computer networks - birla institute of technology and ... · computer networks lecture-2 january...

BITS Pilani Pilani | Dubai | Goa | Hyderabad

Computer Networks Lecture-2 January 10, 2012

Rahul Banerjee, PhD (CSE)

Professor, Department of Computer Science & Information Systems

E-mail: [email protected]

BITS Pilani, Deemed to be University under Section 3 of UGC Act, 1956

A Recap of the types of applications and services benefitting from networking

Interconnecting Networks for forming Internetworks Architecture of the Internet What is the Internet today? The Internet and the World-Wide Web Who decides about the Internet? Of The Internet, Intranet and Extranet Protocols, Layers, Interfaces, Logical / Virtual Communication &

Services Of Network Architectures & Network Reference Models Select References to the literature Summary

Interaction Points

Examples of Types of Applica1ons benefi5ng from Networking

•  Types of applications & services: –  hard real-time applications & services, –  soft real-time applications & services, –  non-real-time / best-effort / delay-tolerant applications /

services

•  Examples of each kind of applications and services •  About the significance of application-driven and

economics-constrained nature of network system design approaches

•  Case-study of the Networking aspects of the Microsoft Easy Living Research Experiment

10/01/12 (c) Dr. Rahul Banerjee, BITS Pilani, INDIA 3

How do things work over the Internet?

•  Example-‐1: A web request and its response •  Example-‐2: A desk-‐top video-‐call •  Example-‐3: A Video-‐on-‐Demand over the Internet •  Example-‐4: An Email exchange over the Internet •  Example-‐5: Virtual Private Network services over the Internet

•  Example-‐6: Public cloud-‐based services over the Internet


An Example of a Computer Network

Another Form of Ethernet LAN

6 (c) Dr. Rahul Banerjee, BITS, Pilani, India

The Shared Ethernet hub

Personal Computer

Network Printer

Worksta1on

Worksta1on

Laptop Computer

Worksta1on

Tablet PC

(c) Dr. Rahul Banerjee, BITS Pilani, INDIA 7

Local Area Internetwork / Intranet •  Traditionally, a Campus Internetwork is a campus-wide

internetwork of individual LANs which may be geographically spread over the part or whole of a single campus. This sometimes called campus intranet.

•  In common practice, the entire campus internetwork including its communication subnet is wholly owned by a single organization or institution.

•  Usually, the campus internetworks use LAN technology; however, it is possible to use WAN technology, when so desirable.

•  The latter may be desirable in some cases when the campus is very large and comprises of a vast set of buildings spread over it. Protocols used in both of these cases at the lower layers, are, generally, different. 10/01/12

(c) Dr. Rahul Banerjee, BITS, Pilani, India 8

Some Terms Related to Networks

•  Channel <application-level logical / virtual communication path>

•  Services: Functionalities provided by a layer / protocol / entity

•  Interfaces: Peer-to-Peer / Layer-to-Layer / entity-to-entity

•  Service Access Points: defined addresses / ports through which data / parameters are passed

•  Tunneling <Encapsulation & Decapsulation>


What is an Internetwork?

10/01/12 (c) Dr. Rahul Banerjee, SDET Unit, BITS-‐Pilani, INDIA 9 10/01/12 (c) Dr. Rahul Banerjee, BITS Pilani, INDIA 9


Of the Internet, Intranet and Extranet

•  The Global Public Internetwork: The Internet •  The Wholly Owned / Private Internetwork:

Intranet •  The Hybrid Internetwork-- private networks /

internetworks connected through the Internet: Extranet In the early stages of development, technologies used for the internetworks of all type were essentially the same, except probably at the lowest level. This situation is rapidly changing.

10/01/12


Architecture of the Internet •  Originally, it was a point-to-

point WAN. •  Original architecture that led

to ARPANET has evolved over the years that have passed by.

•  It is loosely hierarchical. •  Currently, Internet

architecture is largely governed by the IAB of the ISoc.

•  Has many sub-organs which facilitate evolution and coordinated maintenance of the Internet.

•  IESG steers the ISoc in a general way the engineering issues are resolved.

