rfc9657v2.txt		rfc9657.txt
	Internet Engineering Task Force (IETF) E. Birrane, III		Internet Engineering Task Force (IETF) E. Birrane, III
	Request for Comments: 9657 JHU/APL		Request for Comments: 9657 JHU/APL
	Category: Informational N. Kuhn		Category: Informational N. Kuhn
	ISSN: 2070-1721 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
	September 2024		September 2024
	Time-Variant Routing (TVR) Use Cases		Time-Variant Routing (TVR) Use Cases
	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 that take into consideration		computations (i.e., routing computations that take into consideration
	skipping to change at line 98 ¶		skipping to change at line 98 ¶
	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 (TVR) can utilize the predictability		level. Time-Variant Routing (TVR) can utilize the predictability
	of the link availability to optimize network connectivity by		of the link availability to optimize network connectivity by
	taking into account endpoint 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. TVR can		server cost or a path cost usage varying over time. TVR can
	exploit the predictability of the path cost to optimize the cost		exploit the predictability of the path cost to optimize the cost
	skipping to change at line 301 ¶		skipping to change at line 301 ¶
	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 preexisting 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
	skipping to change at line 501 ¶		skipping to change at line 501 ¶
	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.
	skipping to change at line 534 ¶		skipping to change at line 534 ¶
	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 TVR		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
	skipping to change at line 776 ¶		skipping to change at line 776 ¶
	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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