Cabling

There are three different types of cables used in networking:

1. Coaxial (coax)
2. Twisted Pair
3. Fiber Optic

Coaxial Cable

Coaxial cable has an inner copper core surrounded by insulating material, and the insulating material is surrounded by a braided wire, that has an outside rubber insulating layer.  The center wire and the braided metal shield share a common axis or centerline.

Coaxial Cables shield data transmissions from electro-magnetic interference (EMI).  Lights, cable televisions, cordless telephones, microwave ovens, refrigerators, anything where the electrical current is being turned on or off, can generate magnetic fields that cause electrical current along the wire.  This type of interference can disrupt transmissions on a network.

The most popular connectors for coaxial cables used to be BNC connectors.

BNC Connector

Vampire connections, sometimes called vampire taps, that pierced the cable, were also popular in early bus topology networks.

Coaxial cable used today is mostly used for connecting to an Internet Service Provider (ISP) via cable modem.  The same type of cable is used to connect televisions to cable boxes and satellite receivers.  An F-type connector that screws on is used to connect the cable.

F-type Connector

Cable modems connect using RG-6 type cables, predominately used in cable television.  Coax cables have an RG rating.  The U.S. military developed the ratings during WWII to provide a quick reference for the different types.  The most important measure of coax cabling is its Ohm rating.  The Ohm rating is the characteristic impedance or electrical resistance of the cable.

If you have a situation where you need to split a single coaxial cable, coaxial splitters can be used to connect two cables together using a barrel connector.  This allows you to add some distance to a connection.

Coaxial Splitter

Barrel Connector

Twisted Pair

The most common type of cabling used in networks is twisted pair, twisted pairs of cables, bundled together.  Networks use two types of twisted pair cabling, shielded twisted pair and unshielded twisted pair.  The twists reduce interference, which is called crosstalk.  The more twists, the better. 

Shielded Twisted Pair

Shielded twisted pair, STP, consists of twisted pairs of wires surrounded by shielding.  This protects the wires from EMI.  Shielded twisted pair is used in areas of excessive electronic noise.  The most common type is the IBM Type 1 cable used in Token Ring network topology.

Unshielded Twisted Pair

Unshielded twisted pair, UTP, is the most common type of network cabling used today.  UTP consists of twisted pairs of wires surrounded by a plastic jacket.  This type of jacket does not provide protection against EMI, so you must be careful when installing to avoid interference.

Telephone systems use STP, so they sometimes present a problem when installing alongside cable.  However, there are installation standards to help those who work with UTP.  Telephones use RJ-11 connectors with two pairs of wires.  Networks use RJ-45 connectors with four-pairs of wires.

UTP cabling has something called category, CAT, ratings to help network installers get the right cable for the right network technology.  CAT ratings are officially rated in megahertz (MHz), indicating the highest frequency the cable can handle.  The maximum amount of data that goes through cable per second is called bandwidth.  CAT 5e cable can handle a throughput of up to 1000 Mbps, even though it is rated to handle a bandwidth of only up to 100 MHz.  Most new cabling installations use CAT 5e, even though a number are using the new CAT 6.  CAT 6a is the latest update, doubling the bandwidth of CAT 6 to 550 MHz to accomodate 10-Gbps speeds up to 100 meters.



Fiber-Optic

Fiber-optic cable transmits light rather than electricity.  Fiber-optic cabling will operate for long distances.  Fiber-optic cabling has many different diameters of core and cladding.  The core is the glass fiber itself.  The cladding is the part that makes the light reflect down the fiber.  Fiber-optic cables require pairs of cables, and are usually clumped together like a lamp cord.  There are single-mode and multimode fiber-optic cables.  Light can be sent down as regular light or as laser light.  Using laser light and single-mode fiber-optic enables a network to achieve very high transfer rates over long distances.

Fiber-optic cables have over one hundred different connector types.  The most common are ST, SC, and LC.  LC is unique in that it is a duplex connector and will accept two fiber cables.

