Introduction to
Presented by
Sandeep Baruah
Scientist ‘C’
Vigyan Prasar
sandeep@vigyanprasar.gov.in
Digital Video Broadcasting – Return Channel via Satellite
DVB-RCS
Digital Video Broadcasting Return Channel via Satellite
Why ‘RCviaS’?
[ Return Channelvia Satellite ]?
One-way multicast satellite systems are used for
IP multicast-based data, audio and video
distribution. Return Channel is not required
here [ This is much like a TV or radio content
which offers little user interface ] and full
interactivity is not possible.
SIT is two-way with full user
interactivity. ‘Return Channel’ is a must.
Speed of Radio Wave 300000 km /second
SINGLE HOPE TIME = 600
millisecond [ 0.6 second ]
DOUBLE HOPE TIME = 1200 millisecond [ 1.2 second ]
Star Network
Star network consists of one
central switch, hub or computer
which acts as a router to transmit
messages.
[ Classroom
Bhubaneswar ]
Reduces chance of network failure
by connecting all of the systems to
a central node.
This central hub rebroadcasts
all transmissions received from
any peripheral node to all
peripheral nodes on the
network, sometimes including the
originating node. All peripheral
nodes may thus communicate with
all others by transmitting to, and
receiving from, the central node
only.
[ Ahmedabad ]
[ Teaching End
New Delhi ]
CLARKE ORBIT
Arthur C Clarke
1945
36,000 km
Non-Interactive transmissions, e.g. TV telecast
The "magic" altitude of 35,786 km at which a satellite's orbital
period matches, or is an integral part of, the period at which the
Earth rotates: once every sidereal day (23 hours 56 minutes). In
that case, the satellite is said to be geosynchronous.
Longitude 74.1439 degrees East
Latitude 0.0758 degrees South
Altitude 35,785.530 km
Azimuth 186.5 degrees
Elevation 56.4 degrees
Radio Frequencies
Above
30 MHz
Edusat frequencies are in the Microwave Range:
11 GHz [ 11,000 MHz ]
14 GHz [ 11,000 MHz ]
Pointing the Antenna
Azimuth refers to the rotation of the whole
antenna around a vertical axis. By
definition North is 0 deg, East is 90 deg,
South is 180 deg and west is 270 deg.
North can also be called 360 deg.
An approximate azimuth angle is normally
sufficient.
Elevation refers to the angle between
the dish pointing direction, directly
towards the satellite, and the local
horizontal plane. It is the up-down
angle.
It is easy to point an
antenna to a GEO
GSAT-3 or EDUSAT is the first
Indian satellite built exclusively for
serving the educational sector. It is
mainly intended to meet the demand
for an interactive satellite based
distance education system for the
country, especially for the
development of the population in
remote and rural locations.
Though Geostationary Satellite covers a large area, it has
a problem called ‘Time Lag’ [ delayed reception of signal ]
Delayed reception of signal
DOUBLE HOPE TIME
= 1200 millisecond [ 1.2 second
]
A theoretical alternative to satellites that is being explored is the use of
ultra-light solar powered airplane or an airship [ Stratellite ] that could
fly in a continuous a circling path perhaps 70,000 feet [ 20 km ] high.
These would act as flying satellites, providing high-speed service to
customers below the aircraft. Since the roundtrip signal distance
would only be 30 miles, the latency caused by the radio wave is an
almost insignificant 0.1 ms under the craft, and 2 ms at the edge of the
covered area, at a 300 km (200 miles) distance.
Travels at a speed of 3,00000 km per second
30,00000 km
Suppose the radio signal has to travel a distance of
30,00000 km; it would take 10 seconds for its one
way journey. To receive a reply back from the target
It would take another 10 seconds. Total 20 seconds!
1 sec [ or in 1000 millisecond ]: 300000 km
1 ms [ 0.001 sec ] : 300 km
To travel 36,000: 36,000
300 km
120 ms
120
ms
120
ms
120
ms
= 120 ms
Latency: A Major Challenge in
digital communication
Satellite communications present one major challenge
with respect to the performance of Internet applications - the communication latency between two earth stations
connected by a satellite. For GEO satellite
communications systems, the latency is at least 250
milliseconds [sometimes framing, queuing, and onboard switching can add extra delays, making the
end-to-end latency as high as 400 milliseconds].
This is approximately 10 times higher than a point-topoint fiber optics connection. The latency might not
affect bulk data transfer and broadcast-type
applications, but it will hurt highly interactive
applications that require extensive handshaking
between two sites. Unfortunately, one of the major
Internet transport protocols, TCP, requires such
interaction.
Radio frequencies
