Networking Essentials Notes Section 1 Section 2 Section 3 Section 4 Section 5 Section 6 Section 7 OSI Layer Model Memory Sheets: Cables IRQ's, 802, Cables, etc

Peer to Peer Networks

• No dedicated server or hierarchy, also called a workgroup.
• Usually 10 or fewer workstations.
• Users act as their own administrator and security.
• Computers are in same general area.
• Limited growth.

Server Based Networks

• 10 or more users.
• Employs specialized servers.
1. File and Print
2. Application
3. Mail
4. Fax
5. Communications (gateways)
• Central administration.
• Greater security.
• Centralized backup.
• Data Redundancy.
• Supports many users

Combination Networks

• Combines the features of both Peer to Peer and Server based networks
• Users can share resources among themselves as well as access server-based resources.

There are 4 basic topologies with variations

Bus Topology

• Bus consists of a single linear cable called a trunk.
• Data is sent to all computers on the trunk. Each computer examines EVERY packet on the wire to determine who the packet is for and accepts only messages addressed to them.
• Bus is a passive topology.
• Performance degrades as more computers are added to the bus.
• Signal bounce is eliminated by a terminator at each end of the bus.
• Barrel connectors can be used to lengthen cable.
• Repeaters can be used to regenerate signals.
• Usually uses Thinnet or Thicknet
• both of these require 50 ohm terminator
• good for a temporary, small (fewer than 10 people) network
• But its difficult to isolate malfunctions and if the backbone goes down, the entire network goes down.

Star Topology

• Computers are connected by cable segments to a centralized hub.
• Signal travels through the hub to all other computers.
• Requires more cable.
• If hub goes down, entire network goes down.
• If a computer goes down, the network functions normally.
• most scalable and reconfigurable of all topologies

Ring Topology

• Computers are connected on a single circle of cable.
• usually seen in a Token Ring or FDDI (fiber optic) network
• Each computer acts as a repeater and keeps the signal strong => no need for repeaters on a ring topology
• No termination required => because its a ring

• Token passing is used in Token Ring networks. The token is passed from one computer to the next, only the computer with the token can transmit. The receiving computer strips the data from the token and sends the token back to the sending computer with an acknowledgment. After verification, the token is regenerated.
• relatively easy to install, requiring ;minimal hardware

Mesh

• The mesh topology connects each computer on the network to the others
• Meshes use a significantly larger amount of network cabling than do the other network topologies, which makes it more expensive.
• The mesh topology is highly fault tolerant.
• Every computer has multiple possible connection paths to the other com-puters on the network, so a single cable break will not stop network communications between any two computers.

Star Bus Topology

• Several star topologies linked with a linear bus.
• No single computer can take the whole network down. If a single hub fails, only the computers and hubs connected to that hub are affected.

Star Ring Topology

• Also known as star wired ring because the hub itself is wired as a ring. This means it's a physical star, but a logical ring.
• This topology is popular for Token Ring networks because it is easier to implement than a physical ring, but it still provides the token passing capabilities of a physical ring inside the hub.
• Just like in the ring topology, computers are given equal access to the network media through
• the passing of the token.
• A single computer failure cannot stop the entire network, but if the hub fails, the ring that the hub controls also fails.

Hybrid Mesh

• most important aspect is that a mesh is fault tolerant
• a true mesh is expensive because of all the wire needed
• another option is to mesh only the servers that contain information that everyone has to get to. This way the servers (not all the workstations) have fault tolerance at the cabling level.

Top of page

Connecting Network Components

• Coaxial Cable
• Twisted-pair
• UTP - Unshielded Twisted Pair
• STP - Shielded Twisted Pair
• Fiber-optic

• Consists of a solid or stranded copper core surrounded by insulation, a braided shield and an insulating jacket.

