Jaringan Komputer�(MIK1624401)

Departemen Informatika

Universitas Diponegoro

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Introduction: 1-1

Chapter 1: roadmap

• What is the Internet?
• What is a protocol?
• Network edge: hosts, access network, physical media
• Network core: packet/circuit switching, internet structure
• Performance: loss, delay, throughput
• Security
• Protocol layers, service models
• History

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Introduction: 1-2

A closer look at Internet structure

Network edge:

• hosts: clients and servers
• servers often in data centers

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Introduction: 1-3

A closer look at Internet structure

Network edge:

• hosts: clients and servers
• servers often in data centers

Access networks, physical media:

• wired, wireless communication links

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Introduction: 1-4

mobile network

home network

enterprise

network

national or global ISP

local or regional ISP

datacenter

network

content

provider

network

A closer look at Internet structure

Network edge:

• hosts: clients and servers
• servers often in data centers

Access networks, physical media:

• wired, wireless communication links

Network core:

• interconnected routers
• network of networks

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Introduction: 1-5

mobile network

home network

enterprise

network

national or global ISP

local or regional ISP

datacenter

network

content

provider

network

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 (WiFi, 4G/5G)

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Introduction: 1-6

mobile network

home network

enterprise

network

national or global ISP

local or regional ISP

datacenter

network

content

provider

network

Access networks: cable-based access

Introduction: 1-7

cable

modem

splitter

…

cable headend

frequency division multiplexing (FDM): different channels transmitted in different frequency bands

Access networks: cable-based access

Introduction: 1-8

cable

modem

splitter

…

cable headend

• HFC: hybrid fiber coax
• asymmetric: up to 40 Mbps – 1.2 Gbps downstream transmission rate, 30-100 Mbps upstream transmission rate
• network of cable, fiber attaches homes to ISP router
• homes share access network to cable headend

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Access networks: digital subscriber line (DSL)

Introduction: 1-9

central office

telephone

network

DSLAM

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• use existing telephone line to central office DSLAM
• data over DSL phone line goes to Internet
• voice over DSL phone line goes to telephone net
• 24-52 Mbps dedicated downstream transmission rate
• 3.5-16 Mbps dedicated upstream transmission rate

DSL

modem

splitter

Access networks: home networks

Introduction: 1-10

to/from headend or central office

Wireless and wired

devices

Wireless access networks

Introduction: 1-11

Shared wireless access network connects end system to router

• via base station aka “access point”

Access networks: enterprise networks

Introduction: 1-12

• companies, universities, etc.
• mix of wired, wireless link technologies, connecting a mix of switches and routers (we’ll cover differences shortly)
• Ethernet: wired access at 100Mbps, 1Gbps, 10Gbps
• WiFi: wireless access points at 11, 54, 450 Mbps

Ethernet

switch

institutional mail,

web servers

institutional router

Enterprise link to

ISP (Internet)

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Access networks: data center networks

Introduction: 1-13

• high-bandwidth links (10s to 100s Gbps) connect hundreds to thousands of servers together, and to Internet

mobile network

home network

enterprise

network

national or global ISP

local or regional ISP

datacenter

network

content

provider

network

Courtesy: Massachusetts Green High Performance Computing Center (mghpcc.org)

Host: sends packets of data

Introduction: 1-14

host sending function:

• takes application message
• breaks into smaller chunks, known as packets, of length L bits
• transmits packet into access network at transmission rate R
• link transmission rate, aka link capacity, aka link bandwidth

R: link transmission rate

host

1

2

two packets,

L bits each

Links: physical media

Introduction: 1-15

• bit: propagates between�transmitter/receiver pairs
• 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

Links: physical media

Introduction: 1-16

Coaxial cable:

• two concentric copper conductors
• bidirectional
• broadband:
• multiple frequency channels on cable
• 100’s Mbps per channel

Links: physical media

Introduction: 1-17

Wireless radio

• signal carried in various “bands” in electromagnetic spectrum
• no physical “wire”
• broadcast, “half-duplex” (sender to receiver)
• propagation environment effects:
• reflection
• obstruction by objects
• Interference/noise

Radio link types:

• Wireless LAN (WiFi)
• 10-100’s Mbps; 10’s of meters
• wide-area (e.g., 4G/5G cellular)
• 10’s Mbps (4G) over ~10 Km
• Bluetooth: cable replacement
• short distances, limited rates
• terrestrial microwave
• point-to-point; 45 Mbps channels
• satellite
• up to < 100 Mbps (Starlink) downlink
• 270 msec end-end delay (geostationary)

