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Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs 1.6 Delay & loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History Brief Bio

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chapter 1 roadmap
Chapter 1: roadmap

1.1 What is the Internet?

1.2 Network edge

1.3 Network core

1.4 Network access and physical media

1.5 Internet structure and ISPs

1.6 Delay & loss in packet-switched networks

1.7 Protocol layers, service models

1.8 History

1: Introduction

brief bio
Brief Bio
  • IBM (10 years): Programmer/manager AIX base operating system, manager of LAN (PCLP, PCNP) and PC/3270 software development
  • Dell Computer Corporation (4 years): manager software (firmware) development, V P of PC Products group
  • VTEL (4 years): senior VP development and general manager
  • eOn Communications (3 years): President & CEO
  • Bynari Inc (1 year): Chairman & CEO
  • UTA Faculty since Summer 2001

1: Introduction

the network edge
end systems (hosts):

run application programs

e.g., WWW, email

at “edge of network”

client/server model

client host requests, receives service from server

e.g., WWW client (browser)/ Web server; email client/mail server

peer-peer model:

host interaction symmetric

e.g.: teleconferencing, groupware, file sharing

“connection”

The network edge:

1: Introduction

network edge connection oriented service
Goal: data transfer between end sys.

handshaking: setup (prepare for) data transfer ahead of time

Hello, hello back human protocol

set up “state” in two communicating hosts

TCP - Transmission Control Protocol

Internet’s connection-oriented service

TCP service[RFC 793]

reliable, in-order byte-stream data transfer

loss: acknowledgements and retransmissions

flow control:

sender won’t overwhelm receiver

congestion control:

senders “slow down sending rate” when network congested

The Internet's

Connection-Oriented

Service

Network edge: connection-oriented service

1: Introduction

network edge connectionless service
Goal: data transfer between end systems

same as before!

UDP - User Datagram Protocol [RFC 768]: Internet’s connectionless service

unreliable data transfer

no flow control

no congestion control

App’s using TCP:

HTTP (WWW), FTP (file transfer), Telnet (remote terminal/login), SMTP (email)

App’s using UDP:

streaming media, teleconferencing, Internet telephony

Network edge: connectionless service

1: Introduction

chapter 1 roadmap7
Chapter 1: roadmap

1.1 What is the Internet?

1.2 Network edge

1.3 Network core

1.4 Network access and physical media

1.5 Internet structure and ISPs

1.6 Delay & loss in packet-switched networks

1.7 Protocol layers, service models

1.8 History

1: Introduction

the network core
mesh of interconnected routers/switches

the fundamental problem for the core: how to get data through an internet (network layer switching)?

circuit switching: dedicated circuit per call, e.g. telephone network

packet-switching: data sent thru net in discrete “chunks”, e.g. ??

The Network Core

1: Introduction

network core circuit switching
End-end resources reserved for “call”

link bandwidth, switch capacity, queues/buffers

dedicated resources: no sharing

dedicated circuit-like (guaranteed) performance

call setup required

Network Core: Circuit Switching

1: Introduction

network core circuit switching10
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”

frequency division (FDM)

time division (TDM)

FDM:

1

2

3

4

frequency

time

TDM:

frequency

time

Network Core: Circuit Switching

1: Introduction

network core circuit switching tdm example
T1 Circuit

1.536 Mbps bandwidth, 24 time “slots”

500msec setup time

Yields:

1.536Mbps/24 =

64Kbps per slot or “circuit”

How long to send:

80KByte file?

1MByte file?

Network Core: Circuit Switching TDM Example

(80 * 103 * 8) / (64 * 103 ) = 640/64 = 10 (+ 0.5 sec = 10.5 sec)

(1 * 106 * 8 ) / (64 * 103 ) = 8000/64 = 125 (+ 0.5 sec = 125.5 sec)

1: Introduction

network core packet switching
each end-end data stream divided into packets

users A & B packets share network resources

each packet uses full link bandwidth

resources used as needed,

Bandwidth division into “pieces”

Dedicated allocation

Resource reservation

Network Core: Packet Switching

resource contention:

  • aggregate resource demand can exceed amount available
  • congestion: packets queue, wait for link use
  • store and forward: packets move one hop at a time
    • transmit over link
    • wait turn at next link

1: Introduction

network core packet switching13
Packet-switching versus circuit switching: human restaurant analogy

other human analogies?

D

E

Network Core: Packet Switching

10 Mbps

Ethernet

C

A

statistical multiplexing

1.536 Mbps

B

45 Mbps

queue of packets

waiting for output

link

1: Introduction

packet switching store and forward
Takes L/R seconds to transmit (push out) packet of L bits onto link or R bps

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

delaytrans = 3L/R

Example:

L = 7.5 Mbits

R = 1.5 Mbps

delay (transmission) = 15 sec

“message” switching

vs.

