Layer

Function

Protocols

Network Components

Application=

User Interface

used for applications specifically writ= ten to run over the network
allows access to network services that support applications;
directly represents the services that directly support user applications
handles network access, flow control and error recovery
Example apps are file transfer,e-mail, NetBIOS-based applications

DNS; FTP; TFTP; BOOTP; SNMP;RLOGIN; SMTP; MIME; NF= S; FINGER; TELNET; NCP; APPC; AFP; SMB

Gateway

Presentati= on

Translation

Translates from application to network = format and vice-versa
all different formats from all sources = are made into a common uniform format that the rest of the OSI model c= an understand
responsible for protocol conversion, ch= aracter conversion,data encryption / decryptio= n, expanding graphics commands, data compression
sets standards for different systems to provide seamless communication from multiple protocol stacks
not always implemented in a network pro= tocol

Gateway

Redirector

Session

"syncs and sessions"

establishes, maintains and ends sessions across the network
responsible for name recognition (identification) so only the designated parties can participate in= the session
provides synchronization services by pl= anning check points in the data stream =3D> if session fails, only data after the most recent checkpoint need be transmitted
manages who can transmit data at a cert= ain time and for how long
Examples are interactive login and file transfer connections, the session would connect and re-connect if there was an interruption; recognize names in sessions and register names in history

NetBIOS

Names Pipes

Mail Slots

RPC

Gateway

Transport

packets; flow control & error-handling

additional connection below the session= layer
manages the flow control of data between parties across the network
divides streams of data into chunks or packets; the transport layer of the receiving computer reassembles= the message from packets
"train" is a good analogy =3D= > the data is divided into identical units
provides error-checking to guarantee error-free data delivery, with on losses or duplications
provides acknowledgment of successful transmissions; requests retransmission if some packets don’t arrive error-free
provides flow control and error-handlin= g

TCP, ARP, RARP;

SPX

NWLink

NetBIOS / NetBEUI

ATP

Gateway

Advanced Cable Tester

Router

Network

addressing; routing

translates logical network address and = names to their physical address (e.g. computername<= /span> =3D=3D> MAC address)
responsible for

addressing
determining routes for sending =
managing network problems such as pack= et switching, data congestion and routing

if router can’t send data frame as large as the source computer sends, the network layer compensates by breaking the data into sma= ller units. At the receiving end, the network layer reassembles the dat= a
think of this layer stamping the addres= ses on each train car

IP; ARP; RARP, ICMP; RIP; OSFP;

IGMP;

IPX

NWLink

NetBEUI

OSI

DDP

DECnet

Router

Frame Relay Device

ATM Switch

Advanced Cable Tester

= Data Link

data frames to bits

turns packets into raw bits 100101 and at the receiving end tur= ns bits into packets.
handles data frames between the Network= and Physical layers
the receiving end packages raw data fro= m the Physical layer into data frames for delivery to the Network layer<= /span>
responsible for error-free transfer of = frames to other computer via the Physical Layer
this layer defines the methods used to transmit and receive da= ta on the network. It consists of the wiring, the devices use to conn= ect the NIC to the wiring, the signaling involved to transmit / receive data and the ability to detect signaling errors on the network med= ia

Logical Link Control

error correction and flow control
manages link control and defines SAPs

802.1 OSI Model

802.2 Logical Link Control <= /p>

Bridge

Switch

ISDN Router

Intelligent Hub

NIC

Advanced Cable Tester

Media Access Control

communicates with the adapter card
controls the type of media being used: =

802.3 CSMA/CD (Ethernet)

802.4 Token Bus (ARCnet)

802.5 Token Ring

802.12 Demand Priority

Physical

hardware; raw bit stream

transmits raw bit stream over physical = cable
defines cables, cards, and physical asp= ects
defines NIC attachments to hardware, how cable is attached to NIC
defines techniques to transfer bit stre= am to cable

IEEE 802

IEEE 802.2

ISO 2110

ISDN

Repeater

Multiplexer

Hubs

Passive=
Active<= /strong>

TDR

Oscilloscope

Amplifier

= ;

3Dsetstats 3D1

Network Orientation

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.

File and Print <= /li>
Application
Mail
Fax
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 resour= ces among themselves as well as access server-based resources.

Network Topologies

There are 4 basic topologies with variations

Bus Topology

Bus consists of a sing= le 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 topol= ogy.
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 connecte= d by cable segments to a centralized hub.
Signal travels through= the hub to all other computers.
Requires more cable. <= /li>
If hub goes down, enti= re 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 =3D> no need for repeaters on = a ring topology
No termination required =3D> 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 rege= nerated.
relatively easy to inst= all, requiring ;minimal hardware

Mesh

The mesh topology conne= cts each computer on the network to the others
Meshes use a significan= tly larger amount of network cabling than do the other network topologies, which makes it more expensive.
The mesh topology is hi= ghly fault tolerant.

Every computer h= as 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 physi= cal ring, but it still provides the token passing capabilities of a physic= al ring inside the hub.
Just like in the ring topology, computers are given equal access to the network media throug= h
the= passing of the token.
A single computer failu= re 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 expensi= ve because of all the wire needed
an= other option is to mesh only the servers that contain information that every= one has to get to. This way the servers (not all the workstations) have fa= ult tolerance at the cabling level.

Connecting Network Components

Primary Cable Types

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

Coaxial Cable

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 cabl= es can use (see pp. 80-81 for pics)

BNC cable connect= ors,
BNC barrel connec= tors
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 connector= s
50 ohm terminat= ors

Can carry signals <= span style=3D'font-size:13.5pt'>185 meters or 607 feet.
Types: (pics on page 78)

Coaxial C= able 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 <= span class=3DSpellE>ARCnet can use fiber optic or twisted pair.<= /p>

each cable must have a terminator whose impedance matches the cable type
impedance =3D current resistance measured in ohms
te= rminators 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 th= an 1024 workstations per network.
Entire network trunk le= ngth 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 repea= ters 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 networ= ks, linear bus topology
transmits at 10 Mbps
Uses DIX or AUI (Attach= ment 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
bet= ter resistance to electrical interference than thinne= t.
MORE expensive than thinnet.

Twisted-Pair Cab= le

Consists of two insula= ted copper wires twisted around each other.
Twisting cancels out electrical noise from adjacent pairs (crosstalk) and external sources.=
Uses RJ-45 telephone-t= ype 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 i= s 100 meters or 328 feet (10BaseT).

Types:

Cat 1 Voice gra= de telephone cable.

Cat 2 Data grad= e 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

Cat 3 Data grad= e up to 10 Mbps, four pairs w/3 twists/ft.

Cat 4 Data grad= e up to 16 Mbps, four twisted pairs.

Cat 5 Data grad= e 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 allo= wed 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 =3D> attenuation is the biggest problem here.

Shielded Twisted Pair (STP)

Uses a woven copper br= aid jacket and a higher quality protective jacket. Also uses foil wrap bet= ween and around the wire pairs.
Much less susceptible = to interference and supports higher transmission rates than UTP.
Shielding makes it somewhat harder to install.
sa= me 100 meter limit as UTP.
harder to tap
used in AppleTalk a= nd Token Ring networks

Fiber Optic= Cable

Consists of a small cor= e of glass or plastic surrounded by a cladding layer and jacket.
Fibers are unidirection= al (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 spee= d, long distance data transmission.
NOT subject to electric= al interference.
Cable can't be tapped a= nd data stolen =3D> high security
Most expensive a= nd difficult to work with.
Immune to tapping.
can transmit at 100 = Mbps and way up to 2 Gbps
up<= /span> to 2000 meters without a repeater.
Supports data, voice and video.
nee= ds specialized knowledge to install =3D> expensive all round.

