Broadband Technologies
Part 2
Overview
Broadband Overview
Why broadband?
• Broadband is generally defined as any sustained
speed of 128K or more.
• Broadband can allow remote office staff and small
office, home office (SOHOs) to connect to the
central office (CO) LAN at high speeds.
• The Internet is moving from dialup modems and
slow connections to a world of high-speed
broadband using a variety of technologies.
• The most common problem with broadband access
What is broadband? From
Whatis.com
• In general, broadband refers to telecommunication in
which a wide band of frequencies is available to transmit
information. Because a wide band of frequencies is
available, information can be multiplexed and sent on
many different frequencies or channels within the band
concurrently, allowing more information to be transmitted
in a given amount of time (much as more lanes on a
highway allow more cars to travel on it at the same time).
Related terms are wideband (a synonym), baseband (a
one-channel band), and narrowband (sometimes
meaning just wide enough to carry voice, or simply "not
broadband," and sometimes meaning specifically
between 50 cps and 64 Kpbs).
• Various definers of broadband have assigned a
Broadband
• Broadband can be delivered to SOHOs via
the following technologies:
– Satellite
– Wireless
– Cable
– DSL
Satellites
Satellite options
• Older deployments from satellite data providers
used asymmetric data paths a satellite
downstream to the customer, and a dialup
modem for the return path to the provider.
• Today, a transmitter and a receiver are installed
for communications.
• Satellite services deliver data at downstream
speeds up to 1,500 kbps, and upstream speeds
Satellite options
• The typical satellite system requires:
– small 1.2 m (3.9 ft) satellite dish
– two standard coaxial cables to connect the satellite
disk to a satellite modem
– the satellite modem that connects to a PC through
an Ethernet or USB port.
• Satellite networks include:
• geostationary orbit satellites (GSOs) (22,300
Satellite
Extras
Satellite
• big repeaters in the sky
• transponders = repeater units carried by the
satellite
• 10 to 46 transponders per satellite
• each transponder can carry up to 3,000 DS-0, (64
Satellite
Extras
Geosynchronous / Geostationary satellites
• orbits earth at an altitude of 22,300 miles
above the equator
• takes 24 hours to orbit earth
Satellite
Extras
Advantages
• large footprint
broadcast,
send once receive many
• cost effective
for remote
areas
• 3 - 4 satellites
can cover the
earth
Satellite
Extras
Disadvantages
• promulgation delay: long delay, .12
seconds for a “single hop” or .24 seconds
(1/4 second) for “roundtrip”
• limited “orbit space” or positions for these
satellites
Satellite
Extras
Low Earth Orbit Satellites (LEO)
• non-stationary satellites of lower orbits
which has a smaller promulgation delay
• home satellite dishes act more like cellular
phones, jumping from satellite to satellite as
the satellites move in and out of range
Satellite
Extras
• “An orbiting global constellation of 1,000 small,
advanced, semi-autonomous, inter-connected
satellites.”
• prevents the signal delays inherent in the use of
conventional geostationary communication
satellites which operate at a higher altitude
Wireless Introduction
802.11 Frames – This isn’t
Ethernet!
Distribution System (DS)
IP Packet
General 802.11 Frame
L IP Packet
L
C
• 802.11 has some similarities with Ethernet but it is a
different protocol.
• Access Points are translation bridges.
• From 802.11 to Ethernet, and from Ethernet to 802.11
Station Connectivity
Authentication Process
• On a wired network, authentication is implicitly
provided by the physical cable from the PC to
the switch.
• Authentication is the process to ensure that
stations attempting to associate with the network
(AP) are allowed to do so.
Authentication Process – OpenSystem
• Open-system authentication really “no
authentication”.
• Open-system authentication is the only method
required by 802.11
Authentication Process –
Shared-Key
• Shared-key authentication uses WEP (Wired
Equivalent Privacy) and can only be used on
products that support WEP.
• WEP is a Layer 2 encryption algorithm based on
the RC4 algorithm.
Authentication Process
• We’ll look at the configuration of the client and AP
later!
• Example of open-system authentication.
