INFO 331 Computer Networking Technology II

1
INFO 331Computer Networking Technology II

• Network Design Intro
• Glenn Booker

2
Network Design

• Through the Kurose text weve covered
• The application, transport, network, link
  layers
• Wireless and multimedia technologies
• Security
• Network management
• Not bad!
• So how does all this come together to help create
  a network?

3
Network Design

• Ok, thats not a small question well just
  tickle the surface (not even scratch!)
• Main resources for this section are
• McCabe, James D. (2003). Network Analysis,
  Architecture Design (2nd Ed.). San Francisco
  Morgan Kaufmann Publishers. Chapters 1-5, 10
• Teare, Diane. (2004). CCDA Self-Study Designing
  for Cisco Internetworking Solutions (DESGN).
  Indianapolis Cisco Press.

4
Network Design Objective

• Ultimately, our network design must answer some
  pretty basic questions
• What stuff do we get for the network?
• How do we connect it all?
• How do we have to configure it to work right?
• Traditionally this meant mostly capacity planning
  having enough bandwidth to keep data moving
• May be effective, but result in over engineering

5
Network Design Objective

• And while some uses of the network will need a
  lot of bandwidth (multimedia), we may also need
  to address
• Security
• Considering both internal and external threats
• Possible wireless connectivity
• Reliability and/or availability
• Like speed for a car, how much are you willing
  to afford?

6
Network Design Phases

• Designing a network is typically broken into
  three sections
• Determine requirements
• Define the overall architecture
• Choose technology and specific devices

(McCabe, 2003)
7
Systems Methodology

• Theres lots of room for refining these sections
  (Teare, 2004)
• Identify customer requirements
• Characterize the existing network
• Design topology
• Plan the implementation
• Build a pilot network
• Document the design
• Implement the design, and monitor its use

8
Two Main Principles

• For a network design to work well, we need to
  balance between
• Hierarchy how much network traffic flows
  connect in tiers of organization
• Like tiers on an org chart, hierarchy provides
  separation and structure for the network
• Interconnectivity offsets hierarchy by allowing
  connections between levels of the design, often
  to improve performance between them

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Two Main Principles
(McCabe, 2003)
10
Plan Ahead!

• The 80/20 rule applies here
• 80 of the cost of a network is its operation
  and support
• Only 20 is the cost of designing and
  implementing it
• So plan for easy operation, maintenance, and
  upgrade of the network

11
Requirements? Booooring!

• Yes, determining the requirements for a network
  probably isnt as much fun as shopping for really
  expensive hardware
• And that may be why many networks are poorly
  designed no one bothered to think through
  their requirements!
• Many people will jump to a specific technology or
  hardware solution, without fully considering
  other options the obvious solution may not be
  the best one

12
Requirements

• We need to develop the low level design and the
  higher level architecture, and understand the
  environment in which they operate
• We also need to prove that the design weve
  chosen is just right (Southey, 1837)
• Is that 2 million network backbone really enough
  to meet our needs?
• How do we know 500,000 wouldnt have been good
  enough?

13
Requirements

• Part of this process is managing the customers
  expectations
• They may expect a much simpler or more expensive
  solution than is really needed
• Showing analysis of different design options,
  technologies, or architectures can help prove
  you have the best solution

14
Requirements

• We need to use a systems approach for
  understanding the network
• The system goes far beyond the network hardware,
  software, etc.
• Also includes understanding the users,
  applications or services, and external
  environment
• How do these need to interact?
• What does the rest of the organization expect
  from the network?