Cable Type Compa= risons
Type	Speed	Distance	Installation	Interference	Cost	# of nodes per segment	# of nodes per network
10BaseT	10 Mbps	100 meters	Easy	Highly susceptible	Least expensive	1 computer
100BaseT	100 Mbps	100 meters	Easy	Highly susceptible	More expensive than 10BaseT
STP	16 to 155 Mbps	100 meters	Moderately Easy	Somewhat resistant	More expensive than Thinnet or UTP
10Base2	10 Mbps	185 meters	Medium Difficulty	Somewhat resistant	Inexpensive	30	1024
10Base5	10 Mbps	500 meters	More difficult than Thinnet	More resistant than most cable	More expensive than most cable	100	300
Fiber Optic	100 Mbps to 2 Gbps	2000 meters	Most difficult	Not susceptible to electronic interference	Most expensive type of cable

Signal Transmission

Baseband Transmission -- Digital

Baseband transmission u= ses digital signaling over a single frequency.
Entire communication channel is used to transmit a single signal.
Flow is bi-direction= al. Some can transmit and receive at the same time.
Baseband systems use repeaters to strengthen atte= nuated 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 channel= s or two separate cables must be used.

if enough bandwidth is available, multiple analog transmission systems s= uch as cable TV AND network transmissions can be on the same cable at the same time.
if this is the c= ase, ALL devices must be tuned to use only certain frequencies

Uses amplifiers = for signal regeneration.

Helpful mnemonic to remember the difference:

Baseband is "BEDR"

Bidirectional
Entire channel taken up
Digital
Repeaters used to strengthen signal

IBM Cabling

Uses AWG standard wire size.
Connected with propriet= ary IBM unisex connectors.
Defines cables as types=

Type 1	STP (Shielded twisted-pair)	used for computers and MAU's. 101 m	These three cable t= ypes can be used in Token Ring Networks	16 Mbps 260 computer li= mit
Type 2	STP, Voice and data	100 m&nbs= p;
Type 3	UTP; Voice grade	45 m Most common T= oken Ring Cable	4 Mbps 72 computer limi= t
Type 5	Fiber-optic	industry standard
Type 6	STP; Data patch	used to connect = MSAU's together used to extend T= ype 3 cables from one computer to the MSAU
Type 8	STP Flat; Carpet grade	Limited to= 1/2 the distance of Type 1 cable
Type 9	STP; Plenum grade	used under floo= rs or in ceiling space

Important Cabling Considerations

Installation Logistics

How easy is the cable to work with?

Shielding

Is the area "noisy"?
Do you need plenum gra= de cable =3D> more expensive

Crosstalk

Where data security is important this is a problem
Power lines, motors rel= ays 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 co= mmon
Fiber can go well over = 100 Mbps but costs and requires experts to install.

Cost

Distance costs you money=

Attenuation

Different cables can o= nly transmit so far without causing too many errors

Wireless Local Area Networks

Used where cable isn't possible - remote sites; also when mobility is important.
Use transceivers or acc= ess points to send and receive signals between the wired and wireless netw= ork.

There are 4 techniques for transmitting data

Infrared transmission consists of four types;

Line of sight <= /li>
Scatter: good within 100 ft.
Reflective
Broadband optic= al telepoint: used for multimedia requirements; as= good as cable.

Laser requires direct line-of-sight.
Narrow-band (single frequency) radio

Cannot go throu= gh steel or load-bearing walls.
Requires a serv= ice handler.
Limited to 4.8 = Mbps

Spread-Spectrum Rad= io

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 l= ink 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 wi= th line of site transmission.

Also communicates with printers, bar code readers, etc.

Multipoint Wireless Bridge

Provides a data path <= b>between two buildings.
Uses spread-spectrum r= adio 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 mi= les.
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 dev= ice which has correct address.

Cellular networ= ks.

CDPD <= /b>same as phone, subsecond delays only, real time transmission, can tie into cabled network.

Satellite stati= ons.

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

Slow transmission rate= : 8 Kbps - 19.2 Kbps

Network Adapter Cards

The role of the network Adapter card it to: <= /p>

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 a= nd

Media Access Control <= /li>

functions of the D= ata Link layer of the OSI

Preparing Data

da= ta 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 calle= d 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 addre= ss 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 d= ata

Sending and Controlling Data<= /b>

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

Maximum size of the gr= oups of data being sent

The amount of data to = be sent before confirmation

The time intervals bet= ween send data chunks

The amount of time to = wait before confirmation is sent

How much data each card can hold before it overflows

The speed of the data transmission

Network Card Configuration

IRQ: a uniq= ue setting that requests service from the processor.

IRQ #

Common Use

I/O Address

IRQ 1

Keyboard

IRQ 2(9)

Video Card

IRQ 3

Com2, Com4

2F0 to 2FF

IRQ 4

Com1, Com3

3F0 to 3FF

IRQ 5

Available (Normally LPT2 or sound card )

IRQ 6

Floppy Disk Controller

IRQ 7

Pa= rallel Port (LPT1)

IRQ 8

Real-time clock

IRQ 9

Redirected IRQ2

370 - 37F

IRQ 10

Available (maybe primary SCSI controller)

IRQ 11

Available (maybe secondary SCSI controller)

IRQ 12

PS/2 Mouse

IRQ 13

Math Coprocessor

IRQ 14

Primary Hard Disk Controller

IRQ 15

Available (maybe secondary hard disk controll= er)

Base I/O port: Channel between CPU a= nd hardware

specifies a channel through which information flows between the computer's adap= ter card and the CPU. Ex. 300 to 30F.

Each hardware de= vice 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 addre= ss 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/D= IX connector: Thicknet, for example

Use jumpers on t= he 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 Stand= ard Architecture): original 8-bit and later 16-bit bus of the IBM-PC. =

EISA (Extended Indu= stry 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 Memo= ry:

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 Memor= y:

the network adapter selects a portion of the computer's memory for its us= e.

MOST common

Bus Mastering: =

the adapter card takes temporary control of the computer's bus, freeing t= he CPU for other tasks.

moves data dire= ctly to the computer's system memory

Available on EI= SA and MCA

can improve net= work performance by 20% to 70%

RAM buffering: =

Ram on the adap= ter card acts as a buffer that holds data until the CPU can process it. <= /li>
this keeps the = card from being a bottleneck

On-board microprocessor:

enables the ada= pter 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 t= o 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.

3.

The OSI Model

International Standards Organization (ISO) specifications for network architecture.

Called the Open Systems Interconnect or OSI model.

Seven layered model, hi= gher layers have more complex tasks.

Each layer provides services for the next higher layer.

Each layer communicates logically with its associated layer on the other computer.

Packets are sent from o= ne layer to another in the order of the layers, from top to bottom on the sending computer and then in reverse order on the receiving computer. =

OSI Layers   (Check out the OSI Model Summary Page)

Application

Presentation

Session

Transport

Network

Data Link

Physical

Application Layer

Serves as a window for applications to access network services.

Handles general network access, flow control and error recovery.

Presentation Layer

Determines the format = used to exchange data among the networked computers.

Translates data from a format from the Application layer into an intermediate format.

Responsible for protoc= ol conversion, data translation, data encryption, data compression, chara= cter conversion, and graphics expansion.

Redirector operates at this level.

Session Layer

Allows two applications running on different computers to establish use and end a connection called a Session.

Performs name recognit= ion and security.

Provides synchronizati= on by placing checkpoints in the data stream.

Implements dialog cont= rol between communicating processes.

Transport Layer

Responsible for packet creation.

Provides an additional connection level beneath the Session layer.

Ensures that packets a= re delivered error free, in sequence with no losses or duplications.

Unpacks, reassembles a= nd sends receipt of messages at the receiving end.

Provides flow control, error handling, and solves transmission problems.