• Note: On “some” systems you can configure
Authentication Process
• Authentication
– Open-System
– Shared-Key
(WEP)
or
only
• Encryption
If using Shared
Key (WEP)
authentication you are also using
– None
WEP encryption.
WEP
Open System–authentication
can
take place with or without WEP
encryption.
Hey, I REALLY
didn’t do
anything and I
am on the
Internet!
Station Connectivity
Authentication
Request
Beacon
SSID = tsunami
Authentication
Response
(Open-system)
• If not configured specifically to look for a network,
some client utilities will automatically join the
network that meets their vendor’s criteria (not
specified in 802.11) such as signal strength and
open-system authentication.
Wireless Bridging
Traditional WAN Connectivity
Monthly Leased Line OpEx
2 DS1:
RBOC
DS1
$600
1 DS3: $5000
TOTAL: $5600
DS1
DS3
New remote office
- No DS1 connection
available
RBOC provides guaranteed
level of service via a
Service Level Agreement
(SLA)
802.11b Connectivity
Monthly Line Cost
2 DS1:
RBOC
$600
1 Fractional DS3: $3000
2 Mbps
TOTAL: $3600
2 Mbps
22 Mbps
Wireless Installation Cost
7 350 Series Bridges Installed:
$12,500 USD
Pay Back Period: 3 months
5 Mbps
New building connected
Self managed
802.11a/g Connectivity
Monthly Line Cost
2 DS1:
RBOC
$600
1 DS3: $5000
14 Mbps
TOTAL: $5600
14 Mbps
50 Mbps
Wireless Installation Cost
7 1400 Series Bridges Installed:
$40,000 USD
Pay Back Period: 8 months
27 Mbps
New building connected
Self managed
Optional 2.4GHz Antennas for
Long Range
• 13.5 dBi Yagi
Distances over
7.3 miles @ 2 Mbps
11.7 Km @ 2 Mbps
3.6 miles @ 11 Mbps
5.8 Km @ 11 Mbps
• 21 dBi Solid Dish
For distances up to
25+ miles @ 2 Mbps
40+ Km @ 2 Mbps
20.5 miles @ 11 Mbps
33 Km @ 11 Mbps
802.11b Bridge Application:
School District
Richardson
Elementary
Yagi
Bode
Elementary
Yagi
WeaverRoberts
Special
Middle School
Education
Dish
Dish
High School 2
Bridges
One 12 dBi omni
One Dish
Channel #1
Channel #6
Channel #11
Price
Elementary
Yagi
UNIVERSITY
Administration
2 Bridges
One 12 dBi omni
One Yagi
Lincoln
Elementary
Yagi
Bolich
Dewitt Elementary Middle
School
Yagi
Yagi
Cable Technology
Cable options - Benefits
• Cable users access the Internet through a cable
modem that connects to the service provider
through a cable TV connection.
• In this case, the Internet Service Provider
(ISP) is the cable company.
• Minimum of 27 Mbps downstream to customers
and as much as 9.4 Mbps in the return path.
Cable options - DOCSIS
• Cable specifications are defined by Data
Over Cable Service Interface
Specification (DOCSIS).
• Current specification: DOCSIS 2.0
• Defines the use of data over cable and
other functional details.
– Defines technical specifications for subscriber
locations and cable operators’ headends
(coming).
– Allows for interoperability for multi-vendor
The original
cable plant
Cisco UBR 7223 Cable Modem Router as used for
high speed internet access over cable systems
• Community Antenna Television (CATV),
commonly called cable TV, was invented to solve
a dire consumer problem, which was poor TV
reception.
• Cable service providers (CSPs) offer IP-based
data and voice services to the business market as
an opportunity to substantially expand their
Data over
cable
• Fiber is used to replace cable amplifiers
throughout the plant.
• Amplifiers are placed approximately every 610
m (2000 ft) to ensure all RF signals will be
delivered to the home of the end-users with
enough power and clarity to receive all channels
within the spectrum, which is 50 to 860 MHz.
• In a 20-mile plant, approximately 52 amplifiers
Data over
cable
• The downstream traffic emanates from the
headend and is injected into a trunk cable.