15
Requirements

• Consider how devices communicate

Images from (McCabe, 2003) unless noted otherwise
16
Requirements

• What services are expected from the network?
• Typical performance levels might include
  capacity, delay time, reliability
• Providing 1.5 Mb/s peak capacity to a remote user
• Guaranteeing a maximum round-trip delay of 100 ms
  to servers in a server farm
• Functions include security, accounting,
  scheduling, management
• Defining a security or privacy level for a group
  of users or an organization

17
Requirements

• Service requirements could include the QoS
  (quality of service) guarantees (ATM, Intserv,
  Diffserv, etc.)
• This connects to network management monitoring of
  network performance

18
Requirements

• Capacity refers to the ability to transfer data
• Bandwidth is the theoretical capacity of some
  part of the network
• Throughput is the actual capacity, which is less
  than the bandwidth, due to protocol overhead,
  network delays, etc.
• Kind of like hard drive actual capacity is always
  less than advertised, due to formatting

19
Requirements Analysis

• Given these concepts, how do we describe
  requirements for a network?
• Need a process to filter or classify requirements
• Network requirements (often have high, medium,
  low priorities)
• Future requirements (planned upgrades)
• Rejected requirements (remember for future ref.)
• Informational requirements (ideas, not required)

20
Requirements Analysis

• Requirements can come from many aspects of the
  network system
• User Requirements
• Application Requirements
• Device Requirements
• Network Requirements
• Other Requirements

21
User Requirements

• User requirements are often qualitative and very
  high level
• What is fast enough for download? System
  response (RTT)?
• How good does video need to be?
• Whats my budget?

22
Application Requirements

• What types of apps are we using?
• Mission-critical
• Rate-critical
• Real-time and/or interactive
• How sensitive are apps to RMA (reliability,
  maintainability, availability)?
• What capacity is needed?
• What delay time is acceptable?

23
Application Requirements

• What groups of apps are being used?
• Telemetry/command and control - remote devices
• Visualization and simulation
• Distributed computing
• Web development, access, and use
• Bulk data transport FTP
• Teleservice VOIP, teleconference
• Operations, admin, maintenance, and provisioning
  (OAMP) DNS, SMTP, SNMP
• Client-server ERP, SCM, CRM

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Application Requirements

• Where are the apps located?
• Are some only used in certain locations?

25
Device Requirements

• What kinds of devices are on your network?
• Generic computing devices include normal PCs,
  Macs, laptops, handheld computers, workstations
• Servers include all flavors of server file,
  print, app/computation, and backup
• Specialized devices include extreme servers
  (supercomputers, massively parallel servers),
  data collection systems (POS terminals),
  industry-specific devices, networked devices
  (cameras, tools), stoplights, ATMs, etc.

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Device Requirements

• Specialized devices are often location-specific

27
Device Requirements

• We want an understanding of the devices
  performance its ability to process data from
  the network
• Device I/O rates
• Delay time for performing a given app function

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Device Requirements

• Performance results from many factors
• Storage performance, that is, flash, disk drive,
  or tape performance
• Processor (CPU) performance
• Memory performance (access times)
• Bus performance (bus capacity and arbitration
  efficiency)
• OS performance (effectiveness of the protocol
  stack and APIs)
• Device driver performance

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Device Requirements

• The device locations are also critical
• Often generic devices can be grouped by their
  quantity
• Servers and specialized stuff are shown
  individually

30
Network Requirements

• Network requirements (sounds kinda redundant) are
  the requirements for interacting with the
  existing network(s) and network management
  concerns
• Most networks have to integrate into an existing
  network, and plan for the future evolution of the
  network

31
Network Requirements

• Issues with network integration include
• Scaling dependencies how will the size of the
  existing network affect the new one?
• Will the existing network change structure, or
  just add on a new wing?
• Location dependencies interaction between old
  and new networks could change the location of key
  components
• Performance constraints existing network could
  limit performance of the new one

32
Network Requirements

• Network, system, and support service dependencies
• Addressing, security, routing protocols and
  network management can all be affected by the
  existing network
• Interoperability dependencies
• Changes in technology or media at the interfaces
  between networks need to be accounted for, as
  well as QoS guarantees, if any
• Network obsolescence do protocols or
  technologies become obsolete during transition?

33
Network Requirements

• Network management and security issues need to be
  addressed throughout development
• How will the network be monitored for events?
• Monitoring for network performance?
• What is the hierarchy for management data flow?
• Network configuration?
• Troubleshoot support?

