Internet DRAFT - draft-chen-lsr-tl
draft-chen-lsr-tl
Network Working Group H. Chen
Internet-Draft Futurewei
Intended status: Standards Track A. Wang
Expires: 3 August 2024 China Telecom
G. Mishra
Verizon
Z. Li
China Mobile
Y. Fan
Casa Systems
X. Liu
Alef Edge
L. Liu
Fujitsu
31 January 2024
IGP for Temporal Links
draft-chen-lsr-tl-01
Abstract
This document specifies extensions to OSPF and IS-IS for temporal
links whose costs are functions of time.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119] [RFC8174]
when, and only when, they appear in all capitals, as shown here.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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Internet-Drafts are draft documents valid for a maximum of six months
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on 3 August 2024.
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Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Temporal Link Cost Functions . . . . . . . . . . . . . . . . 3
2.1. Example Network with Temporal Links . . . . . . . . . . . 3
2.2. Periodic Cost Function . . . . . . . . . . . . . . . . . 4
2.3. Change in Given Periods . . . . . . . . . . . . . . . . . 5
2.4. Change in Given Interval . . . . . . . . . . . . . . . . 6
3. Extensions to IGP . . . . . . . . . . . . . . . . . . . . . . 6
3.1. Cost Function Sub-TLVs . . . . . . . . . . . . . . . . . 6
3.2. Procedures . . . . . . . . . . . . . . . . . . . . . . . 9
4. Security Considerations . . . . . . . . . . . . . . . . . . . 9
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
6.1. Normative References . . . . . . . . . . . . . . . . . . 9
6.2. Informative References . . . . . . . . . . . . . . . . . 10
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
The cost of a link is normally a constant such as C forever (i.e.,
from current time to indefinite future, refer to Figure 1) when there
is no change on the cost of the link.
Link Cost
^
|
C|______________________________________________________
|
|
-+------------------------------------------------------> Time
|
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Figure 1: Constant Link Cost
However, there are some links in a network whose costs are functions
of time (refer to Figure 2). These links are called temporal links.
Link Cost
^
|
| C3___________
| C1__________
|
C0|__________ C4_________
| C2________________
|
-+-------------------------------------------------------> Time
|T0 T1 T2 T3 T4
Figure 2: Link Cost of Temporal Link
This document proposes extensions to IGP (i.e., OSPF and IS-IS) for
distributing cost functions of temporal links and handling temporal
links. Every node in the network computes the shortest paths using
the costs of temporal links based on the cost functions.
2. Temporal Link Cost Functions
This section illustrates a few temporal link cost functions through
an example.
2.1. Example Network with Temporal Links
Figure 3 shows an example network topology containing temporal links.
Nodes Sa, Sb and Sc are satellites in a first orbit. Nodes S1, S2
and S3 are satellites in a second orbit, which is adjacent to the
first orbit. Nodes A and B are the nodes on the earth each with a
ground station seeing or connecting a satellite. A satellite has
links from it to its adjacent satellites. These links are stable.
The costs of these links are not changing typically. For example,
node Sa has links from Sa to Sb and S1; node Sb has links from Sb to
Sa, Sc and S2. These links are stable.
A satellite moves around the earth in its orbit. It moves around the
earth once in a period. For example, a starlink satellite moves
around the earth once every 95 minutes (i.e., 5,700 seconds). During
this period, the satellite can see or have link from it to a node on
the earth in a time interval. For example, the time interval is 398
seconds for a starlink satellite. During each period, a satellite
can see or have a link from it to a node on the earth for a time
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interval. For example, when node Sa is a starlink satellite, node Sa
has a link from Sa to A for a time interval such as 398 seconds every
period such as 95 minutes (i.e., 5,700 seconds), node A has a link
from A to Sa for the time interval such as 398 seconds every period
such as 95 minutes (i.e., 5,700 seconds). Similarly, for the links
between Sb and A, Sc and A, S1 and B, S2 and B, and S3 and B.
