25/04/2009 SNAP 1

Satellite Network Access Point (SNAP)

Associate Professor Adrian Barbulescu

(adrian.barbulescu@unisa.edu.au)

Institute for Telecommunications Research

University of South Australia

25/04/2009 SNAP 2

“Necessity, who is the mother of invention.” Plato, 427-347 BCE

“School of Athens”Raphael,Vatican

25/04/2009 SNAP 3

What is necessity? The best technical solution depends on how the answer to this question is formulated.

Example: I want to be able to watch the latest movie release.

25/04/2009 SNAP 4

Historical perspective:

‘80s: one satellite transponder (36 MHz) was used for a singleanalogue TV channel.

(36 MHz per SDTV)

‘90s: one satellite transponder (36 MHz) was used for sixdigital MPEG2 channels transmitted using DVB-S.

(6 MHz per SDTV)

‘00s: one satellite transponder (36 MHz) was used for twentydigital MPEG4 channels transmitted using DVB-S2.

(1.8 MHz per SDTV)

25/04/2009 SNAP 5

Assumptions: • US$3,000/month/MHz for satellite bandwidth• MPEG4 and DVB-S2• an average of 2 MHz bandwidth per video channel.

Necessity #1:“I need access to as many movies I want, at any time I want.”

satellite time used = 24 hours/day

US$6,000/month

25/04/2009 SNAP 6

Necessity #2:“I need to watch a movie a day, any time I want.”

satellite time used = 2 hours/day assuming that one can make a request and receive the movie say, in the next half hour, any time of the day

US$500/month

25/04/2009 SNAP 7

satellite time used = 2 hours/day but, chances are that another 50 people want to watch the

same new release as you. The movie will be downloaded over satellite once and then distributed for free to all 50

users over a WiFi or WiMax network

Necessity #3:“I need to watch a movie a day, any time I want, but I am prepared to order it well in advance.”

US$10/month

25/04/2009 SNAP 8

Have you considered that your individual needs combined with your community needs may define

the optimum satellite based technical solution ?

Telehealth

Internet Education

Local

Government

Local

Business Telehealth

Internet Education

LocalBusiness

LocalGovernment

Think

aggregation

of

services !

25/04/2009 SNAP 9

Are you an informed user when trying to find out the truth about satellite communications solutions?

Q#1: What is the latest available satellite modem technology ?

Q#2: Is the service optimised for my type of traffic?

Q#4: How can the cost of satellite time be reduced ?

Q#5: How does an individual-based solution compare with a community-based solution ?

Most important questions for the optimum solution :

Q#3: How can the amount of satellite traffic be reduced ?

25/04/2009 SNAP 10

Q#1: What is the latest available satellite modem technology ?

25/04/2009 SNAP 11

Non-equiprobable constellations for non-linear satellite channels

25/04/2009 SNAP 12

Bit Error Rate of 10-10 at Eb/N0 = 1.5 dB

Eb/No required for BER < 1E-10

0123

456

QPSK Rate 1/2 QPSK Rate 3/4

Eb/N

o [d

B]

Premier 5 (S-Tec)CDM600 (TPC)M5 (TPC)P300 (TPC)DMD20 (TPC)

Cost of satellite time depends on bandwidth and power !

25/04/2009 SNAP 13

Internet traffic is an ON-OFF process, Self-Similar traffic.

It has a Pareto distribution, not a Poisson distribution.

Q#2: Is the service optimised for my type of traffic?

25/04/2009 SNAP 14

Video transmission over a VSAT link at an average of 256 kbit/s and maximum bandwidth limitation of 512 kbit/s.

25/04/2009 SNAP 15

Video transmission over a SNAP link at an average of 256 kbit/s with bursts of up to 2,048 kbit/s for the same cost.

25/04/2009 SNAP 16

Compression techniques: ratios vary (1.5 to 3.5), more efficient techniques require longer compression and decompression times (1 to 13 seconds)

Example of savings assuming US$2,000,000/year for a 45 Mbit/s transponder using a US$3,000 compression device at each end with an average compression ratio of 2:1.

Ex: http://www.expand.com/solutions/Satellite.htmlhttp://www.juniper.net/products/appaccel/

Q#3: How can the amount of satellite traffic be reduced ?

25/04/2009 SNAP 17

Compression Advantages

Bandwidth: 8-2 Mbit/s 64-64 kbit/sConnection: forward/return symmetricTotal bandwidth: 10Mbit/s 128 kbit/sCost of BW: $444,444/y $5688/yNr. compression devices 2 2Cost of compression devices:$6,000 $6,000

Bandwidth savings: $222,222/y $2,844/y

Payback 10 days 2.1 years

25/04/2009 SNAP 18

(www.cisco.com/en/US/products/ps6587)

Compression Ratios

25/04/2009 SNAP 19

Caching

(www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/)

25/04/2009 SNAP 20

Caching/Pre-fetching

Caching (browser caching and shared caching: Squid, CISCO) is widely used in all terrestrial networks. As a ruleof thumb: 50% hit ratio and 33% bandwidth savings.

