rfc9657.original   rfc9657.txt 
Network Working Group E. Birrane Internet Engineering Task Force (IETF) E. Birrane, III
Internet-Draft JHU/APL Request for Comments: 9657 JHU/APL
Intended status: Informational N. Kuhn Category: Informational N. Kuhn
Expires: 2 September 2024 Thales Alenia Space ISSN: 2070-1721 Thales Alenia Space
Y. Qu Y. Qu
Futurewei Technologies Futurewei Technologies
R. Taylor R. Taylor
Ori Industries Aalyria Technologies
L. zhang L. Zhang
Huawei Huawei
1 March 2024 September 2024
TVR (Time-Variant Routing) Use Cases Time-Variant Routing (TVR) Use Cases
draft-ietf-tvr-use-cases-09
Abstract Abstract
This document introduces use cases where Time-Variant Routing (TVR) This document introduces use cases where Time-Variant Routing (TVR)
computations (i.e. routing computations taking into considerations computations (i.e., routing computations that take into consideration
time-based or scheduled changes to a network) could improve routing time-based or scheduled changes to a network) could improve routing
protocol convergence and/or network performance. protocol convergence and/or network performance.
About This Document
This note is to be removed before publishing as an RFC.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction
2. Resource Preservation . . . . . . . . . . . . . . . . . . . . 4 2. Resource Preservation
2.1. Assumptions . . . . . . . . . . . . . . . . . . . . . . . 5 2.1. Assumptions
2.2. Routing Impacts . . . . . . . . . . . . . . . . . . . . . 5 2.2. Routing Impacts
2.3. Example . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.3. Example
3. Operating Efficiency . . . . . . . . . . . . . . . . . . . . 7 3. Operating Efficiency
3.1. Assumptions . . . . . . . . . . . . . . . . . . . . . . . 8 3.1. Assumptions
3.2. Routing Impacts . . . . . . . . . . . . . . . . . . . . . 8 3.2. Routing Impacts
3.3. Example : Cellular Network . . . . . . . . . . . . . . . 9 3.3. Example: Cellular Network
3.4. Another Example : Tidal Network . . . . . . . . . . . . . 11 3.4. Another Example: Tidal Network
4. Dynamic Reachability . . . . . . . . . . . . . . . . . . . . 11 4. Dynamic Reachability
4.1. Assumptions . . . . . . . . . . . . . . . . . . . . . . . 12 4.1. Assumptions
4.2. Routing Impacts . . . . . . . . . . . . . . . . . . . . . 13 4.2. Routing Impacts
4.3. Example : Mobile Satellites . . . . . . . . . . . . . . . 13 4.3. Example: Mobile Satellites
4.4. Another Example : Predictable Moving Vessels . . . . . . 17 4.4. Another Example: Predictable Moving Vessels
5. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 17 5. Security Considerations
6. Security Considerations . . . . . . . . . . . . . . . . . . . 17 6. IANA Considerations
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 7. Informative References
8. Informative References . . . . . . . . . . . . . . . . . . . 17 Acknowledgments
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18 Authors' Addresses
1. Introduction 1. Introduction
There is a growing number of use cases where changes to the routing There is a growing number of use cases where changes to the routing
topology are an expected part of network operations. In these use topology are an expected part of network operations. In these use
cases the pre-planned loss and restoration of an adjacency, or cases, the pre-planned loss and restoration of an adjacency, or
formation of an alternate adjacency, should be seen as a non- formation of an alternate adjacency, should be seen as a
disruptive event. nondisruptive event.
Expected changes to topologies can occur for a variety of reasons. Expected changes to topologies can occur for a variety of reasons.
In networks with mobile nodes, such as unmanned aerial vehicles and In networks with mobile nodes, such as unmanned aerial vehicles and
some orbiting spacecraft constellations, links are lost and re- some orbiting spacecraft constellations, links are lost and re-
established as a function of the mobility of the platforms. In established as a function of the mobility of the platforms. In
networks without reliable access to power, such as networks networks without reliable access to power, such as networks
harvesting energy from wind and solar, link activity might be harvesting energy from wind and solar, link activity might be
restricted to certain times of day. Similarly, in networks restricted to certain times of day. Similarly, in networks
prioritizing green computing and energy efficiency over data rate, prioritizing green computing and energy efficiency over data rate,
network traffic might be planned around energy costs or expected user network traffic might be planned around energy costs or expected user
data volumes. data volumes.
This document defines three categories of use cases where a route This document defines three categories of use cases where a route
computation might beneficially consider time information. Each of computation might beneficially consider time information. Each of
these use cases includes the following information. these use cases are included as follows:
1. An overview of the use case describing how route computations 1. An overview of the use case describing how route computations
might select different paths (or subpaths) as a function of time. might select different paths (or subpaths) as a function of time.
2. A set of assumptions made by the use case as to the nature of the 2. A set of assumptions made by the use case as to the nature of the
network and data exchange. network and data exchange.
3. Specific discussion on the routing impacts of the use case. 3. Specific discussion on the routing impacts of the use case.
4. Example networks conformant to the use case. 4. Example networks conformant to the use case.
The use cases that are considered in this document are the following. The use cases that are considered in this document are as follows:
1. Resource Preservation (described in Section 2), where there is 1. Resource Preservation (described in Section 2), where there is
information about link availability over time at the client information about link availability over time at the client
level. Time Variant Routing can utilize the predictability of level. Time-Variant Routing (TVR) can utilize the predictability
the link availability to optimize network connectivity by taking of the link availability to optimize network connectivity by
into account end point resource preservation. taking into account endpoint resource preservation.
