CHORIST

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CHORIST

  1. 1. Project number: European Commission - 033685 Project acronym: CHORIST Project title: Integrating Communications for enhanced environmental risk management and citizens safety Instrument: Integrated Project Thematic priority: Information Society Technology Call identifier: FP6-2005-IST-5 Start date of project: 01/06/06 Duration: 36 months Deliverable reference number: SP4.D5 Deliverable title: Report on Broadband Network Definition and Design (PUBLIC VERSION) Version: 1.0 State within Consortium: DRAFT: - FOR APPROVAL: - APPROVED: X Due date of deliverable: MONTH 10 (03/07) Actual submission date: 25/06/07 Lead contractor of this deliverable: EURE Other contributing contractors: THC TKK Project co-funded by the European Commission within the Sixth Framework Programme (2002-2006) DISSEMINATION LEVEL PU Public X PP Restricted to other programme participants (including the Commission Services) RE Restricted to a group specified by the consortium (including the Commission Services) CO Confidential, only for members of the consortium (including the Commission Services)
  2. 2. Project: CHORIST Deliv. ref.: SP4.D5 Deliv. title: Report on Broadband Network Definition and Design EC contract: 033685 Deliv. version: 1.0 Submission date: 25/06/07 CONTENTS 1 INTRODUCTION.........................................................................................................3 1.1 PROJECT SCOPE ................................................................................................................... 3 1.2 PURPOSE OF THE DOCUMENT ................................................................................................ 3 1.3 DOCUMENT VERSIONS SHEET ................................................................................................ 3 2 REFERENCE DOCUMENTS AND ABBREVIATIONS ...............................................4 2.1 REFERENCE DOCUMENTS ...................................................................................................... 4 2.2 ABBREVIATIONS .................................................................................................................... 4 3 EXECUTIVE SUMMARY.............................................................................................6 4 BROADBAND NETWORK ARCHITECTURE OVERVIEW ........................................7 4.1 INTRODUCTION ..................................................................................................................... 7 4.2 FROM OPERATIONAL DEPLOYMENT CHARACTERISTICS TO NETWORK ORGANIZATION ................ 7 4.2.1 Operational deployment characteristics........................................................................................ 8 4.2.2 Mapping into network organization ............................................................................................... 9 4.3 FUNCTIONAL APPROACHES AND CONCEPTS ......................................................................... 11 4.3.1 Label switching framework for efficient QoS management......................................................... 11 4.3.2 Inter-vehicular mobile core network: MAC topology ................................................................... 13 5 COVERAGE EXTENSION OF THE BROADBAND NETWORK ..............................17 5.1 EXTENDING THE BROADBAND ACCESS NETWORK.................................................................. 17 5.2 COMPONENTS IDENTIFICATION ............................................................................................ 18 5.2.1 PHY and MAC layer .................................................................................................................... 18 5.2.2 Routing protocols ........................................................................................................................ 19 5.2.3 Applications ................................................................................................................................. 21 5.3 INTERACTION BETWEEN THE WIMAX AND THE 802.11 PART................................................. 21 6 CONCLUSION ..........................................................................................................23 Page: 2 / 23
  3. 3. Project: CHORIST Deliv. ref.: SP4.D5 Deliv. title: Report on Broadband Network Definition and Design EC contract: 033685 Deliv. version: 1.0 Submission date: 25/06/07 1 INTRODUCTION 1.1 PROJECT SCOPE The CHORIST project will propose solutions to increase rapidity and effectiveness of interventions following natural hazards and industrial accidents, in order to enhance citizens' safety and communications between rescue actors. 1.2 PURPOSE OF THE DOCUMENT This document details the definition of the broadband ad hoc communications systems developed under the frame of the SP4, which will be interconnected to the different systems deployed on the crisis site. This communication system relies on enhancements of WiMAX technology combined with label-switching features. This document described the identified key concepts for enabling fast deployment, communications flows Quality of Service and priority management and interoperability. 1.3 DOCUMENT VERSIONS SHEET Version Date Description, modifications, authors 1.0 25/06/05 First release by EURE and THC Table 1 : Document versions sheet Page: 3 / 23
  4. 4. Project: CHORIST Deliv. ref.: SP4.D5 Deliv. title: Report on Broadband Network Definition and Design EC contract: 033685 Deliv. version: 1.0 Submission date: 25/06/07 2 REFERENCE DOCUMENTS AND ABBREVIATIONS 2.1 REFERENCE DOCUMENTS [1] H. Sollman et al., “Hierarchical MIPv6 Mobility Management,” IETF draft, draft-ietf-mobileip-hmipv6- 05.txt, July 2001, work in progress. [2] E. C. Rosen, A. Viswanathan, and R. Callon, “Multiprotocol label switching architecture,” 2001, Network Working Group, Request for Comments, http://www.ietf.org/rfc/rfc3031.txt. [3] L. Romdhani and C. Bonnet, "Cross-layer's paradigm features in MANET: benefits and challenges", PWC 2005, Colmar, France, August 25-27, 2005. [4] ROHDE & SCHWARZ, Operating Manual, Spectrum Analyzer, FSEA20/30, FSEM20/30, FSEB20/30 [5] Packet Sniffer, http://www.wildpackets.com/products/airopeek/airopeek_nx/overview [6] Sachin Garg, Martin Kappes. ″An experimental Study of Throughput for UDP and VoIP Traffic in IEEE 802.11b Networks,’ Wireless Communicating and Networking″ 2003. IEEE Volume 3, 16-20 March 2003 pages: 1748-1753 vol 3 [7] P. Jacquet, P.Muhlethaler, T.Clausen, A.Laouiti, A.Qayyum and L.Viennot, ″Optimized Link State Routing Protocol for Ad Hoc Networks ″ [8] http://cs.itd.nrl.navy.mil/work/olsr/index.php [9] Joseph P. Macker, Justin Dean, William Chao, Information Technology Division, Naval Research Laboratory, ″Simplified Multicast Forwarding in Mobile Ad hoc Networks″ [10] User guide for RAT v3.0.33, available at, [11] http://www-mice.cs.ucl.ac.uk/multimedia/software/documentation/ug-rat3.0.33-9903.pdf [12] User guide for VIC v2.8, [13] Available at, http://www.vrvs.org/Documentation/Applications/vic-userguide2.pdf [14] Sachin Garg and Martin Kappes, ″Can I add a VoIP call?″, Communications, 2003. ICC '03. IEEE International Conference on [15] Malathi Veeraraghavan, Nabeel Cocker and Tim Moors, ″Support of voice services in IEEE 802.11 wireless LANs″, INFOCOM 2001. Twentieth Annual Joint Conference of the IEEE Computer and Communications Societies. Proceedings. [16] V. Conan et al. ., “System specification – Security, QoS, MAC, routing requirements and interfaces specifications”, IST FP6 WIDENS, Deliverable D2.2, July 2004. 2.2 ABBREVIATIONS HMIP Hierarchical Mobile IP MPLS Multi Protocol Label Switching LSR Label Switching Router LER Label Edge Routers FEC Forwarding Equivalence Class LSP Label Switching Path WiMAX Worldwide Interoperability for Microwave Access Page: 4 / 23
