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CEENET Workshop 2001 Satellite communications Krzysztof Muchorowski NetSat Express [email protected] Introductory remarks.

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Presentation Transcript
introductory remarks
Introductory remarks
  • The purpose of this lecture is to give you a very general overview of satellite communication, it is not meant to be a complete description of the world of satellite communication…
  • I will often mention applications and business services…
  • I will try not to deviate from the main course, but please stop me if I do.
a few reasons of satellite revolution
A few reasons of satellite revolution:
  • A single satellite can provide coverage to over 30% of Earth’s surface.
  • It is often the only solution for developing areas.
  • It is ideal for broadcast applications.
  • It can be rapidly deployed.
  • It is scalable.
  • Depending on application, there is no need for the local loop.
  • Transmission cost is independent on distance.
  • One hop from the backbone, wherever you are.
  • Wide bandwidths (155 Mbps) are available now.
what is a satellite
What is a satellite?
  • Isaac Newton noticed first, that if we throw an object on Earth horizontally with big enough velocity, it will not fall down, but will circulate around Earth indefinitely.
slide5

R=6400 km T=84 minutes

  • R=7100 km T=99 minutes (LEO)
  • R=11400 km T=201 minutes (MEO)
  • R=42350 km T=24 hrs (GEO)
  • So, an object placed at the orbit approx. 36 000 km above the equator will be seen at the same position in the sky from Earth.
  • But roundtrip time will be more than half a second!
  • Is this position actually stable?
slide7
but ...
  • omnidirectional antenna vs directional one
  • what does it mean in terms of available frequency spectrum?

There are (in general) three bands of spectrum available for GEO satellite communication: C, Ku, Ka.

C - 4-7 GHz (5 cm wavelength)

Ku - 10-14 GHz (2.3 cm wavelength)

Ka - 18-30 GHz (1 cm wavelength)

properties of spectrum bands
Properties of spectrum bands
  • C band:
    • large beams
      • The actual footprint of Intersputnik Express 3A
    • little rain fade (but sand storms affect it as well!)
    • large antennas
    • expensive amplifiers
    • lots of noise on the ground!
    • also circular polarization
    • Rx: 3625 to 4200 MHz
    • Tx: 5850 to 6435 MHz
properties of spectrum bands contd
Properties of spectrum bands (contd)
  • Ku-band
    • most widely used today
    • smaller beams (even spot beams)
    • smaller antennas
    • stronger rain fade
    • cheaper amplifiers
    • suitable for home users as well
    • noise on the ground is already often a problem
    • steerable spot beams
    • Rx: 10.95 to 12.75 GHz
    • Tx: 14 to 14.5 GHz
  • Ka band (still at development phase)
slide12

India\'s GSAT Hits Problems

Following its successful launch last week, ISRO\'s GSAT experimental satellite a series of in orbit manoeuvres have used most, if not all, of the available fuel on the spacecraft.

Unfortunately, the GSLV launcher did not place GSAT in exactly the right orbit - the apogee achieved was 32,051 km instead of the 35,975 km expected. Also, the inclination of the orbit was 19.2° instead of the intended 19°. The reason for this slight difference has not yet been determined.

It was originally believed that the intended orbit could be achieved by a series of short thruster burns using the satellite\'s attitude control

thrusters at the expense of the on board fuel and hence satellite lifetime.

Unfortunately, the satellite carries two different propellant tanks, which resulted in an unequal flow of fuel. The resulting imbalance created an impulse that made the spacecraft tilt. All the remaining fuel was then used in order to stabilise the satellite. Two different tanks were used because they were available. The designers were aware of the imbalance in flow rates but did not adequately compensate for its effects.

GSAT is now in a 23 hour 2 minute orbit and is reported to be out of fuel. It is not yet known what, if any use can be made of the spacecraft.

[press release, excerpts, April 2001]

slide13
Ariane 5 Satellites in Wrong Orbit

Following a perfect lift off from its launch site at Kourou, French Guiana, on Thursday Ariane 5 failed to put two comsats in the correct transfer orbit. Initial indications are that the second stage of the rocket shut down prematurely.

The two satellites were intended to be placed in a 35,853 km x 858 km transfer orbit with an inclination of 2.0°. They were actually left in a 17,528 km x 592 km orbit with an inclination of 2.9°.

Early reports are that the second stage, the Astrium manufactured Storable Propellant Stage (EPS), only generated 80% of the intended thrust and cut out 80 seconds early. It should have fired for 16 minutes 20 seconds, but this should have automatically been extended to compensate for the reduced thrust. Telemetry indicated that an anomaly occurred three seconds after ignition. Speculation is that the problem was caused by a propellant leak. The upper stage uses monomethyl hydrazine fuel and nitrogen tetroxide oxidiser, which are fed from pressurised tanks to a single Aestus motor.

In spite of these problems the second stage managed to orient itself correctly and successfully deployed the two satellites, leaving at least the possibility of recovery.

