chapter 1 read (again) chapter 1. csc-3352 computer communicationschapter i2 why use networks?...

Chapter 1

Read (again) chapter 1

CSC-3352 Computer Communications

Chapter I 2

Why use networks?

Resource sharing

Reliability

Cost


Chapter I 3

Network Hardware:Type of Transmission

Broadcast

Multicasting

Point-to-point


Chapter I 4

Network Hardware: Metropolitan Area Networks (MANs)

On the level of a cityThere are no switching elementsExample: Distributed Queue Dual Bus (DQDB) standardized under 802.6

Source

SourceHosts


Chapter I 5

Network Hardware: Wide Area Networks (WANs)

Large Geographical areaSwitching elements (p.s. nodes, I.S, or Data switching exchanges, router)


Chapter I 6

Network Hardware: Topologies

Main characteristics?


Chapter I 7

Network Hardware: Wireless Networks

Wireless does not mean mobile, and mobile does not mean wireless

Wavelan, Cellular Digital Packet Data (CDPD)

802.11


Chapter I 8

Network Hardware: The OSI Reference Model

What is it?

Who created it?

Why was it created?

What is it used for, today?


Chapter I 9

Network Software: Protocol Hierarchy or Layered Design

Host 1

Layer 3

Layer 2

Layer 1

Physical Medium

Layer 2/3 Interface

Layer 1/2 Interface

Host 2

Layer 3

Layer 2

Layer 1

Layer 3 protocol

Layer 2 protocol

Layer 1 protocol

Ser

vice

s ar

e of

fere

d fr

om a

laye

r to

the

laye

rs a

bove

it.


Chapter I 10

OSI - The ModelA layer modelEach layer performs a subset of the required communication functionsEach layer relies on the next lower layer to perform more primitive functionsEach layer provides services to the next higher layerChanges in one layer should not require changes in other layers


Chapter I 11

OSI as Framework for Standardization


Chapter I 12


Application

Presentation

Session

Transport

Network

Data link

Physical

Interface

Host A

Application

Presentation

Session

Transport

Network

Data link

Physical

Host BApplication Protocol

Presentation Protocol

Session Protocol

Transport Protocol

Network Protocol

Data link Protocol

Physical Protocol

Interface

Interface

Interface

Interface

Interface

Serv

ices

are

off

ered

fro

m a

laye

r to

th

e la

yers

ab

ove

it...


Chapter I 13


Application

Presentation

Session

Transport

Network

Data link

Physical

Interface

Host A

Application

Presentation

Session

Transport

Network

Data link

Physical

Host BApplication Protocol (End to End layer)

Presentation Protocol (End to End layer)

Session Protocol (End to End layer)

Transport Protocol (End to End layer)

Network Protocol

Data link Protocol

Physical Protocol

Interface

Interface

Interface

Interface

Interface

Serv

ices

are

off

ered

fro

m a

laye

r to

th

e la

yers

ab

ove

it...

Routing the packets over the net(s)


Chapter I 14

The OSI Reference Model...


Chapter I 15

The OSI Reference Model...


Chapter I 16

The Physical LayerTransports raw bits, Defines the physical (electrical and mechanical) specificationsCharacteristics of transmission mediumSignal levelsData ratesetc.Example: RS232, V24, V35, X.21, ISDN...


Chapter I 17

The Data Link Layer

Has 2 main functions

Error detection and correction

MAC (Medium Access Control)

Examples:SLIP, PPP, Ethernet, HDLC, SDLC


Chapter I 18

The Network Layer

Has 3 main functions addressing

routing

some congestion control

Examples: IP


Chapter I 19

The Transport Layer

It is an end-to-end layer, dealing with flow control

congestion control

may offer end-2-end reliability

Examples: TCP, UDP.


Chapter I 20

The Session Layer

- Used for :• session management

• Synchronization


Chapter I 21

The Presentation Layer

Concerned with “compatibility” (encoding)

encryption (security purposes)


Chapter I 22

The Application Layer

It is communication software directly accessible to the user

Examples: FTP, Telnet, Network Virtual monitor, HTTP….


Chapter I 23

Summary on OSI layers...The International Organization for Standardization (known as ISO, an abbreviation taken from its name in French) has devised a model for the design of communication protocols (known as the open systems interconnection (OSI) model). In this model each communicating entity has seven layers of protocol. The bottom layer (1) is known as the physical layer, and it essentially corresponds to the wire. The next layer (2) is known as the data link layer. It provides the means for putting data on the wire (and for taking it off). An example is ethernet. The next layer (3) is known as the network layer. Its primary responsibility is to see that the data travels to the intended destination (perhaps via a number of intermediate points). The next layer is known as the transport layer. Its job is to see to it that the data, which is transferred between machines by the network layer, reaches the desired party at the destination machine. The notion of a “connection” is maintained by this layer. The next layer is known as the session layer. This layer doesn’t really do very much (if anything); it is responsible for maintaining the notion of a “session.” Sessions might be in one-to-one correspondence with transport connections; there might be two successive sessions on the same connection; or one session might span multiple connections (e.g., the first connection was terminated due to a communication failure, the session continues as soon as

communication is reestablished). The next layer is known as the presentation layer. Its job is to deal with the fact that different machines have different representations for data (i.e. it must somehow translate between data representations) and to deal with such concerns as compression or encryption

of data. Finally, the application layer is where all other software resides. However, it has been discovered that there is “system software” that logically fits above the presentation layer. The only place to put it is in the application layer, so “real” application software sits on top of the application layer.

The bottom three layers are sometimes known as the communications subnet. If our data must pass through a number of machines on their way to the destination, each intermediate machine has an implementation of these lower layers to forward the data on.


Chapter I 24

TCP/IP Protocol Suite

Dominant commercial protocol architectureSpecified and extensively used before OSIDeveloped by research funded US Department of DefenseUsed by the Internet


Chapter I 25

Telnet

TCP UDP

IPEthernet

Telnet

TCP UDP

IPEthernetProtocols

Services

Applicatio

n

Transport

Internet

Physical

link


Chapter I 26

OSI versus TCP/IP

Application

Transport

Network

Physical link


Chapter I 27

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


Chapter I 28

TCP/IP Protocol Architecture(2)

Network Layer Logical interface between end system

and network

Physical Layer Transmission medium Signal rate and encoding


Chapter I 29

PDUs in TCP/IP


Chapter I 30

Some Protocols in TCP/IP Suite


Chapter I 31

Network Standardization

What is it ?

Why ?

How is it done ?

Who does it?


Chapter I 32

Big Standards Organization

International standards ITU (International Telecom. Union) old CCITT ISO IEEE

Internet Standards IAB IRTF, IETF


Chapter I 33

Conclusion

You must be pretty familiar with: the layered view of a communication

system know the function of each layer the mapping of communication

protocols to the layers chapter 1 in textbook

chapter 1 read (again) chapter 1. csc-3352 computer communicationschapter i2 why use networks?...

Documents

protocol layer

layer model

interface layer

lower layer

end layer session protocol

physical medium layer

physical layer transp

protocol services