  5. 5. Project: CHORIST Deliv. ref.: SP4.D5 Deliv. title: Report on Broadband Network Definition and Design EC contract: 033685 Deliv. version: 1.0 Submission date: 25/06/07 UDP User datagram Protocol AODV Ad hoc On Demand Distance Vector AS Autonomous System BSS Basic Service Set CH Cluster Head DCF Distributed Coordination Function E-CDS Essential Connecting Dominating Set IP Internet Protocol MAC Medium Access Control MANET Mobile Ad hoc Networks MPR Multi-Point Relay MPR-CDS Multi-Point Relay Connected Dominating Set NS-MPR Non Source specific Multi-Point Relay OLSR Optimized Link State routing Protocol PCF Point Coordination function PDA Personal Digital Assistant QoS Quality of Services RF Radio Frequency RTP Real Time Protocol SMF Simplified Multicast Forwarding S-MPR Source specific Multi-Point Relay Page: 5 / 23
  6. 6. Project: CHORIST Deliv. ref.: SP4.D5 Deliv. title: Report on Broadband Network Definition and Design EC contract: 033685 Deliv. version: 1.0 Submission date: 25/06/07 3 EXECUTIVE SUMMARY As identified by the deliverables SP4.D1 and SP4.D2, Public Safety units require a reliable communication broadband system and services that does not need heavy management operations involvement in order to allow them to increase their efficiency during their critical interventions. In order to respond to these operational needs, such a deployable communication system has to address to following issues: efficient management of the communication flows, advanced and distributed mechanisms to enable the self- formation of the network to be deployed on the crisis site, automated enforcement of Quality of Service treatment and priority insurance and interconnection with existing communication infrastructure. This document explains how these features can be achieved by relying on advanced combination of WiMAX enhancements and particular reservation scheme based on label-switching operations. Therefore, first an overview of the communication system is provided. More specifically, it analyse the main characteristics of Public Safety units deployment in order to explain the technical choices to structure the deployable network infrastructure. Then it identifies the main functionalities that have to be integrated to the deployed communication equipments in view to automatically set up a communication infrastructure on the crisis-site. Then this document explains how the CHORIST WiMAX mesh could be connected to the world of IP based routing via the edge routers. As a result, standardized 802.11 and 802.16 cell extensions to the WiMAX mesh could be supported via these routers. The cell extensions increase the coverage area and add mobility support to the WiMAX mesh. Especially the 802.11 technology provides a cost effective solution for public safety that has been already tested in practice. The protocol stack that would be used in infrastructure-less and infrastructure based 802.11 cell extensions to the mesh is described. Particularly, the IEEE 802.11b/g PHY and MAC layer parameters are determined.-Then the unicast and multicast applications handling the forwarding of data packets within the MANET routing area are presented. Two critical applications for public safety, namely the VoIP and the real-time video communications are presented; and two open source applications that support multicast voice and video are introduced. Finally, open issues and challenges regarding the interaction between the WiMAX mesh and the 802.11 cell extensions with respect to the QoS provisioning are outlined. The conclusion summarizes the key points of the approach and their benefits. Page: 6 / 23
  7. 7. Project: CHORIST Deliv. ref.: SP4.D5 Deliv. title: Report on Broadband Network Definition and Design EC contract: 033685 Deliv. version: 1.0 Submission date: 25/06/07 4 BROADBAND NETWORK ARCHITECTURE OVERVIEW 4.1 INTRODUCTION As identified by the deliverables SP4.D1 and SP4.D2, Public Safety units require a reliable communication broadband system and services that does not need heavy management operations involvement in order to allow them to increase their efficiency during their critical interventions. In this way, the identified requirements can be classified depending on their level of impact on the different functions instantiated by the communication system that has to be deployed on the crisis site. They can be decomposed as follows: • The requirements impacting on particular efficient management of the communication flows; • The requirements calling for advanced and distributed mechanisms to enable the self-formation of the network to be deployed on the crisis site; • The requirements necessitating the automated enforcement of Quality of Service treatment and priority insurance; • The requirements relying on the interconnection with existing communication infrastructure. Figure 1: Example of Public Safety units deployments characteristics (Source: [16]) Therefore, in view to understand how all these functionalities have to be not only integrated but also orchestrated by the broadband ad hoc network developed under the frame of the SP4, this section explains first how the communication system has been elaborated in order to dynamically fit with operational deployment of Public Safety units, before describing how the chosen approach would allow easy interconnection with current and future telecommunications infrastructure in term of compliance with security architecture/policies and of end-to-end management of performance and Quality of Service. Moreover, after these explanations the following sections will enter into the details of each identified functionalities. 4.2 FROM OPERATIONAL DEPLOYMENT CHARACTERISTICS TO NETWORK ORGANIZATION Before entering into the technical concepts and design of the broadband ad hoc network functionalities, this section details first the key ideas of the global approach extracted from the analysis of the core requirements expressed through the SP1.D6, SP1.D8, SP4.D1 and SP4.D2. In this way, the objective of this section is to Page: 7 / 23
