# Networking Essentials Notes Section 1
Section Titles: Network Orientation | Network Topologies | Primary Cable Types Network Adapter Cards | Wireless Local Area Networks
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 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 resources among themselves as well as access server-based resources.
Network Topologies
There are 4 basic topologies with variations #### Bus Topology Bus consists of a single 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 topology. 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 connected by cable segments to a centralized hub. Signal travels through the hub to all other computers. Requires more cable. If hub goes down, entire 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 => no need for repeaters on a ring topology No termination required => 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 regenerated. relatively easy to install, requiring ;minimal hardware #### Mesh The mesh topology connects each computer on the network to the others Meshes use a significantly larger amount of network cabling than do the other network topologies, which makes it more expensive. The mesh topology is highly fault tolerant. Every computer has 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 physical ring, but it still provides the token passing capabilities of a physical ring inside the hub. Just like in the ring topology, computers are given equal access to the network media through the passing of the token. A single computer failure 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 expensive because of all the wire needed another option is to mesh only the servers that contain information that everyone has to get to. This way the servers (not all the workstations) have fault tolerance at the cabling level.
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# 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 cables can use (see pp. 80-81 for pics) BNC cable connectors, BNC barrel connectors 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 connectors 50 ohm terminators Can carry signals 185 meters or 607 feet. Types: (pics on page 78) Coaxial Cable 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 ARCnet can use fiber optic or twisted pair.
each cable must have a terminator whose impedance matches the cable type impedance = current resistance measured in ohms terminators 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 than 1024 workstations per network. Entire network trunk length 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 repeaters 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 networks, linear bus topology transmits at 10 Mbps Uses DIX or AUI (Attachment 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 better resistance to electrical interference than thinnet. MORE expensive than thinnet.
Twisted-Pair Cable
Consists of two insulated copper wires twisted around each other. Twisting cancels out electrical noise from adjacent pairs (crosstalk) and external sources. Uses RJ-45 telephone-type 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 is 100 meters or 328 feet (10BaseT). Types: Cat 1 Voice grade telephone cable. Cat 2 Data grade 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 grade up to 10 Mbps, four pairs w/3 twists/ft. Cat 4 Data grade up to 16 Mbps, four twisted pairs. Cat 5 Data grade 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 allowed 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 => attenuation is the biggest problem here. #### Shielded Twisted Pair (STP) Uses a woven copper braid jacket and a higher quality protective jacket. Also uses foil wrap between and around the wire pairs. Much less susceptible to interference and supports higher transmission rates than UTP. Shielding makes it somewhat harder to install. same 100 meter limit as UTP. harder to tap used in AppleTalk and Token Ring networks
Fiber Optic Cable
Consists of a small core of glass or plastic surrounded by a cladding layer and jacket. Fibers are unidirectional (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 speed, long distance data transmission. NOT subject to electrical interference. Cable can't be tapped and data stolen => high security Most expensive and difficult to work with. Immune to tapping. can transmit at 100 Mbps and way up to 2 Gbps up to 2000 meters without a repeater. Supports data, voice and video. needs specialized knowledge to install => expensive all round.
Cable Type Comparisons
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 uses digital signaling over a single frequency. Entire communication channel is used to transmit a single signal. Flow is bi-directional. Some can transmit and receive at the same time. Baseband systems use repeaters to strengthen attenuated 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 channels or two separate cables must be used. if enough bandwidth is available, multiple analog transmission systems such as cable TV AND network transmissions can be on the same cable at the same time. if this is the case, 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 proprietary IBM unisex connectors. Defines cables as types
Type 1 | STP (Shielded twisted-pair) | used for computers and MAU's. 101 m | These three cable types can be used in Token Ring Networks | 16 Mbps 260 computer limit
Type 2 | STP, Voice and data | 100 m |
Type 3 | UTP; Voice grade | 45 m Most common Token Ring Cable | 4 Mbps 72 computer limit
Type 5 | Fiber-optic | industry standard |
Type 6 | STP; Data patch | used to connect MSAU's together used to extend Type 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 floors 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 grade cable => more expensive Crosstalk Where data security is important this is a problem Power lines, motors relays 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 common Fiber can go well over 100 Mbps but costs and requires experts to install. Cost Distance costs you money Attenuation Different cables can only transmit so far without causing too many errors
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Wireless Local Area Networks
Used where cable isn't possible - remote sites; also when mobility is important. Use transceivers or access points to send and receive signals between the wired and wireless network. There are 4 techniques for transmitting data Infrared transmission consists of four types; Line of sight Scatter: good within 100 ft. Reflective Broadband optical telepoint: used for multimedia requirements; as good as cable. Laser requires direct line-of-sight. Narrow-band (single frequency) radio Cannot go through steel or load-bearing walls. Requires a service handler. Limited to 4.8 Mbps Spread-Spectrum Radio 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 link 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 with line of site transmission. Also communicates with printers, bar code readers, etc. #### Multipoint Wireless Bridge Provides a data path between two buildings. Uses spread-spectrum radio 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 miles. 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 device which has correct address. Cellular networks. CDPD same as phone, subsecond delays only, real time transmission, can tie into cabled network. Satellite stations. Microwave, most common in USA, 2 X directional antennas, building to building, building to satellite Slow transmission rate: 8 Kbps - 19.2 Kbps
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Network Adapter Cards
The role of the network Adapter card is to: 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 and Media Access Control functions of the Data Link layer of the OSI Preparing Data data 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 called 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 address 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 data Sending and Controlling Data The NICs of the two computers exchanging data agree on the following: Maximum size of the groups of data being sent The amount of data to be sent before confirmation The time intervals between 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 unique 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 | Parallel 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 controller) |
Base I/O port: Channel between CPU and hardware specifies a channel through which information flows between the computer's adapter card and the CPU. Ex. 300 to 30F. Each hardware device 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 address 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/DIX connector: Thicknet, for example Use jumpers on the 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 Standard Architecture): original 8-bit and later 16-bit bus of the IBM-PC. EISA (Extended Industry 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 Memory: 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 Memory: the network adapter selects a portion of the computer's memory for its use. MOST common Bus Mastering: the adapter card takes temporary control of the computer's bus, freeing the CPU for other tasks. moves data directly to the computer's system memory Available on EISA and MCA can improve network performance by 20% to 70% RAM buffering: Ram on the adapter card acts as a buffer that holds data until the CPU can process it. this keeps the card from being a bottleneck On-board microprocessor: enables the adapter 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 to 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.
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Comments and suggestions? E-mail me at grantwil@sk.sympatico.ca
Last Updated: Wednesday, March 10, 1999 | Grant Wilson, Tisdale, SK. Canada