SDR’ ’04 04 – – Phoenix Phoenix SDR Modular Link Layer Functions of Modular Link Layer Functions of a Generic Protocol Stack for a Generic Protocol Stack for Future Wireless Systems Future Wireless Systems L. Berlemann, A. Cassaigne, R. Pabst and B. Walke Chair of Communication Networks (ComNets) RWTH Aachen University, Germany 2004 Software Defined Radio Technical Conference and Product Exposition, November 17 th 2004, Phoenix, USA L. Berlemann, ComNets, RWTH Aachen University
Overview Overview Overview – Introduction – Generic Stack – Modular Approach - Realization - Outlook • Introduction and Motivation • Generic Protocol Stack in the Context of Multi-Mode Capable Wireless Networks • Modular Approach • Realization of Protocol Layers • Conclusion and Outlook L. Berlemann, ComNets, RWTH Aachen University 2
Introduction and Motivation and Motivation Introduction Overview – Introduction – Generic Stack – Modular Approach - Realization - Outlook • Idea: Protocols share a lot of communalities, that can be exploited in an efficient reconfigurable wireless system � Generic Protocol Stack • Advantages: runtime reconfigurability, maintainability, code/resource sharing and accelerated protocol development through reusability • Generic part is crucial: Tradeoff - general usability vs. implementation effort • Two approaches for realization, depending on the abstraction level of identified similarities: – Parameterizable modules including fundamental protocol functions – Inheritance of generic part(s) [1] [1] M. Siebert, B. Walke, “ Design of Generic and Adaptive Protocol Software (DGAPS), ” in Proc. of 3Gwireless '01, San Francisco USA, June 2001 L. Berlemann, ComNets, RWTH Aachen University 3
Generic Protocol Stack Generic Protocol Stack Overview – Introduction – Generic Stack – Modular Approach - Realization - Outlook 4. 3. 2. 1. • Protocol Reconfigurability (step 4) • • • • Development of standard-specific supplements (step 2) Identification of similarities (step 1) Integration to a system specific protocol/layer (step 3) Generic Protocol Stack – Combined with reconfiguration management and – layer by layer analysis – features and functions unique to the respective system – merging of generic and specific parts (modular – provides characteristics for all systems functions: a flexible as well as efficient realization of a composition or inheritance) technology – will serve as a basis for future software design – extraction of common features reconfigurable protocol stack – representation of the individual behavior of a system (reusability) L. Berlemann, ComNets, RWTH Aachen University 4
Enabling Transition between Multiple Modes Enabling Transition between Multiple Modes Overview – Introduction – Generic Stack – Modular Approach - Realization - Outlook … with the help of a Modes Convergence Protocol . protocol status cross stack management information including modes transition management-plane convergence protocol user-plane + control-plane RLC RLC common common part part MAC MAC specific MAC2 specific specific MAC1 MAC2 part part part PHY1 PHY2 PHY2 protocol protocol stack mode 1 stack mode 2 • Separation into specific/generic part in each layer • Management of (parallel existing) protocol stack/layer • Administration of user data (seamless mode transition) • Cross layer optimization (preservation of protocol status info) • Support of network-initiated reconfiguration L. Berlemann, ComNets, RWTH Aachen University 5
Generic Protocol Functions of the Data Link Layer Generic Protocol Functions of the Data Link Layer Overview – Introduction – Generic Stack – Modular Approach - Realization - Outlook • Modern communication protocols cannot be forced into classical layered architecture of ISO/OSI RM • Though belonging to Data Link Layer, common fundamental protocol functions can be found in multiple layers (2-4): • Error handling - Forward Error Correction or Automatic Repeated reQuest protocols [2] • Flow control • Segmentation, concatenation and padding of PDUs* • Multiplexing and De-Multiplexing • Dynamic Scheduling • Ciphering [2] L. Berlemann, A. Cassaigne and B. Walke, • Header Compression “Generic Protocol Functions for Design and Simulative Performance Evaluation of the Link-Layer for Reconfigurable Wireless Systems,” in Proc. of WPMC’04 , Abano Terme Italy, September 2004 L. Berlemann, ComNets, RWTH Aachen University 6