  8. 8. Project: CHORIST Deliv. ref.: SP4.D5 Deliv. title: Report on Broadband Network Definition and Design EC contract: 033685 Deliv. version: 1.0 Submission date: 25/06/07 provide a high level overview of the system by explaining the technical choices identified to respond to Public Safety requirements in view to elaborate future emergency communication systems not only rapidly deployable but also interoperable on the crisis site. 4.2.1 Operational deployment characteristics As reminded previously, one of the key requirements that the broadband has to take into account is its ability to fit with Public Safety units’ characteristics of deployment. Therefore, before explaining how the communication system is intrinsically organized to support emergency operations, it is important to underline the main characteristics of Public Safety units’ deployment. Generally, most of the deployments are constituted of the following entities: • The vehicles, which carry both users and material that have been identified as needed to ensure the emergency intervention. An interesting technical point is that vehicles are equipped with power supplies. In this way, they can embed communication equipments, which require sufficient energy to build an efficient wireless network; • The Public Safety users, which potentially use radio terminals to communicate in view to coordinate their actions. An important technical point is that the radio terminals do not have to impact on the Public Safety users operations. Thereby, the radio terminals have to enable mobility, to be sufficiently small and powerful for required safety applications. An example of a deployment involving the above described entities is illustrated by the Figure 1. In addition, the communication system that Public Safety users deploy on the crisis site can be decomposed into the following functional components, as mentioned by the SP4.D2: • A base station, which manages appropriately the network resources in order to enable communications between radio terminals used by Public Safety users required during emergency operations. In this way, the base station offers to and organizes for the deployed units advanced services necessary during an intervention (e.g. voice group communications); • A set of radio terminals, which can be mobile or not and that are used by Public Safety users to initiate voice communications or to share information; • One or several gateways allowing the interconnection to existing telecommunication infrastructures and to access to particular external services or databases (e.g. maps, medical files). Base Station Radio Terminals Figure 2 : An example of a TEDS communication system Page: 8 / 23
  9. 9. Project: CHORIST Deliv. ref.: SP4.D5 Deliv. title: Report on Broadband Network Definition and Design EC contract: 033685 Deliv. version: 1.0 Submission date: 25/06/07 An example of such functional components deployed to form a communication system on a crisis site is illustrated by the Figure 2, which takes as example the TEDS technology (extracted from the SP4.D2). Therefore, in order to not only fit with Public Safety organizational structures but also to ensure the design of a flexible communication system that would be rapidly deployable and easily interoperable in view to respond to an emergency situation, the broadband communications system elaborated by the SP4 will benefit of the above characteristics in its intrinsic organization to be efficient and reliable. Such a mapping is explained in the following section. 4.2.2 Mapping into network organization As suggested previously and mentioned by the SP4.D2, the broadband communication system will be composed by the following components: • Stationary Nodes, which are semi-mobile communication equipments. These equipments can be embedded into vehicles (e.g. fire truck). Their objective is to spontaneously form an inter-vehicular ad hoc network suitable for the emergency operation. In this way, they constitute a wireless mesh core network, which will have not only to support all the communications between Public Safety users’ terminals but also to provide access to existing telecommunications infrastructures and access to external databases. Note that they can be also interfaced with another wireless mobile ad hoc network or with IP backbones. • Mobile Nodes, which are the mobile equipments used by Public Safety professionals. These mobile nodes integrate all the required applications and services necessary to respond to a particular emergency intervention. Moreover, for particular scenarios, such as a fire in a tunnel or an operation inside a building, the mobile terminals can constitute an ad hoc network extending the coverage of the stationary nodes wireless mesh core network. Note that for flexibility in the design, the mobile nodes can be instantiated by several kind of equipments, such as mobile phones, laptop computers, notebooks or Personal Digital Assistants (PDA). Figure 3 : Conceptual overview of the wireless mobile broadband communication system Page: 9 / 23
  10. 10. Project: CHORIST Deliv. ref.: SP4.D5 Deliv. title: Report on Broadband Network Definition and Design EC contract: 033685 Deliv. version: 1.0 Submission date: 25/06/07 Conceptually, the wireless technologies used for the stationary and the mobile nodes have not to be the same, since the radio coverage required for those two communication equipments is different. In fact, the mobile nodes are used locally around the network constituted by the vehicles: they mainly require small radio range than the vehicles one (however it is not mandatory). The stationary nodes are used, as mentioned, to spontaneously form a wireless core network and therefore need to fit with potentially wide emergency area: their radio range should be as large as possible. The Figure 3 illustrates an example of such a network infrastructure dedicated to Public Safety. Figure 4 : Architecture overview of the rapidly deployable and interoperable broadband emergency communications system In the context of CHORIST, WiMAX and WiFi have been identified as the most appropriate wireless technologies to be investigated and therefore have to be mapped on the previously presented broadband communication system architecture that has to be deployed on the crisis site. Naturally, the WiMAX technology will be used as basis for the elaboration of the mobile core network, since it integrates both long range and QoS capabilities. Moreover, WiMAX can be used to form easily deployable mesh networks, which can constitutes an interesting possibility to elaborate core networks functionalities. However, WiMAX technology, as it is, appears to be limited to fulfil most of the identified Public Safety users requirements and, therefore, needs design enhancements in view to support mobility features and self- formation of emergency communication infrastructure. The details of such extensions integrated to WiMAX technologies are detailed in section 7. Note also that the interconnection with existing telecommunications infrastructures can be implemented by relying on WiMAX technology: in this case a WiMAX backhaul link is integrated within the networks deployed on the emergency area. Page: 10 / 23
