Topology and Design

CCNA Guide to Cisco Networking

Chapter 4: Network Topology And Network Design

Objectives

• Discuss the different physical topologies• Describe various network architecture

models• Determine which types of network media

to use given a set of requirements• Understand horizontal cabling standards

and wiring closets• Consider performance requirements and

improvements for given situations

Objectives (continued)

• Install a telecommunications connector

• Wire a patch panel

• Test network cable

• Discuss LAN design

• Describe the function that network-management tools perform on a network

Physical Topologies

• Bus topology– Bus topology advantages

• Inexpensive• Easy to design• Easy to implement

– Bus topology disadvantages• Difficult to troubleshoot• Requires termination

Physical Topologies (continued)

Physical Topologies (continued)

• Star topology– Star topology advantages

• Break in one cable does not affect other devices (except up links)

• Easy to locate problems• Easy to install• Does not require termination like bus topology

– Star topology disadvantages• Center of star topology device (hub) can be expensive• Hub failure can affect entire topology• Amount of cable is expensive

Physical Topologies (continued)

Physical Topologies (continued)

• Ring topology– Ring topology advantages

• Prevents network collisions• Each station acts like a repeater

– Ring topology disadvantages• Cable break can affect all devices• Temporarily shut down network to add a new

station• Maintenance and monitoring is difficult

Influence Of The 5-4-3 Rule On Topologies

Influence Of The 5-4-3 Rule On Topologies (continued)

Network Architecture

• IEEE 802– Logical Link Control (IEEE 802.2)– CSMA/CD (802.3)– Token Ring (802.5)– Wireless Technologies (802.11)– FDDI

Network Architecture (continued)

Media

• Twisted-Pair cabling have the following in common– Copper based data transmission– Copper wires come in pairs– Each Wire of a pair is twisted around each

other– Copper wires are enclosed in a sheath– All wire pairs are enclosed in a sheath

Media (continued)

• Unshielded twisted-pair (UTP)– Advantages of UTP cable

• Thin and flexible • Easy to install• Many modern buildings come with CAT 5 installed• Small size does not fill up wiring ducts fast• Inexpensive per foot

– Disadvantages of UTP cable• Susceptible to interference• Cable length is 100 meters or 328 feet

• Register Jacks (RJ)– RJ-45

Media (continued)

Media (continued)

• Shielded twisted-pair (STP)– Advantages of STP cable

• Greater protection from interference• Thin and flexible • Overall it is easy to install

– Disadvantages of STP cable• Inexpensive per foot but more than UTP• STP must be grounded, problems exists if not grounded

properly• More difficult to install than UTP• Small size but does fill up wiring ducts faster than UTP

Media (continued)

• Coaxial cabling (Thicknet and Thinnet)– Advantages of coaxial cabling

• Cable lengths are longer than UTP/STP• Less susceptible to interference than UTP• Hubs are not required, direct connection

– Disadvantages of coaxial cabling• Thicknet is very difficult to install• More expensive than UTP• Difficult to troubleshoot

Media (continued)

Media (continued)

Media (continued)

• Thinnet and Thicknet Connectors– RG-58 cabling– BNC– Attachment unit interface (AUI)– Barrel connectors– T-connectors– Terminators

Media (continued)

Media (continued)

• Fiber-Optic cable– Advantages of fiber-optic cabling

• Transmit data over long distances• Not susceptible to EMI• High transmission rates• Not susceptible to eavesdropping• Small cable size

– Disadvantages of fiber-optic cabling• Expensive• Cable can be easily damaged during install making

installations more difficult• Manual termination of ends is time consuming

Media (continued)

Media (continued)

Media (continued)

Signal Degradation

• Three internal factors of attenuation– Resistance– Inductive reactance– Capacitive reactance

• All three combined are called impedance

• External signal degradation– Electromagnetic interference (EMI)– Radio frequency interference (RFI)

Signal Degradation (continued)

• Reduce EMI/RFI– Do not place copper media next to

• Fluorescent lights• Generators/motors• High-voltage electrical wire

– Proper installation– Use quality cable– Use shielded cabling– Use repeaters to strengthen signal on long

cable runs

Horizontal Cabling Standards

• Twisted-pair or fiber-optic connections between wiring closets

• Electronic Industries Alliance and Telecommunications Industry Association (EIA/TIA)

• EIA/TIA-568– UTP horizontal cable run max: 90 meters– Horizontal cross connect max: 6 meters– Workstation to horizontal drop max: 3 meters

Horizontal Cabling Standards (continued)

Wiring Closets

• Wiring closets

• EIA/TIA-568 and EIA/TIA-569

• Catchment area

• Main distribution facility (MDF)

• Intermediate distribution facility (IDF)

Wiring Closets (continued)

• Proximity to the POP

• Backbone– Sometimes called vertical cabling– EIA/TIA-568 specifies four different cables for

backbone installations• 100-ohm UTP• 150-ohm STP• 62.5/125-micron optical fiber• Single mode optical fiber