Other Cables Types

Serial cabling, RS-232, is the recommended standard that all serial cabling is based on.  The most common is the 9-pin, male D-subminiature connector.  Serial ports have very slow data rates...about 56,000 bps.

9-pin d-subminiature connector

25-pin female DB type connector front and rear side

Parallel connections use a 25-pin female DB type connector and run to around 2 Mbps.  The IEEE 1284 committee sets the standards for parallel communications.  Parallel is also limited to point-to-point communications.

FireWire is based on the IEEE 1394 standard and is the next best thing to fiber-optic or UTP.  FireWire is fast and runs up to 800 mbps.  FireWire is point-to-point and has a connector like the one pictured below. Microsoft has removed the ability to network via FireWire in Windows Vista.

Questions 
1.  Which topology requires termination?  Bus topology.
2.  Star-bus is an example of what type of topology? Star-bus in an example of a Hybrid topology.
3.  What topology is the most fault tolerant?  Star topology.
4.  What is a topology?  The interconnectivity of network components.

5.  Coaxial cablesOhm rating, a relative measure of the resistance on the cable.
6. Which type of network topology is mostly seen in wireless networks?   Mesh topology.
7.  What is the most common type of UTP used in new cable installations?  CAT 5e, though CAT 6 is becoming more popular.

Can't get on the Internet?

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Having problems getting on the internet?  Use whatever tool your operating system provides to check your IP address.

Is it an APIPA address?  If the address begins with 169.254, then it is an APIPA address.  This indicates you have a DHCP problem.  DHCP stands for Dynamic Host Configuration Protocol. DHCP automatically assigns an IP address when a computer connects to the network.

An older and less popular protocol is called the Bootstrap Protocol.  BOOTP is common on UNIX/Linux and Macintosh OS X systems.  BOOTP is like DHCP.

A computer configured to use DHCP is called a DHCP client.  When a computer boots up, it automatically sends out a DHCP discovery packet using the broadcast address.  Normally, your ISP sets up your router to act as a DHCP server.  The server responds to DHCP discovery requests with a DHCP offer.  The DHCP server passes out IP addresses from a range, called a DHCP scope, a subnet mask, and a default gateway.

The DHCP client (your computer) sends out a DHCP request (the name is misleading because actually it is accepting the offer).  The DHCP server (your router) then sends a DHCP acknowledgement and lists the MAC address and the IP information.  The DHCP client accepts the DHCP server's data with a lease for a fixed amount of time, determined by the DHCP setup configuration.  At about halfway through the lease time, the DHCP client makes another DHCP discovery message.  The DHCP server looks at the MAC address and will always give the same IP address and IP information unless another computer has taken the lease.

When a DHCP client (your computer) tries to get an IP address from the DHCP server and fails, your computer's operating system generates an error message and the IP address generated begins with 169.254.  This unusual address is APIPA, generated by Automatic Private IP Addressing.   The last two octets of the IP address are generated by the client (your computer).  This allows all of the clients on the network to communicate because they are on the same network ID.  However, you can't get on the internet, because APIPA cannot generate a default gateway, which is required to get on the Internet.

If you can't get on the Internet, and you know you have a DHCP problem because you have a 169.254 address, try to reestablish the lease manually.   In Windows, type the following into the command line interface:

ipconfig /renew

On a Macintosh, go to System Preferences and the Network utility.

Sometimes you still can't get an IP address for whatever reason.  Try to force the computer to release the lease.  In Windows, type

ipconfig /release
(hit enter)
ipconfig /renew
(hit enter)

In UNIX/Linux and Macintosh, use the IFCONFIG command to release.

sudo ifconfig eth0 down

To renew:

sudo ifconfig eth0 up

How DHCP Technology Works:

The TCP/IP Guide

Remote Assistance Instructions

Remote Assistance allows a person that is experiencing computer problems, a novice, to invite a trusted person, an expert, to remotely and interactively assist that person with a problem. Both computers must have Windows XP and be connected to the Internet.  Both the novice and the expert must be sitting at their computers.  Establishing a Remote Assistance Invitation behind a firewall might require you to make a network configuration change to open TCP Port 3389.