The satellites left in limbo by Ariane 510 are Artemis, an experimental European Space Agency telecommunications satellite, and BSAT-2b, a Japanese TV broadcast satellite.

Artemis, with a price tag of US$ 850 million, is ESA\'s most expensive satellite ever. It may carry enough fuel to allow it to reach geostationary orbit where it should be able to use ion propulsion thrusters for station keeping.

Japanese Broadcasting Satellite System\'s BSAT-2b may be a different story - it probably has enough fuel to reach geostationary orbit, but would be left without fuel for station keeping.

This was the tenth launch of an Ariane 5 and the third failure. Ariane 4, by comparison, which is due to be replaced by Ariane 5 in 2003 when the remaining stock of 12 launchers is used up, has had a series of 62 consecutive successful launches.

Before Thursday\'s launch failure, Arianespace was expecting to have three further Ariane 5 launches and three more Ariane 4 launches before the end of the year. The next Ariane 5 was scheduled to launch Atlantic Bird 2 and Insat 3C in September and the next Ariane 4 was to launch Intelsat 902 on 23 August.

An inquiry board has been appointed to investigate the cause of the launch failure. Preliminary conclusions are due at the beginning of August.

[press release from July 2001]

slide14

How much does a satellite cost?

  • How much does it cost to launch it?
  • How many transponders does it carry?
  • How long does it work?
  • What happens at the end of life?
    • Inclined orbit satellites.
other satellite issues to close the topic

Canada

Venezuela

United States

Colombia

Ecuador

Bahamas

Dominican Republic

Puerto Rico

Brazil

Peru

Mexico

Belize

Jamaica

Bolivia

Honduras

Guatemala

Nicaragua

Paraguay

El Salvador

Costa Rica

Panama

Argentina

Chile

Uruguay

SATMEX PROPRIETARY INFORMATION

Other satellite issues (to close the topic)
  • Rights to orbital slots, landing rights.
other satellite issues contd
Other satellite issues (contd)
  • EIRP, G/T
    • Effective Isotropic Radiation Power - EIRP - often expressed in decibels relative to 1W - dBW. Ku-band satellites typically about 50 dBW, C-band satellites typically about 35 dbW
    • G/T - gain by temperature - parameter of satellite antennas and position on Earth.
other satellite issues contd1
Other satellite issues (contd)
  • spring and autumn equinox
    • twice a year, around March 21 and September 23, satellite, earth station and sun are positioned along one line…
    • C band signal are affected more than Ku band signals
    • Stronger carriers are obviously less affected
    • Smaller antennas are less affected because their beamwidth is wider relative to the perceived radiation beamwidth of the sun (there are fewer days of outage, with shorter durations each day).
    • In the Fall, the farther north from the equator the station is, the later the effect occurs (in the Northern Hemisphere, the fall effect occurs after the Equinox). In the Southern Hemisphere, the reverse is true; the Fall effect occurs before the Equinox, and the further south a station is located the earlier it occurs. Satellites in locations east of the ground station have sun outage periods in the morning, and conversely, satellites located west of the station experience sun outages in the afternoon.
contd from previous page
(contd from previous page)
    • No action usually required unless:
        • You have an antenna tracking system, which should be put in standby or manual mode.
        • You want to reroute traffic for the several minutes of outage each day (worst case).
    • For those customers with duplex service, it is important to remember that the outage for your inbound and outbound links may occur at different days and at different times during the day.
  • http://www.ips.gov.au/papers/richard/calc_inter.html
pro s and con s of inclined orbit satellites
Pro-s and con-s of inclined orbit satellites
  • Con-s:
    • One probably only has about a year of service left before the satellite finally dies.
    • One will suffer a large Doppler shift
    • One will need to add tracking to the antenna (typically +$20k for a 2.4m)
  • Pro-s:
    • Price!!!
hardware ground segment
Hardware: ground segment
  • Antenna
  • Receiving/transmitting chain
  • Types of connection
  • Link budget
antenna
Antenna
  • Parabolic or offset
  • diameter - gain (as a function of frequency)
  • noise - temperature (as a function of elevation)
  • cross-polarisation isolation
  • de-icing (if required)
  • wind resistance
  • temperature variations tolerance
  • tracking...
antenna contd1
Antenna (contd)
  • Various kinds of antennas…
  • (what if we used two to transmit…)
antenna contd2
Antenna (contd)
  • Flat antennas (e.g. for Inmarsat phones)

