Bài giảng Mạng máy tính - Chapter 1: Introduction (Part II)

Protocol “Layers”

Networks are complex!

 many “pieces”:

 hosts

Question:

Is there any hope of

organizing structure of

network?

 routers

 links of various

media

 applications

 protocols

Or at least our discussion

of networks?

 hardware,

software

1: Introduction

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Organization of air travel

ticket (complain)

ticket (purchase)

baggage (check)

gates (load)

baggage (claim)

gates (unload)

runway landing

airplane routing

runway takeoff

airplane routing

 a series of steps

1: Introduction

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Organization of air travel: a different view

ticket (complain)

baggage (claim)

gates (unload)

runway landing

airplane routing

ticket (purchase)

baggage (check)

gates (load)

runway takeoff

airplane routing

Layers: each layer implements a service

 via its own internal-layer actions

 relying on services provided by layer below

1: Introduction

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Layered air travel: services

Counter-to-counter delivery of person+bags

baggage-claim-to-baggage-claim delivery

people transfer: loading gate to arrival gate

runway-to-runway delivery of plane

airplane routing from source to destination

1: Introduction

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Distributed implementation of layer functionality

ticket (complain)

baggage (claim)

gates (unload)

runway landing

airplane routing

ticket (purchase)

baggage (check)

gates (load)

runway takeoff

airplane routing

intermediate air traffic sites

airplane routing

1: Introduction

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Next example

Luton,

Anh

quốc

Trại

Mai

Phương

giam

T16

Thị

Chuyển thông điệp

“I lov u” cho TH

_HuyềnTiến thứ trưởng gửi cô

thông điệp “I lov u”

From : Tiến thứ trưởng,

Trại giam T16

To : Hoa hậu MP, Luton

“I lov u”

Bưu cục Hà Tây

Bưu cục Luton

Bưu cục Hà Nội

Bưu cục London

1: Introduction

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Why layering?

Dealing with complex systems:

 explicit structure allows identification,

relationship of complex system’s pieces

 layered reference model for discussion

 modularization eases maintenance, updating of

system

 change of implementation of layer’s service

transparent to rest of system

 e.g., change in gate procedure doesn’t affect

rest of system

 layering considered harmful?

1: Introduction

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Internet protocol stack

 application: supporting network

applications

application

transport

network

link

 ftp, smtp, http

 transport: process-to-process data

transfer

 tcp, udp

 network: routing of datagrams from

source to destination

 ip, routing protocols

physical

 link: data transfer between

neighboring network elements

 ppp, ethernet

 physical: bits “on the wire”

1: Introduction

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Layering: logical communication

application

Each layer:

 distributed

transport

network

link

 “entities”

physical

implement

network

link

physical

layer functions

application

transport

at each node

network

 entities

link

physical

perform

application

transport

network

link

application

actions,

transport

network

link

physical

exchange

messages with

peers

physical

1: Introduction

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Layering: logical communication

data

application

E.g.: transport

transport

 take data from app

network

link

 add addressing,

reliability check

info to form

physical

ack

data

network

link

physical

application

transport

network

link

“datagram”

 send datagram to

peer

data

 wait for peer to

physical

application

transport

network

link

ack receipt

transport

 analogy: post

network

link

office

physical

1: Introduction

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Layering: physical communication

data

application

transport

network

link

physical

network

application

transport

network

link

physical

data

application

transport

network

link

physical

application

transport

network

link

physical

1: Introduction

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Protocol layering and data

Each layer takes data from above

 adds header information to create new data unit

 passes new data unit to layer below

source

destination

message

segment

datagram

frame

M

application

transport

network

link

application

transport

network

link

H_t

H_nH_t

H_lH_nH_t

H_t

H_nH_t

H_lH_nH_t

physical

1: Introduction

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Internet structure: network of networks

 roughly hierarchical

 national/international

local

backbone providers (NBPs)

ISP

 e.g. BBN/GTE, Sprint,

regional ISP

AT&T, IBM, UUNet

NBP B

 interconnect (peer) with

each other privately, or at

public Network Access Point

(NAPs)

NAP

NBP A

regional ISP

 regional ISPs

 connect into NBPs

local

ISP

 local ISP, company

 connect into regional ISPs

1: Introduction

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National Backbone Provider

e.g. BBN/GTE US backbone network

1: Introduction

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Internet History

1961-1972: Early packet-switching principles

 1961: Kleinrock - queueing

theory shows

 1972:

 ARPAnet demonstrated

effectiveness of packet-

switching

publicly

 NCP (Network Control

Protocol) first host-

host protocol

 first e-mail program

 ARPAnet has 15 nodes

 1964: Baran - packet-

switching in military nets

 1967: ARPAnet conceived

by Advanced Reearch

Projects Agency

 1969: first ARPAnet node

operational

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Internet History

1972-1980: Internetworking, new and proprietary nets

 1970: ALOHAnet satellite

Cerf and Kahn’s

network in Hawaii

internetworking principles:

 1973: Metcalfe’s PhD thesis

 minimalism, autonomy -

proposes Ethernet

no internal changes

 1974: Cerf and Kahn -

architecture for

required to

interconnect networks

interconnecting networks

 best effort service

 late70’s: proprietary

architectures: DECnet, SNA,

XNA

 late 70’s: switching fixed

length packets (ATM

precursor)

model

 stateless routers

 decentralized control

define today’s Internet

architecture

 1979: ARPAnet has 200 nodes

1: Introduction

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Internet History

1980-1990: new protocols, a proliferation of networks

 1983: deployment of

 new national networks:

Csnet, BITnet,

TCP/IP

NSFnet, Minitel

 1982: smtp e-mail

protocol defined

 100,000 hosts

connected to

confederation of

networks

 1983: DNS defined

for name-to-IP-

address translation

 1985: ftp protocol

defined

 1988: TCP congestion

control

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Internet History

1990’s: commercialization, the WWW

 Early 1990’s: ARPAnet

Late 1990’s:

decomissioned

 est. 50 million

 1991: NSF lifts restrictions

on commercial use of NSFnet

(decommissioned, 1995)

computers on Internet

 est. 100 million+ users

 backbone links runnning

 early 1990s: WWW

at 1 Gbps

 hypertext [Bush 1945,

Nelson 1960’s]

 HTML, http: Berners-Lee

 1994: Mosaic, later

Netscape

 late 1990’s:

commercialization of the

WWW

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Chapter 1: Summary

Covered a “ton” of

You now hopefully have:

material!

 context, overview,

 Internet overview

 what’s a protocol?

“feel” of networking

 more depth, detail

 network edge, core,

later in course

access network

 performance: loss, delay

 layering and service

models

 backbones, NAPs, ISPs

 history

 ATM network

1: Introduction

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Bài giảng Mạng máy tính - Chapter 1: Introduction (Part II) - Hồ Phương Đắc