2. Operating Efficiency (described in Section 3), where there is a 2. Operating Efficiency (described in Section 3), where there is a
server cost or a path cost usage varying over time. Time Variant server cost or a path cost usage varying over time. TVR can
Routing can exploit the predictability of the path cost to exploit the predictability of the path cost to optimize the cost
optimize the cost of the system exploitation. The notion of a of the system exploitation. The notion of a path cost is
path cost is extended to be a time-dependent function instead of extended to be a time-dependent function instead of a constant.
a constant.
3. Dynamic Reachability (described in Section 4), where there is 3. Dynamic Reachability (described in Section 4), where there is
information about link availability variation between nodes information about link availability variation between nodes in
taking part of the end-to-end path. Time Variant Routing can the end-to-end path. TVR can exploit the predictability of the
exploit the predictability of the link availability to optimize link availability to optimize in-network routing.
in-network routing.
The document does not intend to represent the full set of cases where The document does not intend to represent the full set of cases where
time-variant routing computations could beneficially impact network TVR computations could beneficially impact network performance -- new
performance - new use cases are expected to be generated over time. use cases are expected to be generated over time. Similarly, the
Similarly, the concrete examples within each use case are meant to concrete examples within each use case are meant to provide an
provide an existence proof of the use case, not to present any existence proof of the use case and not to present any exhaustive
exhaustive enumeration of potential examples. It is likely that enumeration of potential examples. It is likely that multiple
there exist multiple example networks that could be claimed as example networks exist that could be claimed as instances of any
instances of any given use case. given use case.
The document focuses on deterministic scenarios. Non-deterministic The document focuses on deterministic scenarios. Non-deterministic
scenarios such as vehicle-to-vehicle communication is out of the scenarios, such as vehicle-to-vehicle communication, are out of the
scope of the document. scope of the document.
2. Resource Preservation 2. Resource Preservation
Some nodes in a network might operate in resource-constrained Some nodes in a network might operate in resource-constrained
environments or otherwise with limited internal resources. environments or otherwise with limited internal resources.
Constraints such as available power, thermal ranges, and on-board Constraints, such as available power, thermal ranges, and on-board
storage can all impact the instantaneous operation of a node. In storage, can all impact the instantaneous operation of a node. In
particular, resource management on such a node can require that particular, resource management on such a node can require that
certain functionality be powered on (or off) to extend the ability of certain functionality be powered on (or off) to extend the ability of
the node to participate in the network. the node to participate in the network.
When power on a node is running low, non-critical functions on the When power on a node is running low, noncritical functions on the
node might be turned off in favor of extending node life. node might be turned off in favor of extending node life.
Alternatively, certain functions on a node may be turned off to allow Alternatively, certain functions on a node may be turned off to allow
the node to use available power to respond to an event, such as data the node to use available power to respond to an event, such as data
collection. When a node is in danger of violating a thermal collection. When a node is in danger of violating a thermal
constraint, normal processing might be paused in favor of a constraint, normal processing might be paused in favor of a
transition to a thermal safe mode until a regular operating condition transition to a thermal safe mode until a regular operating condition
is reestablished. When local storage resources run low, a node might is reestablished. When local storage resources run low, a node might
choose to expend power resources to fuse, delete, or transmit data choose to expend power resources to compress, delete, or transmit
off the node to free space for future data collection. There might data off the node to free up space for future data collection. There
also be cases where a node experiences a planned offline state to might also be cases where a node experiences a planned offline state
save and accumulate power. to save and accumulate power.
In addition to power, thermal, and storage, other resource In addition to power, thermal, and storage, other resource
constraints may exist on a node such that the preservation of constraints may exist on a node such that the preservation of
resources are necessary to preserve the existence (and proper resources is necessary to preserve the existence (and proper
function) of the node in the network. Nodes operating in these function) of the node in the network. Nodes operating in these
conditions might benefit from TVR computations as the connectivity of conditions might benefit from TVR computations as the connectivity of
the node changes over time as part of node preservation. the node changes over time as part of node preservation.
2.1. Assumptions 2.1. Assumptions
To effectively manage on-board functionality based on available To effectively manage on-board functionality based on available
resources, a node must comprehend specific aspects concerning the resources, a node must comprehend specific aspects concerning the
utilization and replenishment of resources. It is expected that utilization and replenishment of resources. It is expected that
patterns of the environment, device construction, and operational patterns of the environment, device construction, and operational
configuration exist with enough regularity and stability to allow configuration exist with enough regularity and stability to allow
meaningful planning. The following assumptions are made with this meaningful planning. The following assumptions are made with this
use case. use case:
1. Known resource expenditures. It is assumed that there exists 1. Known resource expenditures. It is assumed that there exists
some determinable relationship between the resources available on some determinable relationship between the resources available on
a node and the resources needed to participate in a network. A a node and the resources needed to participate in a network. A
node would need to understand when it has met some condition for node would need to understand when it has met some condition for
participating in, or dropping out of, a network. This is participating in, or dropping out of, a network. This is
somewhat similar to predicting the amount of battery life left on somewhat similar to predicting the amount of battery life left on
a laptop as a function of likely future usage. a laptop as a function of likely future usage.
2. Predictable resource accumulation. It is assumed that the 2. Predictable resource accumulation. It is assumed that the
skipping to change at page 5, line 47 skipping to change at line 214
elements of the node as part of on-board resource management. These elements of the node as part of on-board resource management. These
activities can affect data routing in a variety of ways. activities can affect data routing in a variety of ways.
1. Power Savings. On-board radios may be turned off to allow other 1. Power Savings. On-board radios may be turned off to allow other
node processing. This may happen on power-constrained devices to node processing. This may happen on power-constrained devices to
extend the battery life of the node or to allow a node to perform extend the battery life of the node or to allow a node to perform
some other power-intensive task. some other power-intensive task.
2. Thermal Savings. On-board radios may be turned off if there are 2. Thermal Savings. On-board radios may be turned off if there are
thermal considerations on the node, such as an increase in a thermal considerations on the node, such as an increase in a
node’s operating temperature. node's operating temperature.
