Internet Addressing

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1

Chapter 8:

Internet Operation

Business Data Communications, 5e

2

Objectives


Internet Addressing


Internet Routing Protocols


The Need for Speed and Quality of service


Differentiated Services

3

Internet Addressing


32
-
bit global internet address for source &
destination in the IP header


Includes a
network identifier

and a
host identifier


Dotted decimal notation


11000000 11100100 00010001 00111001 (binary)


192.228.17.57 (decimal)

4

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

All addresses begin with binary
110

5

Format of IP Address

6

Network Classes
(cont.)


IP addresses are usually written in:

Dotted Decimal Notation
”, i.e. a
decimal number represent each
byte

of
the 32
-
bit address.


Example:

Binary representation of an IP is :


11000000

11100100

00010001

00111001

Decimal representation is:


192
.
228
.
17
.
57

(decimal).

7

Network Classes
(cont.)


Class A Network begins with 0


Note:


Network addresses


(0000 0000) and


(0111 1111) are reserved


Therefore Class A contains:


(2
7

-

2 = 128
-

2 = 126) network numbers


Range of the 1
st

decimal number for Class A:

1.***.***.*** to 127.***.***.***

8

Network Classes
(cont.)


Class B begin with binary 10

starts from 1000 0000 (128)

ends to 1011 1111 (191)

i.e. Range of the 1
st

decimal number for Class B:


128.***.***.*** to 191.***.***.***

the 2
nd

Byte is also part of class B

i.e. there are 2
14

= 16,384 Class B
addresses

Class

B

9

Network Classes
(cont.)


Class C begin with binary 110

starts from 11000000 (192)

ends to 11011111 (223)


Range of the 1
st

decimal number for class C:

192.***.***.*** to 223.***.***.***

the 2
nd

& 3
rd

Byte is also part of class C

There are 2
21

= 2,097,152 Class C
addresses

10

Subnets & Subnet Masks


To

add

a

number

of

LANs

to

the

internet

and

insulate

their

internal

complexity

within

their

organization

by

assigning

a

single

“network

number”

to

all

the

LANs


From

the

point

of

view

of

the

rest

of

the

internet,

there

is

a

single

network

at

that

site
.


This

simplifies

addressing

and

routing
.

11

Subnets & Subnet Masks
(Cont.)


Then

to

allow

the

Routers

within

the

site

to

function

properly,

each

LAN

is

assigned

a

subnet

number
.

32
-
bit

Source

Address

32
-
bit

Source

Address

12

Subnets & Subnet Masks
(Cont.)


To

include

the

subnet

number,

the

host

portion

of

the

internet

address

is

partitioned

into

a

subnet

number

and

a

host

number

to

accommodate

this

new

level

of

addressing
.

Host Portion:

Class A: 24bit

Class B: 16 bit

Class C: 8 bit

Network Portion:

Class A: 7 + 1bits

Class B: 14+2 bits

Class C: 21+ 3 bits

Network

Host

Network

Subnet

Host

Extended

Network

Number or

Address Mask:

Within

the

subnetted

network,

the

local

Routers

must

route

on

the

basis

of

an

extended

network

number

13

Subnets & Subnet Masks
(Cont.)


The

use

of

address

mask

allows

the

host

to

determine

whether

an

outgoing

datagram

is

destined

for

a

host

on

the

same

LAN

(send

directly)

or

another

LAN

(send

datagram

to

router)


Some

methods

(manual

config
.
)

are

used

to

create

address

masks

and

make

them

known

to

the

local

routers

14

The

effect

of

the

subnet

mask

is

to

erase

the

portion

of

the

host

field

that

refers

to

an

actual

host

on

a

subnet
.

What

remains

is

the

network

number

and

the

subnet

number
.

Subnets & Subnet Masks
(Cont.)

16

A

local

complex

consisting

of

3

LANs

and

2

Routers
.

