Network topology architectureb

Network Topology and Network Topology and DesignDesign

ObjectivesObjectives

• Discuss the different physical topologies

• Determine which type of network media to use given a set of requirements

• Consider performance requirements and improvements for given situations

Network TopologyNetwork Topology

• Topology

There are two types of topology:

physical and logical.

• The physical topology of a network refers to the configuration of cables, computers, and other peripherals.

• Logical topology is the method used to pass the information between workstations.

Physical Topologies:Physical Topologies:BusBus

• All devices are connected to a central cable, called the bus or backbone. Bus networks are relatively inexpensive and easy to install for small networks. It has a single cable with terminators at each end.


• A bus topology connects all stations in a linear fashion

Figure 4-1: Bus topology

Terminator - A device that provides electrical resistance at the end of a transmission line. Its function is to absorb signals on the line, thereby keeping them from bouncing back and being received again by the network.


• Bus topology advantages:– It is inexpensive– It is easy to design and implement because the

stations are simply daisy-chained together

• Bus topology disadvantages:– It is difficult to troubleshoot– It requires termination

Physical Topologies:Physical Topologies:StarStar

• The star network configuration is the most popular physical topology

• In a star configuration, all computers or stations are wired directly to a central location:– Concentrator (a.k.a. hub)– Multistation Access Unit (MAU)

• A data signal from any station goes directly to this central device, which transmits the signal according to the established network access method for the type of network

• The protocols used with star configurations are usually Ethernet or LocalTalk

http://fcit.usf.edu/Network/glossary.htm#ethernet

http://fcit.usf.edu/Network/glossary.htm#local_talk


Figure 4-2:Star topology


• Star topology advantages:– A break in one cable does not affect all other

stations as it does in bus technologies– Problems are easier to locate because symptoms

often point to one station– The second-easiest topology to design and install– Does not require manual termination

• Instead the media is terminated in the station at the transceiver on the NIC and in the hub or MAU


• Star topology disadvantages:– Hubs, which are required for a star topology, are

more expensive than bus connectors– A failure at the hub can affect the entire

configuration and all connected stations– Uses more cable than bus topologies

Physical Topologies:Physical Topologies:Star/bus/TreeStar/bus/Tree

• Bus and star topologies can be combined to form a star/bus or bus/star physical topology

• Hubs that have connectors for coaxial cable as well as for twisted-pair wiring are used to form these types of networks

• When different physical topologies are applied to a network, the result is often called a mixed media network

Physical Topologies:Physical Topologies:Star/Bus/TreeStar/Bus/Tree


Advantages of a Tree Topology

• Point-to-point wiring for individual segments.

• Supported by several hardware and software vendors.


Disadvantages of a Tree Topology

• Overall length of each segment is limited by the type of cabling used.

• If the backbone line breaks, the entire segment goes down.

• More difficult to configure and wire than other topologies.

Physical Topologies:Physical Topologies:RingRing

• A ring network is a network topology in which each node connects to exactly two other nodes, forming a circular pathway for signals - a ring. Data travels from node to node, with each node handling every packet.

• Because a ring topology provides only one pathway between any two nodes, ring networks may be disrupted by the failure of a single link.

•

http://www.answers.com/topic/network-topology-1


• A system of which each node or station is connected to two others, ultimately forming a loop (circular pathway for signals).

• Data are passed in one direction only, being received by each node and then transferred to the next node.

•


• Data travels from node to node, with each node handling every packet.


• Physical rings– Most often seen in Fiber Distributed Data

Interface (FDDI) networks• FDDI is a WAN technology

– Stations on a ring are wired to one another in a circle around the entire network


• Ring topology advantages:– It prevents network collisions because of the

media access method or architecture required

– Each station functions as a repeater, so the topology does not require additional network hardware, such as hubs


• Ring topology disadvantages:– As in a bus network, a failure at one point can

bring down the network– Because all stations are wired together, to add a

station the network must be shut down temporarily

– Maintenance on a ring is more difficult than on a star topology because an adjustment or reconfiguration affects the entire ring

Physical Topologies:Physical Topologies:

Considerations When Choosing a Topology:

• Money. A linear bus network may be the least expensive way to install a network; you do not have to purchase concentrators.

• Length of cable needed. The linear bus network uses shorter lengths of cable.

