What’s the Internet: a service vielopresti/Didattica/RetiWeb/RetiWeb...Chapter 1 Introduction Introduction 1-1 What’s the Internet: a service view communication infrastructure

Chapter 1Introduction

Introduction 1-1

What’s the Internet: a service view

� communication infrastructure enables distributed applications:

❍ Web, VoIP, email, games, e-commerce, file sharing

� communication services

Introduction 1-2

� communication services provided to apps:

❍ reliable data delivery from source to destination

❍ “best effort” (unreliable) data delivery

What’s the Internet: “nuts and bolts” view

� millions of connected computing devices: hosts = end systems

❍ running network apps Home network

Mobile network

Global ISP

Regional ISP

PC

server

wireless

laptopcellular

handheld

� communication links

Introduction 1-3

Institutional network

Regional ISP

router

wired

links

access

points

� communication links� fiber, copper, radio,

satellite

� transmission rate = bandwidth

� routers: forward packets (chunks of data)

What’s the Internet: “nuts and bolts” view

� protocols control sending, receiving of msgs

❍ e.g., TCP, IP, HTTP, Skype, Ethernet

� Internet: “network of networks”

Home network

Mobile network

Global ISP

Regional ISP

Introduction 1-4

networks”❍ loosely hierarchical

❍ public Internet versus private intranet

� Internet standards❍ RFC: Request for comments

❍ IETF: Internet Engineering Task Force

Institutional network

Regional ISP

What’s a protocol?

human protocols:

� “what’s the time?”

� “I have a question”

� introductions

network protocols:

� machines rather than humans

� all communication activity in Internet governed by protocols

Introduction 1-5

… specific msgs sent

… specific actions taken when msgs received, or other events

governed by protocols

protocols define format, order of msgs sent and received among network entities, and actions

taken on msg transmission, receipt

What’s a protocol?

a human protocol and a computer network protocol:

Hi

Hi

TCP connectionreq

TCP connection

Introduction 1-6

Hi

Got thetime?

2:00

TCP connectionresponse

Get http://www.awl.com/kurose-ross

<file>

time

A closer look at network structure:

� network edge:applications and hosts� access networks,

physical media:

Introduction 1-7

physical media:wired, wireless

communication links

� network core:� interconnected routers

� network of networks

The network edge:

� end systems (hosts):❍ run application programs

❍ e.g. Web, email

❍ at “edge of network” peer-peer

� client/server model

Introduction 1-8

client/server

client/server model� client host requests, receives service from always-on server

� e.g. Web browser/server; email client/server

� peer-peer model:� minimal (or no) use of

dedicated servers

� e.g. Skype, BitTorrent

Transmission across a physical link: point-to-point networks

� Bits: propagate between transmitter and receiver

physical link: what lies between transmitter &

TXTXRX

RX

Physical link

Introduction 1-9

� physical link: what lies between transmitter & receiver

� guided media:❍ signals propagate in solid media: copper, fiber, coax

� unguided media:❍ signals propagate freely, e.g., radio

Transmission across a physical link

� Bit sequence modulates a suitable waveform which is sent across the link

TXTXRX

RX

100011 110011

Introduction 1-10

sent across the link

� As the signal travels it experiences❍ Attenuation (absorption)

❍ Distortion (limited bandwidth (frequency))

❍ Noise (interference, thermal noise)

❍ Influenced by medium, bit rate and distance

� Received sequence may be incorrect!!!

Maximum Channel Data Rate

� Shannon Theorem: max data rate of a noisy channel whose bandwidth is H Hz, and whose signal to noise power ratio is S/N, is

Introduction 1-11

H log2 (1+S/N)

❍H frequency interval over which signal is transmitted• Depends on the physical medium

Transmission across a physical link: broadcast networks

� Wired networks❍ Legacy Ethernet

� Wireless networks❍ Wireless LAN

router

Introduction 1-12

basestation

mobilehosts

router

Physical Media: twisted pair

Twisted Pair (TP)� two insulated copper wires

❍ Twisted to reduce interference

� Category 3: traditional phone wires, 10 Mbps Ethernet

Introduction 1-13

wires, 10 Mbps Ethernet� Category 5 TP: 100Mbps Ethernet

Physical Media: coax, fiber

Coaxial cable:� two concentric copper

conductors

� bidirectional

� baseband:

