satellite network technology

Ha Yoon SongFor

ICT, TUWien

Satellite Network Technology

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Satellite Internet Systems

IntroductionSatellite Communication FundamentalsSatellite-Based Internet ArchitecturesSome Examples of Satellite Systems Technical Challenges

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Introduction

Source Material: Y.Hu and V.Li. Satellite-based Internet: a Tutorial, IEEE Comm., March

2001. J.Farserotu and R.Prasad. A Survey of Future Broadband Multimedia

Satellite Systems, Issues and Trends, IEEE Comm., June 2000. E.Lutz, M.Werner and A.Jahn. Satellite Systems for Personal and

Broadband Communications, Springer, Berlin, 2000.

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Introduction

Technical challenges to Internet development Proliferation of applications Expansion in the number of hosts User impose High-speed high-quality services needed to accommodate multimedia

applications with diverse quality of service

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Introduction

Satellite Network Global coverage Inherent broadband capability Bandwidth-on-demand flexibility Mobility support Point-to-multipoint, multipoint-to-multipoint comm.

Satellite communication system is a excellent candidate to provide broadband integrated Internet services to globally scattered users

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Satellite Communication Fundamentals

Construction of a satellite system Space segment: satellites

Geostationary orbit (GSO) Nongeostationary orbit (NGSO)

– Medium earth orbit (MEO)– Low earth orbit (LEO)

Ground segment Gateway stations (GSs) Network control center (NCC) Operation control centers (OCC)

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Orbit Selection

GSO option: Larger Coverage (1/3 of Earth’s Surface) Distance challenge:

Large delay (round-trip delay 250-280 ms) Large propagation loss (requires higher transmitting powers and antenna gains)

NGSO option: Smaller Delay (LEO round-trip delay ~20ms) Variable looking angle challenge:

Requires sophisticated tracking techniques or, most of the times, omni-directional antennas.

Requires support to handoff from one satellite to another.

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Frequency Bands

C Band (4-8 GHz): very congested already.Ku Band (10-18 GHz): Majority of DBS systems, as well as current

Internet DTH systems (DirectPC and Starband).Ka band (18-31 GHz): Offers higher bandwidth with smaller antennas, but

suffers more environmental impairments and is less massively produced as of today (more expensive) when compared to C and Ka.

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Satellite Payload

Bent pipe Satellites act as repeaters. Signal is amplified and retransmitted but

there is no improvement in the C/N ratio, since there is no demodulation, decoding or other type of processing. No possibility of ISL, longer delay due to multiple hops.

Onboard processing (OBP) Satellite performs tasks like demodulation and decoding which

allow signal recovery before retransmission (new coding and modulation). Since the signal is available at some point in baseband, other activities are also possible, such as routing, switching, etc. Allows ISL implementation.

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Satellite-Based Internet Architectures

The satellite-based Internet with bent pipe architecture Lack of direct communication path Low spectrum efficiency and long latency

The satellite-based Internet with OBP and ISL architecture Rich connectivity Complex routing issues

The satellite-based Internet with bent pipe architecture

The satellite-based Internet with OBP and ISL architecture

Next Generation Satellite Systems

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Case Study: Teledesic

Constellation consists of 288 satellites in 12 planes of 24 satellites.Ka-band system. Uplink operates at 28.6–29.1 GHz, downlink at 18.8–

19.3 GHz. It usesSignals at 60 GHz for ISLs between adjacent satellites in each orbital

plane.Full OBP and OBS (on-board switching)."Internet in the sky."Offers high-quality voice, data, and multimedia information services. QoS

performance designed for a BER < 10–10.Multiple access is a combination of multifrequency TDMA (MF-TDMA) on

the uplink and asynchronous TDMA (ATDMA) on the downlink.

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Case Study: Teledesic

Network capacity planned to be 10 Gb/s. User connections of 2 Mb/s on the uplink and 64 Mb/s on the downlink possible.