Wiring Closets (continued)

Wiring Closets (continued)

Performance Considerations

• Connection speeds– Throughput

• Utilization– Video or audio streaming/teleconferencing– Client/server applications– Host/terminal applications– Routing protocols– Routine maintenance tasks– Broadcast traffic– Ethernet collisions

Performance Considerations (continued)

• Solutions for reducing network utilization– Segment network with switch, bridge, or

router– Reduce the number of services provided on

the network– Reduce the number of protocols on the

network– Control access to bandwidth intensive

applications or protocols

Performance Considerations (continued)

• Calculating bandwidth and throughput– Transmission Time = file size/bandwidth – (T = Fs/Bw)– Throughput = file size/download time – (Tp = Fs/Dt)

• Collisions and contention– Protocol analyzer

• Resource placement

Performance Considerations (continued)

Installing Telecommunications Connectors

Installing Telecommunications Connectors (continued)

Installing Telecommunications Connectors (continued)

Patch Panel

Patch Panel (continued)

Patch Panel (continued)

Testing Cable

• Cable testers– Wire map– Attenuation– Noise– Near end crosstalk (NEXT)– Distance measure– Baseline

• Error rates• Collision rates• Network utilization

Testing Cable (continued)

Testing Cable (continued)

Testing Cable (continued)

Testing Cable (continued)

LAN Design Models

• Two basic design strategies– Mesh– Hierarchical

• Three-layer network model– Core– Distribution– Access layer

• Two-layer network model• One-layer network model

LAN Design Models (continued)

LAN Design Models (continued)

LAN Design Models (continued)

Network Management Tools

• Common tools– Cable testers– Network monitors– Network analyzers

• Network monitors and network analyzers have in common– Agent– Manager– Administration system

Network Management Tools (continued)

• Simple Network Management Protocol (SNMP)• Management information base (MIB)• Management tasks include

– Network traffic monitoring– Automatic disconnection of problem nodes– Connection or disconnection of nodes based on time

and/or date– Port isolation for testing purposes– Remote management capabilities

• Common management information protocol (CMIP)

Network Management Tools (continued)

Network Management Tools (continued)

Network Management Tools (continued)

Summary

• There are three basic physical LAN topologies: bus, star, and ring

• These topologies, or layouts, typically involve cable, such as UTP, STP, coaxial, or fiber

• The network architecture used on a LAN defines the physical topology, the media used, and the network access method

• The most popular architectures are 10BaseT, 100baseTx and Token Ring

• The IEEE has defined many standards that have influenced the way networks are designed and implemented

Summary (continued)

• It has also defined different network access methods, which include CSMA/CD, token-passing, and CSMA/CA

• One of the largest contributions from the IEEE is the 802 standard, which has subsets that define Ethernet (802.3),Token Ring (802.5), and wireless (802.11) network architectures

• The 802.2 standard from the IEEE subdivided the OSI Data Link layer into two parts to make functional distinctions between the Media Access Control (MAC) sublayer and the Logical Link Control (LLC) sublayer

• Ethernet is also known by its access method, CSMA/CD (Carrier Sense Multiple Access with Collision Detection)

Summary (continued)

• Token Ring uses an entirely different access method that is governed by token passing

• The token, a small data frame, is passed from station to station around the ring, and a station can transmit only when it has the token

• FDDI uses token-passing like Token Ring networks, but it is not subject to the same limitations

• CSMA/CA is a network access method specified by the wireless LAN standard—802.11

• This standard supports spread spectrum and infrared technologies for use on wireless LANs

Summary (continued)

• CSMA/CA nodes listen before sending but determine when to send based on a random backoff factor

• Before transmitting, CSMA/CA nodes send a notification that they are going to transmit

• Installing media on a network is a multifaceted project

• The layout of the network should be determined and documented

• The number of wiring closets necessary, as well as their locations, must be determined

Summary (continued)

• Standards for wiring closets, cable runs, distances, and cable must be considered when the routes are established

• Obstructions and EMI/RFI must be overcome• After you install cable, you should test it for wiring,

performance, and configuration problems• Cable testers can be used to determine if cables are

wired correctly, if they meet length standards, and if they have attenuation or noise problems

• When implementing a network, you can choose one of three hierarchical network models: one-layer, two-layer, or three-layer

Summary (continued)

• The one-layer network model is the least complex, and is a flat structure where all components function at essentially the same level

• The two-layer model separates the WAN from the rest of the internal network, which is usually done by adding routers with packet filters

• In the three-layer model, the internal LANs are further divided by backbone cabling, which has additional routers with packet filters

• In this model, the WAN connection is called the core layer, the backbone cabling and routers form the distribution layer, and the individual LANs function at the access layer

Summary (continued)

• Network administrators use network monitors and network analyzers to manage a network on a daily basis

• These tools can also be used to troubleshoot abnormal situations

• The main difference between a network monitor and network analyzer is the level of service provided

• The network analyzer typically offers more advanced features, such as SNMP querying, remote administration, and even automatic problem correction