CIS 1110A - Computer Operating Systems and Maintenance


Module 7

This lesson presents an introduction to networking. Objectives important to this lesson:

  1. Network types and Internet connections
  2. Connecting a computer to a network, wired and wireless connections
  3. Configuring and securing  a router
  4. Troubleshooting
  5. Current assignments

Concepts:

The chapter begins with a very general discussion of communications on a network. The text should have mentioned:

  • there are devices that send communications signals
  • the signals are picked up by devices capable of retransmitting them across some medium
  • the signals are sent across the medium (and maybe forwarded in several steps to a semi-final destination)
  • the signals are received by other devices like the ones in the second bullet (such as those at a distant network)
  • those devices distribute the signals to other communications devices that the signals were meant for

A definition of networking is provided in the chapter. A more formal one should be provided. Networking can be defined with five features. Each is emphasized a different way in this list:

  • users sharing resources (like printers or files)
  • across a common medium (like copper wire or a radio frequency)
  • by way of specific rules (like TCP/IP or other network protocols)

The discussion on page 322 adds a bit, with a set of common acronyms based on how large a network is. These three letter acronyms are used for classifying networks based on their physical size (as opposed to how many hosts/nodes/computers they have). People also tend to make up new items for this list, regardless of the lack of need for them.

  • A Personal Area Network (PAN) may cover a work area for one person, or it may be the network formed by your phone, your Bluetooth headset, your tablet, and other personal devices. For this one to be useful, you need to connect to a larger network as well, making the designation a bit lame.
  • A Local Area Network (LAN) covers a small area, like a room, a building, or a campus.
  • A Wireless Mesh Network (WMN) is a network of several wireless devices communicating without central  storage or management, passing signals from one to another until they reach the devices the signals are meant for.
  • A Metropolitan Area Network (MAN) covers a city, linking computers at various locations.
  • A Wide Area Network (WAN) covers an area larger than a MAN. This may be a network between cities or countries.
  • A Virtual Local Area Network (VLAN) is a subset of a LAN. It will not be physically separate from the rest of the LAN, but it will work as though is it a different LAN.(Your text does not mention this one at this time.)

These designations for networks are commonly taught in classrooms, but they are not terribly important when you are creating a network. However, you need to start somewhere, and this classification is easily understood. Networks start small, then build and combine to create larger constructs. Even the Internet once connected only five locations. Now, everyone wants and needs to connect to it.

The author reviews some terms that have been common for some time:

  • ISP - an Internet Service Provider is an entity that sells access to the Internet, a service that is often bundled with cable TV and telephone services
  • bandwidth - as the text has mentioned several times, bandwidth is a measure of how many bits per second can be passed from one device to another; it is common for an ISP to provide two or more levels of bandwidth to customers for different prices
  • throughput - the author makes a distinction between throughput and bandwidth; bandwidth is a measure of the best performance a channel can provide; throughput is a measure of the actual performance of that channel at any given time; in car terms, bandwidth is the estimated mileage on the sticker, and throughput is what actually happens (your mileage may vary)
  • latency - as a signal is passed from device to device, network to network, there will be some delays that happen for various reasons; such delays are called latency, which increases with the complexity of the route a signal follows

These factors apply to each of the connectivity options in table 7.1. General concepts:

  • wired technologies generally can provide better bandwidths than wireless technologies, but DSL technologies can only be provided if the subscriber is inside 17,000 feet from a phone company Central Office switch; this link provides basic information that compares cable and DSL service; the text explains that (coaxial) cable systems are better where they are available. DSL is sometimes available when cable connection is not, but people I know who have had both have all been unhappy with DSL service.
  • the table lists several IEEE standards for wireless network communication; some are discussed below
  • cellular data connections typically have better service with higher technology designations (5G > 4G > 3G), but the coverage area for newer technologies is typically smaller than the coverage area for older ones, and the newest ones are often only available in major urban markets; when a new technology is not available in your current cell (or on your current device), service fails over to an older available technology that your device supports

Computers use electric currents and various forms of electromagnetic waves to communicate. We can class networks as being cabled (wired) or wireless, for obvious reasons.

There have been several types of cable media used in networks over the years. (Follow the link to a Microsoft TechNet article about media. It is not perfect, but it is pretty good.)

