both connection-oriented and connectionless services between initiators and targets. For connection-oriented service, a connection is first established across the network, data is exchanged, and so the connectedness is torn downward. Connectionless is similar to Ethernet, but the frames may arrive out of club, and the standard defines both an acknowledged and an unacknowledged transport mechanism. FC also includes a rich set of storage network management tools, helping to brand FC the preferred selection for high-availability and mission-critical storage systems.

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Creating Network Segments

Jan L. Harrington , in Ethernet Networking for the Small Part and Professional Home Office, 2007

Creating Hierarchical Switched Configurations

Continually replacing a modest switch with 1 that has more ports may not exist the virtually effecitve way—in terms of both toll and perfomance—to build a network. The single-switch pattern means that all network traffic must travel through that single switch. As traffic on the network increases, each bundle will take longer to travel through the switch—the switching table becomes larger and takes longer to search—decreasing the response time of the network.

The solution is to suspension the network into more than one segment, creating a hierarchy of switches (and perhaps hubs). For case, if you take some hubs—don't buy whatever new ones—that you desire to integrate into a unmarried network, you might employ a configuration like that in Effigy 4-13. This network has three standoff domains (ane for each hub), connected by the switch. The switch receives all traffic circulate by each hub. However, if a packet is destined for a device on the same segment from which the package came, the switch ignores it, cut down on the corporeality of traffic the switch needs to handle. The switch therefore only delivers packets that are destined for 1 of the other ii collision domains.

Figure iv-thirteen. A simple hierarchical network using existing hubs

For case, a bundle going from device A1 to device A3 volition exist broadcast out all of Hub A'south ports, including the i going to the switch. However, if the switch has both A1 and A3 in its switching table, it will recognize that they are on the same segment and non carp to transmit the packet. In contrast, if A1 sends a parcel to C1 and both devices are in the switching tabular array, the switch volition transmit the packet out the port to which Hub C is fastened. Hub C volition in turn circulate the packet to all of its ports, at which point the packet is recognized past device C1.

If yous are creating a hierarchical design from scratch, past all ways employ all switches, equally in Effigy four-14. Each switch constitutes a distinct network segment. Unlike the design with hubs, nonetheless, non every bundle reaches the switch at the acme of the bureaucracy. Instead, only those packets destined for other segments are sent to the top switch; each switch on the second level handles traffic for its own devices.

Figure 4-14. A elementary all-switched hierarchical network design

A hierarchical configuration is not limited to 2 levels. In theory, there is no limit to how deep you tin can nest switches. For example, a configuration such as Effigy 4-xv is valid. We often telephone call the switch at the meridian of the hierarchy the cadre switch. Information technology is non necessarily the largest switch (i.eastward., the ane with the most ports), but it should be the fastest.

Figure iv-15. A multilevel switched network

When designing your switching hierarchy, you want to get the best performance possible, which means you need to consider the following:

♦

The deeper the bureaucracy (i.east., the more levels in the hierarchy), the slower traffic will exist between devices on different segments because more switches volition need to handle each bundle.

♦

Devices that communicate often should be grouped on the same segment so that their packets don't need to travel up or down the hierarchy. (The fewer switches through which a packet needs to travel, the faster it will be delivered.)

♦

Some switches tin can handle both UTP and cobweb optic cabling, making them suitable for linking faster and slower network segments.

♦

Fiber optic equipment is more expensive than UTP equipment. Use cobweb optics only when you lot need the fastest operation, such as to shared devices such equally servers. Printers are besides by and large shared, but a printer is a mechanical device that is relatively slow when it produces its output, and therefore putting it on a fast network link may be a waste matter of resources.

♦

Y'all don't necessarily need to fill up all ports on a switch. Having open ports besides gives y'all flexibiity so that you can reconfigure the network to break upwards bottlenecks or to add new devices every bit the network grows.

What devices exercise you identify on which segment? At that place's no straightforward formula, but the following guidelines tin help:

♦

Many computers at present come with Gigabit Ethernet on the motherboard. Given that viii-port UTP Gigabit switches cost less than $100, there is rarely an economical reason not to utilize switched Gigabit if your computers are equipped with information technology. Otherwise, Fast Ethernet over UTP to the desktop is more than adequate.

Note: Of form there will be exceptions to the preceding – in that location are always exceptions to simply about everything! For instance, if y'all are networking a graphics blueprint firm and artists are exchanging large files over the network, then you may desire Gigabit Ethernet throughout the network and feel that the expense of adding Gigabit expansion boards to those computers that aren't equipped with it out of the box to be justified.