Fiber optic cable:� glass fiber carrying light

pulses, each pulse a bit

� high-speed operation:❍ high-speed (e.g., 5 Gps)

point-to-point

Introduction 1-14

� baseband:❍ single channel on cable

❍ legacy Ethernet

� broadband:❍ multiple channel on cable

❍ HFC

high-speed (e.g., 5 Gps) point-to-point

� low error rate: repeaters spaced far apart; immune to electromagnetic noise

Physical Media: radio

� signal carried in electromagnetic spectrum

� no physical “wire”

� bidirectional

propagation

Radio link types:� terrestrial microwave

❍ e.g. up to 45 Mbps channels

� LAN (e.g., WiFi)❍ 11Mbps, 54Mbps

Introduction 1-15

� propagation environment effects:

❍ reflection

❍ obstruction by objects

❍ interference

11Mbps, 54Mbps

� wide-area (e.g., cellular)❍ e.g. 3G: hundreds of kbps

� satellite❍ up to 50Mbps channel (or

multiple smaller channels)

❍ 270 msec end-end delay

❍ geosynchronous versus LEOS

Access networks and physical media

Q: How to connect end systems to edge router?

� residential access nets

� institutional access networks (school, company)

Introduction 1-16

company)

� mobile access networks

Keep in mind: � bandwidth (bits per

second) of access network?

� shared or dedicated?

Residential access: point to point access

� Dialup via modem

❍ up to 56Kbps direct access to router (often less)

❍ Can’t surf and phone at same time: can’t be “always on”

Introduction 1-17

time: can’t be “always on”

� ADSL: asymmetric digital subscriber line

❍ up to 1 Mbps upstream (today typically < 256 kbps)

❍ up to 8 Mbps downstream (today typically < 1 Mbps)

❍ FDM: 50 kHz - 1 MHz for downstream4 kHz - 50 kHz for upstream

0 kHz - 4 kHz for ordinary telephone

Residential access: cable modems

� HFC: hybrid fiber coax

❍ asymmetric: up to 10Mbps downstream, 1 Mbps upstream

� network of cable and fiber attaches homes to ISP router

shared access to router among home

Introduction 1-18

❍ shared access to router among home

❍ issues: congestion, dimensioning

� deployment: available via cable companies, e.g., MediaOne

Cable Network Architecture: Overview

Typically 500 to 5,000 homes

Introduction 1-19

home

cable headend

cable distributionnetwork (simplified)

Typically 500 to 5,000 homes

Company access: local area networks

� company/univ local area network (LAN) connects end system to edge router

� Ethernet:

❍ shared or dedicated link connects end system

Introduction 1-20

connects end system and router

❍ 10 Mbs, 100Mbps, Gigabit Ethernet

� deployment: institutions, home LANs happening now

� LANs: chapter 5

Wireless access networks

� shared wireless access network connects end system to router

❍ via base station aka “access point”

� wireless LANs:base

station

router

Introduction 1-21

� wireless LANs:❍ 802.11g: 54 Mbps

� wider-area wireless access❍ provided by telco operator

❍ 3G ~ 384 kbps

• Will it happen??

❍ WAP/GPRS/EDGE/UMTS in Europe

station

mobilehosts

Home networks

Typical home network components:

� DSL or cable modem

� router/firewall/NAT

� Ethernet

� wireless access

Introduction 1-22

wireless access

point

wireless

access

point

wireless

laptopsrouter/

firewall

cable

modem

to/from

cable

headend

Ethernet

Router

� Forward a chunk of information (called packet) arriving on one of its communication links to one of its outgoing communications link (the next hop on the source-to-destination path)

AB

Introduction 1-23

-Receives the packet-Based on a routing table and the destination address, computes the ‘next hop’ to the destination-Forwards the packet to the next hop-The process of computing and maintaining the routing table is called Routing

-Receives the packet-Based on a routing table and the destination address, computes the ‘next hop’ to the destination-Forwards the packet to the next hop-The process of computing and maintaining the routing table is called Routing

forwardingRouting table

Dest. AddressNext Hop

The Network Core

� mesh of interconnected routers

� fundamental questions: how is data transferred through net? How are network resources shared?