Minimum elevation angle of 40.25 enables achievement of an availability of 99.9 percent.

Enormous complexity to the table in terms of untried technology, onboard switching and inter-satellite capabilities.

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Technical Challenges

Multiple Access ControlRouting Issues in Satellite SystemsSatellite Transport

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Technical Challenges (MAC)

Multiple Access Control (MAC)

1. Performance2. Schemes3. Implementation

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Performance of MAC

- Depends on shared communication media and traffic.

- Long latency in Sat-channels excludes some MAC schemes that are used in terrestrial LAN

- Limited power supply on board constrains computational capacity - Implementation of priorities required

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MAC Schemes

1. Fixed Assignment2. Random Access3. Demand Assignment

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Fixed Assignment

- Techniques include FDMA,TDMA and CDMA- FDMA and TDMA uses dedicated channels- In CDMA, each user is assigned a unique code sequence- Data signal is spread over a wider brand width than the required to

transmit the data.

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Random Access

In RA schemes, each station transmits data regardless of the transmission status of others.

Retransmission after collision creates

- Packet delay - Frequent collisions

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Demand Assignment

- DAMA protocols dynamically allocate systembandwidth in response to user accounts

- Resource Reservation can be made - PODA and FIFO combine requests

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Technical Challenges (Routing Issues)

Routing Issues in LEO ConstellationIP RoutingATM Switching at the satellitesExternal Routing Issues

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Routing Issues in LEO Constellation

Dynamic Topology- Handles Topological variations- ISL Maintenance

DT-DVTR- Works offline- Sets time intervals and remains constant until next time

interval- No of consecutive routing tables are stored and then

retrieved when topology changes VN -Hiding of topology changes from routing

protocols

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IP Routing at SatellitesSeems to be straightforwardDealing with variable-length packetsScalability problemsComputational and processing capacityResearch yet to be made on this scheme


ATM Switching at the satellites

Many proposed systems use ATM as the network protocol

An ATM version of DT-DVTR is investigated

Modified S-ATM packet


External Routing IssuesInternal routing done by

Autonomous systemsInternal routing is handled

by AS’s own internal routing protocol

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Technical Challenges (Satellite Transport)

TCP/IP UDP/IP

These 2 protocols will continue for now as they have tremendous legacy

• Performance will be any way affected by long latency and error prone characteristics of satellite links

• Researchers are still working in NASA on TCP/IP • TCP performance will definitely improve

Technical Challenges (Satellite Transport)

TCP performance over satellite- Positive feedback mechanism- Achieve rate control and reliable delivery

Performance enhancement- TCP selective acknowledgement- TCP for transaction

- Persistent TCP connection - Path Maximum Transfer Unit

Technical Challenges

Satellite Transport Performance Enhancements

TCP spoofing– The divided connections are isolated by the GSs– which prematurely send spoofing acknowledgments upon receiving packets– The GSs at split points are also responsible for retransmitting any missing

data TCP splitting

– Instead of spoofing, the connection is fully split– A proprietary transport protocol can be used in a satellite network without

interference to standard TCP in terrestrial networks– more flexible– some kind of protocol converter should be implemented at the splitting points

Web caching– the TCP connection is split by a Web cache in the satellite network– need not set up TCP connections all the way to servers outside if the

required contents are available from the cache– reduces connection latency and bandwidth consumption

Conclusion

Possible architectures Bent-pipe OBP satellites

Technical Challenges MAC IP routing in LEO Unidirectional routing Satellite transport issues QOS Congestion Control

Satellite ATM Networks: A survey

Introduction

ATM technology offers users integration and the flexibility of accessing bandwidth on demand

Increasing recognition of the benefits and advantages of using satellite transmission systems

Satellite ATM Network- ATM Architecture -

ASIU real-time bandwidth

allocation network access

control system timing and

synchronization control

call monitoring error control traffic control

Key Component


Protocol stack for the satellite ATM network


Interface between the ASIU and other modules

SONET – Synchronous Optical Network SDH – Synchronous Digital Hierarchy PDH – Plesiochronous Digital Hierarchy PLCP – Physical Layer Convergence Protocol