3. Storage Savings. On-board radios may be turned on with the 3. Storage Savings. On-board radios may be turned on with the
purpose of transmitting data off the node to free local storage purpose of transmitting data off the node to free local storage
space to collect new data. space to collect new data.
Whenever a communications device on a node changes its powered state Whenever a communications device on a node changes its powered state
there is the possibility (if the node is within range of other nodes there is the possibility (if the node is within range of other nodes
in a network) that the topology of the network is changed, which in a network) that the topology of the network is changed, which
impacts route calculations through the network. Additionally, impacts route calculations through the network. Additionally,
whenever a node joins a network there may be a delay between the whenever a node joins a network there may be a delay between the
joining of the node to the network and any discovery that may take joining of the node to the network and any discovery that may take
place relating to the status of the node’s functional neighborhood. place relating to the status of the node's functional neighborhood.
During these times, forwarding to and from the node might be delayed During these times, forwarding to and from the node might be delayed
pending some synchronization. pending some synchronization.
2.3. Example 2.3. Example
An illustrative example of a network necessitating resource An illustrative example of a network necessitating resource
preservation is an energy-harvesting wireless sensor network. In preservation is an energy-harvesting wireless sensor network. In
such a network, nodes rely exclusively on environmental sources for such a network, nodes rely exclusively on environmental sources for
power, such as solar panels. On-board power levels may fluctuate power, such as solar panels. On-board power levels may fluctuate
based on various factors including sensor activity, processing based on various factors including sensor activity, processing
demands, and the node's position and orientation relative to its demands, and the node's position and orientation relative to its
energy source. energy source.
Consider a simple three node network where each node accumulates Consider a simple three-node network where each node accumulates
power through solar panels. Power available for Radio Frequency (RF) power through solar panels. Power available for radio frequency (RF)
transmission is shown below in Figure 1. In this figure, each of the transmission is shown in Figure 1. In this figure, each of the three
three nodes (Node 1, Node 2, and Node 3) have a different plot of nodes (Node 1, Node 2, and Node 3) has a different plot of available
available power over time. This example assumes that a node will not power over time. This example assumes that a node will not power its
power its radio until available power is over some threshold, which radio until available power is over some threshold, which is shown by
is shown by the horizontal line on each plot. the horizontal line on each plot.
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
Figure 1: Node Power Over Time Figure 1: Node Power over Time
The connectivity of this three node network changes over time in ways The connectivity of this three-node network changes over time in ways
that may be predictable and are likely able to be communicated to that may be predictable and are likely able to be communicated to
other nodes in this small sensor network. Examples of connectivity other nodes in this small sensor network. Examples of connectivity
are shown in Figure 2. This figure shows a sample of network are shown in Figure 2. This figure shows a sample of network
connectivity at three times: t1, t2, and t3. connectivity at three times: t1, t2, and t3.
* At time t1 Node 1 and Node 2 have their radios powered on and are * At time t1, Node 1 and Node 2 have their radios powered on and are
expected to communicate. expected to communicate.
* At time t2 it is expected that Node 1 has its radio off, but that * At time t2, it is expected that Node 1 has its radio off but that
Node 2 and Node 3 can communicate. Node 2 and Node 3 can communicate.
* Finally, at time t3 it is expected that Node 1 may be turning its * Finally, at time t3, it is expected that Node 1 may be turning its
radio off and that Node 2 and Node 3 are not powering their radios radio off, that Node 2 and Node 3 are not powering their radios,
and there is no expectation of connectivity. and there is no expectation of connectivity.
+----------+ +----------+ +----------+ +----------+ +----------+ +----------+
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 |
+----------+ +----------+ +----------+ +----------+ +----------+ +----------+
skipping to change at page 7, line 35 skipping to change at line 299
3. Operating Efficiency 3. Operating Efficiency
Some nodes in a network might alter their networking behavior to Some nodes in a network might alter their networking behavior to
optimize metrics associated with the cost of a node's operation. optimize metrics associated with the cost of a node's operation.
While the resource preservation use case described in Section 2 While the resource preservation use case described in Section 2
addresses node survival, this use case discusses non-survival addresses node survival, this use case discusses non-survival
efficiencies such as the financial cost to operate the node and the efficiencies such as the financial cost to operate the node and the
environmental impact (cost) of using that node. environmental impact (cost) of using that node.
When a node operates using some pre-existing infrastructure there is When a node operates using some preexisting infrastructure, there is
typically some cost associated with the use of that infrastructure. typically some cost associated with the use of that infrastructure.
Sample costs include the following. Sample costs are included as follows:
1. Nodes that use existing wireless communications such as a 1. Nodes that use existing wireless communications, such as a
cellular infrastructure must pay to communicate to and through cellular infrastructure, must pay to communicate to and through
that infrastructure. that infrastructure.
2. Nodes supplied with electricity from an energy provider pay for 2. Nodes supplied with electricity from an energy provider pay for
the power they use. the power they use.
3. Nodes that cluster computation and activities might increase the 3. Nodes that cluster computation and activities might increase the
temperature of the node and incur additional costs associated temperature of the node and incur additional costs associated
with cooling the node (or collection of nodes). with cooling the node (or collection of nodes).
4. Beyond financial costs, assessing the environmental impact of 4. Beyond financial costs, assessing the environmental impact of
skipping to change at page 8, line 20 skipping to change at line 329
When the cost of using a node's resources changes over time, a node When the cost of using a node's resources changes over time, a node
can benefit from predicting when data transmissions might optimize can benefit from predicting when data transmissions might optimize
costs, environmental impacts, or other metrics associated with costs, environmental impacts, or other metrics associated with
operation. operation.