Modular Approach Modular Approach Overview – Introduction – Generic Stack – Modular Approach - Realization - Outlook • Common protocol functions as parameterizable modules and system- specific modules form a complete protocol layer • Communication inside: generic service primitives and generic PDUs • Functional Module : Realizes funda- mental functionality as black box • Manager : Composition, rearrange- ment, parameterization and data query of modules; Administration of internal communication • Interface : Translation of generic service primitives to specific ones • Service Access Point : Is needed, if a classical layer is demanded for fitting into ordinary stack � Simulation and performance evaluation on several levels: (sub-)layer as well as complete protocol stack L. Berlemann, ComNets, RWTH Aachen University 7
Parameterization of Functional Modules Parameterization of Functional Modules Overview – Introduction – Generic Stack – Modular Approach - Realization - Outlook Parameterization implies: • Specification of a value • Switching on/off of a behavior or functionality • Extension of the modules’ interface Segmentation module as example: • Use of concatenation • Targeted PDU size after handling • Use of Padding, i.e. filling up of a PDU to reach a certain size • Transmitter/Receiver Role • Buffer size for SDUs concatenated in a single PDU • Behavior in case of an error, i.e. interworking with ARQ module L. Berlemann, ComNets, RWTH Aachen University 8
Exemplary Protocol Layers Exemplary Protocol Layers Overview – Introduction – Generic Stack – Modular Approach - Realization - Outlook TCP/UDP/IP UMTS RLC 802.11 MAC L. Berlemann, ComNets, RWTH Aachen University 9
Segmentation Module as Example Segmentation Module as Example Overview – Introduction – Generic Stack – Modular Approach - Realization - Outlook SDU is separated into PDUs to fit to transport channel Here: Segmentation aspects of UMTS RLC in Unacknowledged Mode channel utilization, packet segmentation size of channel = 128 Byte payload / channel capacity 1 = protocol overhead fixed capacity of a channel packet size of payload is 0.9 channel utilization without concatenation � fixed segmentation size increased � increased 0.8 protocol overhead with payload/channel capacity channel utilization � concatenation 0.7 4th channel channel utilization: additional channel required 3rd channel 0.6 0.5 l payload 2nd channel payload = 0.4 l channel capacity packet size payload 0.3 packet size sim.: with concatenation 0.2 sim.: without concatenation analyt.: with concatenation 0.1 analyt.: without concatenation 1st channel packet size of payload is 0 0 50 100 150 200 250 300 350 400 450 500 increased payload packet size l payload [Byte] • Protocol overhead vs. optimized channel utilization • The segmentation module reflects the known behavior � it can be legitimately used in an multi-mode capable protocol stack L. Berlemann, ComNets, RWTH Aachen University 10
Conclusion and Outlook Conclusion and Outlook Overview – Introduction – Generic Stack – Modular Approach - Realization - Outlook The identified similarities are decisive for success • � tradeoff of genericity Generic protocol stack takes up well-proven and known • fundamental protocol functions Existing (as shown) and future protocols (4G) can be • composed out of adequately parameterized modules Library of common functions results in a construction kit for • accelerated protocol development Efficient protocol reconfigurability through parameterization • is enabled on the basis of functional modules The introduced approach is a first step to an efficient multi-mode capable wireless system L. Berlemann, ComNets, RWTH Aachen University 11
Thank you for your attention ! Lars Berlemann ber@comnets.rwth-aachen.de L. Berlemann, ComNets, RWTH Aachen University 12
PIMRC 2005 EW’ ’05 05 PIMRC 2005 EW 11 th European Wireless Conference The 16th Annual IEEE International Symposium on Personal Indoor and “Next Generation Wireless and Mobile Mobile Radio Communications Communications and Services” Nicosia, Cyprus Maritim Hotel, Berlin, Germany April 10 - 13, 2005 September 11 – 14, 2005 http://www.european- http://www.pimrc2005.de wireless2005.de L. Berlemann, ComNets, RWTH Aachen University 13
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