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<front> <front>
<title abbrev="tvr-use-cases">TVR (Time-Variant Routing) Use Cases</title> <title abbrev="TVR Use Cases">Time-Variant Routing (TVR) Use Cases</title>
<seriesInfo name="Internet-Draft" value="draft-ietf-tvr-use-cases-09"/> <seriesInfo name="RFC" value="9657"/>
<author fullname="Ed Birrane"> <author fullname="Edward J. Birrane, III" surname="Birrane, III" initials="E
.">
<organization>JHU/APL</organization> <organization>JHU/APL</organization>
<address> <address>
<email>edward.birrane@jhuapl.edu</email> <email>edward.birrane@jhuapl.edu</email>
</address> </address>
</author> </author>
<author fullname="Nicolas Kuhn"> <author fullname="Nicolas Kuhn" surname="Kuhn" initials="N.">
<organization>Thales Alenia Space</organization> <organization>Thales Alenia Space</organization>
<address> <address>
<email>nicolas.kuhn.ietf@gmail.com</email> <email>nicolas.kuhn.ietf@gmail.com</email>
</address> </address>
</author> </author>
<author fullname="Yingzhen Qu"> <author fullname="Yingzhen Qu" surname="Qu" initials="Y.">
<organization>Futurewei Technologies</organization> <organization>Futurewei Technologies</organization>
<address> <address>
<email>yingzhen.ietf@gmail.com</email> <email>yingzhen.ietf@gmail.com</email>
</address> </address>
</author> </author>
<author fullname="Rick Taylor"> <author fullname="Rick Taylor" surname="Taylor" initials="R.">
<organization>Ori Industries</organization> <organization>Aalyria Technologies</organization>
<address> <address>
<email>rick.taylor@ori.co</email> <email>rtaylor@aalyria.com</email>
</address> </address>
</author> </author>
<author fullname="Li zhang"> <author fullname="Li Zhang" surname="Zhang" initials="L.">
<organization>Huawei</organization> <organization>Huawei</organization>
<address> <address>
<email>zhangli344@huawei.com</email> <email>zhangli344@huawei.com</email>
</address> </address>
</author> </author>
<date year="2024" month="March" day="25"/> <date year="2024" month="September"/>
<area>Routing</area>
<area>RTG</area>
<workgroup>tvr</workgroup>
<keyword>Time-variant</keyword> <keyword>Time-variant</keyword>
<keyword>Routing</keyword> <keyword>Routing</keyword>
<keyword>Mobility</keyword> <keyword>Mobility</keyword>
<keyword>Green computing</keyword> <keyword>Green computing</keyword>
<keyword>Resource management</keyword> <keyword>Resource management</keyword>
<abstract> <abstract>
<?line 101?> <t>This document introduces use cases where Time-Variant Routing (TVR)
computations (i.e., routing computations that take into consideration
<t>This document introduces use cases where Time-Variant Routing (TVR) computati time-based or scheduled changes to a network) could improve routing
ons (i.e. routing computations taking into considerations time-based or schedule protocol convergence and/or network performance.</t>
d changes to a network) could improve routing protocol convergence and/or networ
k performance.</t>
</abstract> </abstract>
<note removeInRFC="true">
<name>About This Document</name>
<t>
Status information for this document may be found at <eref target="https
://datatracker.ietf.org/doc/draft-ietf-tvr-use-cases/"/>.
</t>
<t>
Discussion of this document takes place on the
Time Variant Routing Working Group mailing list (<eref target="mailto:tv
r@ietf.org"/>),
which is archived at <eref target="https://mailarchive.ietf.org/arch/bro
wse/tvr/"/>.
Subscribe at <eref target="https://www.ietf.org/mailman/listinfo/tvr/"/>
.
</t>
<t>Source for this draft and an issue tracker can be found at
<eref target="https://github.com/NasaDtn/tvr-bof-use-cases"/>.</t>
</note>
</front> </front>
<middle> <middle>
<?line 105?>
<section anchor="introduction"> <section anchor="introduction">
<name>Introduction</name> <name>Introduction</name>
<t>There is a growing number of use cases where changes to the routing top <t>There is a growing number of use cases where changes to the routing
ology are an expected part of network operations. In these use cases the pre-pla topology are an expected part of network operations. In these use cases,
nned loss and restoration of an adjacency, or formation of an alternate adjacenc the pre-planned loss and restoration of an adjacency, or formation of an
y, should be seen as a non-disruptive event.</t> alternate adjacency, should be seen as a nondisruptive event.</t>
<t>Expected changes to topologies can occur for a variety of reasons. In n <t>Expected changes to topologies can occur for a variety of reasons. In
etworks with mobile nodes, such as unmanned aerial vehicles and some orbiting sp networks with mobile nodes, such as unmanned aerial vehicles and some
acecraft constellations, links are lost and re-established as a function of the orbiting spacecraft constellations, links are lost and re-established as
mobility of the platforms. In networks without reliable access to power, such as a function of the mobility of the platforms. In networks without
networks harvesting energy from wind and solar, link activity might be restrict reliable access to power, such as networks harvesting energy from wind
ed to certain times of day. Similarly, in networks prioritizing green computing and solar, link activity might be restricted to certain times of
and energy efficiency over data rate, network traffic might be planned around en day. Similarly, in networks prioritizing green computing and energy
ergy costs or expected user data volumes.</t> efficiency over data rate, network traffic might be planned around
<t>This document defines three categories of use cases where a route compu energy costs or expected user data volumes.</t>
tation might beneficially consider time information. Each of these use cases inc <t>This document defines three categories of use cases where a route
ludes the following information.</t> computation might beneficially consider time information. Each of these
<ol spacing="normal" type="1"><li> use cases are included as follows:</t>
<t>An overview of the use case describing how route computations might <ol spacing="normal" type="1">
select different paths (or subpaths) as a function of time.</t> <li>An overview of the use case describing how route computations
</li> might select different paths (or subpaths) as a function of time.</li>
<li> <li>A set of assumptions made by the use case as to the nature of
<t>A set of assumptions made by the use case as to the nature of the n the network and data exchange.</li>
etwork and data exchange.</t> <li>Specific discussion on the routing impacts of the use case.</li>
</li> <li>Example networks conformant to the use case.</li>
<li>
<t>Specific discussion on the routing impacts of the use case.</t>
</li>
<li>
<t>Example networks conformant to the use case.</t>
</li>
</ol> </ol>
<t>The use cases that are considered in this document are the following.</ <t>The use cases that are considered in this document are as follows:</t>
t>
<ol spacing="normal" type="1"><li> <ol spacing="normal" type="1">
<t>Resource Preservation (described in <xref target="Resource-Preserva <li>Resource Preservation (described in <xref
tion"/>), where there is information about link availability over time at the cl target="Resource-Preservation"/>), where there is information about
ient level. Time Variant Routing can utilize the predictability of the link avai link availability over time at the client level. Time-Variant Routing (T
lability to optimize network connectivity by taking into account end point resou VR)
rce preservation.</t> can utilize the predictability of the link availability to optimize
</li> network connectivity by taking into account endpoint resource
<li> preservation.</li>
<t>Operating Efficiency (described in <xref target="Operating-Efficien <li>Operating Efficiency (described in <xref
cy"/>), where there is a server cost or a path cost usage varying over time. Tim target="Operating-Efficiency"/>), where there is a server cost or a
e Variant Routing can exploit the predictability of the path cost to optimize th path cost usage varying over time. TVR can exploit
e cost of the system exploitation. The notion of a path cost is extended to be a the predictability of the path cost to optimize the cost of the system
time-dependent function instead of a constant.</t> exploitation. The notion of a path cost is extended to be a
</li> time-dependent function instead of a constant.</li>
<li> <li>Dynamic Reachability (described in <xref
<t>Dynamic Reachability (described in <xref target="Dynamic-Reachabili target="Dynamic-Reachability"/>), where there is information about
ty"/>), where there is information about link availability variation between nod link availability variation between nodes in the
es taking part of the end-to-end path. Time Variant Routing can exploit the pred end-to-end path. TVR can exploit the predictability
ictability of the link availability to optimize in-network routing.</t> of the link availability to optimize in-network routing.</li>
</li>
</ol> </ol>
<t>The document does not intend to represent the full set of cases where t <t>The document does not intend to represent the full set of cases where
ime-variant routing computations could beneficially impact network performance - TVR computations could beneficially impact network
new use cases are expected to be generated over time. Similarly, the concrete performance -- new use cases are expected to be generated over time.