3.1. Assumptions 3.1. Assumptions
The ability to predict the impact of a node's resource utilization The ability to predict the impact of a node's resource utilization
over time presumes that the node exists within a defined environment over time presumes that the node exists within a defined environment
(or infrastructure). Some characteristics of these environments are (or infrastructure). Some characteristics of these environments are
listed as follows. listed as follows:
1. Cost Measureability. The impacts of operating a node within its 1. Cost Measurability. The impacts of operating a node within its
environment can be measured in a deterministic way. For example, environment can be measured in a deterministic way. For example,
that the cost-per-bit of data over a cellular network or the the cost-per-bit of data over a cellular network or the cost-per-
cost-per-kilowatt of energy used are known. kilowatt of energy used are known.
2. Cost Predictability. Changes to the impacts of resource 2. Cost Predictability. Changes to the impacts of resource
utilization are known in advance. For example, if the cost of utilization are known in advance. For example, if the cost of
energy is less expensive in the evening than during the day, energy is less expensive in the evening than during the day,
there exists some way of communicating this change to a node. there exists some way of communicating this change to a node.
3. Cost Persistent. Changes to the cost of operating in the 3. Cost Persistent. Changes to the cost of operating in the
environment persist for a sufficient amount of time such that environment persist for a sufficient amount of time such that
behavior can be adjusted in response to changing costs. If costs behavior can be adjusted in response to changing costs. If costs
change too rapidly it is likely not possible to meaningfully change too rapidly, it is likely not possible to meaningfully
react to their change. react to their change.
4. Cost Magnitude. The magnitude of cost changes is such that a 4. Cost Magnitude. The magnitude of cost changes is such that a
node experiences a minimum threshold cost reduction through node experiences a minimum threshold cost reduction through
optimization. A specified time period is designated for optimization. A specified time period is designated for
measuring the cost reduction. measuring the cost reduction.
3.2. Routing Impacts 3.2. Routing Impacts
Optimizing resource utilization can affect route computation in ways Optimizing resource utilization can affect route computation in ways
similar to those experienced with resource preservation. The route similar to those experienced with resource preservation. The route
computation may not change the available path but the topology as computation may not change the available path, but the topology as
seen by an end point would be different. Cost optimization can seen by an endpoint would be different. Cost optimization can impact
impact route calculation in a variety of ways, some of which are route calculation in a variety of ways, some of which are described
described as follows. as follows:
1. Link Filtering. Data might be accumulated on a node waiting for 1. Link Filtering. Data might be accumulated on a node waiting for
a cost-effective time for data transmission. Individual link a cost-effective time for data transmission. Individual link
costs might be annotated with cost information such that costs might be annotated with cost information such that
adjacencies with a too-high cost might not be used for adjacencies with a too high cost might not be used for
forwarding. This effectively filters which adjacencies are used forwarding. This effectively filters which adjacencies are used
(possibly as a function of the type of data being routed). (possibly as a function of the type of data being routed).
2. Burst Planning. In cases where there is a cost savings 2. Burst Planning. In cases where there is a cost savings
associated with fewer longer transmissions (versus many smaller associated with fewer longer transmissions (versus many smaller
transmissions), nodes might refuse to forward data until a transmissions), nodes might refuse to forward data until a
sufficient data volume exists to justify a transmission. sufficient data volume exists to justify a transmission.
3. Environmental Measurement. Nodes that measure the quality of 3. Environmental Measurement. Nodes that measure the quality of
individual links can compute the overall cost of using a link as individual links can compute the overall cost of using a link as
a function of the signal strength of the link. If link quality a function of the signal strength of the link. If link quality
is insufficient due to environmental conditions (such as clouds is insufficient due to environmental conditions (such as clouds
on a free-space optical link or long distance RF transmission in on a free-space optical link or long distance RF transmission in
a storm) the cost required to communicate over the link may be a storm) the cost required to communicate over the link may be
too much, even if access to infrastructure is otherwise in a less too much, even if access to infrastructure is otherwise in a less
expensive time of day. expensive time of day.
In each of these cases, some consideration of the efficiency of In each of these cases, some consideration of the efficiency of
transmission is prioritized over achieving a particular data rate. transmission is prioritized over achieving a particular data rate.
Waiting until data rate costs are lower takes advantage of platforms Waiting until data rate costs are lower takes advantage of platforms
using time-of-use rate plans – both for pay-as-you-go data and using time-of-use rate plans -- both for pay-as-you-go data and
associated energy costs. Accumulating data volumes and choosing more associated energy costs. Accumulating data volumes and choosing more
opportune times to transmit can also result in less energy opportune times to transmit can also result in less energy
consumption by radios and, thus, less operating cost for platforms. consumption by radios and, thus, less operating cost for platforms.
3.3. Example : Cellular Network 3.3. Example: Cellular Network
One example of a network where nodes might seek to optimize operating One example of a network where nodes might seek to optimize operating
cost is a set of nodes operating over cellular connections that cost is a set of nodes operating over cellular connections that
charge both On-Peak and Off-Peak data rates. In this case, charge both peak and off-peak data rates. In this case, individual
individual nodes may be allocated a fixed set of "On-Peak" minutes nodes may be allocated a fixed set of "peak" minutes such that
such that exceeding that amount of time results in expensive overage exceeding that amount of time results in expensive overage charges.
charges. Generally, the concept of On-Peak and Off-Peak minutes Generally, the concept of peak and off-peak minutes exists to deter
exists to deter the use of a given network at times when the cellular the use of a given network at times when the cellular network is
network is likely to encounter heavy call volumes (such as during the likely to encounter heavy call volumes (such as during the workday).
workday).
Just as pricing information can act as a deterrent (or incentive) for Just as pricing information can act as a deterrent (or incentive) for
a human cellular user, this pricing information can be codified in a human cellular user, this pricing information can be codified in
ways that also allow machine-to-machine (M2M) connections to ways that also allow machine-to-machine (M2M) connections to
prioritize Off-Peak communications for certain types of data prioritize off-peak communications for certain types of data
exchange. Many M2M traffic exchanges involve schedulable activities, exchange. Many M2M traffic exchanges involve schedulable activities,
such as nightly bulk file transfers, pushing software updates, such as nightly bulk file transfers, pushing software updates,
synchronizing datastores, and sending non-critical events and logs. synchronizing datastores, and sending noncritical events and logs.