•  IETF workgroups do the ground work and by a democratic process helps community in building up engineering solutions through IETF drafts and standards (RFCs) etc.


What is the Internet today? •  Wide Area Network of variety of networks •  Global •  Public •  Not transparent, as yet •  Hybrid topology but largely hierarchical •  No single controller •  Internet Society (ISoc) oversees, assists --- does

not control •  QoS, Security continue to have issues – partly at

least •  Web, mail, commerce, education, entertainment,

sharing continue to dominate its application space

References •  Larry L. Peterson & Bruce S. Davie: Computer Networks: A Systems Approach,

Fifth Edition, Morgan Kaufmann / Elsevier, New Delhi, 2011. <System design approach>

•  S. Keshav: Computer Networking: An Engineering Approach, Pearson Education, New Delhi, 1997.

•  A. S. Tanenbaum: Computer Networks, Fifth Edition, Pearson Education, New Delhi, 2012. <Conceptual Approach>

•  Y. Zheng and S. Akhtar: Networks for Computer Scientists and Engineers, Oxford University Press, New York, 2002. <Structural approach>

•  A. Leon Garcia and I. Widjaja: Communication Networks: Fundamental Concepts and Key Architectures, Second Edition, Tata McGraw-Hill, New Delhi, 2004.

•  Mohammed G. Gouda: Elements of Network Protocol Design, Wiley Student Edition, John Wiley & Sons (Pte.) Ltd., Singapore, 2004.

•  Thomas G. Robertazzi: Computer Networks and Systems: Queuing Theory and Performance Evaluation, Third Edition, Springer-Verlag, New York, 2000. <Analytical approach>

© Dr. Rahul Banerjee, BITS, Pilani (India) 10/01/12 (c) Dr. Rahul Banerjee, BITS Pilani, INDIA 13


Interac1on Points •  Examples of Types of Applications benefitting from Networking

–  hard real-time, soft real-time, non-real-time / best-effort / delay-tolerant applications / services <with examples>

–  case-study movie –  Constituent networking components of a smart room setup

•  The Internet & its Evolution •  About Internet Architecture •  Who decides about the Internet? •  The Internet versus the World-Wide Web •  Protocols, Layers, Interfaces, Virtual Communication and

Services •  Select References to the literature •  Questions and Answers / Summary


Conven1onal Classifica1on of Computer Networks

•  Class One: Function-based classification

•  Data Networks •  Voice Networks •  Multimedia Networks ……

•  Class Two: Location-and-Distance-based classification

•  Personal Area Networks (PANs)

•  Local Area Networks (LANs)

•  Metropolitan Area Networks (MANs)

•  Wide Area Networks (WANs) ….

• Class Three: Forwarding-‐based classifica1on

•  Switched Networks •  Circuit-‐Switched Networks •  Packet-‐Switched Networks

•  Shared Networks • Hybrid Networks

• Class Four: Ownership-‐based classifica1on

•  Public Networks •  Private Networks • Virtual Private Networks

10/01/12


Comparing Computer Networks with Distributed Systems

•  Terms Computer Network and Distributed System must NOT be used interchangeably since: –  In the former, locations and elements of network

remain visible to the user; –  In the latter, the underlying network remains

transparent to the user who sees the system as a large uni-processor system.

•  Similar differences can be cited in case of Network Operating

Systems and Distributed Operating Systems.

10/01/12

Robert Metcafe’s Ethernet •  The original Ethernet protocol proposed and

implemented by Robert Metcafe was actually based on 1-p CSMA/CD protocol

•  It did have a scheme that allowed greedy access to the channel by a station which led to lower efficiency

•  Schemes like Random Back-off / Exponential Back-off were devised to improve the efficiency to a certain extent

10/01/12 (c) Dr. Rahul Banerjee, SDET Unit, BITS-Pilani, INDIA 17

An Ethernet LAN


Personal Computer

Worksta1on

Worksta1on Workstation

Frames: Factors that maaer!