examples within each use case are meant to provide an existence proof of the use Similarly, the concrete examples within each use case are meant to
case, not to present any exhaustive enumeration of potential examples. It is li provide an existence proof of the use case and not to present any
kely that there exist multiple example networks that could be claimed as instanc exhaustive enumeration of potential examples. It is likely that multiple
es of any given use case.</t> example networks exist that could be claimed as instances of any given
<t>The document focuses on deterministic scenarios. Non-deterministic scen use case.</t>
arios such as vehicle-to-vehicle communication is out of the scope of the docume <t>The document focuses on deterministic scenarios. Non-deterministic
nt.</t> scenarios, such as vehicle-to-vehicle communication, are out of the
scope of the document.</t>
</section> </section>
<section anchor="Resource-Preservation"> <section anchor="Resource-Preservation">
<name>Resource Preservation</name> <name>Resource Preservation</name>
<t>Some nodes in a network might operate in resource-constrained environme <t>Some nodes in a network might operate in resource-constrained
nts or otherwise with limited internal resources. Constraints such as available environments or otherwise with limited internal resources. Constraints,
power, thermal ranges, and on-board storage can all impact the instantaneous ope such as available power, thermal ranges, and on-board storage, can all
ration of a node. In particular, resource management on such a node can require impact the instantaneous operation of a node. In particular, resource
that certain functionality be powered on (or off) to extend the ability of the n management on such a node can require that certain functionality be
ode to participate in the network.</t> powered on (or off) to extend the ability of the node to participate in
<t>When power on a node is running low, non-critical functions on the node the network.</t>
might be turned off in favor of extending node life. Alternatively, certain fun <t>When power on a node is running low, noncritical functions on the
ctions on a node may be turned off to allow the node to use available power to r node might be turned off in favor of extending node life. Alternatively,
espond to an event, such as data collection. When a node is in danger of violati certain functions on a node may be turned off to allow the node to use
ng a thermal constraint, normal processing might be paused in favor of a transit available power to respond to an event, such as data collection. When a
ion to a thermal safe mode until a regular operating condition is reestablished. node is in danger of violating a thermal constraint, normal processing
When local storage resources run low, a node might choose to expend power resou might be paused in favor of a transition to a thermal safe mode until a
rces to fuse, delete, or transmit data off the node to free space for future dat regular operating condition is reestablished. When local storage
a collection. There might also be cases where a node experiences a planned offli resources run low, a node might choose to expend power resources to
ne state to save and accumulate power.</t> compress, delete, or transmit data off the node to free up space for futur
<t>In addition to power, thermal, and storage, other resource constraints e
may exist on a node such that the preservation of resources are necessary to pre data collection. There might also be cases where a node experiences a
serve the existence (and proper function) of the node in the network. Nodes oper planned offline state to save and accumulate power.</t>
ating in these conditions might benefit from TVR computations as the connectivit <t>In addition to power, thermal, and storage, other resource
y of the node changes over time as part of node preservation.</t> constraints may exist on a node such that the preservation of resources
is necessary to preserve the existence (and proper function) of the
node in the network. Nodes operating in these conditions might benefit
from TVR computations as the connectivity of the node changes over time
as part of node preservation.</t>
<section anchor="assumptions"> <section anchor="assumptions">
<name>Assumptions</name> <name>Assumptions</name>
<t>To effectively manage on-board functionality based on available resou <t>To effectively manage on-board functionality based on available
rces, a node must comprehend specific aspects concerning the utilization and rep resources, a node must comprehend specific aspects concerning the
lenishment of resources. It is expected that patterns of the environment, device utilization and replenishment of resources. It is expected that
construction, and operational configuration exist with enough regularity and st patterns of the environment, device construction, and operational
ability to allow meaningful planning. The following assumptions are made with th configuration exist with enough regularity and stability to allow
is use case.</t> meaningful planning. The following assumptions are made with this use
<ol spacing="normal" type="1"><li> case:</t>
<t>Known resource expenditures. It is assumed that there exists some <ol spacing="normal" type="1">
determinable relationship between the resources available on a node and the res <li>Known resource expenditures.
ources needed to participate in a network. A node would need to understand when It is assumed that there exists
it has met some condition for participating in, or dropping out of, a network. T some determinable relationship between the resources available on a
his is somewhat similar to predicting the amount of battery life left on a lapto node and the resources needed to participate in a network. A node
p as a function of likely future usage.</t> would need to understand when it has met some condition for
</li> participating in, or dropping out of, a network. This is somewhat
<li> similar to predicting the amount of battery life left on a laptop as
<t>Predictable resource accumulation. It is assumed that the accumul a function of likely future usage.</li>
ation of resources on a node are predictable such that a node might expect (and <li>Predictable resource accumulation.
be able to communicate) when it is likely to next rejoin a network. This is sim It is assumed that the
ilar to predicting the time at which a battery on a laptop will be fully charged accumulation of resources on a node are predictable such that a node
.</t> might expect (and be able to communicate) when it is likely to next
</li> rejoin a network. This is similar to predicting the time at which a
<li> battery on a laptop will be fully charged.</li>
<t>Consistent cost functions. It is assumed that resource management <li>Consistent cost functions.