34
Network Requirements

• Security analysis can include the severity
  (effect) of an attack, and its probability of
  occurrence

35
Other Requirements

• Requirements can come from other outside sources
  your customer, legal requirements, larger scale
  organization (enterprise) requirements, etc.
• Additional requirements can include
• Operational suitability how well can the
  customer configure and monitor the system?
• Supportability how well can the customer
  maintain the system?

36
Other Requirements

• Confidence what is the data loss rate when the
  system is running at its required throughput?
• Financial requirements can include not only the
  initial system cost, but also ongoing maintenance
  costs
• System architecture may be altered to remain
  within cost constraints
• This is a good reason to present the customer
  with design choices, so they see the impact of
  cost versus performance

37
Other Requirements

• Enterprise requirements typically include
  integration of your network with existing
  standards for voice, data, or other protocols

38
Requirements Spec and Map

• A requirements specification is a document which
  summarizes the requirements for (here) a network
• Often it becomes a contractual obligation, so
  assumptions, estimates, etc. should be carefully
  spelled out
• Requirements are classified by Status, as noted
  earlier (core/current, future, rejected, or
  informational requirement)

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Requirements Spec and Map

• Priority can provide additional numeric
  distinction within a given Status (typically on
  a 1-3 or 1-5 scale)
• Sources for Gathering requirements can be
  identified, or give basis for Deriving it
• Type is user, app, device, network or other

40
Requirements Spec and Map

• Requirements Mapping can show graphically where
  stuff is, what kind of apps are used, and
  existing connectivity

41
Requirements Analysis Process

• So, how do we determine what the requirements are
  for our network?
• Collect requirements service metrics, and delays
  to help develop and map requirements

42
Gather and List Requirements

• A great starting point is the very beginning
• What initial conditions are you facing?
• What type of project is this?
• New network, Modifying an existing network,
  Analysis of network problems, Outsourcing,
  Consolidation, Upgrade
• What is the overall scope of the project?
• Network size, Number of sites, Distance between
  sites

43
Initial Conditions

• Why is the network being designed? What are the
  goals for its architecture design?
• Upgrade technology and/or vendor
• Improve performance to part or all of network
• Support new users, applications, or devices
• Solve perceived problems within system
• Increase security
• Support a new capability in system

44
Initial Conditions

• What project constraints are there?
• Funding, organizations involved, existing
  network, facility limitations, schedule,
  political, etc.
• Are users receptive to the new network?
• Are user needs homogeneous, or are there multiple
  tiers of performance needs?
• The former is easier to handle, of course

45
Customer and User

• Customer expectations need to be set quickly
• What order of magnitude is the project, and does
  that match what they thought?
• Better to find out early on if theres a big gap!
• Working with users is important, to know how they
  use the network and what problems they find
  important
• Surveys, phone calls, personal meetings, and/or
  group discussions could be used

46
Customer and User

• Look for red flags in early discussions
• Abuse of the term "real-time"
• Availability as solely a percentage (99.99)
• "High performance" without verification or
  clarification
• Highly variable, inconsistent requirements
• Unrealistic expectations from the customer
• Measure application performance using existing
  network (if possible) or a test bed

47
Requirements Management

• The requirements you develop need to be tracked
  and managed, just like any systems requirements
• Identify requirements by some form of ID and
  short name
• Need a tool to track requirements, their status,
  changes, sources, etc.
• Map location of apps and devices of the existing
  network

48
Service Metrics

• Service metrics are characteristics measured or
  derived from the network
• Metrics must be configurable, measurable, and
  verifiable
• RMA metrics might include
• Reliability mean time between failures (MTBFs)
  and mean time between mission critical failures
  (MTBCFs)
• Maintainability mean time to repair (MTTR)
• Availability MTBF, MTBCF, and MTTR

49
Service Metrics

• Related RMA metrics include
• Uptime and downtime (percentage of total time)
• Error and loss rates at various levels, such as
  packet error rate, bit error rate (BER), cell
  loss ratio (CLR), cell misinsertion ratio (CMR),
  frame and packet loss rates
• Service metrics for capacity include
• Data rates peak data rate, sustained data rate,
  and minimum data rate
• Data sizes burst sizes and durations

