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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
2
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
3
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
4
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?
5
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
6
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)
7
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
8
X-DSL data rates
ADSL modem is the most commonly used
Rates Downstream: 8 Mbps
Upstream: 800 Kbps – 1 Mbps
9
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
10
Bandwidth vs distance
11
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
12
ADSL: equipment configuration
13
ADSL equipment
14
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
15
ADSL access multiplexer
Transmission between the end office and customer is done using the ADSL layer
Speeds are limited to 1.5 Mbps
16
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
17
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
19
The ADSL reference model architecture
DSLAM can support Up to 64 homes
20
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
21
Residential access: cable modems
Diagram: http://www.cabledatacomnews.com/cmic/diagram.html
22
Cable Network Architecture: Overview
home
cable headend
cable distributionnetwork (simplified)
Typically 500 to 5,000 homes
23
Cable Network Architecture: Overview
home
cable headend
cable distributionnetwork
server(s)
24
Cable Network Architecture: Overview
home
cable headend
cable distributionnetwork (simplified)
25
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):
26
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
27
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
28
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
29
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”