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Chapter 8: Internet Operation
Network Classes
• Class A: Few networks, each with many
hosts
All addresses begin with binary 0
• Class B: Medium networks, medium hosts
All addresses begin with binary 10
• Class C: Many networks, each with few
hosts
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)
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
Subnet Mask Calculations
Subnetworking Example
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
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
Border Gateway Protocol (BGP)
• Preferred ERP for the Internet
• BGP-4 is the current version
• Three functional procedures
– Neighbor acquisition
– Neighbor reachability
– Network reachability
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
Autonomous System Example
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
The “Need for Speed” and
Quality 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
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
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
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
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
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
Application Delay Sensitivity
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.
DS Service:
Performance Parameters
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Service performance parameters
Constraints on ingress/egress points
Traffic profiles
Disposition of excess traffic
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
SLA Example
MCI 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
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