Topics in Computer Networks 2010 � Introduction, What is CrossLayer Design ? Mesh Network Cross Layer Design : Seminar 3 � Taxonomy of cross-layer methods � Detailed overview on cross-layer interactions Jonas Karlsson Karlstad Universitet Summary Summary Email: jonas.karlsson@kau.se Slides adopted from ”Cross-layer Air Interface Design for Wireless Systems” - Dr. Giovanni Giambene, “Cross Layer Overview” - Murad Khalid and “Cross-Layer Design in Wireless Networks” - Philipp Hurni ISO/OSI reference model: end ISO/OSI reference model: end- -to to- -end dialogue 1/2 end dialogue 1/2 Source Destination User-to-network Application Application Interface Presentation Presentation Session Session Relaying Transport Transport Network Network Network Network Link Link Link Link Physical level Phy. Lev. Phy. Lev. Physical level Introduction Physical medium End System, A Intermediate System End System, B (network) Communication Systems are organized and divided into layers. Each layer is � built on top of the one below it. � Reduced Complexity: each layer should fulfill a limited and well defined purpose. Each layer offers services to the respective higher layer. It encapsulates the � implementation specific details and provides an abstract interface for its service 1
ISO/OSI reference model: end ISO/OSI reference model: end- -to to- -end dialogue 2/2 end dialogue 2/2 ISO/OSI reference model: Advantages ISO/OSI reference model: Advantages � Interface should provide only a limited set of � Modularity/Simplicity primitives ◦ implementation details are hidden behind abstract Interfaces – facilitates programming tasks � No assumptions / dependencies with the layer � Layer interfaces can be easily standardized above. ◦ only rely on primitive operations of the adjacent ◦ facilitates interoperability among different software, lower layer network hardware, and operating systems � “Divide and Conquer” � Each layer adds header and/or trailer information. ◦ complex problem is broken into smaller manageable problems ◦ This information is only intended for the peer layer in the destination stations and not for lower � Flexibility/ interchangeability / least impact on layers. (i.e. reading the header/trailer changes information of layer 4 in layer 3) ◦ changes/updates in one layer do not affect the � Information exchange and coupling between upper and lower layers layers should be kept as low as possible. ◦ layers can be replaced, new layers can be introduced Current view of the Internet protocol stack Challenging characteristics of wireless communications Challenging characteristics of wireless communications � The TCP/IP protocol stack follows Applications the OSI reference model guidelines � Lack of channel reliability (need of to a large degree. countermeasures: coding, retransmissions, modulation techniques, diversity, etc.) � The success of the TCP/IP based RTP Internet and the fast progress is � Dynamically varying channel characteristics based on its modular layer TCP � Bandwidth shortage : architecture. UDP ◦ Necessity of managing the bandwidth in an � TCP/ IP has been designed and fits efficient way to support broadband applications very well for point-to-point communication in wireline IPv6/MIPv6 � QoS support for multimedia traffic classes communication systems. � Pathloss / inaccuracies ( what exactly is a Eth 3G, Blu WiFi, AD “link” ? ) Sate ern WiM eTo SL ax llite et oth 2
Disadvantages of the OSI model Layered design and wireless communications Layered design and wireless communications � The OSI layered approach has some ‘limits’ in the case of wireless communications: � The needs of a service provided by the communication system to its users are ◦ Lack of flexibility : It is not flexible enough to cope with the defined at the top-level. The hierarchy and dynamics of mobile networks. the overall performance of the system is ◦ Redundancy & inefficiency : it is inadequate to optimize each however build upon the bottom-level. layer independently in the wireless scenario. There exists tight interdependence between layers. � Each layer can be considered as a black-box, with a simple send/receive API. Such ◦ Restrictive : layer N may need access to lower layers than N-1. information hiding is a simple approach, but � Multiradio/multichannel, directional antenna, MIMO can lead to poor performance. � Multi-hop: � The bottom level does not communicate ◦ Accumulated effect directly, but through all higher layers with the � MAC, routing, and transport protocols have to work top-level. Information is lost during this layer- together with the physical layer. by-layer conversion. � Layers are independently optimized. Available approaches for cross Available approaches for cross- -layering layering Available approaches for cross Available approaches for cross- -layering layering Application Application Application � Vertical Coupling Application Transport Transport Transport ◦ The QoS metric at application layer is used Transport Network Network Network to fine tune all the lower layer parameters Network DATA + PHY Data Link at the application layer; e.g., delay Data Link ( new protocol for Data Link requirement metric is used to tune the MAC Layer Physical multipacket Phy ) level ARQ timer and modulations and at Physical Merging Physical Info. network layer must use routing protocol to ( Multipacket capability ) route packets through congestion free Coupling Design routes Information coupling between layers Coupling � Vertical ◦ Static Vertical Coupling ◦ Defines additional interface between non-adjacent layers to exchange parametric info. for Coupling performance optimization � Parameters are defined based on some metric Merging layers � at design time ◦ PHY and MAC layer exchange information more frequently and therefore can be merged as “MAPHY”; e.g, link adaptation for link QoS ◦ Dynamic Vertical Coupling Design coupling between layers � � Parameters are exchanged in runtime to ◦ A new protocol at a layer is designed to accommodate new features of another layer; e.g., tweak the values for some pre-defined metric multi-packet capture at Phy layer needs modification at MAC layer Vineet Srivastava, Mehul Motani, "Cross-Layer Design: A Survey and the Road Ahead", IEEE Communcations Magazine , December 2005, pp. 112-119 Vineet Srivastava, Mehul Motani, "Cross-Layer Design: A Survey and the Road Ahead", IEEE Communcations Magazine , December 2005, pp. 112-119 3
Cross-layer exchange of information Detailed view of possible cross Detailed view of possible cross- -layer interactions layer interactions QoS requirements, QoS requirements, priority level, service class, etc. priority level, service class, etc. Application Application Scaling of multimedia Scaling of multimedia flow flow � Although interfaces between adjacent layers are in TCP version, TCP version, Transport Transport cwnd & ssthresh cwnd & ssthresh general preferable, there can be the need for efficient values values Receiver congestion Receiver congestion indication indication and direct interaction between non-adjacent layers ; in Network Network general, a layer should be aware of the other layers of the Explicit congestion Explicit congestion notification notification (network congestion) (network congestion) protocol stack. AQM AQM Link Link Link capacity Link capacity saturation saturation (link congestion) (link congestion) � Cross-layer information can be exchanged from higher to Need of a cell Need of a cell handover and handover and Physical Physical lower layers ( top-down approach ) or from lower to higher related resource related resource Selected Selected allocation with allocation with ACM mode ACM mode re-routing in the re-routing in the layers ( bottom-up approach ). Coordination of both network network End host End host exchanges is necessary to avoid loops in the system and oscillating behaviors. Examined papers Examined papers � The following papers provide a good description on cross-layer methods in different scenarios. ◦ Q. Wang, M.-A. Abu-Rgheff, “Cross-layer Signalling for Next-Generation Wireless Systems”, IEEE Wireless Communications and Networking Taxonomy of cross-layer methods Conference (WCNC) , 16-20 March 2003, New Orleans, USA. ◦ M. Conti, J. Crowcroft, G. Maselli, G. Turi, “A Modular Cross-Layer Architecture for Ad Hoc Networks”, Chapter 1 in Handbook on Theoretical and Algorithmic Aspects of Sensor, Ad Hoc Wireless, and Peer-to-Peer Networks , Jie Wu (editor), CRC Press, New York, 2005. ◦ V. Vardhan, D. G. Sachs, W. Yuan, A. F. Harris, S. V. Adve, D. L. Jones, R. H. Kravets, K. Nahrstedt,“GRACE: A Hierarchical Adaptation Framework for Saving Energy”, Computer Science, University of Illinois Technical Report UIUCDCS-R-2004-2409 , February 2004. 4
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