These activities are usually already scheduled to minimize impact on These activities are usually already scheduled to minimize impact on
businesses and customers, but can also be scheduled to minimize businesses and customers but can also be scheduled to minimize
overall cost. overall cost.
Consider a simple three node network, similar to the one pictured in Consider a simple three-node network, similar to the one pictured in
Figure 1, except that in this case the resource that varies over time Figure 1, except that in this case the resource that varies over time
is the cost of the data exchange. This case is illustrated below in is the cost of the data exchange. This case is illustrated below in
Figure 3. In this figure, a series of three plots are given, one for Figure 3. In this figure, a series of three plots are given, one for
each of nodes Node 1, Node 2, and Node 3. Each of these nodes exists each of the three nodes (Node 1, Node 2, and Node 3). Each of these
in a different cellular service area which has different On-Peak and nodes exists in a different cellular service area that has different
Off-Peak data rate times. This is shown in each figure by times when peak and off-peak data rate times. This is shown in each figure by
the cost is low (Off-Peak) and when the cost is high (On-Peak). times when the cost is low (off-peak) and when the cost is high
(peak).
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
Figure 3: Data Cost Over Time Figure 3: Data Cost over Time
Given the presumption that peak times are known in advance, the cost 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 of data exchange from Node 1 through Node 2 to Node 3 can be
calculated. Examples of these data exchanges are shown in Figure 4. calculated. Examples of these data exchanges are shown in Figure 4.
From this figure, both times t1 and t3 result in a smaller cost of From this figure, both times t1 and t3 result in a smaller cost of
data exchange than choosing to communicate data at time t2. data exchange than choosing to communicate data at time t2.
+-----------+ +-----------+ +-----------+ +-----------+ +-----------+ +-----------+
t1 | Node N1 |---LOW----| Node N2 |---HIGH---| Node N3 | t1 | Node N1 |---LOW----| Node N2 |---HIGH---| Node N3 |
+-----------+ +-----------+ +-----------+ +-----------+ +-----------+ +-----------+
skipping to change at page 11, line 17 skipping to change at line 467
queue data at Node 2 until time t3 for delivery to Node 3. This case queue data at Node 2 until time t3 for delivery to Node 3. This case
is shown in Figure 5. is shown in Figure 5.
+-----------+ +-----------+ +-----------+ +-----------+
t1 | Node N1 |---LOW----| Node N2 | t1 | Node N1 |---LOW----| Node N2 |
+-----------+ +-----------+ +-----------+ +-----------+
+-----------+ +-----------+ +-----------+ +-----------+
t3 | Node N2 |----LOW---| Node N3 | t3 | Node N2 |----LOW---| Node N3 |
+-----------+ +-----------+ +-----------+ +-----------+
Figure 5: Data Cost using Storage Figure 5: Data Cost Using Storage
3.4. Another Example : Tidal Network 3.4. Another Example: Tidal Network
Another example related to operating efficiency is what is often Another example related to operating efficiency is often referred to
referred to as a 'tidal network,' in which traffic volume undergoes as a "tidal network," in which traffic volume undergoes significant
significant fluctuations at different times. Take, for instance, a fluctuations at different times. Take, for instance, a campus
campus network, where thousands of individuals go to classrooms and network, where thousands of individuals go to classrooms and
libraries during the daytime and retire to the dormitories at night. libraries during the daytime and retire to the dormitories at night.
This results in a regular oscillation of network traffic across This results in a regular oscillation of network traffic across
various locations within the campus. various locations within the campus.
In the context of a tidal network scenario, energy-saving methods may In the context of a tidal network scenario, energy-saving methods may
include the deactivation of some or all components of network nodes. include the deactivation of some or all components of network nodes.
These activities have the potential to alter network topology and These activities have the potential to alter network topology and
impact data routing in a variety of ways. Ports on network nodes can impact data routing in a variety of ways. Ports on network nodes can
be selectively disabled or enabled based on traffic patterns, thereby be selectively disabled or enabled based on traffic patterns, thereby
reducing the energy consumption of nodes during periods of low reducing the energy consumption of nodes during periods of low
network traffic. network traffic.
More information on Tidal Network can be found in [TIDAL]. More information on tidal networks can be found in [TIDAL].
4. Dynamic Reachability 4. Dynamic Reachability
When a node is placed on a mobile platform, the mobility of the When a node is placed on a mobile platform, the mobility of the
platform (and thus the mobility of the node) may cause changes to the platform (and thus the mobility of the node) may cause changes to the
topology of the network over time. The impacts on the dynamics of topology of the network over time. The impacts on the dynamics of
the topology can be very important. To the extent that the relative the topology can be very important. To the extent that the relative
mobility between and among nodes in the network and the impacts of mobility between and among nodes in the network and the impacts of
the environment on the signal propagation can be predicted, the the environment on the signal propagation can be predicted, the
associated loss and establishment of adjacencies can also be planned associated loss and establishment of adjacencies can also be planned
for. for.
Mobility can cause the loss of an adjacent link in several ways, such Mobility can cause the loss of an adjacent link in several ways, such
as the following. as that which follows:
1. Node mobility can cause the distance between two nodes to become 1. Node mobility can cause the distance between two nodes to become
large enough that distance-related attenuation causes the mobile large enough that distance-related attenuation causes the mobile
node to lose connectivity with one or more other nodes in the node to lose connectivity with one or more other nodes in the
network. network.
