Lesson 1: Networking Basic

This lesson covers the very basics of networking. We’ll start with a little history that describes how the networking industry evolved. We’ll then move on to a section that describes how a LAN is built: essentially the necessary components (like NIC cards and cables). We then cover LAN topologies. And finally we’ll discuss the key networking devices: hubs, bridges, switches, and routers.

This module is an overview only. It will familiarize you with much of the vocabulary you hear with regards to networking. Some of these concepts are covered in more detail in later lessons

The Agenda

- Networking History

- How a LAN Is Built

- LAN Topologies

- LAN/WAN Devices

Networking History

Early networks

From a historical perspective, electronic communication has actually been around a long time, beginning with Samuel Morse and the telegraph. He sent the first telegraph message May 24, 1844 from Washington DC to Baltimore MD, 37 miles away. The message? “What hath God wrought.”

Less than 25 years later, Alexander Graham Bell invented the telephone – beating out a competitor to the patent office only by a couple of hours on Valentine’s Day in 1867. This led to the development of the ultimate analog network – the telephone system.

The first bit-oriented language device was developed by Emile Baudot – the printing telegraph. By bit-oriented we mean the device sent pulses of electricity which were either positive or had no voltage at all. These machines did not use Morse code. Baudot’s five-level code sent five pulses down the wire for each character transmitted. The machines did the encoding and decoding, eliminating the need for operators at both ends of the wires. For the first time, electronic messages could be sent by anyone.

Telephone Network

But it’s really the telephone network that has had the greatest impact on how businesses communicate and connect today. Until 1985, the Bell Telephone Company, now known as AT&T, owned the telephone network from end to end. It represented a phenomenal network, the largest then and still the largest today.

Let’s take a look at some additional developments in the communications industry that had a direct impact on the networking industry today.

Developments in Communication

In 1966, an individual named “Carter” invented a special device that attached to a telephone receiver that would allow construction workers to talk over the telephone from a two-way radio.

Bell telephone had a problem with this and sued – and eventually lost.

As a result, in 1975, the Federal Communications Commission ruled that devices could attach to the phone system, if they met certain specifications. Those specifications were approved in 1977 and became known as FCC Part 68. In fact, years ago you could look at the underside of a telephone not manufactured by Bell, and see the “Part 68” stamp of approval.

This ruling eventually led to the breakup of American Telephone and Telegraph in 1984, thus creating nine regional Bell operating companies like Pacific Bell, Bell Atlantic, Bell South, Mountain Bell, etc.
The break up of AT&T in 1984 opened the door for other competitors in the telecommunications market. Companies like Microwave Communications, Inc. (MCI), and Sprint. Today, when you make a phone call across the country, it may go through three or four different carrier networks in order to make the connection.

Now, let’s take a look at what was happening in the computer industry about the same time.

1960's - 1970's Communication

In the 1960’s and 1970’s, traditional computer communications centered around the mainframe host. The mainframe contained all the applications needed by the users, as well as file management, and even printing. This centralized computing environment used low-speed access lines that tied terminals to the host.
These large mainframes used digital signals – pulses of electricity or zeros and ones, what is called binary -- to pass information from the terminals to the host. The information processing in the host was also all digital.

Problems faced in communication

This brought about a problem. The telephone industry wanted to use computers to switch calls faster and the computer industry wanted to connect remote users to the mainframe using the telephone service. But the telephone networks speak analog and computers speak digital. Let’s take a closer look at this problem.

Digital signals are seen as one’s and zero’s. The signal is either on or off. Whereas analog signals are like audio tones – for example, the high-pitched squeal you hear when you accidentally call a fax machine. So, in order for the computer world to use the services of the telephone system, a conversion of the signal had to occur.

The solution

The solution – a modulator/demodulator or “modem.” The modem takes the digital signals from the computer and modulates the signal into analog format. In sending information from a desktop computer to a host using POTS or plain old telephone service, the modem takes the digital signals from the computer and modulates the signal into analog format to go through the telephone system. From the telephone system, the analog signal goes through another modem which converts the signal to digital format to be processed by the host computer.
This helped solve some of the distance problems, at least to a certain extent.

