CSC 535 Communication Networking I Chapter 2 Layered Architectures Dr. Cheer-Sun Yang.

CSC 535Communication Networking I

Chapter 2Layered Architectures

Dr. Cheer-Sun Yang

2

Protocol StacksTypically, communications is achieved via the

cooperation of software and hardwareCommunication software and hardware are

grouped into manageable sets called layersWe use the term network architecture to refer

to a set of protocols that specify how every layer is to function

A reference model, called a protocol stack, is used for understanding various networking protocols and their relations

OSI (7 layers) vs. TCP/IP (5 layers)

3

Examples of Layering-Web BrowsingA client/server model A server process waits for incoming

requests by listening to a port.A client process makes requests as

desired.The server program usually is executed in

the background and is referred to as a daemon. For example, httpd refers to the server daemon for HTTP

Copyright 2000 McGraw-Hill Leon-Garcia and Widjaja Communication Networks

4

The user clicks on a link to indicate which document is to be retrieved.

The browser must determine the address that contains the document. It does this by sending a query to its local name server.

Once the address is known the browser establishes a connection to the specified machine, usually a TCP connection. In order for the connection to be successful, the specified machine must be ready to accept TCP connections.

The browser runs a client version of HTTP, which issues a request specifying both the name of the document and the possible document formats it can handle.

The machine that contains the requested document runs a server version of HTTP. It reacts to the HTTP request by sending an HTTP response which contains the desired document in the appropriate format.

The TCP connection is then closed and the user may view the document.

1.

2.

3.

4.

5.

6.

Figure 1.4 - Introduces topic


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HTTPserver

HTTPclient

Request

Response

Figure 2.1


6

HTTPserver

HTTPclient

TCP TCP

GET 80, #

#, 80 STATUS

Port 80

Ephemeral

Port #

Figure 2.2

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The OSI Reference ModelA layer model defined by the ISO as an effort

to develop a seven-layer reference model for open system interconnection (OSI).

Each layer performs a subset of the required communication functions

Each layer relies on the next lower layer to perform more primitive functions

Each layer provides services to the next higher layer

Changes in one layer should not require changes in other layers

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How do layers work together?A concept called data encapsulation is

applied.In each layer, the smallest unit of data is

called a Protocol Data Unit (PDU). Each PDU contains a header, which contains protocol control information, and usually user information in the form of a service data unit (SDU).

“Conversations” occur between peer entities on different hosts.


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nentity

n-PDUs

nentity

Figure 2.3


10

n+1entity

n-SAP

n+1entity

n-SAP

n entity n entity

n-SDU

n-SDU

n-SDU

H

H n-SDU

n-PDU

Figure 2.4

11

OSI as Framework for Standardization

12

Layer Specific Standards


13

n-SDU

n-PDU n-PDU n-PDU

n-SDU

n-PDU n-PDU n-PDU

Segmentation Reassembly

n-PDU

n-SDU

n-PDU

Blocking Unblocking

n-SDUn-SDUn-SDUn-SDUn-SDU

(a)

(b)

Figure 2.5

14

OSI Layers (1)Physical

Physical interface between devicesMechanicalElectricalFunctionalProcedural

Data Link Means of activating, maintaining and

deactivating a reliable link Error detection and control Higher layers may assume error free

transmission

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OSI Layers (2)Network

Transport of information Higher layers do not need to know about underlying

technology Not needed on direct links

Transport Exchange of data between end systems Error free In sequence No losses No duplicates Quality of service

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OSI Layers (3)Session

Control of dialogues between applications Dialogue discipline Grouping Recovery

Presentation Data formats and coding Data compression Encryption

Application Means for applications to access OSI environment

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Use of a Relay


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ApplicationLayer

PresentationLayer

SessionLayer

TransportLayer

NetworkLayer

Data LinkLayer

PhysicalLayer

ApplicationLayer

PresentationLayer

SessionLayer

TransportLayer

NetworkLayer

Data LinkLayer

PhysicalLayer

NetworkLayer

Electrical and/or Optical Signals

Application A Application B

Data LinkLayer

PhysicalLayer

NetworkLayer

Data LinkLayer

PhysicalLayer

Communication Network

Figure 2.6


19

G

G

G

G

G

net 1

net 2

net 3

net 4

net 5

G = gateway/router

G

Figure 2.8

20

The OSI Environment


21

C

PS

PS

C

PSPS

C

C

C

PS = packet switch

C = computer

Figure 2.7


22

ApplicationLayer

PresentationLayer

SessionLayer

TransportLayer

NetworkLayer

Data LinkLayer

PhysicalLayer

ApplicationLayer

PresentationLayer

SessionLayer

TransportLayer

NetworkLayer

Data LinkLayer

PhysicalLayer

Application A Application Bdata

data

data

data

data

data

data

ah

ph

sh

th

nh

dh

bits

dt

Figure 2.9

23

TCP/IP Protocol SuiteDominant commercial protocol

architectureSpecified and extensively used before OSIDeveloped by research funded US

Department of DefenseUsed by the Internet


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ApplicationLayer

TransportLayer

InternetLayer

NetworkInterface

ApplicationLayer

TransportLayer

InternetLayer

NetworkInterface

(a) (b)

Figure 2.10

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TCP/IP Protocol Architecture(1)Application Layer

Communication between processes or applications

End to end or transport layer (TCP/UDP/…) End to end transfer of data May include reliability mechanism (TCP) Hides detail of underlying network

Internet Layer (IP) Routing of data

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TCP/IP Protocol Architecture(2)Network Layer

Logical interface between end system and network

Physical Layer Transmission medium Signal rate and encoding


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Application

Transport

Internet

Network Interface

Application

Transport

Internet

Network Interface

Internet

Network Interface

Network 1 Network 2

Machine A Machine B

Router/Gateway

Figure 2.11


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HTTP SMTP RTP

TCP UDP

IP

Network

Interface 1

Network

Interface 3

Network

Interface 2

DNS

Figure 2.12

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Some Protocols in TCP/IP Suite


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Net Interface

IP

TCP

HTTP

Net Interface

IP

Net Interface

IP

TCP

HTTP

Ethernet PPP

Router

router

(1,1)

s

(1,2)

w

(2,1)

(1,3) r

(2,2)

PPP

Ethernet

(a)

(b)

Server PC

Figure 2.13


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IP Header

Header containssource and destination physical addresses; network protocol type

Frame Check Sequence

Ethernet Header

Figure 2.14

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PDUs in TCP/IP


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HTTP Request

TCP Header

Header contains source and destination port numbers

Header contains source and destination IP addresses; transport protocol type

IP Header

Header contains source and destination physical addresses; network protocol type

Frame Check Sequence

Ethernet Header

Figure 2.15

34

Required ReadingSections 2.1, 2.2, 2.3Section 2.4 is for next semesterCheck RFC 2068: go to my homepage and

click on “browsing RFCs”

CSC 535 Communication Networking I Chapter 2 Layered Architectures Dr. Cheer-Sun Yang.

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