ITEC 275 Computer Networks – Switching, Routing, and

WANs

Week 3Robert 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.

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?

• 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

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 informatiom• Geographical information• WAN• WAN to LAN• Buildings and floors• 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 sitesEmail and external data access entriesFtp operationsPrinter and file sharing devicesDHCP, DNS, SNMPRouter interface names, firewalls, NAT, IDS, and IPS

Get a Network Map

Gigabit Ethernet

Eugene Ethernet20 users

Web/FTP server

Grants PassHQ

Gigabit Ethernet

FEP (Front End Processor)

IBMMainframeT1

MedfordFast Ethernet

50 users

RoseburgFast Ethernet

30 usersFrame Relay

CIR = 56 KbpsDLCI = 5

Frame RelayCIR = 56 Kbps

DLCI = 4

Grants PassHQ

Fast Ethernet75 users

InternetT1

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

Discontiguous Subnets

Area 1Subnets 10.108.16.0 -

10.108.31.0

Area 0Network

192.168.49.0

Area 2Subnets 10.108.32.0 -

10.108.47.0

Router A Router B

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

TelecommunicationsWiring Closet

HorizontalWiring

Work-AreaWiring

Wallplate

Main Cross-Connect Room(or Main Distribution Frame)

Intermediate Cross-Connect Room(or Intermediate Distribution Frame)

Building A - Headquarters Building B

VerticalWiring

(BuildingBackbone)

CampusBackbone

Campus Network Wiring

Architectural Constraints

• Make sure the following are sufficient– Air conditioning– Heating– Ventilation– Power– Protection from electromagnetic interference– Doors that can lock

Architectural ConstraintsParameter 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 installing 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 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.

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

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 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

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

- Autonegotiation has received it’s share of critism in the past for being inaccurate when setting up a point-to-point link half duplex and full duplex.

- Autonegotiation 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

Enterprise

Segment 1

Segment 2

Segment n

MTBF MTTRDate and Duration of Last Major Downtime

Cause of Last Major Downtime

Fix for Last Major Downtime

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

Tim

e

Utilization

Series1

Network Utilization in Minute Intervals

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

Tim

e

Utilization

Series1

Network Utilization in Hour Intervals

Bandwidth Utilization by Protocol

Protocol 1

Protocol 2

Protocol 3

Protocol n

Relative Network Utilization

Absolute Network Utilization

Broadcast Rate

Multicast Rate

Characterize Packet Sizes

Characterize Response Time

Node A

Node B

Node C

Node D

Node A Node B Node C Node D

X

X

X

X

Check the Status of Major Routers, Switches, and Firewalls

• Show buffers• Show environment• Show interfaces• Show memory• Show processes• Show running-config• Show version

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

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

User CommunitiesUser Community Name

Size of Community (Number of Users)

Location(s) of Community

Application(s) Used by Community

Data StoresData Store Location Application(s) Used by User

Community(or Communities)

Traffic Flow

Destination 1 Destination 2 Destination 3Destination MB/sec MB/secMB/sec MB/sec

Source 1

Source 2

Source 3

Source n

Traffic Flow Example

Administration

Business and Social Sciences

Math and Sciences

50 PCs 25 Macs50 PCs

50 PCs30 PCs

30 Library Patrons (PCs) 30 Macs and 60 PCs in Computing Center

Library and Computing Center

App 1 108 KbpsApp 2 60 KbpsApp 3 192 KbpsApp 4 48 KbpsApp 7 400 KbpsTotal 808 Kbps

App 1 48 KbpsApp 2 32 KbpsApp 3 96 KbpsApp 4 24 KbpsApp 5 300 KbpsApp 6 200 KbpsApp 8 1200 KbpsTotal 1900 Kbps

App 1 30 KbpsApp 2 20 KbpsApp 3 60 KbpsApp 4 16 KbpsTotal 126 Kbps

App 2 20 KbpsApp 3 96 KbpsApp 4 24 KbpsApp 9 80 KbpsTotal 220 Kbps

Arts and Humanities

Server Farm

10-Mbps Metro Ethernet to Internet

Types of Traffic Flow

• 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 ApplicationsTraffic 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• 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

• Frame size• Protocol interaction• Windowing and flow control• Error-recovery mechanisms

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 IETFIETF (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

• Analyzing an Existing Network• Analyzing Traffic in an Existing Network• QoS

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?