Network Edge and Network Core

(1)

Stan Kurkovsky

Computer Networks

Network Edge and

Network Core

Based on Computer Networking, 4th_{Edition by Kurose and Ross}

What

What’’s the Internet: s the Internet: ““Nuts and BoltsNuts and Bolts””ViewView

•

• millions of connected millions of connected

computing devices:

computing devices: hosts hosts = end systems

= end systems

•

• running running network appsnetwork apps •

• communication linkscommunication links •

• fiber, copper, radio, fiber, copper, radio, satellite

satellite

•

• transmission rate = transmission rate =

bandwidth bandwidth

•

• routers:routers:forward packets forward packets

(chunks of data)

Home network

Institutional network Mobile network

Global ISP

Regional ISP

router PC server wireless laptop cellular handheld

wired links access points

(2)

Stan Kurkovsky “

“CoolCool””Internet AppliancesInternet Appliances

Shaver with a LAN connectivity IP picture frame

http://www.ceiva.com/

Web-enabled toaster + weather forecaster

Internet phones

What

What’’s the Internet: s the Internet: ““Nuts and BoltsNuts and Bolts””ViewView

•

• protocolsprotocolscontrol sending, control sending,

receiving of messages

receiving of messages •

• e.g., TCP, IP, HTTP, FTP, PPP, e.g., TCP, IP, HTTP, FTP, PPP, Skype, Ethernet

Skype, Ethernet

•

• Internet: Internet: ““network of networksnetwork of networks””

•

• loosely hierarchicalloosely hierarchical •

• public Internet versus private public Internet versus private intranet

intranet

•

• Internet standardsInternet standards •

• RFC: Request for commentsRFC: Request for comments •

• IETF: Internet Engineering Task IETF: Internet Engineering Task Force

Force

Home network

Institutional network Mobile network

Global ISP

(3)

Stan Kurkovsky What

What’’s the Internet: a Service Views the Internet: a Service View •

• communication communication infrastructure infrastructure

enables distributed applications:

enables distributed applications: •

• Web, email, voice over IP, Web, email, voice over IP, games, e

games, e--commerce, file sharingcommerce, file sharing

•

• communication services provided communication services provided

to apps:

to apps: •

• reliable data delivery from source reliable data delivery from source to destination

to destination

•

• ““best effortbest effort””(unreliable) data (unreliable) data delivery

delivery

What

What’’s a Protocol?s a Protocol?

human protocols:

•

• ““whatwhat’’s the time?s the time?”” •

• ““I have a questionI have a question”” •

• introductionsintroductions

…

…specific specific msgsmsgssentsent …

…specific actions taken when specific actions taken when msgsmsgs received, or other events

received, or other events

network protocols:

•

• machines rather than humansmachines rather than humans •

• all communication activity in Internet all communication activity in Internet governed by protocols

governed by protocols

protocols define format, order of protocols define format, order of msgs

msgssent and received among sent and received among network entities, and actions taken network entities, and actions taken on

on msgmsgtransmission, receipttransmission, receipt

Hi

Got the time?

2:00

TCP connection request TCP connection response

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

(4)

Stan Kurkovsky A closer Look at Network Structure

A closer Look at Network Structure

•

• network edge:

network edge:

•

• applications and hostsapplications and hosts

•

• network core:

network core:

•

• interconnected routersinterconnected routers •

• network of networksnetwork of networks

•

• access networks, physical

access networks, physical

media:

•

• wired and wireless wired and wireless communication links

communication links

The Network Edge

•

• end systems (hosts):

end systems (hosts):

•

• run application programsrun application programs •

• e.g. Web, emaile.g. Web, email •

• at at ““edge of networkedge of network””

•

• client/server model:

client/server model:

•

• client host requests, receives client host requests, receives service from always

service from always--on serveron server

•

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

client/server

•

• peer

peer

-

peer model:

•

• minimal (or no) use of dedicated minimal (or no) use of dedicated servers

servers

•

• e.g. Gnutella, e.g. Gnutella, KaZaAKaZaA, Skype, , Skype,

BitTorrent

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Stan Kurkovsky Network Edge: Reliable Data Transfer Service

Network Edge: Reliable Data Transfer Service

Goal:

data transfer between end systemsdata transfer between end systems

•

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

•

• Hello, hello back human protocolHello, hello back human protocol •

• set up set up ““statestate””in two communicating hostsin two communicating hosts

•

• TCP TCP --Transmission Control Protocol Transmission Control Protocol •

• InternetInternet’’s connections connection--oriented serviceoriented service

TCP service

[RFC 793][RFC 793]

•

• reliable, inreliable, in--orderorderbytebyte--stream data transferstream data transfer •

• loss: acknowledgements and retransmissionsloss: acknowledgements and retransmissions

•

• flow control:flow control: •

• sender wonsender won’’t overwhelm receivert overwhelm receiver

•

• congestion control:congestion control: •

• senders senders ““slow down sending rateslow down sending rate””when network congestedwhen network congested

Network Edge: Best Effort (Unreliable) Data Transfer Service

Goal:

data transfer between end systemsdata transfer between end systems •

• same as before!same as before!