To

the

rest

of

the

internet,

this

complex

is

a

single

network

with

a

class

C

address

of

the

form

192
.
228
.
17
.
X,

where

192

(
1100

0000
)

is

the

network

number

and

x

the

host

number
.

Example of Subnetworking:

Subnets & Subnet Masks (Cont.)

17

Subnets & Subnet Masks (Cont.)

18


Example
1
:

A

datagram

with

the

destination

address

192
.
228
.
17
.
57

arrives

at

R
1

from

the

rest

of

the

internet

or

from

LAN

Y
.

R
1

has

addresses

of

LAN

X,

LAN

Y,

LAN

Z
.

R
1

doesn’t

know

about

hosts

internal

to

these

LANs
.



In

order

to

determine

where

R
1

should

send

the

datagram

with

receiver

address

192
.
228
.
17
.
57
.

R
1

bitwise

AND

the

subnet

mask
:



(
1111

1111
.
1111

1111
.
1111

1111
.
1110

000
)

i
.
e
.

(
255
.
255
.
255
.
224
)


and

IP

address

(
192
.
228
.
17
.
57
)

to

determine

that

destination

address

192
.
228
.
17
.
57

refers

to

subnet
:


(
11000000
.
111
.
00100
.
00010001
.
001
)


i
.
e
.

1
,

which

is

LAN

X,

and

so

forward

the

datagram

to

LAN

X
.

IP Address:192.228.17.57

Host number:25

IP Address:192.228.17.33

Host number:1

Net ID/subnet ID:192.228.17.32

Subnet number:1

Net ID/subnet ID :192.228.17.64

Subnet number:2

IP Address:192.228.17.65

Host number:1

Net ID/subnet ID :192.228.17.96

Subnet number:3

IP Address:192.228.17.97

Host number:1

For both R1 & R2 Routers

The

effect

of

the

subnet

mask

is

to

erase

the

portion

of

the

host

field

that

refers

to

an

actual

host

on

a

subnet
.

What

remains

is

the

network

number

and

the

subnet

number
.

Subnets &

Subnet Masks
(Cont.)

19

IP Address & Subnet Masks

Binary Representation

Dotted
Decimal

IP Address

11000000
.
11100100
.
00010001
.001110
01

192.228.17.5
7

Subnet Mask for both
R1 & R2 Routers

111111
.
1111111
.
11111111
.11100000

255.255.255.
224

Bitwise AND of
address and mask
(resultant
network/subnet
number)

1100000
.
11100100
.
00010001
.0010000
0

192.228.17.3
2

Subnet number

11000000
.
11100100
.
00010001
.001

1

Host number

00000000
.
00000000
.
00000000
.000110
01

25

1

1

0

0

0

0

0

0

.

1

1

1

0

0

1

0

0

.

0

0

0

1

0

0

0

1

.

0

0

1

1

1

0

0

1

192.228.17.57

1

1

1

1

1

1

1

1

.

1

1

1

1

1

1

1

1

.

1

1

1

1

1

1

1

1

.

1

1

1

0

0

0

0

0

255.255.255.224

1

1

0

0

0

0

0

0

.

1

1

1

0

0

1

0

0

.

0

0

0

1

0

0

0

1

.

0

0

1

0

0

0

0

0

192.228.17.32

1

1

0

0

0

0

0

0

.

1

1

1

0

0

1

0

0

.

0

0

0

1

0

0

0

1

.

0

0

1

1

0

0

0

0

0

0

0

0

.

0

0

0

0

0

0

0

0

.

0

0

0

0

0

0

0

0

.

0

0

0

1

1

0

0

1

25

21


Example
2
:

If

a

datagram

with

destination

address

(
192
.
228
.
17
.
57
)

arrives

at

R
2

from

LAN

Z,

R
2

applies

the

mask

and

then

determines

from

its

forwarding

database

that

datagrams

destined

for

subnet

1

should

be

forwarded

to

R
1


Hosts

must

also

employ

a

subnet

mask

to

make

routing

decisions
.


