Satellite Based Internet
Content
Satellite-based Internet
Wireless Communication Systems Aitor Ferández
Main features:
Appropiate mobility support Global coverage Inherent broadcast capacity
Bandwith on demand capacity
Appliable to:
Globally scattered users Aeronautical and maritime users Remote, infraestructure lacking
areas Point to multipoint communications Multipoint to multipoint comm.
Offered services:
Broadband access networks Connecting heterogeneous High speed backbone networks
networks Comm. links between users with mobile or fixed terminals
Satellite communication Fundamentals
A satellite system consists of:
Space segment
Ground segment
Satellite communication Fundamentals
Ground segment consists of:
Gateway stations (GS) Network control center (NCC) Operation control center (OCC)
Satellite communication Fundamentals
Space segment consists of: Satellites
Geostationary orbit (GSO) Nongeostationary orbit (NGSO) Medium earth orbit (MEO)
Low earth orbit (LEO)
Satellite communication Fundamentals
GSO Orbit:
35786 Km avobe the equator Appears fixed to an observer on the Earth Sufficient for global coverage 1 GSO Satellite covers one third of Earth surface This area is called footprint
Satellite communication Fundamentals
GSO Orbit:
High launching cost Large antennas and transmission power required Biggest problem: Propagation delay Around 250280 ms Undesirable for realtime traffic
Satellite communication Fundamentals
GSO satellite coverage
Satellite communication Fundamentals
LEO and MEO Orbits: Closer to the earth surface
Smaller antennas and transmission power required Footprint is also smaller Larger number of satellites is necessary Steerable antennas become useful
Satellite communication Fundamentals
MEO Orbit:
From 3000 Km up to the GSO orbit Typical roundtrip propagation delay: 110300 ms 2003000 Km above earth surface Typical roundtrip propagation delay: 2025 ms
LEO Orbit:
Satellite communication Fundamentals
Satellite communication Fundamentals
Satellite payloads:
Responsible of the satellite communications Once launched, a satellite is impossible to upgrade Robust Simple No onboard processing (OBP) on traditional sats
Satellite communication Fundamentals
Satellite payloads:
Some satellites allow OBP (Conform ISL's) Demodulation/remodulation Decoding/recoding Transponder/beam switching Routing Connectivity in space without terrestrial resource is possible
Satellite communication Fundamentals
Frequency bands:
Most commonly used are C, Ku, and Ka bands With higher frequency, and shorter wavelenght
Smaller antenas can be used
Satellite communication Fundamentals
Satellite-based Internet architectures
Several implementation options due to diversity Suggestions to use hybrid GSO-NGSO network Sats can act as a backbone/Hi-speed network
ARPANET became backbone of research network
Satellite-based Internet architectures
The idea of using satellites in last mile is newer
Satellites interact with GS's May be the only access method for remote areas Bent pipe architecture (Fig 1) suffers big latency
Because of the lack of direct communication
Satellite-based Internet architectures
Bent-pipe design
Satellite-based Internet architectures
OBP and ISL's can be combined to create a network in the sky. Both combination access and backbone network. Teledisc or Iridium are examples of this kind of network. Flexibility at cost of more complex routing
Satellite-based Internet architectures
OBP and ISL
Architecture Design
Satellite-based Internet architectures
DBS Model (Direct Broadcast Satellites)
Acces internet directly by satellites. Only download Created because of internet traffic asimetry in which the server transmits much more information than in reverse Upload from the client is made via terrestrial GS's
Satellite-based Internet architectures
DBS architecture
Satellite-based Internet architectures
Astrolink
Satellite-based Internet architectures
Skybridge distribution
Satellite-based Internet architectures
Spaceway architecture scheme
Satellite-based Internet architectures
Teledisc satellite distribution
Satellite-based Internet architectures
Teledisc satellite coverage
Satellite-based Internet architectures
Iridium satellite distribution
Satellite-based Internet architectures
Iridium satellite coverage
Technical challenges
Multiple Access Control (MAC)
Is a set of rules This rules decide how the clients in the footprint of the satellite acces its uplink channel, which is a limited resource Affects to the QoS and higher layers
Technical challenges
Fixed Assignement:
This is the most basic of MAC's It is based in frequency, time or code divixion basis (FDMA, TDMA and CDMA respectively) Very poor resource management. For small networks.