• Future growth. With a star topology, expanding a network is easily done by adding another concentrator.

• Cable type. The most common cable is unshielded twisted pair, which is most often used with star topologies.

WAN TopologiesWAN Topologies

Figure 5-7: WAN topologies

Influence of the 5-4-3 Rule on Influence of the 5-4-3 Rule on TopologiesTopologies

• 5-4-3 rule states that between stations on a LAN, there can be no more than five network segments connected, maximum number of repeaters is four, and maximum number of segments with stations on them is three

Figure 4-3: 5-4-3 rule

Influence of the 5-4-3 Rule on Influence of the 5-4-3 Rule on TopologiesTopologies

Figure 4-4: Mixed topologies

Twisted-Pair CablingTwisted-Pair Cabling

• Common traits of all twisted-pair cabling types and categories:– The wires are copper– The wires come in pairs– The pairs of wires are twisted around each other– The pairs of wires are usually enclosed in a cable

sheath individually and as a group of wires

Twisted-Pair CablingTwisted-Pair Cabling

• Crosstalk– Signal bleed from one cable to another– Usually occurs in poorly wired media

• Cancellation– Insulates the signal from the effects of signal

bleeding

Unshielded Twisted-Pair (UTP)Unshielded Twisted-Pair (UTP)

• Cabling used for a variety of electronic communications

Table 4-1: Categories of UTP


• UTP advantages:– Thin flexible cable that is easy to string between

walls– Most modern buildings come with CAT 5 UTP

already wired into the wall outlets or at least run between the floors

– Because UTP is small, it does not quickly fill up wiring ducts

– Costs less per foot than other type of LAN cable


• UTP disadvantages:– More susceptible to interference than most other

types of cabling• Pair twisting does help, but it does not make the cable

impervious to electrical noise

– Its unrepeated length limit is 100 meters

RJ-45 ConnectorsRJ-45 Connectors

• Registered Jacks (RJ)– Type of telecommunication connector used for

twisted-pair cabling

– Typically RJ-45 connectors resemble the typical RJ-11 connectors that connect the phone to the wall

• Difference between RJ-45 connectors and RJ-11 connectors is that the former has eight wires (four-pair) and the latter four (two-pair)

– Some RJ-11 connectors are used with three-pair (six-wire) UTP

Shielded Twisted-Pair (STP)Shielded Twisted-Pair (STP)

• Cabling often seen in Token Ring networks

• Similar to UTP in that the wire pairs are twisted around each other inside the cable

• The advantage of STP over UTP is that it has greater protection from interference and crosstalk due to the shielding

Shielded Twisted-Pair (STP)Shielded Twisted-Pair (STP)

• STP disadvantages as compared to UTP include:– A higher cost per foot– The shield must be grounded at one end

• Improper grounding can cause serious interference

– Heavier and less flexible– Because of its thickness, STP may not fit down

narrow cable ducts

Coaxial CablingCoaxial Cabling

• Consists of either:– A solid inner core (often made of copper)– Wire strand conductor surrounded by insulation

• The two most commonly used coaxial cable:– Thicknet– Thinnet


• Advantages of coaxial cabling on a LAN include:– The segment lengths are longer than UTP or STP– Coaxial cable has greater interference immunity

than UTP– Hubs between stations are not required


• Disadvantages of coaxial cable:– Not as easy to install as UTP– More expensive than UTP– Supports a maximum bandwidth of only 10 Mbps– Requires more room in wiring ducts than UTP– Is relatively difficult to troubleshoot thinnet and

thicknet networks– Connectors can be expensive.– It is easily damaged and sometimes difficult to work

with, especially in the case of thick coaxial.– Baseband coaxial cannot carry integrated voice, data,

and video signals.