♦

Fiber eyes generally aren't necessary to connect finish user devices or slower devices such as printers.

♦

When y'all take multiple file servers, you may desire to group them on a cobweb optic segment, creating what'south known every bit a server farm. Considering the servers receive the bulk of the network traffic, they demand to be on the fastest segment on the network.

Note: In terms of security, a server farm tin can exist both adept and bad. It increases vulnerability because many servers, possibily containing sensitive information, are congregated together. If a hacker cracks that network segment, then all the servers may be accessible. By the same token, past grouping the servers you cut down the number of places that your network is vulnerable. You can concentrate your security efforts on that single bespeak of vulnerability, rather than needing to secure servers at many locations. You can find more about security issues in Chapter 12 .

♦

Devices that communicate with each other frequently should be on the same network segment. For instance, if y'all take a workgroup printer used by the advertising department, identify it on the same segment every bit the advertising department's stop user machines.

Note: Y'all can find examples of a variety of hierarchical switched configurations in the case studies at the cease of this volume ( Chapters 14 , 15, and sixteen).

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Using the Business Origami Technique to Sympathise Complex Ecosystems

Doug Fox , in Studying and Designing Technology for Domestic Life, 2015

Introduction

Imagine you have an Internet service that is one hundred times faster than traditional cable or DSL services. What would you practice with that blazon of speed? Stream HD movies without fear of the dreaded "buffering spinner" on Netflix? Dominate your friends on your favorite online video games? Or but upload hundreds of videos of your cat being cute and mischevious to YouTube?

These were the questions we were faced with on the Google Fiber User Feel Enquiry team. Google Fiber is a fiber-optic Cyberspace service that provides Internet download speeds up to one hundred times faster than cablevision or DSL services, with a 1-gigabit connexion. These speeds are currently rare within the United states, and we were interested to acquire how the beliefs of Google Fiber users would evolve every bit a result of this high-speed Cyberspace connection.

Because of the high costs of installing cobweb-optic cabling in multiple locations, Kansas Metropolis, Kansas, U.s.a., was chosen as the starting time market for Google Cobweb. We wanted to make sure information technology was worth Google's investment to build this network, so we started with simply one market and planned to extend the service based on the uptake and demand. Kansas City was a market that was highly eager for a better Internet experience. Its citizens even held marketing campaigns encouraging Google Cobweb to build the fiber optic network in that location, and the city authorities was a good partner in helping us get the permissions nosotros needed to build the infrastructure for the network.

We wanted to sympathize the affect of Google Cobweb from this installation bespeak onward, so we started exploring the Internet usage patterns of users who were the outset in Kansas City to take the new service installed in their homes. By removing many of the constraints and frustrations of today's traditional Internet experiences, such equally slow connections, bandwidth caps, and unreliable service, nosotros wanted to know what, if anything, would change about our users' behaviors. Would they come up with new uses for the Internet that nosotros had not imagined, or would they but practice the same activities withal more efficiently? The possibilities were seemingly limitless. For the Google Cobweb team, it was important to understand how families used the Internet and so we could adapt our services to their particular behaviors. From a business perspective, it was important to larn almost changes in Net usage so Google could build services or products that better matched user behaviors with a faster Internet connection.

Nosotros adapted and employed a method known as the Business Origami Technique to learn how multiple members of a household used the Internet when continued using Google Fiber. The Business concern Origami Technique is a method that traditionally uses "pop-up" paper tokens—newspaper cut-outs folded so they stand upright—as representations of various people, locations, and technologies in an ecosystem (McMullin 2010). It provided usa with a fashion to sympathize how the Net was existence used in each household, past whom, and in which locations. The method also immune us to gather rich details of user behavior that we believe would have been difficult to acquire through an interview or survey of users' online practices.

Go on in mind that, in lodge to learn about the impact of the Google Fiber Internet service, we needed more than just a snapshot of what multiple family unit members did online. We needed to sympathize changes over fourth dimension, and learn when and how behaviors evolved. Thus, this written report was conducted over a flow of one year. The longitudinal nature of the study provided unique challenges that required adaptations to the Business Origami Technique.

In this chapter, I discuss the steps we took to employ the Business Origami Technique beyond xv multi-member households. I besides talk over the benefits and limitations of this method over other research methods, such as interviews, contextual inquiries, and surveys. Throughout the chapter, I share steps and best practices to accommodate the Business Origami Technique from the traditional paper format to a digital format so that the origami map may exist more easily used for longitudinal studies. I also document the challenges nosotros faced in adapting and employing the method digitally. These challenges included explaining the exercise to remote participants, ensuring they complete the exercise in a timely way, and working around technological failures and issues of engineering literacy.