\ \
\ \
- - - - - - [ Sa ]----------[ S1 ] - - - - - - - - - -
/ \ \ \
/ \ \ \
/ \ \ \
[ A ] - - - - - - - - [ Sb ]----------[ S2 ] - - - - - - - - [ B ]
\ \ \ /
\ \ \ /
\ \ \ /
- - - - - - - - - [ Sc ]----------[ S3 ] - - - - - -
\ \
\ \
Figure 3: Network with Temporal Links
The link between a satellite node and a node on the earth is laser or
microwave. The quality or cost of the link is affected by weather
conditions. In a cloudy condition for a time interval, the link
bandwidth is reduced. When Bw is the bandwidth of the link in an
ideal weather condition, Bw is reduced to P*Bw in a cloudy condition,
wherein P is a percentage such as 50 percents. When the cost of the
link is C in the ideal condition and is calculated using a reference
bandwidth, the cost of the link is increased to C/P in the cloudy
condition in the time interval. When P = 50 percents, the cost of
the link is increased to 2C (= C/0.5) in the time interval.
2.2. Periodic Cost Function
Figure 4 shows an example of a periodic temporal link cost function
(or periodic cost function for short). The cost of a temporal link
such as link from A to Sa is C0 for a time interval such as 400
seconds from a given time T0, in every time period such as 95 minutes
(i.e., 5,700 seconds). When the given time T0 is now, the cost of
the link is C0 for 400 seconds and then Infinity for 5,300 seconds in
every 95 minutes (i.e., 5,700 seconds). That is that the cost of the
link is C0 from now for 400 seconds, and then Infinity for 5,300
seconds (i.e., the rest of the first 95 minutes); C0 from 95 minutes
later for 400 seconds and then Infinity for 5,300 seconds (i.e., the
rest of the second 95 minutes); C0 from 2x95 minutes later for 400
seconds and then Infinity for 5,300 seconds (i.e., the rest of the
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third 95 minutes); and so on.
Link Cost
^
| C1 = Infinity
| C1_____________ C1_____________ C1_____________
|
|
C0|______ C0______ C0______
|
|
-+---------------------------------------------------------->Time
|T0 T1 T2 T3 T4 T5
| 400s |<- 5,300s ->| 400s |<- 5,300s ->| 400s |<- 5,300s ->|
|<-- 95m(5,700s) -->|<-- 95m(5,700s) -->|<-- 95m(5,700s) -->|
Figure 4: Periodic Temporal Link Cost Function
2.3. Change in Given Periods
The cost of a temporal link is C0 for a time interval in every time
period except for some given periods. In each of the given periods,
the cost of the link is C0', for example, C0' = 2*C0.
When given periods are two periods from given time T0' as shown in
Figure 5, for each of the two periods from time T0', the cost of the
link is C0' for 400 seconds for the period (95 minutes from T0' or 95
minutes from T2') and then Infinity for the rest of the period. In
the first given period (i.e., 95 minutes from T0'), the cost of the
link is C0' from T0' for 400 seconds and then Infinity for 5,300
seconds (i.e., the rest of the first given period); in the second
given period (i.e., 95 minutes from T2'), the cost of the link is C0'
from T2' for 400 seconds and then Infinity for 5,300 seconds (i.e.,
the rest of the second given period).
Link Cost
^
| C1 = Infinity
| C1__ ... C1___________ C1___________
|
|
| C0'______ C0'______
C0|______ ... C0______
|
-+----------------------------------------------------------->Time
|T0 T0' T1' T2' T3' T4 T5
| | 400s |<-5,300s->| 400s |<-5,300s->| 400s |
| |<--95m(5,700s)-->|<--95m(5,700s)-->|
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Figure 5: Periodic Link Cost with C0' in Given Periods
2.4. Change in Given Interval
The cost of a temporal link is C0 for a time interval in every time
period except for a given time interval. In the given interval, the
cost of the link is Ca, for example, Ca = 3*C0.