Multiplexing or muxing

Another problem is how to connect multiple terminals to a single cable. The technology solution is multiplexing or muxing.
What we can do with multiplexing is we can take multiple remote terminals, connect them back to our single central site, our single mainframe at the central site, but we can do it all over a single communications channel, a single line.
So what you see is we have some new terminology here in our diagram. Our single central site we refer to as a broadband connection. That's referred to as a broadband connection because whenever we talk about broadband we're talking about carrying multiple communications channels over a single communication pipe.
So what we're saying here is we have multiple communication channels as in four terminals at the remote site going back to a single central site over one common channel.
But again in the case of our definition of broadband here, we're referring to the fact that we have four communication channels, one for each remote terminal over a single physical path.
Now out at the end stations at the terminals, you see we have the term Baseband and what we mean by the term Baseband is, in our example, between the terminal and the multiplexer we have a single communication channel per wire, so each of those wires leading into the multiplexer has a dedicated channel or a dedicated path.
Now the function of the multiplexer is to take each of those Baseband paths and break it up and allocate time slots.
What that allows us to do is allocate a time slot per terminal so each terminal has its own time slot across that common Baseband connection between the remote terminals and the central mainframe site.
That is the function of the multiplexer is to allocate the time slots and then also on the other side to put the pieces back together for delivery to the mainframe.
So muxing is our fundamental concept here. Let’s look at the different ways to do our muxing.

Baseband and broadband

You see again the terms here, Baseband and broadband.
Again, the analogy that they're using here is that in the case of Baseband we said we had a single communications channel per physical path.
An example of some Baseband technology you're probably familiar with is Ethernet for example.
Most implementations of Ethernet use Baseband technology.
We have a single communications channel going over a single physical path or a single physical cable.
On the other hand on the bottom part of our diagram you see a reference to broadband and the analogy here would be multiple trains inside of a single tunnel.
Maybe we see that in the real world, we're probably familiar with broadband as something we do every day, is cable TV.
With cable TV we have multiple channels coming in over a single cable.
We plug a single cable into the back of our TV and over that single cable certainly we know we can get 12 or 20 or 40 or 60 or more channels over that single cable.
So cable TV is a good example of broadband.

Given the addition of multiplexing and the use of the modem, let’s see how we can grow our network.

How networks are growing

Example:-

Using all the technology available, companies were able to team up with the phone company and tie branch offices to the headquarters. The speeds of data transfer were often slow and were still dependent on the speed and capacity of the host computers at the headquarters site.

The phone company was also able to offer leased line and dial-up options. With leased-lines, companies paid for a continuous connection to the host computer. Companies using dial-up connections paid only for time used. Dial-up connections were perfect for the small office or branch.

Birth of the personal computer

The birth of the personal computer in 1981 really fueled the explosion of the networking marketplace. No longer were people dependent on a mainframe for applications, file storage, processing, or printing. The PC gave users incredible freedom and power.

The Internet 1970's - 1980's

The 70’s and 80’s saw the beginnings of the Internet. The Internet as we know it today began as the ARPANET — The Advanced Research Projects Agency Network – built by a division of the Department of Defense essentially in the mid ‘60's through grant-funded research by universities and companies. The first actual packet-switched network was built by BBN. It was used by universities and the federal government to exchange information and research. Many local area networks connected to the ARPANET with TCP/IP. TCP/IP was developed in 1974 and stands for Transmission Control Protocol / Internet Protocol. The ARPANET was shut down in 1990 due to newer network technology and the need for greater bandwidth on the backbone.
In the late ‘70’s the NSFNET, the National Science Foundation Network was developed. This network relied on super computers in San Diego; Boulder; Champaign; Pittsburgh; Ithaca; and Princeton. Each of these six super computers had a microcomputer tied to it which spoke TCP/IP. The microcomputer really handled all of the access to the backbone of the Internet. Essentially this network was overloaded from the word "go".
Further developments in networking lead to the design of the ANSNET -- Advanced Networks and Services Network. ANSNET was a joint effort by MCI, Merit and IBM specifically for commercial purposes. This large network was sold to AOL in 1995. The National Science Foundation then awarded contracts to four major network access providers: Pacific Bell in San Francisco, Ameritech in Chicago, MFS in Washington DC and Sprint in New York City. By the mid ‘80's the collection of networks began to be known as the “Internet” in university circles. TCP/IP remains the glue that holds it together.
In January 1992 the Internet Society was formed – a misleading name since the Internet is really a place of anarchy. It is controlled by those who have the fastest lines and can give customers the greatest service today.
The primary Internet-related applications used today include: Email, News retrieval, Remote Login, File Transfer and World Wide Web access and development.

1990's Globle Internetworking

With the growth and development of the Internet came the need for speed – and bandwidth. Companies want to take advantage of the ability to move information around the world quickly. This information comes in the form of voice, data and video – large files which increase the demands on the network. In the future, global internetworking will provide an environment for emerging applications that will require even greater amounts of bandwidth. If you doubt the future of global internetworking consider this – the Internet is doubling in size about every 11 months.

How a LAN can build

In the previous section, we discussed how networking evolved and some of the problems involved in the transmission of data such as conflict and multiple terminals. In this section some of the basic elements needed to build local area networks (LANs) will be described.