• A cable system consists of the headend and its
connected coaxial cables and subscribers.
• The operator of a cable system is referred to as
a cable operator.
• The headend is where the cable operator puts
the different channels on the frequencies that
Data over cable
• Headend at Dascom’s Minnesota Facility - a 45
channel system
Data over cable
• The distribution network, which is made up of
fiber and coaxial cabling, delivers television
signals to the subscriber.
• The last part and also one of the best known
parts of the cable network is what is called the
subscriber drop.
• The subscriber drop includes the following:
– All cable splitters, couplers, and amplifiers running
Data over cable
• Broadcast analog
signal strength
attenuates or
weakens as it moves
through conducting
material (coax).
• Outside noise,
weather, and
temperature all affect
the impact signal
strength through
coaxial cable.
• To combat these
problems, cable
www.knology.com
Hybrid fiber-coaxial (HFC)
architecture
Scientific-Atlanta CMTS
• To deliver data services over a cable network:
– one 6 MHz television channel that is in the 50 MHz to
750 MHz range is typically allocated for downstream
traffic to homes
– one 6 MHz channel in the 5 MHz to 42 MHz band is
used to carry upstream signals
• A headend cable modem termination system
Hybrid fiber-coaxial (HFC)
architecture
www.twcarolina.com
• The cable modem network only operates at
Layers 1 and 2
Hybrid fiber-coaxial (HFC)
architecture
Scientific-Atlanta
CMTS
• An individual cable modem subscriber may
experience access speeds from 500 kbps to 2.5
Mbps, depending on the network architecture
and traffic load.
• If congestion does begin to occur due to high
usage, cable operators have the flexibility to
HFC
www.synchronous.net
• Another option for adding bandwidth is to
subdivide the physical cable network by running
fiber-optic lines deeper into neighborhoods.
• This reduces the number of homes served by
each network segment, and it increases the
Digital signals over RF channels
• When an FM radio is tuned to different radio
stations across the spectrum, that radio is being
tuned to different electromagnetic
frequencies across the spectrum.
• Cable works the same way. Cable carries TV
channels or data carriers at different
frequencies.
• The equipment in the subscriber home can be
tuned to those different frequencies.
Identifying cable technology
terms
• Broadband refers to the ability to frequency-division
multiplex (FDM) many signals in a wide RF bandwidth
over an HFC network.
– It also refers to the ability to handle vast amounts of information.
• CATV is originally an acronym for community antenna
television.
– Today the term is generally accepted to mean cable TV.
• Coaxial Cable is the principal physical media with which
CATV systems are built.
– Coaxial cable is used to transport RF signals.
– Coaxial cable signal loss or attenuation is a function of the
diameter of the cable, dielectric construction, ambient
temperature, and operating frequency (f).
• Headend is the location where the cable company
aggregates, combines, mixes, and modulates all signals
DSL Technology
What is DSL?
• While considered an end-to-end solution, DSL
only operates on the local loop between the
customer premises equipment (CPE) and the
DSL access multiplexer (DSLAM).
• A DSLAM is a device in the central office (CO)
What is DSL?
• DSL uses the high frequency range of up to
about 1 MHz.
• For example, asymmetric digital subscriber line
(ADSL) uses the frequency range of about 20
kHz to 1MHz.
– ADSL does not overlap the plain old telephone
service (POTS) voice frequency range. (300 – 3,400
DSL Implementations
• Asymmetric
– Faster downstream than upstream transfer
rate
– ADSL
– G.lite ADSL
– RADSL
– VDSL
• Symmetric
– Same downstream and upstream transfer
rates
– SDSL
DSL limitations
• The distance from CO to the DSL CPE must be
considered.
– The longer the distance, the lower the speed.
• The gauge of wire used in the local loop is
ADSL
My Alcatel
ADSL Modem
uses DMT
• An installer must check with the service provider
to determine which modulation technique is
being used.
• The modulation method used must be matched
ADSL and POTS coexistence
www.consultronics.com/ psts450.htm
• There is a POTS splitter at the central office (CO)
(or at home) to split up the POTS called voice and
ADSL called data traffic.
