THE HARDWARE

• Baseband – means the cable will use all its bandwidth for each transmission
• Broadband – the cable can split its bandwidth for many simultaneous transmissions

• Cat1: Standard phone lines
• Cat2: Speeds to 4 Mbps
• Cat3: Speeds to 16 Mbps
• Cat4: Speeds to 20 Mbps
• Cat5: Speeds to 100 Mbps
• Cat5e: Speeds to 350Mbps
• Cat6: Speeds to 1000Mbps

Shielded twisted pair – (generic picture FTP)

• Transmits light rather than electricity
• Complete immunity from interference (EMI and RFI)
• Broadband
• Multi-mode
  • Cheaper transmitters (LEDs)
  • Lower bandwidth
  • Shorter distance
• Single-mode
  • More expensive transmitting device (laser)
  • Higher bandwidth
  • Longer distance
• Hybrid cables
• Media converters (to multi, single, CATx)

Connectors

Twisted Pair – RJ-x (Registered Jack)

*Note: Historically even though pins 4,5,7, and 8 are not used, it is mandatory that they be present in the cable.

Standard or crossed-over wire order

A standard cable order is used from computer to hub. A crossed over cable order is used from computer to computer, or hub to hub.

Just have one end crossed over, both ends would be a "crossed-over cross over" – which puts you right back to standard J.

• The basic BNC connector is a male type mounted at each end of a cable. This connector has a center pin connected to the center cable conductor and a metal tube connected to the outer cable shield. A rotating ring outside the tube locks the cable to any female connector.
• BNC T-connectors (used with the 10Base-2 or thin-net systems) are female devices for connecting two cables to a network interface card (NIC).

  

• 10Base5 or thick net does not use a T-connector. Thick Net uses AUI (Attachment Unit Interface) cable and external transceivers.

  

NICs

Plug into MOBO (or USB or PC Card Bus) and physically manage network communications. Converts data from parallel to serial and into appropriate signals for transmission media.

MODEMS

• Computers "speak" digital
• Telephone connections have historically "spoken" analog – they were designed to carry sound

Digital data had to be converted to something that the POTS (plain old telephone system) could understand – and that is sound waves.

Modems do this: they Modulate from digital to analog and then Demodulate from analog to digital.

Direction – these are generic modem / networking terms - Very A+

Put it all into single file!

• Computers have many wires to carry each bit of data – Parallel
• The POTS has fewer data wires (like uh, two) – Serial

Converting parallel to serial and back is done with a UART (Universal Asynchronous Receiver Transmitter)

The UART chip determines the speed and efficiency of your serial port. External modems use the UART on the MOBO, internal modems use their own. Device Manager/Ports/COM1/Port Settings/Advanced

• The original IBM UART chip was the 8250. It came in three variations, none of which could communicate above 9600 BPS.
• Although standard modems cannot go this fast, the 16550A UART in most PCs allows data rates of up to 115k/bps.
• One of the latest PC UARTs, the 16650, allows for data rates as high as 230Kbps and has a 32-bit FIFO buffer. If you are using a connection that goes above the 115Kbps limit of the 16550 (certain new ISDN connections come to mind) then you will need to upgrade the UART by probably purchasing a serial port expansion card.

Public switched telephone network (PSTN)

• Communication backbone for most PC users worldwide
• Originally designed with enough bandwidth to carry voice signals
• This limited bandwidth is what has kept traditional phone modems from entering the "broadband" age

Serial Transfer Modes

There are two modes of transfer when using a serial data communications link.

• Harder to implement across various systems
• In this data transfer method, a GROUP of bytes are "encapsulated"
• Constant flow of data
• CRC (Cyclical Redundancy Check) – more reliable than parity
• BOTH sides must agree on protocol

Error detection and correction
Modems support advanced error detection protocols at the hardware level.  Detection and correction is achieved using such protocols as:

• MNP (Microcom Networking Protocol) - a protocol developed by Microcom for full-duplex, error free communication.  MNP was developed to detect, and correct, errors resulting from noisy telephone connections.
• ITU-T (The International Telecommunication Union) is a home for various other protocols, known for their names, which start with a V (otherwise known as the V-Dot Standards).
  • V.42: An error control standard for 9600 bps modems.  This standard supports MNP-2 through MNP-4.
  • V.34:  An error control standard for 28,800 bps modems/14,400 bps faxes.
  • V.90:  An error control standard for 56,000 bps modems.
  • V.92: QuickConnect, Modem-on-Hold and PCM Upstream

Compression
Due to the low transmission speeds achieved by modems, most modems support a variety of data compression protocols.  Using these protocols, the data throughput can rise by an average of 50%.