Network Layer

Responsible for addres= sing messages and translating logical addresses and names into physical addresses.

Determines the route f= rom the source to the destination computer.

Manages traffic such as packet switching, routing and controlling the congestion of data.

Data Link Layer

Sends data frames from= the Network layer to the Physical layer.

Packages raw bits into frames for the Network layer at the receiving end.

Responsible for provid= ing error free transmission of frames through the Physical layer.

Physical Layer

Transmits the unstruct= ured raw bit stream over a physical medium.

Relates the electrical, optical mechanical and functional interfaces to the cable.

Defines how the cable = is attached to the network adapter card.

Defines data encoding = and bit synchronization.

The 802 Project Model

Defines Standards for t= he Data Link and Physical Layers.

Network Adapter Cards <= /li>
WAN components

Components used to crea= te twisted-pair and coaxial cable networks.

A crazy mnemonic for th= is table, but it works :-)

I Like Chan= ging Boxers Rarely. My Butt Feels Very Sexy= With Denim

802.1

Internet working

802.2

Division of Data Link Layer into sublayers

LLC (Logical Li= nk Control)

Media Access Control (MAC)

802.3

CSMA/CD - Ethernet

802.4

Token Bus LAN (ARCnet)

802.5

Token Ring LAN

802.6

MAN (Metropolitan Area Network)

802.7

Broadband Technical Advisory Group

802.8

Fiber-Optic Technical Advisory Group

802.9

Integrated Voice/Data Networks

802.10

Network Security

802.11

Wireless Networks

802.12

Demand Priority Access L= an, 100 Base VG - AnyLAN

OSI Model Enhancements

The bottom two layers - Data Link and Physical - define how multiple computers can simultaneously use the network without interfering with each other.

Divides the Data-link layer in to the Logical Link Control and Media Access Control sublayers.

Logical Link Contro= l

manages error and flow control and

defines logical interface points called Service Access Points (SAP's). These SAP's= are used to transfer information to upper layers

Media Access Contro= l

communicates directly with the network adapter card and

is responsible for delivering error-free data between two computers.
Categories

802.3

802.4

802.5 and

802.12 define standards for both this sublayer and the= Physical layer

<= /o:p>

Drivers

a device driver is software that tells the computer how to drive or work with the device so that the device performs the job it's supposed to. =

Drivers are called = ;

Network Drivers,

MAC drivers,

NIC drivers.

Provide communication between a network adapter card and the redirector in the computer.
Resides in the Media Ac= cess Control sublayer of the Data Link layer. Therefore, the NIC driver ensures direct communication between the computer and the NIC

the Media Access Control driver is another name for the network card device driver

When installing a drive= r, you need to know these things

IRQ

I/O Port Address

Memory Mapped (B= ase Memory Address)

Transceiver Type=

Packets

Data is broken down into smaller more manageable pieces called packets.

Special control informa= tion is added in order to:

disassemble pack= ets

reassemble packe= ts

check for errors=

Types of data sent includes

Can contain information such as messages or files.

Computer control data a= nd commands and requests.

Session control codes s= uch as error correction and retransmission requests.

Original block of data = is converted to a packet at the Transport layer.

Packet Components

Header

Alert signal to = indicate packet is being transmitted

Source address. =

Destination addr= ess.

Clock synchronization information.

Data

Contains actual = data being sent.

Varies from 512 = to 4096 bytes (4K), depending on the network

Trailer

Content varies by protocol.

Usually contains= a CRC.

Packet Creation

Look at the example on= pp. 201 - 204

Begins at the Applicat= ion layer where data is generated.

Each layer subsequently adds information to the packet; the corresponding layer on the receivi= ng machine reads the information.

Transport layer breaks= the data into packets and adds sequencing information needed to reassemble data at the other end =3D> the structure of the packets is defined = by the common protocol being used between the two computers.

Data is passed through= the Physical layer to the cable.

Packet Addressing

every NIC sees all pac= kets sent on its cable segment but only interrupts the computer if the pack= et address matches the computer's address

a broadcast type addre= ss gets attention of all computers on the network

<= /o:p>

Protocols

Protocols are rules and procedures for communication.

How Protoc= ols Work

The Sending Computer

Breaks data into packe= ts.

Adds addressing information to the packet

Prepares the data for transmission.

The Receiving Computer (same steps in reverse)

Takes the packet off the cable.

Strips the data from the packet.

Copies the data to a bu= ffer for reassembly.

Passes the reassembled = data to the application.

Protocol Stacks (or Suites)

A combination of protoc= ols, each layer performing a function of the communication process.

Ensure that data is prepared, transferred, received and acted upon.

The Binding Process

Allows more than one protocol to function on a single network adapter card. (e.g. both TCP/= IP and IPX/SPX can be bound to the came card

Binding order dictates which protocol the operating systems uses first.

bin= ding also happens with the Operating System architecture: for example, TCP/= IP may be bound to the NetBIOS session layer above and network card driver below it. The NIC device driver is in turn bound to the = NIC.

Standard Stacks

ISO/OSI

IBM SNA (Systems Network Architecture)

Digital DECnet

Novell NetWare

Apple AppleTalk

TCP/IP

Protocol types map roughly to the OSI Model into three layers:

Application Level Service Users

Application Layer
Presentation Layer
Session Layer

Transport Services

Transport Layer

Network Services

Network Layer
Data Link Layer
Physical Layer

Application Protocols

Work at the upper layer of the OSI model and provide application to application interaction and data exchange.

Examples:

APPC-IBM's peer to peer SNA protocol used on AS400's

FTAM: an OSI file acce= ss protocol.

X.400: international e-mail transmissions.

X.500: file and direct= ory services across systems.

SMTP: Internet e-mail.=

FTP: Internet file transfer

SNMP: Internet network management protocol.

Telnet: Internet proto= col for logging on to remote hosts.

Microsoft SMB: client shells and redirectors.

NCP: Novell client she= lls or redirectors.

AppleTalk and AppleSha= re: Apple's protocol suite.

AFP: Apple's protocol = for remote file access.

DAP (data access protocol): DECnet file access protocol.

Transport Protocols

These protocols provide communication sessions between computers and ens= ure data is moved reliably between computers.

Examples:

TCP (transmission cont= rol protocol): internet protocol for guaranteed delivery of sequenced data= .

SPX (sequenced packet exchange): Novell protocol suite.

N= WLink: Microsoft implementation of IPX/SPX.

NetBEUI: establishes communications sessions between computers and provides the underlying = data transport services.

ATP, NBP: Apple's communication session and transport protocols.

Network Protocols

These provide link services

They also

handle

addressing and routing,

error checking = and

retransmission requests.

Define rules for Ether= net or Token Ring.

Examples:

IP (Internet Protocol): packet forwarding and routing.

IPX: (Internetwork Pac= ket Exchange): Novell's protocol for packet forwarding and routing.

N= WLink: Microsoft implementation of IPX/SPX.

NetBEUI: Transport for NetBIOS sessions and applications.

DDP (datagram delivery protocol): An AppleTalk data transport protocol.

The IEEE protocols at the Physical Layer

802.3 (CSMA /CD - Ethernet)

logical bus network
can transmit at 10 Mbp= s

data is transmitted on= the wire to every computer but only those meant to receive respond

CSMA /CD protocol list= ens and allows transmission when the wire is clear

802.4 (Token Passing)

bus layout that used t= oken passing

every computer receives all of the data but only the addressed computers respond

token determines which computer can send

802.5 (Token Ring)

logical ring network; physical set up as star network

transmits at 4 Mbps or = 16 Mbps

token determines which computer can send

Important Protocols

TCP/IP

Provides communicatio= ns in a heterogeneous environment.

Routable, defacto standard for internetworking.

SMTP, FTP, SNMP are protocols written for TCP/IP

Disadvantages are size and speed.