• The POTS traffic goes to the voice switch in the
CO, and the ADSL traffic goes to the DSLAM in the
CO.
ADSL channels and encoding
• There are two competing and incompatible
standards (modulation methods) for ADSL.
– The official ANSI and ITU standard for ADSL is a
system called discrete multitone (DMT).
• Most of the ADSL equipment installed today uses DMT.
– An earlier and more easily implemented modulation
method was the carrierless amplitude/phase (CAP)
system, which was used on many of the early
ADSL channels and encoding
• CAP divides the signals on the telephone line into
three distinct bands on a single channel.
– Voice: 0-kilohertz to 4-kilohertz (kHz) band, same as
POTS circuits.
– The upstream channel: between 25 and 160 kHz.
– The downstream channel: begins at 240 kHz and goes
up to a point that varies depending on a number of
conditions, which are line length, line noise, and number
ADSL channels and encoding
• DMT also divides signals into separate
channels.
• DMT divides the data into 250 separate
channels, each 4 kHz wide.
• Each channel is monitored.
• If the quality is too impaired, the signal is shifted
to another channel.
Data over ADSL with bridging
• DSL is a high-speed Layer 1 transmission
technology that works over copper wires.
• ATM is used as the data-link layer protocol
over DSL.
Data over ADSL with bridging
• A DSLAM is basically an ATM switch with DSL
interface cards in it.
• The DSL Layer 1 connection from the CPE is
terminated at the DSLAM.
• The DSLAM terminates the ADSL connections
and then switches the traffic over an ATM
network to an aggregation router (I.e. via
Data over ADSL with bridging
• To encapsulate an IP packet over an ATM/DSL
connection, there are three major approaches:
1. RFC 1483/2684 Bridged (Not covered – We need to
examine BVI, Bridge Virtual Interfaces to properly
cover this.)
2. PPP over Ethernet (PPPoE)
3. PPP over ATM (PPPoA)
Data over ADSL: PPPoE
• To encapsulate an IP packet over an
ATM/DSL connection, there are three
major approaches:
1. RFC 1483/2684 Bridged
2. PPP over Ethernet (PPPoE)
Data over ADSL: PPPoE
• PPPoE is a bridged solution similar to RFC
1483/2684 bridging.
• The CPE is bridging the Ethernet frames from
the PC of the end-user to an aggregation router
over ATM, like RFC 1483/2684 bridging.
• However, in this case, the Ethernet frame is
Data over
ADSL:
PPPoE
DSL Modem acting as the client
• In the PPPoE architecture, the PC of the enduser runs the PPPoE client software to connect
to the ADSL service.
• The PPPoE client software first encapsulates the
end-user data into a PPP frame, and then the
How does
PPPoE
work?
• PPP normally works over a point-to-point
connection only.
• Additional enhancements to PPP were needed
to support PPP over an Ethernet multiaccess
environment.
• As specified in RFC 2516, PPPoE has two
distinct stages.
How does
PPPoE
work?
• There are four steps to the Discovery stage.
• PC or router must first identity the Ethernet MAC
address of the peering device and establish a
PPPoE SESSION ID.
1. PC or CPE router sends an Initiation packet (PADI).
2. DSLAM responds with an Offer packet (PADO).
3. PC or CPE router continues with the Session phase
(PADR)
Data over ADSL: PPPoE
• To encapsulate an IP packet over an
ATM/DSL connection, there are three
major approaches:
1. RFC 1483/2684 Bridged
2. PPP over Ethernet (PPPoE)
Data over ADSL with PPPoA
• PPPoA is a routed solution, unlike RFC 1483,
which is a bridged solution where the CPE is set
up as a bridge.
• The CPE is routing the packets from the PC of
the end-user over ATM to an aggregation router.
• The PPP session is established between the
CPE and the aggregation router.
Data over ADSL with PPPoA
• The aggregation router that authenticates the
users can either use a local database on the
aggregation router or a Radius (AAA) Server.
• The PPPoA session authentication can be based
on PAP or CHAP.
• Once the PPP username and password is
authenticated, IPCP negotiation takes place, and
the IP address is assigned to the CPE.