(A short break from the main course of the lecture :)

high performance outdoor unit antenna rf
High Performance Outdoor UnitAntenna & RF
  • Flat panel antenna
  • RF Unit on rear
  • Single cable - no rf
  • All digital & DC
  • Self leveling tripod
  • Fixed mount available
  • Audio tone for antenna pointing
compact indoor unit
Compact Indoor Unit
  • 5 phone / fax jacks
  • 9.6 Kb. Data
  • 56 / 64 Kb HSD
  • Plug in Interfaces forRS-232,-449, V.35,X.21, and S0 ISDN
  • Menu in 5 languages
  • Speakerphone
go anywhere package
“Go Anywhere” Package
  • Entire system packs in a soft carry case
  • Case contains:
    • Antenna
    • RF Unit
    • Indoor Unit
    • Power Unit
    • Cables
    • Manual
great accessories for a great product
Great Accessories for a Great Product
  • The VIDEO EXPLORER
    • Briefcase video conferencing
  • TOKO BROADCAST VIDEO
    • Store & forward video at up to 2 Mb anywhere
  • STU-III Secure Phones at 9.6 Kb.
  • Datacom Accessories & Routers
  • Muxes, PBXs, Cordless Phones
the video explorer h 320 video conferencing in a briefcase
The Video ExplorerH.320 Video Conferencing in a Briefcase
  • 2 way, live video
  • Camera with 12X zoom & autofocus
  • 6” color display
  • supports 56-384Kb.ISDN Network
  • weighs approx 18 lbs.
  • Internal Phone

End of break - back to main course

receiving transmitting devices
LNA (Low Noise Amplifier) or LNB (Low Noise Block)

LNA - amplifies RF signal from the antenna and feeds it into frequency converter (typically IF of 70/140 MHz)

LNB - amplifies RF signal from the antenna and converts it to an L-band signal (950-2100 MHz)

LNA is more precise and stable but more expensive than LNB (LO stability).

Transmit power amplifiers provide amplification of signals to be transmitted to the satellite

Transceiver takes 70/140 MHz signal and amplifies it to either C or Ku-band final frequency.

Block UpConverter takes L-band signal and amplifies it to either C or Ku-band final frequency.

What is better?

Receiving/transmitting devices
amplifiers
Amplifiers
  • How much power is necessary?
    • Answer requires link budget…
    • typically, a few Watts for Ku-band, a few tens of Watts for C-band.
    • SSPA (Solid State Power Amplifiers) will be enough in almost every case.
modems
Modems
  • Satellite modem:
    • modulates input digital signal into analog signal and vice versa: demodulates input analog signal to digital data.
  • Typical parameters
    • supported modulations
    • FEC, Reed-Solomon
    • maximum speed
    • interfaces (on both sides)
    • compatibility… (this you never know until you try)
modem parameters
Modem parameters
  • Modulations/coding
    • How many bits per symbol (cycle, 1 Hz)?
      • 1 - BPSK
      • 2 - QPSK
      • 3 - 8PSK
      • 4 - 16QAM
          • (cable modems have typically 64QAM or perhaps even better now…)
    • FEC - forward error correction
      • QPSK 3/4, 7/8
      • 8PSK 2/3, 5/6
      • 16QAM 3/4, 7/8
      • Turbo coding
    • Reed-Solomon - additional performance improvement, but extra 188/204 factor
modem parameters contd
Modem parameters (contd)
  • Interfaces:
    • on IDU side:
      • V.35 (up to a few Mbps)
      • EIA-422, 449, 530 (up to 8 and 18 Mbps)
      • HSSI (up to 52 Mbps)
      • G.703 (as above)
      • OC-3c (exactly 155.52 Mbps)
    • on ODU side:
      • 70/140 MHz (to transceiver)
      • L-band (to BUC)
ird instead of a modem
IRD instead of a modem
  • Integrated receiver decoder (IRD) performs same functions as demodulator except that it typically provides as its interfaces:
    • Ethernet
    • Video/audio outputs
    • Audio outputs
  • Don’t assume any compatibility between IRDs until you experimentally verify it.
  • IRDs are children of DVB era, direct-to-home and broadcast applications.
redundancy
Redundancy
  • What is redundancy?
  • When is it required?
  • How is it done?
  • What remains a single point of failure?
bit error rate
Bit Error Rate
  • A demod’s BER performance is specified as a function of (signal energy per bit)-to-(noise power density per hertz) ratio - Eb/N0
  • The Eb/N0 ratio is so important because the bit error rate for digital data is a decreasing function of this ratio.
  • To ensure that a specified BER is met, a link budget analysis must be performed in order to ensure that the required Eb/N0 ratio is provided to the demodulator.
link budget
Link budget
  • Satellite transponders have two resources: bandwidth (Hz) and power (dbW). A proportional amount of transponder power is allocated across the transponder BW.
  • Power Equivalent Bandwidth (PEB) is the greater of two variables:
    • allocated bandwidth (a function of the data rate, modulation/coding scheme, carrier spacing)
    • allocated power (minimal power assignment which is sufficient to produce desired Eb/N0 ratio at the demodulator in the receiving station).
link budget contd
Link budget (contd)
  • What is needed as an input to link budget?
    • Satellite, its performance (EIRP, G/T)
    • location of both ground stations (elevation, rain zone)
    • data rate
    • required Eb/N0 ratio
    • any other limitations (e.g. maximum antenna diameter)
link budget contd1
Link budget (contd)
  • Therefore, link budget calculations tell us what is the optimum modulation/coding scheme used to maximize bandwidth utilisation, how much power we need to transmit certain amount of bandwidth (i.e. how powerful BUC should we buy), how big our antenna should be etc. etc.
  • Example calculation of allocated bandwidth:
    • 2 Mbps data stream, QPSK 3/4, Reed-Solomon coding, standard carrier spacing:

