webpointmorpheus Computer Info
Intro to Networking

     Overview      Definitions      Ethernet      Token Ring      Cable Categories      UTP Cable Config
     Modems      NOS      Protocols      Network Tools      Wireless      PCMCIA

©2005 - material compiled by Bob Carnaghi, www.webpointmorpheus.com

Overview     Top of Page

Networking of computers is the process of sharing files or data between the computers. Networks come in different sized and flavors, from small 'peer-to-peer' home networks to the Internet. There are four requirements for successful networking:

1. Hardware - commonly a NIC, cable modem, or wireless modem, installed on each computer. Ethernet or Token Ring type.
2. Connection Method - typically a system of cables, or more recently a wireless system. UTP, etc.
3. PC operating system - must be capable of communicating with the NIC, as well as the other nodes on the network.
4. Network Operating System (NOS) - server software which gives out information and/or services.

This document undertakes an overall approach to and definition of computer networking. Listed below are several protocols for connecting and cabling computers, as well as topologies.

Definitions     Top of Page

APIPA: Automatic Private IP Addressing. Configured to issue an IP address when DHCP fails.

Bus Topology: A method of connecting computers using coaxial cable which is similar to a party line telephone system. If any one of the systems in the segment goes down, the entire segment goes down.

Collision: Packets that collide on a network system when sent at the same time. CSMA/CD (Carrier Sense Multiple Access/Collision Detection negotiates and corrects the collisions.

CRC: Cyclic Redundancy Check. A method of checking the integrity of data which is contained in a transmission.

Crossover Cable: A wire specifically designed for connecting a host to a host or a server to a server on a 10*BaseT network.

DHCP: Dynamic Host Configuration Protocol. A method of dynamically assigning IP addresses on a network.

Full/Half duplex: A configuration to place the system into full 'send and receive' or 'send or receive' mode, respectively.

Hardware Protocol: The definition of standards for moving data from one point to another on a network. There are two Hardware Protocols which dominate the current PC world of networks:

1. Ethernet
2. Token Ring

Hub: Hardware unit for connecting computers into an Ethernet Star topology.

LAN: Local Area Network. A collection of computers privately connected and protected from the Internet.

MAC Address: Media Access Controller. A unique number given to each and every NIC (Network Interface Card) that is manufactured. This ensures that the location of installation for that card is unique, and can be found on any network. There are 12¹⁶ (184,884,258,895,036,416) MAC addresses available.

MAN: Metropolitan Area Network. A WAN that would cover a community or city.

MAU/MSAU: Multi-Station Access Unit. The equivalent of a Token Ring hub.

NIC: Network Interface Card. A hardware device for connecting and cabling computers to a network. This device has a unique MAC address, and is capable of breaking data transmissions into manageable packets, and re-assembling the packets into intelligent information again.

Packet: (also called Frame or Datagram) The smallest unit of data which can be intelligently transmitted over a network. A document, file, or other collection of information is broken down into data packets. These packets contain information about the sending computer, the receiving computer, the 'payload' data, and CRC.

Router: Hardware unit to interface a LAN with the Internet.

Switch: Same purpose as a hub, newer technology, with bandwidth compensation features.

Topology: The physical layout of a network.

UTP: Unshielded Twisted Pair. Networking cable with levels and standards that define data transfer rates.

WAN: A larger network of computers (or LANs) which are typically geographically diverse.

Ethernet Networks     Top of Page

Ethernet comes in three main types, basically defined by cabling types which are listed below. A certain amount of mixing the types is permitted.