2. Node mobility can also be used to maintain a required distance 2. Node mobility can also be used to maintain a required distance
from other mobile nodes in the network. While moving, external from other mobile nodes in the network. While moving, external
characteristics may cause the loss of links through occultation characteristics may cause the loss of links through occultation
or other hazards of traversing a shared environment. or other hazards of traversing a shared environment.
3. Node mobility can cause the distance between two nodes to vary 3. Node mobility can cause the distance between two nodes to vary
quickly over the time making it complicated to establish and quickly over time, making it complicated to establish and
maintain connectivity. maintain connectivity.
4. Nodes equipped with communication terminals capable of adjusting 4. Nodes equipped with communication terminals capable of adjusting
their orientation or moving behind and emerging from barriers their orientation or moving behind and emerging from barriers
will also establish and lose connectivity with other nodes as a will also establish and lose connectivity with other nodes as a
function of that motion. function of that motion.
Mobile nodes, like any node, may have concerns regarding resource Mobile nodes, like any node, may encounter issues regarding resource
preservation and cost efficiency. However, they also face unique preservation and cost efficiency. In addition, they may face unique
challenges associated with their mobility. The intermittent challenges associated with their mobility. The intermittent
availability of links can lead to dynamic neighbor relationships at availability of links can lead to dynamic neighbor relationships at
the node level. This use case aims to examine the routing the node level. This use case aims to examine the routing
implications of motion-induced changes to network topology. implications of motion-induced changes to network topology.
4.1. Assumptions 4.1. Assumptions
Predicting the impact of node mobility on route computation requires Predicting the impact of node mobility on route computation requires
some information relating to the nature of the mobility and the some information relating to the nature of the mobility and the
nature of the environment being moved through. Some information nature of the environment being moved through. Some information
presumed to exist for planning is listed as follows. presumed to exist for planning is listed as follows:
1. Path Predictability. The path of a mobile node through its 1. Path Predictability. The path of a mobile node through its
environment is known (or can be predicted) as a function of (at environment is known (or can be predicted) as a function of (at
least) time. It is presumed that mobile nodes using time-variant least) time. It is presumed that mobile nodes using TVR
algorithms would not exhibit purely random motion. algorithms would not exhibit purely random motion.
2. Environmental Knowledge. When otherwise well-connected mobile 2. Environmental Knowledge. When otherwise well-connected mobile
nodes pass through certain elements of their environment (such as nodes pass through certain elements of their environment (such as
a storm, a tunnel, or the horizon) they may lose connectivity. a storm, a tunnel, or the horizon), they may lose connectivity.
The duration of this connectivity loss is assumed to be The duration of this connectivity loss is assumed to be
calculable as a function of node mobility and the environment calculable as a function of node mobility and the environment
itself. itself.
4.2. Routing Impacts 4.2. Routing Impacts
Changing a network topology affects the computation of paths (or Changing a network topology affects the computation of paths (or
subpaths) through that topology. In particular, the following subpaths) through that topology. In particular, the following
features can be implemented in a network with mobile nodes such that features can be implemented in a network with mobile nodes such that
different paths might be computed over time. different paths might be computed over time:
1. Adjacent Link Expiration. A node might be able to predict that 1. Adjacent Link Expiration. A node might be able to predict that
an adjacency will expire as a function of that node's mobility, an adjacency will expire as a function of that node's mobility,
the other node's mobility, or some characteristic of the the other node's mobility, or some characteristic of the
environment. Determining that an adjacency has expired allows a environment. Determining that an adjacency has expired allows a
route computation to plan for that loss, rather than default to route computation to plan for that loss rather than default to an
an error recovery mechanism. error recovery mechanism.
2. Adjacent Link Resumption. Just as the loss of an adjacency can 2. Adjacent Link Resumption. Just as the loss of an adjacency can
be predicted, it may be possible to predict when an adjacency be predicted, it may be possible to predict when an adjacency
will resume. will resume.
3. Data Rate Adjustments. The achievable data rate over a given 3. Data Rate Adjustments. The achievable data rate over a given
link is not constant over time, and may vary significantly as a link is not constant over time and may vary significantly as a
function of both relative mobility between a transmitter and function of both relative mobility between a transmitter and
receiver as well as the environment being transmitted through. receiver as well as the environment being transmitted through.
Knowledge of both mobility and environmental state may allow for Knowledge of both mobility and environmental state may allow for
prediction of data rates which may impact path computation. prediction of data rates, which may impact path computation.
4. Adjacent Link Filtering. Separate from the instantaneous 4. Adjacent Link Filtering. Separate from the instantaneous
presence or absence of an adjacency, a route computation might presence or absence of an adjacency, a route computation might
choose to not use an adjacency if that adjacency is likely to choose to not use an adjacency if that adjacency is likely to
expire in the near future or if it is likely to experience a expire in the near future or if it is likely to experience a
significant drop in predicted data rate. significant drop in predicted data rate.
4.3. Example : Mobile Satellites 4.3. Example: Mobile Satellites
A relatively new type of mobile network that has emerged over the A relatively new type of mobile network that has emerged over the
past several years is the Low Earth Orbit (LEO) networked past several years is the Low Earth Orbit (LEO) networked
constellation (LEO-NC). There are a number of such constellations constellation. There are a number of such constellations being built
being built by both private industry and governments. While this by both private industry and governments. While this example
example describes LEO satellites systems, the mobility events can be describes LEO satellite systems, the mobility events can be applied
applied to satellite systems orbiting at different altitude to satellite systems orbiting at different altitudes (including Very
(including Very LEO (V-LEO) or Medium Earth Orbit (MEO)). LEO (V-LEO) or Medium Earth Orbit (MEO)).