“packet” switching

Packet-switching: store-and-forward

L

R

R

R

1: Introduction

packet switching message segmenting
Now break up the message into 5000 packetsPacket Switching: Message Segmenting
  • Each packet 1,500 bits
  • 1 msec to transmit each packet on one link
  • pipelining: each link works in parallel
  • Delaytrans reduced from 15 sec to 5.002 sec

1: Introduction

packet switching versus circuit switching
1 Mbps link

each user:

generates traffic at 100Kbps when “active”

is active 10% of time

Capacity:

circuit-switching:

10 users

packet switching:

with 35 users, probability > 10 active less than .0004

Packet switching allows more users to use (i.e. “share) the network!

Packet switching versus circuit switching

N users

1 Mbps link

1: Introduction

packet switching versus circuit switching17
Great for bursty data

resource sharing

no call setup

Excessive congestion (load): packet delay and loss

protocols needed for reliable data transfer, congestion control

Q: How to provide circuit-like behavior?

bandwidth guarantees needed for audio/video and real-time applications

in practice, solutions still evolving (chapter 6)

Is packet switching a “slam dunk winner?”

Packet switching versus circuit switching

1: Introduction

packet switched networks routing forwarding
Goal: move packets through routers from the source (router) to the destination (router)

we’ll study several path selection algorithms (chapter 4)

datagram network:

destination address determines next hop

routes may change during session

analogy: driving, asking directions

virtual circuit network:

each packet carries tag (virtual circuit ID), tag determines next hop

fixed path determined at call setup time, remains fixed thru call

routers/switches maintain per-call state

Packet-switched networks: routing/forwarding

1: Introduction

network taxonomy
Packet-switched

networks

Circuit-switched

networks

FDM

TDM

Datagram

Networks

Networks

with VCs

Network Taxonomy

Telecommunication

networks

  • A datagram network is not either connection-oriented or connectionless (i.e., it can be both).
  • The Internet provides both connection-oriented (TCP) and connectionless services (UDP) to apps.

1: Introduction

chapter 1 roadmap20
Chapter 1: roadmap

1.1 What is the Internet?

1.2 Network edge

1.3 Network core

1.4 Network access and physical media

1.5 Internet structure and ISPs

1.6 Delay & loss in packet-switched networks

1.7 Protocol layers, service models

1.8 History

1: Introduction

access networks and physical media
Q: How to connect end systems to edge router?

residential access nets

institutional access networks (school, company, organization)

mobile access networks

Key considerations:

bandwidth (bits per second) of access network?

shared or dedicated?

Access networks and physical media

1: Introduction

residential access point to point access
Dialup via modem (PPP)

up to 56Kbps direct access to router (conceptually, often less)

not “always on”

still most prevalent access means

ADSL: asymmetrical digital subscriber line

up to 1 Mbps home-to-ISP router (typically < 256 Kbps)

up to 8 Mbps ISP router-to-home (typically < 1.5 Mbps)

Uses FDM with 3 contiguous frequency bands

downstream channel: 50 kHz – 1 MHz band

upstream channel: 4 kHz – 50 kHz band

telephone channel: 0 – 4 kHz band

ADSL deployment: rapidly evolving

Residential access: point to point access

1: Introduction

residential access cable modems
HFC: hybrid fiber coax (cable)

asymmetric: up to 10Mbps downstream, 1 Mbps upstream

requires cable modem at access point

network of cable and fiber attaches homes to ISP router

shared access to router among homes

issues: congestion, dimensioning

deployment: widely available via cable companies, e.g., AT&T(Comcast), AOL Time- Warner, Charter, etc.

Residential access: cable modems

1: Introduction

residential access cable modems24
Shared broadcast mediumResidential access: cable modems

Now, OC-192

Diagram: http://www.cabledatacomnews.com/cmic/diagram.html

1: Introduction

cable network architecture overview
Cable Network Architecture: Overview

Typically 500 to 5,000 homes

cable headend

home

cable distribution

network (simplified)

1: Introduction

cable network architecture overview26
Cable Network Architecture: Overview

cable headend

home

cable distribution

network (simplified)

1: Introduction

cable network architecture overview27
server(s)Cable Network Architecture: Overview

cable headend

home

cable distribution

network

1: Introduction

cable network architecture overview28
C

O

N

T

R

O

L

D

A

T

A

D

A

T

A

V

I

D

E

O

V

I

D

E

O

V

I

D

E

O

V

I

D

E

O

V

I

D

E

O

V

I

D

E

O

5

6

7

8

9

1

2

3

4

Channels

Cable Network Architecture: Overview

FDM:

cable headend

home

cable distribution

network

1: Introduction

institutional access local area networks
company/univ. local area network (LAN) connects end system to edge router

