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Chapter 1: roadmap1.1 What is the Internet?

1.2 Network edge end systems, access networks, links

1.3 Network core circuit switching, packet switching, network structure

1.4 Delay, loss and throughput in packet-switched networks

1.5 Protocol layers, service models

1.6 Networks under attack: security

1.7 History

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A closer look at network structure: network edge:

applications and hosts

access networks, physical media: wired, wireless communication links

network core: interconnected

routers network of networks

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The network edge: end systems (hosts):

run application programs e.g. Web, email at “edge of network”

client/server

peer-peer

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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Access networks and physical mediaQ: 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 second)

of access network? shared or dedicated?

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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”

DSL: digital subscriber line deployment: telephone company (typically) up to 1 Mbps upstream (today typically < 256 kbps) up to 8 Mbps downstream (today typically < 1 Mbps) dedicated physical line to telephone central office

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Access networks

There are three ways to provide access to the internet to home

Over the telephone ADSL-based modems

Over the television plant Cable-based modems

Over an optical fiber Passive Optical Networks (APON or EPON)

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The ADSL-based access network

ADSL is one of the access technologies that

Can be used to convert the telephone line

into a high-speed digital link

is a part of a family of technologies called The x-type digital subscriber line (x-DSL)

Where x takes on different values

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X-DSL data rates

ADSL modem is the most commonly used

Rates Downstream: 8 Mbps

Upstream: 800 Kbps – 1 Mbps

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Bandwidth vs. distance

VDSL 52 Mbps/6.4 Mbps up to 1000 feet (300 m)

13 Mbps/1.6 Mbps up to 5000 feet (1.5 km)

ADSL Downstream

2 Mbps up to 5.4 Km

8 Mbps up to 2.7 Km

Upstream 64 Kbps to 800 Kbps

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Bandwidth vs distance

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Digital subscriber line

Some of the key features DSL allows analog voice signals and digital data

To be sent over the same local loop wiring

The local loop must be connected to sthg besides A traditional voice switch at the end office

A device called DSL access multiplexer (DSLAM) is used

Provides high speed access to end users

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ADSL: equipment configuration

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ADSL equipment

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ADSL deployment: at the customer’s permise

ADSL + POTS signals Travel together down the twisted pair

Using filter you will be isolating each signal

ADSL Transmission Unit at the customerpremises end

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ADSL access multiplexer

Transmission between the end office and customer is done using the ADSL layer

Speeds are limited to 1.5 Mbps

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Discrete multi-tone technique

The twisted pair bandwidth extends to 1.1 Mbps

is divided into 256 sub-channels Each occupying 4.3125 KHz

Sub-channel 0 is reserved For the voice band region

Sub-channels 1-5 separate data and POTS signal

The remaining sub-channels are used by ADSL

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Upstream and upstream data

In ADSL Both the upstream and downstream data

Are sent over the same twisted pair

This can be implemented using Frequency division multiplexing (FDM)

Up to 32 sub-channels for the upstream direction

Up to 218 downstream sub-channels

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Discrete multi-tone technique

ADSL 8 Mbps in the downstream

1 Mbps in the upstream

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The ADSL reference model architecture

DSLAM can support Up to 64 homes

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Residential access: cable modems

HFC: hybrid fiber coax asymmetric: up to 30Mbps downstream, 2 Mbps

upstream network of cable and fiber attaches homes to ISP router

homes share access to router deployment: available via cable TV companies

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Residential access: cable modems

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

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Cable Network Architecture: Overview

home

cable headend

cable distributionnetwork (simplified)

Typically 500 to 5,000 homes

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Cable Network Architecture: Overview

home

cable headend

cable distributionnetwork

server(s)

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Cable Network Architecture: Overview

home

cable headend

cable distributionnetwork (simplified)

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Cable Network Architecture: Overview

home

cable headend

cable distributionnetwork

Channels

VIDEO

VIDEO

VIDEO

VIDEO

VIDEO

VIDEO

DATA

DATA

CONTROL

1 2 3 4 5 6 7 8 9

FDM (more shortly):

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Company access: local area networks company/univ local area

network (LAN) connects end system to edge router

Ethernet: 10 Mbs, 100Mbps,

1Gbps, 10Gbps Ethernet modern configuration:

end systems connect into Ethernet switch

LANs: chapter 4

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Physical Media

Bit: propagates betweentransmitter/rcvr 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

Twisted Pair (TP) two insulated copper

wires Category 3: traditional

phone wires, 10 Mbps Ethernet

Category 5: 100Mbps Ethernet

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Physical Media: coax, fiberCoaxial cable: two concentric copper

conductors bidirectional baseband:

single channel on cable legacy Ethernet

broadband: multiple channels on

cable HFC

Fiber optic cable: glass fiber carrying light

pulses, each pulse a bit high-speed operation:

high-speed point-to-point transmission (e.g., 10’s-100’s Gps)

low error rate: repeaters spaced far apart ; immune to electromagnetic noise

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The Network Core

mesh of interconnected routers the fundamental question: how

is data transferred through net? circuit switching:

dedicated circuit per call: telephone net

packet-switching: data sent thru net in discrete “chunks”