ITEC 275
Computer Networks – Switching,
Routing, and WANs
Week 3
Robert D’Andrea
2015
Agenda
• Review
• Learning Activities
– Analyzing an Existing Network
– Analyzing Traffic in an Existing Network
– QoS
• Introduce homework problems
What’s the Starting Point?
• According to Abraham Lincoln:
– “If we could first know where we are and
whither we are tending, we could better judge
what to do and how to do it.”
Where Are We?
When we characterize the infrastructure of
a network, we develop a set of network maps
and locate major devices and network segments.
Developing a network map should involve
understanding traffic flow, performance
characteristics of network segments, and insight
into where the users are concentrated and the
level of traffic a network design must support.
Everything you can think of to understand your
customers network.
Where Are We?
Developing an understanding of your
customers existing network’s structure, involves
it’s uses, and behavior, then you have a better
chance of determining if you’re design goals are
realistic.
Where Are We?
• Characterize the existing internetwork in
terms of:
– Its infrastructure
• Logical structure (modularity, hierarchy, topology)
• Physical structure
– Addressing and naming
– Wiring and media
– Architectural and environmental constraints
– Over all health of their network
How to Start?
• Characterization can start by using a topdown approach.
– Starting with a map or set of maps depicting a
high-level abstraction of information
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Geographical information
WAN
WAN to LAN
Buildings, floors, and wiring within the building
Rooms containing servers, routers, mainframes, and
switches
• Virtual information
How to Start?
• Characterizing large complex networks should reflect
influence from the OSI reference model.
• A network map should depict applications and
services used by the network users.
Internal and external web sites
Email and external data access entries
Ftp operations
Printer and file sharing devices
DHCP, DNS, SNMP
Router interface names, firewalls, NAT, IDS, and
IPS
How to Start?
Use tools that automate diagram representation of the
network.
IBM’s Tivoli
What’s Up Gold from ipswitch
LAN surveyor
Microsoft Visio Professional
Get a Network Map
Medford
Fast Ethernet
50 users
Roseburg
Fast Ethernet
30 users
Frame Relay
CIR = 56 Kbps
DLCI = 5
Frame Relay
CIR = 56 Kbps
DLCI = 4
Grants Pass
HQ
Gigabit
Ethernet
Gigabit
Ethernet
Grants Pass
HQ
Fast Ethernet
75 users
FEP
(Front End
Processor)
IBM
Mainframe
T1
Web/FTP server
Eugene
Ethernet
20 users
T1
Internet
Characterize Large Internetworks
Developing one map might be difficult to
do for a large internetwork. Many approaches
might be needed for dissecting and
understanding the problem.
• Apply a top-down method influenced by the
OSI reference model
• Develop a series of maps (high (high level of
abstraction) to low level)
• Develop a logical map (shows applications,
and services used by network users)
Characterize Large Internetworks
Develop a map of internal server functions:
Web
Email
sftp
Printing
File sharing
Characterize Large Internetworks
Develop a map of external server functions:
Web
Email
sftp
Mobile
Web caching servers on your map must be
identified because they can affect your traffic
flow.
Characterize Large Internetworks
Develop a map of network services:
• Terminal Access Controller Access Control
System (TACACS) server(s)
• Remote Authentication Dial-In User Service
(RADIUS) server(s)
• Dynamic Host Configuration Protocol (DHCP)
• Domain Name System (DNS)
• Simple Network Management Protocol (SNMP)
• Location and reach of virtual private networks
(VPN)
• Dial-in and dial-out servers
• WAN
• Internet
Characterize Large Internetworks
Develop a map of network services:
• Layer 3 topology of the internetwork (Cisco notation
s0/0 ). This layer of information may reflect a
network of devices from a single vendor or a mix of
vendors.