Introduction 1-24

resources shared?❍ circuit switching:dedicated resources (circuit) per call: telephone net

❍ packet-switching: data sent thru net in discrete “chunks”. Resources allocated on demand

Network Core: Circuit Switching

End-end resources reserved for “call”

� link bandwidth, switch capacity

dedicated resources:

Introduction 1-25

� dedicated resources: no sharing

� circuit-like (guaranteed) performance

� call setup required


� 3 phases1. Call setup

❒ Resources Allocation

2. Data transfer❒ Resources Usage

Call Teardown

Introduction 1-26

3. Call Teardown❒ Resources Release

❒ required for all connection-based services


� network resources (e.g., bandwidth) divided into “pieces”

❍ pieces allocated to calls

Introduction 1-27

TXRX

TXTXRX

RX

Physical linkTXRX


� FDM: Frequency Division Multiplexing❍ Different frequency intervals allocated to different calls

Introduction 1-28

TXRX

TXTXRX

RX

Physical linkTXRX

time

freq

uenc

y


� TDM: Time Division Multiplexing❍ Different time intervals allocated to different calls

❍ For each call: one slot per frame

slot frame

Introduction 1-29

TXRX

TXTXRX

RX

Physical linkTXRX

time

freq

uenc

y

Network Core: Packet Switching

A

B

C10 MbsEthernet

1.5 Mbs

queue of packetswaiting for output

Introduction 1-30

each end-end data stream divided into packets� user A, B packets share network resources� each packet uses full link bandwidth store and forward� Entire packet must arrive at router before it can be

transmitted on next link� packets move one hop at a time

❍ transmit over link❍ wait turn at next link

waiting for outputlink

Network Core: Packet Switching

A

B

C10 MbsEthernet

1.5 Mbs

queue of packetswaiting for output

statistical multiplexing

Introduction 1-31

Statistical Multiplexing: Sequence of A & B packets does not have fixed pattern

� resources used as neededresource contention:� aggregate resource demand can exceed

amount available� congestion: packets queue, wait for link

use❍ May get dropped if buffer gets full

waiting for outputlink

Bandwidth division into “pieces”

Dedicated allocation

Resource reservation

Packet switching versus circuit switching

� 1 Mbit link

� each user: ❍ 100 kbps when “active”

❍ active 10% of time

Packet switching allows more users to use network!

Introduction 1-32

❍ active 10% of time

� circuit-switching: ❍ 10 users

� packet switching: ❍ with 35 users,

probability > 10 active less than .0004

N users

1 Mbps link

Packet switching versus circuit switching

� Packet switching: Great for bursty data

❍ resource sharing

❍ simpler, no call setup

� Excessive congestion: packet delay and loss

❍ protocols needed for reliable data transfer,

Introduction 1-33

❍ protocols needed for reliable data transfer, congestion control

� Q: How to provide circuit-like behavior?

❍ bandwidth guarantees needed for audio/video apps

❍ still an unsolved problem (chapter 6)

Packet-switching vs Message Switching

� Takes L/R seconds to transmit (push out) packet of L bits on to link or R bps

Example:

� L = 7.5 Mbits

� R = 1.5 Mbps

R R R

L

Introduction 1-34

packet of L bits on to link or R bps

� Entire packet must arrive at router before it can be transmitted on next link: store and forward

� delay = 3L/R

� R = 1.5 Mbps

� delay = 15 sec

Packet Switching: Message Segmenting

Now break up the message into 5000 packets

� Each packet 1,500 bits

� 1 msec to transmit packet on one link

Introduction 1-35

packet on one link

� pipelining: each link works in parallel

� Delay reduced from 15 sec to 5.002 sec

Packet Switching: Virtual Circuits Networks� Connection Based

1. Call setup❍ fixed path determined

at call setup time, remains fixed

❍ link, bandwidth, buffers may be allocated to VC

2. Data transfer❍ each packet carries VC

identifier

3. Teardown

Introduction 1-36

applicationtransportnetworkdata linkphysical


1. Initiate call 2. incoming call

3. Accept call4. Call connected5. Data flow begins 6. Receive data

may be allocated to VC• to get circuit-like perf

Packet Switching: Datagram Networks(The Internet Model)

� no call setup

� routers: no state about end-to-end connections❍ no network-level concept of “connection”

