Protocol Protocol Architectures for Architectures for

Satellite ATM Satellite ATM Broadband Broadband NetworksNetworks

ContentContent

1.1. IntroductionIntroduction

2.2. Short overview of ATM Short overview of ATM (Asynchronous Transfer Mode)(Asynchronous Transfer Mode)

3.3. ATM cell encapsulation (Data Link ATM cell encapsulation (Data Link Control)Control)

4.4. S-ATM protocolS-ATM protocol

5.5. Comparrison between Partial Packet Comparrison between Partial Packet Discard (PPD) and Data Link Control Discard (PPD) and Data Link Control (DLC)(DLC)

1. Reasons for using 1. Reasons for using ATMATM

- ATM networks can rapidly and ATM networks can rapidly and economically extend boundaries of economically extend boundaries of any terrestrial networkany terrestrial network

- To provide coverage to remote ATM To provide coverage to remote ATM usersusers

- The demand for satellite The demand for satellite communication at the Ka frequency communication at the Ka frequency bands (20/30 GHz) increasedbands (20/30 GHz) increased

AimAim

To bring the ATM functionality To bring the ATM functionality closer to the user terminal, without closer to the user terminal, without violating its connection-oriented violating its connection-oriented nature and guarantee similar quality nature and guarantee similar quality of service (QoS) characteristicsof service (QoS) characteristics

An example scenarioAn example scenario

Network entities and their Network entities and their ATM connection interfacesATM connection interfaces

Entities in a satellite Entities in a satellite network (1)network (1)

Satellite Adaption Unit (SAU)Satellite Adaption Unit (SAU)Non standard, specially designed unit to Non standard, specially designed unit to provide User Terminals access to the provide User Terminals access to the satellite network. It performs all necessary satellite network. It performs all necessary protocol adaption of the User Terminals protocol adaption of the User Terminals (UT). Includes all physical layer (UT). Includes all physical layer functionalities.functionalities.

Gateway Stations (GTW)Gateway Stations (GTW)Land Earth stations that provide Land Earth stations that provide connectivity to external networksconnectivity to external networks

Entities in a satellite Entities in a satellite network (2)network (2)

Network Control Station (NCS)Network Control Station (NCS)Central entity used in GEO satellite Central entity used in GEO satellite system that provides overall control of system that provides overall control of satellite network resources and satellite network resources and operations. Is responsible for call routing, operations. Is responsible for call routing, call managment, authentication, billing, call managment, authentication, billing, registration and deregestration. Usually registration and deregestration. Usually one NCS per GEO satellite.one NCS per GEO satellite.

2. Overview of ATM2. Overview of ATM

Main use as transport technique and Main use as transport technique and in core networksin core networks

Connection-orientetConnection-orientet Multiplexing is possibleMultiplexing is possible Cells of fixed length (53 byte)Cells of fixed length (53 byte) Transfer rates from 155 Mbps to 1.2 Transfer rates from 155 Mbps to 1.2

GbpsGbps

ATM headerATM header

ATM protocol layersATM protocol layers

3. ATM cell encapsulation3. ATM cell encapsulation(Data Link Control (Data Link Control

protocol)protocol)Advantages:Advantages:

- Very simple and easy to implement Very simple and easy to implement technique for passing arbitrary technique for passing arbitrary information through network entitiesinformation through network entities

- Supports different user terminal Supports different user terminal standards through a satellite specific standards through a satellite specific interfaceinterface

Data Link ControlData Link Control

Satellite specific LLC (Logical Link Satellite specific LLC (Logical Link Control) and MAC (Media Access Control) and MAC (Media Access Control) grouped together in the Control) grouped together in the DLC (Data Link Control) protocolDLC (Data Link Control) protocol

DLC is necessary to transfer DLC is necessary to transfer information between the satellite information between the satellite network entities across the air network entities across the air interfaceinterface

Structure of the satellite Structure of the satellite MAC layer packetMAC layer packet

Dimensioning the SCI Dimensioning the SCI fieldfield

Length of the SCI (Satellite Connection Identifier) field Length of the SCI (Satellite Connection Identifier) field needs to be large enough to include the maximum needs to be large enough to include the maximum number of all active connections that can be supported number of all active connections that can be supported at any timeat any time

Uniformly Uniformly distributed distributed satellite switch satellite switch capacity (in Gbps)capacity (in Gbps)