BW = 2048*10^3 /2 *4/3 *204/188 *1.5 = 2.2 MHz

link budget final
Link budget (final)
  • Transponder efficiency usage:
    • an example: two SCPC carriers per transponder, each receivable with 4.5m antenna or one MCPC carrier per transponder, receivable with 2.4m antenna.
    • Single/Multiple Channel Per Carrier - SCPC or MCPC
  • Same applies to transmitting:
    • if two carriers need to be transmitted through the same BUC, it is necessary to reserve more power i.e. two carriers each requiring 2W will need at least 8W BUC if sent through the same transmitting system. Multiplexer makes sense in such case…
  • Reed-Solomon is so useful as it allows to decrease antenna size (Eb/N0 ratio) while still maintaining very low BER.
moving up one layer to layer 2
Moving up one layer to layer 2...
  • OK, so we have a connection, both modems are locked to their carriers, the same stream of 0’s and 1’s is received as it is transmitted, what next?
  • Clear channel or link encapsulation:
    • HDLC
    • PPP
    • ATM
    • Frame Relay

or

    • DVB
to dvb or not to dvb
To DVB or not to DVB?

What is Digital Video Broadcast?

  • World-wide standard for transmission of digital TV via satellite (S), cable (C) or terrestrial (T).
  • Utilizes MPEG-2 compression and packet standard
  • Supports data as well as video transmissions.
  • Supports multiple program streams, each of which can be encrypted
  • Supports sub-multiplexing within a program stream
  • Provides for high degree of forward error correction
dvb delivers multiple ip services over a shared satellite link
DVB Delivers Multiple IP Services Over a Shared Satellite Link
  • In A Shared Link:
    • The satellite carrier is shared by multiple users;
    • User packets are interleaved;
    • Each site filters out its own packets.
  • There are many ways to do this, but DVB has several advantages.
multicast is expected to be a major growth area
Multicast Is Expected To Be A Major Growth Area

SOME MULTICAST APPLICATIONS

  • Radio & TV Networks-distribute commercials, audio & video objects to affiliates
  • Financial Data Feeds
  • Distance learning
  • Corporate Training Video
  • Catalog & Product Information Distribution
  • Caching Feeds for ISP’s and Corporate Intranets
  • Remote Publishing and Printing (example!)
multiplexed multicast technology needs supported facilitated by dvb
Multiplexed, Multicast Technology Needs Supported/Facilitated By DVB
  • High speed multiplexed (shared) satellite uplink
  • Secure delivery of services to entitled users
  • Low cost, one and two-way customer terminals
  • Quality of Service (QoS) management
  • Servers to receive, store and reliably play out streaming data, and data packages
  • Network management, billing, accounting, and customer support services
an content delivery network incorporating dvb

Edge Site

Local

ISP

Client

b - Content Delivery Site hosts data for eventual playout to edge and end sites

An Content Delivery Network Incorporating DVB

News Feed

Edge Sites (ES) include: ISPs, Web Host Facilities, Cable Head Ends etc.

End Sites include corporate locations and SOHO sites

Caching Feed

Content Delivery

Site

c - Content Delivery Site Multicasts Documents to Edge Sites and End Sites

Edge Site

d - Edge Sites store documents in Servers

The Net

End Site

e - End Sites store documents in local Servers or in requesting PC

3 - ES returns document

2 - ISP requests document from “closest” Edge Site

Content Providers

1 - Client requests document

4 - ISP returns document

54

a - Content Providers send web documents to Content Delivery Site

a closer look at dvb features
A Closer Look at DVB Features
  • DVB uses a 188 byte packet format for transmission of all services
  • DVB can multiplex multiple services on the same carrier
  • DVB provides conditional access for security, privacy, and program selectivity
  • For satellites, DVB provides:
    • QPSK Modulation (typically)
    • Reed-Solomon coding
    • Forward error correction rates: 1/2;2/3;3/4;5/6;7/8
    • potential to saturate the carrier, leading to more efficient bandwidth utilization and smaller receive antennas
    • avoids a very annoying problem with interface speed, encountered in SCPC links (!)
dvb packet format
DVB Packet Format
  • MPEG

Overhead

(4 bytes)

Payload

184 bytes

188 bytes

IP Encapsulation

Padded or packed area

IP Packet

16 byte header

MPEG Packets

dvb uplink data flow
DVB Uplink Data Flow

Modulates RF carrier; applies Reed-Solomon coding and FEC

MPEG Video Transport Stream and other multimedia

Internet

IP Packets

R

O

U

T

E

R

DVB

Mod.