Technical challenges
Random Access:
Thanks to small and cheap terminals Less data usage, which turns in a bigger number of terminals which a satellite can cover. Each station transmit data regardless of the others.
Technical challenges
Demand Assignment:
Solves RA's lack of QoS providing Dynamically allocates system bandwidth depending on how many clients request access The transmission for permission becomes the problem, but it is affordable.
Technical challenges
After reservation, bandwidth is segmented in FDMA or TDMA Centralized or Distributed control Resource reservation can be explicitly or implicitly done. Priority Oriented Demand Protocol and First In First Out, combine explicit and implicit requests
Routing Issues
We will refer to LEO satellite systems, as Iridium can be. It is very attractive to be able to design a network in the sky, thanks to OBP and ISL's The routing becomes crucial.
Routing Issues
Dynamic Topology
Satellites have very little visible period to us When a satellite goes out, and another comes in, intersatellite handover happens Each satellite is able to set up 4 to 8 ISL's These can be intraplane or interplane
Routing Issues
Discrete-time Dynamic Virtual Topology Routing
DT-DVTR makes use of the periodic nature of sats Works completely offline System storages visibility data of each interval When topology changes, the best path is choosen
Routing Issues
Virtual Node (VN)
Hidew the topologycal changes from the routing protocols, despite satellites are actually moving Keeps state information, such as routing tables and user data When the satellite covering the node disappears in the horizon, the node is covered by the one that comes
Routing Issues
IP Routing at satellites
IP routing is adopted, based in the VN concept Integrates the space network with terrestrial Internet Supports IP multicast and IP QoS Despite is useful and desirable, implementation problems appear everywhere. Constantly improving.
Routing Issues
ATM Switching
Many proposed systems use ATM as network protocol for the constellation A version of DT-DVTR based in ATM is investigated, grouping the ingress and engress satellites' virtual channel connections in a VPC Possibly, IP over ATM will be implemented
Routing Issues
External Routing Issues
Internal design of communications will probably change constantly to fit manufacturers or clients. Satellite network is isolated of terrestrial network AS (astronomous system) concept. Sat=AS. Only Border Gateways will communicate with these, by BGP
Routing Issues
Unidirectional Routing
DBS is unidirectional. Traditional Routing is invalid Static routing instead of dynamic routing is an option Options:
Routing Protocol Modification Tunnelling
Routing Issues
Routing Protocol Modification
In unidirectional routing, we can only send (feeders) The clients at the other side can only receive (receivers) Make a receiver identify the potential feeders, ignoring unusable data while mantaining neighboring connection The receiver periodically delivers its own routing message to all feeders through terrestial link
Routing Issues
Tunneling:
Offers a link layer approach to hide the asymetry. A tunnel is a virtual link set between a DBS and a receiver by using encapsulation and decapsulation User encapsulates package -> sends to routing protocol via terrestrial nw -> arrives to satellite -> the tunnel decapsulates the message - > forwards it to the routing protocol
Satellite Transport
TCP/IP and UDP/IP protocols are the heart of the Internet. Their solidity and standarization makes them adaptable and unlikely to be discarded Satellite-based Internet will use UDP and TCP. TCP being connection oriented, will receive the great impact of high latencys and error rates.
Satellite Transport
TCP/IP performance over satellite
High latencies will affect TCP's functionality. Timeout based protocols such as this may severely suffer large round-trip times delivered by satellite connections Also suffer from interferences, fading, shadowing, and rain atteunation. This causes Bit Error Rate (BER)
Satellite Transport
Performance enhacenments have been developed over TCP TCP selective acknowledgement (SACK) TCP for transaction (T/TCP) Persistent TCP Connection MTU mechanism FEC
Satellite Transport
TCP extensions solve some limitation of standard TCP TCP Spoofing TCP Splitting Web Caching
THANK YOU!