•

• UDPUDP--User Datagram Protocol [RFC 768]: User Datagram Protocol [RFC 768]: •

• connectionless connectionless •

• unreliable data transferunreliable data transfer •

• no flow controlno flow control •

• no congestion controlno congestion control

App

’

s using TCP:

•

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

App

’

s using UDP:

•

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Stan Kurkovsky Access Networks and Physical Media

Access Networks and Physical Media •

• How to connect end systems to How to connect end systems to

edge router?

edge router? •

• residential access netsresidential access nets •

• institutional access networks institutional access networks (school, company)

(school, company)

•

• mobile access networksmobile access networks

•

• Keep in mind:Keep in mind: •

• bandwidth (bits per second) of bandwidth (bits per second) of access network?

access network?

•

• shared or dedicated?shared or dedicated?

Residential Access: Point to Point Access

Residential Access: Point to Point Access •

• Dialup via modemDialup via modem

•

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

(often less)

•

• CanCan’’t surf and phone at same time: t surf and phone at same time:

can

can’’t be t be ““always onalways on”” •

• DSL:DSL:digital subscriber linedigital subscriber line

•

• deployment: telephone company deployment: telephone company (typically)

(typically)

•

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

typically < 256 kbps)

•

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

typically < 1 Mbps)

•

• dedicated physical line to telephone dedicated physical line to telephone central office

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Stan Kurkovsky Residential Access: Cable Modems

Residential Access: Cable Modems •

• HFC: hybrid fiber coaxHFC: hybrid fiber coax •

• asymmetric: up to 30Mbps downstream, 2 Mbps upstreamasymmetric: up to 30Mbps downstream, 2 Mbps upstream

•

• network of cable and fiber attaches homes to ISP routernetwork of cable and fiber attaches homes to ISP router •

• homes share homes share access to

access to

router

•

• deployment: deployment:

available via available via cable TV cable TV companies companies Diagram: http://

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

Cable Network Architecture: Overview

server(s) _home

cable headend

cable distribution

network (simplified) _{Typically 500 to 5,000 homes} Channels 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 D A T A D A T A C O N T R O L 1 2 3 4 5 6 7 8 9

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Stan Kurkovsky Company Access: Local Area Networks

Company Access: Local Area Networks •

• company/university company/university local area local area network

network(LAN) connects end (LAN) connects end system to edge router

system to edge router

•

• Ethernet:Ethernet:

•

• 10 10 MbsMbs, 100Mbps, 1Gbps, , 100Mbps, 1Gbps,

10Gbps Ethernet

•

• modern configuration: end modern configuration: end systems connect into

systems connect into

Ethernet

Ethernet switchswitch

•

• LANs: chapter 5LANs: chapter 5

Wireless Access Networks

Wireless Access Networks •

• shared shared wirelesswirelessaccess network access network connects end system to router

connects end system to router •

• via base station aka via base station aka ““access access point

point””

•

• wireless LANs:wireless LANs: •

• 802.11b/g (802.11b/g (WiFiWiFi): 11 or 54 Mbps): 11 or 54 Mbps

•

• widerwider--area wireless accessarea wireless access

•

• provided by provided by telcotelcooperatoroperator •

• ~1Mbps over cellular system ~1Mbps over cellular system (EVDO, HSDPA)

(EVDO, HSDPA)

•

• next up (?): next up (?): WiMAXWiMAX(10(10’’s Mbps) s Mbps)

over wide area

base

station

mobile

hosts

router

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Stan Kurkovsky Home Networks

Home Networks

Typical home network components:

•

• DSL or cable modemDSL or cable modem

•

• router/firewall/NATrouter/firewall/NAT

•

• EthernetEthernet

•

• wireless access pointwireless access point

wireless access

point

wireless laptops router/

firewall cable

modem

to/from cable headend

Ethernet

Physical Media

Physical Media •

• Bit:Bit:propagates between propagates between transmitter/receiver pairs

transmitter/receiver pairs

•

• physical link:physical link:what lies between what lies between

transmitter & receiver

•

• guided media:guided media: •

• signals propagate in solid media: signals propagate in solid media: copper, fiber, coax

copper, fiber, coax

•

• unguided media:unguided media: •

• signals propagate freely, e.g., signals propagate freely, e.g., radio

radio

•

• Twisted Pair (TP):Twisted Pair (TP):two insulated two insulated copper wires

copper wires •

• Category 3: traditional phone Category 3: traditional phone

wires, 10 Mbps Ethernet

•

• Category 5: Category 5:

100Mbps Ethernet

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Stan Kurkovsky Physical Media

• Coaxial cable:Coaxial cable:two concentric two concentric copper conductors

copper conductors

•

• bidirectionalbidirectional

•

• baseband:baseband: •

• single channel on cablesingle channel on cable •

• legacy Ethernetlegacy Ethernet

•

• broadband:broadband: •

• multiple channels on cablemultiple channels on cable •

• HFCHFC

•

• Fiber optic cable:Fiber optic cable:glass fiber glass fiber

carrying light pulses, each pulse a

bit

•

• highhigh--speed operation:speed operation:

•

• highhigh--speed pointspeed point--toto--point point transmission (e.g., 10

transmission (e.g., 10’’ss--100100’’s s Gps

Gps))

•

• low error rate: repeaters spaced low error rate: repeaters spaced far apart;

far apart;

•

• immune to electromagnetic noiseimmune to electromagnetic noise

Physical Media

• Radio:Radio:signal carried in electromagnetic spectrumsignal carried in electromagnetic spectrum

•

• no physical no physical ““wirewire”” •

• bidirectionalbidirectional

•

• propagation environment effects:propagation environment effects: •

• reflection reflection •

• obstruction by objectsobstruction by objects •

• interferenceinterference

•

• Radio link types:Radio link types: •

• terrestrial microwaveterrestrial microwave

•

• e.g. up to 45 Mbps channelse.g. up to 45 Mbps channels

•

• LAN (e.g., LAN (e.g., WiFiWiFi))

•

• 2Mbps, 11Mbps, 54 Mbps2Mbps, 11Mbps, 54 Mbps

•

• widewide--area (e.g., cellular)area (e.g., cellular)

•

• e.g. 3G: hundreds of kbpse.g. 3G: hundreds of kbps

•

• satellitesatellite

•

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Stan Kurkovsky The Network Core

The Network Core •

• mesh of interconnected routersmesh of interconnected routers

•

• thethefundamental question:fundamental question:how is how is data transferred through net?

data transferred through net?

•

• circuit switching:circuit switching:dedicated circuit dedicated circuit

per call: telephone net

•

• packetpacket--switching:switching:data sent thru data sent thru net in discrete

net in discrete ““chunkschunks””

Network Core: Circuit Switching

End

-

end resources reserved for

“

call

”

•

• link bandwidth, switch capacitylink bandwidth, switch capacity

•

• dedicated resources: no sharingdedicated resources: no sharing

•

• circuitcircuit--like (guaranteed) like (guaranteed)

performance

•

• call setup requiredcall setup required

•

• network resources (e.g., network resources (e.g.,

bandwidth)

bandwidth) divided into divided into ““piecespieces”” •

• pieces allocated to callspieces allocated to calls •

• resource piece resource piece idleidleif not used by if not used by

owning call

owning call (no sharing)(no sharing)

•

• dividing link bandwidth into dividing link bandwidth into

“

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Stan Kurkovsky Circuit Switching: FDM and TDM

Circuit Switching: FDM and TDM

FDM

frequency

time

TDM

frequency

time

4 users

Example:

Numerical Examples

•

• How long does it take to send a file of 640,000 bits from host

How long does it take to send a file of 640,000 bits from host

A to host B over a circuit

-

switched network?