1. Coaxial
2. UTP (Unshielded Twisted Pair)
3. Fiber Optic

Ethernet Types
Name	Topology	Segment Length	Transfer Rate	How it works
10Base2 (Thin Ethernet)	Bus Topology	185 Meters Max 30 nodes	10 Mbps	Similar to 10Base5 Cheaper to install
10Base5 (Thick Ethernet)	Bus Topology	500 Meters Max 100 nodes	10 Mbps	CSMA/CD Bandwidth shared by all computers Low security Must be terminated to prevent reflection
10*BaseT UTP Ethernet	Star Topology	100 Meters Max 1024 nodes	10 Mbps 100 Mbps 1000 Mbps	Uses Hubs, Switches, or Routers 1 PC max per node Individual node status does not affect network
10BaseFL 100BaseFX	Fiber Optic	Varies (typically fast)	Star Topology	Delicate, expensive, difficult to use Used for trunk lines Not yet popular

Token Ring Networks     Top of Page

Token Ring uses a Star Ring topology that is absolutely incompatible with Ethernet. This system was initially pioneered by IBM. The system continually passes a token, and any communication must be attached to an empty token. Once the communication packets are delivered to the client, the token is cleared. On the next pass, any other communication that has been scheduled is undertaken.

Due to the operational characteristics of the passing token, collisions are non-existent, and the CSMA/CD issues of Ethernet are not necessary in Token Ring.

Token Ring Topology
Cable	Topology	Segment Length	Nodes	Notes
STP	Token Ring	100 Meters	260	Can also use Repeaters. Typical UTP Token Ring networks are hard to distinguish from Ethernet.
UTP	Token Ring	45 Meters	72

UTP Cable Categories     Top of Page

There are several cable types used in networking - Thick Ethernet, Thin Ethernet, UTP, etc. Thick Ethernet is becoming a thing of the past, as is Thin Ethernet. Listed below are UTP Cabling Category parameters.

UTP Category Levels
CAT Level	Speed	Notes
CAT 1	NA	Standard phone line
CAT 2	To 4 Mbps	ISDN & T1
CAT 3	To 16 Mbps
CAT 4	To 20 Mbps
CAT 5	To 100 Mbps
CAT 5e	To 1 Gbps (1,000 Mbps)
CAT 6	To 10 Gbps (10,000 Mbps)

UTP Cable Configuration     Top of Page

Below is a chart listing the two main connection schemes for Unshielded Twisted Pair Cabling. Crossover cables make possible the connection of host-to-host, and server-to-server.

UTP Cabling Chart
Pin #	568A	568B
1	White/Green	White/Orange
2	Green	Orange
3	White/Orange	White/Green
4	Blue	Blue
5	White/Blue	White/Blue
6	Orange	Green
7	White/Brown	White/Brown
8	Brown	Brown

Modems     Top of Page

Modem type dial-up connections are being phased out by recent developments in DSL, Cable, and Wireless. At the time of this writing, dial-up is still common. Listed below are the common Modem Protocols.

Although the baud rate does dictate how fast modem can transmit data and older modems do use the baud rate to measure their speed, the speed of modern modems is measured in bits per second (bps). This is where the difference between Baud and bps comes in: the baud rate indicates how many frequency changes per second can occur, with early modems the baud rate equaled the bits per seconds. For example a 2400 bps modem ran at 2400 baud, but so does a 14,400 bps modem, the difference is that with 14,400 bps modems use 6 times as many different frequencies, simultaneously passing 4 bits per change.

Types of Modem Protocols
Protocol	Description
XMODEM	128 byte blocks with checksum error detection
YMODEM	1024 byte blocks
ZMODEM	1024 byte blocks w/error detection and file streaming

 

Modem Commands     Top of Page

There was a time in the early internet when programming or manipulating a modem was necessary. Listed below are the common commands to achieve this.

Common Modem Commands
Command	Action
ATE0	Turns off screen echo
ATE1	Echoes command to screen
ATM0	Turns speaker off
ATM1	Turns speaker on
ATH or ATH0	Makes the modem hang up
ATH1	Takes phone off hook
ATD	Takes phone off hook and dials the specified number
ATZ	Resets the modem

NOS     Top of Page

Network Operating System architecture can take one of three approaches:

1. Client/Server - typically Novell systems, which have a secure, high quality dedicated server.
2. Peer-to-Peer - classically Windows Workgroups. These networks are limited in number, with security and maintenance issues rising proportionally with the size of the network.
3. Domain Based - typically Windows servers which use Domain Controllers and Active Directory, etc. as server software.

