Chapter 1 Computer Networks and the Internet

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Chapter 1 Computer Networks and the Internet

吳俊興

國立高雄大學資訊工程學系

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Outline

1.1 What

is

the Internet?

1.2 Network edge

1.3 Network core

1.4 Access networks and physical media

1.5 ISPs and Internet backbones

1.6 Delay & loss in packet-switched networks

1.7 Protocol layers and their service models

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

A worldwide network that interconnects millions of computing devices

millions of connected

computing devices:

hosts = end systems

running

network apps

communication links

P fiber, copper, radio, satellite P transmission rate = bandwidth

routers:

forward packets

local ISP

regional ISP

router _workstation server

(4)

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

protocols

control sending,

receiving of msgs

P e.g., TCP, IP, HTTP, FTP, PPP P IP: Internet Protocol

P TCP: Transmission Control

Protocol

Internet:

“network of

networks”

P loosely hierarchical

P public Internet versus private

intranet

Internet standards

P RFC: Request for comments P IETF: Internet Engineering

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What’s a protocol?

human protocols:

“what’s the time?”

“I have a question” introductions

… specific msgs sent

… specific actions taken when msgs received, or other events

network protocols:

machines rather than

humans

all communication

activity in Internet governed by protocols

protocols define

format

,

order

of msgs sent and

received among network

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RFC (Request for Comments)

IETF

P http://www.rfc-editor.org/rfc-index2.html P http://www.rfc-editor.org/rfcxx00.html

RFC791: IP (Internet Protocol)

RFC793: TCP (Transmission Control Protocol)

RFC768: UDP (User Datagram Protocol)

RFC854: TELNET

RFC959: FTP (File Transfer Protocol)

RFC821: SMTP (Simple Mail Transfer Protocol)

RFC1034/1035: DNS (Domain Name System)

RFC1939: POP3 (Post Office Protocol)

RFC2131: DHCP (Dynamic Host Configuration Protocol)

RFC2616: HTTP (Hypertext Transfer Protocol)

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Outline

1.1 What

is

the Internet?

1.2 Network edge

1.3 Network core

1.4 Access networks and physical media

1.5 ISPs and Internet backbones

1.6 Delay & loss in packet-switched networks

1.7 Protocol layers and their service models

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The network edge:

end systems (hosts):

P run application programs P e.g. Web, email

P at “edge of network”

client/server model

P client host requests, receives

service from always-on server

P e.g. Web browser/server;

email client/server

peer-peer model:

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Network edge: connection-oriented service

Goal:

data transfer

between end systems

handshaking:

setup

(prepare for) data

transfer ahead of time

P Hello, hello back human

protocol

P set up “state” in two

communicating hosts

TCP - Transmission

Control Protocol

P Internet’s

connection-TCP service

[RFC 793]

reliable, in-order

byte-stream data transfer

P loss: acknowledgements and

retransmissions

flow control:

(end-to-end)

P sender won’t overwhelm

receiver

congestion control:

P senders “slow down sending

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Network edge: connectionless service

Goal:

data transfer

between end systems

P same as before!

UDP - User Datagram

Protocol [RFC 768]: P connectionless P unreliable data transfer P no flow control P no congestion control

App’s using TCP:

HTTP (Web), FTP (file transfer), Telnet (remote login), SMTP (email)

App’s using UDP:

streaming media,

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Outline

1.1 What

is

the Internet?

1.2 Network edge

1.3 Network core

1.4 Access networks and physical media

1.5 ISPs and Internet backbones

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The Network Core

mesh of interconnected

routers

the

fundamental question:

how is data transferred through net?

P circuit switching: dedicated

circuit per call: telephone net

P packet-switching: data sent

thru net in discrete “chunks”

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Network Core: Circuit Switching

End-end resources

reserved for “call”

link bandwidth, switch

capacity dedicated resources: no sharing circuit-like (guaranteed) performance

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Network Core: Circuit Switching

network resources

(e.g., bandwidth)

divided into “pieces”

pieces allocated to calls resource piece

idle

if

not used by owning call

(no sharing)

dividing link bandwidth

into “pieces”

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Packet-switching: store-and-forward

Takes L/R seconds to

transmit (push out) packet of L bits on to link or R bps

Entire packet must

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Packet-switched networks: forwarding

Goal:

move packets through routers from source to

destination

P we’ll study several path selection (i.e. routing) algorithms

(chapter 4)

datagram network:

P destination address in packet determines next hop

P routes may change during session P analogy: driving, asking directions

virtual circuit network:

P each packet carries tag (virtual circuit ID), tag

determines next hop

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Network Taxonomy

Telecommunication networks Circuit-switched networks FDM _TDM Packet-switched networks Networks

with VCs NetworksDatagram • Datagram network is not either connection-oriented

or connectionless.