� packets forwarded using destination host address❍ packets between same source-dest pair may take

different paths

Introduction 1-37

different paths



1. Send data 2. Receive data

Network Taxonomy

Telecommunicationnetworks

Circuit-switchednetworks

Packet-switchednetworks

Introduction 1-38

networks

FDM TDM

networks

Networkswith VCs

DatagramNetworks

Internet structure: network of networks

� roughly hierarchical

� at center: “tier-1” ISPs (e.g., UUNet, BBN/Genuity, Sprint, AT&T), national/international coverage

❍ treat each other as equals

Tier-1 providers

Introduction 1-39

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

Tier-1 providers interconnect (peer) privately

NAP

Tier-1 providers also interconnect at public network access points (NAPs)

Tier-1 ISP: e.g., Sprint

…peering

to/from backbone

….

POP: point-of-presence

Introduction 1-40

to/from customers

………


� “Tier-2” ISPs: smaller (often regional) ISPs❍ Connect to one or more tier-1 ISPs, possibly other tier-2

ISPs

Tier-2 ISPTier-2 ISP pays

Tier-2 ISPs also peer

Introduction 1-41

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

NAP

Tier-2 ISPTier-2 ISP

Tier-2 ISP Tier-2 ISP

Tier-2 ISP

Tier-2 ISP pays tier-1 ISP for connectivity to rest of Internet� tier-2 ISP is customer oftier-1 provider

also peer privately with each other, interconnect at NAP


� “Tier-3” ISPs and local ISPs ❍ last hop (“access”) network (closest to end systems)

Tier-2 ISP

localISPlocal

ISPlocalISP

localISP Tier 3

ISPLocal and tier-

Introduction 1-42

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

NAP



Tier-2 ISP

ISP ISP

localISP

localISP

localISP

localISP

Local and tier-3 ISPs are customers ofhigher tier ISPsconnecting them to rest of Internet


� a packet passes through many networks!

Tier-2 ISP

localISPlocal

ISPlocalISP

localISP Tier 3

ISP

Introduction 1-43

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

NAP



Tier-2 ISP

ISP ISP

localISP

localISP

localISP

localISP

How do loss and delay occur?

packets queue in router buffers� packet arrival rate to link exceeds output link

capacity

� packets queue, wait for turn

packet being transmitted (delay)

Introduction 1-44

A

B

packet being transmitted (delay)

packets queueing (delay)

free (available) buffers: arriving packets

dropped (loss) if no free buffers

How do loss and delay occur?

� 1. nodal processing:❍ check bit errors

❍ determine output link

� 2. queueing❍ time waiting at output

link for transmission

❍ depends on congestion level of router

Introduction 1-45

A

B

propagation

transmission

nodalprocessing queueing

How do loss and delay occur? (2)

3. Transmission delay:

� R=link bandwidth (bps)

� L=packet length (bits)

� time to send bits into link = L/R

4. Propagation delay:

� d = length of physical link

� s = propagation speed in medium (~2x108 m/sec)

� propagation delay = d/s

Introduction 1-46

link = L/R � propagation delay = d/s

A

B

propagation

transmission

nodalprocessing queueing

Note: s and R are very different quantities!

Nodal delay

� dproc = processing delay❍ typically a few microsecs or less

d = queuing delay

proptransqueueprocnodal ddddd +++=

Introduction 1-47

� dqueue = queuing delay❍ depends on congestion

� dtrans = transmission delay❍ = L/R, significant for low-speed links

� dprop = propagation delay❍ a few microsecs to hundreds of msecs

Queueing delay (revisited)

� R=link bandwidth (bps)

� L=packet length (bits)

� a=average packet arrival rate

Introduction 1-48

traffic intensity = La/R

� La/R ~ 0: average queueing delay small

� La/R -> 1: delays become large

� La/R > 1: more “work” arriving than can be serviced, average delay infinite!

Packet loss

� queue (aka buffer) preceding link in buffer has finite capacity

� when packet arrives to full queue, packet is dropped (aka lost)

� lost packet may be retransmitted by

Introduction 1-49

� lost packet may be retransmitted by previous node, by source end system, or not retransmitted at all

Throughput

� throughput: rate (bits/time unit) at which bits transferred between sender/receiver❍ instantaneous: rate at given point in time❍ average: rate over longer period of time

Introduction 1-50

server, with

file of F bits

to send to client

link capacity

Rs bits/sec

link capacity

Rc bits/sec

pipe that can carry

fluid at rate

Rs bits/sec)

pipe that can carry

fluid at rate

Rc bits/sec)

server sends bits

(fluid) into pipe

Throughput (more)

� Rs < Rc What is average end-end throughput?