  11. 11. Project: CHORIST Deliv. ref.: SP4.D5 Deliv. title: Report on Broadband Network Definition and Design EC contract: 033685 Deliv. version: 1.0 Submission date: 25/06/07 In addition, in view to enable the possibility to develop low cost, open, powerful, mobile and potentially handled devices that will be used by Public Safety users on the field, the WiFi technology will be used for the instantiation of the Local Wireless Cell (i.e. local range wireless technology) and for the instantiation of the ad hoc coverage extensions (allowing to extend the envisaged scenarios to tunnels and buildings emergency operations), since WiFi technology can be used both in infrastructure mode (to form wireless cells) or in ad hoc mode (to spontaneously constitute an ad hoc network). In this way, fulfilling the role of the inter-vehicular mobile core network, the WiMAX enhanced mesh network will require to be complemented by technologies acting on top, which are able to integrate intrinsically end- to-end QoS insurance, communications flows priority and mobility management capabilities. Note that such mechanisms will have to be compliant to QoS approaches used in existing telecommunications infrastructures in order to enable efficient interoperability (e.g. to ensure the required performance of the communications between the Public Safety units deployed on the field and their head quarter or the Public Authorities). The Figure 4 illustrates the broadband communications system architecture dedicated to Public Safety users that will integrate rapid deployment and interoperability capabilities. Before entering into their details, the following section will list the functional building blocks that will be integrated to and orchestrated by the broadband communication system. 4.3 FUNCTIONAL APPROACHES AND CONCEPTS 4.3.1 Label switching framework for efficient QoS management The Multi-Protocol Label Switching elaborated by the IETF [2] provides a common standard to transport IP packets through sub-networks in switched mode. A protocol is in charge of distributing route references or labels what predetermines routes or Label switching paths (LSP) by establishing a link between the IP address of the destination and a label. The nodes are switch-router able to work both at IP level for realising routing processes or at frame level for executing switching decisions. The nodes involved in MPLS are classified in Label Edge Router (LER) and in Label Switched Router (LSR). A LSR is a router placed in the core network which participates in the setting up of a virtual circuit by which the frames will be transported. A LER is an access node to a MPLS network. A LER can have multiple ports allowing to access to different networks, each of them utilising its own switching technique. The LERs play an important role in the setting up of the references. MPLS has many advantages with the label concept. It combines the scalability and flexibility of routing with the performance, quality of service (QoS), and traffic management of layer 2 switching. 4.3.1.1 Identification of the nodes’ role In order to be applied by the inter-vehicular mobile core network, this section provides an overview of the label switching scheme, including a definition of the label and the label routing table. Note that unlike wired networks, the dynamic feature of the multi-hop ad-hoc networks make it challenging to design a reservation scheme to provide end-to-end QoS support. Indeed, providing Quality of Service for the rapidly deployable inter-vehicular core network is a difficult task, due to the fact that: 1. The capacity of the physical links is variable depending on factors such as the distance, signal to noise ratio or interference; Page: 11 / 23
  12. 12. Project: CHORIST Deliv. ref.: SP4.D5 Deliv. title: Report on Broadband Network Definition and Design EC contract: 033685 Deliv. version: 1.0 Submission date: 25/06/07 2. The transmission media is shared between different nodes that have to be synchronized; 3. The wireless nodes are generally mobile and the network topology may change; 4. High signalling overhead due to the recovery of already QoS reservations may be a problem due to the scarce transmission resources. Two functional roles can be identified for the wireless ad hoc nodes, constituting the inter-vehicular mobile core network: • The edge functionality (or access) which can be assimilated to the functionality of the LER in the wired networks in the MPLS framework. It is the first router to apply a label in order to direct the path and affect a priority to the packets. It can have multiple ports allowing to access to different networks, each of them utilising its own switching technique. It plays an important role in the setting up of the references. • The switching functionally which can be assimilated to the functionality of the LSR in the MPLS framework. It is a router inside the core network which participates in the setting up of a virtual circuit by which the frames will be transported based only on Label Switching. 4.3.1.2 Definition of the labels A label is a short, fixed-length identifier. Multiple labels can identify a path or connection from source node to destination node. The structure of the label is shown in Figure 5. Figure 5 : Label Format The first part of the label is related to multicast connection. It contains two parts, the first bit is a multicast flag and the following 3 bits are the number of total connections that come from this node. If the value of the flag is one, it means this is a multicast connection. The maximum number of total connections is eight. If the value of the flag is zero, it means this is a unicast connection and following 3 bits are 001, which means only one connection comes from this node. Page: 12 / 23
  13. 13. Project: CHORIST Deliv. ref.: SP4.D5 Deliv. title: Report on Broadband Network Definition and Design EC contract: 033685 Deliv. version: 1.0 Submission date: 25/06/07 Label is a 20-bit field after the multicast flag, which includes a node identifier. Therefore all labels are unique in the network. Considering wireless network, the coverage of each node could be different because of the power of the radio transmission module and signal propagation around these nodes. If a label could be shared between non-adjacent nodes, it could make a conflict after node movement or radio power adjustment. Also if nodes move quickly, non-adjacent nodes could be adjacent nodes very soon. One label conflict could result in a connection interruption in this scenario. In order to prevent the connection from interrupting, we must make the label unique in our ad hoc networks. After label field there are 3 bits for CoS, which means class of service. Here we have 8 classes of service, from level 0 to level 7. Each level corresponds to one queue. Level 7 is the highest priority level queue and level 0 is the lowest priority level. Queues are processed in strict priority order until all queues are empty. The last field of this label is TTL (time-to-live). All label information has a time-related restriction. Once the time is out for a label, all corresponding entries will be deleted from label routing table. Therefore we can maintain the label routing table and keep it fresh without making it too big. 4.3.1.3 Definition of the label routing table The main idea of this label switching scheme is based on the concept of label, which combines layer 2 and layer 3 together for the purpose of highly efficient routing in the ad hoc network. Instead of IP routing table we create a new table, the label routing table, to implement routing, packet forwarding, and path management. Each entry of the label routing table has the following fields: • Label in is the field for the label of the packet which should be processed. • Label out is the field for the label of the packet which should be forwarded. Label out field is bound with Label in field to identify one path or connection. MAC address of the node of the next hop could be embedded in Label out field to provide higher efficiency. Also this field could have multiple labels for multicast connection. Zero value of this field represents that the destination node of this path is reached and this packet will be transmitted to the host CPU for further processing. • Service level indicates the COS value in the label for QoS service. All service levels of sub- connections in the multicast traffic have the same value, in other words, they are in the same service level. • Source field is the source node ID of this path or connection. • Destination field is the destination node ID of this path or connection • Destination sequence number is the sequence number of destination node • Lifetime is the time-to-live of this path Each entry of the label cache table has the Label in field and Label out field. They are all copied from the label routing table by host CPU. In other words, they are controlled by host CPU and can be deleted anytime. If Label out of a receiving packet is zero, this packet will be transmitted to host CPU for further processing. The MAC address of next node in the path could also be placed in label-out field if the current node isn’t the destination. 