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Outline

1.1 What

is

the Internet?

1.2 Network edge

1.3 Network core

1.4 Access networks and physical media

1.5 ISPs and Internet backbones

1.6 Delay & loss in packet-switched networks

1.7 Protocol layers and their service models

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Access networks and physical media

Q: How to connect end

systems to edge router?

residential access nets institutional access

networks (school, company)

mobile access networks

Keep in mind:

bandwidth (bits per

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Physical Media

Bit: propagates between

transmitter/rcvr pairs

physical link: what lies

between transmitter & receiver

guided media:

P signals propagate in solid

media: copper, fiber, coax

unguided media:

P signals propagate freely,

e.g., radio

Twisted Pair (TP)

two insulated copper

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Physical Media: coax, fiber

Coaxial cable:

two concentric copper

conductors

bidirectional

baseband:

P single channel on cable P legacy Ethernet

broadband:

P multiple channel on cable P HFC

Fiber optic cable:

glass fiber carrying light

pulses, each pulse a bit

high-speed operation:

P high-speed point-to-point

transmission (e.g., 5 Gps)

low error rate: repeaters

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Physical media: radio

signal carried in electromagnetic spectrum no physical “wire” bidirectional propagation environment effects: P reflection P obstruction by objects P interference

Radio link types:

terrestrial microwave

P e.g. up to 45 Mbps channels

PAN/LAN (e.g., Wifi)

P 2Mbps, 11Mbps, 54Mbps

wide-area (e.g., cellular)

P e.g. 3G: hundreds of kbps

satellite

P up to 50Mbps channel (or

multiple smaller channels)

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Outline

1.1 What

is

the Internet?

1.2 Network edge

1.3 Network core

1.4 Access networks and physical media

1.5 Internet structure and ISPs

1.6 Delay & loss in packet-switched networks

1.7 Protocol layers and their service models

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Internet structure: network of networks

roughly hierarchical

at center: “tier-1” ISPs (e.g., MCI/UUNet/WorldCom,

BBN/Genuity, Sprint, AT&T), national/international coverage

P treat each other as equals

(29)

(30)

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Internet structure: network of networks

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

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

Tier 1 ISP Tier 1 ISP Tier 1 ISP NAP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP pays

(32)

Internet structure: network of networks

“Tier-3” ISPs and local ISPs

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

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 local

ISP local

ISP localISP

local local ISP Tier 3 ISP local local local ISP Local and

(33)

Internet structure: network of networks

a packet passes through many networks!

Tier 1 ISP Tier 1 ISP Tier 1 ISP NAP Tier-2 ISP Tier-2 ISP Tier-2 ISP local ISP local

ISP localISP local

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Outline

1.1 What

is

the Internet?

1.2 Network edge

1.3 Network core

1.4 Access networks and physical media

1.5 ISPs and Internet backbones

1.6 Delay & loss in packet-switched networks

1.7 Protocol layers and their service models

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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

A B

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Four sources of packet delay

1. nodal processing:

P check bit errors

P determine output link

A B propagation transmission nodal processing queueing 2. queueing

P time waiting at output

link for transmission

P depends on congestion

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Delay in packet-switched networks

3. Transmission delay:

R=link bandwidth (bps)

L=packet length (bits)

time to send bits into

link = L/R 4. Propagation delay: d = length/distance of physical link s = propagation speed in medium (~2x108 _m/sec) propagation delay = d/s A transmission _propagation

Note: s and R are

very

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Nodal delay

d_proc = processing delay

P typically a few microsecs or less

d_queue = queuing delay

P depends on congestion

d_trans = transmission delay

P = L/R, significant for low-speed links

d_prop = propagation delay

P a few microsecs to hundreds of msecs

(39)

“Real” Internet delays and routes

What do “real” Internet delay & loss look like? Traceroute/tracert program: provides delay

measurement from source to router along end-end Internet path towards destination. For all

i:

P sends three packets that will reach router i on path

towards destination

P router i will return packets to sender

P sender times interval between transmission and reply.