MPEG

Multiplexer

IP

Encapsulator

Private lines

Encapsulates IP Packets within MPEG Transport Stream

Muxes MPEG program streams; encodes bit stream

Conditional

Access System

Controls program entitlements; key words for encryption

dvb integrated receiver decoder ird structure
DVB Integrated ReceiverDecoder (IRD) Structure

Note: IRD shown in this slide is set top box; could also be PC card.

carrier with multiple streams and substreams

NOTE: IRD in this slide is depicted as set top box:

could also be card that fits in PC

LNB

Local PIDs Only

All PIDs

IRD

100 Base T Port

Local router

Serial Port

Common Interface

  • demodulates transport stream
  • filters by PID number
  • provides Conditional Access processing
  • reassembles IP packet
  • could filter on IP or MAC address
an example multiplexed carrier
An Example Multiplexed Carrier
  • PID 1 Internet Access - in the clear, submultiplexed by MAC addresses
  • PID 2 News feed multicast - shared by all ISPs on the carrier (encrypted)
  • PID 3 Caching feed for selected ISPs (encrypted)
  • PID 4 Intranet for Corporation “A” (encrypted)
  • PID 5 Intranet for Corporation “B” (encrypted)
  • PID “n” Intranet for Corporation “C” (encrypted)

NOTE: Each PID has guaranteed bandwidth, but could burst for more, if bandwidth is available

summary of dvb benefits
Summary Of DVB Benefits
  • Low-cost receivers ($100-300 cards; $1000 set top boxes)
  • Tightly controlled filtering/encryption
  • Can mix services on large carriers
    • statistical multiplexing reduces bandwidth costs
    • saturated transponder operation leads to small antennas and more efficient bandwidth utilization
  • Standards base encourages application and enhancement development
  • just please be careful with compatibility issues!
applications
Applications
        • Already mentioned Internet, this is why we are here after all!
  • VSAT networks: full-mesh, star topology
  • not-so-quite POTS: Inmarsat system
  • p-to-p:
    • voice
    • Internet
  • content delivery
    • broadcast: TV, digital radio
    • multicasting: natural advantage
    • cache\'ing: passive, active, pushing content to the edge of the network
satellite internet
Satellite Internet
  • It is not enough to say, that “whatever comes in, comes out, so IP packets are fed from one side and leave on the other”.
  • There are certain specific features of satellite Internet like dynamical bandwidth allocation which are very useful.
  • There are also certain drawbacks of satellite Internet, mostly due to the long propagation delay and its effect on TCP (maximum session speed and slow start).
satnet and mfnet some history
SATNET and MFNET (some history)
  • Early DARPA experiment
  • 64 kb/s links
  • 10-3 BER
  • Demonstrated IP by interconnecting with ARPANET in 1977
  • Department of Energy:
    • Supercomputer star networks
      • UMd - SDSC
      • Arizona - JVNC
slide65
ACTS
  • NASA satellite launched 9/93, ended 6/2000
  • 20 - 30 GHz (so it was Ka-band)
  • Steerable and spot beams
  • Up to OC-12 speeds
effect of propagation delay on tcp networks very pessimistic
Effect of propagation delay on TCP networks(very pessimistic)
  • Geostationary satellites (GEOs) have a minimum round-trip latency (i.e., delay) of 500 msec, and take 700 msec or more with framing delays
  • GEO latency can significantly degrade performance on client/server applications such as Oracle and Exchange Server resulting in slow downs of 10 times or more
    • Small transaction-oriented queries get queued up by GEOs’ high delay
  • GEOs do not work well with fundamental Internet protocols like TCP/IP
    • Most implementations of TCP today provide unacceptable performance (e.g., wasting 93% of bandwidth on a 2 Mbps connection) because they lack “large window” support
    • TCP’s essential congestion control mechanisms degrade performance over GEOs. These mechanisms cannot be removed without potentially causing the "congestive collapse" of the Internet.
    • One proposed solution, ACK spoofing, is incompatible with Internet Protocol security (IPsec) and will not work at all with the next generation protocol, IPv6.
  • Transaction-oriented Internet protocols also suffer from GEO delays because signaling exchange is necessarily sequential
    • HTTP/1.0 and HTTP/1.1, POP3, IMAP4, NNTP
    • Hand-shaking portions of real-time protocols such as H.323 also suffer
effect of propagation delay on tcp networks more realistic
Effect of propagation delay on TCP networks (more realistic)
  • TCP transport layer protocol guarantees delivery of data between hosts by requiring that each host acknowledge the receipt of data from any other host. If a host sends data and does not receive an acknowledgement from the receiving host it must retransmit the unacknowledged data. TCP will only transmit as much data as the receiving end can store before it must acknowledge the receipt of the data. The amount of data that can be stored is known as the advertised Window Size. After sending the maximum number of bytes, the transmitting end must wait for an acknowledgement before sending more data. Here is where satellite latency becomes an issue. With a round trip satellite latency of 500ms, no data will be sent for 500ms after the last bit of the previous message is transmitted. Actually the satellite latency is not the only latency involved. There will typically be 100 ms or more added due to the terrestrial links between the hosts and the satellite earth stations. The total latency is known as the Round Trip Propagation Delay (RTPD). The RTPD = 250 ms * 2 + terrestrial latency. Assuming 100 ms for the terrestrial latency the RTPD = 600 ms. The maximum throughput of a TCP connection is given as:
  • Maximum Throughput Rate = Advertised Window Size/ RTPD
  • With a 32,672-byte Advertised Window size the maximum throughput of a satellite link with a 100 ms terrestrial latency would be:
  • Max Throughput Rate = Window Buffer size / RTPD
      • = 32,672 / .600
      • = 54,453 Bytes/Sec
      • = 435,627 bits/ Sec
  • Slow start is another problem...
effect of propagation delay on tcp networks a bit of relief
Effect of propagation delay on TCP networks (a bit of relief)
  • This effects only a single TCP session! A large number of users, even a single user with Web browser will have numerous TCP sessions, each will have its limit, so bandwidth utilisation is actually not a problem!
  • But it is true, that there is a number of protocols, which are very uncomfortable with such large delay: Oracle, Exchange, telnet, NNTP, voice…