Table 4-2: Coaxial cable types

Thinnet and Thicknet ConnectorsThinnet and Thicknet Connectors

• The most common connectors for RG-58 cabling on thinnet networks are:– Barrel connectors– T-connectors– Terminators

• BNC– Hardware connector for coaxial cable with a

cylindrical shell with two small knobs allowing it to be locked into place when twisted

Thinnet and Thicknet ConnectorsThinnet and Thicknet Connectors

• Attachment unit interface (AUI) port– A 15-pin physical

connector interface between a computer’s network NIC and an Ethernet networking that uses 10Base5 coaxial cableFigure 4-6: Thinnet connectors

Fiber-Optic CableFiber-Optic Cable

• Carries light pulses rather than electrical signals long its fibers

• Made of glass or plastic fibers, rather than copper wire like most other network cabling

• Core of the cable is usually pure glass– Surrounding the glass is a layer of cladding made

of glass or plastic, which traps the light in the core


• Fiber-optic cabling advantages:– Can transmit over long distances– Not susceptible to electromagnetic interference or

crosstalk– Supports extremely high transmission rates– Cable has a smaller diameter and can be used in

narrow wiring ducts– Not susceptible to eavesdropping


• Fiber-optic cabling disadvantages:– More expensive than other types of networking

media– More difficult and more expensive to install than

any other network media– Because it is fragile, it must be installed carefully

and protected after installation

Signal DegradationSignal Degradation

• Degradation sources can be internal or external

• When signals degrade over distance, attenuation results

• Three internal factors can cause attenuation:– Resistance

– Inductive reactance

– Capacitive reactance

Signal DegradationSignal Degradation

• When the internal opposition forces are combined and measured, the measure is called impedance– External forces affecting network signals include:

– Electromagnetic interference (EMI)

– Radio frequency interference (RFI)

– Both types of interference can degrade and corrupt network signals as they travel through a wire

Ways to Reduce EMI/RFI on Ways to Reduce EMI/RFI on Network CablingNetwork Cabling

• Keep network media away from sources of EMI

• Ensure that network media is installed properly

• Use shielded cabling

• Use repeaters

• Ensure that you install high-quality cabling

Horizontal Cabling StandardsHorizontal Cabling Standards

• Horizontal cabling– The twisted-pair or fiber-optic media connecting

workstations and wiring closets

• Electronics Industries Alliance and Telecommunications Industry Association (EIA/TIA)– Defines a set of specifications, EIA/TIA-568, which

covers outlets near the workstation, mechanical terminations in wiring closets, and all cable running along the horizontal path between wiring closet and workstation


Figure 4-7: Horizontal cabling


• EIA/TIA-568B– Specifies that the maximum distance for a UTP

horizontal cable run is 90 meters (295 feet)– Also, patch cords (a.k.a. patch cables) located at

any cross-section cannot exceed six meters (20 feet)

• In addition to UTP, the following cable types may be used for horizontal pathways:– STP – two pairs of 150-ohm cabling– Fiber-optic – a two-fiber 62.5/125 multimode cable

Wiring ClosetsWiring Closets

• Contain the wiring and wiring equipment for connecting network devices, such as routers, bridges, switches, patch panels, and hubs

• EIA/TIA-568 and EIA/TIA-569 standards apply to the physical layout of media and wiring closets, with the latter stating there must be a minimum of one wiring closet per floor– Furthermore, when a given floor area (catchment area)

exceeds 1,000 square meters, or the horizontal cabling more than 90 meters, additional wiring closets are needed

Wiring ClosetsWiring Closets

• The main distribution facility (MDF) is the central junction point for wiring of a star topology

• The additional closets are called intermediate distribution facilities (IDFs)

• IDFs are required when:– Catchment area of MDF is not large enough to capture all

nodes

– The LAN is in a multistory facility

– The LAN encompasses multiple buildings

Proximity to the POPProximity to the POP

• Ensure that main wiring closet is close to the point of presence (POP) to the Internet

Figure 4-8: Network spanning multiple buildings

Proximity to the POPProximity to the POP

Figure 4-9: Network spanning multiple floors

BackboneBackbone

• Backbone cable (sometimes called vertical cabling) connects wiring closets to each other in an extended star topology

• EIA/TIA-568 specifies four different options for backbone cabling:– 100-ohm UTP– 150-ohm STP– 62.5/125-micron optical fiber– Single-mode optical fiber

Performance Considerations:Performance Considerations:Connection SpeedsConnection Speeds

• The real capacity of a network is sometimes referred to as throughput

• Factors affecting throughput include:– Type of network devices being used on the network

– Number of nodes

– Power issues

– Network architecture

– Other variables

Performance Considerations:Performance Considerations:UtilizationUtilization

• Potential causes of high utilization:– Video or audio streaming/teleconferencing– Client/server applications– Host/terminal applications– Routing protocols– Routine maintenance tasks– Broadcast traffic– Ethernet collisions

