A MAC Protocol for over Satellite Dr. H. Bischl, J. Bostic, Matteo Sabattini DLR Oberpfaffenhofen 1
Inhalt 4 Szenarium 4 Problemstellung und Anforderungen an das MAC Protokoll 4 Protokollarchitektur 4 MAC und Scheduling für das System 4 SDL-Realisierung und Implementierung in den Demonstrator 4 Schlussfolgerungen 2
Scenario Satellite with on-board processing (also WCAC (Wireless Connection Admission Control) Group terminal Single user terminal MAC: 4 Uplink: MF-TDMA 4 Downlink: Packet Stream Earth station Core Network 3
in Fixed and Radio Networks Fixed Network Wire Multiplexing/Buffering/Scheduler Outgoing link Only one terminal per switch port point-to-point Bandwidth constraint Radio () Network Feedback channel Air interface Uplink Access Control TDMA: slot scheduling Problems: More than one terminal per switch port! Uplink bandwidth constraint shared medium Receiver From other carrier From ISL Satellite ISL Downlink ISL TDMA: scheduling delay hard limitation CDMA: complexity, back-off power control 4
Anforderungen an das MAC-Protokoll 4 Effiziente Nutzung der verfügbaren Ressourcen im Uplink und im Downlink 4 Unterstützung der Dienstkategorien und Einhaltung der QoS-Garantien 4 Unterstützung der -Signalisierung 4 Möglichst wenig Overhead durch Signalisierung 4 Unterstützung auch einer größeren Anzahl an Terminals 4 Unterstützung der Adressierung der logischen -Switchports im Satelliten 5
Service Categories Service Category CBR CLR X Guarantees Delay Variance X Bandwidth PCR Typical Application Voice, Audio, Video, TV,... rt-vbr X X SCR VBR Video and Audio nrt-vbr X NO SCR Data Transport, Frame Relay ABR X NO MCR Data Transport, TCP/IP UBR NO NO NO Data Transport, TCP/IP UBR+ NO NO MCR Data Transport, TCP/IP GFR NO NO MCR Data Transport, TCP/IP PCR: Peak Cell Rate SCR: Sustained Cell Rate MCR: Minimum Cell Rate 6
Protocol Architecture Satellite Terminal Application Satellite Radio Resource and Mobility Management ILMI ILMI S-MIB M-UNI SNMP M-UNI SNMP S-AAL AAL-X AAL-5 S-AAL AAL-5 L M E Radio DLC Control Plane Radio PHY User Plane S-LLC S-MAC Management Plane L M E Radio DLC Control Plane Radio PHY User Plane S-LLC S-MAC Management Plane 7
Uplink MAC for CBR Services 4 Fixed assignment of resources according to PCR (min. inter-cell interval = 1/PCR) 4 Problem with TDMA: minimum inter-cell interval difficult to guarantee 1/PCR 2 1/PCR 1? 4 Solution: transmission of cells in bursts, traffic shaping to preserve inter-cell interval 1/PCR 1 1/PCR 2 8
How to Guarantee MCR in the Uplink? 4 Necessary for UBR+, GFR, and ABR 4 Algorithm similar to Weighted Round Robin (WRR) 4 Weight is set according to the Minimum Cell Rate Connection 1, MCR =2 Connection 2, MCR =2 Connection 3, MCR =3 Connection 4, MCR =1 Connection 5, MCR =1 Weighted Roundrobin ordering strategy Scheduler Request for one time slot Slots allocation Con 1Con 1 Con 1Con 2Con 3 Con 3Con 4Con 5 If there are still free time slots left: 4 Use free assignment for remaining slot requests 9
How to Guarantee SCR in the Uplink? 4 Necessary for VBR services 4 Token bucket process is active for each flow in satellite (scheduler) 4 The resources are allocated according to the tokens in bucket and resource requests Token rate SCR 4 The maximum number of allocated slots per frame is limited. 4 In the case that there are not enough resources WRR can be used with the weights of SCR Arriving slot requests Current bucket occupancy Departing slot requests Bucket size = B tokens 10
Uplink MAC for UBR Services 4 No cell rate guaranteed (best effort) 4 Dynamic allocation of resources (Bandwidth on Demand) Satellite (Scheduler) Satellite (Scheduler) Bandwidth reallocation Bandwidth request Bandwidth reallocation Terminal UBR buffer: TDMA frame UBR cell Allocated resource for UBR service 11
Concept of the Developed MAC-Protocol 4 Uplink h MF-TDMA with 24 ms frame duration (48 Byte Payload 16 kbit/s) h Terminals transmit cells in bursts h Variable burst length 4 Downlink h -cells and MAC-signaling are broadcast in a continuous bitstream Uplink Downlink BTP Resource request 24 ms BTP Bursts of users Scheduler resource allocation is broadcast in a burst time plan (BTP) every 24 ms BTP Frame, 24 ms Bursts of users BTP 12
Uplink MAC Structure TDMA Frame Reservation area Contention area User 1 User 2 User 3 Movable boundary Movable boundary CBR assigned slots BoDslots Mini-slot (control slot), used for DLC layer signalling Guard time Random access slots, for initial access and out-of-band signaling Slot length = multiple of mini-slot, guard time 13
Features of the DLC Layer Protocol Implemented in the Demonstrator (Complete SDL-Specification) 4 TDMA Frame Synchronisation 4 Authentisation and Registration 4 Connection Setup and Release (incoming and outgoing calls) 4 More than one connection per terminal is possible 4 Uplink data rates: up to 2 Mbit/s, downlink up to 30 Mbit/s (in steps of 16 kbit/s) 4 Dynamic DLC channel allocation for transmission of signaling cells 4 Support of CBR, UBR and UBR+ service categories 4 Addressing of logical switch ports of the modified switch in the satellite 14
Model of DLC Layer Realized in the Demonstrator (Uplink) UNI (LME) UNI (LME) DLC Control CBR VPI/VCI? UBR+ DLC Control, Scheduler TID CTRL TID TID T-DLC PHY Queues Server UBR Sig Cells CTRL S-DLC X 15
Model of DLC Layer Realized in the Demonstrator (Downlink) UNI (LME) UNI (LME) DLC Control DLC Control, Scheduler T-DLC PHY BTP CTRL BTP X Yes TID? or BTP?... No BTP S-DLC TID TID CTRL TID CTRL Pr. 1 Pr. 3 every 24 ms TID Pr. 2 Dummy Bits Pr. 4 TID CTRL... TID TID... TID... BTP 16
Demonstrator (MAC) OC3 Ethernet OC3 Ethernet OC3 Ethernet Terminal 1 DLC PC (MAC, LLC) Terminal 2 DLC PC (MAC, LLC) Terminal 3 DLC PC (MAC, LLC) Uplink, Downlink PC Wireless Link- Emulation: Packet Errors, Collisions, Delay, Broadcasting full-duplex Ethernet Monitor, Control PC Uplink bit rate: 2 Mbit/s Downlink bit rate: up to 32 Mbit/s Satellite DLC PC (Scheduler) Load Generator OC3 Ethernet Fixed network Switch Controller Signalling Workstation OC3 17
Schlussfolgerungen 4 Das MAC Protokoll für das System berücksichtigt die verschiedenen Dienstkategorien 4 Der zentrale Scheduling-Algorithmus im Satelliten garantiert QoS 4 Das MAC Protokoll nutzt effizient die zur Verfügung stehende Bandbreite durch die dynamische Allokierung der Ressourcen (Bandwidth on Demand) 4 Das MAC-Protokoll wurde in SDL spezifiziert und in einem Demonstrator implementiert 18