• Protocols
• Firewalls
• NAT (Network Address Translation)
• IDS (Intrusion Detection System)
• IPS (Intrusion Prevention Detection)
• Layer 2 devices
• LAN devices and interfaces
• Public and private WAMs
Characterize a Logical Architecture
• Determine the logical topology of the network.
Is the network flat, hierarchical, structured or
unstructured, layered or not.
• Geometric shape of network (star, spoke, ring,
or mesh)
• Look for ticking time bombs that could affect
scalability. These are large layer 2 STP
domains that take excessive time to converge.
• Flat topologies do not scale as well as
hierarchical topologies. This affects the ability
to upgrade the network.
Characterize a Logical Architecture
Enterprise Campus
Characterize a Logical Architecture
Enterprise Edge
Characterize Addressing and Naming
• IP addressing for major network devices,
client, server, and private.
• Any addressing oddities, such as discontinuous
subnets?
• Any strategies for addressing and naming?
– Route summarization reduces routes in a router
– For example, sites may be named using airport
codes
• San Francisco = SFO, Oakland = OAK
Characterize Addressing and Naming
• Route summarization reduces routes in a
routing table, routing-table update traffic,
and overall router overhead. Route
summarization improves network stability
and availability, because problems in one
area of the network are less likely to affect
the whole network.
• Dis-contiguous subnet is a subnet that has
been divided into two areas.
Dis-contiguous Subnets
Area 0
Network
192.168.49.0
Router A
Area 1
Subnets 10.108.16.0 10.108.31.0
Router B
Area 2
Subnets 10.108.32.0 10.108.47.0
Characterize Addressing and Naming
• Network addressing scheme might affect the
routing protocols. Some routing protocols do
not support
Classless addressing
Variable-length subnet masking (VLSM)
Dis-contiguous subnets
Characterize the Wiring and Media
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Single-mode fiber
Multi-mode fiber
Shielded twisted pair (STP) copper
Unshielded-twisted-pair (UTP) copper
Coaxial cable
Microwave
Laser
Radio
Infra-red
Characterize the Wiring and Media
Distance information is critical when
selecting data link layer technologies.
It is helpful knowing how much copper
cable might need to be replaced if fiber
cabling is to be used and if there is access for
the replacement.
Determine the type of wiring used
between the wiring closet, cross-connect
rooms, and computer rooms.
Characterize the Wiring and Media
Vertical wiring run between floors of a
building
Horizontal wiring run from the wiring
closet to the wall plate in the office cubicles.
Work-area wiring runs from the wall
plate to the workstation.in a cubicle.
Generally, the distance from the wiring
closet to the workstation are approximately
100 meters.
Campus Network Wiring
Horizontal
Wiring
Work-Area
Wiring
Wallplate
Telecommunications
Wiring Closet
Vertical
Wiring
(Building
Backbone)
Main Cross-Connect Room
(or Main Distribution Frame)
Building A - Headquarters
Intermediate Cross-Connect Room
(or Intermediate Distribution Frame)
Campus
Backbone
Building B
Characterize the Wiring and Media
A time-domain reflectometer (TDR) is
used to determine the distance of a cable. It is
an electronic instrument that uses timedomain reflective technology to characterize
and locate faults in metallic cables (for
example, twisted-pair cable or coaxial cable)
Characterize the Wiring and Media
TDR
Architectural Constraints
• Make sure the following are sufficient
– Air conditioning
– Heating
– Ventilation
– Electrical power
– Protection from electromagnetic interference
– Door locking mechanism
– Environmental issues
– Too close to a right-of-way
Architectural Constraints
Parameter
Copper Twisted Pair
MM Fiber
SM Fiber
Wireless
Distance
Up to 100 meters
Up to 2 kilometers
(Fast Ethernet)
Up to 550 m (Gigabit
Ethernet)
Up to 300 m (10
Gigabit Ethernet)
Up to 10 km (Fast
Ethernet)
Up to 5 km (Gigabit
Ethernet)
Up to 80 km (10
Gigabit Ethernet)
Up to 500 m at 1
Mbps
Bandwidth
Up to 10 Gigabits per
second (Gbps)
Up to 10 Gbps
Up to 10 Gbps or
higher
Up to 54 Mbps
Price
Inexpensive
Moderate
Moderate to
expensive
Moderate
Deployment
Wiring closet
Internode or
interbuilding
Internode or
interbuilding
Internode or
interbuilding
Architectural Constraints
• Make sure there’s space for:
– Cabling conduits
– Patch panels
– Equipment racks
– Work areas for technicians to install and
troubleshooting equipment
Wireless Installation
• Inspect the architecture and environment
constraints of the site to determining the
feasibility of a wireless transmission.