  • twisted pair - has been used in two types:
    • unshielded - UTP does not have an EMI resistant sheath; comes in several types including old fashioned telephone wire
    • shielded - STP has an EMI resistant sheath, which can be foil or braided metal (due to the success of UTP, you are unlikely to run into STP)
  • coaxial - Coax similar to that used for cable TV, and now used by cable providers for network access as well
  • fiber optic - glass or plastic "wave guides" that "conduct" light, often red laser light

For those who don't believe me about cable vs. DSL, Linus Sebastian will clarify the situation.


Systems that do not use cables between nodes fall into two groups:

  • satellite transmission - there are handheld phones that communicate by sending signals to terrestrial satellites which then connect to more conventional networks; people who live in mountainous areas can use these if no cell towers or land lines exist; likewise, satellite TV systems can be used for data upload and download as well as for entertainment downloads
  • cellular systems - the most familiar system is for cellular phones, but private systems exist as well

Waves on the oceanCabled systems connect to a modem, a modulator-demodulator, that converts signals from a computer to signals that can be transmitted across the medium being used to attach to an ISP's network or a private network, or a public data network. It also does the reverse process, converting incoming signals to signals usable by your network. In this role, a cable modem is also a router that connects your network to another network.

Short physics lesson: In a copper wire, electrons don't actually flow from one end of the wire to the other. What happens is more like the movement of a large ripple or wave in water. Imagine a wave moving toward a shore in a lake or an ocean. Do specific water molecules make the whole trip? No. The energy of the wave is passed across a series of molecules. The energy passes across the medium. In the image on the right, floating objects at various depths illustrate that the energy of an ocean wave is more apparent near the surface, but in deep water there is little horizontal movement of the water itself.

For the purists among you, I will note that the speed of electromagnetic waves through the electrical media varies with the nature of the conductor. It can be over 90% of c in a UTP wire, and a bit slower in coax. What's c? The speed of light in a vacuum. The most satisfying answer to "why c" is that the Latin word celeritas means speed.

The graphic shown here illustrates several twisted pairs of wires. Each wire is covered with an insulator, and the two wires in each pair are meant to be used as a circuit. These wires suffer from crosstalk, leakage of signal. The twists help cancel out such leaks. The graphic shows a UTP cable with eight wires in it, making four pairs. As is typical, there is a green pair, a blue pair, an orange pair, and a brown pair. Other color schemes are used, but this one is very common.Twisted pair wire

The wires in each pair are twisted around each other. This type of cable came in several varieties: two pair, three pair and four pair were common, but four pair is the current standard. Also, each variety may be available in grades, such as CAT 1 (Category 1, which is pretty useless on modern networks) and CAT 5 (Category 5, which has been a standard for several years). There are several such categories, and a major difference between them is the number of twists per foot in each pair. CAT 1 will have less than 5 twists per foot, CAT 5 will have 25 or more twists per foot (so it is better, and costs more). Note that the better the class of cable, the less leakage, and the more bits per second can be passed across it.

Connecting a system with twisted pair wiring is easy, with the right tools and parts. In the chart below, the arrangement of wires for the standard known as TIA/EIA 568B is shown. In an alternate standard, TIA/EIA 568A, orange/white is swapped with green/white, and orange is swapped with green. It does not really matter which standard you use, as long as both ends of the cable are connected in the same way. There are two exceptions to this: a crossover cable and a rollover cable. A crossover cable is used to connect directly from one NIC to another, or from one networking device to another, such as connecting two switches. These cables are used less often, since modern devices sense what kind of devices are cabled to them and change their logic accordingly. A rollover cable is used to connect to a Cisco router's console port. Let's save that for Cisco class.

Most references forget to tell you the reason you arrange wires this way instead of however you might like. Read the last two columns in the chart below. Pins 1 and 2 are used for the transmission circuit, which is why they need to be wired with two wires that are twisted around each other in the cable. Using a twisted pair of wires in a circuit reduces the amount of signal lost to other circuits (crosstalk). You need to use a real pair for each circuit that your network requires. Pins 3 and 6 are used for the reception circuit. The odd part is the 3-6 pairing, surrounding the 4-5 pairing. We wire a connector this way so that it follows a pattern of alternating stripes and solids, so a person can remember it, and because that's the way it works. Why did they decide to use the connectors and sockets this way? I don't know. Just know that this works.