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Vocalisation Communications

John Vargo , Ray Hunt , in Encyclopedia of Information Systems, 2003

2. Traditional Telephone Systems and Modern Enhancements

The phone has been one of the most successful and influential inventions in history. The foundation that Bell provided has been enhanced by many farther innovations past others. Improvements in both the bones engineering science for manual and network interconnection, as well as enhanced digital features, have occurred over the years.

In society for the phone to succeed in connecting two phones for a private call, the individual lines must be connected somehow. Individual wires are run from individual homes and businesses to a telephone exchange office (also chosen a key function or end role) where these private lines are connected to make a calling circuit between two phones. Originally this was washed by the caller phoning the exchange office, speaking to a switchboard operator and asking to be connected to someone. The switchboard operator would then literally plug one person's phone line into the other person's phone line creating a dedicated excursion for the phone call. This transmission system was replaced as early as the 1890s with an automatic switching organization in which the caller dialed a number using a rotary dial, the signals sent by the dial directed the switch to connect the caller to a detail phone number. This electromechanical mode of switch remained in broad utilise in phone exchange offices through to the 1970s and 1980s, at which stage they were progressively replaced with electronic and digital switches capable of handling many more simultaneous calls as well as adding new features.

II.A. Technology

Entire books accept been written on the technology supporting the phone organisation! This section nevertheless, focuses on some item aspects of modern telephone technology that back up the additional features nosotros take seen come up into service over recent years, including PBXs and digital exchanges.

II.A.1. PABX

The original phone system continued individual callers to each other. If 2 of those callers happened to work for the same organization in the same building, their telephone call still was connected through the local exchange function some altitude away, and the arrangement may take had to pay for the phone call. The private branch substitution (PBX) was developed every bit a result of this trouble. The PBX was a local version of the original manual switchboard. Yous phoned your organization's phone operator, who then connected you to the extension you desired. This manual PBX was replaced by lower cost private automated co-operative commutation (PABX) equipment every bit electronic and digital equipment fell in toll. Modern PABX equipment permits you to dial an extension phone number in your arrangement and be automatically connected to that number. It can likewise allow external callers to direct dial your number, without having to go through a company switchboard operator. It also may support a range of additional computer-enhanced services, equally discussed below.

II.A.2. Digital Exchanges

Digital and computer-controlled exchanges began replacing electromechanical one in the 1960s and 1970s and became the prevalent form of phone substitution during the 1980s. This type of computer-controlled phone exchange was necessary to enable the introduction of a range of other digital technologies and services including ISDN, direct long-distance dialing, call waiting, caller ID, voice mail, and other features. Together with cobweb optic cabling, digital exchanges provide the foundations for modern voice and data communication over a common infrastructure.

II.B. Features

Bell's original invention was delivered as a device to permit two individuals to speak to one another synchronously at a altitude. However, this is only a subset of human communication with many instances of one-to-many and many-to-many vox advice occurring everyday. Meetings, speeches, homilies, and lectures are everyday examples.

II.B.1. Conference Calling

A conference call involves more than a unmarried sender and receiver. The briefing telephone call may involve a range of setups including one sender and multiple receivers who are in the same room using a speaker phone system to permit them all to participate in the call. Alternatively it could involve multiple parties, for example three or 4 people, all in separate locations, being connected into a unmarried phone conversation. This type of briefing telephone call will typically require help from the telecommunications provider to set upwards.

2.B.2. Call Forwarding/Diversion

Given the high level of mobility today, phone call forwarding or diversion is a pop feature of modern telephone systems. This feature permits users to be at a different location and telephone number and still receive their phone calls. People dialing their normal phone number will be diverted so that the phone at the unlike location rings instead. This feature has been made unnecessary for many users by the development of the prison cell telephone, only is still very useful where cell phone coverage is non bachelor or jail cell reception is particularly poor.

2.B.three. Caller ID

This characteristic involves the automatic identification of the phone number placing a telephone call. And then using a database, the owner of that phone is looked up. The owner's phone number, and in some cases their proper name, will be displayed while the phone is ringing. This feature requires a special phone or attachment to allow brandish of the caller ID.