Different frequencies have different
propagation characteristics
MICROWAVE
1-300 GHz
HF 3-30 MHz
Wavelengths approximately:
30 cm [ frequency = 1 GHz ]
to 1 mm [ 300 GHz ]
Frequencies between 3000 MHz
[ 3×108 Hz ] and
300 GHz [ 3×1011 Hz ]
Ku band
[ Edusat uses 14 & 11 GHz ]
• The Ku band (pronounced "kay-yoo";
Kurtz-under band) is a portion of the
electromagnetic spectrum in the
microwave range of frequencies ranging
from 12 to 18 GHz.
• Ku band is primarily used for satellite
communications, particularly for satellite
backhauls from remote locations
• High bandwidth
– satellite can deliver throughput at gigabits per second
rates.
• Inexpensive
– A satellite communications system is relatively
inexpensive because there are no cable-laying costs,
and one satellite covers a very large area.
• Untethered communication
– Users can enjoy untethered communication anywhere
within the footprints of the satellite.
• Simple network topology
– Compared with the mesh interconnection model of the
terrestrial Internet, GEO satellite networks have much
simpler delivery paths. The simpler topology often
results in more manageable network performance.
Bandwidth
30.75 – 31.50 MHz We get
bandwidth of 750 kHz only [
0.75 MHz ]
But say if we use 13.75-14.50
MHz we 750 MHz [ 0.75 GHz ]
lower frequency bands are virtually immune to
radio attenuation, but are crowded, expensive
and require larger antennas.
It makes sense then to explore the possibility of
reliable all-weather communication using higher
bands (namely Ku and Ka), which are more
sensitive to attenuation but less expensive.
Limitations
Ku band signals can be affected by rain
attenuation. In case of TV reception, only heavy
rainfalls (>100 mm/hr) will have noticeable effect
for the user.
Due to ‘Latency’, possibility of ‘Link Failure’.
RECEIVE ONLY SIT
TWO-WAY SIT
RADIO
TV
ONE WAY
SITS can be used for
+ INTERACTIVE [ TWO WAY ]
The link from Hub to SIT is called Forward Link (FL)
The Hub is primarily responsible for carrying Internet Protocol (IP)
traffic between Satellite Interactive Terminals (SITs) & other external
networks. It is also responsible for overall network management &
SITs management.
The IP traffic at Hub is encapsulated in to MPEG-TS in DVB format.
After necessary stages for modulation, frequency conversion,
amplification etc., the same traffic is uplinked for SITs.
Moving Picture Experts Group or MPEG is a working group of ISO/IEC
charged with the development of video and audio encoding standards
The link from Hub to SIT is called Forward Link (FL) and it uses a
standard Digital Video Broadcasting (DVB) format. It allows data rate
up to 45 MSPS. Presently FL is configured for 10 MSPS considering
satellite resources available & total traffic expected among all the
SITs.
The FL is like big pipe & carries the combined traffic for all SITs.
MSPS – Mega Samples Per Second.
The IP traffic at SIT is encapsulated in to either MPEG or ATM cell. After
necessary stages for modulation, frequency conversion, amplification etc.,
the same traffic is uplinked for Hub.
The link from SIT to Hub is called Return Link (RL) and it is responsible to
carry the return link traffic using Multi-Frequency Time Division Multiple
Access (MF-TDMA) based on ATM or MPEG standard. Single SIT allows
data rate up to 2 Mbps. Presently each SIT is configured in Hub for
Maximum 624 / 512 Kbps data. The RL BW for SIT is controlled by
controlling nos. of time slots.
In MF-TDMA, each carrier is divided in nos. of logical time slots. The Hub
assigns un-assigned time slots to particular SIT. The SIT sends the traffic
(either ATM/ MPEG cell) to hub using these time slots.
Asynchronous Transfer Mode (ATM) is a cell relay, Circuit switching network
and data link layer protocol which encodes data traffic into small (53 bytes; 48
bytes of data and 5 bytes of header information) fixed-sized cells. This differs from
other technologies based on packet-switched networks (such as the Internet
Protocol or Ethernet), in which variable sized packets (sometimes known as
frames) are used. ATM is a connection-oriented technology, in which a logical
connection is established between the two endpoints before the actual data
exchange begins.
MPEG
Moving Picture Experts Group or MPEG is a working group of
ISO/IEC charged with the development of video and audio encoding
standards
Data Rate up to 45 MSPS [MSPS – Mega Samples Per Second.
Sampling rate for analog to digital converters. ]
Asynchronous Transfer Mode (ATM) is a cell relay, Circuit switching
network and data link layer protocol which encodes data traffic into
small (53 bytes; 48 bytes of data and 5 bytes of header information)