What? Did I say voice? Voice-over-IP? Has someone rang me?

effect of propagation delay on tcp networks contd
Effect of propagation delay on TCP networks (contd)
  • Technical issues with Long Fat Networks - no longer just a satellite problem
  • Approaches include SACK (RFC 1072, 2018), TCP spoofing, Transaction TCP (T/TCP),
    • …and LEO
tcp ip accelerator
TCP/IP Accelerator
  • TCP/IP spoofing improves TCP/IP throughput over satellite.
  • Resides on a proxy server at both ends of the link.
  • Interfaces with the user and the host via TCP uses UDP over
  • the satellite. UDP does not require acknowledgements.
  • Large receive window
  • Selective NAKs to provide guaranteed delivery
  • Data compression.
  • The end result is a higher speed TCP/IP connections
  • (upto T1 rates) in high latency environments such as satellite communications. Results in higher speed and reduced bandwidth utilization.
  • This is usually a premium service. It will not work with IPv6.
voip on satellite networks
VoIP on satellite networks
  • Excellent application, widely used:
    • 10 kbps per phone call instead of 64 kbps
    • simple setup for both termination and origination
    • some legal problems might be on the way

(but it may only increase possible profits :-)

    • satellite delay is a little bit of a problem, one must get used to it.
    • but this satellite delay is constant so there is no jitter!
    • end-to-end bandwidth is fully guaranteed!
back to satellite internet
Back to satellite Internet
  • Types of connections:
    • bi-directional:
      • symmetric
      • asymmetric (typically 1:4)
    • uni-directional (receive-only)
  • Routing issues:
    • on bi-directional links
    • on receive-only links;
  • Burstability
bi directional satellite internet connections
Bi-directional satellite Internet connections
  • capacity may be symmetric or asymmetric, depending on needs, applications etc.
  • typically, for asymmetric setup, 1:4 of outgoing/incoming bandwidth is assumed.
  • one needs to assume about $10-20k for such hardware
receive only satellite internet connections
Receive-only satellite Internet connections
  • Simple to use and set up
  • usually no problems with licensing
  • cheap hardware ($1k-$3k)
  • but performance is difficult to guarantee!
burstability
Burstability
  • This is a unique feature of satellite networks. It works best in case of wide C-band beams, which span several timezones.
  • It allows users to get their guaranteed capacity (CIR or CBR), but if bandwidth in carrier is available, it can be used at little or no charge.

This is often a ‘selling point’ so be careful!

