NETWORKING ESSENTIALS STUDY GUIDE

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					                            NETWORKING ESSENTIALS STUDY GUIDE



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Network Types
Topologies
Cabling
Network Devices
OSI Model
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--TYPES OF NETWORKS--
1) PEER TO PEER
A peer to peer network is one in which lacks a dedicated server and every computer acts as both a client
and a server. This is a good networking solution when there are 10 or less users that are in close proximity
to each other. A peer to peer network can be a security nightmare, because the people setting permissions
for shared resources will be computer idiots and the right people will never have access to the right
resources. Thus is only recommended in situations where security is not an issue.

2) CLIENT/SERVER
This type of network is designed to support a large Number of users and uses dedicated server/s to
accomplish this. Clients log on to the server/s in order to run applications or obtain files. Security and
permissions can be managed by 1 or more administrators which cuts down on the aforementioned computer
illiterates from medling with things that they shouldn't be. This type of network also allows for convenient
backup services, reduces network traffic and provides a host of other services that come with the network
operating system(NOS).

3) CENTRALIZED
This is also a client/server based model that is most often seen in UNIX environments, but the clients are
"dumb terminals". This means that the client may not have a floppy drive, hard disk or CDROM and all
applications and processing occur on the server/s. As you can imagine, this requires fast and damn
expensive server/s. Security is very high on this type of network, although a similar level of security can be
achieved using an NT server and setting appropriate permissions.

--NETWORK TOPOLOGIES--
1) BUS
This topology is old school and essentially has each of the computers on the network daisy-chained to each
other. This type of network is usually peer to peer and uses Thinnet(10base2) cabling. It is configured by
connecting a "T-connector" to the network adapter and then connecting cables to the T-connectors on the
computers on the right and left. At both ends of the chain the network must be terminated with a 50 ohm
impedance terminator.
ADVANTAGES: Cheap, simple to set up.
DISADVANTAGES: Excess network traffic, a failure may affect many users, Problems are difficult to
troubleshoot.




As you can see if computer #1 sends a packet to computer #4, it must pass through computers #2 and #3,
creating excess traffic.
2) STAR
The star is probably the most commonly used topology today. It uses twisted pair(10baseT or 100baseT)
cabling and requires that all devices are connected to a hub.
ADVANTAGES: centralized monitoring, failures do not affect others unless it is the hub, easy to modify.
DISADVANTAGES: If the hub fails then everything connected to it is down. This is like if you were to
burn down the phone company's central office, then anyone connected to it wouldn't be able to make any
phone calls.




3) RING
The ring topology looks the same as the star, except that it uses special hubs and ethernet adapters. The
Ring topology is used with Token Ring networks(will be discussed later).
ADVANTAGES: Equal access.
DISADVANTAGES: Difficult to troubleshoot, network changes affect many users, failure affects many
users.
4) MESH
Mesh topologies are combinations of the above and are common on very large networks. For example, a
star bus network has hubs connected in a row(like a bus network) and has computers connected to each
hub.

--CABLING--
TYPES
       Cable Type           Also Known As            Connector               Maximum Length
       10Base5      RG-8 or RG-11, Thicknet coax AUI/DIX                     500 meters(1640 ft)
       10Base2      RG-58, thinnet coax              BNC connector           185 meters(607 ft)
       10BaseT      Cat 3, 4, 5 twisted pair         RJ-45                   100 meters(328 ft)
       100BaseT     Cat 5 twisted pair               RJ-45                   100 meters(328 ft)


       10baseFL     Fiber Optic                      Fiber Optic connector 2 Kilometers(6562 feet)



SPEED
                                    Cable Type      Transmission Speed
                                  Thicknet          10mbps
                                  Thinnet           10 mbps
                                  cat 2 twisted pair 4 mbps
                                  cat 3 twisted pair 10 mbps
                                  cat 4 twisted pair 16 mbps
                                  cat 5 twisted pair 100 mbps
                                  Fiber Optic       100 mbps - 1 gbps
MISC CABLE STUFF
--Shielded twisted pair(STP) differs from UTP in that it has a foil jacket that helps prevent crosstalk.
Crosstalk is overflow from an adjacent wire.

--The 5-4-3 rule: this rule states that on a 10base2 network can have 5 cable segment connected with 4
repeaters, but only 3 of these segments can be occupied by computers. There is also a maximum of 30
computers per segment.

--Thicknet cables are 0.5 inches thick and have a 50 ohm impedance.

--Thinnet cables are 0.25 inches thick and have a 50 ohm impedance.

--Plenum grade cabling is required if the cabling will be run between the ceiling and the next floor(this is
called the plenum). Plenum grade is resistant to fire and does not emit poisonous gasses when burned.

--Thicknet is often used as a backbone. A transceiver with a vampire tap penetrates the core of the cable.
From the transceiver a DB-15 connector plugs into the AUI port on a given device.

--Fiber Optic cabling has an built in security as you can't intercept data as you can with other cable
mediums.

--Baseband= Digital, single frequency, bidirectional communications and uses a repeater to regenerate
signals. Broadband= Analog, multiple frequencies, unidirectional communications, uses amplifiers to boost
signals.