To send a Remote Assistance Invitation

To send out a request for help/support, to send an Invitation for Remote Assistance, select from the Windows Start menu, Programs/Remote Assistance.  This starts up the Windows XP Help and Support Center/Remote Assistance page.

There are three methods to sending an invitation.  You can send an invitation via Microsoft Windows Messenger, via email using Microsoft Outlook Express, or via saving an invitation as a file on a shared folder on the network, thus allowing you to use other email programs.  Select the method you want to use.

Enter your name and define how long the invitation stays open, then click Continue.

For security, it is highly recommended for you to define a password, which must be used by the expert recipient to connect to your novice system.

It is your job to advise the expert of the password, either by email or phone.

When selecting 'Save Invitation', you will be asked to define the location to save the file.  (For example, to My Documents).

Remote Assistance gives you a few last instructions.  The instructions notify the novice the Invitation has been saved successfully and where it has been saved.  It tells the novice to send the Invitation to the assistant by email or place it in a shared folder.  It also instructs the novice to tell the assistant to open the Invitation in order to start the Remote Assistance session.  It further instructs the novice, that if the Invitation is accepted, the novice will be notified that the recipient is ready to connect to their computer.

Click Send Invitation.

If you have a problem sending the Invitation

Verify that Remote Assistance is enabled.  In Control Panel, select the System icon or right click My Computer and select Properties.

Select the Remote Tab.

By default, Remote Assistance is activated.  Check the Advanced settings.  (Note:  the other option on this tab, Remote Desktop, is NOT available for Windows XP Home Edition.)

Define whether you allow the expert only to view your activities or whether the expert can also take control, i.e., use his mouse and keyboard to operate the system.

Define the maximum amount of time the Invitation can remain open.

Important note:  While waiting for the expert to connect, make sure your TCP/IP address does NOT change!  Do NOT terminate your connection, or when you reconnect you might get another IP address and your invitation is invalid. 

To respond to a Remote Assistance Invitation sent from a novice

Once the expert has received the Invitation on the remote Windows XP system, double-click on the Invitation file, which opens the Remote Assistance window.  If a password was defined, enter it now.  Continue with YES.  

Your system is then connecting to the novice system.  Once an expert connects to a novice system, a confirmation message is displayed.  The novice must click on YES to allow the expert to continue and to view the novice system. The expert will then see the novice windows of Remote Assistance.

After the Remote Assistance connection is established, the novice will see a User Console and the expert will see a Helper Console.

The User Console allows you to chat via keyboard... type under 'Message Entry' or via 'Start Talking', if both the novice and the expert are equipped with a sound-card with speakers and a microphone. 

If allowed in the settings of the invitation, the expert can take control of the system of the novice by selecting the Toolbar 'Take Control' on the Helper Console.  

When the expert clicks 'Take Control', a message will pop-up on the screen of the novice informing about the request. 

If you agree to this request, accept it by clicking 'Yes'. 

Once the 'novice' accepts the request, a message will pop-up on the 'expert' system to advise about having control and to press Esc or any key sequence or combination including the Esc-key to return control to the 'novice'.

The section 'Chat History' of the User Console will show that control has been taken by the 'expert'.
The 'expert' now uses the mouse and/or keyboard of the expert system to operate the novice system to identify the problem, checking for example, the Control Panel, Device Manager, Event Log.

To terminate a 'Remote Assistance' connection, both the expert and the novice can select in their Console section to 'Disconnect'.
The expert will be informed about the disconnection from the system of the novice.

File Recovery

Free software for file recovery can be found here:  Pandora Recovery - Free software

CNET also has a free app called Tech Tracker that will tell you when the software is out of date and lets you download an update.  You can also choose to be emailed when there is an update to Pandora Recovery.  What's better than that!

