Chapter 8: Internet Operation

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Chapter 8: Internet Operation

Business Data Communications,
6e

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 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” 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


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 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

Model for Defining Packet
Delay Variation