NetBEUI

NetBIOS extended user interface.

Originally, NetBIOS and NetBEUI were tightly tied together but, NetBIOS has been separated out= to be used with other routable protocols. NetBIOS acts as a tool to allow applications to interface with the network; by establishing a session = with another program over the network

NetBIOS operates at th= e Session layer.

Small, fast and effici= ent.

Compatible with most M= icrosoft networks.

Not routable and compatible only with Microsoft networks.

X.25

Protocols incorporate= d in a packet switching network of switching services.

Originally establishe= d to connect remote terminals to mainframe hosts.

XNS

Xerox Network System. =

Developed for Ethernet LANs but has been replaced by TCP/IP.

Large, slow and produc= es a lot of broadcasts.

IPX/SPX and NWLink

Used for Novell networ= ks.

Small and fast.

Routable.

APPC

Advanced Program to Program Communication

Developed by IBM to su= pport SNA.

de= signed to enable application programs running on different computers to communicate and exchange data directly.

AppleTalk

Apple's proprietary protocol stack for Macintosh networks.

OSI Protocol Suite

each protocol maps directly to a single layer of the OSI model

DECnet

Digital Equipment's proprietary protocol stack

Defines communications over Ethernet, FDDI MAN's and WAN's.

D= ECnet can also use TCP/IP and OSI protocols as well as its own protocols
Routable.

<= /o:p>

Putting data on the Cable

Access Methods

The 4 major methods

Carrier Sense Multi= ple Access Methods

with collisi= on detection (CSMA/CD)

with collisi= on avoidance (CSMA/CA)

Token passing that allows only a singe opportunity to send data

A Demand Priority method

Carrier Sense Multi= ple Access with Collision Detection. (CSMA/CD)

Computer senses that the cable is free.

Data is sent. <= /li>
If data is on t= he cable, no other computer can transmit until the cable is free again. =

If a collision occurs, the computers wait a random period of time and retransmit.

Known as a contention method because computers compete for the opportunity to se= nd data. (Database apps cause more traffic than other apps)

This can be a s= low method

More computers cause the network traffic to increase and performance to degrade.
The ability to "listen" extends to a 2,500 meter cable length =3D> segm= ents can't sense signals beyond that distance.

Carrier Sense Multi= ple Access with Collision Avoidance (CSMA/CA)

in CSMA/CA, the computer actually broadcasts a warning packet before it begins transmitting on the wire. This packet eliminates almost all collisions on the network because each computer on the network does n= ot attempt to broadcast when another computer sends the warning packet. =

All other compu= ters wait until the data is sent.

The major drawb= ack of trying to avoid network collisions is that the network traffic is = high due to the broadcasting of the intent to send a message.

Token Passing <= /li>

Special packet = is passed from computer to computer.

A computer that wants to transmit must wait for a free token.

Computer takes control of the token and transmits data. Only this computer is allowe= d to transmit; others must wait for control of the token.

Receiving compu= ter strips the data from the token and sends an acknowledgment.

Original sending computer receives the acknowledgment and sends the token on.

the token comes from the Nearest Active Upstream Neighbor and when the computer= is finished, it goes to the Nearest Active Downstream Neighbor

uses "beaconing" to detect faults =3D> this method is fault tolerant

NO contention =3D> equal access to all computers on the network

NO collisions <= /li>

Demand Priority=

100 Mbps standa= rd called 100VG-AnyLAN. "Hub- based".

Repeaters manage network access by performing cyclical searches for requests to send f= rom all nodes on the network. The repeater or HUB is responsible for noti= ng all addresses, links and end nodes and verifying if they are all functioning. An "end node" can be a computer, bridge, route= r or switch.

Certain types of data are given priority if data reaches the repeater simultaneously. = If two have the same priority, BOTH are serviced by alternating between = the two.

Advantages over CSMA/CD

Computers Uses four pairs of wires which can send and receive simultaneously.

Transmissions = are through the HUB and are not broadcast to all other computers on the network.

There is only communication between the sending computer, the hub and the destinat= ion computer.

Other methods

Appletalk

The cabling system fo= r an AppleTalk network is called LocalTalk.

= LocalTalk uses CSMA/CA

AppleTalk has a dynam= ic network addressing scheme.

During bootup, the AppleTalk card broadcasts a random = number on the network as its card address. If no other computer has claimed = that address, the broadcasting computer configures the address as its own.= If there is a conflict with another computer, the computer will try to u= se different IP combinations until it finds a working configuration.

ARCNet

= ARCNet uses a token passing method in a logical ring similar to Token Ring networks.

However, the computer= s in an ARCNet network do not have to be connec= ted in any particular fashion.

ARCNet can utilize a star, bus, or star bus top= ology.

Data transmissions are broadcast throughout the entire network, which is similar to Ethernet.=

However, a token is u= sed to allow computers to speak in turn.

The token is n= ot passed in a logical ring order because ARCNet does not use the ring topology; instead the token is passed to the ne= xt highest numerical station

Use DIP switch= es to set the number (the Station Identifier) of the workstations, which= you want to be beside each other so the token is passed to the next compu= ter efficiently.

= ARCNet isn't popular anymore =3D> ARCNet speed= s are a mere 2.5 Mbps.

Most important ARCNet facts for you to know:=

= ARCNet uses RG-62 (93 ohms) cabling;

it can be wired as a star, bus, or star bus; and

i= t uses a logical-ring media access method.

Summary Chart

Feature or Function

CSMA/CD

CSMA/CA

Token Passing

Demand Priority

Type of Communication

Broadcast-based

Broadcast-based

Token-based

Hub-based

Type of Access Method

Contention

Contention

Non-contention

Contention

Type of Network

Ethernet

LocalTalk

Token Ring
ARCnet

100VG-AnyLAN

4.

Network Architectures

Ethernet

Baseband signaling. <= /li>
Linear or star-bus topology.

Usually transmits at = 10 Mbps with 100 Mbps possible.

Uses CSMA/CD for traf= fic regulation.

IEEE specification 80= 2.3.

Uses thicknet, thinnet or UTP cabling

Media is passive =3D&= gt; it draws power from the computer

Ethernet Frames

Ethernet breaks data into frames. A frame can be from 64 to 1,518 bytes = long in total. The ethernet frame itself takes up 18 bytes, so the actual data can be from 46 to 1,500 bytes.

Preamble: marks= the start of a frame.

Destination and Sou= rce: addressing information.

Type: Identifies network layer protocol.

CRC: error chec= king data.

Ethernet Topologies

10 Mbps Topologies

10Base-T

(10 =3D 10 M= bps; Base=3D Baseband; T =3D Twisted Pair)

10 Mbps, baseba= nd over UTP.

Usually wired i= n a physical star with a hub or multiport repeater. Internally it uses a bus s= ignaling system like other Ethernet configurations

Maximum segment length 100 meters (328 feet).

Minimum between computers 2.5 meters (8 feet).

1024 nodes maxi= mum on the LAN

Category 3, 4 o= r 5 UTP.

RJ-45 connector= s, 4 twisted pair.

Coaxial or Fiber backbone for larger LAN's

10BaseT UTP NETWORK LAYOUT
Limitations

maximum segment lengt= h of 100 Meters

Hub to Hub or repeate= r to repeater links limited to 100 Meters

Rules

star topology

4 repeater/5 segment r= ule of 10Base5 is retained

only two nodes per seg= ment are allowed

Cabling

RJ-45 Connectors

Category 3 UTP minimum, preferably Category 5

10Base-2

(10 =3D 10 = Mbps; Base=3D Baseband; 2 =3D 2x 100 meters)

10 Mbps, baseb= and over thinnet.

Uses bus topology.

Maximum segment length 185 meters (607 feet).