– Wireless transmission is RF (radio frequency)
– A wireless expert should be hired
– Network designers can install access point(s)
where people tend to concentrate
– Signal loss occurs between the access point and the
user of the access point.
Wireless Installation
• A wireless site survey is used to describe the
process of evaluating the a site to see if it will
be appropriate for wireless transmission.
• An access point is likely to be placed in a
location based on an estimate of signal loss
that will occur between the access point and
the users of the WLAN. An access point is a
device that transmits and receives data for
users on a WLAN. Generally, it is a point on
interconnection between the WLAN and
wired Ethernet network.
RF Phenomena Wireless Installations
1. Reflection causes the signal to bounce back
on itself.
2. Absorption occurs as the signal passes
through materials
3. Refraction is when a signal passes through
one medium of one density and then through
another medium of another density. Signal will
bend.
4. Diffraction when a signal can pass in part
through a medium more easily in one part than
another
RF Phenomena Wireless Installations
1. Reflection signal causes the signal to bounce
back on itself. The signal can interfere with itself
in the air and affect the receiver’s ability to
discriminate between the signal and noise in the
environment. Reflection is caused by metal
surfaces such as steel girders, scaffolding,
shelving units, steel pillars, and metal doors.
Implementing a Wireless LAN (WLAN) across a
parking lot can be tricky because of metal cars
that come and go.
Reflective Wireless Signal
Reflective Wireless Signal
Reflective Wireless Signal
RF Phenomena Wireless Installations
2. Absorption. Some of the electromagnetic energy of
the signal can be absorbed by the material in objects
through which it passes, resulting in a reduced signal
level. Water has significant absorption properties, and
objects such as trees or thick wooden structures can
have a high water content. Implementing a WLAN in a
coffee shop can be tricky if there are large canisters of
liquid coffee. Coffee-shop WLAN users have also
noticed that people coming and going can affect the
signal level. (On StarTrek, a non-human character once
called a human “an ugly giant bag of mostly water”!)
Absorption Wireless Signal
RF Phenomena Wireless Installations
3. Refraction. When an RF signal passes from a medium
with one density into a medium with another density,
the signal can be bent, much like light passing through a
prism. The signal changes direction and may interfere
with the non-refracted signal. It can take a different path
and encounter other, unexpected obstructions, and arrive
at recipients damaged or later than expected. As an
example, a water tank not only introduces absorption,
but the difference in density between the atmosphere
and the water can bend the RF signal.
Reflective Wireless Signal
RF Phenomena Wireless Installations
4. Diffraction. Diffraction, which is similar to
refraction, results when a region through which
the RF signal can pass easily is adjacent to a
region in which reflective obstructions exist. So,
a signal can pass in part through a medium more
easily in one part than another. Like refraction,
the RF signal is bent around the edge of the
diffractive region and can then interfere with that
part of the RF signal that is not bent.
Diffraction Wireless Signal
RF Phenomena Wireless Installations
• A wireless Site Survey should be performed on
the existing network for signal propagation,
strength, and accuracy in different areas.
