The document provides a comprehensive overview of techniques for characterizing and analyzing computer networks, focusing on aspects such as infrastructure, traffic flow, and quality of service. It emphasizes the importance of developing detailed network maps and understanding various network components to gauge performance and reliability. Additionally, it discusses methods for assessing network health, including packet loss measurements, response times, and the impact of different physical mediums on network efficiency.

1. ITEC 275
Computer Networks – Switching,
Routing, and WANs
Week 3
Robert D’Andrea
Some slides provide by Priscilla
Oppenheimer and used with permission
Accuracy is a measurement of lost packets.
This measurement is achieved by keeping track
of lost packets while measuring response time.

2. Agenda
• Review
• Learning Activities
– Analyzing an Existing Network
– Analyzing Traffic in an Existing Network
– QoS
• Introduce homework problems

3. 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.”

4. 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.

5. 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.

6. 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
– Health

7. How to Start?
• Characterization can start by using a top-
down approach.
– Starting with a map or set of maps depicting a
high-level abstraction of information
• Geographical information
• WAN
• WAN to LAN
• Buildings and floors
• Rooms containing servers, routers, mainframes, and
switches
• Virtual information

8. 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

9. 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

10. Get a Network Map
Gigabit
Ethernet
Eugene
Ethernet
20 users
Web/FTP server
Grants Pass
HQ
Gigabit
Ethernet
FEP
(Front End
Processor)
IBM
Mainframe
T1
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
Fast Ethernet
75 users
Internet
T1

11. 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 to low level)
• Develop a logical map (shows applications,
and services used by network users)

12. Characterize Large Internetworks
Develop a map of internal server functions:
Web locations
Email
sftp
Printing
File sharing

13. 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.

14. 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

15. 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
• IDS
• IPS
• Layer 2 devices
• LAN devices and interfaces
• Public and private WAMs

16. 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.

17. Characterize a Logical Architecture
Enterprise Campus

18. Characterize a Logical Architecture
Enterprise Edge

19. Characterize Addressing and Naming
• IP addressing for major devices, client
networks, server networks, private needing
translation, and so on
• 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

20. 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.

21. 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

22. Dis-contiguous Subnets
Area 1
Subnets 10.108.16.0 -
10.108.31.0
Area 0
Network
192.168.49.0
Area 2
Subnets 10.108.32.0 -
10.108.47.0
Router A Router B

23. Characterize the Wiring and Media
• Single-mode fiber
• Multi-mode fiber
• Shielded twisted pair (STP) copper
• Unshielded-twisted-pair (UTP) copper
• Coaxial cable
• Microwave
• Laser
• Radio
• Infra-red

24. Characterize the Wiring and Media
Topologies:
http://www.youtube.com/watch?v=DsPGYvb
K8VU
Hubs, Switches, and routers
http://www.youtube.com/watch?v=Ofjsh_E4H
FY

25. 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.

26. 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.

27. 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 time-domain
reflective technology to characterize and
locate faults in metallic cables (for
example, twisted-pair cable or coaxial cable)

28. Characterize the Wiring and Media
TDR

29. Telecommunications
Wiring Closet
Horizontal
Wiring
Work-Area
Wiring
Wallplate
Main Cross-Connect Room
(or Main Distribution Frame)
Intermediate Cross-Connect Room
(or Intermediate Distribution Frame)
Building A - Headquarters Building B
Vertical
Wiring
(Building
Backbone)
Campus
Backbone
Campus Network Wiring

30. Architectural Constraints
• Make sure the following are sufficient
– Air conditioning
– Heating
– Ventilation
– Power
– Protection from electromagnetic interference
– Doors that can lock
– Environmental issues
– Too close to a right-of-way

31. 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

32. Architectural Constraints
• Make sure there’s space for:
– Cabling conduits
– Patch panels
– Equipment racks
– Work areas for technicians installing and
troubleshooting equipment

33. 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 points will be
located and where the people concentration will be
located
– Access point is based on signal loss between the
access point and the user of the access point.

34. 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.