Protocols     Top of Page

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1. NetBEUI - An older IBM network protocol that does not lend itself well to routing.
2. IPX/SPX - Typically associated with Novell Netware.
3. TCP/IP - The most popular, and the default protocol for the Internet.
4. AppleTalk - Used on Mac systems prior to OS X.

IP Network Addressing Scheme
Network Class	Address Range	Addresses Available	Number of Host Nodes Supported	Notes
A	1-126	129	16,777,214 (224±)	127.0.0.1 = Loopback 10.0.0.1 = Class A Private 172.16.0.1 = Class B Private 192.168.0.0 = Class C Private 169.254.0.1 = APIPA Range
B	128-191	16,384 (214)	65534 (216±)
C	192-223	2,097,152 (221)	254 (28±)

Network Troubleshooting Tools     Top of Page

There are several tools which will assist in troubleshooting network configuration and connection. A list with brief description is below.

Network Troubleshooting Commands
Command	Common Name	Description	Options (partial list)
arp	Address Resolution Protocol.	Displays and modifies the IP-to-Physical address translation tables used by address resolution protocol (ARP).
ftp	File Transfer Protocol	This is the popular internet protocol for transferring files from host to host. The utility can be run from the command line. There are several user-interface programs that greatly facilitate this utility.	Several options, too many to list.
ipconfig	Internet Protocol Configuration	Shows the current TCP/IP configuration for a local computer. Permits releasing and renewing of DHCP assigned address.	/all /release /renew
nbstat	NetBios Status	Similar to netstat, for NetBios connections
netstat	Network Status	Displays protocol statistics and current TCP/IP network connections.
ping	Portable Internet Groper	Verifies the connectivity of another host on the network.
tracert	Trace Route	Shows the route between hosts, with time between each hop on the journey.
winipconfig	Windows IP Configuration	An applet version of IPConfig available only in Windows 95.

Wireless     Top of Page

Wireless is the latest craze among computer hardware. The use of wireless network components eliminates the burden of the conglomeration of cables that tend to lie behind desks, tables, and shelves, etc. Wireless must be consciously secured, because as it comes 'out of the box' it isn't secure. There are specific steps to secure a wireless network:

1. SSID - (the network name) of the network to limit access.
2. MAC Filtering - List only those devices which are allowed to connect to the wireless network.
3. WEP/WPA - Wireless Equivalency Privacy/Wi-Fi Protected Access. The method of encrypting the data packets during transit.

Wireless Network Terminology & Standards
Standard	802.11a	802.11b	802.11g
Max. Throughput	54 Mbps	11 Mbps	54 Mbps
Max. Range	150 ft.	300 ft.	300 ft.
Frequency	5 Ghz.	2.4 Ghz.	2.4 Ghz
Security	SSID, MAC Filtering, Industry-standard WEP, WPA	SSID, MAC Filtering, Industry-standard WEP, WPA	SSID, MAC Filtering, Industry-standard WEP, WPA
Compatibility	802.11a	802.11b	802.11b, 802.11g
Spread-spectrum method	DSSS	DSSS	DSSS
Communication Mode	Ad-hoc or infrastructure	Ad-hoc or infrastructure	Ad-hoc or infrastructure
Description	This standard defines the 'Wi-Fi Certified.' Eight available channels. Less prone to interference than 802.11b and 802.11g.	This standard defines the 'Wi-Fi Certified.' Fourteen available channels in the 2.4 GHz band (only 11 available in the US due to FCC restrictions.) Three non-overlapping channels.	This standard defines the 'Wi-Fi Certified.' Fourteen available channels in the 2.4 GHz band (only 11 available in the US due to FCC restrictions.) Three non-overlapping channels.

PCMCIA     Top of Page

PCMCIA is a type of expansion card used widely in laptops for connections to LANs, Dial-up, Ethernet, Wi-Fi, etc. Listed below are the three common types, and their sizes. PCMCIA slots are found on virtually all portables.

Types of PCMCIA Cards
Card	Size	Use
Type 1	3.5 mm	Memory expansion cards, ROM and RAM
Type 2	5.0 mm	Communication devices such as modems and NICs
Type 3	10.5 mm	Portable hard disks