•  Synchronization: Transmitter & Receiver need to be in sync

•  Start Delimiter: Required to mark starting bit •  End Delimiter: Required to mark the end bit •  Control Information: Information suggesting data

handling and interpretation •  Error Detection / Correction / Retransmission •  Flow Control: Required for avoiding data loss

due to overflow at receiving end •  Data Length: Needed if data-field is not of fixed

size 19 (c) Dr. Rahul Banerjee,

BITS, Pilani, India

A Sample Frame Format

n-‐Byte Preamble Start-‐of -‐Frame Delimiter Des1na1on Add. Source Address Length of Data

Data Field Pad Field

Checksum


Network Elements of a Node •  A typical network node has following

hardware elements of relevance, at the least: – Processor (CPU) with / without registers / caches – Optional External Cache(s) – RAM (Main Memory) – ROM / PROM / EPROM / EEPROM / EAPROM – Optional Secondary / Tertiary Memory / Storage

(Flash, Disk, MBM etc.) – Network Adapter / Network Interface Controller – Slots / Ports for connectivity to other node(s) – Power-provisioning – Bus / Lines (Control, Address, Data, Power)

Elements of a Network Interface Controller / Network Adapter

•  A Network Adapter / Interface Controller Unit / Chip / Dongle often comprises of the following elements: –  Host bus / line / link –  Control Status Registers (often called CSR or simply even as Control

Registers) •  logically readable / writable by the CPU

–  --à often, a copy of the contents of the CSR is located in some pre-specified location in memory making it simple for CPU to perform R/W operations, as per need

»  --à Actual writing to the NIC’s CSR is done by the Device Driver though –  Bus Interface Unit –  Internal storage (buffer included) –  Transceivers for transmission and reception at the physical level

•  Data Transfer Methods: DMA (no worry for the CPU) or Programmed I/O (PIO) based Data Transfer (CPU needs to work herein) from the memory of the host node to the NIC / Adapter

A Diagramma1c View of NIC

hap://www.plxtech.com/images/about/news/images/image042505.gif

hap://commons.wikimedia.org/wiki/File:Ethernet_NIC_100Mbit_PCI.jpg

hap://www.dansdata.com/images/gigabit/gbcard440.jpg

hap://www.altera.co.jp/products/ip/ampp/morethanip/images/m-‐m1p-‐10g_etherpcs_fig1.gif

Examples of Ethernet Adapters

Source: hap://www.altera.co.jp/products/ip/ampp/morethanip/images/m-‐m1p-‐10g_etherpcs_fig1.gif (c)


Based on IEEE documents with instructional modifications Copyright: IEEE Inc., N.Y.

The IEEE 802.x Architecture and Specifications revisited

Operation of a Bridge with Two LANs


Source Destination

S

H

H H H

H H

H

Hub

Some Common Layer-‐2 Switches Cisco L2 Managed Switches

© Cisco, Inc.

Fixed Lasers

Electronic Switches

GxG MEMS

Group 1

LxM Crossbar

Linecard 1

Linecard 2

Linecard L

Group 2

LxM Crossbar

Linecard 1

Linecard 2

Linecard L

LxM Crossbar

Linecard 1

Linecard 2

Linecard L

Group G

MxL Crossbar

Linecard 1

Linecard 2

Linecard L

Electronic Switches

Optical Receivers

Group 1

MxL Crossbar

Linecard 1

Linecard 2

Linecard L

Group 2

MxL Crossbar

Linecard 1

Linecard 2

Linecard L

Group G

GxG MEMS

GxG MEMS

GxG MEMS

1

2

3

M

Static MEMS

1

2

3

M

1

2

3

M

1

2

3

M

1

2

3

M

1

2

3

M

1

2

3

M

An Example of a Hybrid Switching Fabric

© Dr. Nick McKeown, Stanford University <modified version>

An Example of Network (LAN) Switches

Cisco Catalyst 3750 Series Switches

© Cisco, Inc.

Cisco Catalyst 4500 Series of Switches Cisco Catalyst 4500 Series Switches

(Used in several places in the Institute as Distribution Switches)

© Cisco, Inc.

Cisco Catalyst 6500 Series of Switches Cisco Catalyst 6500 Series

Switches

(One of these is OUR Core Switch located in the IPC

System Room)

© Cisco, Inc.