fixed-sized cells. This differs from other technologies based on
packet-switched networks (such as the Internet Protocol or
Ethernet), in which variable sized packets (sometimes known as
frames) are used. ATM is a connection-oriented technology, in which
a logical connection is established between the two endpoints
before the actual data exchange begins.
Hub FL [ Forward Link ]
Class Room RL [ Return Link ] : Link from SIT to Hub 624 KBPS
TDMA [ Time Division Multiple Access ]
SIT RL MPEG: 11 time slots x 56.75 KBPS data rate = 624 KBPS
SIT RL ATM: 24 time slots x 16 KBPS = 384 KBPS
•
•
•
•
•
•
•
•
•
•
•
•
A kilobit per second (kbit/s or kbps or kBaud) is a unit of data transfer rate equal to 1,000 bits per second. It is
sometimes mistakenly thought to mean 1,024 bits per second, using the binary meaning of the kilo- prefix, though
this is incorrect.
Examples:
56K modem — 56,000 bit/s
128 kbit/s mp3 — 128,000 bit/s [1]
64k ISDN — 64,000 bit/s [2]
1536k T1 — 1,536,000 bit/s (1.536 Mbit/s)
Most digital representations of audio are measured in kbit/s:
(These values vary depending on audio data compression schemes)
4 kbit/s – minimum necessary for recognizable speech (using special-purpose speech codecs)
8 kbit/s – telephone quality
32 kbit/s – MW quality
96 kbit/s – FM quality
• 192 kbit/s – Nearly CD quality for a file compressed in the MP3
format
•
1,411 kbit/s – CD audio (at 16-bits for each channel and 44.1 kHz)
RBDC : Rate-Based Dynamic Capacity
VBDC : Volume-Based Dynamic Capacity
Traffic Time Slots: T1 to T11
Carrier Frequencies: F1 to F8
Time slots used by particular SIT in MPEG Frame
At present carrier carrying the MPEG cells is divided in 11 nos. of
traffic time slots. Single time slot supports 56.75 kbps data rate. Each
Teaching End (TE) is configured permanently (CRA) in Hub with such
11 time slots which will support up to 624 (56.75*11) Kbps RL traffic.
Traffic Time Slots: T1 to T32
Carrier Frequencies: F1 to F15
Time slots used by particular SIT in ATM Frame
At present carrier carrying the ATM cells is divided in 32 nos. of traffic
time slots & single time slot supports 16 kbps data rate. Each Class
Room (CR) is configured in Hub with request based 24 time slots. I.e.
4 RBDC & 20 VBDC. This will supports up to 384 (16*24) kbps RL
traffic.
Return Link [ RL ] traffic is brought to
Hub with use of 4 types of time slots.
The SIT can be configured with one or
more types of time slots.
[1] Constant Rate Assignment [ CRA ]
This type of time slots is assigned by
Hub when particular SIT logs ON
(Switch ON). CRA provides guaranteed
RL bandwidth. It is most suitable for
real time traffic like Video & Voice
Conferencing & other non-real time
applications. Each TE is configured with
this type of time slots.
[2] Rate Based Dynamic Control [ RBDC ]
This type of time slots is assigned by Hub when particular SIT
demands/requests for allotment of time slots. RBDC provides [on
demand] RL bandwidth. Hub will allot the number of time slots
proportional to data rate at the LAN port of SIT. It is suitable for real
time traffic like Voice Conferencing & other non-real time
applications like file transfer. Each CR is configured for this type of
time slots.
Voice Conferencing [ Real time ]
File Transfer [ Non-real time]
Return Link RL- Types of Time Slots
[3] Volume Based Dynamic Control [ VBDC ]
This type of time slots is assigned by Hub when particular
SIT demands/requests for allotment of time slots. VBDC
provides (on demand) RL bandwidth. Hub will allot the
number of time slots proportional to data Volume at
the LAN port of SIT. It is suitable for non-real time
applications. Each CR is additionally configured for this
type of time slots.
RL- Types of Time Slots
[ 4 ] Free Capacity Assignment (FCA)
In pool of time slots with Hub, some time slots are free.
The free time slots are assigned by Hub to SIT to fulfill the
requirement of data transfer. It is like bonus to SIT. It is
suitable for non-real time applications.
Hub Overview
The system can be divided into two segments: SIT and Hub. The SIT
segment represents what is installed on the customer’s site. The Hub
segment represents the equipment used by the service provider.
Satellite
FLSS
ODU
ODU
IDU
IDU
RLSS
End
User
Router
Router
SNMP
Manager
To
Internet
End
User
End
User
End
User
End
User
Hub-Sub systems
The communication between SITs is always through Hub. The data
transmitted from one SIT is first received by Return Link Sub
system (RLSS) of Hub. The data received by RLSS is routed to
Forward Link Sub System (FLSS) for re-transmission. The retransmitted data is received by another SIT.
The complete Hub consists of FLSS & RLSS.
The FLSS consists of

