chapter 8: internet operation. network classes class a: few networks, each with many hosts all...
TRANSCRIPT
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Chapter 8: Internet Operation
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Network Classes
• Class A: Few networks, each with many hostsAll addresses begin with binary 0
• Class B: Medium networks, medium hostsAll addresses begin with binary 10
• Class C: Many networks, each with few hosts
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Internet Addressing
• 32-bit global Internet address
• Includes network and host identifiers
• Dotted decimal notation– 11000000 11100100 00010001 00111001
(binary)– 192.228.17.57 (decimal)
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Subnets & Subnet Masks
• Allows for subdivision of internets within an organization
• Each LAN can have a subnet number, allowing routing among networks
• Host portion is partitioned into subnet and host numbers
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Subnet Mask Calculations
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Subnetworking Example
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Internet Routing Protocols
• Responsible for receiving and forwarding packets between interconnected networks
• Must dynamically adapt to changing network conditions
• Two key concepts– Routing information– Routing algorithm
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Autonomous Systems
• Key characteristics– Set of routers and networks managed by single
organization– group of routers exchanging information via a common
routing protocol– connected (in a graph-theoretic sense); that is, there is a
path between any pair of nodes
• Interior Router Protocol (IRP) passes information between routers in an AS (Autonomous systems)
• Exterior Router Protocol (ERP) passes information between routers in different AS
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Border Gateway Protocol (BGP)
• Preferred ERP for the Internet
• BGP-4 is the current version
• Three functional procedures– Neighbor acquisition– Neighbor reachability– Network reachability
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Open Shortest Path First (OSPF)
• Widely used as IRP in TCP/IP networks• Uses link state routing algorithm• Routers maintain topology database of AS
– Vertices• Router• Network
– Transit– Stub
– Edges• Connecting router vertices • Connecting router vertex to network vertex
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Autonomous System Example
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Open Shortest Path First (OSPF) Protocol
• Widely used interior protocol to TCP/IP networks
• Computes a route through the network that incurs the least cost
• User can configure the cost as a function of:-delay-data rate-cost
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The “Need for Speed” andQuality of Service (QoS)
• Image-based services on the Internet (i.e., the Web) have led to increases in users and traffic volume– Resulting need for increased speed– Lack of increased speed reduced demand
• QoS provides for varying application needs in Internet transmission
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Emergence of High-Speed LANs
• Until recently, internal LANs were used primarily for basic office services
• Two trends in the 1990s changed this– Increased power of personal computers– MIS recognition of LAN value for client/server and
intranet computing
• Effect has been to increase volume of traffic over LANs
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Corporate WAN Neds
• Greater dispersal of employee base
• Changing application structures– Increased client/server and intranet– Wide deployment of GUIs– Dependence on Internet access
• More data must be transported off premises and into the wide area
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Digital Electronics
• Major contributors to increased image and video traffic
• DVD (Digital Versatile Disk)– Increased storage means more information to
transmit
• Digital cameras– Camcorders– Still Image Cameras
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QoS on the Internet
• Elastic Traffic– Can adjust to changes in delay and throughput
access– Examples: File transfer, e-mail, web access
• Inelastic Traffic– Does not adapt well, if at all, to changes– Examples: Real-time voice, audio and video
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Requirements of Inelastic Traffic
• Throughput– Minimum value may be required
• Delay– Services like market quotes are delay-sensitive
• Delay variation– Real-time applications, like teleconferencing, have
upper bounds on delay variation
• Packet loss– Applictions vary in the amount of packet loss
allowable
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Application Delay Sensitivity
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Differentiated Services
• Provide QoS on the basis of user needs rather than data flows
• IP packets labeled for differing QoS treatment • Service level agreement (SLA) established between the
provider (internet domain) and the customer prior to the use of DS.
• Provides a built-in aggregation mechanism.• Implemented in routers by queuing and forwarding
packets based on the DS octet.• Routers do not have to save state information on packet
flows.
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DS Service:Performance Parameters
• Service performance parameters
• Constraints on ingress/egress points
• Traffic profiles
• Disposition of excess traffic
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Service Level Agreements (SLA)
• Contract between the network providor and customer that defines sepecific aspects of the service provided.
• Typically includes:-Service description-Expected performance level-Monitoring and reporting process
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SLA ExampleMCI Internet Dedicated Service
• 100% availability
• Average round trip transmissions of ≤ 45 ms with the U.S.
• Successful packet delivery rate ≥ 99.5%
• Denial of Service response within 15 minutes
• Jitter performance will not exceed 1 ms between access routers
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IP Performance Metrics
• Three Stages of Metric Definitions-Singleton-Sample-Statistical
• Active techniques require injecting packets into the network
• Passive techniques observe and extract metrics