BRIEF DESCRIPTION OF DRAWING
The terms used in describing the figures are defined and given in the table Definition List 1.
FIG. 1 illustrates a simple example of SGA cell layout. There is only one layer of neighbor SGA cells in the area of a Radio Coverage Region (RCR). 101 points to the estimated boundary of the RCR. 102 points to the estimated region of the center SGA cell. 103 points to a neighboring SGA cell surrounding the center SGA cell. The relative SGA cell arrangement is tiled in a hexagonal pattern.
FIG. 2 illustrates another example of SGA cell layout. There are about two layers of neighbor SGA cells in the area of a RCR. 201 points to the estimated boundary of the RCR. 202 points to the estimated region of the center SGA cell. 203 points to two neighboring SGA cells surrounding the center SGA cell. The relative SGA cell arrangement is tiled in a hexagonal pattern.
FIG. 3 illustrates a different example of SGA cell layout. There are approximately two layers of neighbor SGA cells in the area of a Radio Coverage Region (RCR). 301 points to the estimated boundary of the RCR. 302 points to the estimated region of the center SGA cell. 303 points to an outer neighboring SGA cell surrounding the center SGA cell. The relative SGA cell arrangement is tiled in a rectangular pattern.
FIG. 4 illustrates the trace of a route request REQ packet, originated by 401 the source node-2, in search of 402 the destination node-I 8. An example of the trace 403 is originated from the source node. Node-1 is a neighbor of node-18 is sending the reply REP packet to the source node. The REQ packet is being forwarded by only one node in each SGA cell. The SGA-DSR works fine in a sparse network.
FIG. 5 illustrate the trace of a REQ packet, originated by 501 the source node-2, in search of 502 the destination node-12. An example of the trace 503 is clearly seen as originated from 501, node-2. The number of nodes involved in forwarding the REQ packet is very limited. In every one SGA cell, there is approximately one node taking the responsibility to forward the REQ packet. The forwarding node appears to be an arbitrary one in a given SGA cell. The SGA-DSR works fine in a dense network.
DETAILED DESCRIPTION
The SGA-DSR Concept and Terms Definitions: The terms are defined so that the concept and method of the SGA-DSR can be better described.
DEFINITION LIST
The concepts of SGA-DSR can be better presented with the terms defined.
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Definition List 1
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Term
Definition
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PS
Positioning System: It is a system that provides the nodes in the network
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of their positions. There are two kinds of PS. The positions can be an
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absolute geographical position or a relative position from a known
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reference point. Therefore, there are two kinds of PS: Global Positioning
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System (GPS) Type: The node equipped with GPS capability would be able
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to know its own geographical location and therefore be able to identify
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which SGA cell its is currently in. Relative Positioning Type: The network
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establishes a set of reference points. The reference points could be
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some specific nodes or land marks. The position coordinates are defined
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in reference to the reference points. This invention relies on the support
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of such a Positioning System, for example GPS.
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PA
Position Assisted: When not all the nodes are equipped with PS
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capability, the neighbor nodes may be able to help. The SGA-DSR
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protocol requires the mobiles to be location aware, most of the time.
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Sometimes, a mobile may not have the immediate knowledge of its own
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position, but by overhearing the location-broadcast of other mobiles, it
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would be able to guess approximately its own position. The SGA-DSR
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does not require the mobile to have very accurate position knowledge.
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The mobile position knowledge can be obtained from a Positioning
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System (PS), such as GPS.
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RCR
Radio Coverage Region: It is defined as the average coverage area by
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how far a node can directly communicate with another node in the
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network. Two nodes within each other's RCR would have good chance
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to be able to communicate. The actual communication can be severely
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influenced by the channel impairments and conditions due to object
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shadowing, channel fading, etc.
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SGA
Small Geographical Area: A SGA is a small cell. The boundary of a SGA
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cell is defined in the coordinates of the supporting PS. The size of RCR is
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multiple times the size of the SGA. The SGA cell boundaries can be
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slightly overlapped. There could be regions that are blank, not belonging
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to any SGA cells. The nodes located in the overlapped and blank region
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can identify themselves as just anyone cell among the closest candidate
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SGA cells. The SGA cells are tiled regularly over the whole area. SGA cells
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are fixed in the coordinates of the PS. While nodes may move from cell
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to cell. A node in a given SGA cell may be able to directly communicate
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to another node across a few SGA cell territories.
