Internet DRAFT - draft-huang-rsca-sdm-eon
draft-huang-rsca-sdm-eon
Networking Group Sh.G. Huang
Internet Draft S. Yin
Intended status: Informational BUPT
Expires: November 2022 Ch.G Wang
S. Zhou
BUPT
May 13, 2022
RSCA method with Dividing Frequency Slots Area in Space Division
Multiplexing Elastic Optical Networks
draft-huang-rsca-sdm-eon-08
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Abstract
This documentary provides a routing, spectrum and core assignment
method with the dividing frequency slots area for space division
multiplexing elastic optical networks. This effective RSCA method to
solve this problem better. The proposed method utilizes the Frequency
Slots Area (FSA) concept and first-last fit policy of frequency slots
assignment to have less spectrum fragments, lower crosstalk, smaller
traffic blocking probability and higher spectrum resource utilization.
Table of Contents
1. Introduction ................................................ 2
1.1. Terminology ............................................ 3
2. Conventions used in this document ............................ 3
3. Overview ...................................................... 4
3.1. Elastic Optical Networks ................................ 4
3.2. Multi-Core Fiber ........................................ 4
4. RSCA ........................................................ 5
5. The proposed spectrum and core assignment method ............. 5
6. Formal Syntax ............................................... 7
7. Security Considerations ...................................... 7
8. IANA Considerations ......................................... 7
9. Conclusions ................................................. 7
10. References ................................................. 7
10.1. Normative References ................................... 7
10.2. Informative References ................................. 8
11. Acknowledgments ............................................ 8
1. Introduction
With the rapid development of Internet technology and the emergence
of new applications such as intense social networking, real-time
gaming, High Definition audio-video streaming and cloud computing,
the demand for network capacity has increased greatly. The capacity
of traditional single-mode fiber is close to its physical capacity
limit, so the SDM technology that can greatly improve the network
capacity has received more and more attention. In SDM technology, MCF
is one of the most promising technology. On the other hand, for the
sake of flexible and effective use of spectrum resources, EON has
been widely accepted as the next generation high-speed network. In
the elastic optical network, the spectrum resources are divided into
finer frequency slots, which can be more flexible and effective used
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by traffic requests. In elastic optical networks, spectrum resources
are assigned flexibly according to connections' requirements. This
flexibility based on fine-grained resource provisioning can reduce
the amount of spectrum resources wasted, compared with traditional
rigid spectrum assignments. At the network level, the RSA problem is
the most important problem concerning elastic optical networks. There
are two continuity constraints for an assigned spectrum in the RSA
problem. These constraints require the same and continuous spectrum
to be assigned for all links on the selected transmission route if
there is no wavelength converter. Because it is necessary to satisfy
the spectral constraints of the RSA problem according to traffic
demands, which change dynamically, dynamic resource allocation can
effectively improve the performance of optical networks.
The advantage of SDM-EONs is that it greatly improves the capacity of
the network, allowing for more flexible and efficient use of spectrum
resources. However, it brings the RSCA problem with serious crosstalk
and high computing complexity. Crosstalk refers to the mutual
interference generated by the transmission of signals on the same
frequency between adjacent cores. With the increasing number of cores
in the fiber, the core-pitch is getting smaller and smaller, and the
crosstalk between adjacent cores is becoming more and more serious.
At the same time, compared to the traditional EONs, the new core
dimension in MCF-EONs makes its computational complexity higher.
However, in the RSCA problem, the impact of inter-core crosstalk can
be alleviated by properly assigning the core and spectrum resources
to requests. Therefore, how to solve the RSCA problem effectively in
SDM-EON is a challenge cannot be ignored.
1.1. Terminology
SDM: Space Division multiplexing.
EON: Elastic Optical Network.
RSA: Routing and spectrum assignment problem.
RSCA: Routing, Spectrum and Core Assignment problem.
FSA: Frequency Slots Area.
2. Conventions used in this document
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 RFC 2119 [RFC2119].
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3. Overview
In elastic optical network, the traffic requests are constantly
changing with time, so it is very important to choose a dynamic
solution to the RSCA problem. However, with the continuous
establishment and release of the traffic requests, there will be
fragments between the frequency slots. In order to improve the
utilization of spectrum resources in SDM-EON, it is essential to
solve the problem of spectrum fragmentation.
