Protocol Layering

inexpensivedetailedΔίκτυα και Επικοινωνίες

23 Οκτ 2013 (πριν από 4 χρόνια και 20 μέρες)

72 εμφανίσεις

10/23/2013

CST 415
-

Computer Networks

1

Protocol Layering

CST 415

10/23/2013

CST 415
-

Computer Networks

2

Topics


Definitions


Protocol Layer Boundaries


ISO OSI Model


7 Layer Model mapping onto TCP/IP

10/23/2013

CST 415
-

Computer Networks

3

Definitions

ISO

I
nternational
S
tandards
O
rganization


OSI

O
pen
S
ystems
I
nterconnect


TCP

T
ransmission
C
ontrol
P
rotocol


IP

I
nternet
P
rotocol

10/23/2013

CST 415
-

Computer Networks

4

Definitions

Protocol Layering


This is a concept that every student in this class
should be familiar with.


Good software design always involves precise
definition of functionality.


Interfaces must also be well defined.


Layering of protocol does just this.

»
Each layer has a job to do.

»
Each layer has an interface defined.

10/23/2013

CST 415
-

Computer Networks

5

Definitions

Protocol Layering


In development of communication software, the
engineer can choose to implement only those
layers relevant to their problem domain.


The catch…all lower layers must also be
implemented to have a correctly working system.

»
e.g. If I decide that layer 4 will solve the problem I am
dealing with, I must implement layer 1, 2, and 3 also.

10/23/2013

CST 415
-

Computer Networks

6

Protocol Layer Boundaries

Service

A set of primitive operations (functions) that a layer
provides to the layer above it.


Operations the layer will perform on behalf of it’s
users.


A service does not define anything related to
implementation.


A service relates to the interface between the two
layers.

»
The lower layer is the service provider.

»
The upper layer is the service client.

10/23/2013

CST 415
-

Computer Networks

7

Protocol Layer Boundaries

Service Definitions and Connection Behavior



Service and protocol definitions combine to
determine the “end
-
to
-
end” connection
behavior.


I can have a packet switched network
(connectionless) provide the services of a
connection oriented network.

10/23/2013

CST 415
-

Computer Networks

8

Protocol Layer Boundaries

Five service primitives for implementing a
simple connection
-
oriented service.

10/23/2013

CST 415
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Computer Networks

9

Protocol Layer Boundaries

Packets sent in a simple client
-
server interaction on
a connection
-
oriented network.

10/23/2013

CST 415
-

Computer Networks

10

Protocol Layer Boundaries

Protocol

A set of rules governing the format and meaning the
messages exchanged by peer entities in a specific layer.


Protocols are used to implement service definitions.


Peer
-
to
-
peer protocols can be changed without impacting
services.


Service definitions can be changed independent of
protocols.


Service definitions and protocol definitions are completely
decoupled.

10/23/2013

CST 415
-

Computer Networks

11

Protocol Layer Boundaries

A UML Model of
the relationship of
a
Service

and a
Protocol



Hmmm….

Crazy


Once again, the
idea of a “well defined
interface” and the
implementation.

TCP

Protocol

Transport

Service

listen()

connect()

send()

receive()

disconnect()

SPX Protocol

10/23/2013

CST 415
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Computer Networks

12

Protocol Layer Boundaries

The relationship between a service and a protocol.

10/23/2013

CST 415
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Computer Networks

13

Protocol Layer Boundaries


Peer layers
communicate
through protocol
definitions.



Parent, child
layers
communicate
through service
definitions

10/23/2013

CST 415
-

Computer Networks

14

Protocol Layer Boundaries

The philosopher
-
translator
-
secretary architecture.

Beer

Beer

Beer

Beer

Beer

Beer

10/23/2013

CST 415
-

Computer Networks

15

OSI 7
-
Layer Reference Model


Out of the International Standards
Organization Open Systems Interconnect
definition came the 7
-
layer reference model
for network communications.


This turned out to be a good model.


All communication protocols can be mapped
to this model.

10/23/2013

CST 415
-

Computer Networks

16

The OSI
reference
model.

10/23/2013

CST 415
-

Computer Networks

17

OSI 7
-
Layer Reference Model


Physical Layer


Transmission of raw bits.


signal voltage levels


bit timing


physical connection establishment/destruction



Data Link Layer


Data framing for
transformation of raw data.


sending a receiving “ack” frames.


flow control

10/23/2013

CST 415
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Computer Networks

18

OSI 7
-
Layer Reference Model


Network Layer


Controls operation of the
subnet.


Packet routing and route determination.


Network congestion control.


Address resolution and translation.



Transport Layer


Packet fragmentation and
reassembly.


end
-
to
-
end packet delivery.

10/23/2013

CST 415
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Computer Networks

19

OSI 7
-
Layer Reference Model


Session Layer


communication session
establishment and management.


dialog control (whose turn it is to transmit)


dialog synchronization and check pointing



Presentation Layer


Syntax and semantics of
transmitted information.


10/23/2013

CST 415
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Computer Networks

20

OSI 7
-
Layer Reference Model


Application Layer


applications that use
network services.


FTP


Telnet


HTTP


SMTP


POP


Other things that you write.


10/23/2013

CST 415
-

Computer Networks

21

7
-
Layer Mapping to TCP/IP

The TCP/IP reference model and OSI model

10/23/2013

CST 415
-

Computer Networks

22

7
-
Layer Mapping to TCP/IP


Transport Layer (TCP/UDP)


Guaranteed and
datagram packet delivery services.


Packet fragmentation and reassembly


end
-
to
-
end delivery



Internet Layer (IP)


Allow a host computer to send
information packets into a network and have them
show up at the desired destination computer.


Packet routing


Congestion control


10/23/2013

CST 415
-

Computer Networks

23

7
-
Layer Mapping to TCP/IP


Host
-
to
-
network


The host computer must connect
to the network so IP packets can be sent and
received. This is the layer that encompasses the
physical layer and the MAC layer.


Ethernet


ATM


etc.



Application


This is where the user application
protocols reside.


Telnet


ftp


etc.


10/23/2013

CST 415
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Computer Networks

24

7
-
Layer Mapping to TCP/IP

Protocols and networks in the TCP/IP model.