Minimum between computers 0.5 meters (20 inches).

Maximum of 30 computers per segment.

Obeys 5-4-3 ru= le: Five segments, joined by four repeaters, 3 populated giving a total length of 925 meters (3035 feet).

Physical Bus Cable Limits

10Base2 THIN ETHERNET NETWORK LAYOUT
Limitations

maximum number of trunk segments =3D 5

maximum trunk segment length =3D 607 feet (185 meters)

maximum network trunk cable =3D 3035 feet (925 meters)

maximum number of stat= ions on a trunk segment =3D 30

minimum distance betwe= en T connectors =3D 1.5 feet (0.5 meters)

Rules

each end of the trunk segment is terminated in 50-ohms

one of the terminators = is grounded

connector splices are k= ept to a minimum

Cabling

BNC-T type connectors=

RG58-AU 50-ohm cable, 0.2"

Note that you can't mix RG58 /AU and RG58 /U cable on the same network.

10Base-5

(10 =3D 10 M= bps; Base=3D Baseband; 5 =3D 5 x 100 meters)

10 Mbps, baseba= nd over thicknet.

Also called Standard Ethernet

Designed to sup= port a backbone for a large department or building. Transceivers attach to= the thicknet cable and the cable AUI connector plugs into a repeater . The branching segm= ents of thinnet plug into the repeater and con= nect to the computers on the network.

Uses bus topology.

Maximum segment length 500 meters.

Minimum between transceivers 2.5 meters (8 feet)

100 computers p= er segment, 300 per network.

Obeys 5-4-3 = rule: maximum distance can be extended to 2500 meters (8200 ft) using 4 repeaters and 3 populated segments.

Transceiver is attached to main segment with a vampire tap.

DIX or AUI conn= ector is used to attach the transceiver to the network card. Maximum comput= er to transceiver distance is 50 meters. This distance is not included in the 5-4-3 calculation.

10Base-5 Summary

Maximum segment length

500m (1640 ft)

Typically used = as backbone to connect Thinnet-based networ= k.

Speed

10 Mbps

Maximum taps

100

Maximum segments

5

Maximum repeaters

4

Maximum segment with nodes

3

Due to attenuati= on, only 3 of 5 segments can actually contain network connection. Other 2 segments can be used to connect the network over long distance.

Maximum nodes per segment

100

Maximum nodes for network

300

Minimum distance between nodes

2.5m (8 ft)

Maximum overall length with repeaters

2.5 km

Maximum AUI drop cable length

50m

10Base-F?

(10 =3D 10 Mb= ps; Base=3D Baseband; FL =3Dfibre optic) =

Allows long cable runs between repeaters, like between buildings

Maximum segment length 2000 meters.

10BaseF= L - Used for linking computers in a LAN environment.

10BaseF= P - Used for linking computers with passive hubs from maximum cable dista= nce up to 500m

10BaseF= B - Used as a backbone between hubs.

Baseband signal over a fiber-optic cable.

Need concentrator (fiber-optic hub) ® Star wired (star topology) . Either active or passive

Long dista= nce.

Very expensive. Difficult to install.

Maximum segment length - 2000m
Maximum segments- 1024
Maximum segment with nodes- 1024
Maximum nodes per segment- 1
Maximum nodes per network- 1024
Maximum hubs in a chain- 4

<= /o:p>

100 Mbps Topologies

100VG-AnyLAN (IEEE 802.12)

100 Mbps data rate.

Star topology = over Category 3, 4 and 5 UTP.

Uses demand priority access.

Combines eleme= nt of traditional Ethernet and Token Ring and supports Ethernet and token ring packets.

Faster than Ethernet

Demand priority access method =3D> two priority levels, low and high

Intellig= ent hubs can filter individually addressed frames for enhanced privacy. <= /li>
Expensiv= e

Uses RJ-= 45.

Cable - require 4 pairs wire

Categor= ies 3, 4 UTP- 100m

Categor= y 5 UTP   - 150m

Fiber-o= ptic- 2000m

Uses star topology and defines how child hub can be connected to a parent hub to extend the network.

Minimum length between nodes - 2.5m
Maximum segments- 1024
Maximum nodes per segment- 1
Maximum nodes for network- 1024

100BaseT? (Fast Ethernet)

Uses CSMA/CD o= n a star-wired bus.

There are 3 specifications:

100BaseT4: Us= es pair category 3, 4 or 5 UTP.

100BaseTX: Us= es 2-pair category 5 UTP or STP.

100BaseFX: Us= es 2-strand fiber-optic.

Ethernet Frame t= ypes

Ethernet 802.2 - NetWare 3.12 and 4.x -= IEEE 802.3 standard compliance.

Includes field in Ethernet 802.3 and LLC (Logical Link Control)

Ethernet 802.3 - NetWare 3.11 and before

Includes CRC

Ethernet SNAP (SubNetwork Address Pro= tocol) - AppleTalk

Ethernet II - TCP/IP

Segmentation

Can be performed with bridges or routers.

Reduces traffic on net= work segments to increase performance.

Token Ring

IEEE 802.5 specificat= ion.

Star wired ring topol= ogy (logical ring)

Uses token passing ac= cess method.

Can have higher transmission speeds than Ethernet

It has larger frames = than Ethernet =3D> more can get transferred over the wire in any given t= ime.

Uses IBM STP Types 1,= 2 and 3 cabling. (Can be UTP)

Transmits at 4 and 16 Mbps. (16 Mbps cards will slow down to 4 Mbps if put on that kind of network, but the 4 Mbps cards can't speed up.

Baseband transmission=

Data travels in one direction only

Each computer acts as= a unidirectional repeater

Deterministic method = of cable access. Computers cannot use the cable unless they have the toke= n. Therefore, computers can't force their way onto the network like CSMA/= CD (Ethernet)

First computer online= is assigned to monitor network activity.

Token Ring Components

M= ultistation Access Units (MAU's)

M= ultistation Access Units (MSAU's)

Smart Multistation Access Units (SMAU's)

Computers attach direc= tly to the MSAU in a physical star to form a logical ring.

Each MSAU has 10 connection ports =3D=3D> can suppo= rt 8 clients with 2 ports for ring in and ring out.

Each ring can have as = many as 33 MSAU's

70 computers wi= th UTP

260 computers w= ith STP.

Up to 12 MSAU's can connect to each other

The MSAU can sense if a computer is down and then disconnect it from the ring =3D> built-in= fault tolerance

Cabling

Most token ring systems use IBM type 3 cabling.

STP or UTP to a hub, IBM type 1,2,3 cable

Type 1: 101m f= rom MSAU to PC

STP: 100m from MSAU to PC

UTP: 45m from = MSAU to PC

Type 3: 150 fe= et from MSAU to PC

Token ring netw= orks are well suited to fiber optic cable: data travels in only one direct= ion in it.

Here are some limitations of Token Ring:

The maximum number of workstations is 260 on Type 1 or fiber optic cable at 16 Mbps.

The maximum number of workstations is 72 on Type 3 cable at 4 Mbps.

The distance between = MSAUs (Multistation = Access Units) is 100 meters (Type 1 cabling) to 45 meters (Type 2 cabling). <= /li>
Each ring can have up= to 33 MSAUs.

Maximum distance of t= he ring is 4 kilometers with fiber optic cable.

Token Ring and Ethernet Comparison
Token Ring

can have higher transmission speeds than Ethernet

supports more computer= s on a single segment (up to 260)

more expensive than Ethernet

harder to install than Ethernet

is more fault tolerant because of the beaconing process

AppleTalk

local talk

CSMA/CA access method

3 things happen when devices attached

device assigns itself an address randomly

device broadca= sts the address to see if it's used

if not, the de= vice will use it the next time it's online again

bus or tree
STP

max. 32 devices

Apple share

file server on = an AppleTalk network

divided into zo= nes

E= therTalk

802.3

allows protocol= s to run on ethernet coaxial cable

T= okenTalk

802.5

allows Macintos= h to connect to token ring network

ARCnet

IEEE 802.4 specificati= on - almost

Cable

Uses RG-62 (93 = ohm) (most common)or

RG-59 (75ohm) coaxial cable.