When the given interval is 5,000 seconds from given time T0' as shown
in Figure 6, the cost of the link is Ca from T2 for (T1' - T2)
seconds, C0 from T1' for (T3 - T1') seconds, and then Infinity for
the rest of the period (95 minutes from T2 to T4). For the time
period from T0' to T2, which overlaps with the time period from T1 to
T2, the cost of the link is Infinity, which is the bigger cost
(Infinity > Ca) in the overlapped period (i.e., from T0' to T2). For
the time period from T2 to T1', which overlaps with the time period
from T2 to T3, the cost of the link is Ca, which is the bigger cost
(Ca > C0) in the overlapped period (i.e., from T2 to T1').
Link Cost
^
| C1 = Infinity
| C1___________ C1___________ C1___________
|
| Ca____
|
C0|______ ____C0 C0______
| |<-5,000s->|
-+--------------------------------------------------------->Time
|T0 T1 T0' T2 T1' T3 T4 T5
| 400s | | 400s | | 400s | |
|<-- 95m(5,700s) -->|<-- 95m(5,700s) -->|<--95m(5,700s)-->|
Figure 6: Periodic Link Cost with Ca in Given Interval
3. Extensions to IGP
This section defines cost function Sub-TLVs for representing a cost
function of a temporal link and describes procedures for handling
temporal links.
3.1. Cost Function Sub-TLVs
Three link cost function Sub-TLVs are defined. They are Recurrent
time interval Sub-TLV, Limited Recurrent time interval Sub-TLV and
Fixed time interval Sub-TLV.
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Recurrent time interval Sub-TLV is shown in Figure 7. Its value
contains Start-time, Interval-length and Period. This Sub-TLV with
Start-time = T0, Interval-length = 400 and Period = 5,700 represents
a cost function similar to the one as shown in Figure 4. The cost of
the link is normal link cost such as C0 from a time indicated by
Start-time = T0 for a time interval indicated by Interval-length =
400 seconds in every period indicated by Period = 5,700 seconds, and
Infinity for the rest of time in every period.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type (TBD1) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Start-time |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interval-length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Period |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: Recurrent Time Interval Sub-TLV
Limited Recurrent time interval Sub-TLV is shown in Figure 8. Its
value contains Start-time, Interval-length, Period, Number-periods,
and Cost. This Sub-TLV with Start-time = T0', Interval-length = 400,
Period = 5,700, Number-periods = 2 and Cost = C0' represents a part
of a cost function similar to the one as shown in Figure 5. The cost
of the link is Cost = C0' from a time indicated by Start-time = T0'
for a time interval indicated by Interval-length = 400 seconds in
each period indicated by Period = 5,700 seconds for the number of
periods indicated by Number-periods = 2 periods, and Infinity for the
rest of time in each of these 2 periods.
This Sub-TLV with Start-time = T0', Interval-length = 400, Period =
5,700, Number-periods = 2 and Cost = C0' and Recurrent time interval
Sub-TLV with Start-time = T0, Interval-length = 400 and Period =
5,700 represent a cost function similar to the one as shown in
Figure 5.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type (TBD2) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Start-time |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interval-length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Period |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Number-periods | Cost |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: Limited Recurrent Time Interval Sub-TLV
Fixed time interval Sub-TLV is shown in Figure 9. Its value contains
Start-time, Interval-length and Cost. This Sub-TLV with Start-time =
T0', Interval-length = 5,000 and Cost = Ca represents a part of a
cost function similar to the one as shown in Figure 6. The cost of
the link is Cost = Ca from a time indicated by Start-time = T0' for a
time interval indicated by Interval-length = 5,000 seconds.