Pin Assignments for TIA/EIA 568B
Pin Color Color Signal Circuit
1 Orange/White
Orange White
TX data + Orange Circuit
2 Orange Orange TX data - Orange Circuit
3 Green/White
Green White
RX data + Green Circuit
4 Blue Blue unused Blue Circuit
5 Blue/White
Blue White
unused Blue Circuit
6 Green Green RX data - Green Circuit
7 Brown/White
Brown White
unused Brown Circuit
8 Brown Brown unused Brown Circuit

Pin pairs:

  • 1 and 2 - left side pair, orange
  • 7 and 8 - right side pair, brown
  • 4 and 5 - center pair, blue
  • 3 and 6 - pair surrounding the center pair, green

When you are inserting the wires into a connector, do it with the gold contacts up so you can see the wires enter each channel in the plastic.

RJ-45 ethernet connectorUTP network cables are usually connected to devices with RJ-45 connectors. Your text shows an RJ-45 connector and an RJ-11 connector on page 239. In the enlarged picture on the right, note the eight gold-colored contacts for the eight wires usually found in UTP cables. The wires are used in pairs to form two to four circuits.

RJ-11 connectors are typically used for plain old telephone service (POTS) connections. They look like RJ-45s, but they are narrower, and typically have only four (or six) contacts instead of eight. Modern phones may use RJ-45 connectors and CAT 5 or CAT 6 cable, but modular phone jacks often require an RJ-11. (RJ stands for Registered Jack.)

In the video below, the presenter has some good ideas, and some that are not so good. He knows how to connect the wires to the RJ-45 plugs, so let's enjoy his presentation and discuss it in class. (Spoiler: orange white, orange, green white, blue, blue white, green, brown white, brown)


Coaxial cable is called that because it has two conductors, one wire in center and a conductive sheath around it, that share a common axis, hence coax. Most people have seen this style of cable used with cable television. When coaxial cable was first used for networking, you could not use the same kind of cable that is used for cable TV. Improved products have allowed the same type to be used for both services.

There have been many standards set by the Institute of Electrical and Electronic Engineers (IEEE), notably the IEEE 802.11 wireless standards. The text discusses some of them in more detail.

  • 802.11 - Described how a wireless LAN might be implemented using either radio waves or some form of light that humans cannot perceive. Only provided bandwidths of 1 or 2 Mbps.
  • 802.11b - Added technology to increase bandwidth to 5.5 or 11 Mbps, and to allow devices to be up to 350 feet apart. When stations are located increasingly farther apart, the bandwidth between those stations is dropped down to lower levels.
  • 802.11a - This standard supports data rates of 54, 48, 36, 24, 18,12, 9, and 6 Mbps.Sounds great, but its effective range was much less than 802.11b. The text states that devices could be no more than 100 feet apart.
  • 802.11g - This standard included the best features of the 802.11a and 802.11b standards. It offered the bandwidth selections of the 802.11a standard, and the range of the 802.11b standard.
  • 802.11n - This standard provided the potential of using two frequencies at once to increase throughput up to 600 Mbps. Range was supposed to increase, but the IEEE only reports the same effective range as 802.11g. Its new Wi-Fi Alliance name is Wi-Fi 4.
  • 802.11ac - This standard uses the 5 GHz band, eliminating interference from devices that are commonly on the 2.4 GHz band, such as microwave ovens and cordless phones. Its new Wi-Fi Alliance name is Wi-Fi 5.
  • 802.11ax - This one adds the 2.4 GHz band back into its standard, and increases throughput by doing so. Its new Wi-Fi Alliance name is Wi-Fi 6.

frequency
channels, channel bandwidth
data throughput range
802.11a
5 GHz band
52, 23 not overlapping, 20 MHz each
up to 54 Mbps 25-75 feet
802.11b
2.4 GHz band
14, 3 not overlapping, 22 MHz each
up to 11 Mbps
100-150 feet
802.11g
2.4 GHz band 14, 3 not overlapping, 22 MHz each 54 Mbps 100-150 feet
802.11n
Wi-Fi 4
2.4 or 5 GHz bands, or both with multiple antennas 14, 3 not overlapping, 20 or 40 MHz each
65 to 600 Mbps 100-150 feet
802.11ac
Wi-Fi 5
5 GHz band 20, 40, 60 and 80 MHz, up to 160 MHz wide
78 Mbps to 433 Mbps/data stream
115 feet
802.11ax
Wi-Fi 6
2.4 and 5 GHz bands 20, 40, 60, and 80 MHz, 2/80 MHz wide
866.7 Mbps/data stream
about the same as Wi-Fi 5 (unless using a mesh system)

Page 329 begins a section on adding a computer to an Ethernet network. (Ethernet is a kind of network invented by Bob Metcalf at Xerox PARC in 1975 Xerox invented a lot of things.) It assumes you are connecting a Windows computer to an existing network. The text gives us two pages on using a wired connection, and another two on a wireless connection. It also describes connection through a VPN (Virtual Private Network) and through a dial-up (telephone) connection.

