Top-Down Network Design Chapter Four Characterizing Network Traffic Oppenheimer

Top-Down Network DesignTop-Down Network Design

Chapter Four Chapter Four

Characterizing Network Traffic Characterizing Network Traffic

Oppenheimer

To expose to the students about techniques for characterizing traffic flow, traffic volume, and protocol behavior

ObjectivesObjectives

1

2 To analyze network traffic patterns that help you in selecting appropriate logical and physical network design solutions

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In this step the flow of the traffic both existing and to be added or changed will be accounted for

This is done by identifying◦Traffic flow◦Location of traffic sources and data stores◦Traffic load/volume◦Traffic behavior◦Quality of Service (QoS) requirements

Copyright 2000-2011 Kenneth M. Chipps Ph.D. www.chipps.com 3

Characterizing Network TrafficCharacterizing Network Traffic

To determine the sources and destinations of traffic; first we need to identify the user communities◦A user community is a collection of staff that do

basically the same thing, such as the accounting program users

◦This may be a limited group, isolated to a single area or building or it may be the email users who are widely geographically distributed

◦Create a chart of these groups

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Characterizing Traffic Flow Characterizing Traffic Flow

Community

Name

Number

of Users

Location Application

Enterprise Accounting

5 Building B

Floor 2

Rooms 3-5

MAS90

CEO Accounting

1 Building A

Corner Office

Quicken

Network

Managers

3 Building C

Deep Dark

Basement

OpenView

Network

Managers

3 Building C

Deep Dark

Basement

AlertPage

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User Community listUser Community list

Next identify where the data stores of these user communities are located

This could be a Server Server Farm Mainframe offsite NAS

Create a chart of these sites along with the user communities

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Data Store

Name

Location Application Used By

Accounting

Data

Building C

Even Deeper and Darker Basement

MAS90 Enterprise Accounting

CEO‘s Budget Building A

Corner Office

Quicken CEO

OpenView

Logs

Building C

Deep Dark

Basement

OpenView Network

Managers

AlertPage

Logs

Building C

Deep Dark

Basement

AlertPage Network

Managers

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Data Store listData Store list

For the data flow from the user communities to their data stores, measure or estimate the traffic flow over the links

Use a network analyzer or network management tool for this

This is not likely to be exactIt is being used to identify bottlenecks

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Application Traffic Type

Protocols Used

User Community

Data Store Bandwidth Needed

QoS

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Traffic Flow listTraffic Flow list

The type of traffic is importantThis will influence the type of link requiredAt this stage the QoS is important as well since it

will affect the type of link◦Only some link types can support QoS

Again a chart is used to collect this information

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Types of trafficTypes of traffic

Different traffic types have different characteristics◦Terminal/Host

Applications based on Terminal / Host are low - volume character traffic. The traffic from the terminal will be a few characters while the host returns screen full of characters.

◦Client/Server The traffic flow in Client / server environment is bi-directional

where clients send queries and requests to a server and the server responds with data or permission for the client to send data.

Traffic sent to the host is usually less than 100 bytes and the return traffic from the host can be more than 1500 bytes.

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◦Server-to-Server The flow depends on the relationship between the servers It includes transmissions between servers and

transmissions between servers and management applications

◦Distributed Computing Several computers join together to solve a single problem Normally the exchange is quite high (volume of traffic) It is bi-directional

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◦Peer-to-peer The flow is usually bi-directional. Communicating entities

transmit approximately equal amounts of information. ◦Thin-client:

It is a computer or a computer program which depends heavily on some other computer (its server) to fulfill its traditional computational roles.

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Application Type of

Traffic

Protocol User

Community

Data

Store

Bandwidth QoS

Enterprise

Accounting

Client/Server

Browser/Server

IP Enterprise

Accounting

Accounting

Data

Average

of 2 Mbps

from 8 to 5 weekdays

None

Note this is blank

Because the CEO’s

Quicken Data

Does not leave CEO’s office

NA NA NA

OpenView Terminal/Server IP Average of 2 Kbps

24X7X365

OpenView

Logs

Average of 2 Kbps

24X7X365

None

AlertPage Terminal/Server IP Average of

65 Kbps

Every hour

24X7X365

AlertPage

Logs

Average of

65 Kbps

Every hour

24X7X365

None

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Types of traffic listTypes of traffic list

A quick estimate of traffic flow can be made by using the following table

This table shows the average flows for the different types of data

In many cases, especially when tools such as a base-lining tool or protocol analyzer are not available, this is the best that can be done

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Types of TrafficTypes of Traffic

Type of Application Typical Data Size

Kbytes

Type of Application Typical Data Size

Kbytes

Terminal Screen 4 Graphical Screen 500

Email 10 Presentation Document

2,000

Web Page 50 High Resolution Image

50,000

Spreadsheet 100 Multimedia Object 100,000

Word Processing Document

200 Database 1,000,000

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Traffic Flow Estimates ListTraffic Flow Estimates List

Traffic Flow Traffic Flow ExampleExample

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

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Purpose:To avoid a design with any critical bottleneck.To avoid bottleneck:◦Research for application usage patterns, idle times

between packets and sessions, frame sizes, and other traffic behavioral patterns for application and system approach.

◦Give large amounts of bandwidth at a problem. LAN bandwidth is extremely cheap, Gigabit Ethernet also most

organizations can afford.

