CS 447 Networks and Data Communication

Network Protocols and OSI 7-layer Reference Model

Department of Computer ScienceSouthern Illinois University Edwardsville

Fall, 2015

Dr. Hiroshi FujinokiE-mail: hfujino@siue.edu

Network Protocol/001

Organization of a Computer Connected to a Computer Network

Wire (Computer Network)

Computer A Computer B

ApplicationProgram

ApplicationProgram

Network

ProtocolNetworkProtocol

CS 447 Networks and Data Communication

Network Protocol/003

Protocol and Interface

Wire (Computer Network)

Computer A Computer B

ApplicationProgram

ApplicationProgram

Protocol Protocol

CS 447 Networks and Data Communication

Network Protocol/002

Definitions

A network protocol is:

a set of rules

that governs communication between two hosts

implemented as software

Example

- TCP

- IP

- IPX/SPX (Novel Netware)

- NetBIOS (Windows)

- etc.

CS 447 Networks and Data Communication

Network Protocol/003

Protocol and Interface

Wire (Computer Network)

Computer A Computer B

ApplicationProgram

ApplicationProgram

TCPIP

MAC

TCPIP

MAC

ProtocolStack

Protocol

Interface

Interface: a set of rules that governs communication between two directly facing protocol layers

Layered structure

CS 447 Networks and Data Communication

Network Protocol/004

Summary

• A network protocol is a set of rules that govern communication between two host computers (in the same level)

• An interface is a set of rules that govern communication between two directly facing protocol layers (within a host computer)

CS 447 Networks and Data Communication

“End-to-end” and “point-to-point”

OSI_SevenLayer/001

Host A Host B

Intermediate Routers

Point-to-point

NIC

End-to-end

CS 447 Networks and Data Communication

OSI_SevenLayer/002

OSI Seven Layer Model

Wire (Network Cable)

Application Program

Layer 7

Layer 6

Layer 5

Layer 4

Layer 3

Layer 2

Layer 1

Application Layer

Presentation Layer

Session Layer

Transport Layer

Network Layer

Datalink Layer

Physical Layer Dealing with electric signals

Provide reliable point-to-point connection

Manage point-to-point connection

Provide reliable end-to-end connection

Manage end-to-end connection

Data filters (compression, encryption)

Interface to user programs

signals

Purposes

NIC

CS 447 Networks and Data Communication

Application Layer

Presentation Layer

Session Layer

Transport Layer

Physical Layer

Datalink Layer

Network Layer

NFS(Network File Server)

XDR(External Data Rep.)

RPC(Remote Proc. Call)

Network Hardware

TCP UDP

IP ARP RARP

Telnet, FTP, SMTP, rlogin, DNS, HTTP, rcp, finger, etc.

TCP/IP Protocol Suite:

OSI_SevenLayer/003

CS 447 Networks and Data Communication

Layer 1: Physical Layer

Major Function: Dealing with electric signals

Example: • Manchester Signal Encoding

• NRZI Signal Encoding

• Bipolar-AMI Signal Encoding

Define how the signals are represented

OSI_SevenLayer/004

• Interpret electric signals, represent them as 1’s or 0’s

CS 447 Networks and Data Communication

Layer 2: Data Link Layer

• Try to detect and correct signal errors, if any

Major Functions:

• Forward the received signals to the network layer

• If uncorrectable errors, gives an error warning to the network layer

• Provide Media Access Control (MAC)

- For “shared” network, control who can use the network first

Examples of Shared Network:

Ring Bus

OSI_SevenLayer/005

Star (=hub)

CS 447 Networks and Data Communication

Layer 3: Network Layer

Major Function:

• Maintain an point-to-point connection

- Keep track of the sequence number

- Establish a connection

- Continue to check the status of a connection

- Delete a connection when it is done

OSI_SevenLayer/006

CS 447 Networks and Data Communication

Layer 4: Transport Layer

Major Functions:

• Try to detect and correct packet errors (error control) for E2E

• Perform flow control

- If the receiver wants to slow down, reduce transmission rate

- If the network is congested, reduce the transmission rate

Layer 5: Session Layer

Major Functions:

• Establish/Manage/Delete (E2E) connections

• Full-Duplex/Half-Duplex Control

• QoS (specify maximum tolerable delay)OSI_SevenLayer/007

CS 447 Networks and Data Communication

Layer 6: Presentation Layer Major Functions: Encryption, compression, etc

Presentation Layer

Encrypted Data

Raw Data

Encryption

Presentation Layer

Compressed Data

Raw Data

Compression

Major Function: Interface to your application programs

Layer 7: Application Layer

Example: Network API (Application Program Interface)

OSI_SevenLayer/008

CS 447 Networks and Data Communication

Full-Duplex and Half-Duplex

Full-duplex: a connection two host can talk simultaneously

Half-duplex: a connection one of the two hosts can talk at a time

Full-Duplex Circuit

TransmittingCircuit

ReceivingCircuit

TransmittingCircuit

ReceivingCircuit

NIC at host A

NIC at host B

MultiplexerOSI_SevenLayer/009

CS 447 Networks and Data Communication

Half-Duplex Circuit

TransmittingCircuit

ReceivingCircuit

TransmittingCircuit

ReceivingCircuit

NIC at host A

NIC at host B

Switch

OSI_SevenLayer/009

Half-duplex: One-way communication at a time

CS 447 Networks and Data Communication