Δίκτυα και Επικοινωνίες

29 Οκτ 2013 (πριν από 4 χρόνια και 6 μήνες)

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1

Chapter 8:

Internet Operation

2

Objectives

Internet Routing Protocols

The Need for Speed and Quality of service

Differentiated Services

3

32
-
bit global internet address for source &

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

0

Class B
: Medium networks, medium hosts

10

Class C
: Many networks, each with few hosts

110

5

6

Network Classes
(cont.)

IP addresses are usually written in:

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

of
the 32
-

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:

(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

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

10

To

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

and

routing
.

11

(Cont.)

Then

to

allow

the

Routers

within

the

site

to

function

properly,

each

LAN

is

assigned

a

subnet

number
.

32
-
bit

Source

32
-
bit

Source

12

(Cont.)

To

include

the

subnet

number,

the

host

portion

of

the

internet

is

partitioned

into

a

subnet

number

and

a

host

number

to

accommodate

this

new

level

of

.

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

Within

the

subnetted

network,

the

local

Routers

must

route

on

the

basis

of

an

extended

network

number

13

(Cont.)

The

use

of

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

and

make

them

known

to

the

local

routers

14

The

effect

of

the

subnet

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
.

(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

of

the

form

192
.
228
.
17
.
X,

where

192

(
1100

0000
)

is

the

network

number

and

x

the

host

number
.

Example of Subnetworking:

17

18

Example
1
:

A

datagram

with

the

destination

192
.
228
.
17
.
57

arrives

at

R
1

from

the

rest

of

the

internet

or

from

LAN

Y
.

R
1

has

of

LAN

X,

LAN

Y,

LAN

Z
.

R
1

doesn’t

know

hosts

internal

to

these

LANs
.

In

order

to

determine

where

R
1

should

send

the

datagram

with

192
.
228
.
17
.
57
.

R
1

bitwise

AND

the

subnet

:

(
1111

1111
.
1111

1111
.
1111

1111
.
1110

000
)

i
.
e
.

(
255
.
255
.
255
.
224
)

and

IP

(
192
.
228
.
17
.
57
)

to

determine

that

destination

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
.

Host number:25

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

Host number:1

Net ID/subnet ID :192.228.17.96

Subnet number:3

Host number:1

For both R1 & R2 Routers

The

effect

of

the

subnet

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 &

(Cont.)

19

Binary Representation

Dotted
Decimal

11000000
.
11100100
.
00010001
.001110
01

192.228.17.5
7

R1 & R2 Routers

111111
.
1111111
.
11111111
.11100000

255.255.255.
224

Bitwise AND of
(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

(
192
.
228
.
17
.
57
)

arrives

at

R
2

from

LAN

Z,

R
2

applies

the

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

to

make

routing

decisions
.

The

default

subnet

for

a

give

class

of

is

a

null

which

yields

the

same

network

and

host

number

as

the

non
-
subnetted

.

Host number:25

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

Host number:1

Net ID/subnet ID :192.228.17.96

Subnet number:3

Host number:1

Subnets &

(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

to

a

static

-
permanent
-

route

based

on

the

traffic

makes

it

a

dynamic

route)

Must

dynamically

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

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
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

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
-

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,
-
-
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)

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

(e
.
g
.

stock

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

Packet loss

RT

applications

can

sustain

packet

loss

with

varying

amount

36

Requirements of Inelastic Applications

1. Application need to state their requirements
either:

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

.

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

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

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

)

field
.

Differentiated
service field

Explicit congestion

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

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

or

the

Traffic

Class

field

of

IP
v
6

.

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

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

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