on a node is deterministic such that the management of a node as a function of It is assumed that resource
resource expenditure and accumulation is consistent enough for link planning.</t management on a node is deterministic such that the management of a
> node as a function of resource expenditure and accumulation is
</li> consistent enough for link planning.</li>
</ol> </ol>
</section> </section>
<section anchor="routing-impacts"> <section anchor="routing-impacts">
<name>Routing Impacts</name> <name>Routing Impacts</name>
<t>Resource management in these scenarios might involve turning off elem ents of the node as part of on-board resource management. These activities can a ffect data routing in a variety of ways.</t> <t>Resource management in these scenarios might involve turning off elem ents of the node as part of on-board resource management. These activities can a ffect data routing in a variety of ways.</t>
<ol spacing="normal" type="1"><li> <ol spacing="normal" type="1">
<t>Power Savings. On-board radios may be turned off to allow other n <li>Power Savings. On-board radios may be turned off to allow other
ode processing. This may happen on power-constrained devices to extend the batte node processing. This may happen on power-constrained devices to
ry life of the node or to allow a node to perform some other power-intensive tas extend the battery life of the node or to allow a node to perform
k.</t> some other power-intensive task.</li>
</li> <li>Thermal Savings. On-board radios may be turned off if there are
<li> thermal considerations on the node, such as an increase in a node's
<t>Thermal Savings. On-board radios may be turned off if there are t operating temperature.</li>
hermal considerations on the node, such as an increase in a node’s operating tem <li>Storage Savings. On-board radios may be turned on with the
perature.</t> purpose of transmitting data off the node to free local storage
</li> space to collect new data.</li>
<li>
<t>Storage Savings. On-board radios may be turned on with the purpos
e of transmitting data off the node to free local storage space to collect new d
ata.</t>
</li>
</ol> </ol>
<t>Whenever a communications device on a node changes its powered state there is the possibility (if the node is within range of other nodes in a networ k) that the topology of the network is changed, which impacts route calculations through the network. Additionally, whenever a node joins a network there may be a delay between the joining of the node to the network and any discovery that m ay take place relating to the status of the nodes functional neighborhood. Duri ng these times, forwarding to and from the node might be delayed pending some sy nchronization.</t> <t>Whenever a communications device on a node changes its powered state there is the possibility (if the node is within range of other nodes in a networ k) that the topology of the network is changed, which impacts route calculations through the network. Additionally, whenever a node joins a network there may be a delay between the joining of the node to the network and any discovery that m ay take place relating to the status of the node's functional neighborhood. Duri ng these times, forwarding to and from the node might be delayed pending some sy nchronization.</t>
</section> </section>
<section anchor="example"> <section anchor="example">
<name>Example</name> <name>Example</name>
<t>An illustrative example of a network necessitating resource preservat ion is an energy-harvesting wireless sensor network. In such a network, nodes re ly exclusively on environmental sources for power, such as solar panels. On-boar d power levels may fluctuate based on various factors including sensor activity, processing demands, and the node's position and orientation relative to its ene rgy source.</t> <t>An illustrative example of a network necessitating resource preservat ion is an energy-harvesting wireless sensor network. In such a network, nodes re ly exclusively on environmental sources for power, such as solar panels. On-boar d power levels may fluctuate based on various factors including sensor activity, processing demands, and the node's position and orientation relative to its ene rgy source.</t>
<t>Consider a simple three node network where each node accumulates powe <t>Consider a simple three-node network where each node accumulates powe
r through solar panels. Power available for Radio Frequency (RF) transmission i r through solar panels. Power available for radio frequency (RF) transmission i
s shown below in <xref target="Resource-Example-Plots"/>. In this figure, each o s shown in <xref target="Resource-Example-Plots"/>. In this figure, each of the
f the three nodes (Node 1, Node 2, and Node 3) have a different plot of availabl three nodes (Node 1, Node 2, and Node 3) has a different plot of available power
e power over time. This example assumes that a node will not power its radio un over time. This example assumes that a node will not power its radio until ava
til available power is over some threshold, which is shown by the horizontal lin ilable power is over some threshold, which is shown by the horizontal line on ea
e on each plot.</t> ch plot.</t>
<figure anchor="Resource-Example-Plots"> <figure anchor="Resource-Example-Plots">
<name>Node Power Over Time</name> <name>Node Power over Time</name>
<artwork type="ascii" align="center"><![CDATA[ <artwork type="ascii-art" align="center"><![CDATA[
Node 1 Node 2 Node 3 Node 1 Node 2 Node 3
P | P | ------- P | -- P | P | ------- P | --
o | ---- -- o | / \ o | / \ o | ---- -- o | / \ o | / \
w |~/~~~~\~~~~~/~~\~~ w |~/~~~~~~~~~\~~~~~~ w |~~~~~~~~/~~~~\~~~~ w |~/~~~~\~~~~~/~~\~~ w |~/~~~~~~~~~\~~~~~~ w |~~~~~~~~/~~~~\~~~~
e |/ \ / \ e |/ \ e | / \ e |/ \ / \ e |/ \ e | / \
r | --- - r | ----- r |------- --- r | --- - r | ----- r |------- ---
+---++----++----++- +---++----++----++- +---++----++----++- +---++----++----++- +---++----++----++- +---++----++----++-
t1 t2 t3 t1 t2 t3 t1 t2 t3 t1 t2 t3 t1 t2 t3 t1 t2 t3
Time Time Time Time Time Time
]]></artwork> ]]></artwork>
</figure> </figure>
<t>The connectivity of this three node network changes over time in ways
that may be predictable and are likely able to be communicated to other nodes i <t>The connectivity of this three-node network changes over time in
n this small sensor network. Examples of connectivity are shown in <xref target= ways that may be predictable and are likely able to be communicated to
"Resource-Example-Schedule"/>. This figure shows a sample of network connectivi other nodes in this small sensor network. Examples of connectivity are
ty at three times: t1, t2, and t3.</t> shown in <xref target="Resource-Example-Schedule"/>. This figure
shows a sample of network connectivity at three times: t1, t2, and
t3.</t>
<ul spacing="normal"> <ul spacing="normal">
<li> <li>
<t>At time t1 Node 1 and Node 2 have their radios powered on and are <t>At time t1, Node 1 and Node 2 have their radios powered on and
expected to communicate.</t> are expected to communicate.</t>
</li> </li>
<li> <li>
<t>At time t2 it is expected that Node 1 has its radio off, but tha <t>At time t2, it is expected that Node 1 has its radio off but
t Node 2 and Node 3 can communicate.</t> that Node 2 and Node 3 can communicate.</t>
</li> </li>
<li> <li>
<t>Finally, at time t3 it is expected that Node 1 may be turning its <t>Finally, at time t3, it is expected that Node 1 may be turning
radio off and that Node 2 and Node 3 are not powering their radios and there is its radio off, that Node 2 and Node 3 are not powering their
no expectation of connectivity.</t> radios, and there is no expectation of connectivity.</t>
</li> </li>
</ul> </ul>
<figure anchor="Resource-Example-Schedule"> <figure anchor="Resource-Example-Schedule">
<name>Topology over Time</name> <name>Topology over Time</name>
<artwork type="ascii" align="center"><![CDATA[ <artwork type="ascii-art" align="center"><![CDATA[
+----------+ +----------+ +----------+ +----------+ +----------+ +----------+
t1 | Node 1 |--------| Node 2 | | Node 3 | t1 | Node 1 |--------| Node 2 | | Node 3 |
+----------+ +----------+ +----------+ +----------+ +----------+ +----------+
+----------+ +----------+ +----------+ +----------+ +----------+ +----------+
t2 | Node 1 | | Node 2 |--------| Node 3 | t2 | Node 1 | | Node 2 |--------| Node 3 |
+----------+ +----------+ +----------+ +----------+ +----------+ +----------+
+----------+ +----------+ +----------+ +----------+ +----------+ +----------+
t3 | Node 1 | | Node 2 | | Node 3 | t3 | Node 1 | | Node 2 | | Node 3 |
skipping to change at line 187 skipping to change at line 256
+----------+ +----------+ +----------+ +----------+ +----------+ +----------+
t2 | Node 1 | | Node 2 |--------| Node 3 | t2 | Node 1 | | Node 2 |--------| Node 3 |
+----------+ +----------+ +----------+ +----------+ +----------+ +----------+
+----------+ +----------+ +----------+ +----------+ +----------+ +----------+
t3 | Node 1 | | Node 2 | | Node 3 | t3 | Node 1 | | Node 2 | | Node 3 |
+----------+ +----------+ +----------+ +----------+ +----------+ +----------+
]]></artwork> ]]></artwork>
</figure> </figure>
</section> </section>
</section> </section>
<section anchor="Operating-Efficiency"> <section anchor="Operating-Efficiency">