The

default

subnet

mask

for

a

give

class

of

addresses

is

a

null

mask,

which

yields

the

same

network

and

host

number

as

the

non
-
subnetted

address
.


IP Address:192.228.17.57

Host number:25

IP Address:192.228.17.33

Host number:1

Net ID/subnet ID:192.228.17.32

Subnet number:1

Net ID/subnet ID :192.228.17.64

Subnet number:2

IP Address:192.228.17.65

Host number:1

Net ID/subnet ID :192.228.17.96

Subnet number:3

IP Address:192.228.17.97

Host number:1

Subnets &

Subnet Masks
(Cont.)

22

Internet Routing Protocols


Routers

are

responsible

for

receiving

and

forwarding

packets

between

interconnected

networks


Routers

make

decisions

based

on

the

knowledge

of

the

topology

and

traffic/delay

conditions

of

the

Internet
.

(based

on

topology

leads

to

a

static

-
permanent
-

route

based

on

the

traffic

makes

it

a

dynamic

route)


Must

dynamically

adapt

to

changing

network

conditions

to

avoid

congested

and

failed

portions

of

the

network
.


Two

key

concepts

to

distinguish

in

routing

function
:


Routing

information

RI
:

Information

about

topology

&

delays


Routing

algorithm
:

The

algorithm

used

to

make

a

routing

decision

for

a

particular

datagram,

based

on

the

current

RI

23

Autonomous Systems (AS)

To proceed with Routing Protocol let’s introduce AS:


Key characteristics of an AS


Set of routers and networks managed by a
single
organization


Set 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
within

an AS


Exterior Router Protocol

(ERP) passes information
between routers
in different

ASs

24

Application of Interior and Exterior Routing Protocols

Interior router Protocol

Exterior router protocol

Autonomous System 1

Autonomous System 2

25

IRP & ERP


IRP: Interior router protocol


Needs to build up a detailed model of the
interconnection of routers within an AS in order to
calculate the
least
-
cost path

from a given router to
any network within the AS


ERP: Exterior router protocol


Supports the exchange of
summary

reachability
information between separately administered ASs.
Use of
summary information

means that an ERP is
simpler and uses less detailed information than an
IRP

26

Border Grouping Protocol (BGP)


BGP was designed to allow routers (called
gateways) in different AS to cooperate in the
exchange of routing information.


BGP has become the preferred
ERP

for the
internets that employ TCP/IP suite.


BGP has 3 functional procedures:

1. Neighbor acquisition

2. Neighbor reachability

3. Network reachability

27

Open Shortest Path First (OSPF)



Widely used as
IRP

in TCP/IP networks


Uses
link state routing

algorithm


Routers maintain topology database of AS


Topology is express as
directed graph

consisting of:

Router


Network

Transit:


Stub:

Vertices or Nodes:

Carry data that neither originates
nor terminates on an end system
attached to this network

If it is not a transit network

Edges

Connecting router vertices of two router connected by point
-
to
-
point link.

Connecting router vertex to network vertex of directly connected.

28

Open Shortest Path First (OSPF)
Cnt’d

An Autonomous System

Directed Graph of the
Autonomous System

29

Open Shortest Path First (OSPF)
Cnt’d

An Autonomous System

Directed Graph of the
Autonomous System

SPF tree for R6

30

SPF tree & Routing Table for Router R6

Routing Table for R6

SPF tree for R6

31

The need for speed and QoS

The Emergence of High
-
Speed LANs



Role of PCs & requirements of LANs in need for High
-
speed:

1.
More powerful PCs, graphical applications & GUI

2.
-
MIS Recognition of LAN as a viable computing platform,
-
C/S computing in business,
-
Graphics in transaction,
-
interactive applications on the Internet,
-
need to reduce the
acceptable delay on data transfer creating large volume of data to be handled over
LANs. So that 10Mbps Ethernets and 16 Mbps token rings are not adequate for High
-
speed LANs.