A VPN is a secure communication channel that is often used by people who need to connect to their usual network when they are traveling, working from home, or are otherwise away from their usual work location. A VPN may pass traffic across the Internet, but it can be considered as secure because all traffic passed from one end of the channel to the other is encrypted. Using a VPN provides a level of security that an unsecured data channel cannot provide. Each end of a VPN channel is called an endpoint.

Dial-up connections are typically over analog phone lines, and they are painfully slow by modern expectations. As noted about other technologies, however, it sure beats not being able to connect at all. I tried to find a video that would be educational, but most just wallow in the old tech with little explanation. Don't do it, children! You'll throw away your entire life!

The author reminds us that almost any kind of connection to a network can be set up on a Windows computer through the Network and Sharing Center, which is a utility in Windows, not a charitable organization.

In the course of setting up a computer to function on a network, you will need to either hard code an IP address for the computer (a static address), or allow the computer to be assigned an address by a network device (a dynamic address). The purpose of an IP address is to identify each unique device on each unique network. On an IP network, each device is known as a host, and every host must have an address. The addresses we discuss are usually IP version 4 addresses. (IPv6 addresses have 16 bytes (128 bits).) IPv4 addresses are numeric addresses, stored as four bytes, which is equal to 32 bits. When we write these addresses, we usually place dots between the bytes, but the dots do not exist in the addresses as used. Dr. Andrews points out that most networks still use IPv4 addressing, so she discusses it the most.

Since the TCP/IP protocol suite was invented with networking in mind, IP addresses contain two parts: one to identify the address of the network a host is on, and the other part to identify the host itself. Every network is assigned an address which, according to the original plan, could be one, two, or three bytes, depending on the class of the network (A, B, or C). The remaining byte or bytes are typically used for hosts on networks. (There are other ways to do it as well.)

Each byte in an IPv4 address will hold a number in the range 0 through 255. To pass some certification tests associated with this course, students have been expected to convert decimal notation to binary notation and vice versa, by hand. Pencil and paper. Really. Dr. Andrews does not go into this skill at this time, so we will let it slide for now.

Dynamic Host Configuration Protocol (DHCP) service allows us to dynamically assign IP addresses to hosts on an IP network. You need to understand that, as far as IP is concerned, "host" means any device on the network. It can also set the subnet mask, the default gateway, and the DNS server. (A subnet mask is a template that defines which part of an IP address is for the network and which part is for the host.)

Three methods for assigning addresses:

  • Automatic Allocation: DHCP assigns a permanent IP address to a host.
  • Dynamic Allocation: An IP address is assigned to a host for a limited period of time (or until the host relinquishes the address). Also called address leasing.
  • Manual Allocation: This method requires that an administrator assign the address. DHCP simply delivers the address to the host. Read that carefully: you can make the assignment, but you tell the DHCP server to deliver it, so you don't have to visit the host yourself.

The text discusses what you will see if DHCP fails. Automatic Private IP Addressing (APIPA) could be described as an error condition, if you are using DHCP on your Windows-based network. The first clue may be that a workstation cannot reach the Internet, because APIPA does not set a default gateway. What it does is to set a private IP address instead of one that matches your network scheme. It will be in the range 169.254.0.0 - 169.254.255.254. APIPA is meant to be a fallback method of assigning addresses. It will result in communications failures if some of your workstations have APIPA addresses, and others have DHCP assigned addresses. The two groups will essentially be on two different networks. The trouble they encounter is meant to be a flag that leads you to repairing the failure.

If a Windows workstation is configured for DHCP, but has an address in the APIPA range, try opening a command line interface and entering two commands:

ipconfig -release
ipconfig -renew

The first command tells the computer to let go of the lease it has (or thinks it has). The second command tells the computer to start a DHCP discover, offer, request, acknowledge sequence.

  • The device needing an address discovers DHCP servers by sending a broadcast request.
  • Any servers available offer addresses.
  • The device needing the address requests the offered address from a selected server.
  • The DHCP server acknowledges that the address has been assigned to the requesting host.
  • These commands will have no effect if your DHCP server is not running, or not reachable.

