What s the Internet: a service view. Chapter 1 Introduction. What s the Internet: nuts and bolts view. What s the Internet: nuts and bolts view

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Chapter 1 Introduction

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 laptop cellular 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

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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 connection req TCP connection Introduction 1-6 Hi Got the time? 2:00 TCP connection response 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

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Transmission across a physical link:

point-to-point networks

Bits: propagate between transmitter and receiver

physical link:what lies between transmitter & TX TX RX 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 TX TX RX 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 log

₂

(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 base station mobile hosts router

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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?

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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 downstream

4 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

networkof 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 distribution network (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

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Wireless access networks

shared wirelessaccess

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 mobile hosts

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 laptops router/ 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 hopon the source-to-destination path)

A

B

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

forwarding

Routing table

Dest. Address Next 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

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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

Network Core: Circuit Switching

3 phases 1. 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 Core: Circuit Switching

network resources (e.g., bandwidth) divided into

“pieces”

❍ _{pieces allocated to calls}

Introduction 1-27 TX RX TX TX RX RX Physical link TX RX

Network Core: Circuit Switching

FDM: Frequency Division Multiplexing

❍ _{Different frequency intervals allocated to different calls}

Introduction 1-28 TX RX TX TX RX RX Physical link TX RX time fr e q u e n cy

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Network Core: Circuit Switching

TDM: Time Division Multiplexing

❍ Different time intervals allocated to different calls ❍ For each call: one slot per frame

slot frame Introduction 1-29 TX RX TX TX RX RX Physical link TX RX time fr e q u e n cy

Network Core: Packet Switching

A B C 10 Mbs Ethernet 1.5 Mbs queue of packets waiting for output

Introduction 1-30

each end-end data stream divided into packets user A, B packets sharenetwork 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 output link

Network Core: Packet Switching

A B C 10 Mbs Ethernet 1.5 Mbs queue of packets waiting for output

statistical multiplexing

Introduction 1-31

Statistical Multiplexing: Sequence of A & B packets does not have fixed pattern resources used as needed

resource contention:

aggregate resource demand can exceed amount available

congestion: packets queue, wait for link use

❍ May get dropped if buffer gets full

waiting for output link

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

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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 application transport network data link physical application transport network data link physical 1. Initiate call _{2. incoming call}

3. Accept call 4. Call connected

5. Data flow begins 6. Receive data

may be allocated to VC

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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 application transport network data link physical application transport network data link physical 1. Send data _{2. Receive data}

Network Taxonomy

Telecommunication networks Circuit-switched networks Packet-switched networks Introduction 1-38 networks FDM TDM networks Networks with VCs Datagram Networks

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 … … …

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Internet structure: network of networks

“Tier-2” ISPs: smaller (often regional) ISPs

❍ Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs

Tier-2 ISP Tier-2 ISP pays

Tier-2 ISPs also peer Introduction 1-41 Tier 1 ISP Tier 1 ISP Tier 1 ISP NAP Tier-2 ISP Tier-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 of tier-1 provider also peer privately with each other, interconnect at NAP

Internet structure: network of networks

“Tier-3” ISPs and local ISPs

❍ last hop (“access”) network (closest to end systems)

Tier-2 ISP local ISP local ISP local ISP local ISP Tier 3 ISP Local and

tier-Introduction 1-42 Tier 1 ISP Tier 1 ISP Tier 1 ISP NAP Tier-2 ISP Tier-2 ISP

Tier-2 ISP

ISP ISP

local

ISP local_ISP local_ISP

local ISP Local and

tier-3 ISPs are customers of higher tier ISPs connecting them to rest of Internet

Internet structure: network of networks

a packet passes through many networks!

Tier-2 ISP local ISP local ISP local ISP local ISP Tier 3 ISP Introduction 1-43 Tier 1 ISP Tier 1 ISP Tier 1 ISP NAP Tier-2 ISP Tier-2 ISP

Tier-2 ISP

ISP ISP

local

ISP local_ISP local_ISP

local ISP

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

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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 nodal processing 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 nodal processing queueing

Note: s and R are very different quantities!