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SGA-DNE
SGA-Direct Neighbor Extension is an extended area from a given SGA, to
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include the direct neighboring SGA area in the definition. SGA-DNE is
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used in the data path construction. A data path in SGA-DSR is defined as
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a sequence of SGA cells in which on air data packets can be forwarded
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from cell to cell. In such data path if SGA-DNE is used then the nodes
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involved in the forwarding activity will be confined by larger SGA-DNE
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instead of the smaller SGA.
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Network Domain
The network domain can be regarded in two different meanings. First,
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the domain can be defined as a city or a town. It is a geographic domain.
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Second, the network domain can be defined as a fixed number of SGA-
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cells away, respective to a given cell. The SGA-DSR works fine with both
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definitions.
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SGA-Cell-Layout
It is a network map using the coordinates in the given PS to define the
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SGA cell layouts, cell boundaries, and cell Identities (ID). The average
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size of a RCR is first estimated. Then the size of a SGA cell is
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determined so that the area of a RCR can cover any SGA cell, and at least
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one layer of its surrounding neighbor SGA cells. It is preferred, but not
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limited, to have approximately 2 layers of surrounding SGA cells under
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the coverage of a RCR.
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SGA-ID method
SGA Identifying method: A node use the current position information to
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associate itself to the SGA cell ID. The SGA cells boundaries are
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predetermined in the SGA-Cell-Layout map. If the current position is in
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the overlapped region of multiple SGA cells, or a blank region with no
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SGA cells. Then the node can pick a candidate cell that is closest to the
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cell center.
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OKA
Optional Keep-alive: It is an option that the mobile should beacon its
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keep-alive message. SGA-DSR protocol works both with and without the
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keep-alive beacon. Broadcasting the mobile identity and location helps
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the Route Request to find the destination more effectively but it is not a
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prerequisite (See definition UAM). Periodic broadcasting of keep-alive
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may increases the routing overhead.
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REQ
Route Request: A route request message that is being sent by the source
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node in search for a path to the destination node. Each time the REQ
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packet is being forwarded by any intermediate node, the node ID and
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the associated SGA cell ID are included in the REQ packet. When the REQ
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packet has arrived the destination node, the whole path from the source
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node to the destination node is recorded in the REQ packet.
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REP
Route Reply: The destination node sends a route path back to the
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source node via a route reply message. Besides the destination node,
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any node, which has the route information, in the network may also send
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the REP message to the source node.
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MCR
Momentary Cell Representative: As a mobile is about to send out a route
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request packet (REQ), or continue forwarding a REQ, it will actively select
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a few nodes, known as momentary cell representatives (MCR) in its
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neighborhood to propagate the REQ. The selecting of MCR is purely adhoc
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and local to the single transmission. If there were N SGA cells under
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its radio coverage, it would pick N MCR, one from each SGA cell. The
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MCR name list of nodes is attached to the REQ in the broadcasting. The
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MCR name list is only meaningful in the local broadcast. All neighbor
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mobiles would overhear of the REQ but only a few would actually take
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the responsibility to continue propagate the REQ. Since, the MCR nodes
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were located in different cells, scattering in all directions, and preferably
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only those cells at the edge of the radio coverage, the number of nodes
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involved in actual radio broadcasting is limited to the number of SGA
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cells in the RCR. If only the edge cells were considered for selecting the
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MCR, then the number of MCR will be further reduced. This method
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guarantees the REQ to be forwarded in all directions, and eventually
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reaching out to every corner of the network. And the number of SGA
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cells in the network limits the total number of transmissions, triggered
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by a single request. The routing overhead of flooding of the destination
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search (REQ) in a dense network would not increase with the number of
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nodes in the network.
