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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.
Physical Topologies:Physical Topologies:BusBus
• 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.
Physical Topologies:Physical Topologies:BusBus
• 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
Physical Topologies:Physical Topologies:StarStar
• 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
Physical Topologies:Physical Topologies:StarStar
• 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.
Physical Topologies:Physical Topologies:Star/Bus/TreeStar/Bus/Tree
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.
•
Physical Topologies:Physical Topologies:RingRing
• 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.
•
Physical Topologies:Physical Topologies:RingRing
• Data travels from node to node, with each node handling every packet.
Physical Topologies:Physical Topologies:RingRing
• 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
Physical Topologies:Physical Topologies:RingRing
• 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
Physical Topologies:Physical Topologies:RingRing
• 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.
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
Unshielded Twisted-Pair (UTP)Unshielded Twisted-Pair (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
Unshielded Twisted-Pair (UTP)Unshielded Twisted-Pair (UTP)
• 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
Coaxial CablingCoaxial Cabling
• 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
Coaxial CablingCoaxial Cabling
• 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.
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 CableFiber-Optic Cable
• 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 CableFiber-Optic Cable
• 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
Horizontal Cabling StandardsHorizontal Cabling Standards
• 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
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
Installing Telecommunication Installing Telecommunication ConnectorsConnectors
Figure 4-12:UTP wires
Installing Telecommunication Installing Telecommunication ConnectorsConnectors
Figure 4-13: Jack wiring
Installing Telecommunication Installing Telecommunication ConnectorsConnectors
• 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
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: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: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
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
LAN Design ModelsLAN Design Models
• 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
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
Network-Management ToolsNetwork-Management Tools
• The most common network-management tools are:– Cable testers– Network monitors– Network analyzers
Table 4-4: Monitor and analyzer
Network-Management ToolsNetwork-Management Tools
• 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