Internal Architecture of ASIU

The Cell Transport Method

PDH

some inefficiencies too many ADD operate stuffing bit rerouting(e.g. network fail) – extremely difficult


SDH Advantage

without multiplexing stage directly identifies the position of the payload very accurate clock rate easier and lower cost multiplexing

Disadvantage overhead; pointer byte incorrect pointer -> incorrect payload


PLCP IEEE P802.6 DS3(44.736Mbps); 125us – 53byte


PLCP POI (Path Overhead Indicator) POH (Path OverHead)

Link Layer-Satellite Link Access Methods-

FDMA, TDMA, CDMAMF-TDMA (Multi-Frequency TDMA)

inefficiency – the destination of the bursts reduce satellite antenna sizes and transmission power increase satellite network bandwidth

DAMA Dynamic allocation – satellite power and bandwidth Random Access & QoS guarantee

DAMA with MF-TDMA or SCPC achieve a greater efficiency in satellite ATM networks

※ SCPC(single channel per carrier) – userside ATM UNI interface channel

Link Layer-Error Control-

The Impact of Burst Error Characteristics HIGHER BER than Terrestrial Network HIGHER RTT (Round Trip Time) – time for error detection? Burst error; satellite ATM HEC(Head Error Check); burst error cannot be correct CRC can detect burst error

ALL1 and ALL3/4 the length of burst error is beyond 10 the error may not be detected

ALL5 32-bit CRC; powerful overhead / not optimal solution


ATM cell Cell header and Payload

Interleaving Mechanism; (similarly ATM cell) efficient way to solve the burst error problem may still contain errors

The SAR-PDU format of ALL1 The SAR-PDU format of ALL3/4


Error Recovery Algorithm ARQ: stop-and-wait, Go-Back-N, selective-repeat

Coding Scheme for Improving Error Performance FEC (Forward error correction) code RS (Reed Solomon) code

cost-effective solution

Traffic Management-Performance Aspects-

Necessary to maintain the QoS of ATM connections over satellite

QoS parameters CLR (Cell Loss Ratio)

most stringent criteria for satellite ATM network CTD (Cell Transfer Delay)

marks the difference between ATM and satellite links CDV (Cell Delay Variation)

synchronization between different connections CER (Cell error ratio)

the sum of successfully cells / errored cells SECBR (Severely Errored Cell Block Ratio) CMR (Cell Miss-insertion Ratio)

caused by an undetected cell header error

Traffic Management -The Impact of Transmission Delay Characteristics

ATM technology – most of capabilitySatellite ATM network – the long delay

Video and Voice Serv. Real-time – very sensitive to the delay the satellite can provide a connection of high quality

Text or Data Serv. not very sensitive to delay

Video Telephony ITU-T Recommendation H.261 is greater than the satellite delay But, future video telephony will demand less delay

CSCW App. acceptable from the app’s point of view But, maybe the poor performance

Traffic Management-Traffic Control-

Traffic Control (for ATM -> for terrestrial ATM networks) Traffic shaping

changes the traffic char. of a cell stream to achieve a desired modification of those traffic char.

CAC (Connection Admission Control) the set of actions taken by a network to establish whether an ATM connection can be accepted or rejected in order to avoid

congestion

Traffic Management-Congestion Control-

Selective Cell Discard CLP = 0 or 1 ; priority

EFCI (Explicit Forward Congestion Indication) convey congestion notification to source

FECN (Forward Explicit Congestion Notification inappropriate in satellite ATM a one-way propagation delay

BECN (Backward ECN) send a notification in the reverse direction of the congested path faster than FECN

BufferingVC(Virtual Channel)

