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Network Topologies
• LANs and WANs - Geographical coverage
• LANs
- A single geographical location, such as office building,
school, etc
- Typically High speed and cheaper.
• WANs
- Spans more than one geographical location often
connecting separated LANs
- Slower
- Costly hardware, routers, dedicated leased lines and
complicated implementation procedures.
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Network Topologies
• Topology - Physical and logical network
layout
– Physical – actual layout of the computer cables
and other network devices
– Logical – the way in which the network appears
to the devices that use it.
• Common topologies:
– Bus, ring, star, mesh and wireless
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Bus topology
- Uses a trunk or backbone to which all of the computers on
the network connect.
- Systems connect to this backbone using T connectors or
taps.
- Coaxial cablings ( 10Base-2, 10Base5) were popular
options years ago.
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Bus Topology
Does not use any specialized network Difficult to troubleshoot. equipment.
A break in the cable will prevent all systems from accessing the network.
Require less cable
Network disruption when computers are added or removed
Cheap and easy to implement
Advantages Disadvantages
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Star Topology
• All computers/devices connect to a central
device called hub or switch.
• Each device requires a single cable
• point-to-point connection between the
device and hub.
• Most widely implemented
• Hub is the single point of failure
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Star Topology
Easy to troubleshoot and isolate More difficult to implement problems
A central connecting device allows for a single point of failure
Cable failure affects only a single user
Easily expanded without disruption Requires more cable to the network
Advantages Disadvantages
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Mesh Topology
• Each computer connects to every other.
• High level of redundancy.
• Rarely used.
- Wiring is very complicated
- Cabling cost is high
- Troubleshooting a failed cable is tricky
- A variation hybrid mesh – create point to point
connection between specific network devices, often
seen in WAN implementation.
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Mesh Topology
The network can be expanded Complicated implementation without disruption to current uses
Requires more cable than the other LAN topologies
Provides redundant paths between devices
Advantages Disadvantages
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IEEE and Networking standards
• Institute of Electrical and Electronic
Engineers (IEEE) developed a series of
networking standards
– Networking technologies developed by
manufacturers are Compatible
– Cabling, networking devices and protocols are
all interchangeable under the banner of a
specific IEEE
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802.12 100Mbps technologies, including 100BASEVG-AnyLAN
802.11 Wireless networks
Standards for Interoperable LAN/MAN Security (SILS) (Network Security)
802.9 Integrated Voice and Data Networks
802.8 Fiber-Optic Technical Advisory Group
802.7 Broadband Technical Advisory Group
802.6 Metropolitan Area Network (MAN)
802.5 Token Ring networks
802.4 A token passing bus
CSMA/CD ( Carrier Sense Multiple Access with Collision Detection) for Ethernet networks
802.2 The LLC(Logincal Link Control) sublayer
802.1 Internetworking
Specification Name
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802.3 IEEE standard
- Defines characteristics for Ethernet networks.
- New additions,
- 802.3u for Fast Ethernet
- 802.3z for Gigabit Ethernet, referred to as 802.3x.
- … …
- 802.3ac 10gbits/s, expe. 2009
- … …
- Speed: Original 10Mbps, Fast Ethernet 100Mbps, Gigabit Ethernet
1000Mbps
- Topology: bus or star.
- Media: Coaxial and twisted pair cabling, also fiber optic cable.
- Access method: CSMA/CD
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802.5 IEEE standard
• Specifies the characteristics for Token Ring
Networks.
• Introduced by IBM in the mid 80s, network
topology of choice until the rise of the popularity
of Ethernet.
• Speed: 4 to 16Mbps
• Topology: logical ring and most often a physical
star. Logical ring is often created in the
Multistation Access Unit (MSAU)
• Media: twisted pair cabling.
• Access method: token passing.
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Token passing
Fiber-optic Twisted pair/CDDI
FDDI 100Mbps Dual Ring Ring
802.11b 11Mbps Wireless Bus Radio waves CSMA/CA
Token passing
4Mbps and Star Ring Twisted pair 16Mbps
(802.3z) 1000Mbps Star Bus Twisted pair CSMA/CD
100Mbps( Fast Star Bus Twisted pair CSMA/CD Ethernet)
(802.3u)
Coaxial and CSMA/CD Twisted pair
802.3 10Mbps Bus and Star
Access Method
Logical Media Topology
Physical Topology
Standard Speed