35. RF Phenomena Wireless Installations
• Reflection causes the signal to bounce back on
itself.
• Absorption occurs as the signal passes through
materials
• Refraction is when a signal passes through one
medium of one density and then through another
medium of another density. Signal will bend.
• Diffraction when a signal can pass in part through
a medium more easily in one part than another

36. 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.

37. 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 the 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

38. 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.

39. 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.

40. 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.

41. 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.

42. 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.

43. 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

44. Characterize Availability
Enterprise
Segment 1
Segment 2
Segment n
MTBF MTTR
Date and Duration
of Last Major
Downtime
Cause of Last
Major
Downtime
Fix for Last
Major
Downtime

45. Network Utilization
0 1 2 3 4 5 6 7
17:10:00
17:07:00
17:04:00
17:01:00
16:58:00
16:55:00
16:52:00
16:49:00
16:46:00
16:43:00
16:40:00
Time
Utilization
Series1
Network Utilization in Minute Intervals

46. Network Utilization
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5
17:00:00
16:00:00
15:00:00
14:00:00
13:00:00
Time
Utilization
Series1
Network Utilization in Hour Intervals

47. Bandwidth Utilization by Protocol
Protocol 1
Protocol 2
Protocol 3
Protocol n
Relative
Network
Utilization
Absolute
Network
Utilization
Broadcast
Rate
Multicast
Rate

48. Characterize Packet Sizes

49. Characterize Response Time
Node A
Node B
Node C
Node D
Node A Node B Node C Node D
X
X
X
X

50. Check the Status of Major Routers,
Switches, and Firewalls
• Show buffers
• Show environment
• Show interfaces
• Show memory
• Show processes
• Show running-config
• Show version

51. Tools
• Protocol analyzers
• Multi Router Traffic Grapher (MRTG)
• Remote monitoring (RMON) probes
• Cisco Discovery Protocol (CDP)
• Cisco IOS NetFlow technology
• CiscoWorks

52. Network Traffic Factors
• Traffic flow
• Location of traffic sources and data stores
• Traffic load
• Traffic behavior
• Quality of Service (QoS) requirements

53. User Communities
User Community
Name
Size of
Community
(Number of
Users)
Location(s) of
Community
Application(s)
Used by
Community

54. Data Stores
Data Store Location Application(s) Used by User
Community(or
Communities)

55. Traffic Flow
Destination 1 Destination 2 Destination 3 Destination
MB/sec MB/sec MB/sec MB/sec
Source 1
Source 2
Source 3
Source n

56. Traffic Flow
Example
Administration
Business and Social
Sciences
Math and
Sciences
50 PCs 25 Macs
50 PCs
50 PCs
30 PCs
30 Library Patrons (PCs)
30 Macs and 60 PCs in
Computing Center
Library and Computing Center
App 1 108 Kbps
App 2 60 Kbps
App 3 192 Kbps
App 4 48 Kbps
App 7 400 Kbps
Total 808 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
App 1 30 Kbps
App 2 20 Kbps
App 3 60 Kbps
App 4 16 Kbps
Total 126 Kbps
App 2 20 Kbps
App 3 96 Kbps
App 4 24 Kbps
App 9 80 Kbps
Total 220 Kbps
Arts and
Humanities
Server Farm
10-Mbps Metro
Ethernet to Internet

57. Types of Traffic Flow
• Terminal/host
• Client/server
• Thin client
• Peer-to-peer
• Server/server
• Distributed computing

58. 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.

59. 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

60. 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.

61. Size of Objects on Networks
• 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

62. 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

63. Network Efficiency
• Frame size
• Protocol interaction
• Windowing and flow control
• Error-recovery mechanisms

64. 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.

65. 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)

66. 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

67. 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.

68. 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.

69. 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

70. 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?

71. 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?

72. This Week’s Outcomes
• Analyzing an Existing Network
• Analyzing Traffic in an Existing Network
• QoS

73. Due this week
• 2-1 – Concept questions 2

74. Next week
• 3-1 – Concept questions 3
• FranklinLive session 4
• Ensure you have the VMware View Client
installed
• Examine the MIMIC simulator software

75. Q & A
• Questions, comments, concerns?