50
Service Metrics

• Service metrics for delay include
• End-to-end or round-trip delay
• Latency
• Delay variation
• SNMP or CMIP (Common Management Information
  Protocol) can be used to configure these metrics,
  which are kept in the Management Information
  Base (MIB)

51
Service Metrics

• MIB Variables often used as service metrics
• Bytes in/out (per interface)
• IP packets in/out (per interface)
• Dropped ICMP messages per time per interface
• Service-level agreement (SLA) metrics (per user)
• Capacity limit
• Burst tolerance
• Delay
• Downtime

52
Metrics Tools

• Tools for making service metric measurements
  include
• Ping, pathchar, traceroute, TCPdump
• Packet capture utilities Ethereal, Sniffer, and
  Etherpeak
• Then summarize the metrics collection approach

53
Characterizing Behavior

• Next we can analyze how users and apps use the
  existing network
• We could use simulations or models to assess
  network behavior
• Thats way beyond the scope here!
• User behavior is looking for patterns in how
  people use apps
• How many users, how frequently, how long per
  session, how much data they use

54
Characterizing Behavior

• Application behavior includes looking at how each
  app uses the network
• Communication between client/server parts
• Multicast or broadcast transmissions how often,
  how big
• Focus on the most critical apps (mission
  critical, real time, interactive, etc.)
• Models can be simple or complex, as project size
  and time constraints dictate

55
RMA Requirements

• Reliability is a common measurement
• Mean time between mission critical failure
  (MTBCF) focuses on failures during certain time
  periods, excluding planned down times
• Mean time between failure (MTBF) includes failure
  at any time
• Maintainability is typically captured with mean
  time to repair (MTTR)

56
RMA Requirements

• Availability relates failures to repair time
• Scheduled maintenance time doesnt count against
  availability
• Uptime and downtime measure those percentages
  when the system is up or down
• The upper practical limit is 99.999 uptime,
  which is 5.3 minutes of downtime per year
• Uptime of 99.99 is fairly common
• How many events occur is also important

57
RMA Requirements

• Thresholds and limits can be defined for RMA
  measures
• MTBF is typically a couple thousand hours
• MTTR may be a few hours
• Different parts of the system may have different
  requirements

58
Delay Requirements

• Various delays can have a strong impact on
  network requirements
• Interaction delay (INTD) is how long a user will
  wait for a response from the system
• Human response time (HRT) is when a system delay
  becomes noticable to a user
• Network propagation delay is how long it takes
  for a command to cross the network and get the
  reply

59
Delay Requirements

• INTD and HRT help distinguish burst from bulk apps

60
Delay Requirements

• End-to-end and round-trip delays can be network
  requirements
• Weve used ping to get RTT (round trip time)
• Delay variation can be defined for multimedia
  apps typically is 1-2 of end-to-end delay

61
Capacity Requirements

• Much of the needed capacity of a network derives
  from key applications that are especially intense
  in such areas
• Peak data rate
• Minimum acceptable data rate
• Sustained (long term) data rate
• We need to distinguish apps that CAN use a lot of
  capacity (if its available), versus those that
  MUST use a lot

62
Data Rates

• Data rates for an app can be measured at many
  levels of the protocols
• App, network, etc.
• Most TCP apps will take whats available, but
  back off when the network gets crowded (why?)
• Often we may need to identify where the
  performance bottleneck is located
• It helps to get a rough idea of typical app
  performance

63
Typical App Capacity Needs
64
Data Rates

• Sometimes a range of values is more helpful
• Processing credit card info might take 5-10
  seconds, and require 100-1000 bytes of data
• Multimedia rates are well known, and depend on
  the protocol and level of compression and quality
  desired
• Low- and high-performance realms are completely
  subjective there are no industry or generic
  numbers to set them apart

65
Supplemental Performance

• Other non-functional requirements can be
  important to a network
• Operational Suitability is making sure your
  customer can operate the network once its
  running
• How often are manual network adjustments needed?
• How often does network configuration change?
• How much monitoring is automated?