Chapter 1: roadmap

• What is the Internet?
• What is a protocol?
• Network edge: hosts, access network, physical media
• Network core: packet/circuit switching, internet structure
• Performance: loss, delay, throughput
• Security
• Protocol layers, service models
• History

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Introduction: 1-18

The network core

• mesh of interconnected routers
• packet-switching: hosts break application-layer messages into packets
• network forwards packets from one router to the next, across links on path from source to destination

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Introduction: 1-19

mobile network

home network

enterprise

network

national or global ISP

local or regional ISP

datacenter

network

content

provider

network

Two key network-core functions

Forwarding:

• aka “switching”
• local action: move arriving packets from router’s input link to appropriate router output link

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Introduction: 1-20

Routing:

• global action: determine source-destination paths taken by packets
• routing algorithms

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Introduction: 1-21

routing

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Introduction: 1-22

forwarding

forwarding

22

Packet-switching: store-and-forward

• packet transmission delay: takes L/R seconds to transmit (push out) L-bit packet into link at R bps
• store and forward: entire packet must arrive at router before it can be transmitted on next link

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Introduction: 1-23

source

R bps

destination

1

2

3

L bits

per packet

R bps

Packet-switching: queueing

Introduction: 1-24

A

B

C

R = 100 Mb/s

R = 1.5 Mb/s

D

E

queue of packets

waiting for transmission over output link

Packet-switching: queueing

Packet queuing and loss: if arrival rate (in bps) to link exceeds transmission rate (bps) of link for some period of time:

• packets will queue, waiting to be transmitted on output link
• packets can be dropped (lost) if memory (buffer) in router fills up

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Introduction: 1-25

A

B

C

R = 100 Mb/s

R = 1.5 Mb/s

D

E

queue of packets

waiting for transmission over output link

Alternative to packet switching: circuit switching

end-end resources allocated to, reserved for “call” between source and destination

• in diagram, each link has four circuits.
• call gets 2^nd circuit in top link and 1^st circuit in right link.
• dedicated resources: no sharing
• circuit-like (guaranteed) performance
• circuit segment idle if not used by call (no sharing)

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Introduction: 1-26

* Check out the online interactive exercises for more examples: http://gaia.cs.umass.edu/kurose_ross/interactive

• commonly used in traditional telephone networks

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Circuit switching: FDM and TDM

Frequency Division Multiplexing (FDM)

• optical, electromagnetic frequencies divided into (narrow) frequency bands

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Introduction: 1-27

Time Division Multiplexing (TDM)

• time divided into slots

• each call allocated its own band, can transmit at max rate of that narrow band

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• each call allocated periodic slot(s), can transmit at maximum rate of (wider) frequency band (only) during its time slot(s)

Packet switching versus circuit switching

Introduction: 1-28

example:

• 1 Gb/s link
• each user:
• 100 Mb/s when “active”
• active 10% of time

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Q: how many users can use this network under circuit-switching and packet switching?

* Check out the online interactive exercises for more examples: http://gaia.cs.umass.edu/kurose_ross/interactive

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• circuit-switching: 10 users

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Packet switching versus circuit switching

Introduction: 1-29

• great for “bursty” data – sometimes has data to send, but at other times not
• resource sharing
• simpler, no call setup
• excessive congestion possible: packet delay and loss due to buffer overflow
• protocols needed for reliable data transfer, congestion control
• Q: How to provide circuit-like behavior with packet-switching?
• “It’s complicated.” We’ll study various techniques that try to make packet switching as “circuit-like” as possible.

Is packet switching a “slam dunk winner”?

Q: human analogies of reserved resources (circuit switching) versus on-demand allocation (packet switching)?

Internet structure: a “network of networks”

• hosts connect to Internet via access Internet Service Providers (ISPs)
• access ISPs in turn must be interconnected
• so that any two hosts (anywhere!) can send packets to each other
• resulting network of networks is very complex
• evolution driven by economics, national policies

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Let’s take a stepwise approach to describe current Internet structure

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Internet structure: a “network of networks”

Introduction: 1-31

Question: given millions of access ISPs, how to connect them together?

Internet structure: a “network of networks”

Introduction: 1-32

Question: given millions of access ISPs, how to connect them together?

connecting each access ISP to each other directly doesn’t scale: O(N²) connections.

Internet structure: a “network of networks”

Introduction: 1-33

Option: connect each access ISP to one global transit ISP?

Customer and provider ISPs have economic agreement.

Internet structure: a “network of networks”

Introduction: 1-34

ISP A

ISP C

ISP B

But if one global ISP is viable business, there will be competitors ….

Internet structure: a “network of networks”

Introduction: 1-35

ISP A

ISP C

ISP B

But if one global ISP is viable business, there will be competitors …. who will want to be connected