IP Router.

IP Encapsulator & DVB Multiplexer

PCR Inserter (Part of RLSS)

L-Band DVB Modulator

Ku-Band SSPB & Antenna
Hub-Sub systems
The RLSS consists of

Antenna & LNBC

Multi Carrier Demodulator (MCD) Board

Signaling (SIG) Board

Traffic (TRF) Board

Operation, Administration and Management (OAM) plus PCR
Monitor Board

DVB Demodulator (For RCR Monitoring function)

IP Router
The OAM stores the database of all-valid SITs like MAC address, IP
address, configuration files including permissible Max. bandwidth,
type of access etc.
SIT Overview
The satellite interactive terminal (SIT) is composed of the outdoor
unit (ODU), which includes the antenna and RF transceiver, and the
indoor unit (IDU).
Ku - RL
Ku - FL
Transceiver
Antenna
Subsystem
Mechanical Subsystem
ODU
InterFacility
Link
IDU
Ethernet
Interface
To local private
LAN or directly to
Host
SIT ODU [ OutDoor Unit ]
 Provides RF interface with the satellite
 Ku-band transmit up-converted from an L-Band
IDU signal
 Ku-Band receive and down-converted for L-band
IDU
 Series 3000 IDU supports up to 2W SSPB
 ODU Mainly composed of:
 Reflector
 SSPB (Solid State Power Block Converter)
 LNB (Low Noise Block)
 Feed Horn/OMT (Ortho-Mode Translator)
[ Low Noise Block Converter ]
Converts Ku Band [ 10.712.75 GHz ] signals to LBand [ 0.950 -2.150 GHz ]
Ku-band linear-polarised LNBAs microwave
satellite signals do not easily pass through
walls, roofs, or even glass windows,
satellite antennas are required to be
outdoors, and the signal needs to be
passed indoors via cables. When radio
signals are sent through coaxial cables, the
higher the frequency, the more losses occur
in the cable per unit of length.
SIT ODU

General Safety
 Danger area near Antenna
 General rule: Don’t stand in front of the Antenna!
SIT Grounding