This Sub-TLV with Start-time = T0', Interval-length = 5,000 and Cost
= Ca and Recurrent time interval Sub-TLV with Start-time = T0,
Interval-length = 400 and Period = 5,700 represent a cost function
similar to the one as shown in Figure 6.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type (TBD3) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Start-time |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interval-length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cost |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9: Fixed Time Interval Sub-TLV
Every node distributes a cost function configured on each temporal
link of the node to the other nodes in the network. For OSPFv2, the
cost function Sub-TLVs for a cost function configured on a temporal
link of the node is distributed in the OSPFv2 Extended Link TLV for
the link in the OSPFv2 Extended Link Opaque LSA with LS Type 10
defined in [RFC7684].
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For OSPFv3, the cost function Sub-TLVs for a cost function configured
on a temporal link of the node is distributed in the Router-Link TLV
for the link in the OSPFv3 E-Link-LSA defined in [RFC8362].
For IS-IS, the cost function Sub-TLVs for a cost function configured
on a temporal link of the node is included in the Extended IS
Reachability TLV of TLV type 22 for the link in a Link State Protocol
data unit (PDU) (LSP).
3.2. Procedures
Every node in a network maintains status of each of temporal links in
its link state database (LSDB). The status includes cost function
such as cost function Sub-TLVs for the link, the down or up state of
the link. Every node also maintains the earliest link change time
(ELCT) at which the cost of a temporal link will change from C (which
is not Infinity) to Infinity or vice versa.
Every node computes the shortest paths using the costs of links at
ELCT before ELCT and builds a next routing/forwarding table (NRT)
based on the paths. When the time is ELCT, every node uses its NRT
as its current routing/forwarding table, and then every node finds a
new ELCT, computes the shortest paths using the costs of links at the
new ELCT before the new ELCT and builds a new next routing/forwarding
table (NRT) based on the paths. Note that the clocks on all the
nodes in a network must be synchronized.
4. Security Considerations
TBD.
5. IANA Considerations
TBD.
6. References
6.1. Normative References
[ISO10589] ISO, "Information technology -- Telecommunications and
information exchange between systems -- Intermediate
System to Intermediate System intra-domain routing
information exchange protocol for use in conjunction with
the protocol for providing the connectionless-mode network
service (ISO 8473)", ISO/IEC 10589:2002, Second Edition,
November 2002.
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic
Engineering", RFC 5305, DOI 10.17487/RFC5305, October
2008, <https://www.rfc-editor.org/info/rfc5305>.
[RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W.,
Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute
Advertisement", RFC 7684, DOI 10.17487/RFC7684, November
2015, <https://www.rfc-editor.org/info/rfc7684>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8362] Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and
F. Baker, "OSPFv3 Link State Advertisement (LSA)
Extensibility", RFC 8362, DOI 10.17487/RFC8362, April
2018, <https://www.rfc-editor.org/info/rfc8362>.
6.2. Informative References
[RFC7356] Ginsberg, L., Previdi, S., and Y. Yang, "IS-IS Flooding
Scope Link State PDUs (LSPs)", RFC 7356,
DOI 10.17487/RFC7356, September 2014,
<https://www.rfc-editor.org/info/rfc7356>.
Acknowledgments
The authors would like to thank Bruno Decraene, and Donald E.
Eastlake for the valuable comments and suggestions on this draft.
Authors' Addresses
Huaimo Chen
Futurewei
Boston, MA,
United States of America
Email: Huaimo.chen@futurewei.com
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Aijun Wang
China Telecom
Beiqijia Town, Changping District
Beijing
102209
China
Email: wangaj3@chinatelecom.cn
Gyan S. Mishra
Verizon
13101 Columbia Pike
Silver Spring, MD 20904
United States of America
Phone: 301 502-1347
Email: gyan.s.mishra@verizon.com
Zhenqiang Li
China Mobile
No.32 Xuanwumenxi Ave., Xicheng District
Beijing
100032
P.R. China
Email: li_zhenqiang@hotmail.com
Yanhe Fan
Casa Systems
United States of America
Email: yfan@casa-systems.com
Xufeng Liu
Alef Edge
United States of America
Email: xufeng.liu.ietf@gmail.com
Lei Liu
Fujitsu
United States of America
Email: liulei.kddi@gmail.com
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