Rs bits/sec Rc bits/sec

R > R What is average end-end throughput?

Introduction 1-51

� Rs > Rc What is average end-end throughput?

Rs bits/sec Rc bits/sec

link on end-end path that constrains end-end throughput

bottleneck link

Throughput: Internet scenario

Rs

Rs

Rs

R

� per-connection end-end throughput:

Introduction 1-52

10 connections (fairly) share backbone bottleneck link R bits/sec

Rc

Rc

Rc

Rthroughput: min(Rc,Rs,R/10)

� in practice: Rc or Rs is often bottleneck

Protocol “Layers”

Networks are complex!

� many “pieces”:

❍ hosts

❍ routers

❍ links of various

Question:Is there any hope of organizing structure of

Introduction 1-53

❍ links of various media

❍ applications

❍ protocols

❍ hardware, software

organizing structure of network?

Or at least our discussion of networks?

Example: Plato and Archimedes…

Philosopher (Plato)

Secretary

Philosopher (Archimedes)

Secretary

Message to Archimedes

Introduction 1-54

� a series of steps

Mailbox

Mail Truck

Mailbox

Mail TruckMail Truck

Mailbox

Mail Truck

Plato & Archimedes: a different view

Philosopher (Plato)

Secretary


SecretaryTransfer message from sender to receiver

Discuss Metaphysic’s Principles

Introduction 1-55

Mailbox

Mail Truck

Mailbox


Mailbox

Mail Truck

� Layers: each layer implements a service❍ relying on services provided by layer below

Move mail from one mailbox to the next

Transfer mail from sender to receiver

Plato & Archimedes: a different view

Philosopher (Plato)

Secretary


Secretary

Exchange Ideas

Exchange Letters

Move Move

Introduction 1-56

Mailbox

Mail Truck

Mailbox


Mailbox

Mail Truck

� Layers: each layer implements a service❍ via its own internal-layer actions

• governed by rules (protocols)

Move Mail

Move Mail

Move Truck

Move Truck

Why layering?

Dealing with complex systems:� Decompose the system into subsystems

❍ Each implementing a subset of overall functionalities

� layered subsystems as reference model for discussion

� modularization eases maintenance, updating of

Introduction 1-57

� modularization eases maintenance, updating of system❍ change of implementation of layer’s service transparent to rest of system

❍ e.g., change from mail-truck to bike (environmental concerns…)

� layering considered harmful?

Layered Architecture

� Network provides communications services to applications

Introduction 1-58

Process A

ProcessB

Message exchange

Host A Host B

Network


� Network provides communications services to applications

Introduction 1-59

Process A

ProcessB

Message exchange

Host A Host B


� Abstract Model of the communication environment

� Communication system as composed of ordered set of layers

❍ Each implementing a subset of overall functionalities

Introduction 1-60

Process A

ProcessB

Message exchange

Host A Host B

Physical media

Process A

ProcessB

Message exchange


� Systems logically decomposed in subsystems

� Layer: collection of subsystems at the same level❍ (N) Layer: Layer at level N

Introduction 1-61

Physical media

(3)-Layer

Process A

ProcessB

Message exchange


� Each layer provides a service (to the layer above)❍ Service: set of functions offered to the layer above

• Error Control, Flow Control

❍ relying on services provided by layer below❍ via its own internal-layer actions

Introduction 1-62

Physical media

(3)-Layer

Process A

ProcessB

Message exchange


� Each layer provides a “value added” (communication) service with respect to the service provided by the layer below

Introduction 1-63

Physical media

(3)-Layer

Process A

ProcessB

Message exchange

Entities

�Active layers’ elements❍ (N)-Layer entity: (N)-Entity

Introduction 1-64

Physical media

(3)-Layer(3)-Entity (3)-Entity

Process A

ProcessB

Message exchange

Entities

� Implement layer functions at nodes❍ Require entities cooperation, exchanging messages with

peers❍ Using the (communication) service provided by the layer

immediately below

Introduction 1-65

Physical media

Process A

ProcessB

Message exchange

(3)-Layer(3)-Entity (3)-EntityMessage exchange

Layer Service

� (N)-layer provides the (N)-service to the (N+1)-entities ((N)-service users)