66
Operational Suitability

• How many shifts of operators will there be?
• How well trained are the network operators?
• How often will hardware changes be needed?
• What hardware can the operators change?
• What level of component is an operator expected
  to be able to change? Chip, board, rack unit,
  entire rack? (Line-Replaceable Unit, LRU)
• All of this can result in a Concept of Operations
  description

67
Supportability

• Can the networks level of performance be
  sustained over time?
• Is affected by
• RMA of the architecture and design
• Workforce, including training and staffing levels
• System procedures and technical documentation
• Tools, both ordinary and special
• Spare and repair parts

68
Supportability

• Maintenance of a system expects
• Components are located where they can be
  maintained without affecting the rest of the
  system much
• Spare parts are supplied to allow replacement of
  failed and soon-failed components
• Reliability can be formally modeled with
  reliability block diagrams (RBDs) or failure mode
  and effect analysis (FMECA)

69
Supportability

• Workforce should be equivalent to the ones being
  replaced or at least as cheap overall
• Documentation typically includes
• Technical documentation of the system
  configuration, design, parts, etc.
• Maintenance procedures describe routine actions
• Casualty or corrective procedures describe how
  to troubleshoot, debug, or otherwise fix basic
  problems

70
Supportability

• Tools and test equipment describe what tools are
  needed to maintain the system
• How are faults detected?
• How is performance being monitored?
• What capabilities will be available to remotely
  diagnose, reconfigure, or reset components?
• Stuff breaks and wears out, so spare parts are
  needed to improve availability
• How much are you will to invest in parts?

71
Supportability

• All of this produces a concept for support of a
  network
• Important to state assumptions about the
  knowledge, skills, and availability of support
  personnel
• Spares are an ongoing investment the customer
  needs to be aware of their cost
• Often results in at least three tiers of support
  (onsite, central maintenance, and vendor)

72
Supportability
73
Confidence

• Confidence is the ability of a network to provide
  throughput at an acceptable error or loss rate
• Often thought of at the device or link level,
  but can also be considered end-to-end
• Measure by percent of traffic lost during a given
  time period (e.g. 2 loss up to 1 min)
• Ping might be used to measure losses

74
Environment-specific Limits

• What constitutes acceptable performance depends
  wildly on the industry or particular environment
  of the network
• High-performance devices often drive the
  acceptable thresholds or limits
• Also consider if predictable or guaranteed
  performance is important
• May lead to high QoS requirements, since best
  effort may not be good enough

75
Map and Spec

• Then, as mentioned earlier, map out the
  requirements, and write them in a specification
• Make sure you and your customer are in agreement
  on the needs of the network
• Prioritize requirements, so if something has to
  give, its not critical to your customer

76
Flow Analysis

• The requirements map is a great place to start
  analysis of flows in your network
• We dont want to model EVERY traffic (data) flow,
  just the important ones
• A traffic flow describes data movement, e.g.
• Source and/or destination addresses
• Type of information
• Directionality (bidirectional or unidirectional)
• Other aspects, such as QoS needs

77
Flow Analysis

• Later, flows can be broken down into subnet or
  link level flows
• A key purpose of flow analysis is to understand
  the balance between hierarchy and
  interconnectivity needed

78
Flow Analysis

• Flows can be individual, or grouped into
  composites
• Flows can be critical (and often drive
  architecture and design)

79
Flow Analysis

• The requirements spec should be able to define
  flows by user, app, device, network
• Looks for important flows by application,
  location, user type, device, type of function
  (multimedia, mission critical)
• Define capacity (Kbps or Mbps), delay
  requirements (ms), reliability requirement ()
• Map flows geographically

80
Flow Analysis
81
Consolidate Flows
82
Data Sources and Sinks

• Look for devices (servers, special devices) which
  generate lots of data (sources) or take in a lot
  of data (sinks)
• Consider also WHEN the flows occur are there
  specific times that are critical?
• Consider worst-case and normal-usage scenarios

