5 th ACM MobiHoc – Tokyo, May 24, 2004 Istituto di Informatica e Telem atica More realistic energy models Open issues: 6/11 TC literature: emphasis is on reducing the transmit power, i.e., the power consumed by the RF amplifier In practical settings, the transmit power contributes only in part to the power consumption of the wireless transceiver Example: the sleep:idle:rx:tx min :tx max ratio is – 0.056 : 1 : 1 : 1.044: 1.418 in a CISCO Aironet 802.11 wireless card – 0.440 : 1 : 1.006 :0.872 : 1.114 in a Medusa II sensor node Open issue: how do these energy models impact the performance of TC protocols? 5 th ACM MobiHoc – Tokyo, May 24, 2004 Istituto di Informatica e Telem atica More accurate analysis with mobility Open issues: 7/11 More work needs to be done to investigate the effect of mobility on TC: – Is mobility beneficial or detrimental? o On one hand, mobility increases message overhead o On the other hand, it balances the node energy consumption o Open issue: which is the overall effect on network lifetime? – Determination of the optimal frequency for reconfiguration o In general, there is a trade off between the frequency of re-execution of the TC protocol and “quality” of the topology o Open issue: given a certain constraint (on the network lifetime, or on the QoS), and given a TC protocol, which is the optimal frequency for reconfiguration? o Preliminary step in this direction: the determination of the information exchange period for the LMST protocol [Li et al.03b] 5 th ACM MobiHoc – Tokyo, May 24, 2004 Istituto di Informatica e Telem atica The effect of multi-hop traffic Open issues: 8/11 Implicit message in the current literature on TC: the sparser communication graph the better Is this true, if the designer goal is to extend network lifetime? The effect of multi-hop data traffic must be carefully investigated: – In a very sparse communication graph (e.g., the MST), the average path length between source/destination pairs is relatively long – Given the same quantity of packet delivered, the overall number of messages circulating in the network is relatively larger for relatively sparser graphs – In very sparse graphs, the data traffic might be very unbalanced – Open issue: which is the overall effect on network lifetime? 5 th ACM MobiHoc – Tokyo, May 24, 2004 Istituto di Informatica e Telem atica TC in the protocol stack Open issues: 9/11 Where should TC be positioned in the protocol stack? No clear answer in the literature Our view: Routing Layer MAC Layer TC Layer 5 th ACM MobiHoc – Tokyo, May 24, 2004 Istituto di Informatica e Telem atica TC and Routing Open issues: 10/11 One possible view: Routing Protocol TC Protocol Trigger route updates Trigger TC execution 5 th ACM MobiHoc – Tokyo, May 24, 2004 Istituto di Informatica e Telem atica TC and MAC Open issues: 11/11 One possible view: TC Protocol MAC Layer Trigger TC execution (new neighbors) Set the power level Remark: a lot of work still to be done on this issue!!! 5 th ACM MobiHoc – Tokyo, May 24, 2004 Istituto di Informatica e Telem atica Towards an implementation of TC Level-based TC: 1/16 To end this tutorial, we present two protocols (CLUSTERPOW and KNeighLev) that explicitly take into account a feature of current wireless transceivers: the transmit power can be set only to relatively few (5-6) levels For instance: – The CISCO Aironet 350 802.11 wireless card has the following transmit power levels: 1mW, 5mW, 20mW, 30mW, 50mW, 100mW – The transceiver of the Rockwell’s Wins sensor node has the following transmit power levels: 0.12mW, 0.30mW, 0.96mW, 2.51mW, 3.47mW, 13.8mW, 19.1mW, 36.3mW 5 th ACM MobiHoc – Tokyo, May 24, 2004 Istituto di Informatica e Telem atica The CLUSTERPOW protocol Level-based TC: 2/16 The protocol is an extension of the COMPOW protocol of [Narayanaswamy et al.02] The goal of the CLUSTERPOW [KawadiaKumar03] is to overcome a problem of COMPOW: when the node distribution is not “uniform”, the protocol performs very poorly Basic idea: every node u in the network maintains one routing table for each power level The routing table for level i, RT i , is updated by a routing daemon (one for each level), and contains all the nodes that are reachable by u using power at most i 5 th ACM MobiHoc – Tokyo, May 24, 2004 Istituto di Informatica e Telem atica The CLUSTERPOW protocol (2) Level-based TC: 3/16 This way, CLUSTERPOW induces a node clustering: for every node u, several clusters are defined, with the cluster at level i formed by the nodes in RT i When u needs to send a message to v, it sends the message with power level j, where j is the minimum level such that v ∈ RT j Intermediate nodes relay the message according to the same rule, until v is reached 5 th ACM MobiHoc – Tokyo, May 24, 2004 Istituto di Informatica e Telem atica The CLUSTERPOW protocol (3) Level-based TC: 4/16 1mW cluster u 100mW 100mW v 10mW 1mW 10mW cluster 100mW cluster n 1 n 2 n 3 . reconfiguration? o Preliminary step in this direction: the determination of the information exchange period for the LMST protocol [Li et al.03b] 5 th ACM MobiHoc – Tokyo, May 24, 2004 Istituto di Informatica e. reconfiguration o In general, there is a trade off between the frequency of re-execution of the TC protocol and “quality” of the topology o Open issue: given a certain constraint (on the network. the RF amplifier In practical settings, the transmit power contributes only in part to the power consumption of the wireless transceiver Example: the sleep:idle:rx:tx min :tx max ratio is –