My name is Ryon

I am a computer technician. I have broken down my studies to the areas that I felt I was weaker on and left some of my stronger areas aside. I hope this could help others in the industry like myself and could also be useful to anyone else as the information is in good detail.

Good luck on your exams !!

 

Application Layer	provides flow control and error recovery	SMB, NCP	GATEWAY
Presentation Layer	provides protocol conversions, encrypting and data compression.	NCP	GATEWAY
Session Layer	provides synchronisation	-	GATEWAY
Transport Layer	provides packet handling, repackaging, error handling	TCP, SPX, NWLink, NetBEUI	GATEWAY
Network Layer	provides addressing, determining routes, packet switching, routing, data congestion, reassembling data	IP, IPX, NetBEUI,Decnet, DLC	ROUTER BROUTER
Data-link Layer	sends data frames to the physical layer LLC - Manages link control and defines SAP’s MAC - Communicates with the adapter	-	BRIDGE BROUTER SWITCH REMOTE BRIDGE
Physical Layer	Transmits data over a physical medium	-	REPEATER MULTIPLEXER

Routable Protocols: DECnet, IP, IPX/SPX, OSI, XNS, DDP(appletalk)

NON-Routable: LAT, NetBEUI, DLC

• A routing table stores computer and network addresses
• Bridges create broadcast storms… routers eliminate them
• Network Analysers work at a number of the upper OSI layers due to their complex tasks
• Disabling rarely used network cards is the least expensive way of increasing network performance
• Raid 5 provides the fastest read speed for a fault tolerant system - due to striping with parity
• IPX/SPX is a fast protocol for small and large novell networks, it is routable and can be known as NWLink in Windows NT.
• DECnet defines communications over FDDI MAN’s and is also routable
• Appletalk is a small apple protocol that is used in small LAN’s. It is routable and is used for file and printer sharing
• RIP - Routers use this protocol to communicate
• Common TCP/IP problems are caused by incorrect subnet masks and default gateways
• Repeaters are used to solve attenuation problems, segments joined must use the same media access method
• Connection orientated mediums provide assurance of packet delivery
• Computer name and share name define and UNC path
• 10 base2 = Coax = 607 feet = 185 metres
• 10 baseT = UTP = 328 feet = 100 metres
• ARCNET uses RG 62A/U coax cabling
• Use DLC to connect PC’s to IBM mainframes
• SLIP is associated with TCP/IP
• ARP(address resolution protocol) is used to map IP addresses to NIC addresses
• ATP(part of appletalk suite) is able to store information in routing tables
• Transport protocols are able to store information in routing tables
• The send windows size should be greater than the receive window size in a sliding windows scenario - to increase network performance.
• 10baseT and 10base2 connectors have onboard or built in transceivers
• 10base5 is used with an external transceiver
• IEEE provides unique blocks of addresses for NIC manufacturers
• netBIOS broadcasts can only be received by the computers in the local subnet
• If you want UNIX workstations to be able to view NT Server files you need to install FTP and NFS on the server
• WINS does not allow duplicate netBIOS names
• Max. throughput for linked modems is (modem speed) / 8 *100*(no of modems)
• A protocol analyser is used to detect a faulty network card
• When in doubt it’s gotta be protocol analyser and ATM
• Token ring to ethernet transfer differences are due to FRAME SIZE DIFFERENCES not TCP window or ethernet
• Broadband technology provides unidirectional signal flow
• Frame relay transmits variable length packets at the data link layer along the most cost effective path
• RAID 0 - Divides data in 64k blocks and spreads over the array equally
• RAID 1 - Mirrors disk to disk, duplexing has a 2^nd controller (adding redundancy)
• RAID 2 - Data blocks broken up and spread across all drives in the array and provides error checking
• RAID 3 - Same as above but with one drive dedicated to parity information
• RAID 4 - Complete blocks of data spread across all drives in the array
• RAID 5 - Spreads data and parity info across all drives in the array. Min.3 disks
• NT supports RAID 0,1,5
• UTP cable is the most susceptible to crosstalk
• Share level security provides the least amount of administration
• Peer to peer networks are also called workgroups
• Daily backups would be your primary defence against data loss
• A packet header contains source, destination and alert signal. NOT CRC
• Four types of infrared networks are: line of sight, scatter, reflective and broadband optical telepoint
• DNS - (Domain name services) Resolves DNS host names to IP addresses
• WINS - (Windows internet naming service) resolves netBIOS names to IP addresses
• HOST files have mapping’s between DNS host names and their IP addresses
• LMHOST files contain mapping’s between netBIOS names and their IP addresses
• Jitter = Instability in a signal wave
• TDR’s send sonar like pulses to check for shorts or breaks
• Infrared networks can broadcast at 10MB
• Packet creation begins at the application layer
• With ISDN the 64 bit channels are know as B channels
• CSMA/CD = ethernet
• CSMA/CA = appletalk
• Token Passing = token ring
• Thinnet coax = .25inch
• Thicknet coax = .5inch
• STP helps reduce crosstalk and helps prevent elctro-inteference
• Baseband uses digital signalling over a single frequency and sends bi-directionally
• Broadband uses analog over a range of frequencies and transmits uni-directionally

PACKET SWITCHING NETWORKS:

 

X.25	Designed to connect remote terminals to mainframe host systems. Is very slow because of the constant error checking
Frame Relay	PTP using digital leased lines. Bandwidth on demand. A bridge or router must be frame relay capable
ATM	Transmits data in 53 byte cells, capable of speeds of 155 - 622+ Mbps Can transmit voice and video well
ISDN	128K/sec - 2x64k B channels and 1x16k D channel which does link management and signalling
FDDI	100Mb/s token passing using Fibre Optic. Uses dual ring topology for redundancy. Uses beaconing for troubleshooting

APPLICATION PROTOCOLS: SMB, FTP, NFS

DVM - DIGITAL VOLT METERS - Measures voltage passing through a resistance, used in network cable troubleshooting

TDR - TIME DOMAIN REFLECTOMETER - Sends sonar pulses to find breaks, shorts or crimping

This tool can be very accurate in locating a fault.

OSCILLISCOPE - Measures signal voltage per unit of time

NETWORK MONITOR - Examines packet types, errors and traffic between computers

PROTOCOL ANALYSER - Looks inside a packet to find the cause of a problem. Built in TDR !!!