Many LEO-NCs have a similar operational concept of hundreds-to- Many LEO networked constellations have a similar operational concept
thousands of inexpensive spacecraft that can communicate both with of hundreds to thousands of inexpensive spacecraft that can
their orbital neighbors as well as down to any ground station that communicate both with their orbital neighbors as well as down to any
they happen to be passing over. A ground station is a facility used ground station that they happen to be passing over. A ground station
to communicate with satellites in low Earth orbit. The relationship is a facility used to communicate with satellites in LEO. The
between an individual spacecraft and an individual ground station relationship between an individual spacecraft and an individual
becomes somewhat complex as each spacecraft may only be over a single ground station becomes somewhat complex as each spacecraft may only
ground station for a few minutes at a time. Moreover, as a function be over a single ground station for a few minutes at a time.
of the constellation topology, there are scenarios where (1) the Moreover, as a function of the constellation topology, there are
inter-satellite links need to be shut down for interference avoidance scenarios where (1) the inter-satellite links need to be shut down
purposes or (2) the network topology changes, which modifies the for interference avoidance purposes or (2) the network topology
neighbors of a given spacecraft. changes, which modifies the neighbors of a given spacecraft.
A LEO-NC represents a good example of planned mobility based on the A LEO networked constellation represents a good example of planned
predictability of spacecraft in orbit. While other mobile vehicles mobility based on the predictability of spacecraft in orbit. While
may encounter unpredictable fluctuations in velocity, spacecraft other mobile vehicles may encounter unpredictable fluctuations in
operate in an environment with relatively stable velocity conditions. velocity, spacecraft operate in an environment with relatively stable
This determinism makes them an excellent candidate for time-variant velocity conditions. This determinism makes them an excellent
route computations. However, inter-satellite link failures could candidate for TVR computations. However, inter-satellite link
still introduce unpredictability in the network topology. failures could still introduce unpredictability in the network
topology.
Consider three spacecraft (N1, N2, and N3) following each other Consider three spacecraft (N1, N2, and N3) following each other
sequentially in the same orbit. This is sometimes called a string of sequentially in the same orbit. This is sometimes called a "string
pearls configuration. Spacecraft N2 always maintains connectivity to of pearls" configuration. Spacecraft N2 always maintains
its two neighbor spacecraft, N1 which is behind in the orbit and N3 connectivity to its two neighbor spacecraft: N1, which is behind in
which is ahead in the orbit. This configuration is illustrated in the orbit, and N3, which is ahead in the orbit. This configuration
Figure 6. While these spacecraft are all mobile, their relative is illustrated in Figure 6. While these spacecraft are all mobile,
mobility ensures continuous contact with each other under normal their relative mobility ensures continuous contact with each other
conditions. under normal conditions.
.--. .--. .--. .--. .--. .--.
####-| N1 |-#### <---> ####-| N2 |-#### <---> ####-| N3 |-#### ####-| N1 |-#### <---> ####-| N2 |-#### <---> ####-| N3 |-####
\__/ \__/ \__/ \__/ \__/ \__/
Figure 6: Three Sequential Spacecraft Figure 6: Three Sequential Spacecraft
Flying over a ground station imposes a non-relative motion between Flying over a ground station imposes a non-relative motion between
the ground and the spacecraft - namely that any given ground station the ground and the spacecraft -- namely that any given ground station
will only be in view of the spacecraft for a short period of time. will only be in view of the spacecraft for a short period of time.
The times at which each spacecraft can see the ground station is The times at which each spacecraft can see the ground station is
shown in the plots in Figure 7. In this figure, ground contact is shown in the plots in Figure 7. In this figure, ground contact is
shown when the plot is high, and a lack of ground contact is shown shown when the plot is high, and a lack of ground contact is shown
when the graph is low. From this, we see that spacecraft N3 can see when the graph is low. From this, we see that spacecraft N3 can see
ground at time t1, N2 sees ground at time t2, and spacecraft N1 sees ground at time t1, N2 sees ground at time t2, and spacecraft N1 sees
ground at time t3. ground at time t3.
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
Figure 7: Spacecraft Ground Contacts Over Time Figure 7: Spacecraft Ground Contacts over Time
Since the ground station in this example is stationary, each Since the ground station in this example is stationary, each
spacecraft will pass over it, resulting in a change to the network spacecraft will pass over it, resulting in a change to the network
topology. This topology change is shown in Figure 8. At time t1, topology. This topology change is shown in Figure 8. At time t1,
any message residing on N3 and destined for the ground could be any message residing on N3 and destined for the ground could be
forwarded directly to the ground station. At time t2, that same forwarded directly to the ground station. At time t2, that same
message would need to, instead, be forwarded to N2 and then forwarded message would need to, instead, be forwarded to N2 and then forwarded
to ground. By time t3, the same message would need to be forwarded to ground. By time t3, the same message would need to be forwarded
from N2 to N1 and then down to ground. from N2 to N1 and then down to ground.
skipping to change at page 16, line 36 skipping to change at line 689
t3 | N1 |----------| N2 |----------| N3 | t3 | N1 |----------| N2 |----------| N3 |
+---+--+ +------+ +------+ +---+--+ +------+ +------+
| |
/|\ /|\
\___/ \___/
/ \ / \
Ground Ground
Station Station
------------------------------------------------------------------ ------------------------------------------------------------------
Figure 8: Constellation Topology Over Time Figure 8: Constellation Topology over Time
This example focuses on the case where the spacecrafts fly over a This example focuses on the case where the spacecrafts fly over a
ground station and introduce changes in the network topology. There ground station and introduce changes in the network topology. There
are also scenarios where the in-constellation network topology varies are also scenarios where the in-constellation network topology varies
over time following a deterministic time-driven operation from the over time following a deterministic time-driven operation from the
ground system. More information on in-constellation network topology ground system. More information on in-constellation network topology
can be found in [LHAN-PROB] and [LWOOD-SCN]. For this example, and can be found in [SAT-CONSTELLATION] and [SCN]. For this example, and
in particular for within constellation network topology changes, TVR in particular for within constellation network topology changes, the
approach is important to avoid the Interior Gateway Protocol (IGP) TVR approach is important to avoid the Interior Gateway Protocol
issues mentioned in [LHAN-PROB]. (IGP) issues mentioned in [SAT-CONSTELLATION].