❍ (N) Service: a collection of (N) functions

� (N)-function is carried out by the (N)-entities❍ Requires entities cooperation

Introduction 1-66

❍ Requires entities cooperation

❍ Using the (N-1)-service

(N)-Entity (N)-Entity

(N+1)-Entity (N+1)-EntityMessage exchange

data

Message exchangedataH

(N-1)-service

(N)-service(N)-Layer

(N)-Protocol

� Cooperation among (N)-entities is governed by (N)-protocols

❍ Syntax of message types: what fields in messages & how fields are delineated

❍ Semantics of the fields, ie, meaning of information in fields

❍ Rules for when and how processes send & respond to

Introduction 1-67

❍ Rules for when and how processes send & respond to messages


(N+1)-Entity (N+1)-EntityMessage exchange

data


(N-1)-service

Logical Communication

Introduction 1-68

(N+1)-Entity (N+1)-Entitydata

(N)-service

Logical Communication

� Ex: Reliable (N)-Service over unreliable (N-1) service

Introduction 1-69


(N+1)-Entity (N+1)-Entitydata

data1

(N-1)-service

dataACK 1


�Highest level: application level

Process A Process BMessage exchangedata

(N)-service

Introduction 1-70

� Lowest level directly interface with the physical media

(N)-service

Physical media

(1)-Entity (1)-Entity

Protocol Data Unit (PDU)

� (N)-PDU❍ Messages exchanged between (N)-Entities

❍ Comprises• (N)-Service Users data

• Header (to carry out (N)-functions)

Introduction 1-71



Process ProcessMessage exchange

data


Protocol Data Unit (PDU)

� (N)-PDU❍ Messages exchanged between (N)-Entities

❍ Comprises• (N)-Service Users data


Introduction 1-72



Process ProcessMessage exchange

data


(N-1)-Entity (N-1)-EntityMessage exchangedataH

(N-2)-Entity (N-2)-EntityMessage exchangedataH

H

HH

Connection oriented and Connectionless Service

� Connection Oriented (N)-Service❍ E.g. telephone call

❍ To communicate, (N)-users • Setup Connection

• Transfer Data

• Tear-down Connection

Introduction 1-73

• Tear-down Connection

� Connectionless (N)-service❍ E,g,Postal service

❍ Trasfer Data

Layered Architecture: Models

�OSI (Open System Interconnection)❍ ’70 Standard de iure

❍ 7 levels

❍ Architecture first

Protocols later…if any

Introduction 1-74

❍ Protocols later…if any

� TCP/IP Model❍ ’80… Standard de facto

❍ 5 levels

❍ Protocols first

OSI (Open System Interconnection): Principles

�Minimize the number of layers

� Establish boundaries at points where interaction is minimum

� Layers should include different functions

Introduction 1-75

� Layers should include different functions

� Layers could be redesigned without affecting interfaced with adjacent layers

� Each layer should add value

OSI (Open System Interconnection)

Introduction 1-76

OSI Layers

Introduction 1-77

Physical Layer

� Coordinates the functions required to transmit a bit stream over a physical medium

�Defines

Introduction 1-78

Defines ❍ the characteristics of interfaces and media

❍ Bit representation

❍ Transmission rate

❍ Bit Synchronization

❍ Line configuration, transmission mode, etc.

Physical Layer

Introduction 1-79

Data Link Layer: Node-to-Node Delivery

Introduction 1-80

Data Link Layer

� Transforms the physical layer – which is error prone - to a reliable link

� Responsibilities

Introduction 1-81

� Responsibilities❍ Framing

❍ Physical Addressing

❍ Flow control

❍ Error Control

❍ Access Control• Important in broadcast network

Data Link Layer

Introduction 1-82

Network Layer: End-to-end delivery

Introduction 1-83

Network Layer

� Source to destination delivery of packets

� Responsibilities❍ Logical Addressing

Introduction 1-84

❍ Logical Addressing

❍ Routing

Network Layer

Introduction 1-85

Transport Layer

� Process to process delivery of messages

� Responsibilities❍ Service-point addressing

Introduction 1-86

❍ Service-point addressing

❍ Segmentation and reassembly

❍ Connection control

❍ Flow control

❍ Error control

Transport Layer

Introduction 1-87

Process-to-Process Communication

Introduction 1-88

Session Layer

� Session Management

� Responsibilities❍ Dialog Control

Introduction 1-89

❍ Dialog Control

❍ Synchronization

Session Layer

Introduction 1-90

Presentation Layer

�Deals with syntax and semantics of exchanged information❍ Make communication not dependent from data encoding