The same set of commands can be useful on devices running Linux/UNIX/osX by running the Linux version of these commands:

sudo ifconfig eth0 down
sudo ifconfig eth0 up

In a home network, the DHCP assignment is typically provided as a service on your router/WAP/cable modem. In a work setting, the service may be running on an actual server. As noted above, you can hard code an IP address to a machine. This is useful for devices like switches, routers, printers, and other devices whose IP addresses need to be known and shared with other devices.

The text briefly discusses Network Interface Cards (NICs). We have talked about NICs already. Remember that a computer's NIC is where its MAC address is located and that you should check the indicator lights on a NIC to diagnose problems.

A router connects two or more networks together. Its purpose is to find routes and pass traffic from one network to another. A router is also a host device on each network it is directly connected to. Network addresses are used to pass data from one network to another, but hardware addresses are usually used to pass data to hosts on the same network. In the diagram on page 345, the small office/home office router is being used as a switch, to connect four devices in a LAN. It is also connected being used as a router connecting its own network to an ISP's network, passing signals to that network through a cable or DSL modem.

Many cable modems and home routers also provide Wi-Fi service, which make them wireless access points (WAPs). Your device may also provide firewall service, rejecting traffic from known bad sources. With all the things your router can do, it is reasonable to get a good one, but it is also reasonable to put some of your eggs in a different basket.

The text presents a walk-through of configuring a router. Depending on what you have, your experience should be both similar and different. You will need to know the ID and password for a user the router will recognize as an administrator. If you do not, you will need to look up the default ID and password for your brand and model, press the factory reset button on the router, then log in and make the darn thing secure again. Never leave a device in a state in which factory default ID/password combinations exist. The exercise continues with configuring DHCP, reserving IP addresses (for network equipment, servers, and printers), MAC address filtering, and providing Quality of Service priority to a device or application.

The text discusses the same issues as they relate to a wireless LAN (WLAN), along with some unique issues through page 364. It continues with several utilities found on most Windows workstations.

  • ping - can be issued on a command line, and has an extensive list of options. Usually, the options are unnecessary.
    • ping -a address will return the DNS name of the address
    • ping -t address will ping the address until you tell it to stop with ctrl-c
    • Be aware that you can ping an address or a fully qualified domain name.
  • tracert (Trace Route) - This command will show how long each link in a route takes, as well as showing links that fail to pass packets to the next link. Successful transfers of data will report the total time to the destination. You can limit the trace to a specific number of hops with the command tracert -h hop_limit
    (where hop_limit is a number)
  • netstat - Can be used to view the status of current connections using TCP, UDP, ICMP, and IP. The status messages are a bit cryptic, so you will want to keep a reference for them handy when using this command.
    • netstat  (all by itself)  This will tell you about all network connections on the current network. It will continue scanning and updating until you press ctrl-c.
    • netstat  >> filename This will send the output of the netstat command to a file, appending new lines until you press ctrl-c to stop the process. The append operator (>>) is necessary because the tool continues to update over time.
  • ipconfig - shows useful information on Windows NT and later machines, like the IP address, default router, and subnet mask.
    • More information is shown if the command is entered as ipconfig /all
    • ipconfig /release This will release the currently held IP address to the DHCP server that gave it.
    • ipconfig /renew will obtain a new lease from the DHCP server for an IP address
  • arp - ARP stands for Address Resolution Protocol. In standard Ethernet networks, machines may communicate inside the network with their MAC addresses. Communications across networks are more likely to use IP addresses. An ARP cache is a table that lists the IP addresses and MAC addresses of devices on a network. This table can be consulted to change from one kind of addressing to the other.
    • For example, if I issue the command
      arp -a
      I get the ARP cache of my computer: its own IP and MAC addresses, and those of my default router, and other devices on my LAN.
  • nslookup - This can be used to report the IP address of a DNS name. It does not send a ping to the named server. You will probably get data on your default router as well.
  • hostname - This command will respond with the name of your device in your domain.
  • nbtstat - The name of this utility is NetBIOS over TCP/IP Statistics. Not very enlightening. You need to know that your computer will typically hold the names and IP addresses of several devices in memory. Sometimes those devices go offline, and others come online. This may make it desirable to check what is in memory:
    nbtstat -a



Assignments

  1. Read the chapter, and the next one for next week.
  2. Complete the assignments and class discussion made in this module, which are due by 6pm next week.