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UAM
Unsolicited Assistant Mode: In UAM, when a mobile overheard of a
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forwarding request (such as REQ, or Reply Packet, etc), it will make itself
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ready to carry on the forwarding by waiting a random time (for example,
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in a range of 5 to 250 milliseconds). If indeed no one else in its cell is
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forwarding the packet during its waiting time. It will take action to
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forward the packet unsolicited, as if it has been selected to do so. The
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use of random time is to reduce the chance of multiple forwarding of the
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same request in a single SGA-cell. If mobile A is aware of its neighbor,
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the MCR method will be used. But MCR will be backed up by UAM to
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ensure that a packet will be forwarded if MCR failed to find any
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representatives.
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UAN
Unsolicited Assistant Node: The node, which is exercising the UAM.
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UAN-CS
Unsolicited Assistant Node - Candidate Set: Normally all the nodes in a
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SGA cell is automatically a member of the UAN-CS. However, if there are
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too many nodes in a SGA cell, the network density is exceeding the
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capacity of the media access control (MAC), then not all the nodes
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should be participated in the UAM at a given time. Then number of
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nodes participating in UAM is limited by the capacity of the MAC layer.
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Now, set two threshold sizes (THS) for the UAN-CS. THS-1 is the
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minimum size threshold, THS-2 is the maximum size threshold. The
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nodes in a GSA cell will join into, or release themselves from the UAN-CS
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club from time to time. When the number of members in the UAN-CS is
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falling below the THS-1 then the nodes outside the UAN-CS club will
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contend to join with a probability within a given time frame. During the
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whole process, every node is also monitoring the size increments in
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UAN-CS against the THS-1. If the size is already exceeded the THS-1
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then the node will pause, or slow down, its joining process until the size
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is falling below the THS-1 again. When the number of members in the
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UAN-CS is exceeding the THS-2 then the nodes inside the UAN-CS club
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will contend to release themselves with a certain probability within a
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given time frame. At the same time every node is also monitoring the
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size of decrements in the UAN-CS club against the THS-2. If the size is
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already below the THS-2 then the node will pause, slow down, it
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releasing process until the size is exceeding the THS-2 again.
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CS-MR
Candidate Set - Membership Rotation: Rotation and circulation of the
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membership in UAN-CS club is also executed to ensure fairness in
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supporting the network. Every node in the UAN-CS club will increase its
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probability to release itself from the club over the age of its membership
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if the UAN-CS size has been above THS-1. Therefore the nodes staying
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long enough in the UAN-CS will be more likely to release from the
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UAN_CS club. The process will cause a dynamic circulation of
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membership in the UAN-CS club. The nodes, which are currently the
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active members of the UAN-CS club, will be able to readily access the
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network via the MAC layer.
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ERP
Explicit Route Path: It is a path represented by a sequence of SGA cells.
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ERP is extracted from the routing table. It is used to indicate how a
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packet can be forwarded.
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RG
Route Graph: The SGA cell is the building unit of the RG. It is a
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mathematical model - graph. The RG represents the network topology
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learned by the node in the recent time. An edge in the RG represents the
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existence of connectivity between two SGA cells. The edges are
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weighted and timed. The edge will be removed if it has been time out.
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The edge weight is given a value to reflect the order of priority. For
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example, a newly learned edge, against older edges, will be given a
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better weight.
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NT
Node Table: The NT keeps the mappings of a node to a SGA cell. When a
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node is storing a learned path into the routing table. The information of
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node ID mapped to SGA cell ID is extracted and stored in the NT. The
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path sequence of SGA cells is decomposed into edges and stored in the
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RG. The node in NT is also timed. The node to SGA cell mapping will be
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removed if it has been time out.
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Node-Timer
Each node in the NT is timed. The default value of the timer is a
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predetermined system parameter. The node will be refreshed by
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receiving packets having the newly obtained route information, or by
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overheard such packets.
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Edge-Timer
Each edge in the RT is timed. The default value of the timer is a
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predetermined system parameter. The node will be refreshed by
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receiving packets having the newly obtained route information, or by
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overheard such packets.
