Panko, Chapter 4

Core concerns Quality of service (QoS)Network designSelection among alternativesOngoing management (OAM&P)Network visibility (SNMP) © 2011 Pearson Education, Inc. Publishing as Prentice Hall 2

3 Networking must go beyond the systems development life cycle to the full system life cycle over the network’s life. It also needs to understand the business system in which each network component operates. Networking must go beyond the systems development life cycle to the full system life cycle over the network’s life. It also needs to understand the business system in which each network component operates.

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 4 User demand is growing much faster than network budgets. Cost efficiency is always critical. User demand is growing much faster than network budgets. Cost efficiency is always critical.

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 5

 Legacy Decisions ◦ Decisions that lock your network in for a considerable period of time ◦ Multi-year leases ◦ Decisions about alternate strategic directions to take ◦ Deserve very careful attention © 2011 Pearson Education, Inc. Publishing as Prentice Hall 6

Core concerns Quality of service (QoS) Network designSelection among alternativesOngoing management (OAM&P)Network visibility (SNMP) © 2011 Pearson Education, Inc. Publishing as Prentice Hall 7

 Networks today must work well.  Companies measure quality-of-service (QoS) metrics to measure network performance.  Examples: ◦ Speed ◦ Availability ◦ Cost ◦ And so on © 2011 Pearson Education, Inc. Publishing as Prentice Hall 8

PrefixMeaningExample kbps*1,000 bps17,000 bps is 17 kbps 3 kbps is 3,000 bps 34.7 kbps is 3,700 bps Mbps1,000 kbps8,720,000 bps is 8.7 Mbps Mbps is 14,750,000 bps Gbps1,000 Mbps87 Gbps = 87,000,000,000 bps Tbps1,000 Gbps © 2011 Pearson Education, Inc. Publishing as Prentice Hall 9 *Note that the metric prefix kilo is abbreviated with a lowercase k

 Rated Speed ◦ The speed a system should achieve, ◦ According to vendor claims or the standard that defines the technology.  Throughput ◦ The speed a system actually provides to users ◦ (Almost always lower) © 2011 Pearson Education, Inc. Publishing as Prentice Hall 10

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 11 Individual throughput Aggregate throughput Rated speed

 Availability ◦ The time (percentage) a network is available for use  Example: 99.9% ◦ Downtime is the amount of time (minutes, hours, days, etc.) a network is unavailable for use.  Example: An average of 12 minutes per month © 2011 Pearson Education, Inc. Publishing as Prentice Hall 12

 Error Rates ◦ Errors are bad because they require retransmissions. ◦ More subtly, when an error occurs, TCP assumes that there is congestion and slows its rate of transmission. ◦ Packet error rate: the percentage of packets that have errors. ◦ Bit error rate (BER): the percentage of bits that have errors. © 2011 Pearson Education, Inc. Publishing as Prentice Hall 13

 Latency ◦ Latency is delay, measured in milliseconds. ◦ When you ping a host’s IP address, you get the latency to the host. ◦ When you use tracert, you get average latency to each router along the route. ◦ Beyond about 250 ms, turn-taking in conversations becomes almost impossible. ◦ Latency hurts interactive gaming. © 2011 Pearson Education, Inc. Publishing as Prentice Hall 14

 Application Response Time © 2011 Pearson Education, Inc. Publishing as Prentice Hall 15

 Service Level Agreements (SLA) ◦ Guarantees are often written on a percentage of time basis  “No worse than 100 Mbps 99.95% of the time”  As percentage of time requirement increases, the cost to provide service increases exponentially  So SLAs cannot be met 100% of the time © 2011 Pearson Education, Inc. Publishing as Prentice Hall 16

 Service Level Agreements (SLA) ◦ SLAs specify worst cases (minimum performance to be tolerated)  Penalties if worse than the specified performance  Example: latency no higher than 50 ms 99.99% of the time ◦ If specified the best case (maximum performance), you would rarely get better  Example: No higher than 100 Mbps 99% of the time. Who would want that? © 2011 Pearson Education, Inc. Publishing as Prentice Hall 17

Core concernsQuality of service (QoS) Network design Selection among alternativesOngoing management (OAM&P)Network visibility (SNMP) © 2011 Pearson Education, Inc. Publishing as Prentice Hall 18

 To manage a network, it helps to be able to draw pictures of it. ◦ Network drawing programs do this. ◦ There are many network drawing programs. ◦ One is Microsoft Office Visio.  Must buy the correct version to get network and computer templates ◦ We will show examples from OPNET IT Guru. © 2011 Pearson Education, Inc. Publishing as Prentice Hall 19

 Nodes are hosts, switches, routers, and so on. 20 © 2011 Pearson Education, Inc. Publishing as Prentice Hall Just drag nodes onto the canvas.

© 2011 Pearson Education, Inc. Publishing as Prentice Hall 21 Then drag link icons between nodes. There are many types of link icons. Then drag link icons between nodes. There are many types of link icons.

