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IRQ (Interrupt Requests)
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-
-
IRQ 0 |
System Timer |
IRQ 1 |
Keyboard |
IRQ 2(9) |
Video Card |
IRQ 3 |
Com2, Com4 |
IRQ 4 |
Com1, Com3 |
IRQ 5 |
Available (Normally LPT2 or sound card ) |
IRQ 6 |
Floppy Disk Controller |
IRQ 7 |
Parallel Port (LPT1) |
IRQ 8 |
Real-time clock |
IRQ 9 |
Redirected IRQ2 |
IRQ 10 |
Available |
IRQ 11 |
Available |
IRQ 12 |
PS/2 Mouse |
IRQ 13 |
Math Coprocessor |
IRQ 14 |
Hard Disk Controller |
IRQ 15 |
Available |
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Standard Topologies
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-
Bus - A single cable (trunk) that connects all
computers in a single line.
-
Star - Computers connect to a centralized hub
via cable segments.
-
Ring - Connects all computers on a single cable.
Ends are not terminated, but form a full loop connecting the last
computer to the first computer.
-
Mesh - Commonly used in WAN configurations. Routers
are connected to multiple links for redundancy and to give the
ability to determine the quickest route to a destination.
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Access Methods
-
-
CSMA/CD - Collision Detection; listens to cable
prior to sending data. (EtherNet)
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CSMA/CA - Collision Avoidance; Announces intention
to send data. (Appletalk)
-
Token-Passing - Token revolves around ring, computer
which has token is permitted to data. (TokenRing)
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One device designated media administrator. Secondary
device waits to be polled by primary device to check if it has
data to be sent.
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Cables
-
-
Thinnet Coaxial - .25 inches thick, carries signal
185 meters. Known as RG-58 family, and has a 50 ohm impedance.
-
-
Types of Thinnet Coaxial
RG-58 /U (50 ohm) |
Solid Copper Core |
RG-58 A/U (50 ohm) |
Stranded Wire Core |
RG-58 C/U |
Military Specification of RG-58 A/U |
RG-59 |
Broadband transmission (Television Cable) |
RG-62 (93 ohm) |
ArcNet Network Cable |
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-
When troubleshooting thinnet coaxial cable, the cable
terminator must read 50ohms.
-
Thicknet Coaxial - .5 inches thick, carries signal
500 meters. A transceiver (Vampire Tap) is used to make a physical
connection with the thicknet core.
-
Unshielded Twisted Pair - Twisted pair wiring,
carries signal 100 meters. Is susceptible to crosstalk.
-
Shielded Twisted Pair - Twisted pair wiring, carries
signal 100 meters. Has foil or braided jacket around wiring to
help reduce crosstalk and to prevent electromagnetic interference.
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UTP/STP Category
|
Speeds
|
Cat 1 |
Voice Only |
Cat 2 |
4 mbps |
Cat 3 |
10 mpbs |
Cat 4 |
16 mbps |
Cat 5 |
100 mbps |
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Fiber-Optic - Carries light pulse signals through
glass core at speeds of between 100Mbps - 200,000Mbps.
-
Attenuation - The degrading of a signal as it
travels farther from its origination.
-
Crosstalk - Signal overflow from one wire to another
adjacent wire.
-
Jitter - Instability in a signal wave; Caused
by signal interference or an unbalanced FDDI ring or Token Ring.
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Ethernet Specifications
-
-
-
-
Type
|
Cable types
|
Connection Type |
Max Length |
10Base2 |
RG-58 thinnet coaxial cable |
BNC T Connector |
185 meters (607 ft) |
10Base5 |
Thicknet coaxial cable |
DIX/AUI |
500 meters (1640 ft) |
10BaseT |
Category 3, 4, or 5 UTP cable |
RJ-45 |
100 meters (328 ft) |
100BaseT |
Category 5 UTP cable |
RJ-45 |
100 meters (328 ft) |
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Signal Transmissions
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-
Baseband - Uses digital signalling over a single
frequency. Transmits birectionally.
-
Broadband - Uses analog signalling over a range
of frequencies. Transmits unidirectionally. Uses amplifiers for
signal regeneration.
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OSI Model
OSI Layers
|
Application Layer |
Allows applications to use the network. Handles
network access, flow control and error recovery. |
Presentation Layer |
Translates data into a form usable by the application
layer. The redirector operates here. Responsible for protocol
conversion, translating and encrypting data, and managing data
compression. |
Session Layer |
Allows applications on connecting systems to establish
a session. Provides synchronization between communicating computers. |
Transport Layer |
Responsible for packet handling. Ensures error-free
delivery. Repackages messages, divides messages into smaller
packets, and handles error handling. |
Network Layer |
Translates system names into addresses. Responsible
for addressing, determining routes for sending, managing network
traffic problems, packet switching, routing, data congestion,
and reassembling data. |
Data Link Layer |
Sends data from network layer to physical layer.