Configuring your modem using the AT command set

Basic Dialing Commands - all commands (except A/ and +++) end with the Enter key. Red stuff is known A+ material…

DSL

Advantages of DSL:

• You can leave your Internet connection open and still use the phone line for voice calls - low-pass filters
• The speed is much higher than a regular modem (1.5 Mbps vs. 56 Kbps)
• DSL doesn't necessarily require new wiring; it can use the phone line you already have
• The company that offers DSL will usually provide the modem as part of the installation - DSL transceiver or ATU-R
• ADSL provides a dedicated connection from each user back to the DSLAM

Disadvantages of DSL:

• A DSL connection works better when you are closer to the provider's central office - distance-sensitive technology
• The connection is sometimes faster for receiving data than it is for sending data over the Internet - asymmetric DSL (ADSL)
• The service is not available everywhere

Other Types of DSL

• Very high bit-rate DSL (VDSL) - This is a fast connection, but works only over a short distance.
• Symmetric DSL (SDSL) - This connection, used mainly by small businesses, doesn't allow you to use the phone at the same time, but the speed of receiving and sending data is the same.
• Rate-adaptive DSL (RADSL) - This is a variation of ADSL, but the modem can adjust the speed of the connection depending on the length and quality of the line.

• Always on connection
• The speed is much higher than a regular modem (1.5 Mbps vs. 56 Kbps)
• Cable uses your existing cable TV connection
• The company that offers Cable will usually provide the modem as part of the installation
• Not distance-sensitive

Disadvantages of Cable:

• Share common bandwidth within cable neighborhood - up to ~1000 customers
• The connection is faster for receiving data than it is for sending data over the Internet
• The service is not available everywhere

DOCSIS: Data Over Cable Service Interface Specification. The dominating cable modem standard. Defines technical specifications for both cable modem and Cable Modem Termination System - CMTS.

Wireless – Very A+

The term wireless networking refers to technology that enables two or more computers to communicate using standard network protocols, but without network cabling.

There are two basic types of wireless networks

• Ad-hoc (or peer to peer)
  
  
  Each host can connect directly to another host
  
  
  
  
  
  
  
  
• Access point
  

  Dedicated hardware or software (computer with wireless card)

Wireless standards

802.11 is the most common standard for the technology underlying wireless. There are various flavors of 802.11. Typical indoor range is 150-300 feet. Outdoor range ~1000 feet. These devices use antennae, so direction or use of the antennae is a consideration. Most manufacturers like the antennae to be straight up.

• 802.11a
  • 5Ghz band
  • 54Mbps
• 802.11b
  • 2.4Ghz band
  • 11Mbps
• 802.11g
  • 2.4Ghz band
  • 54Mbps - (orthogonal WD Mux)
• 802.1n
  • Backwards compatible with a and b and g
  • Wider and double channels in either 2.4Ghz or 5Ghz
  • Starts at 135Mbps and could go to 540Mbps - (orthogonal WD Mux)
  • Greater coverage
  • True 802.11n due 2006

Wireless technology should be able to interoperate between venders, utilize multiple access points and roam between them, interconnect two LANs, do Internet Connection Sharing – pretty cool when it works.

Security

• WEP (wireless encryption protocol) uses up to 128 bits for security
• Allow only specific computers (based on MAC address)
• Broadcast SSID
  • A SSID is the unique name shared among all points in a wireless network. The SSID must be identical at each point in the wireless network. It is case sensitive and may consist of any character on your keyboard
  • An SSID of ANY will try and connect to any avialable access point
  • Is broadcast from access point
  • For security purposes you may choose to turn SSID broadcasting off

• There are some inherent security issues with WEP. In practice it has proven to pose a security risk due to poor encryption and static keys. Programs like WEP-crack and AirSnort have been used to crack the encryption in WEP.

• WPA – Wi-Fi Protected Access is the new security method for Wi-Fi. WPA uses extra-strong encryption algorithms. In addition encryption keys are automatically changed (called rekeying) and authenticated between devices after a specified period of time or after a specified number of packets has been transmitted.