4.3.2 Inter-vehicular mobile core network: MAC topology The following figure depicts the general architecture of the CHORIST SP4 inter-vehicular mesh broadband network where we distinguish different types of nodes, namely Cluster-head (CH), Mesh router (MR), Isolated Node (IN) and Edge Router (ER). Page: 13 / 23
  14. 14. Project: CHORIST Deliv. ref.: SP4.D5 Deliv. title: Report on Broadband Network Definition and Design EC contract: 033685 Deliv. version: 1.0 Submission date: 25/06/07 Cluster-Head Mesh Router Isolated Node Edge Router Other Access Technology Label 1 – Voice communication Label 2 – Video communication Figure 6 : Inter-vehicular mobile core network – MAC-layer topology Each node in the MAC topology will assume one of these roles at a given time instant depending on different parameters, namely geographic position, traffic distribution, presence of other access technologies and propagation-related effects which impact connectivity. It may assume the role of ER in addition to one of the other roles. We now describe in more detail each of these roles. 4.3.2.1 Role of Cluster-Head The primary role of the CH is to manage radio resources in their cluster. The cluster is defined as the set of nodes which are characterized by one-hop connectivity with the cluster-head. One-hop connectivity is further defined as the capacity to reliably receive and transmit basic signalling channels with the cluster-head using at least at the lowest data-rate communication mode. Reliable communication is defined by a transmission which falls below a maximal error probability threshold. CH can only be connected to MR on the same frequency-carrier since they use the same temporal resources as other CH. Thus direct CH CH communication is not possible on the same frequency carrier. The downlink (CH MR) signalling channels allow for the CH to schedule transmission of labels (in the form of time and frequency mappings on the radio resource) which each carry different types of traffic throughout the mesh network. The Uplink (UL) signalling channels (MR -> CH) are used for relaying bandwidth requirement indicators and channel quality measurements from nodes within the cluster. These feed the scheduling algorithms residing in the CH and allow for proper resource allocation satisfying quality-of-service (QoS) negotiations carried out using Layer 3 (L3) signalling. Page: 14 / 23
  15. 15. Project: CHORIST Deliv. ref.: SP4.D5 Deliv. title: Report on Broadband Network Definition and Design EC contract: 033685 Deliv. version: 1.0 Submission date: 25/06/07 The CH further provides mechanisms for measurement reporting to L3 (e.g. for routing, QoS management or labelling). This is achieved by a set of signalling channels which relay measurement information (UL) for the nodes in the cluster to the CH. The CH processes these raw measurements into a form which is expected by L3 mechanisms. Some CH can assume the role of network synchronization by sending special synchronization pilots (see section 4.3.2.6). These will be called Primary CH when network synchronization is achieved using this method. Other CH using this method are called Secondary CH. 4.3.2.2 Role of Mobile Router The primary role of an MR is to interpret the scheduling information from the CH on the DL signalling channels in order to route the traffic corresponding to the scheduled labels on the allocated physical resources. MR can be connected to other MR (direct link) in the same cluster. MR can also be connected to more than one cluster at the same time. It is also expected to using the UL signalling channels to relay measurements to the CH with which is connected. A secondary role of some MR is to search, on behalf of the CH, for IN which need to be connected to the mesh. These MR use a special signalling resource to exchange basic topological parameters with the IN which then results in overall network topology updates. If several IN are contending for access with the cluster, joint processing of the requests will be performed by the mesh during topology adjustments. The most likely nodes to assume this role will be those at the extremities of the mesh. 4.3.2.3 Role of Isolated Node The role of the isolated node is to achieve connectivity with the mesh as quickly as possible. It is thus a temporary state attributed to a node. It uses the basic signalling channel from the MR to obtain the information necessary to convey its’ request on the contention channel (RACH) which is relayed by the MR to its CH. 4.3.2.4 Role of Edge Routers (from MAC-layer perspective) An edge router is either a CH or MR with an IP interface to another network. The role of ER is to aggregate traffic (ingress) from IP flows to MPLS-like labels for transmission in the mesh. On reception it must demultiplex traffic (degress) from MPLS-like labels to IP for traffic exiting the mesh. Edge routers, potentially all CH and MR, must have MAC-layer interfaces to IP in order to perform these functions. 4.3.2.5 Common roles Moreover, MAC provides services to mesh routing mechanisms (MPLS-like) such that every node in the network acts as label-switching router. Furthermore, broadcast flows from all nodes in mesh for route discovery and maintenance are provided. The latter allow for all nodes in MESH to use a three-way hand- shaking protocol (label REQ, label REP, label ACK) for label management in the mesh. This further provides a means for path discovery and path maintenance which remains as local as possible. This label-switching protocol uses the same signalling resources as the L2 topology management services described above. 4.3.2.6 Network Synchronization The MAC and PHY layers both require tight network synchronization, at least between adjacent clusters. This must be on the order of a few microseconds. Three mechanisms are supported. Firstly, a secondary synchronization source (e.g. GPS) can be used as a common time reference by all nodes. Secondly, one CH (Primary CH) in the network use a special synchronization signal which has longer range than the range Page: 15 / 23
  16. 16. Project: CHORIST Deliv. ref.: SP4.D5 Deliv. title: Report on Broadband Network Definition and Design EC contract: 033685 Deliv. version: 1.0 Submission date: 25/06/07 of communication, in order to cover the region which a common time reference. This is suitable for small networks. Finally the method of distributed relaying of synchronization is possible. This is a method by which all nodes propagate a time reference. Nodes switch between reception (for timing acquisition and tracking) and transmission of the reference. This guarantees coverage of network synchronization over long distances in the absence of a secondary synchronization source. Page: 16 / 23