83
Flow Models

• Model the flows using common examples
• Peer-to-peer
• Client-server
• Hierarchical client-server
• Distributed computing
• These models differ in directionality (or lack
  thereof), hierarchy, and interconnectivity

84
Peer-to-Peer Flow Model

• All users or apps are equal
• Flows are all critical or none are
• Flows are all equivalent (have same specification)

85
Client-Server Flow Model

• Requests are small data amounts compared to
  responses, so these flows are asymmetric toward
  the clients
• ERP, video editing, and web apps often follow
  this model

86
Hierarchical Client-Server
87
Distributed Computing

• Behavior varies inverse client-server,
  peer-to-peer, hybrid, etc.

88
Flow Prioritization

• Flows are typically prioritized based on many
  factors, only a couple of which are technical
• Capacity, delay, RMA, and/or QoS requirements
• Security requirements
• Number of users or apps affected by each flow
• Business or political objectives, and the impact
  of the flow on the customers business
• Who pays for it!

89
Flow Specification

• Like the requirements, the flows can be
  summarized in a specification of some kind
• Critical for identifying priorities, in case
  everyone cant be happy with your design
• Balancing flow requirements can be done with a
  flowspec algorithm
• Best effort algorithms only consider capacity
• Predictable flow reqts consider capacity, delay,
  and RMA
• Guaranteed flow reqts are treated separately

90
Network Architecture

• Now that we FINALLY have requirements and flows
  defined, we can consider how all this will affect
  the architecture of our network
• The architecture of a house needs many views to
  understand not only the exterior appearance, but
  also where the wires run, where the pipes are,
  ductwork for heating and cooling, etc.
• Similarly, we need several views of a network

91
Network Architecture

• Avoid thinking of just the physical components of
  a network (routers, hubs, etc.)
• Think of the functions its performing
  (addressing, routing, security, network
  management, performance) as an integral part of
  the components
• E.g. routing or switching can be affected by
  security
• So think of functional entities, not just HW

92
Network Architecture

• Measure network success by how well user, app,
  and device reqts are met functionally
• Also connects easier to traffic flows
• And scales well to large networks
• Each function will be defined by a component
  architecture combine them to get the overall
  reference architecture
• See house analogy a couple slides back

93
Network Architecture

• The design of a network is more detailed,
  technology- and location-specific description
  than its architecture
• Component architectures describe the hardware and
  software mechanisms needed to make a type of
  function work
• Each component is sort of a subsystem so well
  need to understand how they work together

94
Network Functions

• The key functions are
• Addressing and routing
• Network management
• Performance
• Security
• Functions may also include storage and
  infrastructure, but well focus on other ones
• Making this work may require trade-offs!

95
Basic Design Rules Regions

• Divide the network into regions, based on similar
  traffic flows
• Edges (access regions) are where flows start or
  stop
• Distribution regions are where flows collect and
  terminate (app or storage servers)
• Core (backbone) regions let collections of flows
  pass through
• External interfaces (DMZs) collect flows leaving
  or entering the network from outside

96
Addressing/Routing

• Addressing applies MAC or IP addresses for
  devices
• Routing establishes connectivity within and
  between networks
• This component architecture defines how user and
  management flows are forwarded, and how hierarchy
  interconnectivity are balanced in subnets

97
Addressing/Routing

• Mechanisms for this architecture could be
• Addressing subnetting, supernetting, dynamic vs
  private addressing, VLANs, IP v4 versus v6, NAT
• Routing CIDR, mobile IP, multicast, and various
  routing protocols (BGP, RIP, etc.), establish
  routing policies
• Notice at the architecture level were just
  choosing the types of mechanisms, not deciding
  exact structures

98
Network Management Arch.

• This decides how the network will be monitored
  and managed
• Types of mechanisms include
• Monitoring, instrumentation, configuration,
  security management components, does mgmt data
  flow in band or out?, how centralized is mgmt?,
  mgmt capacity needs, duplicate mgmt mechanisms,
  MIB selection

