Computer Networks CS321

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Computer Networks CS321

Dr. Ramana

I.I.T Jodhpur

Dr. Ramana ( I.I.T Jodhpur ) Computer Networks CS321 1 / 22

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1 Introduction

OSI Reference Model Internet Protocol Performance Metrics

2 Packet Switching Technologies

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Key elements of a Network

Ethernet switch Ethernet

switch Router

Router Standalone

Mainframe

Router

Router Wide Area Network

(e.g. ATM) Local Area

Network

Local Area Network Wide Area Network

(e.g. ATM)

Information server

LAN PCs and workstations

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Layer 7 (Application)

Layer N

Layer 1 (Physical)

•

• Total

Communication

Function Decompose (modularity, information-hiding)

Layer N entity Service to Layer N+1

Service from Layer N–1

Protocol with peer Layer N

OSI-wide standards (e.g., network management, security)

Figure 2.8 The OSI Architecture as a Framework for Standardization

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OSI Reference Model

Application

Presentation

Session

Transport

Network

Data Link

Physical

Concerned with transmission of unstructured bit stream over physical medium; deals with the mechanical, electrical, functional, and procedural characteristics to access the physical medium.

Provides for the reliable transfer of information across the physical link; sends blocks (frames) with the necessary synchronization, error control, and flow control.

Provides upper layers with independence from the data transmission and switching technologies used to connect systems; responsible for establishing, maintaining, and terminating connections.

Provides reliable, transparent transfer of data between end points; provides end-to-end error recovery and flow control.

Provides the control structure for communication between applications; establishes, manages, and terminates connections (sessions) between cooperating applications.

Provides independence to the application processes from differences in data representation (syntax).

Provides access to the OSI environment for users and also provides distributed information services.

The OSI Layers

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Physical Layer

Physical characteristics of interfaces and media Representation of bits

Data rate - number of bits per second

Synchronization between sender and receiver Line configuration - point-to-point or multi-point Physical topology - bus/star/ring/mesh

Transmission mode - simplex/half duplex/duplex Data Link Layer

Framing

Physical addressing - local address Flow control

Error control Access control Network Layer

Logical addressing - global address Forwarding

Routing

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(Cont.)

Transport Layer

Service-point addressing Segmentation and reassembly Connection control

Flow control Error control Session Layer

Dialog Control Synchronization Presentation Layer

Translation Encryption Compression Application Layer

Enabling users to access the network services/resource

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(Cont.)

ISO OSI Protocol Stack

• Wireless link (WiFi)

• Wired link (Ethernet)

• Radio spectrum

• Infrared

• Fiber

• Copper

• Source-to-destination (IP)

• Routing

• Address resolution

• Reliable (TCP)

• Real-time (RTP) Visit http://en.wikipedia.org/wiki/OSI_model for more details on the OSI Reference Architecture

• Data translation (MIME)

• Encryption (SSL)

• Compression

• Application services (SIP, FTP, HTTP, Telnet, …)

• Dialog control

• Synchronization

7: Application 6: Presentation 5: Session 4: Transport 3: Network 2: Link 1: Physical

MAC

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(Cont.)

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A Comparison of the OSI and TCP/IP Protocol Architectures Physical

Network Access Internet Application

Transport (host-to-host)

TCP/IP Application

Presentation Session Transport

Network Data Link

Physical OSI

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(Cont.)

BGP = Border Gateway Protocol FTP = File Transfer Protocol HTTP = Hypertext Transfer Protocol ICMP = Internet Control Message Protocol IGMP = Internet Group Management Protocol IP = Internet Protocol

MIME = Multipurpose Internet Mail Extension

OSPF = Open Shortest Path First RSVP = Resource ReSerVation Protocol SMTP = Simple Mail Transfer Protocol SNMP = Simple Network Management Protocol TCP = Transmission Control Protocol UDP = User Datagram Protocol

Some Protocols in the TCP/IP Protocol Suite

FTP HTTP

TCP SMTP MIME

TELNET

SNMP

UDP

IGMP OSPF

BGP

IP

RSVP ICMP

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User data

headerTCP

headerIP

Network header

Application byte stream

segmentTCP

datagramIP

Network-level packet

Protocol Data Units (PDUs) in the TCP/IP Architecture

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Data Rate : Number of bits per second

Throughput: Amount of data transmitted over time

Latency = Transmission Time + Propogation Time + Queuing Time Transmission Time: Time to emit the data on to medium = _DataRate ^DataSize Propgation Time: Time taken to propagate bits from the

transmitter to the receiver = SpeedOfLight ^Distance

Speed of Light in Vacuum 3 × 10

⁸

m/s Speed of Light in Copper 2.3 × 10

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m/s Speed of Light in Fiber 2 × 10

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m/s Round Trip Time is roughly 2×Latency

BDP (Bandwidth Delay Product) aka Data Rate × Latency

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(a) Circuit switching

requestCall signal

acceptCall signal propagation

delay processing delay

(b) Virtual circuit packet switching

requestCall packet

acceptCall packet

link link link

1 2 3 4

Nodes: 1 2 3 4

Acknowledge- ment signal

Acknowledge- ment packet

(c) Datagram packet switching

1 2 3 4

Userdata

Pkt1 Pkt2 Pkt3 Pkt1

Pkt2 Pkt3 Pkt1

Pkt2 Pkt3

Pkt1 Pkt2 Pkt3 Pkt1

Pkt2 Pkt3 Pkt1

Pkt2 Pkt3

Figure 10.12 Event Timing for Circuit Switching and Packet Switching

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Virtual Circuit (VC) Switching

B

A

E

F C

D

Personal computer Personal computer

Mainframe

Personal computer

Personal computer Server

Figure 10.13 The Use of Virtual Circuits Packet-Switching

Network

Solid line = physical link Dashed line = virtual circuit

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21

32 3 2 1

3

(c) 1

3 (b) (a)

(d)

(e) 2 1

32 1

Figure 10.10 Packet Switching: Virtual-Circuit Approach

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Packet Switching

21 3 2 1

3

(c) 3

1 2

(b) (a)

(d)

(e) 2 1

3

32 1

Figure 10.9 Packet Switching: Datagram Approach

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(Cont.)

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1 Data1

Data Header

(a) 1-packet message (b) 2-packet message (c) 5-packet message (d) 10-packet message

Data

Data2 Data 1

Data2

1 2 3 4 5 6 7 8 9 10

1 2 3 4 5 6 7 8 9 10 2

3 4 5

1 2 3 4 5

Figure 10.11 Effect of Packet Size on Transmission Time

X a b Y

Computer Networks CS321