Chapter 8: Internet Operation

Business Data Communications, 6e

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

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 AP• Exterior Router Protocol (ERP) passes

information between routers in different Aps

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

Directed Graph of Example

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

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

• Service performance parameters• Constraints on ingress/egress points• Traffic profiles• Disposition of excess traffic

DS Services Provided

• Traffic offered at service level A will be delivered with low latency.

• Traffic offered at service level B will be delivered with low loss.

• 90% of in-profile traffic delivered at service level C will experience no more than 50 ms latency.

• 95% of in-profile traffic delivered at service level D will be delivered.

• Traffic offered at service level E will be allotted twice the bandwidth of traffic delivered at service level F

• Traffic with drop precedence X has a higher probability of delivery than traffic with drop precedence Y.

DS Field• Packets labeled for handling in 6-bit DS field in the IPv4

header, or the IPv6 header• Value of field is “codepoint”• 6-bits allows 64 codepoints in 3 pools

– Form xxxxx0 - reserved for assignment as standards.– Form xxxx11 - reserved for experimental or local use.– Form xxxx01 - also reserved for experimental or local use, but

may be allocated for future standards action as needed.• Precedence subfield indicates urgency

– Route selection, Network service, Queuing discipline• RFC 1812 provides two categories of recommendations

for queuing discipline– Queue Service– Congestion Control

DS Configuration Diagram

DS Configuration & Operation

• Routers are boundary or interior nodes• Forwarding treatment is per-hop behavior (PHB)• Boundary nodes handle traffic conditioning

– Classifier– Meter– Marker– Shaper– Dropper

Traffic Conditioning Diagram

Token Bucket Scheme

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 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

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

Model for Defining Packet Delay Variation