4.4. Another Example : Predictable Moving Vessels 4.4. Another Example: Predictable Moving Vessels
Another relevant example for this use case involves the movement of Another relevant example for this use case involves the movement of
vessels with predictable trajectories, such as ferries or planes. vessels with predictable trajectories, such as ferries or planes.
These end points often rely on a combination of satellite and These endpoints often rely on a combination of satellite and
terrestrial systems for Internet connectivity, capitalizing on their terrestrial systems for Internet connectivity, capitalizing on their
predictable journeys. predictable journeys.
This scenario also covers situations where nodes employ dynamic This scenario also covers situations where nodes employ dynamic
pointing solutions to track the mobility of other nodes. In such pointing solutions to track the mobility of other nodes. In such
cases, nodes dynamically adjust their antennas and application cases, nodes dynamically adjust their antennas and application
settings to determine the optimal timing for data transmission along settings to determine the optimal timing for data transmission along
the path. the path.
5. Acknowledgments 5. Security Considerations
Many thanks to Tony Li, Peter Ashwood-Smith, Abdussalam Baryun,
Arashmid Akhavain, Dirk Trossen, Brian Sipos, Alexandre Petrescu,
Haoyu Song, Hou Dongxu, Tianran Zhou, Jie Dong, Nkosinathi Nzima and
Vinton Cerf for their useful comments that helped improve the
document.
6. Security Considerations
While this document does not define a specific mechanism or solution, While this document does not define a specific mechanism or solution,
it serves to motivate the use of Time-Based Validation and Revocation it serves to motivate the use of time-based validation and revocation
(TVR). Therefore, security considerations are anticipated to be strategies. Therefore, security considerations are anticipated to be
addressed elsewhere, such as within a TVR schedule definition or addressed elsewhere, such as within a TVR schedule definition or
through a protocol extension utilizing a TVR schedule. However it's through a protocol extension utilizing a TVR schedule. However, it's
important to note that time synchronization is critical within a important to note that time synchronization is critical within a
network employing a TVR schedule. Any unauthorized changes to network employing a TVR schedule. Any unauthorized changes to
network clocks can disrupt network functionality, potentially leading network clocks can disrupt network functionality, potentially leading
to a Denial of Service (DoS) attack. to a Denial of Service (DoS) attack.
7. IANA Considerations 6. IANA Considerations
This document has no IANA actions. This document has no IANA actions.
8. Informative References 7. Informative References
[LHAN-PROB] [SAT-CONSTELLATION]
Han, L., Li, R., Retana, A., Chen, M., Su, L., Jiang, T., Han, L., Li, R., Retana, A., Chen, M., Su, L., and T.
and N. Wang, "Problems and Requirements of Satellite Jiang, "Problems and Requirements of Satellite
Constellation for Internet", n.d., Constellation for Internet", Work in Progress, Internet-
<https://datatracker.ietf.org/doc/draft-lhan-problems- Draft, draft-lhan-problems-requirements-satellite-net-06,
requirements-satellite-net/>. 4 January 2024, <https://datatracker.ietf.org/doc/html/
draft-lhan-problems-requirements-satellite-net-06>.
[LWOOD-SCN] [SCN] Wood, L., "Satellite Constellation Networks",
Wood, L., "SATELLITE CONSTELLATION NETWORKS", Internetworking and Computing over Satellite Networks, pp.
Internetworking and Computing over Satellite Networks , 13-34, DOI 10.1007/978-1-4615-0431-3_2, April 2003,
2003, <http://personal.ee.surrey.ac.uk/Personal/L.Wood/ <https://link.springer.com/
publications/zhang-book/zhang-book-wood-chapter-2.pdf>. chapter/10.1007/978-1-4615-0431-3_2>.
[TIDAL] Zang, L., Zhou, T., Dong, J., and N. Nzima, "Use Case of [TIDAL] Zhang, L., Zhou, T., Dong, J., and N. Nzima, "Use Case of
Tidal Network", n.d., <https://datatracker.ietf.org/doc/ Tidal Network", Work in Progress, Internet-Draft, draft-
draft-zzd-tvr-use-case-tidal-network/>. zzd-tvr-use-case-tidal-network-02, 28 July 2023,
<https://datatracker.ietf.org/doc/html/draft-zzd-tvr-use-
case-tidal-network-02>.
Acknowledgments
Many thanks to Tony Li, Peter Ashwood-Smith, Abdussalam Baryun,
Arashmid Akhavain, Dirk Trossen, Brian Sipos, Alexandre Petrescu,
Haoyu Song, Hou Dongxu, Tianran Zhou, Jie Dong, Nkosinathi Nzima, and
Vinton Cerf for their useful comments that helped improve the
document.
Authors' Addresses Authors' Addresses
Ed Birrane Edward J. Birrane, III
JHU/APL JHU/APL
Email: edward.birrane@jhuapl.edu Email: edward.birrane@jhuapl.edu
Nicolas Kuhn Nicolas Kuhn
Thales Alenia Space Thales Alenia Space
Email: nicolas.kuhn.ietf@gmail.com Email: nicolas.kuhn.ietf@gmail.com
Yingzhen Qu Yingzhen Qu
Futurewei Technologies Futurewei Technologies
Email: yingzhen.ietf@gmail.com Email: yingzhen.ietf@gmail.com
Rick Taylor Rick Taylor
Ori Industries Aalyria Technologies
Email: rick.taylor@ori.co Email: rtaylor@aalyria.com
Li zhang Li Zhang
Huawei Huawei
Email: zhangli344@huawei.com Email: zhangli344@huawei.com
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