Can also use UT= P.

Uses token passing on a star-bus topology.

Token moves from compu= ter to computer in numerical order.

Transmits at 2.5 Mbps.=

A= rcNet plus - 20 Mbps

connected by cable to = hub

93 ohm RG-62 A/= U - 610m max., star

93 ohm RG-62 A/= U - 305m max., bus <=3D notice less distance on hub

RJ-11, RJ-45 UT= P - max. 244m on star or bus

Hubs can be

Passive =3D> merely relay signal

Active =3D> regenerate and relay signal

Smart =3D> a= dd diagnostic features, such as reconfiguration detection

Here are some limitations of ARCNet: =

Bus segment length for coaxial cable is a maximum of 1000 feet, with a limit of 8 workstations per coaxial segment.

Bus segment length for twisted pair is a maximum of 400 feet, with a limit of 10 workstations= per twisted-pair segment.

There is a maximum of= 255 workstations per network.

Workstations can be located up to 600 feet from the active hub.

The maximum distance = from passive hubs to active hubs is 100 feet; the maximum distance between = two active hubs is 2000 feet.

The maximum distance allowed between workstations is 20,000 feet.

There can be no more = than four workstations on a passive hub, no more than 100 feet from a hub. =

Passive hubs cannot be connected to other passive hubs.

5.
Fault Tolerant Systems - Windows NT supports Raid 0,1 and 5. For the exam, worry only about them.

RAID 0 - di= sk striping

disk striping divides data into 64k block and spreads it equally in a fixed rate = and order among all disks in an array

NOT FAULT&nbs= p; TOLERANT

RAID 1 -

disk mirro= ring - actually duplicates a partition and moves the duplication onto another physical disk

disk duplexing - is a mirrored pair of disks w= ith an addition disk controller on the second drive

The only RAID solution that can house the system files in the Boot partition

RAID 4 - di= sk guarding

one drive is a dedicated parity drive, data is striped to multiple drives and then= its parity sum is calculated, which is written to the dedicated parity drive

works best for large block operations

RAID 5 - st= riping with parity

data is strip= ed across multiple drives and then its parity sum is calculated, which= is also striped across multiple drives (not a dedicated parity drive) =

sector spar= ing - hot fixing

automatically adds sector - recovery capabilities to the file system while the computer is running

if bad sectors are found during disk I/O, the fault tolerance driver will attempt to move the data to good sector and map out the bad se= ctor - only for SCSI, not ESDI or IDE

6.

Larger Networks<= /span>

Some components can be installed which will increase the size of the net= work within the confines of the limitations set by the topology. These components can:

Segment existing LANs = so that each segment becomes its own LAN.

Join two separate LANs= .

Connect to other LANs = and computing environments to join them into a larger comprehensive networ= k.

Modems

Modems share these characteristics

a serial (RS-232) interface

an RJ-11C teleph= one line connector

tel= ephones use analog signal; computers use digital signal. A modem translates between the two

BAUD refers to t= he speed of the oscillation of the sound wave on which a bit of data is carried over the telephone wire

the= BPS can be greater than the baud rate due to compression and encode da= ta so that each modulation of sound can carry more than one bit of data is carried over the telephone line. For example, a modem that modulates at 28,000 baud can actually send at 115,200 bps =3D> bps is the most important parameter when looking at throughput.

There are 2 types of mo= dems

Asynchronous Communications (Async) <= /p>

use common phone line= s

data is transmitted i= n a serial stream

not synchronized, no clocking device =3D> no timing

both sending and receiving devices must agree on a start and stop bit sequence

error control =

a parity bit is used in an error checking and correction scheme called parity checkin= g

It checks to s= ee if the # of bits sent =3D # of bits received

the receiving computer checks to make sure that the received data matches what was sent.

25 % of the da= ta traffic in async communications consists = of data control and coordination

MNP (Microcom Network Protocol) has become the stand= ard for error control

Later LAPM (Li= nk Access Procedure for Modems) is used in V.42 modems (57,600 baud).

It uses MNP Class 4.

LAPM is used between two modems that are V.42 compliant

If one or the other modems is MNP 4 - compliant, the correct protocol would be MNP Class 4

Communication perform= ance depends on

1.&n= bsp;     signaling or channel speed - how fast the bi= ts are encoded onto the communications channel

2.&n= bsp;     throughput - amount of useful information go= ing across the channel

you can double the throughput by using compress= ion. One current data compression standard is the MNP Class 5 compression protocol

V.42 bis is even faster because of compression.

bis =3D> second modification

terbo =3D> third, the bis standard was modified

This is a good combination:

0.&n= bsp;     V.32 signaling

1.&n= bsp;     V.42 error control

2.&n= bsp;     V.42bis compression

Standard

BPS

V.22 bis

2400

V.32

9600

V.32bis

14,400

V.32terbo

19,200

V.FastClass (V.FC)

28,800

V.34

28,800

V.42

57,600

Synchronous Communication

relies on a timing sch= eme coordinated between two devices to separate groups of bits and transmit them in blocks known as frames

NO start and stop bits= =3D. a continuous stream of data because both know whe= n the data starts and stops.

if there's error, the = data is retransmitted

some synchronous proto= col perform the following that asynchronous protocols don't:

format data into blocks

add control inf= o

check the info = to provide error control

the primary protocols = in synchronous communication are:

Synchronous data link control (SDLC)

High-level data link control (HDLC)

binary synchron= ous communication protocol (bisync)

Synchronous communicat= ions are used in almost all digital and network communications

2 types of telephone lines:

public dial network lines (dial-up lines) - manually dial up to make a connec= tion

leased (dedicated) lines - full time connection that do not go through a series of switches, 56 Kbps to 45 Mbps

Repeaters

Repeaters

EXTEND the netw= ork segment by REGENERATING the signal from one segment to the next

Repeaters regenerate BASEBAND, digital signals

don't translate= or filter anything

is the least expensive alternative

work at the Physical layer of OSI

Both segments being connected must use the same access method e.g. an 802.3 CSMA/CD= (Ethernet) LAN segment can't be joined to a 802.5 (Token Ring) LAN segment. Another way of saying this is the Logi= cal Link Protocols must be the same in order to send a signal.

BUT repeaters CAN m= ove packets from one physical medium to another: for example can take = an Ethernet packet from a thinnet coax and pa= ss it on to a fiber-optic segment. Same access method is being used on both segments, just a different medium to deliver the signal

They send every bit of data on =3D> NO FILTERING, so they <= b>can pass a broadcast storm along from on segment to the next and back.= So you want to use a repeater when there isn't much traffic on either seg= ment you are connecting.

There are limits on the number of repeaters which can be used. The repeater counts as a single node in the maximum node count associated with the Ethernet standard [= 30 for thin coax].

Repeaters also allow isolation of segments in the event of failures or fault conditions. Disconnecting one side of a repeater effectively isolates the associat= ed segments from the network.

Using repeaters simply allows you to extend your network distance limitations. It does not gi= ve you any more bandwidth or allow you to transmit data faster.

Why only so many repea= ters are allowed on a single network: "propagation delay". In cas= es where there are multiple repeaters on the same network, the brief time each repeater takes to clean up and a= mplify the signal, multiplied by the number of repeaters can cause a noticeab= le delay in network transmissions.

It should be noted tha= t in the above diagram, the network number assigned to the main network segment and the network number assigned to the other side of the repea= ter are the same.