<name>Operating Efficiency</name> <name>Operating Efficiency</name>
<t>Some nodes in a network might alter their networking behavior to optimi ze metrics associated with the cost of a node's operation. While the resource pr eservation use case described in <xref target="Resource-Preservation"/> addresse s node survival, this use case discusses non-survival efficiencies such as the f inancial cost to operate the node and the environmental impact (cost) of using t hat node.</t> <t>Some nodes in a network might alter their networking behavior to optimi ze metrics associated with the cost of a node's operation. While the resource pr eservation use case described in <xref target="Resource-Preservation"/> addresse s node survival, this use case discusses non-survival efficiencies such as the f inancial cost to operate the node and the environmental impact (cost) of using t hat node.</t>
<t>When a node operates using some pre-existing infrastructure there is ty pically some cost associated with the use of that infrastructure. Sample costs i nclude the following.</t> <t>When a node operates using some preexisting infrastructure, there is ty pically some cost associated with the use of that infrastructure. Sample costs a re included as follows:</t>
<ol spacing="normal" type="1"><li> <ol spacing="normal" type="1"><li>
<t>Nodes that use existing wireless communications such as a cellular <t>Nodes that use existing wireless communications, such as a
infrastructure must pay to communicate to and through that infrastructure.</t> cellular infrastructure, must pay to communicate to and through that
infrastructure.</t>
</li> </li>
<li> <li>
<t>Nodes supplied with electricity from an energy provider pay for the <t>Nodes supplied with electricity from an energy provider pay for
power they use.</t> the power they use.</t>
</li> </li>
<li> <li>
<t>Nodes that cluster computation and activities might increase the te <t>Nodes that cluster computation and activities might increase the
mperature of the node and incur additional costs associated with cooling the nod temperature of the node and incur additional costs associated with
e (or collection of nodes).</t> cooling the node (or collection of nodes).</t>
</li> </li>
<li> <li>
<t>Beyond financial costs, assessing the environmental impact of opera <t>Beyond financial costs, assessing the environmental impact of
ting a node may also be modeled as a cost associated with node operation, to inc operating a node may also be modeled as a cost associated with node
lude achieving carbon credits or other incentives for green computing.</t> operation, to include achieving carbon credits or other incentives
for green computing.</t>
</li> </li>
</ol> </ol>
<t>When the cost of using a node's resources changes over time, a node can <t>When the cost of using a node's resources changes over time, a node
benefit from predicting when data transmissions might optimize costs, environme can benefit from predicting when data transmissions might optimize
ntal impacts, or other metrics associated with operation.</t> costs, environmental impacts, or other metrics associated with
operation.</t>
<section anchor="assumptions-1"> <section anchor="assumptions-1">
<name>Assumptions</name> <name>Assumptions</name>
<t>The ability to predict the impact of a node's resource utilization ov <t>The ability to predict the impact of a node's resource utilization
er time presumes that the node exists within a defined environment (or infrastru over time presumes that the node exists within a defined environment
cture). Some characteristics of these environments are listed as follows.</t> (or infrastructure). Some characteristics of these environments are
listed as follows:</t>
<ol spacing="normal" type="1"><li> <ol spacing="normal" type="1"><li>
<t>Cost Measureability. The impacts of operating a node within its e <t>Cost Measurability. The impacts of operating a node within its
nvironment can be measured in a deterministic way. For example, that the cost-pe environment can be measured in a deterministic way. For example,
r-bit of data over a cellular network or the cost-per-kilowatt of energy used ar the cost-per-bit of data over a cellular network or the
e known.</t> cost-per-kilowatt of energy used are known.</t>
</li> </li>
<li> <li>
<t>Cost Predictability. Changes to the impacts of resource utilizati <t>Cost Predictability. Changes to the impacts of resource
on are known in advance. For example, if the cost of energy is less expensive in utilization are known in advance. For example, if the cost of
the evening than during the day, there exists some way of communicating this ch energy is less expensive in the evening than during the day, there
ange to a node.</t> exists some way of communicating this change to a node.</t>
</li> </li>
<li> <li>
<t>Cost Persistent. Changes to the cost of operating in the environm <t>Cost Persistent. Changes to the cost of operating in the
ent persist for a sufficient amount of time such that behavior can be adjusted i environment persist for a sufficient amount of time such that
n response to changing costs. If costs change too rapidly it is likely not possi behavior can be adjusted in response to changing costs. If costs
ble to meaningfully react to their change.</t> change too rapidly, it is likely not possible to meaningfully react
to their change.</t>
</li> </li>
<li> <li>
<t>Cost Magnitude. The magnitude of cost changes is such that a node <t>Cost Magnitude. The magnitude of cost changes is such that a
experiences a minimum threshold cost reduction through optimization. A specifie node experiences a minimum threshold cost reduction through
d time period is designated for measuring the cost reduction.</t> optimization. A specified time period is designated for measuring
the cost reduction.</t>
</li> </li>
</ol> </ol>
</section> </section>
<section anchor="routing-impacts-1"> <section anchor="routing-impacts-1">
<name>Routing Impacts</name> <name>Routing Impacts</name>
<t>Optimizing resource utilization can affect route computation in ways <t>Optimizing resource utilization can affect route computation in
similar to those experienced with resource preservation. The route computation m ways similar to those experienced with resource preservation. The
ay not change the available path but the topology as seen by an end point would route computation may not change the available path, but the topology
be different. Cost optimization can impact route calculation in a variety of way as seen by an endpoint would be different. Cost optimization can
s, some of which are described as follows.</t> impact route calculation in a variety of ways, some of which are
described as follows:</t>
<ol spacing="normal" type="1"><li> <ol spacing="normal" type="1"><li>
<t>Link Filtering. Data might be accumulated on a node waiting for a <t>Link Filtering. Data might be accumulated on a node waiting for
cost-effective time for data transmission. Individual link costs might be annot a cost-effective time for data transmission. Individual link costs
ated with cost information such that adjacencies with a too-high cost might not might be annotated with cost information such that adjacencies
be used for forwarding. This effectively filters which adjacencies are used (pos with a too high cost might not be used for forwarding. This
sibly as a function of the type of data being routed).</t> effectively filters which adjacencies are used (possibly as a
function of the type of data being routed).</t>
</li> </li>
<li> <li>
<t>Burst Planning. In cases where there is a cost savings associated <t>Burst Planning. In cases where there is a cost savings
with fewer longer transmissions (versus many smaller transmissions), nodes migh associated with fewer longer transmissions (versus many smaller
t refuse to forward data until a sufficient data volume exists to justify a tran transmissions), nodes might refuse to forward data until a
smission.</t> sufficient data volume exists to justify a transmission.</t>
</li> </li>
<li> <li>
<t>Environmental Measurement. Nodes that measure the quality of indi <t>Environmental Measurement. Nodes that measure the quality of
vidual links can compute the overall cost of using a link as a function of the s individual links can compute the overall cost of using a link as a
ignal strength of the link. If link quality is insufficient due to environmental function of the signal strength of the link. If link quality is
conditions (such as clouds on a free-space optical link or long distance RF tra insufficient due to environmental conditions (such as clouds on a
nsmission in a storm) the cost required to communicate over the link may be too free-space optical link or long distance RF transmission in a
much, even if access to infrastructure is otherwise in a less expensive time of storm) the cost required to communicate over the link may be too
day.</t> much, even if access to infrastructure is otherwise in a less
expensive time of day.</t>
</li> </li>
</ol> </ol>
<t>In each of these cases, some consideration of the efficiency of trans <t>In each of these cases, some consideration of the efficiency of
mission is prioritized over achieving a particular data rate. Waiting until dat transmission is prioritized over achieving a particular data rate.