Effect has been to increase volume of traffic over LANs
:



Examples of requirements calling for high speed LAN

1.
Centralized server farm (e.g. color publishing operation)

2.
Power workgroup (e.g. software developers, CAD users transferring huge files across
the Internet to share with piers.)

3.
High
-
speed local backbone (i.e. interconnection of these LANs)

4.
Convergence and unified communications (voice/video, and collaborative applications
have increased the LAN traffic)

32

The need for speed and QoS


Corporate Wide Area Networking


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



Digital Versatile Disc (DVD)


Increased storage means more information to transmit


Digital Still Camera


Camcorders


Still Image Cameras

33

Quality of Service (QoS)


Real
-
time voice and video don’t work well under
the Internet’s “best effort” delivery service


Best effort?


fair delivery service, internet treats all packets equally.

During congestion packet delivery slows down.

In severe congestions, packets are dropped at random to
ease congestion.

No distinction is made in terms of the relative importance or
timeliness of traffic/packets.

(ATM
-
Asynchronous Transfer Mode, a packet switching with
fix size cells of 53 octet)



QoS provides for varying application needs in
Internet transmission

34

Categories of Traffic


Elastic


Can adjust to changes in delay and
throughput access


Examples: File transfer, e
-
mail, web access



Inelastic


Does not adapt well, if at all, to changes


Examples: Real
-
time voice, audio and video

35

Inelastic Traffic Requirements


Throughput


Requires a firm
minimum

value for throughput


Delay


result

in

acting

late

to

disadvantage

(e
.
g
.

stock

trading)


Delay Variation


RT

applications

(e
.
g
.

teleconferencing)

require

an

upper

bound
.

As

the

allowable

delay

gets

larger,

real

delay

in

delivering

the

data

gets

longer

and

a

larger

delay

buffer

is

required

at

the

receivers



Packet loss


RT

applications

can

sustain

packet

loss

with

varying

amount

36

Requirements of Inelastic Applications


1. Application need to state their requirements
either:


In advance by service request


on the fly by means of fields in the IP



The 1st approach is preferred because the network can
anticipate demands and deny new requests if the resources
are limited.



2. During congestion, elastic traffic need still be
supported by:


introducing a
reservation protocol

to deny service
requests that would leave too few resources
available to handle current elastic traffic

37

Sensitivity ==> demand Qos to provide TIMELY and HIGH data rate

Criticality ==> QoS to provide RELIABILITY

A Comparison of Application Delay Sensitivity and Criticality in an
Enterprise

38

Differentiated Services
(DS)


Functionality

in

the

internet

and

private

internets

to

support

specific

QoS

requirements

for

a

group

of

users
,

all

of

whom

use

the

same

service

label

in

IP

packets
.


All

the

traffic

on

the

Internet

is

split

into

groups

with

different

QoS

requirements

and

that

routers

recognize

different

groups

on

the

basis

of

a

label

in

the

IP

header
.

39

Differentiated Services (DS)
-
Cont.


Provides

QoS

based

on

“user

group

needs”

rather

than

traffic

flows


Key

characteristics

of

DS
:


Differing

QoS

are

labeled

using

the


6
-
bit

DS

field”

in

the

IPv
4

and

IPv
6

headers


Service
-
Level

Agreements

(SLA)

govern

DS,

eliminating

need

for

application
-
based

assignment


DS

provides

a

built
-
in

aggregation

mechanism
.

All

traffic

with

the

same

DS

octet

is

treated

the

same

by

the

network

service


DS

is

implemented

in

individual

router

by

queuing

and

forwarding

packets

based

on

the

DS

octet

40

Ip
v
4 Header

Type of

Service Field

Allows the user

to guide IP and router.


This field was not used

until recent

introduction of

Differentiated Services

41

Ip
v
4 Type of Service Field

DS/ECN

(
8

bits)
:

Prior

to

the

introduction

of

differentiated

services,

this

field

was

referred

to

as

the

Type

of

Service

field

and

specified

reliability,

precedence,

delay,

and

throughput

parameters
.

This

interpretation

has

now

been

superseded
.