Nodal delay

d_proc= processing delay

❍ _{typically a few microsecs or less}

d = queuing delay prop trans queue proc nodal

d

=

+

Introduction 1-47

d_queue= queuing delay

❍ _{depends on congestion}

d_trans= 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

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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 R_sbits/sec link capacity R_cbits/sec pipe that can carry

fluid at rate R_sbits/sec)

pipe that can carry fluid at rate

R_cbits/sec) server sends bits

(fluid) into pipe

Throughput (more)

R

_s

< R

_c

What is average end-end throughput?

R_sbits/sec R_cbits/sec

R > R

What is average end-end throughput?

Introduction 1-51

R

_s

> R

_c

What is average end-end throughput?

R_sbits/sec R_cbits/sec

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

bottleneck link

Throughput: Internet scenario

R_s R_s R_s R

per-connection

end-end

throughput:

Introduction 1-52

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

R_c R_c R_c R

throughput:

min(R

_c

,R

_s

,R/10)

in practice: R

_c

or

R

_s

is often

bottleneck

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Protocol “Layers”

Networks are complex!

many “pieces”:

❍hosts ❍routers

❍links of various

Question:

Is there any hope of organizingstructure of Introduction 1-53 ❍links of various media ❍applications ❍protocols ❍hardware, software organizingstructure 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 Truck Mail Truck Mailbox Mail Truck

Plato & Archimedes: a different view

Philosopher (Plato) Secretary Philosopher (Archimedes) Secretary

Transfer message from sender to receiver Discuss Metaphysic’s Principles

Introduction 1-55 Mailbox Mail Truck Mailbox Mail Truck Mail Truck 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 Philosopher (Archimedes) Secretary Exchange Ideas Exchange Letters Move Move Introduction 1-56 Mailbox Mail Truck Mailbox Mail Truck Mail Truck 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

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Why layering?

Dealing with complex systems:

Decompose the system into subsystems

❍ Each implementing a subset of overall functionalities

layered subsystems as reference modelfor

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 Process B Message exchange Host A Host B

Network

Layered Architecture

Network provides communications services to

applications Introduction 1-59 Process A Process B Message exchange Host A Host B

Layered Architecture

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 Process B Message exchange Host A Host B Physical media Process A Process B Message exchange

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Layered Architecture

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 Process B Message exchange

Layered Architecture

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 Process B Message exchange

Layered Architecture

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 Process B Message exchange

Entities

Active layers’ elements

❍ (N)-Layer entity: (N)-Entity

Introduction 1-64 Physical media (3)-Layer (3)-Entity (3)-Entity Process A Process B Message exchange

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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 Process B Message exchange (3)-Layer

(3)-Entity Message (3)-Entity

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 Message (N+1)-Entity

exchange data Message exchange data H (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 Message (N+1)-Entity

exchange data Message exchange data H (N-1)-service

Logical Communication

Introduction 1-68

(N+1)-Entity _data (N+1)-Entity

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Logical Communication

Ex: Reliable (N)-Service over unreliable

(N-1) service

Introduction 1-69

(N+1)-Entity _data (N+1)-Entity

data 1

(N-1)-service

dataACK 1

Layered Architecture

Highest level: application level

Process A Message Process B

exchange data

(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 Message Process

exchange data Message exchange data H

Protocol Data Unit (PDU)

(N)-PDU

❍Messages exchanged between (N)-Entities ❍Comprises

• (N)-Service Users data

Introduction 1-72

Process Message Process

exchange data Message exchange data H

(N-1)-Entity Message (N-1)-Entity

exchange

data H

(N-2)-Entity Message (N-2)-Entity exchange data H H H H

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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)

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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

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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

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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

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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

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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

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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:

commercializationof the Web

Naptser)

network security to

forefront

est. 50 million host, 100

million+ users

backbone links running