LAN(Local Area Netwok)

The term local-area network, or LAN, describes of all the devices that communicate together—printers, file server, computers, and perhaps even a host computer. However, the LAN is constrained by distance. The transmission technologies used in LAN applications do not operate at speed over long distances. LAN distances are in the range of 100 meters (m) to 3 kilometers (km). This range can change as new technologies emerge.
For systems from different manufacturers to interoperate—be it a printer, PC, and file server—they must be developed and manufactured according to industry-wide protocols and standards.
More details about protocols and standards will be given later, but for now, just keep in mind they represent rules that govern how devices on a network exchange information. These rules are developed by industry-wide special interest groups (SIGs) and standards committees such as the Institute of Electrical and Electronics Engineers (IEEE).

Most of the network administrator’s tasks deal with LANs. Major characteristics of LANs are:

- The network operates within a building or floor of a building. The geographic scope for ever more powerful LAN desktop devices running more powerful applications is for less area per LAN.

- LANs provide multiple connected desktop devices (usually PCs) with access to high-bandwidth media.

- An enterprise purchases the media and connections used in the LAN; the enterprise can privately control the LAN as it chooses.

- LANs rarely shut down or restrict access to connected workstations; local services are usually always available.

- By definition, the LAN connects physically adjacent devices on the media.

So let’s look at the components of a LAN.

Components of LAN

- Network operating system(NOS)

In order for computers to be able to communicate with each other, they must first have the networking software that tells them how to do so. Without the software, the system will function simply as a “standalone,” unable to utilize any of the resources on the network.
Network operating software may by installed by the factory, eliminating the need for you to purchase it, (for example AppleTalk), or you may install it yourself.

- Network interface card(NIC)

In addition to network operating software, each network device must also have a network interface card. These cards today are also referred to as adapters, as in “Ethernet adapter card” or “Token Ring adapter card.”
The NIC card amplifies electronic signals which are generally very weak within the computer system itself. The NIC is also responsible for packaging data for transmission, and for controlling access to the network cable. When the data is packaged properly, and the timing is right, the NIC will push the data stream onto the cable.
The NIC also provides the physical connection between the computer and the transmission cable (also called “media”). This connection is made through the connector port. Examples of transmission media are Ethernet, Token Ring, and FDDI.

- Writing Hub

In order to have a network, you must have at least two devices that communicate with each other. In this simple model, it is a computer and a printer. The printer also has an NIC installed (for example, an HP Jet Direct card), which in turn is plugged into a wiring hub. The computer system is also plugged into the hub, which facilitates communication between the two devices.
Additional components (such as a server, a few more PCs, and a scanner) may be connected to the hub. With this connection, all network components would have access to all other network components.
The benefit of building this network is that by sharing resources a company can afford higher quality components. For example, instead of providing an inkjet printer for every PC, a company may purchase a laser printer (which is faster, higher capacity, and higher quality than the inkjet) to attach to a network. Then, all computers on that network have access to the higher quality printer.

- Cables or Transmission Media

The wires connecting the various devices together are referred to as cables.

- Cable prices range from inexpensive to very costly and can comprise of a significant cost of the network itself.

- Cables are one example of transmission media. Media are various physical environments through which transmission signals pass. Common network media include twisted-pair, coaxial cable, fiber-optic cable, and the atmosphere (through which microwave, laser, and infrared transmission occurs). Another term for this is “physical media.” *Note that not all wiring hubs support all medium types.

The other component shown in this fig1. is the connector.

- As their name implies, the connector is the physical location where the NIC card and the cabling connect.

- Registered jack (RJ) connectors were originally used to connect telephone lines. RJ connectors are now used for telephone connections and for 10BaseT and other types of network connections. Different connectors are able support different speeds of transmission because of their design and the materials used in their manufacture.

- RJ-11 connectors are used for telephones, faxes, and modems. RJ-45 connectors are used for NIC cards, 10BaseT cabling, and ISDN lines.

Network Cabling

Cable is the actual physical path upon which an electrical signal travels as it moves from one component to another.
Transmission protocols determine how NIC cards take turns transmitting data onto the cable. Remember that we discussed how LAN cables (baseband) carry one signal, while WAN cables (broadband) carry multiple signals. There are three primary cable types:

- Twisted-pair (or copper)

- Coaxial cable and

- Fiber-optic cable

Twisted-pair (or copper)

Unshielded twisted-pair (UTP) is a four-pair wire medium used in a variety of networks. UTP does not require the fixed spacing between connections that is necessary with coaxial-type connections. There are five types of UTP cabling commonly used as shown below:

- Category 1: Used for telephone communications. It is not suitable for transmitting data.

- Category 2: Capable of transmitting data at speeds up to 4 Mbps.

- Category 3: Used in 10BaseT networks and can transmit data at speeds up to 10 Mbps.

- Category 4: Used in Token Ring networks. Can transmit data at speeds up to 16 Mbps.

- Category 5: Can transmit data at speeds up to 100 Mbps.

Shielded twisted-pair (STP) is a two-pair wiring medium used in a variety of network implementations. STP cabling has a layer of shielded insulation to reduce EMI. Token Ring runs on STP.