In addition, the traff= ic generated on one segment is propagated onto the other segment. This ca= uses a rise in the total amount of traffic, so if the network segments are already heavily loaded, it's not a good idea to use a repeater.

A repeater works at the Physical Layer by simply repeating all data from one segment to anothe= r.

Summary of Repeater features

increase traffi= c on segments

limitations on = the number that can be used

propagate error= s in the network

cannot be administered or controlled via remote access

no traffic isolation or filtering

Summary:

A repeater

Connects two segments of similar or dissimilar media

Regenerates the signal to increase the distance transmitted

Functions in the Physical Layer of the OSI model

Passes ALL TRAF= FIC in both directions

Use a repeater to impr= ove performance by dividing the network segments, thus reducing the number= of computers per segment (This is what i= t says in the book, but it doesn't make sense to me)

Do NOT use a repeater when:

There is heavy network traffic

Segments are us= ing different access methods

You need any ki= nd of data filtering.

Amplifiers are just like repeaters, but gener= ate a BROADBAND, analog signal. That analog signal can have different frequenci= es and carry both voice and data.

<= /o:p>

Bridges

have all the abilitie= s of a repeater

Bridges can

take an overlo= aded network and split it into two networks, therefore they can divide the network to isolate traffic or problems and reduce the traffic on both segments

expand the distance of a segment

link UNLIKE PHYSICAL MEDIA such as twisted-pair (10Base T) and coaxial Ethernet (10Base2)

VERY IMPORT= ANT: they can link UNLIKE ACCESS CONTROL METHODS, on different segments su= ch as Ethernet and Token Ring and forward packets between them. Exam Cram says this is a Tran= slation Bridge that c= an do this - not all bridges - but my observation is questions don't necessarily mention the distinction.

Bridges work at the Da= ta Link Layer of the OSI model =3D> they do= n't distinguish one protocol from the next and simply pass protocols along= the network. (use a bridge to pass NetBEUI, a non-routable protocol, along= the network)

Bridges actually work = at the MEDIA ACCESS CONTROL (MAC) sublayer. I= n fact they are sometimes called Media Access Control layer bridges. Here's h= ow they deal with traffic:

They listen to = all traffic. Each time the bridge is presented with a frame, the source address is stored. The bridge builds up a table which identifies the segment to which the device is located on. This internal table is then used to determine which segment incoming frames should be forwarded t= o. The size of this table is important, especially if the network has a large number of workstations/servers.

they check the source and destination address of each PACKET

They build a routing table based on the SOURCE ADDRESSES. Soon they know which computers are on which segment

Bridges are intelligent enough to do some routing:

if the destination address is on the routing table and is on the SAME SEGMENT, the packet isn't forwarded. Therefore, the bridge can SEGME= NT network traffic

If the destina= tion address is the routing table, and on a remote segment, the bridge forwards the packet to the correct segment

if the destination address ISN'T on the routing table, the bridge forwa= rds the packet to ALL segments.

BRIDGES SIM= PLY PASS ON BROADCAST MESSAGES, SO they too contribute to broadcast stor= ms and don't help to reduce broadcast traffic

Remote Bridges =

two segments are joined by a bridge on each side, each connected to a synchronous modem and a telephone line

there is a possibility that data might get into a continuous loop between LANs <= /li>
The SPANNING TR= EE ALGORITHM (STA)

senses the existence of more than one route

determines whi= ch is the most efficient and

configures the bridge to use that route

this route can be altered if it becomes unusable.

Transparent bridges (also known as spanning tree, IEEE 802.1 D) make all rou= ting decisions. The bridge is said to be transparent (invisible) to the workstations. The bridge will automatically initialize itself and configure its own routing information after it has been enabled.

Comparison of Bridg= es and Repeaters

Bridges =

regenerate dat= a at the packet level

accommodate mo= re nodes than repeaters

provide better network performance than repeaters because they segment the network =

Implementing a Brid= ge

it can be an external, stand-alone piece of equipment

or be installed= on a server

Summary from MOC:

Bridges have all the features of a repeater

They connect two segments and regenerate the signal at the packet level

They function at the Data Link layer of the OSI model

Bridges are not suited to WANs slower than 56k

They cannot take advantage of multiple paths simultaneously

They pass all broadcasts, possibly creating broadcast storms

Bridges read the source and destination of each packet

they PASS packe= ts with unknown destinations

Use Bridges to:=

Connect two segments to expand the length or number of nodes on the network

reduce traffic= by segmenting the network

Connect

unlike MEDIA ( e.g. 10BaseT and 10Base2)

unlike ACCESS CONTROL METHODS (Ethernet and Token Ring)

The advantages of bridges are

increase the number of attached workstations and network segments

since bridges buffer frames, it is possible to interconnect different segments which use different MAC protocols

since bridges = work at the MAC layer, they are transparent to higher level protocols

by subdividing= the LAN into smaller segments, overall reliability is increased and the network becomes easier to maintain

used for non routable protocols like NetBEUI which must be bridged

help localize network traffic by only forwarding data onto other segments as requir= ed (unlike repeaters)

The disadvantages of bridges are

the bufferi= ng of frames introduces network delays

bridges may overload during periods of high traffic

bridges which combine different MAC protocols require the frames to be modifi= ed before transmission onto the new segment. This causes delays

in complex networks, data is not sent over redundant paths, and the shortest pat= h is not always taken

bridges pass on broadcasts, giving rise to broadcast storms on the network

Sample Question:
You want to connect an Ethernet network in one part of an office building= to a Token-ring network down the hall. Both networks use NWLink IPX but must eliminate the IPX addressing and use only NetBEUI on both segments when they are joined. Which connectivity device do you choose wh= ich will allow the two networks to communicate, but at the same time reduce network levels.

device should you use?

repeater

bridge

router

gateway

B - they are testing here to see if you kno= w what a translation bridge can do.
Some bridges can't connect different segments that use different media schemes, but a translation bridge can. A translation bridge will also reduce network traffic because it can analyze packets based on MAC address and if it finds them to be from the same segment as the originating they = are simply discarded instead of being passed on to a non-local segment. The bridge can do this using address information stored in its bridging table= .

<= /o:p>

Routers

Determine the best path for sending data and filtering broadcast traffic to the local= segment. They DON'T pass on broadcast traffic

work at the Network layer of OSI =3D> they can switch and route packets across netw= ork segments

They provide these functions of a bridge

filtering and isolating traffic

connecting net= work segments

routing table contain= s

1.&n= bsp;     all known network addresses

2.&n= bsp;     how to connect to other networks

3.&n= bsp;     possible paths between those routers

4.&n= bsp;     costs of sending data over those paths

5.&n= bsp;     not only network addresses but also media access control sublayer addresses for each node

Routers

REQUIRE specif= ic addresses: they only understand network numbers which allow them to t= alk to other routers and local adapter card addresses

only pass Packets to the network segment they are destined for.

routers don't = talk to remote computers, only to other routers

they can segme= nt large networks into smaller ones

they act as a safety barrier (firewall) between segments

they prohibit broadcast storms, because broadcasts and bad data aren't forwarded
are slower than most bridges

can join dissimilar access methods: a router can route a packet from a TCP/IP Ethernet network to a TCP/IP Token Ring network

Routers don't look at= the destination computer address. They only look at the NETWORK address an= d they only pass on the data if the network address is known =3D> less traffic

Routable protocols: <= /li>

DECnet, IP, IPX, OSI, XNS, DDP (Apple)

Routable proto= cols have Network layer addressing embedded

Non-routable protocol= s:

LAT, NetBEUI, = DLC

Non-routable protocols don't have network layer addressing

Choosing Paths

routers can choose the best path for the data to follow

r= outers can accommodate multiple active paths between LAN segments. To determi= ne the best path, it takes these things into account:

If one path is down, the data can be forwarded over on alternative route

routers can listen and determine which parts of the network are busiest.

it decides the path the data packet will follow by determining the number of hops between internetwork segments

OSPF (Open Shortest Path First)

is a link-state routing algorithm

routes are calculated based on

# of hops
line speed
traffic

cost

TCP/IP supports OSPF

RIP (Routing Information Protocol)

RIP is the protocol used to determine the # of hops to a distant segment.

uses distance-vector algorithm to determine routes

TCP/IP & I= PX support RIP

NLSP (NetWare Link Services Protocol)

is a link-state algorithm for use with IPX

There are 2 types of routers

Static - manually setup and config the routing tab= le and to specify each route

Dynamic=

automatic dis= covery of routers

use informati= on from other routers

Distinguishing between Bridges and R= outers

Both bridges and routers

forward packets between networks

send data across WAN links

A Bridge

recognizes t= he address of EACH computer on it's segment and forwards packets on the basis of the destination address

either recogniz= es the address or it doesn't, and forwards the packet accordingly

forwards all broadcast messages to all ports, except to the port from which the broadcast message came. Every computer on every segment receives this broadcast

A Router

works at the NETWORK layer and thus takes more information into account when determining what to forward and where to forward it to.

Routers recogni= ze the addresses of other routers and determine which packets to forward= to which routers

Multiple Paths-- important

Bridges recognize O= NE PATH between networks

Routers can search between multiple paths and determine the best path at the moment <= /li>

The 4 KEY pieces of information that distinguish bridges and routers:

Bridges

Routers

recognize the = MAC sublayer addresses (i.e. the addresses of the network cards on its own segment)

Routers recogn= ize network addresses not individual computer addresses

forwards everything it doesn't recognize and

forwards all addresses it knows, but only out the appropriate port

routers filter addresses.

It forwards particular protocols to particular addresses (other routers)

if the router doesn't recognize a destination address, the packet is usually disca= rded

works with all protocols

only works with routable protocols

Non-Routable =3D NetBEUI, DLC, LAT

Because they make path choices and filter out packets the segment doe= sn't need to receive they

help lessen network congestion

conserve resources
boost data throughput=

make data delivery mo= re reliable

Because is works at the network layer, a router can connect networks = that use

Different architecture= s

Different media access control methods -- for example, they can connect an Ethernet segment t= o a Token-Ring segment

Summary of Router features

use dynamic routing
operate at the protocol level

remote administration = and configuration via SNMP

support complex networ= ks

the more filtering don= e, the lower the performance

provides security

segment networks logic= ally

broadcast storms can be isolated

often provide bridge functions also

more complex routing protocols used [such as RIP, IGRP, OSPF]

Brouters

Combine the best qualities of both bridges and routers

First, a brouter checks to see if the protocol is routabl= e or non-routable

Route selected routab= le protocols.

They can bridge non-routable protocols. Like a Bridge, they use the MAC address to for= ward to destination. They act like a router for one protocol and a bridge f= or all the others

More cost effective t= han individual bridges and routers.

SO, use a brouter when you have routable and non-routable protocols.

Hubs

There are many types of hubs:

Passive hubs are don't require power and are simple splitters or combiners that group workstations into a single segment

Active hubs req= uire power and include a repeater function and are thus capable of supporti= ng many more connections.

Intelligent hubs provi= de

packet switchin= g

traffic routing=

Gateways

The TRANSLATOR -- allo= ws communications between dissimilar systems or environments

A gateway is usually a computer running gateway software connecting two different segments. F= or example an Intel-based PC on one segment can both communicate and share resources with a Macintosh computer or an SNA mainframe. Use gateways = when different environments need to communicate. One common use for gateway= s is to translate between personal computers and mainframes

GSNW is a gateway to a= llow Microsoft clients using SMB to connect to a NetWare server using NCP. =

Gateways work at the Application --> Transport layer

They make communication possible between different architectures and environments

They perform protocol = AND data conversion / translation.

they takes the data fr= om one environment, strip it, and re-package it in the protocol stack from the destination system

they repackage and con= vert data going from one environment to another so that each environment can understand the other environment's data

gateway links two syst= ems don't use the same

protocols

data formatting structure

languages

architecture

they are task speci= fic in that they are dedicated to a specific type of conversion: e.g. "Windows NT Server -> SNA Server Gateway"

us= ually one computer is designated as the gateway computer. This adds a lot of traffic to that segment

Disadvantages <= /li>

They slow things down because of the work they do

they are expens= ive

difficult to configure

Remember, gateways can translate

protocols e.g. IPX/SPX --> TCP/IP

and data (PC --= > Mac)

e-mail standards --> an e-mail gateway that translates on e-mail format i= nto another (such as SMTP) to route across the Internet.

IRQ #	Common Use	I/O Address
IRQ 1	Keyboard
IRQ 2(9)	Video Card
IRQ 3	Com2, Com4	2F0 to 2FF
IRQ 4	Com1, Com3	3F0 to 3FF
IRQ 5	Available (Normally LPT2 or sound card )
IRQ 6	Floppy Disk Controller
IRQ 7	Pa= rallel Port (LPT1)
IRQ 8	Real-time clock
IRQ 9	Redirected IRQ2	370 - 37F
IRQ 10	Available (maybe primary SCSI controller)
IRQ 11	Available (maybe secondary SCSI controller)
IRQ 12	PS/2 Mouse
IRQ 13	Math Coprocessor
IRQ 14	Primary Hard Disk Controller
IRQ 15	Available (maybe secondary hard disk controll= er)

802.1	Internet working
802.2	Division of Data Link Layer into sublayers LLC (Logical Li= nk Control) Media Access Control (MAC)
802.3	CSMA/CD - Ethernet
802.4	Token Bus LAN (ARCnet)
802.5	Token Ring LAN
802.6	MAN (Metropolitan Area Network)
802.7	Broadband Technical Advisory Group
802.8	Fiber-Optic Technical Advisory Group
802.9	Integrated Voice/Data Networks
802.10	Network Security
802.11	Wireless Networks
802.12	Demand Priority Access L= an, 100 Base VG - AnyLAN

Feature or Function	CSMA/CD	CSMA/CA	Token Passing	Demand Priority
Type of Communication	Broadcast-based	Broadcast-based	Token-based	Hub-based
Type of Access Method	Contention	Contention	Non-contention	Contention
Type of Network	Ethernet	LocalTalk	Token Ring ARCnet	100VG-AnyLAN

Maximum segment length	500m (1640 ft) Typically used = as backbone to connect Thinnet-based networ= k.
Speed	10 Mbps
Maximum taps	100
Maximum segments	5
Maximum repeaters	4
Maximum segment with nodes	3 Due to attenuati= on, only 3 of 5 segments can actually contain network connection. Other 2 segments can be used to connect the network over long distance.
Maximum nodes per segment	100
Maximum nodes for network	300
Minimum distance between nodes	2.5m (8 ft)
Maximum overall length with repeaters	2.5 km
Maximum AUI drop cable length	50m

Standard	BPS
V.22 bis	2400
V.32	9600
V.32bis	14,400
V.32terbo	19,200
V.FastClass (V.FC)	28,800
V.34	28,800
V.42	57,600

Bridges	Routers
recognize the = MAC sublayer addresses (i.e. the addresses of the network cards on its own segment)	Routers recogn= ize network addresses not individual computer addresses
forwards everything it doesn't recognize and forwards all addresses it knows, but only out the appropriate port	routers filter addresses. It forwards particular protocols to particular addresses (other routers) if the router doesn't recognize a destination address, the packet is usually disca= rded
works with all protocols	only works with routable protocols Non-Routable =3D NetBEUI, DLC, LAT