Chap 2

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Oct 26, 2013 (3 years and 10 months ago)

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Chapter 2

Network

Models

Copyright
©
The McGraw
-
Hill Companies, Inc. Permission required for reproduction or display.

Components of Communication


Sender


Receiver


Message


Transmission medium


Protocol

Effectiveness of Communication


Delivery (correct delivery)


Accuracy


Timeliness


Jitter


a subset of timeliness

2.
3

Data Flow


Simplex


Half
-
Duplex


Duplex

2.
4

Connection Types


Point
-
to
-
Point


Multi
-
point

2.
5

Physical Topologies


Bus


Ring


Star


Mesh


Compound

2.
6

Physical Topology Links


Let n=# of nodes. The number of links is:


Bus


n
-
1


Ring


n


Star


n
-
1 (includes the hub)


Mesh


n*(n
-
1)/2

2.
7

Network Types


LAN


nodes belonging to an address
space that is part of a well defined
domain

(where the
domain

is an address sub
-
domain).


WAN


When two or more LANs are linked
together.

2.
8

Chapter 2: Outline


2
.
1

Protocol

Layering


2
.
2

TCP/IP

Protocol

Suite


2
.
3

OSI

Model



2.
10

2
-
1 PROTOCOL LAYERING


A

protocol

defines

the

rules

that

the

sender,

receiver

and

all

intermediate

devices

must

follow

to

communicate

effectively
.

2.
11

2.1.1
Scenarios

Consider

two

scenarios
.


Scenario

1
:

communication

is

so

simple

it

occurs

in

one

layer
.


Scenario

2
:

communication

takes

place

in

three

layers
.

2.
12

2
-
1 PROTOCOL LAYERING


When

communication

is

simple,

one

simple

protocol

may

be

enough
;



When

the

communication

is

complex,

a

protocol

may

be

required

at

each

“layer”
.

2.
13

Figure 2.1
:
A single
-
layer protocol

2.
14

Figure 2.2
:
A three
-
layer protocol

2.
15

2.1.2 Principles of Protocol Layering

Consider

two

principles

of

protocol

layering
.

2.
16

2.1.2 Principles of Protocol Layering

Consider

two

principles

of

protocol

layering
.


1
.

For

half
-
duplex

or

full

duplex

data

flow,

each

layer

must

perform

a

forward

operation

and

the

corresponding

inverse

operation
.


2.
17

2.1.2 Principles of Protocol Layering

Consider

two

principles

of

protocol

layering
.


2
.

The

two

objects

under

each

layer

at

both

sites

should

be

identical
.

2.
18

Figure 2.2
:
A three
-
layer protocol

2.
19

2.1.3

Logical
Connections

The

principles

of

protocol

layering

lead

to

a

logical

connection

between

the

layers

at

sending

and

receiving

ends

of

the

communication
.

2.
20

Figure 2.3
:
Logical connection between peer layers

2.
21

2
-
2 TCP/IP PROTOCOL SUITE


A

protocol

defines

the

rules

that

both

the

sender

and

receiver

and

all

intermediate

devices

must

follow

to

communicate

effectively
.


2.
22

2
-
2 TCP/IP PROTOCOL SUITE


TCP/IP

is

a

five

layer

protocol

suite
.

2.
23

2
-
2 TCP/IP PROTOCOL SUITE


TCP/IP

is

a

five

layer

protocol

suite
.


Application

Layer

2.
24

2
-
2 TCP/IP PROTOCOL SUITE


TCP/IP

is

a

five

layer

protocol

suite
.


Application

Layer


Transport

Layer

2.
25

2
-
2 TCP/IP PROTOCOL SUITE


TCP/IP

is

a

five

layer

protocol

suite
.


Application

Layer


Transport

Layer


Network

Layer

2.
26

2
-
2 TCP/IP PROTOCOL SUITE


TCP/IP

is

a

five

layer

protocol

suite
.


Application

Layer


Transport

Layer


Network

Layer


Data

Link

Layer

2.
27

2
-
2 TCP/IP PROTOCOL SUITE


TCP/IP

is

a

five

layer

protocol

suite
.