The

first

6

bits

of

the

TOS

field

are

now

referred

to

as

the

DS

(differentiated

services)

field
.


The

remaining

2

bits

are

reserved

for

an

ECN

(explicit

congestion

notification
)

field
.

Differentiated
service field

Explicit congestion
notification field

42

DS Framework Document


A

DS

framework

document

lists

the

following

detailed

performance

parameters

that

might

be

included

in

an

SLA
:



Service

performance

parameters

(e
.
g
.

expected

throughput,

drop

probability,

and

latency)



Constraints

on

the

ingress

(right

to

enter)

and

egress

(right

of

going

out)

points

at

which

the

service

is

provided,

indicating

the

scope

of

the

service



Traffic

profiles

that

must

be

adhered

to

for

the

requested

service

to

be

provided,

such

as

token

bucket

parameters



Disposition

of

traffic

submitted

in

excess

of

the

specified

profile

43

DS Framework Document


The

framework

document

also

gives

some


examples

of

services

that

might

be

provided
:



Qualitative

Examples
:

1.
Traffic

offered

at

service

level

A

will

be

delivered

with

low

latency

2.
Traffic

offered

at

service

level

B

will

be

delivered

with

low

loss


Quantitative

Examples
:

3.
90
%

of

in
-
profile

traffic

delivered

at

service

level

C

will

experience

no

more

than

50

ms

latency

4.
95
%

of

in
-
profile

traffic

delivered

at

service

level

D

will

be

delivered
.


Mixed

Qualitative

and

Quantitative

Examples
:

5.
Traffic

offered

at

service

level

E

will

be

allotted

twice

the

bandwidth

of

traffic

delivered

at

service

level

F

6.
Traffic

with

drop

precedence

X

has

a

higher

probability

of

delivery

than

traffic

with

drop

precedence

Y

44

DS Octet

Packets

are

labeled

for

service

handling

by

means

of

the

DS

octet
,

which

is

placed

in

the

Type

of

Service

field

of

an

IP
v
4

header

or

the

Traffic

Class

field

of

IP
v
6

header
.

IP Header

47

DS Field


6 bit DS field is used to label packets for service
handling.


The value of the DS field is referred to as the
DS
codepoint
.


6 bits provide 64 (i.e. 2
6

= 64) classes of traffic.


6 bit code point is divided into 3 categories.


48

DS Field/DS Octet Format


R
equest

F
or

C
omments

2474 defines the DS octet as having the
following format:



The left most
6

bits form a DS
codepoint

and the rightmost
2

bits are
currently
unused
.


The DS
codepoint

is the DS label used to
classify packets

for
differentiated services.


With a
6
-
bit codepoint, there are, in principle,
64

different
classes

of
traffic that could be defined.


These
64

codepoints are allocated across
3

pools (categories)

of
codepoints, as follows:

49

DS Octet Format

(x is either 0 or 1)

1. Standard

2. Experimental/Local Use

3. Experimental/Local Use

or Future Standards

Default Packet Class

(best
-
effort forwarding)

Backward Compatibility

(or equivalent)
with the IPv4 precedence service

50

DS Octet Format

(x is either 0 or 1)

1. Standard

2. Experimental/Local Use

3. Experimental/Local Use

or Future Standards

00 00 00 Default Packet Class

(best
-
effort forwarding), in order they are
received, and as soon as link capacity becomes available.

51

DS Field


To explain the requirement of Codepoints,
precedence
field
of IPV4 should be described.


The original IPv4 includes “
type of service
” field which has
two subfields:



a 3
-
bit precedence subfield, and



a 4
-
bit TOS


These subfields serve complementary functions:


TOS provides guidance to the IP entity in the source or router
on selecting the next hop for each datagram.

The precedence subfield provides guidance about the relative
allocation of router resources for the datagram.


xxx 000 Backward Compatibility

(or equivalent)
with the IPv4 precedence service.

52

What is Precedence Field?