a rate costs are lower takes advantage of platforms using time-of-use rate plans Waiting until data rate costs are lower takes advantage of platforms
both for pay-as-you-go data and associated energy costs. Accumulating data vo using time-of-use rate plans -- both for pay-as-you-go data and
lumes and choosing more opportune times to transmit can also result in less ener associated energy costs. Accumulating data volumes and choosing more
gy consumption by radios and, thus, less operating cost for platforms.</t> opportune times to transmit can also result in less energy consumption
by radios and, thus, less operating cost for platforms.</t>
</section> </section>
<section anchor="example-cellular-network"> <section anchor="example-cellular-network">
<name>Example : Cellular Network</name> <name>Example: Cellular Network</name>
<t>One example of a network where nodes might seek to optimize operating <t>One example of a network where nodes might seek to optimize
cost is a set of nodes operating over cellular connections that charge both On- operating cost is a set of nodes operating over cellular connections
Peak and Off-Peak data rates. In this case, individual nodes may be allocated a that charge both peak and off-peak data rates. In this case,
fixed set of "On-Peak" minutes such that exceeding that amount of time results i individual nodes may be allocated a fixed set of "peak" minutes
n expensive overage charges. Generally, the concept of On-Peak and Off-Peak minu such that exceeding that amount of time results in expensive overage
tes exists to deter the use of a given network at times when the cellular networ charges. Generally, the concept of peak and off-peak minutes exists
k is likely to encounter heavy call volumes (such as during the workday).</t> to deter the use of a given network at times when the cellular network
<t>Just as pricing information can act as a deterrent (or incentive) for is likely to encounter heavy call volumes (such as during the
a human cellular user, this pricing information can be codified in ways that al workday).</t>
so allow machine-to-machine (M2M) connections to prioritize Off-Peak communicati <t>Just as pricing information can act as a deterrent (or incentive)
ons for certain types of data exchange. Many M2M traffic exchanges involve sched for a human cellular user, this pricing information can be codified in
ulable activities, such as nightly bulk file transfers, pushing software updates ways that also allow machine-to-machine (M2M) connections to
, synchronizing datastores, and sending non-critical events and logs. These acti prioritize off-peak communications for certain types of data
vities are usually already scheduled to minimize impact on businesses and custom exchange. Many M2M traffic exchanges involve schedulable activities,
ers, but can also be scheduled to minimize overall cost.</t> such as nightly bulk file transfers, pushing software updates,
<t>Consider a simple three node network, similar to the one pictured in synchronizing datastores, and sending noncritical events and
<xref target="Resource-Example-Plots"/>, except that in this case the resource t logs. These activities are usually already scheduled to minimize
hat varies over time is the cost of the data exchange. This case is illustrated impact on businesses and customers but can also be scheduled to
below in <xref target="Efficiency-Example-Plots"/>. In this figure, a series of minimize overall cost.</t>
three plots are given, one for each of nodes Node 1, Node 2, and Node 3. Each o <t>Consider a simple three-node network, similar to the one pictured
f these nodes exists in a different cellular service area which has different On in <xref target="Resource-Example-Plots"/>, except that in this case
-Peak and Off-Peak data rate times. This is shown in each figure by times when t the resource that varies over time is the cost of the data
he cost is low (Off-Peak) and when the cost is high (On-Peak).</t> exchange. This case is illustrated below in <xref
target="Efficiency-Example-Plots"/>. In this figure, a series of three
plots are given, one for each of the three nodes (Node 1, Node 2, and
Node 3). Each of these nodes exists in a different cellular service
area that has different peak and off-peak data rate times. This is
shown in each figure by times when the cost is low (off-peak) and when
the cost is high (peak).</t>
<figure anchor="Efficiency-Example-Plots"> <figure anchor="Efficiency-Example-Plots">
<name>Data Cost Over Time</name> <name>Data Cost over Time</name>
<artwork type="ascii" align="center"><![CDATA[ <artwork type="ascii-art" align="center"><![CDATA[
Node 1 Node 2 Node 3 Node 1 Node 2 Node 3
C | +--------- C |--+ C |-------------+ C | +--------- C |--+ C |-------------+
o | | o | | o | | o | | o | | o | |
s | | s | | s | | s | | s | | s | |
t |-------+ t | +---------------- t | +------- t |-------+ t | +---------------- t | +-------
| | | | | |
+---++----++----++-- +----++----++----++-- +----++----++-----++-- +---++----++----++-- +----++----++----++-- +----++----++-----++--
t1 t2 t3 t1 t2 t3 t1 t2 t3 t1 t2 t3 t1 t2 t3 t1 t2 t3
Time Time Time Time Time Time
]]></artwork> ]]></artwork>
</figure> </figure>
<t>Given the presumption that peak times are known in advance, the cost
of data exchange from Node 1 through Node 2 to Node 3 can be calculated. Example <t>Given the presumption that peak times are known in advance, the
s of these data exchanges are shown in <xref target="Efficiency-Example-Schedule cost of data exchange from Node 1 through Node 2 to Node 3 can be
"/>. From this figure, both times t1 and t3 result in a smaller cost of data exc calculated. Examples of these data exchanges are shown in <xref
hange than choosing to communicate data at time t2.</t> target="Efficiency-Example-Schedule"/>. From this figure, both times
t1 and t3 result in a smaller cost of data exchange than choosing to
communicate data at time t2.</t>
<figure anchor="Efficiency-Example-Schedule"> <figure anchor="Efficiency-Example-Schedule">
<name>Data Exchange Cost over Time</name> <name>Data Exchange Cost over Time</name>
<artwork type="ascii" align="center"><![CDATA[ <artwork type="ascii-art" align="center"><![CDATA[
+-----------+ +-----------+ +-----------+ +-----------+ +-----------+ +-----------+
t1 | Node N1 |---LOW----| Node N2 |---HIGH---| Node N3 | t1 | Node N1 |---LOW----| Node N2 |---HIGH---| Node N3 |
+-----------+ +-----------+ +-----------+ +-----------+ +-----------+ +-----------+
+-----------+ +-----------+ +-----------+ +-----------+ +-----------+ +-----------+
t2 | Node N1 |---HIGH---| Node N2 |---HIGH---| Node N3 | t2 | Node N1 |---HIGH---| Node N2 |---HIGH---| Node N3 |
+-----------+ +-----------+ +-----------+ +-----------+ +-----------+ +-----------+
+-----------+ +-----------+ +-----------+ +-----------+ +-----------+ +-----------+
t3 | Node N1 |---HIGH---| Node N2 |----LOW---| Node N3 | t3 | Node N1 |---HIGH---| Node N2 |----LOW---| Node N3 |
+-----------+ +-----------+ +-----------+ +-----------+ +-----------+ +-----------+
]]></artwork> ]]></artwork>
</figure> </figure>
<t>While not possible in every circumstance, a highly optimized plan cou
ld be to communicate from Node 1 to Node 2 at time t1 and then queue data at Nod <t>While not possible in every circumstance, a highly optimized plan
e 2 until time t3 for delivery to Node 3. This case is shown in <xref target="Ef could be to communicate from Node 1 to Node 2 at time t1 and then
ficiency-Example-Store"/>.</t> queue data at Node 2 until time t3 for delivery to Node 3. This case
is shown in <xref target="Efficiency-Example-Store"/>.</t>
<figure anchor="Efficiency-Example-Store"> <figure anchor="Efficiency-Example-Store">
<name>Data Cost using Storage</name> <name>Data Cost Using Storage</name>
<artwork type="ascii" align="center"><![CDATA[ <artwork type="ascii-art" align="center"><![CDATA[
+-----------+ +-----------+ +-----------+ +-----------+
t1 | Node N1 |---LOW----| Node N2 | t1 | Node N1 |---LOW----| Node N2 |
+-----------+ +-----------+ +-----------+ +-----------+
+-----------+ +-----------+ +-----------+ +-----------+
t3 | Node N2 |----LOW---| Node N3 | t3 | Node N2 |----LOW---| Node N3 |
+-----------+ +-----------+ +-----------+ +-----------+
]]></artwork> ]]></artwork>
</figure> </figure>
</section> </section>
<section anchor="another-example-tidal-network"> <section anchor="another-example-tidal-network">
<name>Another Example : Tidal Network</name> <name>Another Example: Tidal Network</name>
<t>Another example related to operating efficiency is what is often refe <t>Another example related to operating efficiency is often referred to
rred to as a 'tidal network,' in which traffic volume undergoes significant fluc as a "tidal network," in which traffic volume undergoes significant fluctuations
tuations at different times. Take, for instance, a campus network, where thousan at different times. Take, for instance, a campus network, where thousands of in
ds of individuals go to classrooms and libraries during the daytime and retire t dividuals go to classrooms and libraries during the daytime and retire to the do