32

A Bus Topology based Computer Network

SHARED BUS

(c) Dr. Rahul Banerjee, BITS-Pilani, INDIA

N1 N2 N3 N4

33

A Ring Topology based Computer Network

C

C

C

C

C


34

A Ring Topology based Computer Network

C

C

C

C

C


35

A Tree Topology based Computer Network

NC1 NC2

NC11

NR

NC21

NC22

NC12


36

A Star Topology based Computer Network

C

C

C

Switch


S

N1

N2

N3

N4


Summary of Network Topologies •  Bus Topology

–  Shared –  Switched

•  Tree Topology •  Ring Topology

–  Single –  Double

•  Star Topology •  Irregular Topology •  Complete Topology

Network Architecture & Reference Models

•  Architecture versus Reference Model: A simplistic perspective: – Architecture: It may be seen as a detailed

generic blueprint with unambiguous definitions of services, interfaces, organization and defined protocols that helps in design and implementation of a set of relevant protocol stack / suite based network / internetwork

– Reference Model: It is the same as the architecture minus the specifically defined readily usable protocols.

Tuesday 10 January 12 38 (c) Dr. Rahul Banerjee, BITS-‐Pilani, INDIA

Network Architectures & Reference Models

•  Examples: –  TCP/IP Architecture &

TCP/IP Reference Model

–  OSI Reference Model & OSI Architecture

–  ATM Reference Model & ATM Architecture

–  Our own Hypothetical Reference Model (slide-5)

Tuesday 10 January 12 39 (c) Dr. Rahul Banerjee, BITS-‐Pilani, INDIA

LLC Sub-layer

MAC Sub-layer

Physical layer

40

Data Link Layer

Physical Layer

Transport Layer

Network Layer

Applica9on Layer

Presenta9on Layer

Session Layer

The ISO OSI Reference Model

(c) Dr. Rahul Banerjee, BITS-‐Pilani, INDIA

41

The ISO OSI Reference Model


Copyright: Dr. Rahul Banerjee BITS, Pilani (India) 42

Data Link Layer

Physical Layer

Transport Layer

Network Layer

Applica9on Layer

A Hypothetical Network Reference Model for Easy Conceptual Understanding

Layer-‐5

Layer-‐4

Layer-3

Layer-2

Layer-1

Often on the NIC card or chip

43

A Simplified Network Reference Model <for Instruction>

Host-1 Host-2

Application Layer Application Layer

Upper Layer-‐to-‐ Lower Layer Interface Upper Layer-‐to-‐ Lower Layer Interface



Same Layer -to- Same Layer Virtual Communication Interface




Same Layer -to- Same Layer Physical Communication Interface



Application Layer •  Application Layer is a layer of the Network Architecture

that is primarily concerned with getting TPDU from the lower layer (usually Transport Layer) and delivering it to the Application and vice-versa (with or without explicit presentation and session management support).

•  Examples: HTTP, DHCP, DNS, SNMP, FTP (in the context of the TCP/IP Architecture).

•  Web-services, Video-on-Demand over the network, Video/Voice-conferencing over the network etc. are examples of Applications that reside atop the protocols belonging to this layer.


Application Layer Responsibilities

•  It primarily deals with: –  Accepting messages from

the Application Layer through the APIs

–  Processing these messages and generating APDUs

–  Deciding transport connection requirements (for further transmitting this DU after encapsulating it within an APDU)

–  Passing this packet through the SAP to the lower layer (TL)

n  It also deals with ... q  Accep1ng APDU from the lower

layer through the SAP q  Processing the APDU q  Removing the encapsula1on and

passing the messages to the respec1ve des1na1on applica1on

q  Provide diagnos1c support for network monitoring, configura1on, management and trouble-‐shoo1ng at the Applica1on Layer or lower layer


Transport Layer: What is it?

•  Transport Layer is a layer of the Network Architecture that is primarily concerned with: – getting TPDU from the upper layer (usually

Application Layer) and – delivering it to the same layer at the intended

destination node (through the underlying Network Layer).