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DP
Data Path: A DP is a route path that is currently being used, carrying
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data traffic. In contrast, an ERP is only an entry in the information
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database. An ERP is obtained directly from the RG and NT. The
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continuously use of a DP, in return is refreshing the route paths in the
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RG and NT. The nodes in the SGA cells defined in the ERP carries the
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data-forwarding task via MCR and UAM. But the scope of MCR and UAM
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would apply to SGA cells confined by the ERP.
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DP-W
Data Path-Widened: Data Path - Widened (DP-W) is a widened data path
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based on an existing DP. DP-W is an extension feature to the DP. DP-W
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uses the SGA-DNE cell for data forwarding instead of SGA cells. Each
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SGA-DNE is directly mapped to the corresponding SGA cell in the DP.
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The number of nodes increases, in serving the data traffic. The DP-W
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serves better when the network is, no having enough nodes, a sparse
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network.
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SD
Shortcut to Downstream: An SD is local a route repair mechanism. When
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a packet forwarding along the DP is stopped by a broken link, the node
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will initiate an SD, a route request to find a shortcut to the downstream
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nodes in the ERP. The SD request has a very short (Time To Live) TTL,
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such as one. Any near-by nodes (including the SD sender itself) that
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have the path to any SGA cells in the downstream nodes of the ERP will
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reply to the sender. The SD sender will collect the new path information
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and bring it back to the source node in an RTP. The source node upon
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receiving the RTP will recalculate the path to the destination. Packets are
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then sent out along a new ERP. If the Path Tracking is successful, the
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data packet forwarding will continue at the SD sender node. If SD failed
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to find any path to the downstream of the path, then the packet is
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dropped.
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DESCRIPTIONS
The SGA-DSR is a new protocol design based on the special relationship of the SGA cell arrangement to the area of RCR. The special relationship enables many different routine features of SGA-DSR that are not found in any other ad-hoc network protocols.
The SGA-DSR is composed of two major methods: SGA-DSR Route Discovery and SGA-DSR Route Maintenance.
Route Discovery:
- (1) Route Request (REQ)
- In SGA-DSR, if OKA is enabled, all route paths to the direct neighbor nodes are readily available. Regardless OKA is enabled or not, all mobiles must support Unsolicited Assistant Mode (UAM).
- With no knowledge of where to find a destination mobile, the mobile may have to send out a route request packet (REQ) for route discovery. This packet contains a route record, a record of the sequence of SGA cell ID, and node ID traversed by the REQ, as it propagates through the network.
- It also contains a request id, to identify the duplicate (or old) packets from the given source node.
- If a node has heard of the REQ and it has the requested path information. It will send a reply packet (REP) back via the return path. On the way back to the source node, if the return path link is broken, then the reply REP will be dropped.
- If a node receives a route request packet with a source address and a request id already received, it discards the packet. Otherwise, it appends its node ID and SGA cell ID to the route record.
- Upon receiving a REQ packet, the node must prepare itself in the Unsolicited Assistant Mode (UAM). If it finds its node ID in the MCR name list of the REQ, it will propagate the REQ, if the destination route information is not available in its route table. If it is not in the MCR list, it will be waiting in UAM process. It will transmit the REQ packet when the UAM timer expired, if no other node has already transmitted the same REQ packet during its waiting period. If it detects another transmission by a neighbor node that is located in the same cell, then it will discard the REQ packet immediately. No further action is required.
- The use of MCR and UAM ensures that the REQ packet with limited radio resource and the packet is being heard in all directions. The limited number of SGA cells also limits the number of transmissions of a single REQ in the search of a destination in the whole network. The route request overhead has been significantly reduced.
- (2) Route Reply (REP)
- A route reply packet (REP) contains the requested path information (from source node to the destination node).
- It also contains an Explicit Route Path (ERP) back to the source node. The path information or the Explicit Route is a sequence of the SGA cells that a packet can be forwarded to the destination. The REP packet forwarding is not done by a SGA cell, but by one of the nodes currently inside the cell. Therefore the design of the cell radius should not be too small.
- Forwarding along the explicit path of SGA cells, a packet may be carried away by a moving node to the near-by cell, which may no longer be on the path, ERP. The respective node should continue to forward the packet to the downstream cells, if possible.