Traffic Management-Satellite Bandwidth Management-

BTP (Burst Time Plan) indicates the position and lengths of bursts in the transmission frame

such as video, voice, data, BTP can be considered

Other Open Issues

L(M)AN Interconnection Using Satellite ATMRequirements for Multimedia Services

TCP and SSCOP

TCP error-free flow a large number of packets are retransmitted even if only a single packet is

damaged due to error default windows size (16kB) -> to tune the timeout and window size parameters

SSCOP defined by ITU-T Recommendation Q.2110 selective retransmission protocol with 24bit sequence number

allow to be set to a size much larger window size

Satellite Transport Protocol(STP):

An SSCOP-based Transport Protocol for Datagram Satellite Networks

CONTENTS

INTRODUCTION

HISTORY AND RELATED WORK

BASIC OPERATION OF STP

NEW STP FEATURES

SIMULATION RESULTS

CONCLUSION

INTRODUCTION

TCP Protocol inefficient for Satellite Networks

Solution with four basic strategies the use of either standard or non-standard options or protocol changes

double format; complex striping spoofing splitting

SSCOP in ATM network targeted for large BW X RTD(BandWidth Round Trip Delay) networks necessary modifications and additions

SSCOP – Service Specific Connection Oriented Protocol

HISTORY AND RELATED WORK

SSCOP the result of and international standardization effort from 1990-1994 currently being used for ATM signaling at both the UNI and NNI

not being used for user data transfer

the goals of SSCOP optimization for high speed operation efficient operation in networks with large BW*RTD

the sequence number is 24 bits the protocol is 32 bit aligned error recovery is based only on selective retransmission control and information flow is separated protocol logic is decoupled form timers transmitter and receiver can be decoupled

SSCOP and SCPS-TP discrimination between lost and errored segments in the flow control algorithm flow control also useful for satellite networks


Basic STP packet types


Basic STP packet types Sequenced Data packet

user data : variable length

seq.number : 24bit No control data

– no timestamp

POLL periodically, transmitter

sends a POLL packet to the receiver

contains a timestamp contains the seq.# of the

next in-seq SD packet#


Basic STP packet types STAT

include the current window value of the receiver

seq.# of the highest in-seq.packet to have been successfully received

a listing of all gaps in the seq.# space

– from highest in.seq to seq.#

can be segmented, if larger


Basic STP packet types USTAT

receiver can independently report on missing packets

help to exchange less frequently (POLL and STAT)


Example of SSCOP operation T sends a packet #0~#4 T sends a POLL packet

tells that next packet is #5 R returns a STAT

packet #0~#4 is OK T sends a packet #5~#9

ex) packet #7 is lost R sends USTAT

when R receives #8 T sends a POLL packet (R returns a STAT)

include request #7 but, avoids duplicate retransmission

with a timestamp T receives USTAT(#7 lost)

immediately resends #7

NEW STP FEATURES

Modifications to SSCOP for operation over IP reception of a duplicate packet

redundant data packets -> silent discard presence of a sequence gap

does no necessarily indicate that a packet lost Retransmission, when miss-ordering packet exist (too long delay)

if (STAT_ts – stored_ts > k*mdev) retransmit;– k – constant– mdev – deviation in RTT

USTAT message based on– not strictly– but, without the need for a frequent POLL/STAT exchage– to delay the sending of USTATs

» until the seq.# has exceeded the missing packet by n packet

NEW STP FEATURES

Problems of TCP flow control ACK message

departures of packet -> arrival of ACK not smooth

unlike flow control in satellite Networks

Solution adapts to the amount of rate control

from no rate control (distributed TCP) to tight rate control (explicit network) the delayed send timer

estimated RTT is obtained by comparing the timestamp in a received STAT ALL type 5 CRC

NEW STP FEATURES

Origins of STP protocol features

SIMULATION RESULTS-Topologies-

Simulated in GEO RTT – 532ms, excluding queuing and transmission delays

SIMULATION RESULTS -Topologies-

Simulated in LEO

SIMULATION RESULTS-TCP configuration-

TCP two testbed

TCP-Sack TCP Reno

ns defaults for all parameters except for the windows size timeout interval – 500ms ACK is sent for every 2 segments