  17. 17. Project: CHORIST Deliv. ref.: SP4.D5 Deliv. title: Report on Broadband Network Definition and Design EC contract: 033685 Deliv. version: 1.0 Submission date: 25/06/07 5 COVERAGE EXTENSION OF THE BROADBAND NETWORK 5.1 EXTENDING THE BROADBAND ACCESS NETWORK The CHORIST SP4 WiMAX hot spot with 802.11 ad hoc, WiFi and WiMAX cell extensions is depicted on the Figure 7. One can see the different types of network stations that form the clustered WiMAX mesh. The Cluster Head (CH) is responsible for topology maintenance and for scheduling of the network resources to the mesh routers located within its cluster. The edge routers could be considered as normal mesh routers with scenario-based enhanced functionality: They would be responsible for connecting the CHORIST WiMAX hot spot to the world of IP based routing and vice versa. For instance, two 802.11 IP-based networks that are located far away from each other could be interconnected via the CHORIST WiMAX mesh. The CHORIST mesh would support negotiated QoS guarantees for multiple traffic flows, even of different kind between any pairs of the edge routers. However, the QoS guarantees would not be supported between two stations that belong to different cell extensions of the WiMAX mesh. Figure 7 : Ad hoc WLAN, WiFi and standard WiMAX cell extensions to CHORIST WiMAX hot spot Page: 17 / 23
  18. 18. Project: CHORIST Deliv. ref.: SP4.D5 Deliv. title: Report on Broadband Network Definition and Design EC contract: 033685 Deliv. version: 1.0 Submission date: 25/06/07 Note that the CHORIST WiMAX hot spot is based on the mesh inter-vehicular WiMAX solution that is currently under development. On the other hand the IP-based WiMAX extension to the mesh considers the standard solution using the 802.16 point-to-multipoint mode. The benefits of using the standardized 802.11 and 802.16 broadband cell extensions to the CHORIST WiMAX hot spot are mainly related to the coverage extension of the mesh and the mobility support for public safety users. The inter-vehicular WiMAX mesh configuration would be deployed on the crisis site and it would be semi- mobile. This practically means that isolated nodes would mostly remain static after joining the mesh. The WiMAX mesh would be capable of providing the QoS guarantees under a low mobility attribute too. However, the need for higher mobility support among the public safety users is indispensable. The mobility feature is currently available for both DCF and PCF modes of the 802.11 standard and by the 802.16e standard. Furthermore, the broadband cell extensions would offer the opportunity to extend the coverage of the WiMAX mesh towards regions that the mesh could not be deployed. Note that the mesh consists of inter- vehicular stations that would not be possible to be deployed in every place. For instance, consider an indoor public safety scenario. However the WiMAX mesh offers a QoS-capable backbone to interconnect two public safety hot spots that are located far from each other. In addition there are some specific benefits rising from the deployment of an 802.11 based cell extension to the mesh. These benefits are related to the equipment cost of the technology and its wide availability at present. Indeed, 802.11 is a cost effective solution for the public safety needs. It is also currently available and in practice it has been already used successfully for other needs. For instance, note that just the first WiMAX boards have been currently released. However, there are some inherent drawbacks in 802.11 technology related mainly to the QoS provisioning. These drawbacks are routed to the incapability of the MAC layer to differentiate and give prioritization to the different stations and their traffic. For instance, time-bounded and data services are considered to have the same priority in an 802.11 network. The inherent drawbacks due to the 802.11 MAC layer limitations are also the reason that no QoS guarantees could be offered outside the CHORIST WiMAX mesh. The QoS problem is further intensified within multi-hop 802.11 networks due to the hidden and the exposed terminal problems. Under the 802.11 PCF the QoS is only degraded by the incapability of the access point to estimate the traffic demands for each user. Basic prioritization mechanisms could be provided by the access point. However, the single-hop limitation and the enormous bandwidth waste might reduce the usability of the technology in the public safety. Finally, the IEEE 802.11e version that has built in QoS is not currently available. 5.2 COMPONENTS IDENTIFICATION The different protocols used by the 802.11 based cell extensions at the different levels of the protocol stack are presented from section 5.2.1 to section 5.2.3. For demonstration and testing purposes all the involved protocols have been integrated in a test bed of four nodes. Some of the findings regarding the test bed performance in the presence of multicast traffic have been presented in the CHORIST SP4.D3 deliverable. 5.2.1 PHY and MAC layer The methods to extract the PHY and the MAC layer parameters utilized by the test bed are described in the CHORIST SP4.D3 deliverable extensively. To give a short overview, the transmission power and the receiver’s sensitivity are measured by a spectrum analyzer [4]. Then, most of the 802.11 MAC layer parameters are measured by using a packet sniffer [5]. Finally, the PHY preamble and the header duration, and the size of the minimum contention window are deduced based on the comparison of the maximum UDP throughput values obtained by the test bed and calculated based on the standards [6]. Page: 18 / 23
  19. 19. Project: CHORIST Deliv. ref.: SP4.D5 Deliv. title: Report on Broadband Network Definition and Design EC contract: 033685 Deliv. version: 1.0 Submission date: 25/06/07 The IEEE 802.11b PHY and MAC layer parameters used by the test bed are summarized in the Table 2: Parameter Value(s) Transmission power 16.5 dBm @ (1, 2, 5.5 and 11) Mbps Sensitivity -77.5 @ 11 Mbps DIFS 50 µs SIFS 10 µs Slot duration 20 µs Minimum contention window 31 Slots PHY preamble and Header duration 96 µs Beacon Size 74 Bytes Beacon Interval 100 ms 2 Mbps with IBSS Bit rate for beacon transmission 1 Mbps with BSS 8 Bytes UDP Size for the headers 20 Bytes IP 34 Bytes MAC MAC layer ACK size 14 Bytes Table 2 : IEEE 802.11b PHY and MAC layer parameters in the test bed The IEEE 802.11g PHY and MAC layer parameters used by the test bed are summarized in the Table 3: Parameter Value(s) 10 dBm @ 54 Mbps and 48 Mbps Transmission power 12 dBm @ 36 Mbps and 24 Mbps 13 dBm @ 18 Mbps and 12 Mbps -67.4 dBm @ 54 Mbps -69.8 dBm @ 48 Mbps Sensitivity -73.8 dBm @ 36 Mbps -74.6 dBm @ 24 Mbps DIFS 50 µs SIFS 10 µs Slot duration 20 µs Minimum contention window 15 Slots PHY preamble and Header duration 20 µs Beacon Size 74 Bytes Beacon Interval 100 ms Bit rate for beacon transmission 1 Mbps with BSS 8 Bytes UDP Size for the headers 20 Bytes IP 34 Bytes MAC MAC layer ACK size 14 Bytes Table 3 : IEEE 802.11g PHY and MAC layer parameters in the test bed 5.2.2 Routing protocols The basic limitation of 802.11 based networks is the limited coverage. However the coverage beyond the single-hop propagation horizon could be extended by allowing the network nodes to forward the data packets. For that a routing mechanism is required. The unicast and the multicast routing protocols that would be used in the 802.11 ad hoc cell extension of the WiMAX mesh are now described. Page: 19 / 23