– NIC cards ship with utilities on them to measure
signal strength
– Signal strength can be determined using a protocol
analyzer
– Access points send beacon frames every 100
milliseconds (ms). Use a protocol analyzer to
analyze the signal strength being emitted from the
different grid locations of the access points.
RF Phenomena Wireless Installations
- Use a protocol analyzer to capture CRC
errors. These errors stem from
corruption and collisions.
- Observe if frames are being lost in
transmission
- Observe if acknowledgment (ACK) and
frame retries after a missing ACK.
ACK is called a control frame. Clients
and access points use them to
implement a retransmission mechanism
RF Phenomena Wireless Installations
• Wired Ethernet
Detects collisions through CSMA/CD
(802.11)
Ethernet uses CSMA/CA as the access
method to gain access of the wire. An ACK
control frame is returned to a sender for
packet received. If a frame does not
receive an ACK, it is retransmitted.
Check the Health of the Existing
Internetwork
• Baseline network performance with sufficient time and at a
typical time
• Baseline availability gather information from the customer
on MTBF and MTTR
• Baseline bandwidth utilization during a specific time
frame. This is usually a percentage of capacity.
• Accuracy is an upper layer protocol’s responsibility. A
frame with a bad CRC is dropped and retransmitted. A
good threshold rule for handling errors is that there should
be no more than one bad frame per megabyte of data.
Check the Health of the Existing
Internetwork
Accuracy is a measurement of lost packets.
This measurement is achieved by keeping track
of lost packets while measuring response time.
-Switches have replaced hubs.
- There should be fewer than 0.1
percent of frames encounter collisions.
- There should be no late collisions.
Indicate bad cabling, cabling longer than
100 meters, bad NIC, or duplex mismatch.
Check the Health of the Existing
Internetwork
Auto-negotiation has received it’s share
of criticism in the past for being inaccurate
when setting up a point-to-point link half
duplex and full duplex.
Auto-negotiation of speed is usually not
a problem. If set up incorrectly, it does not
work. The speeds are 10 Mbps, 100 Mbps, or
1000 Mbps.
Check the Health of the Existing
Internetwork
Category 3 cable will support 10MBps, but not
100 MBps and higher. Errors increase.
• Efficiency is linked to large frame sizes. Bandwidth
utilization is optimized for efficiency when
applications and protocols are in large sized frames.
– Change window sizes on clients and servers. Increasing
maximum transmission unit (MTU).
– Able to ping and telnet but not be able to send HTTP,
and FTP.
– A hump exist on the sides of the average transmission.
– Runt frames (less than 64 bytes) are a result of
collisions on the same shared Ethernet segment.
Check the Health of the Existing
Internetwork
• Response time can be measured using the
round-trip time (RTT) ping command.
Observe response time on a user
workstation. Run typical applications to
get a response.
Response time for network services
protocols, such as, DHCP and DNS.
• Status of major routers, switches, and
firewalls
Characterize Availability
MTBF
Enterprise
Segment 1
Segment 2
Segment n
MTTR
Date and Duration
of Last Major
Downtime
Cause of Last
Major
Downtime
Fix for Last
Major
Downtime
Network Utilization in Minute Intervals
Network Utilization
16:40:00
16:43:00
16:46:00
16:49:00
Time
16:52:00
16:55:00
Series1
16:58:00
17:01:00
17:04:00
17:07:00
17:10:00
0
1
2
3
4
Utilization
5
6
7
Network Utilization in Hour Intervals
Network Utilization
13:00:00
Time
14:00:00
15:00:00
Series1
16:00:00
17:00:00
0
0.5
1
1.5
2
2.5
Utilization
3
3.5
4
4.5
Bandwidth Utilization by Protocol
Relative
Network
Utilization
Protocol 1
Protocol 2
Protocol 3
Protocol n
Absolute
Network
Utilization
Broadcast
Rate
Multicast
Rate
Characterize Packet Sizes
Characterize Response Time
Node A
Node A
Node B
Node C
Node D
Node B
Node C
Node D
X
X
X
X
Check the Status of Major Routers,
Switches, and Firewalls
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Show buffers
Show environment
Show interfaces
Show memory
Show processes
Show running-config
Show version
Check the Status of Major Routers,
Switches, Hubs, and Firewalls
Hubs (bit cloning machine)
Span every connection on a hub
Cheap
Wasteful of bandwidth
Sends replicated packet data on all ports
When monitoring (Wireshark) a network,
see redundant traffic
Check the Status of Major Routers,
Switches, and Firewalls
Switches
Less complicated than routers
Used for Ethernet and WiFi medium based on
MAC address (burnt on NIC)
Initially, a switch table is empty. Broadcasts on all
ports until all port connections are discovered.