•

• All links are 1.536 MbpsAll links are 1.536 Mbps •

• Each link uses FDM with 24 Each link uses FDM with 24 channels/frequencies

channels/frequencies

•

• 500 500 msecmsecto establish endto establish end--toto--end end circuit

circuit

•

• All links are 1.536 MbpsAll links are 1.536 Mbps

•

• Each link uses TDM with 24 Each link uses TDM with 24

slots/sec

•

• 500 500 msecmsecto establish endto establish end--toto--end end circuit

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Stan Kurkovsky Network Core: Packet Switching

Network Core: Packet Switching each end

each end--end data stream divided end data stream divided into

into packetspackets •

• user A, B packets user A, B packets sharesharenetwork network resources

resources

•

• each packet uses full link each packet uses full link

bandwidth

•

• resources used resources used as neededas needed

resource contention:

•

• aggregate resource demand can aggregate resource demand can exceed amount available

exceed amount available

•

• congestion: packets queue, wait congestion: packets queue, wait for link use

for link use

•

• store and forward: packets move store and forward: packets move one hop at a time

one hop at a time •

• Node receives complete packet Node receives complete packet

before forwarding

Bandwidth division into

Bandwidth division into ““piecespieces”” Dedicated allocation

Dedicated allocation

Resource reservation

Packet Switching: Statistical Multiplexing

Sequence of A & B packets does not have fixed pattern, shared on

Sequence of A & B packets does not have fixed pattern, shared ondemand demand

Î

Îstatistical multiplexingstatistical multiplexing

A

B

C

10 Mb/s Ethernet

1.5 Mb/s

D

_E

statistical multiplexing

queue of packets waiting for output

(14)

Stan Kurkovsky Packet Switching: Store

Packet Switching: Store--andand--ForwardForward

•

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

bps

•

• Entire packet must arrive at router before it can be transmitteEntire packet must arrive at router before it can be transmitted on next d on next

link:

link: store and forwardstore and forward

•

• delay = 3L/R (assuming zero propagation delay)delay = 3L/R (assuming zero propagation delay)

•

• Example:Example: •

• L = 7.5 L = 7.5 MbitsMbits

•

• R = 1.5 MbpsR = 1.5 Mbps •

• Transmission delay = 15 secTransmission delay = 15 sec

R R R

L

Packet Switching versus Circuit Switching

Packet Switching versus Circuit Switching •

• Packet switching allows more users to use network!Packet switching allows more users to use network!

•

• Great for Great for burstyburstydatadata •

• resource sharingresource sharing •

• simpler, no call setupsimpler, no call setup

•

• Excessive congestion:Excessive congestion:packet delay and losspacket delay and loss •

• protocols needed for reliable data transfer, congestion controlprotocols needed for reliable data transfer, congestion control

•

• Q: How to provide circuitQ: How to provide circuit--like behavior?like behavior?

•

• bandwidth guarantees needed for audio/video appsbandwidth guarantees needed for audio/video apps •

• still an unsolved problemstill an unsolved problem

•

• Q: What are human analogies?Q: What are human analogies? •

• reserved resources (circuit switching) reserved resources (circuit switching) •

• onon--demand allocation (packetdemand allocation (packet--switching)switching)

N users

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Stan Kurkovsky Internet Structure: Network of Networks

Internet Structure: Network of Networks •

• roughly hierarchicalroughly hierarchical

•

• at center: at center: ““tiertier--11””ISPs ISPs (e.g., Verizon, Sprint, AT&T, Cable and Wireless), (e.g., Verizon, Sprint, AT&T, Cable and Wireless),

national/international coverage

•

• treat each other as equalstreat each other as equals

Tier 1 ISP

Tier-1 providers interconnect (peer) privately

Tier

Tier--1 ISP: e.g., Sprint1 ISP: e.g., Sprint

…

to/from customers peering to/from backbone

…

.

…

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Stan Kurkovsky Internet Structure: Network of Networks

• ““TierTier--22””ISPs: smaller (often regional) ISPsISPs: smaller (often regional) ISPs •

• Connect to one or more tierConnect to one or more tier--1 ISPs, possibly other tier1 ISPs, possibly other tier--2 ISPs2 ISPs

Tier 1 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 customerof tier-1 provider

Tier-2 ISPs also peer privately with each other.

Internet Structure: Network of Networks

• ““TierTier--33””ISPs and local ISPs ISPs and local ISPs •

• last hop (last hop (““accessaccess””) network (closest to end systems)) network (closest to end systems)

Tier 1 ISP

Tier-2 ISP local

ISP local

ISP localISP local

ISP Tier 3 ISP

local Local and

tier-3 ISPs are

customersof

higher tier ISPs connecting them to rest of Internet

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Stan Kurkovsky Internet

Internet StructureStructure: : NetworkNetworkof of NetworksNetworks

•

• a packet passes through many networksa packet passes through many networks

Tier 1 ISP

Tier-2 ISP local

ISP local

ISP localISP

local ISP

local

ISP Tier 3 ISP

local

ISP localISP

local ISP