  • Surely, DVB is ideal for large, powerful carriers where burst is likely to give you most benefit.
routing if we also have 2 nd connection
Routing (if we also have 2nd connection)
  • BGP4
    • Ideal case. Works for both bi-directional and receive-only links. Load-balancing remains an issue, but may be managed.
  • Static routing:
    • Option 1: static BGP announcement by the satellite provider (when we own at least a C-class), but BGP announcements must be similar!
    • Option 2: Using IP addresses and cooperative upstream ISP
    • Option 3: Using IP addresses and non-cooperative upstream ISP
    • NAT and proxy (uses IP addresses from the satellite provider)
more about routing for ro links
More about routing for RO links.
  • Option 1: Both satellite provider and your local ISP announce your routes. The smallest block which can advertised to the Internet is a full Class C block.
  • Option 2: Satellite provider alone announces your routes. In this option you must have addresses that no on else is advertising. Again, it must be at least Class C. With this option, your local ISP will be seeing traffic originate from within your network that does not have a source address that he has assigned to you. This option will require that your local ISP pass this traffic.
  • Option 3: Satellite provider alone announces your routes and your local ISP is non-cooperative and will block this traffic. Some ISP’s will not allow you to obtain address space from other sources and will block traffic that originates with a foreign source address. The solution is to encapsulate this traffic in a GRE tunnel. Traffic will leave your network encapsulated with a source address that your local ISP will pass. This traffic will be de-encapsulated at satellite provider’s NOC and will then be forwarded to the proper site on the Internet. This has two disadvantages. First, traffic will have to transverse the Internet twice. Traffic destined for Microsoft.com will first arrive at satellite provider’s NOC and only then will it be redirected to Microsoft.com. Second, the encapsulation /de-encapsulation process takes time and is CPU intensive as every packet must be processed.
what is multicast
What is Multicast ?
  • Multicast is the transmission of information (a lot of information, usually) that should be transmitted to various (but usually not all) hosts over an internet.
  • One common situation in which it is used is when distributing real time audio and video to the set of hosts which have joined a distributed conference.
  • Multicast is much like radio or TV in the sense that only those who have tuned their receivers (by selecting a particular frequency they are interested on) receive the information. That is: you hear the channel you are interested in, but not the others.
the problem with unicast
The Problem with Unicast
  • When you send a packet and there is only one sender and one recipient then this is unicast. TCP is, by its own nature, unicast oriented.
  • If you are to send audio and video, which needs a huge amount of bandwidth compared to web applications, you had, until multicast came into scene- two options:to establish a separate unicast connection with each of the recipients, or use broadcast.
  • The first solution is not affordable: if we said that a single connection sending audio/video consumes a huge bandwidth, imagine having to establish hundreds or, may be, thousands of those connections. Both the sending computer and your network would collapse.
what about broadcast
What about Broadcast ?
  • Broadcast seems to be a solution, but it\'s not certainly the solution. If you want all the hosts in your LAN to attend the conference, you may use broadcast. Packets will be sent only once and every host will receive them as they are sent to the broadcast address. The problem is that perhaps only a few of the hosts and not all are interested in those packets. Furthermore: perhaps some hosts are really interested in your conference, but they are outside of your LAN, a few routers away. And you know that broadcast works fine inside a LAN, but problems arise when you want broadcast packets to be routed across different LANs.
multicast the best solution
Multicast the Best Solution !
  • The best solution seems to be one in which you send packets to a certain special address(like a certain frequency in radio/TV transmissions). Then, all hosts which have decided to join the conference will be aware of packets with that destination address, read them when they traverse the network. This is similar to broadcasting in that you send only one broadcast packet and all the hosts in the network recognize and read it; it differs, however, in that not all multicast packets are read and processed, but only those that were previously registered as being "of interest".
satellite is the answer to multicasting at least partly
Satellite is the answer to multicasting!(at least partly :-)
  • Leverage off of Broadcast Nature of Satellite
  • Take advantage of Low Cost DVB Receivers, security not an issue!
  • IP Multicast
  • News - Usenet is a perfect example!
  • Stock Quotes, other financial data
  • Multimedia
  • Web Casting, active and passive cache’ing
  • Distance Learning Applications
  • Business Applications

Pushing the content to the edge of the network.

I wanted to add a few adds about Cisco Content Delivery Networks (CDN), but there is another talk tomorrow...

how to select a satellite internet service provider
How to select a satellite Internet service provider?
  • Which satellite: band, footprint, elevation... require link budget.
  • Internet is already a commodity, like water, gas, electricity… (almost). So, does it matter where it comes from?
  • But (local) support quality is not a commodity!
  • Choose inclined orbit satellites only if you know very well what you are doing. This could be well a second or third link, should not be a main one!
  • Do not sign longer commitment than 12 months, unless you have to or receive a bonus in pricing.
  • Look for warranty of service in the contract.
  • What pricing you may expect?

There are Mazdas, Porsches, Ladas, Skodas, and Daewoos. Each may carry you to your destination.