Switch uplink port can be used to connect to
router(s).
Switches deliver packets directly to the correct
destination without spanning all port connections.
Check the Status of Major Routers,
Switches, and Firewalls
Switch table
Interface
MAC Addresses
1
AA-AA-AA-AA-AA-AA
2
CC-CC-CC-CC-CC-CC
3
DD-DD-DD-DD-DD-DD
Check the Status of Major Routers,
Switches, and Firewalls
Router
Routers connect networks
Support NAT and DHCP
Utilize the IP protocol
Internal Ethernet switch built-in
Check the Status of Major Routers,
Switches, and Firewalls
Hubs, Switches, and Routers
Each of these devices operates at a
different layer.
Network
Link
Physical
IP protocol
194.78.0.163
Medium over which the packet is traveling.
Ethernet and WiFi . MAC Address
01-DE-89-0A-77-BB
Raw 01001000111100…
Tools
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Protocol analyzers
Multi Router Traffic Grapher (MRTG)
Remote monitoring (RMON) probes
Cisco Discovery Protocol (CDP)
Cisco IOS NetFlow technology
CiscoWorks
Network Traffic Factors
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Traffic flow
Location of traffic sources and data stores
Traffic load
Traffic behavior
Quality of Service (QoS) requirements
User Communities
User Community
Name
Size of
Community
(Number of
Users)
Location(s) of
Community
Application(s)
Used by
Community
Data Stores
Data Store
Location
Application(s)
Used by User
Community(or
Communities)
Traffic Flow
Destination 1
MB/sec
Source 1
Source 2
Source 3
Source n
Destination 2
MB/sec
Destination 3
MB/sec
Destination
MB/sec
Library and Computing Center
Traffic Flow
Example
App 2
App 3
App 4
App 9
Total
20
96
24
80
220
30 Library Patrons (PCs)
30 Macs and 60 PCs in
Computing Center
Server Farm
Kbps
Kbps
Kbps
Kbps
Kbps
10-Mbps Metro
Ethernet to Internet
App 1
App 2
App 3
App 4
App 7
Total
108
60
192
48
400
808
Kbps
Kbps
Kbps
Kbps
Kbps
Kbps
25 Macs
50 PCs
50 PCs
Arts and
Humanities
Administration
App 1
App 2
App 3
App 4
Total
30 PCs
Business and Social
Sciences
30
20
60
16
126
Kbps
Kbps
Kbps
Kbps
Kbps
App 1
48 Kbps
App 2
32 Kbps
App 3
96 Kbps
App 4
24 Kbps
App 5 300 Kbps
App 6 200 Kbps
App 8 1200 Kbps
Total 1900 Kbps
Math and
Sciences
50 PCs
Types of Traffic Flow
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Terminal/host
Client/server
Thin client
Peer-to-peer
Server/server
Distributed computing
Traffic Flow for Voice over IP
• The flow associated with transmitting
the audio voice is separate from the
flows associated with call setup and
teardown.
– The flow for transmitting the digital voice is
essentially peer-to-peer.
– Call setup and teardown is a client/server
flow
• A phone needs to talk to a server or
phone switch that understands phone
numbers, IP addresses, capabilities
negotiation, and so on.