II.B.4. Call Waiting

This characteristic permits someone in the middle of one call to put the caller on hold and then he tin take an incoming phone call. Business phones with digital PABX services accept had the "hold" feature for one-time, however this feature is but more than recently available for residential users through the use of modern digital exchanges.

II.B.5. Voice Mail service

Vocalization mail is a more flexible version of the venerable answer phone, with both providing call answering and vocalisation messaging facilities. If the receiver is unavailable to answer the telephone after a specified number of rings, the computerized vocalisation mail system will answer with a prerecorded bulletin, maybe tailored to the caller using Caller ID features, and permits the caller to leave a message or perchance punch an alternative number. See Section 5 for more than on voice postal service.

Two.B.6. Automated Attendant

Enhanced features for lowering the company's telecommunication neb can include an automated attendant every bit an alternative to direct dial numbers, whereby the caller dials into the visitor master number and the telephone call is handled by an automated attendant. This estimator-based arrangement responds to the caller with a voice message asking the caller to fundamental in the extension number if they know it, otherwise to press 0 and the operator will attend to them. See the discussion beneath on voice-activated systems for more on this type of technology.

Two.B.seven. Other Features

A range of other features accept been incorporated into the modernistic phone system. Further examples include last number redial, speed dialing of multiple numbers from a retention in the phone, speaker telephone systems, call transfer to another extension, and voice dialing. This latter forth with other voice activation services are covered in the adjacent department.

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MCSE 70-293: Planning, Implementing, and Maintaining a Routing Strategy

Martin Grasdal , ... Dr. Thomas W. Shinder Technical Editor , in MCSE (Test 70-293) Report Guide, 2003

Selecting Connectivity Devices

For pocket-size, segmented networks with relatively lite traffic between subnets, a software-based routing solution such as the Windows Server 2003 RRAS might be ideal. On the other hand, a large number of network segments with a broad range of performance requirements would probably necessitate some kind of hardware-based routing solution. Evaluating your routing options includes selecting the proper connectivity devices: hubs, bridges, switches, or routers. You also should understand where these devices fit in the OSI reference model.

Head of the Class…

A Review of the OSI Model

The Open System Interconnection (OSI) reference model is an International Organization for Standardization (ISO) standard for worldwide communications. OSI defines a network framework for implementing an agreed-upon format for communicating between vendors. The model identifies and defines all the functionality required to establish, use, define, and dismantle a communication session between two network devices, no affair what the device is or who manufactured it.

All communication processes are defined in 7 distinct layers with specific functionality. Microsoft and other proprietary systems may combine multiple-layer functionality into ane layer in their particular version, but most, if not all, of the functionality of the original OSI model layers are incorporated. Information technology is for this reason that well-nigh discussions of computer-to-estimator advice begin with a discussion of this model. Table four.1 shows the layers in the OSI reference model.

Tabular array 4.one. The OSI Reference Model Layers

Layer Description
vii Application
half dozen Presentation
5 Session
four Transport
3 Network
2 Data Link
1 Physical

Layer 1 of the OSI reference model is often referred to as the bottom layer. This is the Concrete layer, which is actually responsible for the transmission of the data. As a result, the Concrete layer operates with only ones and zeros. It receives incoming streams of data, one bit at a time, and passes them up to the Data Link layer. Examples of transmission media associated with Layer 1 include coaxial cabling, twisted-pair wiring, and fiber-optic cabling.

Layer ii is the Data Link layer, which is responsible for providing stop-to-stop validity of the data being transmitted. This layer deals with frames. The frame contains the data and local destination instructions. This means that the Physical and Information Link layers provide all the data required for communication on the local LAN. Figure 4.16 illustrates a Data Link layer domain.

Figure 4.16. The Physical and Information Link Layers

At Layer 3, the Network layer, internetworking is enabled and the road to be used betwixt the source and the destination is determined. There is, however, no native manual error detection/correction method. Some manufacturers' Information Link layer technologies back up reliable delivery, only the OSI reference model does non brand this assumption. For this reason, Layer 3 protocols such equally IP presume that Layer iv protocols such as TCP will provide this functionality. Effigy 4.17 illustrates a network similar to the one shown in Figure 4.16, but with a second, identical network continued via a router. The router effectively isolates the ii Information Link layer domains. The only way the two domains tin communicate is via the use of Network layer addressing.

Effigy iv.17. This Network Requires Network Layer Addressing

The Network layer implements a protocol that can transport information beyond the LAN segments or even across the Net. These protocols are known as routable protocols because their data tin be forwarded past routers across the local network. These protocols include IP, Novell's Internetwork Parcel Substitution (IPX), and AppleTalk. Each of these protocols has its own Layer 3 addressing compages. IP has emerged as the dominant routable protocol. Unlike the first ii layers, which are required for all applications, the use of the Network layer is required only if the two communicating systems reside on different networks or if the ii communicating applications require its service.