Introduction 1-91

� Responsibilities❍ Translation

❍ Encryption

❍ Compression

Presentation Layer

Introduction 1-92

Application Layer

� Enables users to access the network ❍ Providing user interfaces and support for services

Specific services:

Introduction 1-93

� Specific services:❍ Network virtual terminal

❍ File transfer, access and management

❍ Mail services

❍ Directory services

Application Layer

Introduction 1-94

Internet protocol stack

� application: supporting network applications

❍ FTP, SMTP, HTTP

� transport: app-to-app data transfer❍ TCP, UDP

� network: routing of datagrams from

application

transport

network

Introduction 1-95

� network: routing of datagrams from source to destination

❍ IP, routing protocols

� link: data transfer between neighboring network elements

❍ PPP, Ethernet

� physical: bits “on the wire”

network

link

physical

OSI vs. TCP/IP

� No presentation/ session layers in TCP/IP

� OSI provide connection and connectionless

application

transport

application

presentation

session

transport

Introduction 1-96

connectionless service at all layers

❍ TCP/IP network layer is connectionless (IP)

transport

network

link

physical

transport

network

link

physical

OSI TCP/IP

Internet History

� 1961: Kleinrock - queueing theory shows effectiveness of packet-switching

� 1964: Baran - packet-switching in military nets

� 1972:

❍ ARPAnet demonstrated publicly

❍ NCP (Network Control Protocol) first host-

1961-1972: Early packet-switching principles

Introduction 1-97

1964: Baran - packet-switching in military nets

� 1967: ARPAnet conceived by Advanced Research Projects Agency

� 1969: first ARPAnet node operational

Protocol) first host-host protocol

❍ first e-mail program

❍ ARPAnet has 15 nodes

Internet History

� 1970: ALOHAnet satellite network in Hawaii

� 1973: Metcalfe’s PhD thesis proposes Ethernet

� 1974: Cerf and Kahn -architecture for

Cerf and Kahn’s internetworking principles:

❍ minimalism, autonomy -no internal changes required to interconnect networks

1972-1980: Internetworking, new and proprietary nets

Introduction 1-98

architecture for interconnecting networks

� late70’s: proprietary architectures: DECnet, SNA, XNA

� late 70’s: switching fixed length packets (ATM precursor)

� 1979: ARPAnet has 200 nodes

required to interconnect networks

❍ best effort service model

❍ stateless routers

❍ decentralized control

define today’s Internet architecture

Internet History

� 1983: deployment of TCP/IP

� 1982: SMTP e-mail protocol defined

1983: DNS defined

� new national networks: Csnet, BITnet, NSFnet, Minitel

� 100,000 hosts connected to

1980-1990: new protocols, a proliferation of networks

Introduction 1-99

� 1983: DNS defined for name-to-IP-address translation

� 1985: FTP protocol defined

� 1988: TCP congestion control

connected to confederation of networks

Internet History

� Early 1990’s: ARPAnet decommissioned

� 1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995)

Late 1990’s – 2000’s:� more killer apps: instant

messaging, peer2peer file sharing (e.g., Naptser)

1990, 2000’s: commercialization, the Web, new apps

Introduction 1-100

(decommissioned, 1995)

� early 1990s: Web

❍ hypertext [Bush 1945, Nelson 1960’s]

❍ HTML, HTTP: Berners-Lee

❍ 1994: Mosaic, later Netscape

❍ late 1990’s: commercialization of the Web

Naptser)� network security to

forefront� est. 50 million host, 100

million+ users� backbone links running

at Gbps

What’s the Internet: a service vielopresti/Didattica/RetiWeb/RetiWeb...Chapter 1 Introduction Introduction 1-1 What’s the Internet: a service view communication infrastructure

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