Ethernet:

shared or dedicated cable connects end system and router

10 Mbps, 100Mbps, Gigabit Ethernet

deployment: institutions, home LANs

LANs: chapter 5

Institutional access: local area networks

1: Introduction

wireless access networks
shared wireless access network connects end system to router

wireless LANs:

radio spectrum (unlicensed band) replaces wire

e.g., Linksys 802.11g

wider-area wireless access (MAN/WAN)

CDPD: wireless access to ISP router via cellular network

3G/EV-DO, GSM, WAP

WiMax/IEEE 802.16

router

base

station

mobile

hosts

Wireless access networks

1: Introduction

home networks
Typical home network components:

ADSL or cable modem

router/firewall/NAT

Ethernet

wireless access

point

Home networks

wireless

laptops

to/from

cable

headend

cable

modem

router/

firewall

wireless

access

point

Ethernet

(switched)

1: Introduction

physical media
physical link: transmitted data bit propagates across link

guided media:

signals propagate in solid media: copper, fiber

unguided media:

signals propagate freely, e.g., RF, IR

Twisted Pair (TP)

two insulated copper wires

Category 3: traditional phone wires, 10 Mbps Ethernet

Category 5 TP: 10/100/1000Mbps Ethernet

Category 6 TP now standard: Up to 650 Mbps

Physical Media

1: Introduction

physical media coax fiber
Coaxial cable:

wire (signal carrier) within a wire (shield)

baseband: single channel on cable

broadband: multiple channel on cable

bi-directional

use in 10Mbs Ethernet (10Base2) and cable networks

Physical Media: coax, fiber

Fiber optic cable:

  • glass fiber carrying light pulses
  • high-speed operation:
    • 100Mbps Ethernet
    • high-speed point-to-point transmission (e.g., 5 Gbps)
  • low error rate

1: Introduction

physical media radio
signal carried in electromagnetic spectrum

no physical “wire”

bi-directional

propagation environment effects:

reflection

obstruction by objects

interference

Physical media: radio

Radio link types:

  • terrestrial microwave
    • e.g. up to 45 Mbps channels
  • LAN (e.g., AirConnect)
    • 2Mbps, 11Mbps (802.11b)
    • 50+ Mbps (802.11a/g)
  • wide-area (e.g., cellular)
    • e.g. CDPD, 10’s Kbps
  • satellite
    • up to 50Mbps channel (or multiple smaller channels)
    • 270 msec end-end delay
    • geosynchronous versus LEOS

1: Introduction

chapter 1 roadmap35
Chapter 1: roadmap

1.1 What is the Internet?

1.2 Network edge

1.3 Network core

1.4 Network access and physical media

1.5 Internet structure and ISPs

1.6 Delay & loss in packet-switched networks

1.7 Protocol layers, service models

1.8 History

1: Introduction

internet structure network of networks
roughly hierarchical

at center: “tier-1” ISPs (e.g., Sprint, AT&T, MCI, Level3, Qwest, Cable & Wireless),

national/international coverage

treat each other as equals

NAP

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

Tier-1 providers interconnect (peer) privately

Internet structure: network of networks

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

1: Introduction

tier 1 isp e g sprint
Tier-1 ISP: e.g., Sprint

Sprint US backbone network

1: Introduction

tier 1 isp e g mci
Tier-1 ISP: e.g., MCI

MCI U.S. backbone network

1: Introduction

tier 1 isp e g mci39
Tier-1 ISP: e.g., MCI

MCI US-Intercontinental backbone network

1: Introduction

internet structure network of networks40
“Tier-2” ISPs: smaller (often regional) ISPs

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

NAP

Tier-2 ISPs also peer privately with each other, or interconnect at NAP

  • Tier-2 ISP pays tier-1 ISP for connectivity to rest of Internet
  • tier-2 ISP is customer of

tier-1 provider

Tier-2 ISP

Tier-2 ISP

Tier-2 ISP

Tier-2 ISP

Tier-2 ISP

Internet structure: network of networks

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

1: Introduction

internet structure network of networks41
“Tier-3” ISPs and local ISPs

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

Tier 3

ISP

local

ISP

local

ISP

local

ISP

local

ISP

local

ISP

local

ISP

local

ISP

local

ISP

NAP

Local and tier- 3 ISPs are customers of

higher tier ISPs

connecting them to rest of Internet

Tier-2 ISP

Tier-2 ISP

Tier-2 ISP

Tier-2 ISP

Tier-2 ISP

Internet structure: network of networks

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

1: Introduction

internet structure network of networks42
a packet passes through many networks!

Tier 3

ISP

local

ISP

local

ISP

local

ISP

local

ISP

local

ISP

local

ISP

local

ISP

local

ISP

NAP

Tier-2 ISP

Tier-2 ISP

Tier-2 ISP

Tier-2 ISP

Tier-2 ISP

Internet structure: network of networks

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

1: Introduction

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