 Congestion causes latency because switches and routers must store frames and packets waiting to send them out.  Buffers are small, so packets are often lost. © 2011 Pearson Education, Inc. Publishing as Prentice Hall 22

 Overprovisioning is providing far more capacity than the network normally needs.  This avoids nearly all momentary traffic peaks but is wasteful. © 2011 Pearson Education, Inc. Publishing as Prentice Hall 23

 With priority, latency-intolerant traffic, such as voice, is given high priority and will go first if there is congestion.  Latency-tolerant traffic, such as , must wait.  More efficient than overprovisioning; also more labor-intensive. © 2011 Pearson Education, Inc. Publishing as Prentice Hall 24

 QoS guarantees reserved capacity for some traffic, so this traffic always gets through.  Other traffic, however, must fight for the remaining capacity. © 2011 Pearson Education, Inc. Publishing as Prentice Hall 25

 Overprovisioning, priority, and QoS reservations deal with congestion; traffic shaping prevents congestion by limiting incoming traffic. © 2011 Pearson Education, Inc. Publishing as Prentice Hall 26

 Compression can help if traffic chronically exceeds the capacity on a line.  Data often contains redundancies and can be compressed. © 2011 Pearson Education, Inc. Publishing as Prentice Hall 27

 Often, the design of a building naturally constrains the topology of a design.  In a multistory building, for in- stance, it often makes sense to place an Ethernet workgroup switch on each floor and a core switch in the basement. © 2011 Pearson Education, Inc. Publishing as Prentice Hall 28

 Network drawing tools show the elements of the network and how they are interconnected.  Network simulation software goes farther by creating a computer model of the network, not just a picture. ◦ The model has the capacity and configuration of each node and transmission link. ◦ Simulation can indicate congestion points, underused lines, and so on. © 2011 Pearson Education, Inc. Publishing as Prentice Hall 29

Core concernsQuality of service (QoS)Network design Selection among alternatives Ongoing management (OAM&P)Network visibility (SNMP) © 2011 Pearson Education, Inc. Publishing as Prentice Hall 30

 Comparing Alternatives ◦ Designers must select among competing approaches and even competing technologies. ◦ When learning about technologies and network designs, you need to look carefully at pros and cons. ◦. © 2011 Pearson Education, Inc. Publishing as Prentice Hall 31

 4.22: Scalability © 2011 Pearson Education, Inc. Publishing as Prentice Hall 32

 Minimum Requirements ◦ Specifications that set particular requirements must be met. ◦ Noncompliant products that do not meet a minimum requirement cannot be considered further. ◦ A failure to scale to meet expected traffic would be an example. © 2011 Pearson Education, Inc. Publishing as Prentice Hall 33

 Multicriteria decision making is a disciplined way to look at and evaluate all aspects of alternatives. © 2011 Pearson Education, Inc. Publishing as Prentice Hall 34 Product AProduct B Criterion Weight (Max 5) Product Rating (Max 10) Criterion Score Product Rating (Max 10) Criterion Score Functionality Ease of management Cost* Total Score6468 *Higher cost ratings indicate lower cost.

 Cost is difficult to measure.  Systems Development Life Cycle Costs ◦ Hardware: full price—base price plus necessary optional components ◦ Software: full price—base price plus necessary optional modules ◦ Labor costs: Network staff and user costs during development ◦ Outsourced development cost ◦ Total development cost © 2011 Pearson Education, Inc. Publishing as Prentice Hall 35

Core concernsQuality of service (QoS)Network designSelection among alternatives Ongoing management (OAM&P) Network visibility (SNMP) © 2011 Pearson Education, Inc. Publishing as Prentice Hall 36

 Described as OAM&P  Operations ◦ Moment-by-moment traffic management ◦ Network operations center  Administration ◦ Paying bills, administering contracts, and so on ◦ Dull but necessary © 2011 Pearson Education, Inc. Publishing as Prentice Hall 37

 Described as OAM&P  Provisioning (providing service) ◦ Includes physical installation ◦ Includes setting up user accounts and services ◦ Reprovisioning when things change ◦ Deprovisioning when accounts and services are no longer appropriate ◦ Collectively, extremely expensive © 2011 Pearson Education, Inc. Publishing as Prentice Hall 38

Core concernsQuality of service (QoS)Network designSelection among alternativesOngoing management (OAM&P) Network visibility (SNMP) © 2011 Pearson Education, Inc. Publishing as Prentice Hall 39

 It is desirable to have network visibility—to know the status of all devices at all times.  The simple network management protocol (SNMP) is designed to collect information needed for network visibility. © 2011 Pearson Education, Inc. Publishing as Prentice Hall 40

 Central manager program communicates with each managed device.  Actually, the manager communicates with a network management agent on each device. © 2011 Pearson Education, Inc. Publishing as Prentice Hall 41

 Network visualization programs analyze information from the MIB to portray the network, do troubleshooting, and answer specific questions.  SNMP interactions are standardized, but network visualization program functionality is not, in order not to constrain developers of visualization tools. © 2011 Pearson Education, Inc. Publishing as Prentice Hall 42