Manages physical layer communications between connecting systems. |
- LLC - (802.2) Manages link control and defines SAP's (Service
Access Points).
|
- MAC - (802.3, 802.4, 802.5, 802.12) Communicates with adapter
card.
|
Physical Layer |
Transmits data over a physical medium. Defines cables,
cards, and physical aspects. |
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IEEE 802 Specifications
-
802.1 |
Internetworking |
802.2 |
LLC (Logical Link Control) |
802.3 |
CSMA/CD - Ethernet |
802.4 |
Token Bus LAN |
802.5 |
Token Ring LAN |
802.6 |
MAN (Metropolitan Area Network) |
802.7 |
Broadband Techincal Advisory Group |
802.8 |
Fiber-Optic Techical Advisory Group |
802.9 |
Integrated Voice/Data Networks |
802.10 |
Network Security |
802.11 |
Wireless Networks |
802.12 |
Demand Priority Access Lan, 100 Base VG - AnyLAN |
-
- LAN Enhancement Components
-
Component |
Function
|
Repeater |
Regenerates signals for retransmission. Moves packets from
one physical media to another. Will pass broadcast storms. Cannot
connect different network topologies or access methods. |
Bridge |
Bridges are used to segment networks. They forward packets
based on address of destination node. Uses RAM to build a routing
table based on hardware addresses. Some bridge types are capable
of connecting dissimilar network topologies. Will forward all
protocols. Regenerates the signal at the packet level |
Remote Bridge |
Same as bridge, but used for telephone communications. Uses
STA (Spanning Tree Algorithm). |
Router |
Routes packets across multiple networks. Uses RAM to build
a routing table based on network addresses (i.e. TCP
address). Shares status and routing information to other routers
to provide better traffic management and bypass slow connections.
Will not pass broadcast traffic. Are slower than bridges due
to complex functions. Strips off Data Link Layer source and
destination addresses and then recreates them for packets. Routers
can accomodate multiple active paths between LAN segments. Will
not pass unroutable protocols. |
Brouter |
Will act as a router for specified protocols and as a bridge
for other specified protocols. |
Gateway |
Used for communications between different NOS's (i.e. Windows
NT and IBM SNA). Takes the packet, strips off the old protocol
and repackages it for the receiving network. |
Multiplexer |
Device that can divide transmissions into two or more channels. |
Switches |
Hub with bridging capabilities. Switch filters traffic through
MAC addresses. Creates sessions on ports within the hub. Used
when upgrading to 100mb Fast Ethernet. |
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Component
|
Which OSI layer it resides on
|
Repeater |
Physical |
Bridge |
Data Link (MAC Sublayer) |
Remote Bridge |
Data Link (MAC Sublayer) |
Router |
Network |
Brouter |
Data Link and Network |
Gateway |
Transport, Session, Presentation and Application |
Mulitplexer |
Physical |
Switch |
Data Link |
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-
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Spanning Tree Algortithm - was developed for bridges
to determine the most efficient network in path when there are multiple
paths to choose from.
-
Multiplexing - Several signals from different sources
are collected into the component and are fed into one cable for
transmission.
-
Protocols
-
-
Routable - TCP/IP, IPX/SPX, OSI, AppleTalk, DECnet,
XNS.
-
Non-routable - NetBEUI, DLC, LAT.
-
NetBEUI - Microsoft protocol designed for small
LANs; non-routable. Not compatible with UNIX networks.
-
IPX/SPX - Fast protocol for small and large Novell
networks; is routable. Also known in NT as NWLink.
-
TCP/IP - Internet protocol; is routable. Used by
UNIX networks.
-
DECnet - Defines communciations over FDDI MANs;
is routable.
-
Appletalk - Apple protocol designed for small LAN
file and print sharing; is routable.
-
-
OSI layer
|
Protocols residing here
|
Application |
SMB, NCP |
Presentation |
NCP |
Session |
None |
Transport |
TCP, SPX, NWLink, NetBEUI |
Network |
IP, IPX, NetBEUI, DLC, DecNET |
Data Link |
None |
Physical |
None |
-
RIP (Routing Information Protocol) - Routers use
this to communicate with each other to determine the least busy
and shortest network routes.
-
-
SLIP (Serial Line IP) - Provides dial-up communications,
but is unable to simultaneously transfer multiple protocols.
-
PPP (Point-to-Point Protocol) - Performs dynamic
IP addressing, multi-protocol support, password login and error
control.