o the dormitories at night. This results in a regular oscillation of network tra rmitories at night. This results in a regular oscillation of network traffic acr
ffic across various locations within the campus.</t> oss various locations within the campus.</t>
<t>In the context of a tidal network scenario, energy-saving methods may include the deactivation of some or all components of network nodes. These acti vities have the potential to alter network topology and impact data routing in a variety of ways. Ports on network nodes can be selectively disabled or enabled based on traffic patterns, thereby reducing the energy consumption of nodes duri ng periods of low network traffic.</t> <t>In the context of a tidal network scenario, energy-saving methods may include the deactivation of some or all components of network nodes. These acti vities have the potential to alter network topology and impact data routing in a variety of ways. Ports on network nodes can be selectively disabled or enabled based on traffic patterns, thereby reducing the energy consumption of nodes duri ng periods of low network traffic.</t>
<t>More information on Tidal Network can be found in <xref target="TIDAL "/>.</t> <t>More information on tidal networks can be found in <xref target="I-D. zzd-tvr-use-case-tidal-network"/>.</t>
</section> </section>
</section> </section>
<section anchor="Dynamic-Reachability"> <section anchor="Dynamic-Reachability">
<name>Dynamic Reachability</name> <name>Dynamic Reachability</name>
<t>When a node is placed on a mobile platform, the mobility of the platfor <t>When a node is placed on a mobile platform, the mobility of the
m (and thus the mobility of the node) may cause changes to the topology of the n platform (and thus the mobility of the node) may cause changes to the
etwork over time. The impacts on the dynamics of the topology can be very import topology of the network over time. The impacts on the dynamics of the
ant. To the extent that the relative mobility between and among nodes in the net topology can be very important. To the extent that the relative mobility
work and the impacts of the environment on the signal propagation can be predict between and among nodes in the network and the impacts of the
ed, the associated loss and establishment of adjacencies can also be planned for environment on the signal propagation can be predicted, the associated
.</t> loss and establishment of adjacencies can also be planned for.</t>
<t>Mobility can cause the loss of an adjacent link in several ways, such a <t>Mobility can cause the loss of an adjacent link in several ways, such a
s the following.</t> s that which follows:</t>
<ol spacing="normal" type="1"><li> <ol spacing="normal" type="1"><li>
<t>Node mobility can cause the distance between two nodes to become la rge enough that distance-related attenuation causes the mobile node to lose conn ectivity with one or more other nodes in the network.</t> <t>Node mobility can cause the distance between two nodes to become la rge enough that distance-related attenuation causes the mobile node to lose conn ectivity with one or more other nodes in the network.</t>
</li> </li>
<li> <li>
<t>Node mobility can also be used to maintain a required distance from other mobile nodes in the network. While moving, external characteristics may c ause the loss of links through occultation or other hazards of traversing a shar ed environment.</t> <t>Node mobility can also be used to maintain a required distance from other mobile nodes in the network. While moving, external characteristics may c ause the loss of links through occultation or other hazards of traversing a shar ed environment.</t>
</li> </li>
<li> <li>
<t>Node mobility can cause the distance between two nodes to vary quic kly over the time making it complicated to establish and maintain connectivity.< /t> <t>Node mobility can cause the distance between two nodes to vary quic kly over time, making it complicated to establish and maintain connectivity.</t>
</li> </li>
<li> <li>
<t>Nodes equipped with communication terminals capable of adjusting th eir orientation or moving behind and emerging from barriers will also establish and lose connectivity with other nodes as a function of that motion.</t> <t>Nodes equipped with communication terminals capable of adjusting th eir orientation or moving behind and emerging from barriers will also establish and lose connectivity with other nodes as a function of that motion.</t>
</li> </li>
</ol> </ol>
<t>Mobile nodes, like any node, may have concerns regarding resource prese
rvation and cost efficiency. However, they also face unique challenges associate <t>Mobile nodes, like any node, may encounter issues regarding resource
d with their mobility. The intermittent availability of links can lead to dynami preservation and cost efficiency. In addition, they may face unique
c neighbor relationships at the node level. This use case aims to examine the ro challenges associated with their mobility. The intermittent availability of
uting implications of motion-induced changes to network topology.</t> links can lead to dynamic neighbor relationships at the node level. This use
case aims to examine the routing implications of motion-induced changes to
network topology.</t>
<section anchor="assumptions-2"> <section anchor="assumptions-2">
<name>Assumptions</name> <name>Assumptions</name>
<t>Predicting the impact of node mobility on route computation requires some information relating to the nature of the mobility and the nature of the en vironment being moved through. Some information presumed to exist for planning i s listed as follows.</t> <t>Predicting the impact of node mobility on route computation requires some information relating to the nature of the mobility and the nature of the en vironment being moved through. Some information presumed to exist for planning i s listed as follows:</t>
<ol spacing="normal" type="1"><li> <ol spacing="normal" type="1"><li>
<t>Path Predictability. The path of a mobile node through its enviro <t>Path Predictability. The path of a mobile node through its
nment is known (or can be predicted) as a function of (at least) time. It is pre environment is known (or can be predicted) as a function of (at
sumed that mobile nodes using time-variant algorithms would not exhibit purely r least) time. It is presumed that mobile nodes using TVR
andom motion.</t> algorithms would not exhibit purely random motion.</t>
</li> </li>
<li> <li>
<t>Environmental Knowledge. When otherwise well-connected mobile nod <t>Environmental Knowledge. When otherwise well-connected mobile
es pass through certain elements of their environment (such as a storm, a tunnel nodes pass through certain elements of their environment (such as
, or the horizon) they may lose connectivity. The duration of this connectivity a storm, a tunnel, or the horizon), they may lose connectivity. The
loss is assumed to be calculable as a function of node mobility and the environm duration of this connectivity loss is assumed to be calculable as
ent itself.</t> a function of node mobility and the environment itself.</t>
</li> </li>
</ol> </ol>
</section> </section>
<section anchor="routing-impacts-2"> <section anchor="routing-impacts-2">
<name>Routing Impacts</name> <name>Routing Impacts</name>
<t>Changing a network topology affects the computation of paths (or subp aths) through that topology. In particular, the following features can be implem ented in a network with mobile nodes such that different paths might be computed over time.</t> <t>Changing a network topology affects the computation of paths (or subp aths) through that topology. In particular, the following features can be implem ented in a network with mobile nodes such that different paths might be computed over time:</t>
<ol spacing="normal" type="1"><li> <ol spacing="normal" type="1"><li>
<t>Adjacent Link Expiration. A node might be able to predict that an <t>Adjacent Link Expiration. A node might be able to predict that
adjacency will expire as a function of that node's mobility, the other node's m an adjacency will expire as a function of that node's mobility,
obility, or some characteristic of the environment. Determining that an adjacenc the other node's mobility, or some characteristic of the
y has expired allows a route computation to plan for that loss, rather than defa environment. Determining that an adjacency has expired allows a
ult to an error recovery mechanism.</t> route computation to plan for that loss rather than default to an
error recovery mechanism.</t>
</li> </li>
<li> <li>
<t>Adjacent Link Resumption. Just as the loss of an adjacency can be <t>Adjacent Link Resumption. Just as the loss of an adjacency can
predicted, it may be possible to predict when an adjacency will resume.</t> be predicted, it may be possible to predict when an adjacency will
resume.</t>
</li> </li>
<li> <li>
<t>Data Rate Adjustments. The achievable data rate over a given link <t>Data Rate Adjustments. The achievable data rate over a given
is not constant over time, and may vary significantly as a function of both rel link is not constant over time and may vary significantly as a
