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Satellite Network Technology
Ha Yoon Song
For
ICT, TUWien
Satellite Internet Systems
Introduction
Satellite Communication Fundamentals
Satellite-Based Internet Architectures
Some Examples of Satellite Systems
Technical Challenges
2
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.
3
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
4
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
5
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)
6
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, omnidirectional antennas.
 Requires support to handoff from one satellite to another.
7
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)

9
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.
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
10
The satellite-based Internet with bent pipe architecture
The satellite-based Internet with OBP and ISL architecture
Next Generation Satellite Systems
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 uses
Signals 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.
15
Technical Challenges
Multiple Access Control
Routing Issues in Satellite Systems
Satellite Transport
16
Technical Challenges (MAC)
Multiple Access Control (MAC)
1.
2.
3.
17
Performance
Schemes
Implementation
Technical Challenges (MAC)
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
18
Technical Challenges (MAC)
MAC Schemes
1.
2.
3.
19
Fixed Assignment
Random Access
Demand Assignment
Technical Challenges (MAC)
Fixed Assignment
-
-
20
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.
Technical Challenges (MAC)
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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Technical Challenges (MAC)
Demand Assignment
- DAMA protocols dynamically allocate system
bandwidth in response to user accounts
- Resource Reservation can be made
- PODA and FIFO combine requests
22
Technical Challenges (Routing Issues)
Routing Issues in LEO Constellation
IP Routing
ATM Switching at the satellites
External Routing Issues
23
Technical Challenges (Routing Issues)
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

24
Technical Challenges (Routing Issues)
IP Routing at Satellites
Seems to be straightforward
Dealing with variable-length packets
Scalability problems
Computational and processing capacity
Research yet to be made on this scheme
25
Technical Challenges (Routing Issues)
ATM Switching at the
satellites
Many proposed systems
use ATM as the network
protocol
An ATM version of DTDVTR is investigated
Modified S-ATM packet
Technical Challenges (Routing Issues)
External Routing Issues
Internal routing done by
Autonomous systems
Internal routing is handled
by AS’s own internal
routing protocol
Technical Challenges (Routing Issues)
28
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
Satellite ATM Network
- ATM Architecture Protocol stack for the satellite ATM network
Satellite ATM Network
- ATM Architecture -
Interface between the ASIU and other modules
SONET – Synchronous Optical Network
 SDH – Synchronous Digital Hierarchy
 PDH – Plesiochronous Digital Hierarchy
 PLCP – Physical Layer Convergence Protocol

Satellite ATM Network
- ATM Architecture Internal Architecture of ASIU
The Cell Transport Method
PDH

some inefficiencies

too many ADD operate
 stuffing bit
 rerouting(e.g. network fail) – extremely difficult
The Cell Transport Method
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
The Cell Transport Method
PLCP

IEEE P802.6
 DS3(44.736Mbps); 125us – 53byte
The Cell Transport Method
PLCP

POI (Path Overhead Indicator)
 POH (Path OverHead)
Link Layer
-Satellite Link Access MethodsFDMA, TDMA, CDMA
MF-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 ControlThe 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
Link Layer
-Error ControlATM 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
Link Layer
-Error ControlError 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 AspectsNecessary to maintain the QoS of ATM connections over satellite
QoS parameters

CLR (Cell Loss Ratio)


CTD (Cell Transfer Delay)


marks the difference between ATM and satellite links
CDV (Cell Delay Variation)


most stringent criteria for satellite ATM network
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 capability
Satellite 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 ControlTraffic 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 ControlSelective 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
Buffering
VC(Virtual Channel)
Traffic Management
-Satellite Bandwidth ManagementBTP (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 ATM
Requirements 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 OPERATION OF STP
Basic STP packet types
BASIC OPERATION OF STP
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 OPERATION OF STP
Basic STP packet types

STAT

include the current
window value of the
receiver
 seq.# of the highest inseq.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 OPERATION OF STP
Basic STP packet types

USTAT

receiver can
independently report on
missing packets
 help to exchange less
frequently (POLL and
STAT)
BASIC OPERATION OF STP
Example of SSCOP operation

T sends a packet #0~#4
 T sends a POLL packet


R returns a STAT


packet #0~#4 is OK
T sends a packet #5~#9


tells that next packet is #5
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


presence of a sequence gap


redundant data packets -> silent discard
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


the delayed send timer


from no rate control (distributed TCP) to tight rate control (explicit
network)
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
-TopologiesSimulated in GEO

RTT – 532ms, excluding queuing and transmission delays
SIMULATION RESULTS
-TopologiesSimulated in LEO
SIMULATION RESULTS
-TCP configurationTCP

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 controlFlow 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
70
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 TCPSack and TCP-Reno
SIMULATION RESULTS
STP performance in a high BER environment

Forward throughput performance
of STP on 1Mbps channel

Reverse channel bandwidth required
for STP as a function of BER
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 Link
UDL : User Data Link
LDD : Long Distance Dependent
LEO : Low Earth Orbit
MEO : 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 network
3.1. 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 network
3.2. 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 network
3.3.2 Network Topology
4. Hierarchical Satellite Routing Protocol
4.1. 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 Protocol
4.2. Key features of the HSRP protocol
Topology state routing protocol
The logical satellite location
Dynamic routing
Route selection that satisfies QoS connection
requests
Support for hierarchical HSRP networks
4. Hierarchical Satellite Routing Protocol
4.3. Hierarchical Satellite Routing Protocol
4.3.1. Hierarchical topology initialization
Step 1. Generation of Neighbor Topology
Step 2. Sending Neighbor Topology Information
Step 3. Aggregation of Peer Group Topology
Step 4. Generation of Hierarchical Topology
Step 5. Sending Hierarchical Topology Information
Step 6. Path selection
5. Performance Evaluation
5.1. Simulation Model
5. Performance Evaluation
5.2. Simulation Results
• loads are 2000 calls/min, and the mean call duration is 3 minutes.
flat satellite network (FSN)
5. Performance Evaluation
5.2. Simulation Results