There are no free lunches - you get (at most) what you pay for!

how to configure a network for satellite ro service
How to configure a network for satellite RO service?
  • If you use one of SOHO offerings (like Europeonline, Demos Internet):
    • install Linux (if drivers for the card are available)
    • run either NAT or proxy for LAN
  • if you use a fixed capacity service offering, structure your network so that all incoming/outgoing traffic is handled by one router
    • access lists are easier to manage
how to point an antenna at a given satellite
How to point an antenna at a given satellite?
  • Go to www.satcodx.com and find the satellite of your choice.
  • Write down all analog TV stations on this satellite, see if you can find one which is in the same band range as your LNB
  • Use elevation calculator to find roughly position of the satellite in the sky (e.g. http://www.comsym.com/IESS412.htm)
  • Pre-program TV tuner for analog TV stations and connect a TV.
  • Find this bird! You may want to start from another satellite, with a stronger signal. Remember about polarisation!
  • If there are no analog TV stations on this satellite, find them on adjacent one - then fine tune with your digital receiver.
  • When you have your antenna pointed, ground it and program your receiver to the carrier’s data and see if you get a lock.
  • Sure, spectrum analyzer tuned to beacon frequency is much more professional, but for RO systems this works fine as well.
satellite positions in the sky in budapest
AimSat 1.1

Satellite data for: Budapest

Latitude: 48ř00\'00" N

Longitude: 19ř00\'00" E

Satellite Slot Azimuth Elev. Skew

-------------------------------------------------------------

Statsionsat 13 80.00 E 112.39 10.43 49.21

Gals 1/2 71.00 E 120.14 16.02 39.54

PanamSat 4 68.50 E 122.40 17.51 37.20

Intelsat 602 63.00 E 127.58 20.69 32.42

Intelsat 604 60.00 E 130.53 22.34 29.99

Intelsat 507/510 57.00 E 133.57 23.92 27.65

Statsionsat 5 54.00 E 136.70 25.43 25.41

Turksat 1B 42.00 E 150.27 30.58 17.01

Arabsat 2B 30.50 E 164.69 33.79 9.16

Kopernicus DSF2 28.50 E 167.31 34.15 7.72

Arabsat 2A&3A 26.00 E 170.62 34.50 5.85

Eutelsat I F4 25.50 E 171.28 34.56 5.47

Kopernicus DSF3 23.50 E 173.95 34.74 3.89

Astra 1/x 19.20 E 179.73 34.92 0.18

Eutelsat II F3 16.00 E 184.03 34.84 -2.65

Eutelsat II F1 13.00 E 188.05 34.61 -5.08

Hot Bird 13.00 E 188.05 34.61 -5.08

Eutelsat II F2 10.00 E 192.03 34.23 -7.35

Eutelsat II F4 7.00 E 195.96 33.70 -9.51

Sirius 1A 5.20 E 198.29 33.31 -10.77

Tele-X 5.00 E 198.55 33.26 -10.91

Telecom 2C 3.00 E 201.10 32.77 -12.28

Tv-Sat 2 0.60 W 205.60 31.73 -14.72

Thor 0.80 W 205.85 31.67 -14.85

Intelsat 702 1.00 W 206.09 31.60 -14.99

Telecom 2B 5.00 W 210.93 30.22 -17.69

Telecom 2A 8.00 W 214.44 29.04 -19.73

Statsionsat 11 11.00 W 217.84 27.77 -21.82

Orion 2 14.80 W 222.01 26.02 -24.53

Tdf 1-2 19.00 W 226.43 23.92 -27.65

New Skies 803 21.45 W 228.92 22.63 -29.55

Intelsat 601 27.50 W 234.81 19.27 -34.54

Hispasat 30.00 W 237.14 17.81 -36.75

Intelsat 603 34.50 W 241.19 15.11 -41.01

Orion F1 37.50 W 243.81 13.26 -44.09

PanamSat 3R 43.00 W 248.44 9.79 -50.45

PanamSat 1 45.00 W 250.08 8.51 -53.06

SatMex 5 116.80 W ------ Below Horizont ----

Satellite positions in the sky in Budapest
antenna pointing contd
Antenna pointing (contd.)
  • Here is what I have chosen:

Program No Satellite Pos Freq Pol Name

(MHz)

500 Hotbird 13E 13E 11727 V RTP

499 Hotbird 13E 13E 11489 V RTL 7

498 Eutelsat W2 16E 11095 V Algeria TV

497 Eutelsat W2 16E 11569 H Syrian TV

496 Eutelsat W1 10E 10987 H NTV

495 Eutelsat W1 10E 11621 V Samanyolu

494 Astra 19E 11494 H ARD

493 Astra 19E 11421 H MTV

492 Turksat 42E 10965 H ATV

491 Turksat 42E 11093 V TRT

490 Telecom 2C 5W 12585 H TV5

489 Telecom 2C 5W 12690 V TF1

what will be in the future
What will be in the future?
  • We will use satellites mostly for moving large amounts of data, pushing content to the edges of Internet, sending Internet TV and radio programs.
  • We will use stronger satellites, more efficient codings into small antennas.
  • There is and will be a market niche for DTH satellite Internet, but p-to-p significance will not grow as it did in the past.
  • With Ka-band we will be able to set up OC-12 links and beyond.
  • Will LEO constellations change the way we think of satellite communication?
conclusions
Conclusions?

Life will deliver its verdict, but one should not view the whole topic as satellite vs fibre war. Satellite is great at some applications, where fibre will never outperform satellites. There will be numerous applications, which will be realised over satellites for the years to come.

Thank you for your time.

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