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Design and Documentation

Honolulu Community College

Cisco Academy Training Center

Semester 1

Version 2.1.1

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Overview Design of physical and logical topologies. Documentation. Wiring closet specifications. Wiring and electrical techniques.

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General Design Process 1. Select the technology (Ethernet). 2. Develop Layer 1 LAN topology.

type of cable. physical (wiring) topology (extended star). Type of Ethernet. Logical topology.

3. Develop Layer 2 LAN topology. Segmentation - reduce congestion & collision

domain size.

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General Design Process 4. Develop Layer 3 topology.

Implement routing to build scalable internetworks. logical structure. segmentation - minimize broadcast domain.

Other concerns: Placement of servers. LANs link to WANs and to the Internet. document your physical and logical topologies.

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Network Design Issues First step: gather information about the

organization. 1.organization's history and current status 2.projected growth 3.operating policies and management procedures 4.office systems and procedures 5.viewpoints of people who will be using LAN

Purpose is to identify and define any issues or problems that need to be addressed.

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Network Design Issues (cont.) Second step: make a detailed assessment of

current and projected requirements. Third step: identify resources and constraints of

the organization. document existing computer hardware and

software. identify and define projected hardware and

software needs. Purpose: determine how much training will be

required, and how many people will be needed to support the LAN.

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Network Design Issues (cont.) These steps will allow you to estimate costs and

develop a budget for the implementation of a LAN.

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Wiring Closet Selection Most important decision is selection of MDF.

Secure location, close to POP. POP is where telecommunications services

connect to the building's communication facilities. TIA/EIA-568-A specifies that in an Ethernet star

topology, every device must be connected to the hub (in wiring closet) by horizontal cabling.

To find location(s) of wiring closet(s), begin with a floor plan of the building, indicating all devices that will be connected to the network.

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Wiring Closet Selection (cont.) Next identify potential locations for wiring closets.

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Determing Number of Wiring Closets Draw circles of radius 50 m from each potential

wiring closet locations. Number of wiring closets is determined by what

is needed to cover the building.

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Extended Star Topology MDF of an extended

star topology Ethernet LAN is usually centrally located.

In high rise building, MDF usually located on a middle floor, even if POP is on the first floor.

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MDF - multi-building campus MDF: a central location, close to the POP,. IDFs are located in each building. Note: main building also requires an IDF.

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Backbone Cabling Cabling between wiring closets is backbone or

vertical cabling. Backbone cabling include:

MCC (main cross-connects), ICC (intermediate cross-connects), mechanical terminations backbone cable runs. Cabling between MDF and POP

Recommended backbone is 62.5/125 µm fiber-optic cable.

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Backbone Cabling (cont.) TIA/EIA 568A specifies four types of networking

media for backbone cabling: 100 UTP, 150 STP, 62.5/125 µm fiber optic,

and single-mode fiber optic cable. TIA/EIA 568A recognizes 50 coaxial cable, but

it is not recommended for new installations. Recommended backbone is 62.5/125 µm fiber-

optic cable (multi-mode fiber).

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MDF to IDF Cabling MCC (main cross connect) is in MDF.

connects backbone cabling to the Internet. HCC (horizontal cross connect) is in IDF.

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MDF to IDF - another method ICC (intermediate cross connect) in an IDF. No work areas or horizontal wiring connects to ICC. HCC (horizontal cross connect) in another IDF.

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No more than one ICC between MCC and HCC.

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Backbone Cabling Lengths TIA/EIA 568A also specifies max lengths when ICC

is used.

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Specs for Backbone Cabling TIA/EIA 568A specifies max lengths for backbone

cabling.

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Electrical Concern - Noise AC line noise, can create errors:

adding unwanted voltages to signals. preventing detection of leading and trailing edges

of square wave signals. Problems can be compounded with poor ground

connections.

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Electrical Concern - ESD Charges can be separated by friction, e.g. by

shuffling you feet across a carpet. Very high voltages (thousands of volts) can be

generated , referred to as static electricity. When you reach for a metal object, a spark

occurs - this is current flow, as the high voltage pushes the free electrons to the metal object.

This is ESD or electro-static discharge. can randomly damage computer chips and/or

data.

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Grounding Network Equipment AC power is supplied though a 3 prong plug. Top 2 connectors are

the power. Other connector is safety

ground (earth ground). Any exposed metal is

connected to safety ground. Computer motherboard’s

ground plane is connected to the chassis and safety ground.

Ground helps dissipate static electricity.

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Safety Ground Purpose - to prevent exposed metal parts

from becoming energized with high voltage should a wiring fault occur.

A wiring fault will cause current through the ground connection, and activate protective devices such as circuit breakers to disconnect the power.

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Safety Ground Connection Problems Using copper media, such as UTP to connect

grounds in different buildings or from different power panels can present an electrical shock hazard.

Different ground voltages can also severely damage delicate computer memory chips.

