Networking Essentials

IRQ (Interrupt Requests)

• 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.

• CSMA/CD - Collision Detection; listens to cable prior to sending data. (EtherNet)
• 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)
• One device designated media administrator. Secondary device waits to be polled by primary device to check if it has data to be sent.

 

Cables

• Thinnet Coaxial - .25 inches thick, carries signal 185 meters. Known as RG-58 family, and has a 50 ohm impedance.

Types of Thin net Coaxial
RG-58 /U	Solid Copper Core
RG-58 A/U	Stranded Wire Core
RG-58 C/U	Military Specification of RG-58 A/U
RG-59	Broadband transmission (Television Cable)
RG-62	ArcNet Network Cable

 

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.

 

 

UTP/STP Category	Speeds
Cat 2	4 Mbps
Cat 3	10 Mpbs
Cat 4	16 Mbps
Cat 5	100 Mbps

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.

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)

Signal Transmissions

• 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.

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.

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 - Any LAN

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. IP 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.

 

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

 

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, 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	Major Protocols residing here
Application	SMB, NCP
Presentation	NCP
Session	NetBIOS, Named Pipes
Transport	TCP, SPX, NWLink, NetBEUI
Network	IP, IPX, NWLink, NetBEUI, DLC, DecNET
Data Link
Physical

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 voice 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.

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Copyright © 2001 Jatoi Solution Providers
Last modified: 11/26/96