Using UTP and STP:

- Speed is usually satisfactory for local-area distances.

- These are the least expensive media for data communication. UTP is cheaper than STP.

- Because most buildings are already wired with UTP, many transmission standards are adapted to use it to avoid costly re-wiring of an alternative cable type.

Coaxial cable

Coaxial cable consists of a solid copper core surrounded by an insulator, a combination shield and ground wire, and an outer protective jacket.
The shielding on coaxial cable makes it less susceptible to interference from outside sources. It requires termination at each end of the cable, as well as a single ground connection.
Coax supports 10/100 Mbps and is relatively inexpensive, although more costly than UTP.
Coaxial can be cabled over longer distances than twisted-pair cable. For example, Ethernet can run at speed over approximately 100 m (300 feet) of twisted pair. Using coaxial cable increases this distance to 500 m.

Fiber-optic cable

Fiber-optic cable consists of glass fiber surrounded by shielding protection: a plastic shield, kevlar reinforcing, and an outer jacket. Fiber-optic cable is the most expensive of the three types discussed in this section, but it supports 100+ Mbps line speeds.

There are two types of fiber cable:

- Single or mono-mode—Allows only one mode (or wavelength) of light to propagate through the fiber; is capable of higher bandwidth and greater distances than multimode. Often used for campus backbones. Uses lasers as the light generating method. Single mode is much more expensive than multimode cable. Maximum cable length is 100 km.

- Multimode—Allows multiple modes of light to propagate through the fiber. Often used for workgroup applications. Uses light-emitting diodes (LEDs) as light generating device. Maximum cable length is 2 km.

Throughput Needs....!!

Super servers, high-capacity workstations, and multimedia applications have also fueled the need for higher capacity bandwidths.
The examples on abow image shows that the need for throughput capacity grows as a result of a desire to transmit more voice, video, and graphics. The rate at which this information may be sent (transmission speed) is dependent how data is transmitted and the medium used for transmission. The “how” of this equation is satisfied by a transmission protocol.
Each protocol runs at a different speed. Two terms are used to describe this speed: throughput rate and bandwidth.

The throughput rate is the rate of information arriving at, and possibly passing through, a particular point in a network.
In this chapter, the term bandwidth means the total capacity of a given network medium (twisted pair, coaxial, or fiber-optic cable) or protocol.

- Bandwidth is also used to describe the difference between the highest and the lowest frequencies available for network signals. This quantity is measured in Megahertz (MHz).

- The bandwidth of a given network medium or protocol is measured in bits per second (bps).

Some of the available bandwidth specified for a given medium or protocol is used up in overhead, including control characters. This overhead reduces the capacity available for transmitting data.

This table shows the tremendous variation in transmission time with different throughput rates. In years past, megabit (Mb) rates were considered fast. In today’s modern networks, gigabit (Gb) rates are possible. Nevertheless, there continues to be a focus on greater throughput rates.

LAN Topologies

You may hear the word topology used with respect to networks. “Topology” refers to the physical arrangement of network components and media within an enterprise networking structure. There are four primary kinds of LAN topologies: bus, tree, star, and ring.

Bus and Tree topology

Bus topology is

- A linear LAN architecture in which transmissions from network components propagate the length of the medium and are received by all other components.
- The bus portion is the common physical signal path composed of wires or other media across which signals can be sent from one part of a network to another. Sometimes called a highway.
- Ethernet/IEEE 802.3 networks commonly implement a bus topology

Tree topology is

- Similar to bus topology, except that tree networks can contain branches with multiple nodes. As in bus topology, transmissions from one component propagate the length of the medium and are received by all other components.

The disadvantage of bus topology is that if the connection to any one user is broken, the entire network goes down, disrupting communication between all users. Because of this problem, bus topology is rarely used today.
The advantage of bus topology is that it requires less cabling (therefore, lower cost) than star topology.

Star topology

Star topology is a LAN topology in which endpoints on a network are connected to a common central switch or hub by point-to-point links. Logical bus and ring topologies re often implemented physically in a star topology.

- The benefit of star topology is that even if the connection to any one user is broken, the network stays functioning, and communication between the remaining users is not disrupted.
- The disadvantage of star topology is that it requires more cabling (therefore, higher cost) than bus topology.

Star topology may be thought of as a bus in a box.

Ring topology

Ring topology consists of a series of repeaters connected to one another by unidirectional transmission links to form a single closed loop.

- Each station on the network connects to the network at a repeater.
- While logically a ring, ring topologies are most often organized in a closed-loop star. A ring topology that is organized as a star implements a unidirectional closed-loop star, instead of point-to-point links.
- One example of a ring topology is Token Ring.

Redundancy is used to avoid collapse of the entire ring in the event that a connection between two components fails.