Network Applications
Traffic Characteristics
Name of
Application
Type of
Traffic Flow
Protocol(s)
Used by
Application
User
Communities
That Use the
Application
Data Stores
(Servers, Hosts,
and so on)
Approximate
Bandwidth
Requirements
QoS
Requirements
Traffic Load
• To calculate whether capacity is sufficient, you
should know:
– The number of stations
– The average time that a station is idle between
sending frames
– The time required to transmit a message once
medium access is gained
• That level of detailed information can be hard
to gather, however.
Size of Objects on Networks
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Terminal screen: 4 Kbytes
Simple e-mail: 10 Kbytes
Simple web page: 50 Kbytes
High-quality image: 50,000 Kbytes
Database backup: 1,000,000 Kbytes or more
Traffic Behavior
• Broadcasts
– All ones data-link layer destination address
• FF: FF: FF: FF: FF: FF
– Doesn’t necessarily use huge amounts of bandwidth
– But does disturb every CPU in the broadcast domain
• Multicasts
– First bit sent is a one
• 01:00:0C:CC:CC:CC (Cisco Discovery Protocol)
– Should just disturb NICs that have registered to receive
it
– Requires multicast routing protocol on internetworks
Network Efficiency
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Frame size
Protocol interaction
Windowing and flow control
Error-recovery mechanisms
Network Efficiency
Network utilization is the measurement of the
amount of bandwidth that is used during a specific
time interval. The measure is expressed in terms of
percentage of capacity. Seventy percent (70%) is
considered a reasonable level for normal link traffic.
QoS Requirements
• ATM service specifications
– Constant bit rate (CBR)
– Realtime variable bit rate (rt-VBR)
– Non-realtime variable bit rate (nrt-VBR)
– Unspecified bit rate (UBR)
– Available bit rate (ABR)
– Guaranteed frame rate (GFR)
QoS Requirements per IETF
IETF (Internet Engineering Task Force)
• IETF integrated services working group
specifications
– Controlled load service
• Provides client data flow with a QoS closely
approximating the QoS that same flow would receive on
an unloaded network
– Guaranteed service
• Provides firm (mathematically provable) bounds on
end-to-end packet-queuing delays
QoS Requirements per IETF
• IETF differentiated services working group
specifications
– RFC 2475
– IP packets can be marked with a differentiated
services code point (DSCP) to influence queuing
and packet-dropping decisions for IP datagrams on
an output interface of a router.
Summary
• Characterize the existing internetwork before
designing enhancements.
• Helps you verify that a customer’s design goals
are realistic.
• Helps you locate where new equipment will be
placed.
• Helps you cover yourself if the new network has
problems due to unresolved problems in the old
network.
Summary
• Continue to use a systematic, top-down
approach
• Don’t select products until you understand
network traffic in terms of:
–
–
–
–
Flow
Load
Behavior
QoS requirements
Review Questions
• What factors will help you decide if the existing
internetwork is in good enough shape to support new
enhancements?
• When considering protocol behavior, what is the
difference between relative network utilization and
absolute network utilization?
• Why should you characterize the logical structure of
an internetwork and not just the physical structure?
• What architectural and environmental factors should
you consider for a new wireless installation?
Review Questions
• List and describe six different types of traffic flows.
• What makes traffic flow in voice over IP networks
challenging to characterize and plan for?
• Why should you be concerned about broadcast
traffic?
• How do ATM and IETF specifications for QoS
differ?
This Week’s Outcomes
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Characterize the Existing Network
Analyzing Traffic in an Existing Network
Determine QoS
Wireless Signals
Due this week
• 2-1 – Concept questions 2
Next week
• 3-1 – Concept questions 3
• FranklinLive session 4
• Ensure you have the VMware View Client
installed
• Examine the MIMIC simulator software
Q&A
• Questions, comments, concerns?