• XP includes special Wireless features (or you can use vender’s proprietary software)
• Other OS may require vender software

• If traffic then wait
• If no traffic then
• If none for more than prescribed time then send
• If none for less than prescribed time then wait a random amount of time and (if still none) then send
• Reciever sends back ACK
• If sender gets ACK then send data immediately
• If sender doesn’t get ACK then start all over again…
• Overhead and interference can cause WiFi to only achieve ~50% of its rated throughput. 
• Reducing data preamble at AP and station improves efficiency

THE SOFTWARE

• Developed but the DOD (Department of Defense) and called ARPANET (Advanced Research Project Agency network).
• The Internet is a global network of networks.
• The default transmission protocol (language, or rules) is called TCP/IP (Transmission Control Protocol / Internet Protocol).
• Designed for WAN
• TCP/IP describes the "packaging and presentation" part of data exchange – and relies on other protocols (Ethernet, Token Ring) to provide the "shipping" part.
• The WWW (World Wide Web) is a graphical way of viewing the Internet
  • HTTP (hypertext transfer protocol - port 80)
  • HTTPS (secure packaging - port 443)
  • SSL (secure connection)
• POP (110) and SMTP (port 25) for email
• Telnet (port 23) for remote access
• FTP (ports 21 & 20)  for file transfer
• DNS (Domain Name Service - port 53) for name resolution
  • provides a hierarchical namespace that maps to IP addresses
  • Set of databases that contain the Domain names and the actual IP address
  • WINS (Windows Internet Naming Service)
• Gateway (your network’s connection to another network goes through a gateway)

Get to know your browser

Tools / Internet Options…

Get to know your System’s Features

ICS (Internet Connection Sharing – 98SE, ME, XP)

• A firewall is used to set restrictions on what information is communicated from your network to and from the Internet
• Dial-up, local area network, PPPoE, or VPN connections
• You should not enable Internet Connection Firewall on virtual private networking (VPN) connections or on client computers because ICF will interfere with file and printer sharing
• Requires two NICs

Get to know your provider

ISP – Internet Service provider
Dial Up Networking – Windows 9x wizard for modem connections to the Internet

Other Non-Dial Up connections (DSL, cable, satellite) uses your NIC to place you "on the net"

Get to know your IP address

IP address (IPv4) – information about network address and host address. 32-bits binary number comprised of 4 bytes (or "octets"). There are enough combinations for over 4 billion different addresses (256 x 256 x 256 x 256).

Network ID and host ID Classes (w.x.y.z).

The address 127 is reserved for loopback testing and interprocess communication on the local computer; it is not a valid network address. 127.0.0.1 is also called localhost

Host IDs 0 and 255 (like 192.168.3.255) should not be assigned to a computer; they are used as broadcast addresses that are typically recognized by all computers.

W Addresses 224 and above are reserved for special protocols and are not used as host addresses.

Internal numbers – Some numbers are not meant to be on the Internet. Non-routable.

10.0.0.0 through 10.255.255.255 (Class A Network)
172.16.0.0 through 172.31.255.255 (Class B Network)
192.168.0.0 through 192.168.255.255 (Class C Network)

Subnet mask – Identifies which portion of the IP address is network ID and which is host ID. Both mask and IP address are required.

Custom subnets – hardware, performance, geography, topology.

Note: All systems connected to the same local area network (or physical segment) must have the same subnet mask.

DHCP - Very A+

Dynamic Host Configuration Protocol (DHCP) is for the automatic allocation of IP addresses.

Static Address Management - Very A+

• YOU pick the numbers

• For life beyond a single network segment.
• Broadcast name resolution – resource consuming
• >=NT     - \%systemroot%\system32\drivers\etc
• = 98     - \%systemroot% (hosts.sam)
• Can be used to steal Internet sites
• http://www.mvps.org/winhelp2002/hosts.htm

Get to know your Clients and Services - Very A+

Client for Microsoft Networks - provides mechanisms for logging on; locating, opening, reading, writing, and deleting files; submitting print requests. Allows for SMB (server message block) communication with other types of SMB-based clients: SAMBA (Linux), WFWG, OS/2 Warp, etc.

Access Control – who controls the security of the resource? (Win9x)

• Share-level – with this method the host of the resource controls access with passwords for each resource shared. (Peer to Peer)
• User-level – with this method a separate server manages resource security based on user and password.

Workgroup – logical group of hosts that handle their own login and security

Domain – hosts in a domain do not handle login and security

Get to know your Utilities - Very A+

Under Windows 95/98/NT/2000, a number of utilities are available to monitor the status of both TCP/IP and NetBIOS, including:

Ping yourself: ping localhost or ping 127.0.0.1

TRACERT – watch all the nodes a message visits on it’s way to its destination

Trace the hops to yahoo: tracert www.yahoo.com

WINIPCFG – check your IP numbers (IPCONFIG for Windows2K and DOS 9x or WNTIPCFG for 2K if you download it)

The following tools are not listed in the A+ objectives. However they are useful and should be learned.

nbtstat –n