Number of Number of satellite spot satellite spot beamsbeams

Max. number of Max. number of active active connections per connections per spot-beamspot-beam

Required number Required number of SCI bitsof SCI bits

22 3232 40964096 1212

55 3232 1024010240 1313

55 256256 12801280 1010

1010 3232 2048020480 1414

1010 128128 51205120 1212

1010 256256 25602560 1111

LLC / CRC / RRM fieldLLC / CRC / RRM field The LLC (Logical link Control) field can The LLC (Logical link Control) field can

be used to multiplex uplink connections be used to multiplex uplink connections coming from the same SAU using the coming from the same SAU using the same SCI valuesame SCI value

The CRC (Cyclic Redundancey Check) The CRC (Cyclic Redundancey Check) field is required to detect errors in the field is required to detect errors in the satellite packet headersatellite packet header

The presence of the RRM (Radio The presence of the RRM (Radio Resource Managment) field depends on Resource Managment) field depends on the selection of the resource the selection of the resource managemant protocolmanagemant protocol

Additional overheadAdditional overhead

2 Bytes for the SCI field (including 2-2 Bytes for the SCI field (including 2-3 Bits for the RRM field)3 Bits for the RRM field)

3 Bytes for the LLC field3 Bytes for the LLC field 1 Byte for Error Correction1 Byte for Error Correction

6 Bytes additional overhead6 Bytes additional overhead

ConclusionConclusion

Minimum processing power at the Minimum processing power at the SAU and GTW stations is neededSAU and GTW stations is needed

BUT:BUT:

6 bytes additional overhead on every 6 bytes additional overhead on every cell (11 bytes including the ATM cell (11 bytes including the ATM header)header)

4. S-ATM protocol4. S-ATM protocol

Uses a modified ATM headerUses a modified ATM header ATM header extraction at the SAUATM header extraction at the SAU ATM header reconstruction at the ATM header reconstruction at the

GTWGTW Combines the function of MAC and Combines the function of MAC and

ATMATM

Structure of the S-ATM Structure of the S-ATM packetpacket

S-ATM header structureS-ATM header structure

The standard VPI/VCI ATM fields are The standard VPI/VCI ATM fields are replaced by the satellite VPI/VCI replaced by the satellite VPI/VCI (SVPI/SVCI) fields, which are used (SVPI/SVCI) fields, which are used by the satellite onboard switchby the satellite onboard switch

CLP field is the same as in the ATM CLP field is the same as in the ATM headerheader

Header length is 5 Bytes (like the Header length is 5 Bytes (like the normal ATM-header)normal ATM-header)

Protocol stack Protocol stack architecturearchitecture

No use of the LLC layer in this No use of the LLC layer in this system because ATM already offers system because ATM already offers multiplexing capabilitymultiplexing capability

Not enough place in the header for a Not enough place in the header for a LLC fieldLLC field

Use of PPD (Partial Packet Discard)Use of PPD (Partial Packet Discard)

Partial Packet Discard Partial Packet Discard (PPD)(PPD)

Mechanism to detect erroneous cells at Mechanism to detect erroneous cells at the satellite switchthe satellite switch

End user is responsible for End user is responsible for acknoledgement and retransmission of acknoledgement and retransmission of higher layer PDUshigher layer PDUs

Erroneous cells and consecutive cells Erroneous cells and consecutive cells that belong to the same PDU get deletedthat belong to the same PDU get deleted

No additional processing power is No additional processing power is neededneeded

ConclusionConclusion

No additional overhead for the ATM No additional overhead for the ATM cellscells

BUTBUT

Extra processing power is needed to Extra processing power is needed to modify the ATM headermodify the ATM header

5. Comparison between PPD 5. Comparison between PPD and DLCand DLC

Calculation of the radio link throughput Calculation of the radio link throughput (in packets / packet transmission time)(in packets / packet transmission time)

(1)(1) PER = 1 – (1 – BER)PER = 1 – (1 – BER)lengthlength

(2)(2) Radio link throughput = (1 – PER) Radio link throughput = (1 – PER) [p/(p+h)][p/(p+h)]

BER = Bit Error RateBER = Bit Error Rate PER = Packet Error RatePER = Packet Error Rate

length = length of a higher layer PDU (in bits)length = length of a higher layer PDU (in bits)

p = payload h = header lengthp = payload h = header length

Comparison between PPD Comparison between PPD and DLCand DLC