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Characterizing Traffic LoadCharacterizing Traffic Load

1. Calculating Theoretical 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

2. Documenting Application-Usage Patterns◦Few data obtained during characterizing traffic flow user

communities, number of users in communities, and the applications that users employ.

◦Additional information required:◦ The frequency of application sessions (number of session per day, week, month, or

whatever time period is appropriate.◦ The length of an average application session◦ The number of simultaneous users of an application

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Characterizing Traffic Load: StepsCharacterizing Traffic Load: Steps

3. Refining Estimates of Traffic Load Caused by Applications◦ Need to research the size of data objects sent by applications, the

overhead caused by protocol layers, and any additional load caused by application initialization.

◦ Table 4-5 shows some estimates for object sizes

4. Estimating Traffic Load Caused by Routing Protocols◦ At this point of designing process, you might not have selected

routing protocols for new network but you should have identified routing protocols running on the existing network.

◦ Use table 4-7 as guidance that shows the amount of legacy distance-vector routing protocols.

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Characterizing Traffic Load: StepsCharacterizing Traffic Load: Steps

Table 4-5 : Approximate Size of Objects that applications transfer across networks

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Size of Objects on NetworksSize of Objects on Networks

Bandwidth used by Legacy Routing Protocols: Bandwidth used by Legacy Routing Protocols: SamplesSamples

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Table 4-7: Bandwidth used by Legacy Routing Protocols

How do you actually determine what size data lines are required

This is often difficult and inexactFormulas are available as discussed below, but

often the best way is to send the normal files over a controlled circuit and time it

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Measuring Traffic Flow and LoadMeasuring Traffic Flow and Load

◦The file isn't going to cross the network in one big monolithic package

◦It will be divided into packets◦Each packet will have a size, hopefully as big as 1500

bytes, but that depends on the protocol, configuration settings, application, operating system, and so on

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◦Each 1500 byte packet will be encapsulated in the Frame Relay header and followed by the 2-byte Frame Check Sequence

◦Also, Frame Relay packets are encapsulated in a 1-byte Flag field at the beginning and end

◦You have to take those bytes into account for each packet

◦That 1500 bytes won't all be data from the file, however

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◦Some of the bytes will be used by A network-layer header A transport-layer header One, or more upper-layer headers

◦The packets will undoubtedly be acknowledged at one or more layers

◦Those ACKs use bytes and time

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◦Will you be using a protocol that allows for a sliding window and can send many packets without waiting for an ACK until the send window slides closed

◦If so, how big is the send window by default◦This usually depends on the recipient's receive window◦Does the window tend to slide closed a lot◦Or will you use a ping pong protocol that requires an

ACK for each packet

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◦Does the recipient tend to store the data in RAM and ACK quickly or does it write to disk, a slow mechanical process, and then ACK

◦This may depend on the state of the receive window, the amount of RAM available, and so forth

◦What sort of negotiation happens before the data can be sent

◦Any transport or session layer establishment, such as a TCP 3-way handshake

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◦How about at the upper layers◦Before file bytes are sent, are there negotiations and

packets related to file size, file name, file access rights◦Is a user name and password sent◦Are these challenged with some sort of security feature,

adding bytes and time to your calculation

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◦Are you using any sort of encryption or compression◦Is this a VPN or IPSec or other tunnel that adds even

more bytes to each packet◦What about the error rate◦Do some packets get dropped due to an error and have

to be retransmitted◦That adds bytes and time

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◦And how about queuing delay at the local routers and any Frame Relay switches inside the provider's network

◦And processing delay◦How quickly does the recipient process the packets and

send ACKs◦What is the turnaround time at the sender◦How quickly does it prepare and output the next set of

packets after an ACK is received

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◦So, in summary, a formula may be mathematically correct

◦But if it is not based on how data is sent on a network, then it will not produce accurate answers

◦So you need to get answers about which protocols and application are sending this data

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1. Broadcast/Multicast BehaviorBroadcasts◦Broadcast frame = frame that goes to all network stations on a LAN◦All 1s in binary 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 domainMulticasts◦Multicast frame = frame that goes to a subset of stations.◦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

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Characterizing Traffic BehaviorCharacterizing Traffic Behavior

2. Network Efficiency◦Efficiency refers to whether applications and protocols

use bandwidth effectively. Efficiency is affected by: Frame size Protocol interaction (refer to page 114 of text book for

examples) Windowing and flow control Error-recovery mechanisms

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Characterizing Traffic BehaviorCharacterizing Traffic Behavior

Besides information about load, you also need to know if the requirements is flexible or inflexible.

Two techniques in analyzing QoS requirements: (you might need to read your text pg 119 –126)

1. 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)

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Characterizing QoS RequirementsCharacterizing QoS Requirements

2. 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

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QoS RequirementsQoS Requirements

IETF differentiated services working group specifications◦ RFC 2475◦ IP packets can be marked with a differentiated services codepoint

(DSCP) to influence queuing and packet-dropping decisions for IP datagrams on an output interface of a router

Grade of Service Requirements for Voice ApplicationsDocumenting QoS Requirements

◦Work closely with your customer and fill in the QoS Requirements column of table 4-4.

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QoS RequirementsQoS Requirements

Continue to use a systematic, top-down approachDon’t select products until you understand

network traffic in terms of:◦Flow◦Load◦Behavior◦QoS requirements – most technical part

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SummarySummary

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?

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Review QuestionsReview Questions

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Top-Down Network Design Chapter Four Characterizing Network Traffic Oppenheimer