99
Performance Architecture

• This component defines how network performance
  will be established and managed
• Defines how network resources are allocated to
  users, apps, and devices
• Capacity planning, traffic engineering, QoS,
  access control, SLAs, policies, resource mgmt
• Balances end-to-end vs per-link prioritization
• DiffServ vs IntServ

100
Security Architecture

• How do you protect system resources and data from
  theft, damage, DoS, and unauthorized access?
• VPN, encryption, firewalls, routing filters, NAT
• Threat analysis, physical vs app security
• Define security zones (cells) for different
  levels of security
• Affects how other architectural components can
  interact with each other

101
Reference Architecture

• All these components need to be reconciled with
  each other
• Can add key reqts and chosen mechanisms to flow
  diagram
• Prioritize mechanisms and how they interact
• The Reference Architecture is the collection of
  all the component architectures

102
Reference Architecture

• Reqts dictate which components are favored, if
  any

103
Architectural Models

• Models for network architecture can be based on
  topology, flow, or functionality
• Generally more than one model is needed
• Often start with topology model and add other(s)
• Topology models are mainly
• The WAN/MAN/LAN model basic hierarchical
  structure
• The core/distribution/access model think of
  getting videos from CNN

104
Topology Models
105
Flow Models

• Weve already seen these (slides 84-87)
• Peer-to-peer
• Client-server
• Hierarchical client-server
• Distributed-computing

106
Functionality Models

• These models focus on supporting key functions in
  the network
• Service-provider like an ISP
• Intranet/Extranet focus on security and privacy
• Single-tier/Multi-tier Performance where flows
  indicate different levels of performance needs
• End-to-end Models where a single flow is
  critical to understand and fulfill
• These all require knowing location data

107
Functionality Models

• Service provider and intranet/ extranet models

108
Functionality Models

• No cartoon for single- or multi-tier model could
  be a combination of the others
• End-to-end model

109
Applying Models

• The flow and functional models overlap in focus
  with the core/distribution/access model

110
System Architecture

• The network (reference) architecture connects to
  the rest of the organization
• Related components and functions may include
  storage, clients and servers, databases, etc.
• How much detail outside of networking you include
  is up to the context of your problem

111
Selecting Technologies

• After the types of mechanisms in the reference
  architecture have been selected, we can start
  choosing more specific design technologies for
  our network
• This is where most people start network design
• Technologies need to be consistent with the goals
  of the network
• What is most important cost, capacity, QoS,
  security, manageability?

112
Selecting Technologies

• The goals may be different in different parts of
  the network
• Consider having a primary goal and one or more
  secondary goals
• Consider graphs to show tradeoffs
• Based on the flow requirements, how do you
  evaluate candidate technologies?
• RMA, capacity, cost, performance, supportability,
  etc. can be your basis for judging technologies

113
Selecting Technologies

• Consider a car-buying analogy if youre buying a
  car, you might consider many characteristics to
  make your choice
• Cost, performance, appearance, safety, comfort,
  load capacity, handling, reputation, reliability,
  etc.
• Here we look to the flowspec and reference
  architecture for the relative importance of each
  desirable characteristic

114
Selecting Technologies

• Consider also design and configuration issues for
  technology, not just price-vs-performance
• For example, many older technologies have
  built-in ARP capability
• Ethernet, Token Ring, and FDDI all do this
• But newer non-broadcast multiple access (NBMA)
  technologies dont have this
• ATM, frame relay, SMDS, HiPPI

115
Selecting Technologies

• As a result, using NBMA technologies requires
  separate support for broadcast and multicast
• Also consider how autonomous systems (ASs) are
  being formed and managed
• What kinds of connections are maintained in the
  network?
• Stateless, hard state, or soft state
• Connections require more work from the network