Precedence field is set to indicate the degree of urgency or priority
to be associated with a datagram. If a router supports the
precedence subfield, there are 3 approaches to responding:


1.
Route selection:

A particular route may be selected if the router
has a smaller queue for that route or if the next hop on that route
supports network precedence or priority (e.g. a token ring network
supports priority).


2.
Network service:

If the network on the next hop supports
precedence, then that service is invoked


3.
Queuing discipline:

A router may use precedence to affect how
queues are handled. For example a router may give preferential
treatment in queues to datagrams with higher precedence.

53

R
equest

F
or

C
omments

1812


RFC 1812 ( Requirementes for IPV4)
provides recommendations for queuing
discipline that falls into 2 categories.



Queue Service


Congestion Control

54

A

DS

domain

consists

of

a

set

of

contiguous

routers,

that

is,

it

is

possible

to

get

from

any

router

in

the

domain

to

any

other

router

in

the

domain

by

a

path

that

does

not

include

routers

outside

the

domain
.

Within

a

domain

interpretation

of

DS

codepoints

is

uniform,

so

that

a

uniform,

consistent

service

is

provided
.

DS Configuration & Operation

55

DS Configuration & Operation

56

DS Configuration & Operation


In

a

DS

domain


Routers

are

either

boundary

nodes

or

interior

nodes


Interior

nodes

use

per
-
hop

behavior

(PHB)

rules

57

DS Configuration & Operation


The

boundary

nodes

include

PHB

mechanisms

but

also

more

sophisticated

traffic

conditioning

mechanisms

required

to

provide

the

desired

service
.

Thus

interior

routers

have

minimal

functionality

and

minimal

overhead

in

providing

the

DS

service,

while

most

of

the

complexity

is

in

the

boundary

nodes
.

The

boundary

node

function

can

also

be

provided

by

a

host

system

attacched

to

the

domain,

on

behalf

of

the

applications

at

that

host

system
.

58

Elements of Traffic Conditioning Functions


Boundary nodes have PHB (per
-
hop behavior) & traffic
conditioning.


The traffic conditioning function consists of five elements:



Classifier: Classifies based on DS codepoints



Meter: Measures that the packet traffic meets packet class or exceeds



Marker: re
-
marking packets that exceed the profile for the best
-
effort



Shaper: Delaying packet stream as necessary.



Dropper: Drops packets if the rate of packets exceeds profile specification.

59

After

a

flow

is

classified
,

its

resource

consumption

must

be

measured
.

The

metering

function

measures

the

volume

of

packets

over

a

particular

time

interval

to

determine

a

flow’s

compliance

with

the

traffic

agreement
.

If

the

host

is

bursty,

a

simple

data

rate

or

packet

rate

may

not

be

sufficient

to

capture

the

desired

traffic

characteristics
.

Relationships Between the Elements of Traffic Conditioning

A token bucket scheme is an example of a way to define a traffic profile to take into
account both packet rate and burstiness.

60

Traffic Conditioning Diagram

61

Token Bucket Scheme

62

Service Level Agreements
(SLA)


Contract between the network provider
and customer that defines specific aspects
of the service provided.


Typically includes:

-
Service description

-
Expected performance level

-
Monitoring and reporting process

63

SLA Example

MCI Internet Dedicated Service


100% availability


Average round trip transmissions of ≤ 45 ms with
the U.S.


Successful packet delivery rate (reliability) ≥
99.5%


Denial of Service response within 15 minutes


Jitter performance will not exceed 1 ms between
access routers

64

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

65

Model for Defining Packet Delay
Variation

66

Token Bucket Scheme





Bucket

represents

a

counter,

indicating

allowable

number

of

octets

Bucket

fills

with

octet

token

R

:
=

average

data

rate

supported

B

:
=

Bucket

size

Therefore,


During

any

time

period

T
:

The

amount

of

data

sent

<

RT

+B

R:=input rate

M:=output rate

T: Duration of the max
-
rate burst

B+RT = MT

T = B/(M
-
R) sec