- (3) The Route Table: Route Graph (RG) and Node Table (NT)
- The route information is stored in a Node Table (NT) and a Route Graph (RG). The node to SGA mapping has an expiration timer, called Node-Timer. The expiration timer should be a configurable system parameter. The RG has a set of edges with weights. An edge is a pair of directly connected SGA cells. The edge is timed with an Edge-Timer. A reasonable expiration timer value could be ranged from a few seconds to a few hours. The timer in the NT and RG entries will be refreshed by new route information.
- In search for a destination, if the route information in NT and RG is not available, then a REQ is sent.
- The node extracts route information from the packet trace it overheard. The refreshed edge weight can be set to a minimum (such as 1). Less weight means more important.
- Route information can be transported. When inserting external route information obtained from other nodes, the original edge weight should be kept. If the edge weight is not available, a less important weight value must be given to those uncertain edge entries.
- The whole network topology is highly distributed in the nodes. No single node is required to have the full knowledge of the network topology. The NT and RG have only the recent routes that it uses. All old routes will be deleted as the timer expired. In the calculation of a destination path, the edge weight (increases with time) would allow the algorithm to choose a more recent and refreshed path.
- In route discovery, when a REQ message sent, does not result in any REP packets coming back to the source. The source node may retry for a number of times. The number of retry is a predetermined system parameter.
Route Maintenance
- (1) Route Tracking
- SGA-DSR does not actively detect network topology changes. But if a data packet has failed to propagate in the data path DP, along an explicit route path ERP, then a Route Tracking Packet (RTP) should be generated and returned to the source node. All intermediate nodes heard of such an RTP should also update its routing table, the NT and RG. The RTP contains the information about the broken link; for example, the broken link is specified as from SGA cell A to SGA cell B. It may also contain potential new path information to the downstream leading to the destination (Ref: Shortcut to Downstream, SD in the next section).
- Each entry in the route table, NT and RG has an expiration timer, the Node-Timer and Edge-Timer. After the timer expires, the entry is removed from the cache. While receiving of packets from the destination, or overheard traces packets, the timer of the associated edge is refreshed. If an RTP is received, the corresponding broken edge, or the node-SGA cell association will be removed from the routing table, RG and NT.
- (2) Local Repair Method
- SGA-DSR does a simple local repair to a broken link, by using SD. Because SD is a short local request, the waiting for a potential reply should be very short.
- In the case that the RTP packet cannot find a route back to the source node of the packet, the RTP will simply be dropped. Since RTP is a kind of error packet, dropping an error packet will not further trigger new error reporting packets.
- In case that the destination node is not found in the last SGA-cell of the ERP, then repair mechanism SD is extended to the last node in the ERP. The node who receives the packet will search (send a one hop request) for the destination in the its direct neighboring SGA-cells. If it is found, the packet will be forwarded to the destination. Else, the packet will be dropped and a RTP will be generated, causing the source to remove the destination node mapping to the existing destination SGA cell.
- The route maintenance is on demanded. No global repair or maintenance is required.
- (3) Data Forwarding and Route Tracking Method
- If the route path to the destination node is found in the routing table, NT and RG, data packet can be sent with an ERP, forming a DP. The DP may be changing slightly as the data packet is actually forwarded from node to node, or cell to cell. The route is refreshed along the path, as the traffic is flowing on such DP. But any route change is also tracked and updated.
- During the data communication, the nodes in the network may have moved over time. At some point of time, the data path may be disrupted by instability of some links. The SD mechanism does the local repair if possible and RTP is also generated to modify the current ERP at the source node.
In SGA-DSR, the route change in the DP due to the node mobility is relatively small. In a dense network, the cells are mostly likely to be filled with nodes. As a SGA cell based forwarding, any node in a specific cell can be momentarily engaged to bridge the communication. In a sparse network, the data path DP would be more likely broken due to the physically breaking of the network.
In SGA-DSR, the network topology information is distributed in different nodes. The nodes only keep the partial network information they needed.
Patent Application
20070280174
