Part III - Physical Network Design
Selecting Technologies &
Devices for Campus Networks
Rab Nawaz Jadoon
Department of Computer Science
DCS
Assistant Professor
COMSATS IIT, Abbottabad
Pakistan
COMSATS Institute of
Information Technology
Telecommunication Network Design (TND)
Physical network design
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Physical network design involves the selection
of LAN and WAN technologies for campus and
enterprise network designs.
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During this phase of the top-down network design
process, choices are made regarding,
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Cabling, physical and data link layer protocols, and
internetworking devices (such as switches, routers, and
wireless access points).
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Campus Network
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A campus network is a set of LAN segments and
building networks in an area that is generally
less than a mile in diameter.
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“Physical Network Design,” is to give you information
about the scalability, performance, affordability, and
manageability characteristics of typical options, to
help you make the right selections for your particular
customer.
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LAN Cabling
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Cabling infrastructure often must last for many
years.
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It is important to design and implement the cabling
infrastructure carefully, keeping in mind availability
and scalability goals, and the expected lifetime of the
design.
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In many cases, your network design must adapt to existing
cabling.
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Cabling topologies
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Two types of cabling schemes are possible:
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A centralized cabling scheme terminates most or all
of the cable runs in one area of the design
environment.
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A star topology is an example of a centralized system.
A distributed cabling scheme terminates cable runs
throughout the design environment.
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Ring, bus, and mesh topologies are examples of distributed
systems.
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Building-Cabling Topologies
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Within a building, either a centralized or
distributed architecture can be used, depending
on the size of the building.
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For small buildings, a centralized scheme with all
cables terminating in a communications room on one
floor is possible.
A centralized scheme offers good manageability
but does not scale.
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For larger buildings, a distributed topology is more
appropriate.
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Building-Cabling Topologies
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Many LAN technologies make an assumption
that workstations are no more than 100 meters
from a telecommunications closet where hubs
or switches reside.
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For this reason, in a tall building with large floors, a distributed
topology is more appropriate
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Campus Cabling Topologies

The cabling that connects buildings is exposed
to more physical hazards than the cabling
within buildings.
A construction worker might dig a trench between
buildings and unintentionally cut cables.
 Flooding, ice storms, earthquakes, and other natural
disasters can also cause problems, as can manmade
disasters such as terrorist attacks.
 In addition, cables might cross properties outside the
control of the organization, making it hard to
troubleshoot and fix problems.
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For these reasons, cables and cabling topologies should be
selected carefully.
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Campus Cabling Topologies
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A distributed scheme offers better availability
than a centralized scheme.
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The centralized topology in Figure (next slide) would
experience a loss of all interbuilding communication
if the cable bundle between Buildings A and B
broken/cutted.
With the distributed topology, interbuilding
communication could resume if a cable cut between
Buildings A and B occurred.
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Campus Cabling Topologies
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Types of Cables
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Campus network implementations use three
major types of cables.
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Shielded copper, including shielded twisted-pair
(STP), coaxial (coax), and twinaxial (twinax) cables.
Unshielded copper (typically UTP) cables
Fiber-optic cables
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Categories of UTP
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LAN Technologies
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Ethernet Basics
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Since its invention in the 1970s by Xerox Corporation,
Ethernet has gained widespread popularity and adapted to
new demands for capacity, reliability, and low prices.
An Ethernet LAN that is accurately provisioned to meet
bandwidth requirements and outfitted with high-quality
components, including NICs, cables, and internetworking
devices, can meet even the most stringent demands for
availability.
Many troubleshooting tools, including cable testers, protocol
analyzers, and network management applications, are
available for isolating the occasional problems caused by
cable breaks, electromagnetic interference, failed ports, or
misbehaving NICs.
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Ethernet standards w.r.t media
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Selecting internetworking devices
for campus networks
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In most cases, the choice will be between a
switch and a router.
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Hubs and bridges are generally no longer used,
although hubs are sometimes placed in a network to
facilitate tapping into a network for protocol analysis,
and bridges are still sometimes used in wireless
networks.
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Comparison of internetworking
devices
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Comparison of internetworking
devices
After you have designed a network topology and made some decisions about
the placement and scope of shared, switched, and routed network segments,
you should then recommend actual switches, bridges, and routers from
various vendors.
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Criteria of selecting internetworking
devices for campus
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Criteria for selecting internetworking devices in
general include the following:
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Number of ports
Processing speed
Amount of memory
Amount of latency introduced when the device relays
data
Throughput in packets per second
Ingress/egress queuing and buffering techniques
LAN and WAN technologies supported
Autosensing of speed (for example, 10 or 100 Mbps)
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Criteria of selecting internetworking
devices for campus
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Auto detection of half- versus full-duplex operation
Media (cabling) supported
Ease of configuration
Cost
Mean time between failure (MTBF) and mean time to
repair (MTTR)
Support for packet filters and other security
measures
Support for hot-swappable components
Support for in-service software upgrades
Support for redundant power supplies
Support for optimization features
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Criteria of selecting internetworking
devices for campus
Support for QoS features
 Availability and quality of technical support
 Availability and quality of documentation
 Reputation and viability of the vendor
 Availability of independent test results that confirm
the performance of the device
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For switches and bridges
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For switches and bridges (including wireless
bridges), the following criteria can be added to
the first bulleted list in this section:
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Bridging technologies supported (transparent
bridging, Spanning Tree Algorithm, remote bridging,
and so on)
Advanced spanning-tree features supported (rapid
reconfiguration of spanning trees and multiple
spanning trees [802.1s])
The number of MAC addresses that the switch or
bridge can learn
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For switches and bridges
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Support for stacking or virtual switching where
multiple switches can be managed as one switch
Support for port security (802.1X)
Support for cut-through switching
Support for adaptive cut-through switching
VLAN technologies supported, such as the VLAN
Trunking Protocol (VTP) and IEEE 802.1Q (VLAN on
ethernet network)
Support for multicast applications (for example, the
ability to participate in the Internet Group
Management Protocol [IGMP] to control the spread
of multicast packets)
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For switches and bridges
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Amount of memory available for switching tables,
routing tables (if the switch has a routing module),
and memory used by protocol routines
Availability of a routing module
802.3af Power over Ethernet (PoE) or 802.3at PoE+
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For routers
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For routers selection
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Network layer protocols supported
Routing protocols supported
Support for multicast applications
Support for advanced queuing, switching, and other
optimization features
Support for compression (and compression
performance if it is supported)
Support for encryption (and encryption performance
if it is supported)
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For wireless access points and
bridges
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For wireless access points and bridges, the
following criteria can be added to the first
bulleted list in this section:
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Wireless speeds supported (11 Mbps, 5.5 Mbps, 54
Mbps, and 600 Mbps)
Wireless standards supported (802.11a, 802.11b,
802.11g, and 802.11n)
Speed of uplink Ethernet port
Support for Dynamic Host Configuration Protocol
(DHCP), Network Address Translation (NAT), and IP
routing
Support for VLANs
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For wireless access points and
bridges
Support for inline power over Ethernet if the access
point is unlikely to be mounted near power outlets
 Antenna range and support for higher-end antenna
attachments
 Transmit power and receive sensitivity
 Ability to tune the transmit power
 Availability of a rugged model for outside use
 Support for authenticating client devices by MAC
address
 An option for disabling Service Set Identifier (SSID)
broadcasts
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For wireless access points and
bridges
Support for 128-bit or better encryption
 Support for Publicly Secure Packet Forwarding (PSPF)
 Support for security standards such as WPA or
802.11i
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