  20. 20. Project: CHORIST Deliv. ref.: SP4.D5 Deliv. title: Report on Broadband Network Definition and Design EC contract: 033685 Deliv. version: 1.0 Submission date: 25/06/07 5.2.2.1 Unicast routing protocol OLSR is a link state routing protocol for mobile wireless ad hoc networks [7]. The protocol is pro-active (or table driven) in nature. This means that the network topology is immediately available all the time for all the nodes in the network. The penalty is the excessive protocol overhead. However, the OLSR protocol unlike the typical link state routing protocols utilizes an intelligent technique called multipoint relay selection for packet forwarding. This means that only a subset of the one-hop neighbors of a node is responsible for the control and data packets forwarding. Each node in the network selects the multipoint relay set among its one-hop neighbors in a way that all its two-hop neighbors are covered. The multipoint relay selection is presented on the Figure 8. The OLSR protocol becomes more efficient and economical compared to the typical link state routing protocols for large and dense ad hoc networks. Indeed, the data and control forwarding overhead would be reduced significantly, especially within dense networks by using the multipoint relay selection technique. The OLSR provides optimal routes in terms of hop counts. Figure 8 : Multipoint relay selection for the middle node NRL OLSR is a link state routing protocol oriented for mobile ad hoc networks (MANET) and is used in the test bed. It is an open source application publicly available at [8]. It is largely based on the Optimized Link State Routing (OLSR) protocol specification. However the NRL OLSR has several additional options and features that are summed up below: • Support for IPv6; • Operational in MS Windows, MacOS, Linux, and various embedded PDA systems (PocketPC); • Full link state topology can be distributed including non-multi-point relay (non-MPR) cross links; • A "willingness" attribute for localized multi-point relay (MPR) activation; • Support for several MPR selection protocols: Classical flooding (CF), non-source-based MPR (NS- MPR), source-based MPR (S-MPR), MPR connected dominating set (MPR-CDS), and essential CDS (E-CDS); • Neighbor link quality assessed by a smoothed hysteresis function; • Many run-time parameters available including: HELLO interval, link state update interval, timeout factors, link quality assessment parameters, MPR willingness, and message type of service (TOS); • Configurable debugging verboseness; • Experimental features such as fuzzy-sighted routing and support for Simplified Multicast Forwarding (SMF); Page: 20 / 23
  21. 21. Project: CHORIST Deliv. ref.: SP4.D5 Deliv. title: Report on Broadband Network Definition and Design EC contract: 033685 Deliv. version: 1.0 Submission date: 25/06/07 5.2.2.2 Multicast routing protocol Simplified multicast forwarding (SMF) provides a basic IP multicast functionality within wireless mobile ad hoc networks [9]. SMF could work as a stand alone multicast routing protocol. In this case it performs classical flooding meaning that every node that receives a non-duplicate packet should immediately forward it. As a result, by using the classical flooding no mechanism to obtain network topology information is required. However SMF could also work in conjunction with a unicast routing protocol like OLSR or AODV. In this case the unicast routing protocol is responsible for defining an efficient set of multipoint relay nodes that are responsible for multicast data packets forwarding. As such, the unicast routing protocol is responsible for collecting the neighbours’ information too. There are many different algorithms for defining an appropriate set of data packets forwarders. Some of them are S-MPR, NS-MPR, MPR-CDS and E-CDS. The NRL SMF is an open source application that is used in the test bed. This software was developed by the Protocol Engineering Advanced Networking Research Group. An inter-process communication "remote control" interface is provided so that a compatible program (usually the NRL OLSR) may issue real-time commands to NRL SMF to control the multicast forwarding process. Currently, NRL SMF only receives and forwards packets on a single, specified network interface for operation within the routing area corresponding to that interface. However, future iterations of NRL SMF will also allow for packet reception and forwarding across multiple interfaces to allow for configurable gateway operation. Both IPv4 and IPv6 operation are supported by the current version of NRL SMF. NRL SMF can be built for the following operating systems: Linux, MacOS, BSD, Win32, and WinCE. 5.2.3 Applications 5.2.3.1 VoIP For voice over IP (VoIP) in the test bed we use the open source Robust Audio Tool (RAT) audio application [10]. RAT uses real time protocol (RTP) above UDP/IP as its transport protocol. It offers both point-to-point and point to multi-point VoIP functionalities. For the latter ones, RAT uses IP multicast and thus all the users involved in the multi-party session must reside on a multicast capable network. RAT software should be installed at each end of the multicast connection. It supports both push-to-talk (PTT) and continuous voice connection in either half duplex or full duplex mode. RAT can support different encoding schemes like L16, PCM, DVI, GSM and LPC. In the test bed we usually apply normal GSM encoding giving theoretical maximum datarate equal to 13.2 kbps. RAT also uses a loss repair mechanism. Redundant transmissions are used as a sender based loss protection. This means that heavily compressed copies of audio packets are piggy-packed onto the next audio packets. 5.2.3.2 Real-time Video For real-time multicast video communication in the test bed we use the open source video conferencing tool (VIC) application Version 2.8 [12]. VIC supports both point-to-point and point to multi-point video communication. It uses RTP protocol running on the top of UDP/IP. VIC offers many encoding formats and support rate adaptation. The maximum number of frames transmitted per second could vary from 1 fps to 30 fps. 5.3 INTERACTION BETWEEN THE WIMAX AND THE 802.11 PART Due to the inherent 802.11 limitations, strict QoS guarantees could be offered only within the WiMAX mesh area for the voice and the real-time data applications. Especially for multi-hop ad hoc networks, the exposed and the hidden terminal problems intensify the MAC layer limitations. The necessary delay, jitter and bandwidth requirements for the time-bounded services could not be guaranteed at all. Page: 21 / 23