Aitor Fernández
Wireless Communication Systems Aitor Ferández
Main features:
Appropiate mobility support Global coverage Inherent broadcast capacity
Bandwith on demand capacity
Appliable to:
Globally scattered users Aeronautical and maritime users Remote, infraestructure lacking
areas Point to multipoint communications Multipoint to multipoint comm.
Offered services:
Broadband access networks Connecting heterogeneous High speed backbone networks
networks Comm. links between users with mobile or fixed terminals
Satellite communication Fundamentals
A satellite system consists of:
Space segment
Ground segment
Satellite communication Fundamentals
Ground segment consists of:
Gateway stations (GS) Network control center (NCC) Operation control center (OCC)
Satellite communication Fundamentals
Space segment consists of: Satellites
Geostationary orbit (GSO) Nongeostationary orbit (NGSO) Medium earth orbit (MEO)
Low earth orbit (LEO)
Satellite communication Fundamentals
GSO Orbit:
35786 Km avobe the equator Appears fixed to an observer on the Earth Sufficient for global coverage 1 GSO Satellite covers one third of Earth surface This area is called footprint
Satellite communication Fundamentals
GSO Orbit:
High launching cost Large antennas and transmission power required Biggest problem: Propagation delay Around 250280 ms Undesirable for realtime traffic
Satellite communication Fundamentals
GSO satellite coverage
Satellite communication Fundamentals
LEO and MEO Orbits: Closer to the earth surface
Smaller antennas and transmission power required Footprint is also smaller Larger number of satellites is necessary Steerable antennas become useful
Satellite communication Fundamentals
MEO Orbit:
From 3000 Km up to the GSO orbit Typical roundtrip propagation delay: 110300 ms 2003000 Km above earth surface Typical roundtrip propagation delay: 2025 ms
LEO Orbit:
Satellite communication Fundamentals
Satellite communication Fundamentals
Satellite payloads:
Responsible of the satellite communications Once launched, a satellite is impossible to upgrade Robust Simple No onboard processing (OBP) on traditional sats
Satellite communication Fundamentals
Satellite payloads:
Some satellites allow OBP (Conform ISL's) Demodulation/remodulation Decoding/recoding Transponder/beam switching Routing Connectivity in space without terrestrial resource is possible
Satellite communication Fundamentals
Frequency bands:
Most commonly used are C, Ku, and Ka bands With higher frequency, and shorter wavelenght
Smaller antenas can be used
Satellite communication Fundamentals
Satellite-based Internet architectures
Several implementation options due to diversity Suggestions to use hybrid GSO-NGSO network Sats can act as a backbone/Hi-speed network
ARPANET became backbone of research network
Satellite-based Internet architectures
The idea of using satellites in last mile is newer
Satellites interact with GS's May be the only access method for remote areas Bent pipe architecture (Fig 1) suffers big latency
Because of the lack of direct communication
Satellite-based Internet architectures
Bent-pipe design
Satellite-based Internet architectures
OBP and ISL's can be combined to create a network in the sky. Both combination access and backbone network. Teledisc or Iridium are examples of this kind of network. Flexibility at cost of more complex routing
Satellite-based Internet architectures
OBP and ISL
Architecture Design
Satellite-based Internet architectures
DBS Model (Direct Broadcast Satellites)
Acces internet directly by satellites. Only download Created because of internet traffic asimetry in which the server transmits much more information than in reverse Upload from the client is made via terrestrial GS's
Satellite-based Internet architectures
DBS architecture
Satellite-based Internet architectures
Astrolink
Satellite-based Internet architectures
Skybridge distribution
Satellite-based Internet architectures
Spaceway architecture scheme
Satellite-based Internet architectures
Teledisc satellite distribution
Satellite-based Internet architectures
Teledisc satellite coverage
Satellite-based Internet architectures
Iridium satellite distribution
Satellite-based Internet architectures
Iridium satellite coverage
Technical challenges
Multiple Access Control (MAC)
Is a set of rules This rules decide how the clients in the footprint of the satellite acces its uplink channel, which is a limited resource Affects to the QoS and higher layers
Technical challenges
Fixed Assignement:
This is the most basic of MAC's It is based in frequency, time or code divixion basis (FDMA, TDMA and CDMA respectively) Very poor resource management. For small networks.