Minimize danger by using “one-hand rule”. “One-hand Rule” - touch electrical equipment with

only one hand (current will not pass across your body through your heart).

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Safety Ground Connection Problems (cont.) TIA/EIA 568A specifications permit the use of

fiber-optic cable for backbone cabling. Fiber does not conduct electricity, eliminating the

shock hazard. Fiber-optic cable is recommended for the

backbone cabling between buildings, and also for linking wiring closets on different floors.

Fiber also beneficial in areas with lightning; it will not conduct lightning strike into the building.

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Classifying Power Problems Three connections on AC power:

Hot, neutral, and safety ground. Power problems classified by

which wires are affected. Normal mode problems - between hot and neutral. Common mode problems - between safety ground

and either hot or neutral. Common mode problems are more serious. Normal mode problems are intercepted by the

computer’s power supply, UPS, or AC line filter.

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Typical Power Line Problems Power disturbance is unwanted excess energy

that is sent to electrical equipment. Typical power disturbances include:

surges sags spikes oscillations.

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Typical Power Disturbances Surge - 10% voltage increase for few secs.

Causes most hardware damage in devices, particularly hubs (sensitive low voltage lines).

Spike - a momentary >100% increase in voltage for 0.5 to 100 secs (very short duration).

Sag - voltage drops below 80% of normal voltage for less than 1 sec.

Brownout - voltage below 80% of normal for greater than 1 sec.

Oscillations - AC voltage harmonics or noise, caused by excessively long wires.

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Surges and Spikes Causes:

Lightning. Utility company

switching operations. Cycling equipment

like HVAC, elevators, copy machines.

Problems: Altered or loss data, lockups, damage to

electrical devices or electronic chips. Addressed with surge suppressors.

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Sags and Brownouts >20% decrease in line voltage (below 80% of

normal). Sags - short duration (<1sec). Brownouts - longer duration (>1sec).

Can cause system crashes, and loss of data. Solved by using an UPS (uninterruptible power

supply).

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Oscillations Can cause excessive noise and erroneous data. Solved by rewiring, to ensure clean and direct

power and ground connections.

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Effectiveness of Surge Suppressors Individual surge suppressors - placed at wall

outlet, close to networking device. Most use a MOV, metal oxide varistor.

Capable of absorbing very large currents without damage (diverts currents to ground).

May not be very effective! Diverting surges to ground avoids equipment

damage, but can cause garbled data by changing ground voltage.

MOVs have limited lifetime; are not the best choice for network protection.

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Best Surge Suppressor Use large commercial

grade surge suppressor at the power panel.

By diverting surges to ground at the power panel you minimize effect of changing ground potentials at your networking devices.

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UPS - for problem of sags & brownouts What devices should be supported by UPS?

Factors to consider: cost, importance of service, quality of ac line power.

Every network file server should have power backup.

Any critical devices (hubs, bridges, switches, routers) should be backed up.

UPS - for outages of short duration. For extended periods of time, a generator is

needed.

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UPS Components Batteries - storage of electrical energy (DC).

Larger batteries (greater storage capacity); UPS can supply backup power longer.

Battery Charger - keeps batteries fully charged when ac line power is available.

Power Inverter - converts DC voltage from batteries into AC line voltage.

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UPS Operation Basic UPS:

Monitors power line. When line power is interrupted, UPS switches to

inverter powered by batteries. Transfer time - time UPS takes to switch over to

inverter power (typically few milli-secs). More expensive on-line UPS:

operates continuously on-line, supplying AC power from inverter. Batteries are charged from AC line voltage.

Transfer time is zero.

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Basic UPS Block Diagram S1 & S2 normally closed, S3 & S4 normally

open. When AC voltage is lost, the inverter switches on,

S1 & S2 open, and S3 & S4 close.

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On-line UPS Block Diagram Operates continuously on-line. Transfer time is zero.

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Intelligent UPS Has data communications capability. Communicates with file server, informing it

when battery power is running low. Informs workstations when a power outage has

occurred.

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Summary General design process.

Select technology (Ethernet, Token Ring, etc) Layer 1 topology. Layer 2 topology. Layer 3 topology.

Network Design Issues 1.Gather information. 2.Analyze requirements. 3.Identify resources and constraints.

Wiring closet specs - TIA/EIA 569. Selecting wiring closets

MDF - secure, central location, close to POP.

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Summary (cont.) Horizontal and Backbone Cabling.

Cat 5 UTP for horizontal cabling. Multi-mode fiber for backbone.

Electrical concerns: AC line noise. ESD. Ground problems.

Power Line Problems. Normal mode and common mode. Surges, spikes, sags, brownouts, oscillations. Surges & spikes addressed with surge supressors.

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Summary (cont.) MOV, metal-oxide varistor, found in individual

surge suppressors. Commercial grade surge suppressor, installed at

the power panel, is best. UPS

Basic and on-line. Troubleshooting

work up through the OSI model.

The End