3.1. Elastic Optical Networks
Elastic optical network is different with traditional wavelength-
division multiplexing (WDM) network because of the flexible use of
spectrum resource. In traditional WDM networks, different traffic
requests are assigned with the same fixed spectrum grid. Therefore,
if the transmission distance of the request is short and demands less
spectrum resource, there will be a lot of spectrum resource wasted in
the fixed grid. In elastic optical network, the spectrum resource is
allocated to the traffic request by flexible grid. That is to say,
the network can choose the modulation format flexibly according to
the length of the optical transmission route to save the spectrum
resource. For example, when the transmission distance of the traffic
is short, the network can choose the modulation formats with high
spectrum utilization, such as 16-quadrature amplitude modulation (QAM)
and 64-QAM, so that the resource utilization of the network can be
improved. On the other hand, if the requested transmission distance
of the traffic is long, the network can choose a modulation format
with lower spectrum resource utilization, such as quadrature phase-
shift keying (QPSK).
3.2. Multi-Core Fiber
Because the transmission capacity of single-mode optical fiber is
close to its physical limit, in order to improve the network capacity
further, SDM has been widely concerned recently. MCF is one of the
most promising transmission technology in SDM system. MCF using
single-mode optical fibers is considered to greatly improve the
transmission capacity of the network. However, one of the major
problems with MCF is the physical impairment of transmitted signals
due to crosstalk between cores during transmission. Large crosstalk
occurs when the signals are transmitted in the same frequency on
adjacent cores. The smaller the distance of the cores, the more
serious the crosstalk will be. As shown in Fig.1, since 1 is used in
both the adjacent core one and core two, large crosstalk occurs
between the core one and core two. Since core one is not adjacent to
core three, even if they both use 2, the crosstalk between them is
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much lower than the crosstalk between cores one and three. Normally,
we can ignore the effects of these low crosstalk.
4. RSCA
The RSA problem is the most important part of the elastic optical
network. In the same way, RSCA is the most important part of EDM-EON.
In the traditional WDM network, wavelength channel is the basic unit
of resource allocation. Nevertheless, in the elastic optical network
basic unit of resource allocation is the frequency slot. The RSA
problem in EON is equivalent to the Routing and Wavelength Assignment
(RWA) problem in the traditional WDM network. However, due to the
flexible resource allocation method of elastic optical network and
the application of SDM technology, the RSCA problem in SDM-EON
becomes more complex and challenging.
In the traditional WDM network, there is a wavelength continuity
constraint, that is, the network must select the same wavelength
channel for each link in the transmission route. In elastic optical
network, there is a similar continuity constraint for frequency slot.
In addition, there is a spectrum contiguity constraint. Spectrum
contiguity constraint ensures that the assigned frequency slots have
to be consecutive in the spectrum resources of the fiber. Spectrum
continuity constraint refers to the frequency slots used by each link
on the selected routing path have to be same. According to the
transmission distance of traffic requests, the elastic optical
network selects different modulation formats to utilize spectrum
resources effectively, and determines the number of consecutive
frequency slots needed for transmission.
In elastic optical network, the traffic requests are constantly
changing with time, so it is very important to choose a dynamic
solution to the RSCA problem. However, with the continuous
establishment and release of the traffic requests, there will be
fragments between the frequency slots. In order to improve the
utilization of spectrum resources in SDM-EON, it is essential to
solve the problem of spectrum fragmentation.
5. The proposed spectrum and core assignment method
Through routing algorithm and wavelength assignment algorithm, we
calculate the K feasible routing of a specific business wavelength. K
feasible routing pathes are arranged according to preset priority,
among them, the ith routing is recorded as Ri , i=1,2,3 We choose
the first reachable optical path and calculate the output power and
OSNR value of the first path, and do the following operations
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In this draft, we use a k-shortest path algorithm based on Yen's
ranking loopless paths algorithm to solve the routing problem .When a
traffic request arrives, we use the routing algorithm to calculate k-
shortest end-to-end routing paths for it. Then we select the path in
order and process the spectrum and core assignment method. If no one
path can meet the two constraints, the traffic request will be
blocked. In SDM-EONs, it is more difficult to provision huger demands
with satisfying continuity constraints due to fragmentation issue .