--NETWORK HARDWARE--
INTERRUPT REQUESTS(IRQ)
                             IRQ                        DEVICE
                            IRQ 0     System Timer
                            IRQ 1     Keyboard
                            IRQ 2/9 Video Card
                            IRQ 3     Open unless needed for Com 2 or 4
                            IRQ 4     Com 1, Com 3
                            IRQ 5     Open unless needed for LPT2 or sound card
                            IRQ 6     Floppy Disk Controller
                            IRQ 7     LPT1(parallel port)
                            IRQ 8     Real time clock
                            IRQ 9/2 linked to IRQ 2
                            IRQ 10 Open
                            IRQ 11 Open
                            IRQ 12 PS/2 Mouse
                            IRQ 13 Math Co-processor
                            IRQ 14 Hard Disk Controller
                            IRQ 15 Open
-Often, if an network card will not function it is due to an IRQ or memory conflict.
-The NDIS specification allows for multiple protocols to be bound to a single network adapter.
-ODI is a specification defined by Novell and Apple that also allows multiple protocols to be bound to a
single network adapter. Similar to NDIS.

LAN CONNECTIVITY DEVICES
1) REPEATERS
Boost signal in order to allow a signal to travel farther and prevent attenuation. Attentuation is the
degradation of a signal as it travels farther from its origination. Repeaters do not filter packets and will
forward broadcasts. Both segments must use the same access method, meaning that you can't connect a
token ring segment to an Ethernet segment. Repeaters will connect different cable types.
2) BRIDGES
Functions the same as a repeater, but can also divide a network in order to reduce traffic problems. A
bridge can also connect unlike network segments(ie. token ring and ethernet). Bridges create routing tables
based on the source address. If the bridge can't find the source address it will forward the packets to all
segments.
3) ROUTERS
A router will do everthing that a bridge will do and more. Routers are used in complex networks because
they do not pass broadcast traffic. A router will determine the most efficient path for a packet to take and
send packets around failed segments. Unroutable protocols can't be fowarded.
4) BROUTERS
A brouter has the best features of both routers and bridges in that it can be configured to pass the
unroutable protocols by imitating a bridge, while not passing broadcast storms by acting as a router for
other protocols.
5) GATEWAYS
Often used as a connection to a mainframe or the internet. Gateways enable communications between
different protocols, data types and environments. This is achieved via protocol conversion, whereby the
gateway strips the protocol stack off of the packet and adds the appropriate stack for the other side.

--OSI 7 LAYER MODEL--
Here is an easy way to memorize the order of the 7 layer model and it is as follows:
All People Seem To Need Data Processing. The first letter of each word corresponds to the first letter of
one of the layers. It is dumb as hell, but it works.
   Layer                          Description                     Device            Protocol
                                                                                    NCP, SMB, SMTP,
               Provides network access for applications, flow
Application                                                       Gateway           FTP, SNMP, Telnet,
               control and error recovery
                                                                                    Appletalk
               Performs protocol conversion, encryption and       Gateway and
Presentation                                                                        NCP, AFP, TDI
               data compression                                   redirectors
               Allows 2 applications to communicate over a
Session        network by opening a session and synchronizing     Gateway           NetBios
               the involved computers
               Repackages messages into smaller formats,
                                                                                    NetBEUI, TCP, SPX,
Transport      provides error free delivery and error handling    Gateway
                                                                                    and NWLink
               functions


               Handles addressing, translates logical addresses
                                                                  Router and        IP, IPX, NWLink,
Network        and names to physical addresses, routing and
                                                                  brouter           NetBEUI
               traffic management.
**Data         Packages raw bits into frames and includes a       Switch, bridge    None
Link          cyclical redundancy check(CRC)                       and brouter
                                                                   Multiplexer and
Physical      Transmits data over physical medium                                  None
                                                                   repeater

**The Data Link layer is divided into 2 sublayers called Media Access Control(MAC) and Logical Link
Control(LLC).
-MAC Sublayer= Communicates with network card and delivers error-free delivery between 2 computers.
-LLC Sublayer= Defines service access points(SAPs) which are used to transfer information to the upper
layers of the OSI model.

ACCESS METHODS
1) CSMA/CD
This stands for "carrier-sense multiple access with collision detection" and is the method used on ethernet
networks whereby all computers on the network check the cable for traffic before attempting to transmit a
packet. If more than 1 transmits at the same time then there will be a collision and both computers will wait
a random amount of time and retransmit.
2) CSMA/CA
Stands for "carrier-sense multiple access with collision avoidance". This access method prevents collisions
by having computers broadcast an intent to send a packet. This is the access method used by Localtalk and
is sometimes described as "chatty". This broadcasting of intent to send can cause excess network traffic and
slow things down.
3) TOKEN PASSING
Token passing is the access method used by token ring networks. With this method, a packet called a token
is passed around the network. A computer that wishes to transmit must wait until it can take control of the
token, allowing only one computer to transmit at a time. This is sort of like the "conch" in Lord of the Flies.
Piggy had all of this crap that he wanted to whine about all of the time, but could only do so if he possessed
the conch.
4) DEMAND PRIORITY
This access method is used with 100VG-AnyLAN networks. The repeaters, bridges, routers or hubs search
the network for requests that are waiting to be sent. If 2 or more requests are received by the network
hardware at once, the data with the highest priority is sent. Priority for different data types can be
controlled by the administrator. A real advantage is that computers can receive and transmit at the same
time with this access method.

				
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