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Rollback a device driver

You have downloaded and installed the latest version of a video card driver for your computer.
Afterwards, you find your Windows XP Professional operating system seems unstable. You need to restore the original version of the device driver.

Open the System applet in Control Panel, and roll back the device driver.  
Device drive rollback allows you to restore a previous version of an updated device driver. Driver rollback affects only the changed hardware device. No other hardware or software on the computer is affected.


Navigate to the Hardware tab, and click Device Manager.  
From Device Manager, select the affected hardware device and click Properties.  
From the Properties dialog box, navigate to the Driver tab and click Roll Back Driver.

You can also open the System Restore utility, and load a restore point from a date before you installed the defective device driver.  System restore points are stored in the C:\Windows\system32\restore directory. 
To access System Restore, click Programs/Accessories/System Tools/System Restore


Using Windows XP, How to Roll Back a Device Driver

Steps to take to Increase Windows XP Performance

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You are running several applications at once in Windows XP, and performance starts to slow down.  What can you do to improve the response time without turning off the computer?

Answer:  Increase the size of the PAGEFILE.SYS.

The virtual memory page file is PAGEFILE.SYS, in Windows XP.  PAGEFILE.SYS is used as a temporary storage area for data when main memory capacity is exceeded.

Increasing the size of this file increases the available storage area and improves system performance.  To change the size of PAGEFILE.SYS, go to the START button.  Click on SETTINGS, CONTROL PANEL, SYSTEM, ADVANCED, PERFORMANCE, OPTIONS, CHANGE. Select the Drive list, and click the drive that contains the paging file you want to change.  Under Paging file size for the selected drive, type a new paging file size in megabytes in the Initial size (MB) or Maximum size (MB) box, then click Set.  The optimal paging file settings allow Windows to manage the paging file size.

Steps To Take to Increase Windows XP Performance

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SCSI Termination

You have both internal and external devices on a SCSI chain.  All devices are Fast SCSI-2 devices.  How should you place terminators for the SCSI bus?

Answer:  Place an active terminator on both end devices on the chain.  Active terminators are required for Fast or Wide SCSI, according to SCSI-2 specification.  Each end of the SCSI bus must be terminated.

SCSI Termination Tutorial

Network Troubleshooting

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A user is unable to connect to a file server on your 10BaseT network (twisted pair Ethernet), although he is able to connect to folders on other computers.  A single hub exists on the network.  10BaseT Twisted Pair Ethernet  What hardware problems should you investigate?

Answer:  Either a defective network interface card (NIC) on the file server or a defective hub port connected to the file server would prevent users from connecting to the file server.  A defective cable between the file server and the hub would prevent communications between users and the server.  Client/server communication problems can also be related to software issues.  The user may not have permission to access the file server, or the user may not have the correct name or address of the file server.  If the network has multiple subnets, problems could occur because of incorrect subnet mask settings or incorrect gateway address. 
Advanced Network Adapter troubleshooting for Windows workstations

Computer Post Beep Codes and What They Mean

Computer Post / Beep codes

Startup Phases for X86 Windows Systems

Troubleshooting Startup

Startup Phases for x86-based Systems


The Windows XP Professional startup process closely resembles that of Microsoft® Windows NT® version 4.0 and Microsoft® Windows® 2000, but significantly differs from Microsoft® MSDOS®, Microsoft® Windows® 95, Microsoft® Windows® 98, and Microsoft® Windows® Millennium Edition (Windows Me).

All computers running Windows XP Professional share the same startup sequence:



Power-on self test (POST) phase



Initial startup phase



Boot loader phase



Detect and configure hardware phase



Kernel loading phase



Logon phase



The preceding startup sequence applies to systems started or restarted after a normal shutdown, and does not apply when you bring your computer out of hibernation or standby.

Cabling

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