1. Chapter 1: roadmap 1.1 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): client/server model
run application programs
e.g. Web,
at “edge of network”
peer-peer
client/server
client/server model
client host requests, receives service from always-on server
e.g. Web browser/server; client/server
peer-peer model:
minimal (or no) use of dedicated servers
e.g. Skype, BitTorrent

4. 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
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
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 ADSL
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
DSL was designed to provide high speed access.

12. ADSL: equipment configuration

13. ADSL equipment
A telephone company technician must install a Network Interface Device on the customer’s permises. This small plastic box marks the end of the telephone company’s property and the start of the customer’s property. Close to the NID is a splitter, that separates the Hz band used by the POTS from data. The POTS signal is routed to the existing telephone or fax machine and the data signal is routed to an ADSL modem.

14. ADSL deployment: at the customer’s permise
ADSL Transmission Unit at the customer
premises end
ADSL + POTS signals
Travel together down the twisted pair
Using filter you will be isolating each signal

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 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

18. Discrete multi-tone technique
What it does is to divide the available 1.1 Mhz spectrum on the local loop into 256 independent channels of 4 Khz each. Channel 0 is used for POTS (Plain Old Telephone Service). Channels 1-5 are not used to keep the voice signal and data signals from interfering. The rest are available for user data. In its ADSL version 32 channels are used for upstream and the rest downstream. The ADSL standard allows speeds of as much as 8 Mbps downstream and 1 Mbps in the upstream
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:

22. Cable Network Architecture: Overview
Typically 500 to 5,000 homes
cable headend
home
cable distribution
network (simplified)

23. Cable Network Architecture: Overview
server(s)
cable headend
home
cable distribution
network

24. Cable Network Architecture: Overview
cable headend
home
cable distribution
network (simplified)

25. Cable Network Architecture: Overview
FDM (more shortly):
Channels V I D E O A T C N R L 1 2 3 4 5 6 7 8 9
cable headend
home
cable distribution
network

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 Twisted Pair (TP) two insulated copper wires
Category 3: traditional phone wires, 10 Mbps Ethernet
Category 5: 100Mbps Ethernet
Bit: propagates between transmitter/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

28. Physical Media: coax, fiber
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
Coaxial cable:
two concentric copper conductors
bidirectional
baseband:
single channel on cable
legacy Ethernet
broadband:
multiple channels on cable
HFC

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”