ative mobility between a transmitter and receiver as well as the environment bei function of both relative mobility between a transmitter and
ng transmitted through. Knowledge of both mobility and environmental state may a receiver as well as the environment being transmitted
llow for prediction of data rates which may impact path computation.</t> through. Knowledge of both mobility and environmental state may
allow for prediction of data rates, which may impact path
computation.</t>
</li> </li>
<li> <li>
<t>Adjacent Link Filtering. Separate from the instantaneous presence <t>Adjacent Link Filtering. Separate from the instantaneous
or absence of an adjacency, a route computation might choose to not use an adja presence or absence of an adjacency, a route computation might
cency if that adjacency is likely to expire in the near future or if it is likel choose to not use an adjacency if that adjacency is likely to
y to experience a significant drop in predicted data rate.</t> expire in the near future or if it is likely to experience a
significant drop in predicted data rate.</t>
</li> </li>
</ol> </ol>
</section> </section>
<section anchor="example-mobile-satellites"> <section anchor="example-mobile-satellites">
<name>Example : Mobile Satellites</name> <name>Example: Mobile Satellites</name>
<t>A relatively new type of mobile network that has emerged over the pas <t>A relatively new type of mobile network that has emerged over the pas
t several years is the Low Earth Orbit (LEO) networked constellation (LEO-NC). T t several years is the Low Earth Orbit (LEO) networked constellation. There are
here are a number of such constellations being built by both private industry an a number of such constellations being built by both private industry and governm
d governments. While this example describes LEO satellites systems, the mobility ents. While this example describes LEO satellite systems, the mobility events ca
events can be applied to satellite systems orbiting at different altitude (incl n be applied to satellite systems orbiting at different altitudes (including Ver
uding Very LEO (V-LEO) or Medium Earth Orbit (MEO)).</t> y LEO (V-LEO) or Medium Earth Orbit (MEO)).</t>
<t>Many LEO-NCs have a similar operational concept of hundreds-to-thousa <t>Many LEO networked constellations have a similar operational concept
nds of inexpensive spacecraft that can communicate both with their orbital neigh of hundreds to thousands of inexpensive spacecraft that can communicate both wit
bors as well as down to any ground station that they happen to be passing over. h their orbital neighbors as well as down to any ground station that they happen
A ground station is a facility used to communicate with satellites in low Earth to be passing over. A ground station is a facility used to communicate with sat
orbit. The relationship between an individual spacecraft and an individual groun ellites in LEO. The relationship between an individual spacecraft and an individ
d station becomes somewhat complex as each spacecraft may only be over a single ual ground station becomes somewhat complex as each spacecraft may only be over
ground station for a few minutes at a time. Moreover, as a function of the const a single ground station for a few minutes at a time. Moreover, as a function of
ellation topology, there are scenarios where (1) the inter-satellite links need the constellation topology, there are scenarios where (1) the inter-satellite li
to be shut down for interference avoidance purposes or (2) the network topology nks need to be shut down for interference avoidance purposes or (2) the network
changes, which modifies the neighbors of a given spacecraft.</t> topology changes, which modifies the neighbors of a given spacecraft.</t>
<t>A LEO-NC represents a good example of planned mobility based on the p <t>A LEO networked constellation represents a good example of planned mo
redictability of spacecraft in orbit. While other mobile vehicles may encounter bility based on the predictability of spacecraft in orbit. While other mobile ve
unpredictable fluctuations in velocity, spacecraft operate in an environment wit hicles may encounter unpredictable fluctuations in velocity, spacecraft operate
h relatively stable velocity conditions. This determinism makes them an excellen in an environment with relatively stable velocity conditions. This determinism m
t candidate for time-variant route computations. However, inter-satellite link f akes them an excellent candidate for TVR computations. However, inter-satellite
ailures could still introduce unpredictability in the network topology.</t> link failures could still introduce unpredictability in the network topology.</t
<t>Consider three spacecraft (N1, N2, and N3) following each other seque >
ntially in the same orbit. This is sometimes called a string of pearls configura <t>Consider three spacecraft (N1, N2, and N3) following each other seque
tion. Spacecraft N2 always maintains connectivity to its two neighbor spacecraft ntially in the same orbit. This is sometimes called a "string of pearls" configu
, N1 which is behind in the orbit and N3 which is ahead in the orbit. This confi ration. Spacecraft N2 always maintains connectivity to its two neighbor spacecra
guration is illustrated in <xref target="Mobility-SOP"/>. While these spacecraft ft: N1, which is behind in the orbit, and N3, which is ahead in the orbit. This
are all mobile, their relative mobility ensures continuous contact with each ot configuration is illustrated in <xref target="Mobility-SOP"/>. While these space
her under normal conditions.</t> craft are all mobile, their relative mobility ensures continuous contact with ea
ch other under normal conditions.</t>
<figure anchor="Mobility-SOP"> <figure anchor="Mobility-SOP">
<name>Three Sequential Spacecraft</name> <name>Three Sequential Spacecraft</name>
<artwork type="ascii" align="center"><![CDATA[ <artwork type="ascii-art" align="center"><![CDATA[
.--. .--. .--. .--. .--. .--.
####-| N1 |-#### <---> ####-| N2 |-#### <---> ####-| N3 |-#### ####-| N1 |-#### <---> ####-| N2 |-#### <---> ####-| N3 |-####
\__/ \__/ \__/ \__/ \__/ \__/
]]></artwork> ]]></artwork>
</figure> </figure>
<t>Flying over a ground station imposes a non-relative motion between th
e ground and the spacecraft - namely that any given ground station will only be <t>Flying over a ground station imposes a non-relative motion between th
in view of the spacecraft for a short period of time. The times at which each sp e ground and the spacecraft -- namely that any given ground station will only be
acecraft can see the ground station is shown in the plots in <xref target="Mobil in view of the spacecraft for a short period of time. The times at which each s
ity-Example"/>. In this figure, ground contact is shown when the plot is high, a pacecraft can see the ground station is shown in the plots in <xref target="Mobi
nd a lack of ground contact is shown when the graph is low. From this, we see th lity-Example"/>. In this figure, ground contact is shown when the plot is high,
at spacecraft N3 can see ground at time t1, N2 sees ground at time t2, and space and a lack of ground contact is shown when the graph is low. From this, we see t
craft N1 sees ground at time t3.</t> hat spacecraft N3 can see ground at time t1, N2 sees ground at time t2, and spac
ecraft N1 sees ground at time t3.</t>
<figure anchor="Mobility-Example"> <figure anchor="Mobility-Example">
<name>Spacecraft Ground Contacts Over Time</name> <name>Spacecraft Ground Contacts over Time</name>
<artwork type="ascii" align="center"><![CDATA[ <artwork type="ascii-art" align="center"><![CDATA[
Spacecraft N1 Spacecraft N2 Spacecraft N3 Spacecraft N1 Spacecraft N2 Spacecraft N3
G | G | G | G | G | G |
r | +--+ r | +--+ r | +--+ r | +--+ r | +--+ r | +--+
o | | | o | | | o | | | o | | | o | | | o | | |
u | | | u | | | u | | | u | | | u | | | u | | |
n |--------------+ +- n |---------+ +------- n |---+ +------------- n |--------------+ +- n |---------+ +------- n |---+ +-------------
d | d | d | d | d | d |
+---++----++----++-- +----++----++----++-- +----++----++----++-- +---++----++----++-- +----++----++----++-- +----++----++----++--
t1 t2 t3 t1 t2 t3 t1 t2 t3 t1 t2 t3 t1 t2 t3 t1 t2 t3
Time Time Time Time Time Time
]]></artwork> ]]></artwork>
</figure> </figure>
<t>Since the ground station in this example is stationary, each spacecra ft will pass over it, resulting in a change to the network topology. This topolo gy change is shown in <xref target="Mobility-Example-Topology"/>. At time t1, an y message residing on N3 and destined for the ground could be forwarded directly to the ground station. At time t2, that same message would need to, instead, be forwarded to N2 and then forwarded to ground. By time t3, the same message woul d need to be forwarded from N2 to N1 and then down to ground.</t> <t>Since the ground station in this example is stationary, each spacecra ft will pass over it, resulting in a change to the network topology. This topolo gy change is shown in <xref target="Mobility-Example-Topology"/>. At time t1, an y message residing on N3 and destined for the ground could be forwarded directly to the ground station. At time t2, that same message would need to, instead, be forwarded to N2 and then forwarded to ground. By time t3, the same message woul d need to be forwarded from N2 to N1 and then down to ground.</t>