• Braided shield prevents noise and crosstalk.
• More resistant to interference and attenuation than twisted pair cabling.
• Both thin and thick cables can use (see pp. 80-81 for pics)
• BNC cable connectors,
• BNC barrel connectors
• BNC T connectors
• BNC terminators.
• Plenum (fire resistant) graded cable can be used in false ceilings of office space or under the floor.
• Can transmit data, voice and video.
• Offers moderate security ----> better than UTP/STP

Thinnet - RG-58 cable

• called
• 0.25" thick.
• Uses
• BNC twist connector,
• BNC barrel connectors
• BNC T connectors
• 50 ohm terminators
• Can carry signals 185 meters or 607 feet.
• Types: (pics on page 78)

Coaxial Cable Types

RG-8 and RG-11	Thicknet (50 ohms)
RG-58 Family
RG-58 /U	Solid copper (50 ohms)
RG-58 A/U	Thinnet, Stranded copper (50 ohms)
RG-58 C/U	Thinnet, Military grade (50 ohms)
RG-59	Broadband/Cable TV (75 ohm) video cable
RG-62 A/U	ARCnet cable (93 ohm) RG-62 A/U is the standard ARCnet cable, but ARCnet can use fiber optic or twisted pair.

• each cable must have a terminator whose impedance matches the cable type
• impedance = current resistance measured in ohms
• terminators are resistors that prevent signal bounce or echo.

Here are some limitations of 10Base2 Ethernet:

• Length of trunk segment may be up to 607 feet.
• A maximum of 30 workstations is allowed per trunk.
• There may be no more than 1024 workstations per network.
• Entire network trunk length can't exceed 3035 feet (925 meters)
• The minimum cable length between workstations is 20 inches.
• The Ethernet 5-4-3 Rule for connecting segments is 5 trunk segments can be connected, with 4 repeaters or concentrators, with no more than 3 populated segments (on coaxial cable).

Thicknet - RG-8 and RG-11 coaxial cable

• 0.5" thick
• used for 10Base5 networks, linear bus topology
• transmits at 10 Mbps
• Uses DIX or AUI (Attachment Unit Interface) connector - also known as DB-15 connector to connect to external transceivers.
• Vampire taps are used to attach a transceiver to the thicknet trunk.
• Can carry signals 500 meters or 1640 feet.
• much less flexible and far more bulky and harder to install than thinnet
• better security than thinnet
• better resistance to electrical interference than thinnet.
• MORE expensive than thinnet.

• Consists of two insulated copper wires twisted around each other.
• Twisting cancels out electrical noise from adjacent pairs (crosstalk) and external sources.
• Uses RJ-45 telephone-type connectors (larger than telephone and consists of eight wires vs. Telephone's 4 wires).
• Generally inexpensive.
• Easy to install.

Unshielded Twisted Pair (UTP)

• Maximum cable length is 100 meters or 328 feet (10BaseT).
• Types:
1. Cat 1 Voice grade telephone cable.
2. Cat 2 Data grade up to 4 Mbps, four twisted pairs.

Category 3 and above is needed for Ethernet networks. Cat 3, 4, and 5 use RJ-45 connectors

1. Cat 3 Data grade up to 10 Mbps, four pairs w/3 twists/ft.
2. Cat 4 Data grade up to 16 Mbps, four twisted pairs.
3. Cat 5 Data grade up to 100 Mbps, four twisted pairs.

This is the cheapest cable to put in. Exam questions ALWAYS take this as a given.

Here are some limitations of 10BaseT Ethernet:

• Workstations may be no more than 328 feet from the concentrator port.
• 1,023 stations are allowed on a segment without bridging.
• The minimum cable length between workstations is 8 feet.

Other Drawbacks

• UTP is particularly susceptible to crosstalk, which is when signals from one line get mixed up with signals from another.
• easily tapped (because there is no shielding)
• 100 meters is shortest distance => attenuation is the biggest problem here.