Performance Considerations:Performance Considerations:UtilizationUtilization

• Solutions for reducing network utilization include:– Segmenting a network with connectivity

– Reducing number of services provided on the segment

– Reducing number of protocols in use on the segment

– Disabling bandwidth-intensive applications or protocols

– Relocating systems consuming the most bandwidth on the segment

Performance Considerations:Performance Considerations:Calculating Bandwidth and ThroughputCalculating Bandwidth and Throughput

• When considering an organization’s bandwidth requirements, discover types of bandwidth-intensive communications conducted on its network

• Transmission time– Time it takes a file to transfer from one location to

another

Performance Considerations:Performance Considerations:Collisions and ContentionCollisions and Contention

• All stations on an Ethernet segment must share the available connection with each other– This means the stations contend with one another for

the opportunity to transmit on the wire

• When considering upgrading an existing network, check the rate of collisions on the network using a protocol analyzer or other network performance-monitoring tool

Performance Considerations:Performance Considerations:Resource PlacementResource Placement

Figure 4-10: Resource placement

Installing Telecommunication Installing Telecommunication ConnectorsConnectors

Figure 4-11:RJ-45 connector


Figure 4-12:UTP wires


Figure 4-13: Jack wiring


• EIA/TIA-568A– Wiring method used to indicate which colors are

assigned to which pin for UTP cable

• Punch tool– Used to punch down cable at the patch panel or

RJ-45 wall jack

Patch PanelPatch Panel

Figure 4-14: Patch panel pins

Patch PanelPatch Panel

Figure 4-15: Patch panel ports

Figure 4-16:110 punch tool

Cable Testers:Cable Testers:Wire MapWire Map

• Important measurement a cable tester makes to check wiring sequence

Table 4-3:Wire map error detection

Cable Testers:Cable Testers:Wire MapWire Map

Figure 4-17: Crossed pairs

Figure 4-18: Split pairs

Cable Testers:Cable Testers:AttenuationAttenuation

• Attenuation is the loss of signal power over the distance of a cable

• Signal injector– Puts traffic on a wire so that a cable tester can

measure attenuation and crosstalk

• The lower the attenuation, the better

Cable Testers:Cable Testers:NoiseNoise

• Alternating current (AC) signal noises are called oscillations and can alter the digital signals that computers receive on the wire

• The motherboard and other internal integrated circuits of a computer use the chassis as their ground

• Faulty AC wiring can also cause problems with transmissions because the signal reference ground is the computer chassis and grounding plate

• A transformer steps voltage up or down where the hot lead originates and the neutral wire is grounded

Cable Testers:Cable Testers:NEXTNEXT

• Near end crosstalk (NEXT)– Measure of interference from other wire pairs

• Causes of NEXT include:– Split pairs– Too much wire untwisted at the patch panel, jack,

or connectors– Bends, kinks, or stretches in the cabling

Cable Testers:Cable Testers:NEXTNEXT

Figure 4-19: NEXT test on a cable analyzer

Cable Testers:Cable Testers:Distance MeasureDistance Measure

• EIA/TIA-568A specifies maximum cable lengths for network media

• Cables that are too long can cause delays in transmission and network errors

• Time-domain reflectometer (TDR)– Cable tester that can detect the overall length of a

cable or the distance to a cable break

Cable Testers:Cable Testers:BaselineBaseline

• Take baseline measurements to tell how well the network is performing at a given moment

• Baseline measurements can include:– Error rates– Collision rates– Network utilization

Network ArchitectureNetwork Architecture

• Logical topology– Describes the way a signal travels in a network,

which is a function of the access method• Usually a bus or a ring

• IEEE 802– Covers issues concerning all types of networks

• LAN, MAN, WAN, and wireless

Logical Link Control (IEEE 802.2)Logical Link Control (IEEE 802.2)

• In the IEEE 802.2 specification, the Data Link layer is divided into:– The Media Access Control (MAC) sublayer– The Logical Link Control (LLC) sublayer

• LLC sublayer is closer to software components of the protocol stack because it controls data link communications and defines Service Access Points (SAP)

• MAC sublayer is closer to the underlying hardware architecture

Logical Link Control (IEEE 802.2)Logical Link Control (IEEE 802.2)