Application

Layer


Transport

Layer


Network

Layer


Data

Link

Layer


Physical

Layer

2.
28

Figure 2.4
:
Layers in the TCP/IP protocol suite

2.
29

2.2.1 Layered Architecture

TCP/IP

protocol

suite

example
:


Consider

three

LANs


Each

LAN

has

a

group

of

hosts

connected

to

a

switch

(aka

2
-
level

switch)
.


Each

switch

is

connected

to

a

router

(aka

3
-
level

switch)

2.
30

Figure 2.5
:
Communication through an internet

2.
31

2.2.2 Layers in the TCP/IP Protocol Suite

Draw

a

diagram

with

multiple

nodes

in

each

LAN


Why

is

it

called

a

2
-
level

switch?


Why

is

a

router

is

3
-
level

switch?

2.
32

Figure 2.6
:
Logical connections between layers in TCP/IP

Logical

connections

2.
33

Network Data Objects

Data

objects
:


message

2.
34

Network Data Objects

Data

objects
:


message


segment


2.
35

Network Data Objects

Data

objects
:


message


segment


datagram

2.
36

Network Data Objects

Data

objects
:


message


segment


datagram


frame

2.
37

Network Data Objects

Network

data

object

taxonomy
:


message


segment


datagram


frame


signals

representing

bits

2.
38

Figure 2.7
:
Identical objects in the TCP/IP protocol suite

Identical objects (messages)

Identical objects (segment or user datagram)

Identical objects (datagram)

Identical objects (frame)

Identical objects (bits)

Identical objects (datagram)

Identical objects (frame)

Identical objects (bits)

2.
39

Network Data Objects

Data

Object

Taxonomy
:


Application

layer

-

message


Transport

layer

-

segment


Network

layer

-

datagram


Data

link

layer

-

frame


Physical

layer



signals

representing

bits

2.
40

2.2.3 The TCP/IP Layers

Descriptions

of

the

TCP/IP

layers

will

come

later
;


next,


we

will

follow

a

data

object

through

the

layers


2.
41

2.2.4 Encapsulation and Decapsulation

One

of

the

important

concepts

in

protocol

layering

in

the

Internet

is

encapsulation/

decapsulation
.



2.
42

2.2.4 Encapsulation and Decapsulation

As

the

object

passes

through

each

layer,

an

information

header

(and

or

trailer)

is

added

to

the

object
.


The

information

header

is

used

to

assist

in

any

of

these

tasks
:

routing

of

the

object,

flow

control,

error

detection,

error

correction,

etc
.


(see

next

slide)

2.
43

Figure 2.8
:
Encapsulation / Decapsulation

Encapsulation payload


Each layer receives an object that is
referred to as the payload, and then
attaches a data header.


Payload can be relative to each layer, or
absolute.


The absolute case refers to the original
object message.

2.
44

Example Encapsulation


Q: What is the efficiency of the link in
figure 2.8, between LANs if each header is
60 bytes and the message is 1000 bytes?


2.
45

Example Encapsulation


Q: What is the efficiency of the link in
figure 2.8, between LANs if each header is
60 bytes and the message is 1000 bytes?


A: 84.7%


2.
46

Example Encapsulation


Q: How does the efficiency change if the
message is only 100 bytes?



2.
47

Example Encapsulation


Q: How does the efficiency change if the
message is only 100 bytes?


A: 35.7%



2.
48

2.
49

Figure 2.9
:
Addressing in the TCP/IP protocol suite

2.
50

2
-
3 OSI MODEL


A

seven

layer

protocol

model
.

It

never

really

caught

on

due

to

the

success

of

TCP/IP

2.
51

Figure 2.11
:
The OSI model

2.
52

Figure 2.12
:
TCP/IP and OSI model

2.
53

2.3.1
OSI versus TCP/IP

When

we

compare

the

two

models,

we

find

that

two

layers,

session

and

presentation,

are

missing

from

the

TCP/IP

protocol

suite
.

These

two

layers

were

not

added

to

the

TCP/IP

protocol

suite

after

the

publication

of

the

OSI

model
.

The

application

layer

in

the

suite

is

usually

considered

to

be

the

combination

of

three

layers

in

the

OSI

model,

as

shown

in

Figure

2
.
12
.