Every bit with the Data Link layer, the fourth layer, the Transport layer, is responsible for the end-to-end integrity of data transmissions. The master departure is that the Send layer can provide this function beyond the local LAN. The layer detects if packets are damaged or lost in transmission and automatically requests the data to be retransmitted. This layer is also responsible for resequencing any data packets that arrived out of guild.

Layer 5 of the OSI model is the Session layer. Many protocols handle the functionality of this layer in the same layer they handle the functionality of the Transport layer. Examples of Session layer services include Remote Procedure Calls (RPCs) and quality of service (QoS) protocols such as RSVP, the bandwidth reservation protocol.

Layer 6, the Presentation layer, is responsible for how the data is encoded. Not every reckoner uses the aforementioned information-encoding scheme. This layer is responsible for translating data between otherwise incompatible encoding schemes. This layer can also be used to provide encryption and decryption services.

Layer 7 is the Application layer. This layer provides the interface between user applications and network services.

Hubs

Hubs, sometimes referred to as repeaters, are devices used to connect advice lines in a primal location and help provide common connections to all other devices on the network. A hub usually has one input and several outputs. These outputs are known as ports, but don't confuse them with TCP/IP ports (every bit in port 80, the i used for HTTP traffic). These ports are just connections and nothing more. They generally take RJ-45 connectors. Think of a hub as similar the center of an old carriage cycle with all the spokes radiating out to the other part of the wheel.

A hub merely takes the data that comes into its ports and sends it out on the other ports of the hub. For this reason, it is sometimes referred to equally a repeater. It doesn't provide or perform whatsoever filtering or redirection of the data from the diverse sources plugged into information technology. Hubs are normally used to connect various network segments of a LAN.

Hubs generally come in iii flavors:

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Passive Serves simply as a pipeline allowing data to move from one device, or network segment, to another.

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Intelligent Sometimes referred to equally an active, managed, or manageable hub, it includes additional features that permit y'all to monitor the traffic passing through the hub and configure each port for specific purposes.

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Switching Reads the destination address of each package and frontwards that package to the right port. Near hubs of this variety also support load balancing.

Bridges

In that location are several definitions for a bridge, each conveying a specific meaning when used in a detail context. In ane context, a bridge can be thought of as a gateway, connecting ane network to another using the same communication protocols and allowing the information to be passed from one to the other. In another context, a bridge can be used to connect two networks with dissimilar communication protocols at the Data Link layer (Layer 2), in much the aforementioned manner every bit a router itself. In that location is likewise a bridge called a bridge router, which supports the functions of both the bridge and the router using Layer 2 addresses for routing.

Here, we'll look at the traditional bridge and the context that is most ofttimes associated with this device. Bridges piece of work at both the Physical (Layer 1) and Information Link (Layer two) layers of the OSI reference model. That means that a span knows nothing about protocols but forrad information depending on the destination accost found in the data packet. This destination accost is non an IP address, only rather a Media Access Command (MAC) address that is unique to each network adapter menu. For this reason, bridges are often referred to every bit MAC bridges.

Basically, all bridges work by edifice and maintaining an address table. This table includes information such as an up-to-date listing of every MAC accost on the LAN, equally well equally the concrete bridge port connected to the segment on which that address is located.

At that place are three basic types of bridges:

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Transparent bridge Links together segments of the same blazon of LAN. A transparent bridge effectively isolates the traffic from one LAN segment from the traffic of another LAN segment, as shown in Figure 4.18.

Effigy 4.xviii. Transparent Bridge
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Translating (or translational) bridge Like a transparent bridge, links together segments of the same type of LAN, just besides tin provide conversion processes needed between dissimilar LAN architectures. This allows y'all to connect a Token Band LAN to an Ethernet LAN, every bit shown in Figure 4.xix.

Figure iv.19. Translating Bridge
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Speed-buffering bridge Used to connect LANs that have similar architectures but different transmission rates. Figure 4.xx shows how you might utilise a speed-buffering bridge to connect a 10-Mbps Ethernet network to a 100-Mbps Ethernet network.

Figure 4.xx. Speed-buffering Bridge

Bridges are self-learning, and so the administrative overhead is small. The functionality of bridges has been built into routers, hubs, and switches.

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