Grounding
 The ODU must be grounded in strict accordance with
National and Local electrical codes.
 ODU copper ground wire should be connected to the
local Lightning Protection System (LPS)
 Where the LPS is not available proper grounding
requires installation of a ground rod(s). The copper
ground wire(s) from the ODU would connect to this
ground system.
Interface with IDU
 Interface
 IDU supplies to SSPB (Tx)
 24V DC
 Transmit signal 950-1450MHz
 10 MHz reference
 IDU receives 950-2150 MHz Rx signal from LNBC (Rx) &
supplies 18 VDC to LNBC (Rx)
 LAN Port interfaces customer’s equipment.
One or more Ethernet IP address based devices (called hosts) all to
gather make one LAN at customer’s site. The one LAN may have
many devices like PC, Server, VOIP, IP address based camera etc.
When each LAN, located at geographically different site is connected
all together through SIT, make one WAN.
The SIT is the part of local LAN & functions to provide connectivity of
Local LAN with WAN.
The IDU acts as a Gateway when traffic is towards WAN. The current
IP plan for SIT is as bellow.
For IDU:
IP Address:
Subnet Mask:
Where
172.21.X.1
255.255.255.0
X: Sequential No. assigned to each IDU.
Teaching End (TE)- Sub Hub
All the SITs in network are physically same. Any SIT of particular user
agency can be configured as a Sub Hub.
The main differences in parameters configured in Hub are:
For Sub Hub
 Multicast facility is enabled.
 Constant (CRA) 624 kbps (Sub Hub to Hub) RL BW is
allotted for Multicast & other traffic.
For Class Room (CR)
 Multicast facility is disabled & BW is of different type &
less (I.e. 384 Kbps with combination of RBDC & VBDC).
Additionally Sub Hub will have more facilities like servers, studio etc.
Pinging is an integral part of SIT functionality test
PING History!
Mike Muuss wrote the program in December, 1983, as a tool to
troubleshoot odd behavior on an IP network. He named it after the
pulses of sound made by a sonar, since its operation is analogous to active sonar
in submarines, in which an operator issues a pulse of energy (a network packet)
at the target, which then bounces from the target and is received by the operator.
"Packet INternet Grouper
(Groper)", also by other people "Packed INternet Gopher", after
the small rodents. Michael John Muuss ( October 16 , 1958 - November
Later David L. Mills provided a backronym,
20, 2000) wrote the freeware network tool Ping. A graduate of Johns Hopkins
University, he was a senior scientist at the U.S. Army Research Lab in Maryland
RUN
START
TYPE CMD
1.
SELF-TEST
If you PING the IP address of your own computer
It ensures the functionality of the
LAN card of your computer
Steps to confirm the full functionality of SIT:
Check that POWER, READY, Satellite TX & RX LED glow.
Ping IP address of PC itself first. The reply is expected within 10 ms.
Ping the IP address of IDU. The reply is expected within 10 ms.
Also Ethernet TX & RX LEDs will glow.
Ping the IP address of Hub Router (ping 192.168.2.1 –t –w 2000)
The reply is expected within 600 ms (single hope satellite delay).
Note: -t is used for repeated ping.
-w 2000 is used for 2000 ms waiting period for reply.
If the reply from Hub is within 600 ms & without any packet loss,
the connectivity of Local station/SIT with Hub can be considered
perfectly OK.
SIT Functionality Checks
(6) Ping the IP address of VP IDU (ping 172.21.1.1 –t –w
2000). The reply is expected within 1200 ms (double hope
satellite delay).
(7) If the reply from remote SIT is within 1200 ms & without any
packet loss, the connectivity of local SIT with VP IDU can
be considered perfectly OK.
Important Instructions
Do

It is recommended that each site must have one low cost
Digital Multi Meter (DMM) to measure the Mains supply &
other preliminary checks for SIT.

Always follow the rules/procedure/guidelines set by HQ for
quick solution to the problem & efficient use of edusat
network.
 Always switch OFF the SIT whenever it is not required for
Prolonged time.
 Always maintain the effectiveness of Earth pit by pouring it
with water at regular interval.
Important Instructions

Always assure that the equipments to be interfaced with
IDU are properly grounded.

While demonstrating the ODU to visitor, students, always
stand in the back side of antenna.

Always go through steps shown in chapter “SIT Routine
Functionality Checks” whenever SIT functionality is doubtful.

Always inspect the ODU & IFL cable for any damage or
misalignment whenever IDU does not lock to FL from Hub.

Always keep the backup of application SW.

Always handle IDU, IFL cables carefully. Assure that IFL
are tension free.
Important Instructions

Always confirm SIT functionality with use of standalone PC
& small cable whenever SIT functionality is doubtful.

Always prefer regulated supply & air-conditioned
environment for operation of SIT.
Important Instructions
Don’t
Don’t stand in front of antenna when IDU is in powered
condition.
Don’t disturb the cement blocks kept on antenna base frame. If
disturbed Antenna may loose its original pointing.
Don’t try to shift antenna. If disturbed from original position,
antenna may loose LOS.
Don’t connect & disconnect IFL cables when IDU is in
powered condition. The IFL carries the DC voltage.
Don’t connect other equipment with dedicated Earth pit
provided for SIT.
Don’t put any thing on IDU.
Important Instructions
Don’t try to extend cable by connecting other type of cable.
The IDU meets the specifications only with supplied cable.
Don’t operate SIT with unreliable power source like Genset,
Locally made Inverter etc.
Don’t try to troubleshoot SIT by your own.
Don’t change SM of PC other than 255.255.255.0
Don’t use any proxy between PC & IDU. The IDU doesn’t
function with any proxy.
Don’t use Ethernet cable more than 100 Mtr. The exact length
depends on quality of Ethernet cable.
Help Desk & on-line support
Help desk is provided in SIT Training Manual.
If SIT has minor fault & two way communication with SIT exists,
the particular SIT can be monitored from Hub & proper actions
can be taken from Hub itself.
However if SIT has major problem like failure of SIT sub-system,
the site requires visit of maintenance engineer from Service
provider. In this case, SIT user has to send Service Call Form
with complete information to service provider prior to site visit by
service engineer.
Hands-on training on
• Assigning IP address to PC
• Accessing IDU
• SIT Fault Diagnosis
• Running of Applications with SIT