To deal with it, we propose that the spectrum resource of the 7-core
MCFs can be divided into several Frequency Slots Areas. This division
reduces the blocking probability. Fig. 1 shows the flowchart of the
proposed method.
The 7-core MCF can be divided into several different areas according
to the number of slots required for traffic requests. In the example,
the number of slots required for traffic requests is three, four and
five respectively. The first half of the core one, core two and the
second half of them are divided into Frequency Slots Area of three
(FSA-3) and Frequency Slots Area of five (FSA-5), respectively. The
first half of the core five, core six is FSA-5, and the second half
is divided into FSA-3.Then we divide the first half and second half
of core three and core four into two different Frequency Slots Areas
of four (FSA-4). In the last, the remaining entire core seven can be
utilized by all the traffic with different frequency slots demand as
a common area. When the traffic request needs three frequency slots,
only the available frequency slots in FSA-3 and common area will be
utilized. In our proposed method, we use first-last fit policy to
find the available frequency slots. In other words, when the first
three-slot traffic request arrives, we use first fit policy to search
for the three available and consecutive frequency slots in FSA-3 and
common area. This means that we will first search FSA-3 of core one
and core two, then search FSA-3 of core four and core five until
there is no available frequency slots and we will search the common
area. When the second three-slot traffic request arrives, the last
fit policy is applied to find required slots in FSA-3 and common area.
That is to say, we take turns using the first fit policy and the last
fit policy in FSA and common area for the traffic requests that
demand the same number of slots. Because of the first-last fit policy,
we can make the distribution of traffic requests with same number of
frequency slots more balanced, while bringing fewer fragments. As a
result of the use of such frequency slots area concept and special
core selected policy, in dealing with a large number of traffic
requests with the same frequency slots number demanded the crosstalk
will be smaller.
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6. Formal Syntax
The following syntax specification uses the augmented Backus-Naur
Form (BNF) as described in RFC-2234 [RFC2234].
7. Security Considerations
This kind of information includes network topology, link state and
current utilization, as well as the capabilities of switches and
routers within the network, which is owing to that the information
should be protected from disclosure to unintended recipients. In
addition, the intentional modification of this information can
significantly affect network operations, particularly due to the
large capacity of the optical infrastructure has been controlled.
8. IANA Considerations
This informational document does not make any requests for IANA
action.
9. Conclusions
This document discussed a routing, spectrum and core assignment
method with dividing frequency slots area in SDM-EONs with 7-core MFC.
The simulation results suggest that the proposed method is effective
in reducing the path blocking probability and enhancing the spectrum
resource utilization.
10. References
10.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Crocker, D. and Overell, P.(Editors), "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, Internet Mail Consortium and
Demon Internet Ltd., November 1997.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2234] Crocker, D. and Overell, P.(Editors), "Augmented BNF for
Syntax Specifications: ABNF", RFC 2234, Internet Mail
Consortium and Demon Internet Ltd., November 1997.
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10.2. Informative References
[3] Faber, T., Touch, J. and W. Yue, "The TIME-WAIT state in TCP
and Its Effect on Busy Servers", Proc. Infocom 1999 pp. 1573-
1583.
[Fab1999] Faber, T., Touch, J. and W. Yue, "The TIME-WAIT state in
TCP and Its Effect on Busy Servers", Proc. Infocom 1999 pp.
1573-1583.
11. Acknowledgments
This document is supported in part by the National Natural Science
Foundation of China (Nos.61601054, 61331008, 61701039 and 61571058),
the National Science Foundation for Outstanding Youth Scholars of
China (No.61622102) and Youth research and innovation program of
BUPT(2017RC14).
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Authors' Addresses
Shanguo Huang
BUPT
No.10, Xitucheng Road,Haidian District
Beijing 100876
P.R.China
Phone: +8613693578265
Email: shghuang@bupt.edu.cn
Shan Yin
BUPT
No.10, Xitucheng Road,Haidian District
Beijing 100876
P.R.China
Phone: +8613488795778
Email: yinshan@bupt.edu.cn
Chenge Wang
BUPT
No.10, Xitucheng Road,Haidian District
Beijing 100876
P.R.China
Phone: +8618800122360
Email: wangchenge@bupt.edu.cn
Shuang Zhou
BUPT
No.10, Xitucheng Road,Haidian District
Beijing 100876
P.R.China
Phone: +8618101053965
Email: zs_yolanda@163.com
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