Technical challenges
Random Access:
Thanks to small and cheap terminals Less data usage, which turns in a bigger number of terminals which a satellite can cover. Each station transmit data regardless of the others.
Technical challenges
Demand Assignment:
Solves RA's lack of QoS providing Dynamically allocates system bandwidth depending on how many clients request access The transmission for permission becomes the problem, but it is affordable.
Technical challenges
After reservation, bandwidth is segmented in FDMA or TDMA Centralized or Distributed control Resource reservation can be explicitly or implicitly done. Priority Oriented Demand Protocol and First In First Out, combine explicit and implicit requests
Routing Issues
We will refer to LEO satellite systems, as Iridium can be. It is very attractive to be able to design a network in the sky, thanks to OBP and ISL's The routing becomes crucial.
Routing Issues
Dynamic Topology
Satellites have very little visible period to us When a satellite goes out, and another comes in, intersatellite handover happens Each satellite is able to set up 4 to 8 ISL's These can be intraplane or interplane
Routing Issues
Discrete-time Dynamic Virtual Topology Routing
DT-DVTR makes use of the periodic nature of sats Works completely offline System storages visibility data of each interval When topology changes, the best path is choosen
Routing Issues
Virtual Node (VN)
Hidew the topologycal changes from the routing protocols, despite satellites are actually moving Keeps state information, such as routing tables and user data When the satellite covering the node disappears in the horizon, the node is covered by the one that comes
Routing Issues
IP Routing at satellites
IP routing is adopted, based in the VN concept Integrates the space network with terrestrial Internet Supports IP multicast and IP QoS Despite is useful and desirable, implementation problems appear everywhere. Constantly improving.
Routing Issues
ATM Switching
Many proposed systems use ATM as network protocol for the constellation A version of DT-DVTR based in ATM is investigated, grouping the ingress and engress satellites' virtual channel connections in a VPC Possibly, IP over ATM will be implemented
Routing Issues
External Routing Issues
Internal design of communications will probably change constantly to fit manufacturers or clients. Satellite network is isolated of terrestrial network AS (astronomous system) concept. Sat=AS. Only Border Gateways will communicate with these, by BGP
Routing Issues
Unidirectional Routing
DBS is unidirectional. Traditional Routing is invalid Static routing instead of dynamic routing is an option Options:
Routing Protocol Modification Tunnelling
Routing Issues
Routing Protocol Modification
In unidirectional routing, we can only send (feeders) The clients at the other side can only receive (receivers) Make a receiver identify the potential feeders, ignoring unusable data while mantaining neighboring connection The receiver periodically delivers its own routing message to all feeders through terrestial link
Routing Issues
Tunneling:
Offers a link layer approach to hide the asymetry. A tunnel is a virtual link set between a DBS and a receiver by using encapsulation and decapsulation User encapsulates package -> sends to routing protocol via terrestrial nw -> arrives to satellite -> the tunnel decapsulates the message - > forwards it to the routing protocol
Satellite Transport
TCP/IP and UDP/IP protocols are the heart of the Internet. Their solidity and standarization makes them adaptable and unlikely to be discarded Satellite-based Internet will use UDP and TCP. TCP being connection oriented, will receive the great impact of high latencys and error rates.
Satellite Transport
TCP/IP performance over satellite
High latencies will affect TCP's functionality. Timeout based protocols such as this may severely suffer large round-trip times delivered by satellite connections Also suffer from interferences, fading, shadowing, and rain atteunation. This causes Bit Error Rate (BER)
Satellite Transport
Performance enhacenments have been developed over TCP TCP selective acknowledgement (SACK) TCP for transaction (T/TCP) Persistent TCP Connection MTU mechanism FEC
Satellite Transport
TCP extensions solve some limitation of standard TCP TCP Spoofing TCP Splitting Web Caching
THANK YOU!
Aitor Fernández