•  Converse is also true of the targeted set of responsibilities of this layer.


Transport Layer Responsibilities <another perspective>

•  It primarily deals with: –  Accepting APDU from the

Application Layer through the Service Access Point (SAP)

–  Processing these APDU –  Deciding transport

connection requirements (for further transmitting this DU after encapsulating it within a TPDU)

–  Passing this packet through the SAP to the lower layer (NL)

n  It also deals with ... q  Accep1ng TPDU from the lower

layer through the SAP q  Processing the TPDU q  Removing the encapsula1on and

passing the messages to the respec1ve des1na1on applica1on

q  Provide diagnos1c support for network monitoring, configura1on, management and trouble-‐shoo1ng at the Applica1on Layer or lower layer


Network Layer •  Network Layer is primarily concerned with getting NLDU / Packets from

the source node and delivering it to the intended destination node (through none or many intermediate nodes).

•  Additional responsibilities of this layer include: –  Providing support for connection-oriented / connectionless services as the

case may be (depending upon the protocol stack and need) –  Provide diagnostic support for network monitoring, configuration,

management and trouble-shooting at the Network Layer or higher layer. •  Packet handling, packet management, Routing are its major

responsibilities.

n  In the context of packet rou1ng, network layer structural design goals include: q  Ensuring the shortest possible delay and thereby the highest throughput at the least

possible cost q  Ensuring acceptably reliable packet delivery (may be op1onal in some cases) q  Ensuring secure packet delivery (may be op1onal in some cases)


Data Link Layer

•  Data Link Layer consists of two sub-layers: –  Media Access Control (MAC) sub-layer & –  Logical Link Control (LLC) sub-layer.

•  Major Issues involved in the design of the Data Link Layer include: –  Which services are to be provided to each of the adjacent

layers? –  Exactly when to provide these services? –  How to provide them? –  To whom should they be provided?


Physical Layer

•  Physical Layer deals with transmission of raw digital data using analog or digital signal.

•  This layer is concerned with the logic type (negative or positive), amplitude of the signal, signal representation, bit-length, direction of transmission etc.

•  It deals with connection-establishment and termination.

n  This layer is, in a nutshell, a layer that deals with various electrical and mechanical characteris1cs of every physical component of a computer network.

n  Exact electrical, mechanical and procedural Interface Defini1on is therefore its responsibility.

n  Choice and use of the physical medium are the Physical Layer Design Issues.


A Few More Networking Terms •  Repeaters / Repeater Hubs / Shared Hubs: where usually Physical

layer / level exist with L1-protocol data unit (raw bits) regeneration and onward transmission

•  Managed Hubs / Layer-2 Switching Hubs: where Physical and Data Link layers / levels exist with ability to handle and deliver Layer-2-protocol data unit (frame)

•  Bridges: where Physical and Data Link layers / levels exist with L2-protocol data unit (frame) processing and forwarding

•  Switches: where Physical and Data Link and / or Network (sometimes even higher) layers / levels exist with Layer-2 and / or Layer-3-protocol data unit (frame / packet) processing, switched routing / forwarding

•  Routers: where Physical and Data Link and Network layers / levels exist with L3-protocol data unit (packet) processing, routing and forwarding

•  Gateways: where two or more different networks meet and may require protocol / message translation capabilities

•  Clouds: abstraction of node connectivity in the networking context <details hidden>

Summary •  Intranet: Completely private network of networks

•  Wireline •  Wireless

– Fixed – Mobile

•  Hybrid •  The Internet: Global public network of networks

•  Wireline •  Wireless

– Fixed – Mobile

•  Hybrid •  Extranet: Intranets interconnected via the Internet

Tuesday 10 January 12 52 (c) Dr. Rahul Banerjee, BITS-‐Pilani, INDIA 10/01/12 (c) Dr. Rahul Banerjee, BITS Pilani, INDIA 52

BITS Pilani Pilani | Dubai | Goa | Hyderabad

Thank you!

Rahul Banerjee


Project BITS-Connect 2.0

computer networks - birla institute of technology and ... · computer networks lecture-2 january...

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