Figure 4-20: 802.2 specification

CSMA/CD (802.3)CSMA/CD (802.3)

• IEEE 802.3 defines the access method used by most Ethernet networks

• Jam signal– 32-bit message to all computers on an Ethernet network

that tells all stations not to transmit

• 10BaseT– Describes an Ethernet network connected by twisted-pair

cable that can support transmissions of 10 Mbps using baseband (digital) signals

CSMA/CD (802.3)CSMA/CD (802.3)

• 10Base2– Also known as thin Ethernet

• 10Base5– Also known as thick Ethernet

• Fast Ethernet– Also known as 100BaseT

• Gigabit Ethernet– A more recent addition to the IEEE 802.3

specifications

Token Ring (802.5)Token Ring (802.5)

• In the 802.5 specification, Token Ring networks use token-passing to keep track of which node is communicating

• Star-ring– Network architecture utilizing physical star topology with

logical ring topology

• Nearest active upstream neighbor (NAUN)• Nearest active downstream neighbor (NADN)

Token Ring (802.5)Token Ring (802.5)

• Active monitor– Computer in a Token Ring network that is

powered on first and that manages the beaconing process

• Beaconing– Fault-detection method implemented in Token

Ring networks

Wireless Technologies (802.11)Wireless Technologies (802.11)

• The 802.11 standard for wireless LANs specifies parameters at both Physical and Data Link layers of OSI model

• At the Physical layer, infrared (IR) or spread spectrum technologies are supported

• At the Data Link layer, 802.11 specifies Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) as the network access method

FDDIFDDI

• Fiber Distributed Data Interface (FDDI) standard– Responsibility of the American National

Standards Institute (ANSI)– Describes a network that can span up to 100

kilometers (62 miles) over single-mode fiber-optic cabling

– Based on the Token Ring (802.5) specification but with different limitations

LAN Design ModelsLAN Design Models

• You can choose many different network design models to implement on your network

• There are two basic designs strategies that are typically followed:– Mesh design– Hierarchical design


Figure 4-21: Mesh network design


• Compared to a mesh design, a hierarchical design:– Is easier to manage– Is easier to troubleshoot– Has improved scalability– Allows easier analysis

Three-Layer Network ModelThree-Layer Network Model

• Divides a network into three connectivity layers

• Consists of:– Core layer– Distribution layer– Access layer

Three-Layer Network ModelThree-Layer Network Model

Figure 4-22: Three-layer network model

Two-Layer Network ModelTwo-Layer Network ModelOne-Layer Network ModelOne-Layer Network Model

• Two-layer network model– Divides a network into two connectivity layers:

• Core

• Access

• One-layer network model– Includes WAN connectivity equipment and organizes

a network so that is can be easily adapted to the two-layer and three-layer design models in the future

Two-Layer Network ModelTwo-Layer Network Model

Figure 4-23: Two-layer network model

One-Layer Network ModelOne-Layer Network Model

Figure 4-24: One-layer network model

Network-Management ToolsNetwork-Management Tools

• The most common network-management tools are:– Cable testers– Network monitors– Network analyzers

Table 4-4: Monitor and analyzer


Table 4-4 (cont.): Monitor and analyzer


• Other sophisticated network-management tools can be used for daily network-management and control functions

• These tools typically have three components:– Agent– Manager– Administration system

Simple Network Management Simple Network Management Protocol (SNMP)Protocol (SNMP)

• A Management Information Base (MIB) is a database that maintains statistics and information the SNMP reports and uses

Figure 4-25:SNMP in action

Simple Network Management Simple Network Management Protocol (SNMP)Protocol (SNMP)

• 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

CMIPCMIP

• Common Management Information Protocol

• Similar to SNMP in that it uses the MIB to monitor the network

• Not as widely implemented as SNMP

• More efficient than SNMP because the client reports the information to the management device

Chapter SummaryChapter Summary

• There are three basic physical LAN topologies

• These topologies typically involve cable

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

• One of the largest contributions from the IEEE is the 802 standard

Chapter SummaryChapter Summary

• Installing media on a network is multifaceted project

• Obstructions and EMI/RFI must be overcome• When implementing a network, you can

choose on of three hierarchical models• Network administrators use network monitors

and network analyzers to manage a network on daily basis

Technology

Network topology architectureb