STP USTAT – 3 POLL per RTT - 3

SIMULATION RESULTS-Flow control-

Flow control policy in STP additive window increases of 1 packet per RTT multiplicative decrease by ½ during the congestion avoidance phase 10% of the bottleneck links

Result In the GEO

occasional bottleneck at the queue at the ingress of the satellite networks In the LEO

occasional bottleneck at either the ingress or the egress of the satellite networks

SIMULATION RESULTS

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Comparison of STP with TCP average of 200

simulation runs, each 60sec

fixed packet size of 1000byte including TCP/IP or STP/IP overhead

Result STP generally

ouperformed TCP-Sack and TCP-Reno

SIMULATION RESULTS

STP performance in a high BER environment

Reverse channel bandwidth re-quired for STP as a function of BER

Forward throughput perfor-mance of STP on 1Mbps chan-nel

CONCLUSION

Refer to modified protocol as the STP ATM based protocol as SSCOP

+ flow control mechanism better than rate or windows control

also available for wireless environment

In Future STP or similar protocol is needed essentiality

Satellite over Satellite (SOS) Network: A Novel Concept of Hierarchical

Architecture and Routing in Satellite Network

Terminology

ISL : Inter-Satellite LinkUDL : User Data LinkLDD : Long Distance DependentLEO : Low Earth OrbitMEO : Medium Earth Orbit

Problem Definition

In case of long distance dependent (LDD) and multimedia traffics are dominate, performances in terms of overall network decrease, because of traffic transfer via many ISLs on routing path.

Proposed Solution

Satellite over satellite (SOS) network that has a hierarchical satellite constellation with multiple layers

3. Modeling of SOS network3.1. Architecture

System Topology Satellites in the lowest layer are clustered to form satellites in

upper layer Each satellite cluster forms a peer group Parent / Child Relations between upper and lower layers

System Connectivity Sat ↔ Terrestrial node: User Data Link (UDL) Sat ↔ Sat within same layer: Inter-Satellite Link (ISL) Sat ↔ Sat between layer: Inter-Orbit Link (IOL)

3. Modeling of SOS network3.2. Example of Communication Scenario

• SOS network with three layers combined LEO, ME0 and GEO

• SDD (Short Distance-Dependent) traffics are transmitted through ISL in the first layer

• LDD traffics are transmitted through IOL up to the second layer with MEO altitudes within QoS boundaries to reduce satellite hops.

3. Modeling of SOS network3.3.2 Network Topology

4. Hierarchical Satellite Routing Protocol4.1. QoS Requirements of HSRP

• h is the satellite altitude • c is the signal propagation speed• Dsd for threshold value of user-to-user delay in a call connection

4. Hierarchical Satellite Routing Protocol4.2. Key features of the HSRP protocol

Topology state routing protocolThe logical satellite locationDynamic routingRoute selection that satisfies QoS connection

requestsSupport for hierarchical HSRP networks

4. Hierarchical Satellite Routing Protocol4.3. Hierarchical Satellite Routing Protocol

4.3.1. Hierarchical topology initialization

Step 1. Generation of Neighbor TopologyStep 2. Sending Neighbor Topology InformationStep 3. Aggregation of Peer Group TopologyStep 4. Generation of Hierarchical TopologyStep 5. Sending Hierarchical Topology InformationStep 6. Path selection

5. Performance Evaluation5.1. Simulation Model

5. Performance Evaluation5.2. Simulation Results

flat satellite network (FSN)

• loads are 2000 calls/min, and the mean call duration is 3 minutes.

5. Performance Evaluation5.2. Simulation Results

satellite network technology

Documents

number of satellite

satellite communication

large delay roundtrip

satellite systemspace

gso orbit

typical roundtrip delay

internet connection

ku band