-
-
NDIS (Microsoft) and ODI (Novell) are used to bind multiple
protocols to a network adapter.
Common TCP/IP problems are caused by incorrect subnet
masks and default gateways.
Incorrect frame types will cause problems between two
systems using IPX/SPX.
-
-
Packet Switching Networks
-
-
Packet Switching - Packets are relayed across network
along the best route available.
Type
|
Function
|
X.25 |
Designed to connect remote terminals to mainframe host systems.
Is very slow due to constant error-checking. |
Frame Relay |
Point-to-point system which uses digital leased lines. Will
provide bandwidth as needed. Requires frame relay capable
bridge or router for transmission. |
ATM |
Advanced implementation of packet switching. Transmits at
speeds of 155Mbps to 622Mbps with capabilities of higher speeds.
Transmits data in 53 byte (48 application, 5 header) cells.
Uses switches as multiplexers to permit several computers
to simultaneously trasmit data on a network. Great for vioce
and video communications. |
ISDN |
Transmits at 128k/sec. Has three data channels - 2 B channels
@ 64k/sec & 1 D channel @ 16k/sec. The B channels carry data
while the D channel performs link management and signalling. |
FDDI |
100 Mbps token-passing ring network which uses fiber-optic
media. Uses a dual-ring topology for redundancy and in case
of ring failure. Each ring is capable of connecting 500 computers
over 100 kilometers (62 miles). Can be used as a network backbone.
Uses beaconing for ring troubleshooting. |
-
Beaconing - Computers are used to detect network
faults, then transmit the fault signal to the server.
-
Security levels
-
-
Share-level security - Used in Windows 95 to share
resources. A password is needed to access the resource.
-
User-level security - Used in Windows NT to share
resources. When you attempt to access a shared resource, the server
will make sure your user account has been authorized to access the
resource.
-
Network Diagnostic Tools
-
-
-
Tool
|
Function
|
Digital Volt Meters (DVM) |
Measures voltage passing through a resistanace. Primarily
used for network cable troubleshooting. |
Time-Domain Reflectors (TDRs) |
Sends sonar-like pulses to look for breaks, shorts or crimps
in cables. Can locate a break within a few feet of actual fault. |
Oscilloscope |
Measures amount of signal voltage per unit of time. Displays
crimps, shorts, opens, etc. |
Network Monitor |
Examines packet types, errors and traffic to and from each
computer on a network. |
Protocol Analyzer |
Look inside the packet to determine cause of problem. Contains
built in Time-Domain Reflector. Gives insights to many problems
including connection errors, bottlenecks, traffic problems,
protocol problems, etc. |
-
Multiple Disk Sets
-
Fault Tolerant Systems protect data by duplicating
data or by placing data in different physical sources.
RAID
|
Function
|
Level 0
Disk Striping |
Divides data into 64k blocks and spreads it equally among
all disks in the array. Is not fault tolerant. |
Level 1
Disk Mirroring |
Duplicates a partition on another physical disk. |
Level 1
Disk Duplexing |
Duplicates a partition on another physical disk that is connected
to another Hard Drive Controller. |
Level 2
Disk Striping w/ ECC |
Data blocks are broken up and distributed across all drives
in array with error checking. |
Level 3
Disk Striping w/ ECC stored as parity |
Data blocks are broken up and distributed across all drives
in array with one drive dedicated to storing parity data. |
Level 4
Disk Striping with large blocks |
Complete blocks of data are distributed across all drives
in the array. |
Level 5
Disk Striping with parity |
Distributes data and parity information across all disks in
the array. The data and the and parity information are arranged
so they are always on separate disks. A parity stripe block
exists for each row accross the disk. The parity stripe is used
for disk reconstruction in case of a failed disk. Supports a
minimum of three disks and a maximum of thirty-two disks. |
Windows NT supports RAID Levels 0, 1, and 5.
-
Sector Sparing - Automatically adds sector-recovery
capabilities to the files system while the computer is running.
Available when using RAID methods. Only available with SCSI drives.
-
Upgrading the network
-
To upgrade a network to 100mbps Ethernet, you must
perform the following:
-
Upgrade all hubs to switches or 100mbps hubs.
-
Upgrade the wiring to CAT 5 UTP/STP.
-
Upgrade all network cards to 100mbps.
-
Computer name resolution
-
-
DNS (Domain Name Services) - Used to resolve DNS
host name to an IP address.
-
WINS (Windows Internet Naming Service) - Used to
resolve NetBIOS computer name to an IP address.
-
HOSTS - File which contains mappings between DNS
host names and their IP addresses.
-
LMHOSTS - File which contains mappings between NetBIOS
computer names and their IP addresses.
|