<figure anchor="Mobility-Example-Topology"> <figure anchor="Mobility-Example-Topology">
<name>Constellation Topology Over Time</name> <name>Constellation Topology over Time</name>
<artwork type="ascii" align="center"><![CDATA[ <artwork type="ascii-art" align="center"><![CDATA[
+------+ +------+ +------+ +------+
t1 | N2 |----------| N3 | t1 | N2 |----------| N3 |
+------+ +---+--+ +------+ +---+--+
| |
/|\ /|\
\___/ \___/
/ \ / \
Ground Ground
Station Station
------------------------------------------------------------------ ------------------------------------------------------------------
skipping to change at line 408 skipping to change at line 613
+---+--+ +------+ +------+ +---+--+ +------+ +------+
| |
/|\ /|\
\___/ \___/
/ \ / \
Ground Ground
Station Station
------------------------------------------------------------------ ------------------------------------------------------------------
]]></artwork> ]]></artwork>
</figure> </figure>
<t>This example focuses on the case where the spacecrafts fly over a gro
und station and introduce changes in the network topology. There are also scenar <t>This example focuses on the case where the spacecrafts fly over a gro
ios where the in-constellation network topology varies over time following a det und station and introduce changes in the network topology. There are also scenar
erministic time-driven operation from the ground system. More information on in- ios where the in-constellation network topology varies over time following a det
constellation network topology can be found in <xref target="LHAN-PROB"/> and <x erministic time-driven operation from the ground system. More information on in-
ref target="LWOOD-SCN"/>. For this example, and in particular for within constel constellation network topology can be found in <xref target="I-D.lhan-problems-r
lation network topology changes, TVR approach is important to avoid the Interior equirements-satellite-net"/> and <xref target="SCN"/>. For this example, and in
Gateway Protocol (IGP) issues mentioned in <xref target="LHAN-PROB"/>.</t> particular for within constellation network topology changes, the TVR approach i
s important to avoid the Interior Gateway Protocol (IGP) issues mentioned in <xr
ef target="I-D.lhan-problems-requirements-satellite-net"/>.</t>
</section> </section>
<section anchor="another-example-predictable-moving-vessels"> <section anchor="another-example-predictable-moving-vessels">
<name>Another Example : Predictable Moving Vessels</name> <name>Another Example: Predictable Moving Vessels</name>
<t>Another relevant example for this use case involves the movement of v <t>Another relevant example for this use case involves the movement of v
essels with predictable trajectories, such as ferries or planes. These end point essels with predictable trajectories, such as ferries or planes. These endpoints
s often rely on a combination of satellite and terrestrial systems for Internet often rely on a combination of satellite and terrestrial systems for Internet c
connectivity, capitalizing on their predictable journeys.</t> onnectivity, capitalizing on their predictable journeys.</t>
<t>This scenario also covers situations where nodes employ dynamic point ing solutions to track the mobility of other nodes. In such cases, nodes dynamic ally adjust their antennas and application settings to determine the optimal tim ing for data transmission along the path.</t> <t>This scenario also covers situations where nodes employ dynamic point ing solutions to track the mobility of other nodes. In such cases, nodes dynamic ally adjust their antennas and application settings to determine the optimal tim ing for data transmission along the path.</t>
</section> </section>
</section> </section>
<section anchor="acknowledgments">
<name>Acknowledgments</name>
<t>Many thanks to Tony Li, Peter Ashwood-Smith, Abdussalam Baryun, Arashmi
d Akhavain, Dirk Trossen, Brian Sipos, Alexandre Petrescu, Haoyu Song, Hou Dongx
u, Tianran Zhou, Jie Dong, Nkosinathi Nzima and Vinton Cerf for their useful com
ments that helped improve the document.</t>
</section>
<section anchor="security-considerations"> <section anchor="security-considerations">
<name>Security Considerations</name> <name>Security Considerations</name>
<t>While this document does not define a specific mechanism or solution, i t serves to motivate the use of Time-Based Validation and Revocation (TVR). Ther efore, security considerations are anticipated to be addressed elsewhere, such a s within a TVR schedule definition or through a protocol extension utilizing a T VR schedule. However it's important to note that time synchronization is critica l within a network employing a TVR schedule. Any unauthorized changes to network clocks can disrupt network functionality, potentially leading to a Denial of Se rvice (DoS) attack.</t> <t>While this document does not define a specific mechanism or solution, i t serves to motivate the use of time-based validation and revocation strategies. Therefore, security considerations are anticipated to be addressed elsewhere, s uch as within a TVR schedule definition or through a protocol extension utilizin g a TVR schedule. However, it's important to note that time synchronization is c ritical within a network employing a TVR schedule. Any unauthorized changes to n etwork clocks can disrupt network functionality, potentially leading to a Denial of Service (DoS) attack.</t>
</section> </section>
<section anchor="iana-considerations"> <section anchor="iana-considerations">
<name>IANA Considerations</name> <name>IANA Considerations</name>
<t>This document has no IANA actions.</t> <t>This document has no IANA actions.</t>
</section> </section>
</middle> </middle>
<back> <back>
<displayreference target="I-D.zzd-tvr-use-case-tidal-network" to="TIDAL"/>
<displayreference target="I-D.lhan-problems-requirements-satellite-net" to="
SAT-CONSTELLATION"/>
<references anchor="sec-informative-references"> <references anchor="sec-informative-references">
<name>Informative References</name> <name>Informative References</name>
<reference anchor="LWOOD-SCN" target="http://personal.ee.surrey.ac.uk/Pers onal/L.Wood/publications/zhang-book/zhang-book-wood-chapter-2.pdf"> <reference anchor="SCN" target="https://link.springer.com/chapter/10.1007/ 978-1-4615-0431-3_2">
<front> <front>
<title>SATELLITE CONSTELLATION NETWORKS</title> <title>Satellite Constellation Networks</title>
<author initials="L." surname="Wood" fullname="Lloyd Wood"> <author initials="L." surname="Wood" fullname="Lloyd Wood">
<organization/> <organization/>
</author> </author>
<date year="2003"/> <date month="April" year="2003"/>
</front>
<seriesInfo name="Internetworking and Computing over Satellite Networks"
value=""/>
</reference>
<reference anchor="TIDAL" target="https://datatracker.ietf.org/doc/draft-z
zd-tvr-use-case-tidal-network/">
<front>
<title>Use Case of Tidal Network</title>
<author initials="L." surname="Zang" fullname="Li Zang">
<organization/>
</author>
<author initials="T." surname="Zhou" fullname="Tianran Zhou">
<organization/>
</author>
<author initials="J." surname="Dong" fullname="Ji Dong">
<organization/>
</author>
<author initials="N." surname="Nzima" fullname="Nkosinathi Nzima">
<organization/>
</author>
<date>n.d.</date>
</front>
</reference>
<reference anchor="LHAN-PROB" target="https://datatracker.ietf.org/doc/dra
ft-lhan-problems-requirements-satellite-net/">
<front>
<title>Problems and Requirements of Satellite Constellation for Intern
et</title>
<author initials="L." surname="Han" fullname="Li Han">
<organization/>
</author>
<author initials="R." surname="Li" fullname="Richard Li">
<organization/>
</author>
<author initials="A." surname="Retana" fullname="Alvaro Retana">
<organization/>
</author>
<author initials="M." surname="Chen" fullname="Meiling Chen">
<organization/>
</author>
<author initials="L." surname="Su" fullname="Li Su">
<organization/>
</author>
<author initials="T." surname="Jiang" fullname="Tianji Jiang">
<organization/>
</author>
<author initials="N." surname="Wang" fullname="Ning Wang">
<organization/>
</author>
<date>n.d.</date>
</front> </front>
<seriesInfo name="DOI" value="10.1007/978-1-4615-0431-3_2"/>
<refcontent>Internetworking and Computing over Satellite Networks, pp. 1
3-34</refcontent>
</reference> </reference>
<!-- [I-D.zzd-tvr-use-case-tidal-network] IESG state: Expired as of 05/20/24 -->
<xi:include href="https://datatracker.ietf.org/doc/bibxml3/draft-zzd-tvr-u
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<!-- [I-D.lhan-problems-requirements-satellite-net] IESG state: I-D Exists as of
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<?line 410?>
</back> <section anchor="acknowledgments" numbered="false" toc="default">
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