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Wireless Embedded Systems (0120442x ) Naming and Addressing

Wireless Embedded Systems (0120442x ) Naming and Addressing. Chaiporn Jaikaeo Chaiporn.j@ku.ac.th Department of Computer Engineering Kasetsart University. Materials taken from lecture slides by Karl and Willig. Names vs. Addresses. Names: Refer to “things”

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Wireless Embedded Systems (0120442x ) Naming and Addressing

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  1. Wireless Embedded Systems(0120442x) Naming and Addressing Chaiporn Jaikaeo Chaiporn.j@ku.ac.th Department of Computer EngineeringKasetsart University Materials taken from lecture slides by Karl and Willig

  2. Names vs. Addresses • Names: Refer to “things” • Nodes, networks, data, transactions, … • May or may not be globally unique • Addresses: Information needed to find these things • Street address, IP address, MAC address • May or may not be globally unique • Services to map between names and addresses • E.g., DNS • Some names are also addresses

  3. Naming in WSN • Nodes are not independent • But collaborate to solve a given task • Better to shift view from naming nodes to naming data

  4. Address Management Issues • Address allocation: Assign an entity an address from a given pool of possible addresses • Distributed address assignment (centralized like DHCP does not scale) • Address deallocation: Once address no longer used, put it back into the address pool • Because of limited pool size • Graceful or abrupt, depending on node actions

  5. Address Management Issues • Address representation • Conflict detection & resolution (Duplicate Address Detection - DAD) • What to do when the same address is assigned multiple times? • Can happen e.g. when two networks merge • Binding • Map between addresses used by different protocol layers • E.g., IP addresses are bound to MAC address by ARP

  6. Uniqueness of Addresses • Globally unique • Appears at most once all over the world • Network-wide unique • Appears at most once in a given network • Locally unique • Appears at most once in a definedneighborhood

  7. Addressing Overhead • The fewer bits per address, the better • Global > Network-wide > Local • Tradeoffs • Address length  management overhead • Typically, address negotiation runs only at the beginning • Except when there is mobility

  8. Distributed Address Assignment • Option 1: Random assignment • Unacceptable high risk of duplicate addresses • No-conflict probability for n addresses and k nodes is • By Stirlings approximation • Similar to the birthday paradox

  9. Distributed Address Assignment • Option 2: Still random, but avoid addresses used in local neighborhood • By overhearing exchanged packets • Good enough in many WSN apps where data sent to a certain sink

  10. Distributed Address Assignment • Option 3: Repair any observed conflicts • Randomly pick a temporary address and a proposed fixed address • Send an address request to the proposed address, using temporary address • If address reply arrives, address already exists • Collisions in temporary address unlikely, as only used briefly • Option 4: Similar to 3, but use a neighbor that already has a fixed address to perform requests

  11. Locally Unique Addresses • Fewer bits are needed, due to • Each address can be reused several times across the same network • Lower-number addresses tend to be used more frequently • Addresses can be compressed • E.g., using Huffman coding

  12. Issues with Asymmetric Links • Assume nodes communicate with bidirectional neighbors • All bidirectional neighbors of each node must have distinct addresses • The address of any inbound neighbor must be different from all bidirectional neighbors

  13. Content-Based Addressing • Recall: Paradigm change from id-centric to data-centric networking in WSN • Supported by content-based names/addresses • Do not described involved nodes (not known anyway), but the content itself the interaction is about • Classical option: Put a naming scheme on top of IP addresses • Done by some middleware systems

  14. Describing Interests • Interests describe relevant data/event • Nodes match these interests with their locally observed data • Format: Attribute-Value-Operation (AVO) • E.g.: <TEMP, 20°C, GE> • Operations:

  15. <type,temperature,EQ> <threshold-from-below,20,IS> <x-coordinate,20,LE> <x-coordinate,0,GE> <y-coordinate,20,LE> <y-coordinate,0,GE> <interval,0.05,IS> <duration,10,IS> <class,interest,IS> <type,temperature,IS> <x-coordinate,10,IS> <y-coordinate,10,IS> <temperature,20.01,IS> <class,data,IS> Data <type,temperature,IS> <x-coordinate,10,IS> <y-coordinate,10,IS> Interest Sensor Describing Interest/Sensor/Data • List of AVOs • E.g.,

  16. Matching Algorithm • Check whether an interest matches the locally available data

  17. Directed Diffusion • An example of data-centric networking

  18. Geographic addressing • Express addresses by denoting physical position of nodes • Considered a special case of content-based addresses • Attributes for x and y (and z) coordinates • Options • Single point • Circle or sphere centered around given point • Rectangle by two corner points • Polygon

  19. Conclusion • Addresses can be assigned distributedly • Non-id-centric addresses give additional expressiveness, enables new interaction patterns than only using standard addresses • These addresses have to be supported by specific protocols, in particular, routing protocols

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