Department of Computer Science
DCS
COMSATS Institute of Information Technology
Analyzing the Existing
Internetwork
Rab Nawaz JadoonAssistant Professor
COMSATS IIT, Abbottabad
Pakistan
Telecommunication Network Design (TND)
Department of Computer Science
Examining the existing network
Examining the existing network includes learning about the topology and physical structure and assessing the network’s performance.
Identifying internetworking devices and links that will need to be replaced because the number of ports or capacity is insufficient for the new design.
Identifying performance problems can help you select solutions to solve problems and develop a baseline for future measurements of performance.
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Department of Computer Science
Examining the existing network
Most network designers do not design networks from scratch.
Instead, they design enhancements to existing networks.
Developing a successful network design requires that you develop skills in characterizing the serving network to ensure interoperability between the existing and anticipated networks.
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Department of Computer Science
Characterizing the network infrastructure
Developing a set of network maps and learning the location of major internetworking devices and network segments.
It also includes documenting the names and addresses of major devices and segments, and identifying any standard methods for addressing and naming.
Documenting the types and lengths of physical cabling and investigating architectural and environmental constraints (specially in wireless environment) are also important aspects of characterizing the network infrastructure.
Network mapping software: http://www.spiceworks.com/free-network-mapping-software/
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Characterizing Large Internetworks
Developing many maps, one for each location.
Another approach is to apply a top-down method.
Start with a map or set of maps that shows the following high-level information.
Geographical information, such as countries, states or provinces, cities, and campuses.
WAN connections between countries, states, and cities
WAN and LAN connections between buildings and between campuses.
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Department of Computer Science
Mapping of Campus
For campus building, the map should have the followings,
Buildings and floors, and possibly rooms or cubicles
The location of major servers or server farms
The location of routers and switches
The location of firewalls, Network Address Translation (NAT) devices, intrusion detection systems (IDS), and intrusion prevention systems (IPS)
The location of mainframes
The location of major network-management stations
The location and reach of virtual LANs (VLAN).
Second method that is influenced by OSI reference model (Layer wise mapping or modeling)
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Characterizing Network Addressing and naming
When drawing detailed network maps, include the names of major sites, routers, network segments, and servers.
Also document any standard strategies your customer uses for naming network elements.
For example, some customers name sites using airport codes (San Francisco = SFO, Oakland = OAK, and so on).
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Department of Computer Science
Characterizing Network Addressing and naming
You should also investigate the network layer addresses your customer uses.
Your customer’s addressing scheme (or lack of any scheme) can influence your ability to adapt the network to new design goals.
For example, your customer might use unregistered IP addresses that will need to be changed or translated before connecting to the Internet.
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Department of Computer Science
Characterizing Wiring and Media
Understand the cabling design and wiring of the existing network.
Existing cabling design can help you plan for enhancements and identify any potential problems.
While exploring the cabling design, assess how well equipment and cables are labeled in the current network.
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Department of Computer Science
Characterizing Wiring and Media
The diagram/map should include information on the number of pairs of wires and the type of wiring (or wireless technology) in use.
The diagram should also indicate how far buildings are from one another. Distance information can help you select new cabling.
For example, if you plan to upgrade from copper to fiber cabling, the distance between buildings can be much longer.
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Department of Computer Science
Checking Architectural and Environmental Constraints
When investigating cabling, pay attention to such environmental issues as the possibility that cabling will run,
near creeks that could flood,
railroad tracks or highways where traffic could jostle cables, or
construction or manufacturing areas where heavy equipment or digging could break cables.
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Department of Computer Science
Cont…
Be sure to determine if there are any legal right-of-way issues that must be dealt with before cabling can be put into place.
For example,
Will cabling need to cross a public street?
Will it be necessary to run cables through property owned by other companies?
For line-of-sight technologies, such as laser or infrared, make sure there aren’t any obstacles blocking the line of sight.
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Checking a Site for a Wireless Installation
A common goal for modern campus network designs is to install a wireless LAN (WLAN) based on IEEE 802.11 standards.
An important environmental constraints of a site is determining the feasibility of using wireless transmission.
The term wireless site survey is often used to describe the process of analyzing a site to see if it will be appropriate for wireless transmission.
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Wireless Site Survey
A site survey confirms signal propagation, strength, and accuracy in different locations.
Many wireless network interface cards (NIC) ship with utilities that enable you to measure signal strength.
Cisco 802.11 NICs ship with the Cisco Aironet Client Utility (ACU), which is a graphical tool for configuring, monitoring, and managing the NIC and its wireless environment.
A site survey can be as simple as walking around with a wireless notebook computer and using the utility to measure signal strength.
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Department of Computer Science
Wireless site survey
A site survey starts with a draft WLAN design.
Where to place access points?
Where the users will be located?
What characteristics of the access points’ antennas, and the location of major obstructions?
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Department of Computer Science
Wireless site survey
The initial placement of an access point is based on,
An estimate of the signal loss that will occur between the access point and the users of the access point.
Estimate depends on how much loss in power a signal would experience in the vacuum of space, without any obstructions or other interference.
This is called the free space path loss and is specified in decibels (dB).
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Department of Computer Science
Wireless site survey
An RF signal traveling through objects of various sorts can be affected by many different problems, including the following:
Reflection
Absorption
Refraction
Diffraction
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Checking the health of the existing internetwork
Developing a baseline of network performance
Analyzing network availability
Analyzing network utilization
Measurement of the amount of bandwidth that is in use during a specific time interval.
Analyzing network accuracy
Specifying network accuracy as a bit error rate (BER). You can use a BER tester (also called a BERT) on serial lines to test the number of damaged bits compared to total bits.
Analyzing network efficiency
Using maximum frame sizes to increase network efficiency.
Analyzing delay and response time
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Department of Computer Science
Cont…
Checking the status of major switches, routers, and firewalls.
Show buffers, show environment, show interfaces, show IP cache flow, show memory, show processes, show running-config, show startup-config, show version etc.
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Department of Computer Science
Network health checklist
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Check Technical Goals
The network topology and physical infrastructure are well documented.
Network addresses and names are assigned in a structured manner and are welldocumented.
Network wiring is installed in a structured manner and is well labeled.
Network wiring has been tested and certified.
Network wiring between telecommunications closets and end stations is no morethan 100 meters.
Network availability meets current customer goals.
Network security meets current customer goals.
There are no collisions on Ethernet full-duplex links.
No LAN or WAN segments are becoming saturated
No routers are overused (5-minute CPU utilization is under 75 percent).
On average, routers are not dropping more than 1 percent of packets.
p-to-date router, switch, and other device configurations have been collected,archived, and analyzed as part of the design study.
The response time between clients and hosts is generally less than 100 ms (1/10th of a second).