Shielded Twisted Pair (STP)

• Uses a woven copper braid jacket and a higher quality protective jacket. Also uses foil wrap between and around the wire pairs.
• Much less susceptible to interference and supports higher transmission rates than UTP.
• Shielding makes it somewhat harder to install.
• same 100 meter limit as UTP.
• harder to tap
• used in AppleTalk and Token Ring networks

• Consists of a small core of glass or plastic surrounded by a cladding layer and jacket.
• Fibers are unidirectional (light only travels in one direction) so two fibers are used, one for sending and one for receiving. Kelvar fibres are placed between the two fibres for strength.
• Good for very high speed, long distance data transmission.
• NOT subject to electrical interference.
• Cable can't be tapped and data stolen => high security
• Most expensive and difficult to work with.
• Immune to tapping.
• can transmit at 100 Mbps and way up to 2 Gbps
• up to 2000 meters without a repeater.
• Supports data, voice and video.
• needs specialized knowledge to install => expensive all round.

Signal Transmission

Baseband Transmission -- Digital

• Baseband transmission uses digital signaling over a single frequency.
• Entire communication channel is used to transmit a single signal.
• Flow is bi-directional. Some can transmit and receive at the same time.
• Baseband systems use repeaters to strengthen attenuated signals.

Broadband Transmission -- Analog

• Broadband uses analog signaling over a range of frequencies.
• Signals are continuous and non-discrete.
• Flow is uni-directional and so two frequency channels or two separate cables must be used.
• if enough bandwidth is available, multiple analog transmission systems such as cable TV AND network transmissions can be on the same cable at the same time.
• if this is the case, ALL devices must be tuned to use only certain frequencies
• Uses amplifiers for signal regeneration.

Baseband is "BEDR"

Bidirectional
Entire channel taken up
Digital
Repeaters used to strengthen signal

IBM Cabling

• Uses AWG standard wire size.
• Connected with proprietary IBM unisex connectors.
• Defines cables as types

Installation Logistics

• How easy is the cable to work with?

Shielding

• Is the area "noisy"?
• Do you need plenum grade cable => more expensive

Crosstalk

• Where data security is important this is a problem
• Power lines, motors relays and radio transmitters cause crosstalk

Transmission Speed (part of the bandwidth)

• Transmission rates are measured in Mbps
• 10 Mbps is common
• 100 Mbps is becoming common
• Fiber can go well over 100 Mbps but costs and requires experts to install.

Cost

• Distance costs you money

Attenuation

• Different cables can only transmit so far without causing too many errors

Top of page

• Used where cable isn't possible - remote sites; also when mobility is important.
• Use transceivers or access points to send and receive signals between the wired and wireless network.

There are 4 techniques for transmitting data

• Infrared transmission consists of four types;
1. Line of sight
2. Scatter: good within 100 ft.
3. Reflective
4. Broadband optical telepoint: used for multimedia requirements; as good as cable.
• Laser requires direct line-of-sight.
• Narrow-band (single frequency) radio
• Cannot go through steel or load-bearing walls.
• Requires a service handler.
• Limited to 4.8 Mbps
• Spread-Spectrum Radio
• Signals over a range of frequencies.
• Uses hop timing for a predetermined length of time.
• Coded for data protection.
• Quite slow; Limited to 250 Kbps.

Point to Point Transmission

• Transfers data directly from PC to PC (NOT through cable or other peripherals)
• Uses a point to point link for fast error-free transmission.
• Penetrates objects.
• Supports data rates from 1.2 to 38.4 Kbps up to
• 200 feet indoors or
• 1/3 of a mile with line of site transmission.
• Also communicates with printers, bar code readers, etc.

Multipoint Wireless Bridge

• Provides a data path between two buildings.
• Uses spread-spectrum radio to create a wireless backbone up to three miles.

Long-Range Wireless Bridge

• Uses spread-spectrum technology to provide Ethernet and Token-Ring bridging for up to 25 miles.
• This costs less than T1, but T1 will transmit at 1.544 Mbps

Mobile Computing

• Uses wireless public carriers to transmit and receive using;
• Packet-radio communication.

Uplinked to satellite, broadcast only to device which has correct address.

• Cellular networks.

CDPD same as phone, subsecond delays only, real time transmission, can tie into cabled network.

• Satellite stations.