Pre-fetching (downloading the embedded objects on a HTML page and send them => reduces downloading time)

Multiple TCP connections, in aggregate, are able to use more of the available bandwidth. Applications designed for satellite links could open multiple simultaneous TCP connections, send part of a file over each connection and reassemble it at the receiver end.

25/04/2009 SNAP 21

The system requirements depend on the peak rates needed:

• video:average rate = 75 kb/s, but peak rate of 384 kb/s

Scenario 1: 10 individual VSAT channels need: average rate = 750 kb/s, but peak rate of 3840 kb/s

Statistical Multiplexing Gain (SMG)

As peaks occur at different moments in time (statistical multiplexing), there is a need of only a small increase of the average rate, say 400 kb/s, to allow enough margin for any user to reach peak rates, the system therefore needs only 750+400 =1150 kb/s instead of 3840 kb/s.

Scenario 2: 1 aggregated channel for 10 users needs: average rate = 750 kb/s, but peak rate of 1150 kb/s

due to statistical multiplexing

25/04/2009 SNAP 22

Statistical Multiplexing Gain (SMG)

SMG = peak bit rate / beam capacity

Traffic scenario for a satellite link of 8,192 kb/s [1]:

• data: non-real-time 64 kb/s with activity factor 1%,

• video: peak rate of 384 kb/s and peak-to-average ratio 5,

• voice: 64 kb/s, activity factor 40%.

[1] T.Le-Ngoc, “Switching for IP-Based Multimedia Satellite Communications”, IEEE Journal on Selected Areas in Communications, VOL.22, NO. 3, pp.462-471, April 2004.

25/04/2009 SNAP 23

Telehealth

Internet Education

Local Government

Local Business

Turbo Coding

Aggregation of applications and services using the latest satellite technologies provides the optimum mechanism to service the communication needs of a community rather than individual users.

Satellite modems

Wireless LANBandwidthManagement

Q#4: How can the cost of satellite time be reduced ?

25/04/2009 SNAP 24

Satellite Network Access Point - antenna

25/04/2009 SNAP 25

Satellite Network Access Point – indoors unit

25/04/2009 SNAP 26

Satellite Network Access Point – traffic shaping

25/04/2009 SNAP 27

Wireless LANCourtesy of www.proxim.com

25/04/2009 SNAP 28

The 100BASE-TX Ethernet connection between ITR and the world was replaced by a 2 Mbit/s Satellite

connection.

Equivalent to an SMG of 50 !!!

25/04/2009 SNAP 29

YESNOCompression, caching

YESNOTraffic Burstiness Capability

CommunityIndividualsEnd users

1 to 20 Mbit/sNOScalability

1.5 dB3 to 5 dBOperating point (Eb/No) for bit error rates less than 1E-10

YESNOTraffic Management (statistical multiplexing, congestion control)

YES (XTP)NO (TCP)Optimised Satellite Protocol

½ to ¼(8/7/8 = 0.14)

1(4/3/2=0.67)

Satellite BW reduction factor (1 / coding rate / modulation)

SNAPVSATParameters

Q#5: How does an individual-based solution compare with a community-based solution ?

25/04/2009 SNAP 30

Satellite communication is EXPENSIVE!

Cost of a GEO satellite: USD500 millionCapacity: 100 GbpsCost per Gbps: USD5,000,000

Cost of a fiber optic cable: USD300 million(US- Japan, 10,000 km long)Capacity: 8 TbpsCost per Gbps: USD37,500

25/04/2009 SNAP 31

O3B Networks (Sep. 2008) http://www.o3bnetworks.com/O3b Networks, funded by Google Inc., Liberty Global, Inc. and HSBC Principal Investments, will deploy the world’s first ultra-low-latency, Medium Earth Orbit (MEO), Ka-band, fiber-speed satellite network designed to improve Internet access for millions of consumers and businesses in emerging markets like Africa. Service activation and ground equipment is scheduled for late 2010.The new Gilat MEO VSAT equipment will enable automatic tracking of the satellites and seamless handoff between satellites. Specific terminals target 3G Cellular/WiMAX backhaul, IP trunking, and broadband connectivity for SMEs and ISP backhaul.

25/04/2009 SNAP 32

“We are questioning beings…who must search out the reason of things, and not accept them from custom and authority”

Socrates469-399 BCE