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“Real” Internet delays and routes

1 cs-gw (128.119.240.254) 1 ms 1 ms 2 ms 2 border1-rt-fa5-1-0.gw.umass.edu (128.119.3.145) 1 ms 1 ms 2 ms 3 cht-vbns.gw.umass.edu (128.119.3.130) 6 ms 5 ms 5 ms 4 jn1-at1-0-0-19.wor.vbns.net (204.147.132.129) 16 ms 11 ms 13 ms 5 jn1-so7-0-0-0.wae.vbns.net (204.147.136.136) 21 ms 18 ms 18 ms 6 abilene-vbns.abilene.ucaid.edu (198.32.11.9) 22 ms 18 ms 22 ms 7 nycm-wash.abilene.ucaid.edu (198.32.8.46) 22 ms 22 ms 22 ms 8 62.40.103.253 (62.40.103.253) 104 ms 109 ms 106 ms 9 de2-1.de1.de.geant.net (62.40.96.129) 109 ms 102 ms 104 ms 10 de.fr1.fr.geant.net (62.40.96.50) 113 ms 121 ms 114 ms 11 renater-gw.fr1.fr.geant.net (62.40.103.54) 112 ms 114 ms 112 ms 12 nio-n2.cssi.renater.fr (193.51.206.13) 111 ms 114 ms 116 ms 13 nice.cssi.renater.fr (195.220.98.102) 123 ms 125 ms 124 ms 14 r3t2-nice.cssi.renater.fr (195.220.98.110) 126 ms 126 ms 124 ms 15 eurecom-valbonne.r3t2.ft.net (193.48.50.54) 135 ms 128 ms 133 ms 16 194.214.211.25 (194.214.211.25) 126 ms 128 ms 126 ms 17 * * * 18 * * * 19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136 ms

traceroute: gaia.cs.umass.edu to www.eurecom.fr

Three delay measements from

gaia.cs.umass.edu to cs-gw.cs.umass.edu

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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

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Outline

1.1 What

is

the Internet?

1.2 Network edge

1.3 Network core

1.4 Access networks and physical media

1.5 ISPs and Internet backbones

1.6 Delay & loss in packet-switched networks

1.7 Protocol layers, service models

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Protocol “Layers”

Networks are complex!

many “pieces”: P hosts P routers P links of various media P applications P protocols P hardware, software

Question:

Is there any hope of

organizing

structure of network?

(44)

Why layering?

Dealing with complex systems:

explicit structure allows identification,

relationship of complex system’s pieces

P layered reference model for discussion

modularization eases maintenance, updating of

system

P change of implementation of layer’s service

transparent to rest of system

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

rest of system

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Internet protocol stack

application: supporting network

applications

P FTP, SMTP, HTTP

transport: host-host data transfer

P TCP, UDP

network: routing of datagrams from

source to destination

P IP, routing protocols

link: data transfer between

neighboring network elements

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Summary

1.1 What is the Internet?

P inter-networking, Internet, protocols

1.2 Network edge

P end-system/host (client/server), P2P, connectionless,

connection-oriented

1.3 Network core

P router, circuit/packet switching, FDM/TDM, store-and-forward,

router, datagram/virtual-circuit networks

1.4 Access networks and physical media 1.5 ISPs and Internet backbones

P 3 tiers

1.6 Delay & loss in packet-switched networks

P types of delay, packet loss

1.7 Protocol layers and their service models

Chapter 1 Computer Networks and the Internet

Chapter 1

Computer Networks and the Internet

吳俊興

國立高雄大學 資訊工程學系

Outline

1.1 What

is

the Internet?

1.2

Network edge

1.3

Network core

1.4

Access networks and physical media

1.5

ISPs and Internet backbones

1.6

Delay & loss in packet-switched networks

1.7

Protocol layers and their service models

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

hosts = end systems

network apps

communication links

routers:

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

protocols

Internet:

What’s a protocol?

protocols define

format

,

order

of msgs sent and

received among network

RFC (Request for Comments)

Outline

1.1

What

is

the Internet?

1.2 Network edge

1.3

Network core

1.4

Access networks and physical media

1.5

ISPs and Internet backbones

1.6

Delay & loss in packet-switched networks

1.7

Protocol layers and their service models

The network edge:

end systems (hosts):

client/server model

peer-peer model:

Network edge: connection-oriented service

Goal:

handshaking:

connection-TCP service

reliable, in-order

flow control:

congestion control:

Network edge: connectionless service

Goal:

App’s using TCP:

App’s using UDP:

Outline

1.1

What

is

the Internet?

1.2

Network edge

1.3 Network core

1.4 Access networks and physical media

1.5 ISPs and Internet backbones

The Network Core

the

國立高雄大學資訊工程學系