Microwave, most common in USA, 2 X directional antennas, building to building, building to satellite

• Slow transmission rate: 8 Kbps - 19.2 Kbps

Top of page

The role of the network Adapter card it to:

• Prepare data from the computer for the network cable
• Send the data to another computer
• Control the flow of data between the computer and the cabling system

NIC's contain hardware and firmware (software routines in ROM) programming that implements the

• Logical Link Control and
• Media Access Control

functions of the Data Link layer of the OSI

Preparing Data

• data moves along paths in the computer called a BUS - can be 8, 16, 32 bits wide.
• on network cable, data must travel in a single bit stream in what's called a serial transmission (b/c on bit follows the next).
• The transceiver is the component responsible for translating parallel (8, 16, 32-bit wide) into a 1 bit wide serial path.
• A unique network address or MAC address is coded into chips in the card
• card uses DMA (Direct Memory Access) where the computer assigns memory space to the NIC
• if the the card can't move data fast enough, the card's buffer RAM holds it temporarily during transmission or reception of data

Sending and Controlling Data

The NICs of the two computers exchanging data agree on the following:

1. Maximum size of the groups of data being sent
2. The amount of data to be sent before confirmation
3. The time intervals between send data chunks
4. The amount of time to wait before confirmation is sent
5. How much data each card can hold before it overflows
6. The speed of the data transmission

Network Card Configuration

• IRQ: a unique setting that requests service from the processor.

•   Base I/O port: Channel between CPU and hardware
• specifies a channel through which information flows between the computer's adapter card and the CPU. Ex. 300 to 30F.
• Each hardware device must have a different base I/O port

• Base Memory address: Memory in RAM used for buffer area
• identifies a location in the computer's RAM to act as a buffer area to store incoming and outgoing data frames. Ex. D8000 is the base memory address for the NIC.
• each device needs its own unique address.
• some cards allow you to specify the size of the buffer ( 16 or 32 k, for example)
• Transceiver:
• sometimes selected as on-board or external. External usually will use the AUI/DIX connector: Thicknet, for example
• Use jumpers on the card to select which to use

Data Bus Architecture

The NIC must

• match the computer's internal bus architecture and
• have the right cable connector for the cable being used

• ISA (Industry Standard Architecture): original 8-bit and later 16-bit bus of the IBM-PC.
• EISA (Extended Industry Standard Architecture): Introduced by consortium of manufacturers and offers a 32-bit data path.
• Micro-Channel Architecture (MCA): Introduced by IBM in its PS/2 line. Functions as either 16 or 32 bit.
• PCI (Peripheral Component Interconnect): 32-bit bus used by Pentium and Apple Power-PC's. Employs plug and play.

Improving Network Card Performance

• Direct Memory Access (DMA):
• data is moved directly from the network adapter card's buffer to computer memory.
• Shared Adapter Memory:
• network adapter card contains memory which is shared with the computer.
• The computer identifies RAM on the card as if it were actually installed on the computer
• Shared System Memory:
• the network adapter selects a portion of the computer's memory for its use.
• MOST common
• Bus Mastering:
• the adapter card takes temporary control of the computer's bus, freeing the CPU for other tasks.
• moves data directly to the computer's system memory
• Available on EISA and MCA
• can improve network performance by 20% to 70%
• RAM buffering:
• Ram on the adapter card acts as a buffer that holds data until the CPU can process it.
• this keeps the card from being a bottleneck
• On-board microprocessor:
• enables the adapter card to process its own data without the need of the CPU

Wireless Adapter Cards

• Used to create an all-wireless LAN
• Add wireless stations to a cabled LAN
• uses a wireless concentrator, which acts as a transceiver to send and receive signals

Remote-Boot PROMS (Programmable Read Only Memory)

• Enables diskless workstations to boot and connect to a network.
• Used where security is important.

Top of page

Comments and suggestions? E-mail me at grantwilson21@yahoo.com I'm sorry, but I can't answer specific network-related, or exam-related questions.
Last Updated: August 6, 2001	Grant Wilson, Edmonton, AB Canada