This document discusses network access and physical media. It begins by defining the network edge as consisting of end systems or hosts that run applications. It then describes various access network types for connecting hosts, including DSL, cable, fiber, wireless networks, and mobile networks. It also covers the different physical media used for communication links, such as twisted pair copper wire, coaxial cable, fiber optic cable, and wireless radio spectrum.

1. Network Edge
Access Networks and Physical Media
Engr. Abbas Abbasi

2. Important Terms Review
 Host or End System
 Communication Link
 Transmission rate
 Packet
 Packet Switching
 Route or Path
 Router
 Link Layer Switch
 ISP
 Protocol
 TCP
 IP
 RFC
 Distributed Application
 API

3. Chapter 1: roadmap
1.1 What is the Internet?
1.2 Network edge
1.3 Network core
Network access and physical media
Internet structure and ISPs
1.4 Delay & loss in packet-switched networks
1.5 Protocol layers, service models
1.6 Networks under attack: security (covered in Chap. 8)
1.7 History

4. A closer look at network structure:
 network edge: applications
and hosts
 network core:
 routers
 network of networks
 access networks, physical
media: communication links

5. End Systems or Hosts
 PCs
 Game Consoles (Xbox, Playstation)
 Internet Ready TVs (Google TV)
 Home Appliances
 IP enabled phones
 Cyber-Physical Systems
 Industrial Systems (ECS)
 Biomedical Devices (Body Area Network: BAN)
 GPS Device

6. Hosts
 They are called hosts because they host (run) applications
 Client
 Servers
 Data Centers
 Content Distribution Networks (CDNs)
 Write down five ways to connect to the Internet

7. The network edge:
 end systems (hosts):
 run application programs
 e.g. Web, email
 at “edge of network”
 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, KaZaA

8. Access Networks

network—the network that physically connects an end system to the first router (Edge Router)
Home Network
 WAN Mobile Network
 Enterprise Network
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DSL (Digital Subscriber Line)
Cable
FTTH (Fiber to the home)
Dial-Up
Satellite
Ethernet
WiFi (Wireless Fidelity)
3G (Third generation)
LTE (Long Term Evolution)

9. Network edge: connection-oriented service
Goal: data transfer between end
systems
 handshaking: setup (prepare
for) data transfer ahead of
time
 Hello, hello back -human
protocol
 set up “state” in two
communicating hosts
TCP service [RFC 793]
 reliable, in-order byte-stream data
transfer
 loss: acknowledgements and
retransmissions
 flow control:
 sender won’t overwhelm receiver
 TCP - Transmission Control  congestion control:
 senders “slow down sending rate”
Protocol
when network congested
 Internet’s connection-oriented
service

10. Network edge: connectionless service
Goal: data transfer between end
systems
 same as before!
 UDP - User Datagram Protocol
[RFC 768]:
connectionless
unreliable data transfer
no flow control
no congestion control
App’s using TCP:
 HTTP (Web), FTP (file
transfer), Telnet (remote
login), SMTP (email)
App’s using UDP:
 streaming media,
teleconferencing, DNS,
Internet telephony, Domain
Name lookup, Time lookup.

11. 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?

12. Residential access
 Dialup via modem
 up to 56Kbps direct access to router
(often less)
 Can not surf and phone at same time:
can’t be “always on”
 DSL: digital subscriber line
 up to 1 Mbps upstream (today typically 500 kbps)
 up to 20 Mbps downstream (today typically 8 Mbps)
 FDM: 50 kHz - 1 MHz for downstream
4 kHz - 50 kHz for upstream
0 kHz - 4 kHz for ordinary telephone

13. DSL Structure
DSLAM: DSL Access Multiplexer

14. Cable Access
CMTS: Cable Modem Termination System

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

16. Cable Network Architecture: Overview
FDM:
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Channels
cable headend
cable distribution
network
home

17. Cable Network Architecture: Overview
server(s)
Fiber
Coax
cable headend
cable distribution
network
home

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

19. Fiber to the home (FTTH)
 Active Optical Network (AON) equivalent to Ethernet
 Passive Optical Network (PON)

20. PON
Downstream: 20Mbps
ONT: Optical Network Terminator
Splitter supports <100 ONT
OLT: Optical Line Terminator
converts optical signals to electrical
signals
Shared Fiber

21. Ethernet LAN

22. Wireless access networks
 shared wireless access network connects
end system to router
 via base station aka “access point”
 wireless LANs:
 802.11b/g (WiFi): 11 or 54 Mbps, @2.4
GHZ (range 100 m),
 802.11a 54 Mbps @ 5 GHz
 wider-area wireless access
 provided by telco operator
 3G ~ 384 kbps
 GPRS in Europe/US
 WiMax in US
router
base
station
mobile
hosts

23. Physical Media
 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
Twisted Pair (TP)
 two insulated copper wires
 Category 3: traditional phone wires, 10
(CAT-5)
Mbps Ethernet
 Category 5:
100 Mbps Ethernet
 Category 7
1 Gbps and 10 Gbps E'net

24. Physical Media: coax, fiber
Coaxial cable:
 two concentric copper
conductors
 bidirectional
 baseband:
 single channel on cable
 legacy Ethernet
 broadband:
 multiple channels on cable
 CATV HFC Fiber-Coax
Optical Fiber 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
Lighted
Fiber

25. Physical media: radio
 signal carried in
electromagnetic spectrum
 no physical “wire”
 bidirectional
 propagation environment
effects:
 reflection
 obstruction by objects
 interference
Radio link types:
 terrestrial microwave
 e.g. up to 45 Mbps channels
 LAN (e.g., WiFi)
 11Mbps, 54 Mbps
 wide-area (e.g., cellular)
 e.g. 4G: several Mbps
 satellite
 Kbps to 45 Mbps channel (or
multiple smaller channels)
 270 msec end-end delay
 geosynchronous versus low
altitude

26. Important Terms
 DSL
 LAN
 DSLAM
 3G
 HFC
 LTE
 CMTS
 WiFi
 FTTH
 Physical Medium Types
 AON
 UTP
 PON
 Shared Medium
 ONT
 OC (Optical Carrier)
 OLT
 Geostationary Satellite
 LEO Satellite