part iii - physical network design selecting … · selecting technologies & devices for campus...

Department of Computer Science

DCS

COMSATS Institute of Information Technology

Selecting Technologies &

Devices for Campus Networks

Rab Nawaz JadoonAssistant Professor

COMSATS IIT, Abbottabad

Pakistan

Telecommunication Network Design (TND)

Part III - Physical Network Design


Physical network design

Physical network design involves the selection of LAN and WAN technologies for campus and enterprise network designs.

During this phase of the top-down network design process, choices are made regarding,

Cabling, physical and data link layer protocols, and internetworking devices (such as switches, routers, and wireless access points).

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Campus Network

A campus network is a set of LAN segments and building networks in an area that is generally less than a mile in diameter.

“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

Cabling infrastructure often must last for many years.

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.

In many cases, your network design must adapt to existing cabling.

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Cabling topologies

Two types of cabling schemes are possible:

A centralized cabling scheme terminates most or all of the cable runs in one area of the design environment.

A star topology is an example of a centralized system.

A distributed cabling scheme terminates cable runs throughout the design environment.

Ring, bus, and mesh topologies are examples of distributed systems.

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Building-Cabling Topologies

Within a building, either a centralized or distributed architecture can be used, depending on the size of the building.

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.

For larger buildings, a distributed topology is more appropriate.

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Building-Cabling Topologies

Many LAN technologies make an assumption that workstations are no more than 100 meters from a telecommunications closet where hubs or switches reside. 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.

For these reasons, cables and cabling topologies should be selected carefully.

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A distributed scheme offers better availability than a centralized scheme.

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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Types of Cables

Campus network implementations use three major types of cables.

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

Ethernet Basics 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

In most cases, the choice will be between a switch and a router.

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

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After you have designed a network topology and made some decisions aboutthe placement and scope of shared, switched, and routed network segments,you should then recommend actual switches, bridges, and routers fromvarious vendors.


Criteria of selecting internetworking devices for campus

Criteria for selecting internetworking devices in general include the following:

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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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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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

For switches and bridges (including wireless bridges), the following criteria can be added to the first bulleted list in this section:

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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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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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

For routers selection

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

For wireless access points and bridges, the following criteria can be added to the first bulleted list in this section:

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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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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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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