  22. 22. Project: CHORIST Deliv. ref.: SP4.D5 Deliv. title: Report on Broadband Network Definition and Design EC contract: 033685 Deliv. version: 1.0 Submission date: 25/06/07 Single-hop 802.11 networks with access point could offer fair QoS guarantees though. For instance, under IEEE 802.11b and DCF mode the number of maximum concurrent full-duplex VoIP calls that a single access point can support has been investigated in [14] for 11 Mbps. Besides the channel bit rate, the number of simultaneous voice connections was found to depend significantly on the size of the audio payload that each data packets carries. A similar study for a single BSS using PCF mode was performed in [15]. Likewise we could carry out experiments supported by simulations studies for real-time data applications. The WiMAX mesh and the 802.11 cell extensions could be seen as two autonomous systems (AS). Thus, the effect of voice and data packet length to the QoS within the mesh should be investigated independently. Then the trade offs in terms of supported QoS within the mesh and within the 802.11 cell extensions for different applications could be discovered. However to make the two autonomous systems work together in practice, we have to take into consideration the enhanced functionality that the edge routers should support. Indeed, the edge routers should run at least an application for packet forwarding between their two interfaces, the LAN and the WiMAX mesh interface. The behaviour of the edge routers would be the same as the one of the normal LAN nodes when the packet forwarding takes place within the MANET area. For instance, the edge routers should perform at the LAN side duplicate packet detection and forward the inbound traffic to the mesh accordingly. The task of the mesh interface of the edge routers is two-folded: to demultiplex the outbound traffic from the mesh into separate IP flows and to aggregate the inbound IP traffic into packets characterized by route- specific labels. These are the egress and ingress functions respectively. Note that the routing within the mesh is performed closer to the MAC layer and the IP packets remains untouched. MPLS-like routing is used instead; thereby the LAN interface of the edge routers considers the routing within the mesh as a single hop. There are a number of issues needed to be addressed in order to interconnect successfully the WiMAX mesh to the IP cell extensions: • Nodes within the 802.11 cells should inform the attached edge routers for their current status (e.g. membership in a multicast group). Mechanisms by which sources and receivers within the 802.11 cells interoperate with the edge routers should be defined (emphasis should be put on multicast traffic). • A packet forwarding mechanism between the two interfaces of the edges routers should be developed • The mesh interface of the edge routers should guarantee that it does not forward duplicate packets towards the LAN interface. The vice versa mechanism is already provided by the NRL OLSR and NRL SMF implementations. Page: 22 / 23
  23. 23. Project: CHORIST Deliv. ref.: SP4.D5 Deliv. title: Report on Broadband Network Definition and Design EC contract: 033685 Deliv. version: 1.0 Submission date: 25/06/07 6 CONCLUSION This document described the concepts and approaches elected to design the deployable, interoperable and reliable communication broadband system that would be required for Public Safety units. In the context of CHORIST, WiMAX and WiFi have been identified as the most appropriate wireless technologies to be investigated. More specifically, the WiMAX technology will be used as basis for the elaboration of the mobile core network, since it integrates both long range and QoS capabilities. The key points of the CHORIST SP4 deployable broadband communications system are the following: • Fulfilling the role of the inter-vehicular mobile core network, the WiMAX enhanced mesh network will be complemented by a Label Switching approach. Such an approach allows for flexible routing decisions, under the control of CHs. QoS is naturally managed by using the Class of Service field of labels. Labels are local to node and allow for local recovery decisions under the control of the Cluster Head. In fact Label Switching approach, which is a set of techniques used to route packets at layer 2.5 (under IP layer) in a domain. IP packets entering a domain through an Edge router is assigned a label. « Ingress Nodes » are pushing labels according to QoS requirements while « Egress Node » remove label when exiting the MPLS domain. Labelled packets are switched by intermediate routers using the route defined by a list of labels. In MPLS a specific protocol (LDP: label distribution protocol) exists to assign labels locally in each router along the route. This method allows for fast packet switching based on QoS, traffic flow aggregation, and provides virtual paths between Ingress and Egress nodes. Based on this concept, it is proposed to follow the label switching paradigm within the mesh network. Each mesh router services terminals on one interface and is connected to other routers on another interface. For the terminals it is acting as a In/Egress node. When relaying traffic, it is acting as a Label Switching Router (LSR). The LDP protocol is completely new: CHs are playing a central role in this respect. CH will allocate the labels of each router residing in their cluster. Note that this approach allows the communication system to be efficient in term of QoS management interoperability (e.g. to ensure the required performance of the communications between the Public Safety units deployed on the field and their head quarter or the Public Authorities). • A novel air interface (enhancing WiMAX) will be developed under the frame of the CHORIST SP4. Its MAC layer is label oriented, where a label corresponds to a particular route within the mesh with negotiated QoS. Nodes in the mesh typically route traffic for several labels at the same time. Moreover, the MAC layer is clustered, where dynamically-allocated cluster-heads (CHs) manage radio resources (MAC/PHY). CHs are typically the best-connected nodes in a particular geographical area. In addition, the MAC layer provides distributed mechanisms for path discovery and maintenance. The mechanisms are based on MAC/PHY measurement reporting. The label switching mesh interconnects with IP at the edges of the mesh network. Edge routers perform aggregation of IP traffic flows and attribution of labels to aggregate flows. Label switching allows for “lite” QoS-routing mechanisms which can interact quickly with L2 (potentially L1 with cooperative transmission mechanisms à la 802.16j). It is important to note that the approach is compatible with security approaches (L3) since IP packets remain untouched within the mesh (e.g. VPNs). At last, it is important to underline that the WiFi and the 802.11 based ad hoc extensions to the WiMAX mesh consists a cost effective solution for extending the coverage and adding mobility support to the mesh. Strict QoS guarantees could be guaranteed only within the mesh using MPLS like routing. On the other hand, within the 802.11 extensions fair QoS could be offered only for the BSS with PCF mode. The trade off between QoS support within the mesh and the WiFi extensions could be investigated with respect to the payload of the related applications. In addition, the problem of the successful interoperability between the mesh and the 802.11 extensions at the position of the edge routers needs to be resolved. Page: 23 / 23

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