116
Technology Functions

• What features and functions will each technology
  offer to users, apps, and devices?
• Does it depend on the local infrastructure?
• Are flows asymmetric, like Web access?
• HFC and DSL both take advantage of this
• Are there distance limitations?
• Affects delay time, buffering, reliability needs,
  and HW

117
Performance Upgrades

• How easily can your design be upgraded?
• Generally focus on capacity, but delay and RMA
  may be affected too
• For examples, SONET optical carrier (OC) levels
  can be easily upped in capacity for ATM or HiPPI
• SONET Level Rate
• OC-3 155.52 Mb/s
• OC-12 622 Mb/s
• OC-48 2.488 Gb/s
• OC-192 9.953 Gb/s
• OC-768 39.812 Gb/s

118
Performance Upgrades
119
Flow Considerations

• The flow spec should help tell which flows have
  similar requirements, and which need special
  consideration for performance, capacity, or other
  needs
• Find backbone flows, which collect smaller flows
• Capacity planning is based on estimating usage,
  to compare against available technologies
• Service planning also compares levels of service
  needed

120
Guidelines for Tech Eval

• Use combined capacities for best-effort flows
  (generic Internet), and RMA, capacity, and/or
  delay requirements for predictable or guaranteed
  services
• Guideline 1 If predictable and/or guaranteed
  requirements are listed in the flow specification
  (service plan), then either the technology or a
  combination of technology and supporting
  protocols or mechanisms must support these
  requirements. This guideline restricts the
  selection of candidate technologies to those that
  can support predictable and/or guaranteed
  requirements.

121
Guidelines for Tech Eval

• For examples which are technology-dependent, for
  predictable service
• Quality-of-service levels in ATM
• Committed information rate levels in frame relay
• Differentiated service or integrated service
  levels in IP
• Guaranteed service gets even messier!

122
Guidelines for Tech Eval

• Guideline 2 When best-effort, predictable,
  and/or guaranteed capacities are listed in the
  flow specification, the selection of technology
  may also be based on capacity planning for each
  flow. Capacity planning uses the combined
  capacities from the flow specification to select
  candidate technologies, comparing the scalability
  of each technology to capacity and growth
  expectations for the network.

123
Guidelines for Tech Eval

• Specific flows in the flow spec can be mapped to
  the best technology solution
• Constraints in terms of RMA, delay, cost or QoS
  can be used to eliminate technologies
• Interaction with existing networks needs to be
  checked for possible conflicts
• Facility or other large scale issues may need to
  be addressed too

124
Segmenting the Network

• Now that we have nailed down technology choices,
  we can address the detailed structure of the
  network how its segmented
• Segmenting focuses technology selection
• We could do it by geography, groups of users
  (even virtual), or flow hierarchy
• Groups of users could belong to different
  organizations would that be a problem for
  security or privacy?

125
Segmenting the Network

• A geographic example of segmenting

126
Segmenting the Network

• A user-based view of segmenting

127
Segmenting the Network

• A flow hierarchy-based example

128
Segmenting the Network

• Segments can include defining broadcast domains,
  collision domains, or the scope of autonomous
  systems (ASs)
• Really large networks can be segmented by the
  type of functions and features involved in each
  segment (WAN, MAN, LAN, specialized equipment
  areas, core business areas, etc.)

129
Segmenting the Network

• Segmenting by types of function and feature

130
Black Box Method

• Once segments have been defined, we can view each
  segment as black box(es)
• Know inputs and outputs, and dont worry about
  the inner details yet
• A segment could have several black boxes

131
Black Box Method

• Then for each black box, determine the exact
  technology needs within it
• This lets us hide irrelevant information, and
  focus our technology decisions on critical info
• Naturally we dont want to have all technology
  decisions made in a vacuum, or wildly different
  or incompatible technologies may be chosen
• Common sense should prevail!

132
Summary

• Network design needs to understand and balance
  requirements from network users, applications,
  devices, and the external environment
• Flow analysis helps capture capacity, delay, QoS,
  reliability, and other critical aspects
• Then technology choices can be made based on
  segmenting the network by geography, user, flow
  spec, or functions provided