Internet DRAFT - draft-kong-sdnrg-routing-optimization-sdn-in-dc
draft-kong-sdnrg-routing-optimization-sdn-in-dc
SDNRG Q. Kong
Internet Draft T. Gao
Intended status: Informational BUPT
Expires: April 2020 D. Wang
Z. Wang
J. Wang
ZTE
B. Guo
S. Huang
BUPT
October 07, 2019
Routing Optimization with SDN in Data Center Networks
draft-kong-sdnrg-routing-optimization-sdn-in-dc-07
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Abstract
With the open and standard programmatic interface and the flexibility
of controlling network, Software Defined Network (SDN) can obviously
simplify and integrate operation and business support systems. As a
consequence, to satisfy the rising switching demand in the data
center network, it is a good option to adopt SDN technology. In
addition, current architecture of data center network is far from
ideality, which results in the low utilization rate in bandwidth
resource. For example, mice flow cannot be well effectively served in
the conventional Wavelength Division Multiplexing (WDM) optical
network with at least 50GHz spectrum interval. From a data center
network perspective, it is necessary to further improve the resource
utilization efficiency and the flexibility of coping with different
traffic.
This document described an optical data center interconnect, which
comprises both the fixed and flexible grid transceivers. A traffic
monitor is implemented in the SDN-based data center network to
evaluate the coming traffic demands and allocate appropriate spectrum
for the request. For instance, mice flow can be served by fixed grid
transceivers, well the elephant flows can be transmitted by the
flexi-grid transceiver using multiple subcarriers to form a
superchannel. Thus, spectrum efficiency is optimized and bandwidth
utilization is improved dramatically.
Table of Contents
1. Introduction ................................................ 3
2. Conventions used in this document ........................... 3
3. Required Technology ......................................... 4
4. Data center interconnect .................................... 5
5. Traffic-Monitor based routing in data center networks ....... 6
6. Dynamic traffic demand recognition scheme ................... 7
7. Security Considerations ..................................... 8
8. IANA Considerations ......................................... 8
9. Conclusions and Use Cases ................................... 8
10. References ................................................. 9
10.1. Normative References .................................. 9
10.2. Informative References ............................... 9
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1. Introduction
The bandwidth bottleneck and growing power requirements have become
central challenges for high performance DCN interconnect. The current
fat tree topology causes communication bottlenecks in the server
interaction process, resulting in power-hungry O-E-O conversions that
limit the minimum latency and the power efficiency of these systems.
Various optical interconnect [KT12] have been proposed to take
advantage of the high bandwidth capacity and low power consumption
offered by optical switching. The optical data center interconnect
also provides interface to control plane for the network control and
operation. This opens the opportunity to implement enhanced network
functions as all components running under the centralized software-
defined networking (SDN) controller through SDN agents. With the
advantage of the flexibility of controlling network and the privacy
of network operations, the concept of SDN is rapidly adopted in data
centers. SDN technology has been mature for the commercial deployment
in data centers, and most notably, Google has realized the
interconnection between its data centers through the two
intercontinental backbone networks. From a data center network
perspective, the research focused on further improving the resource
utilizing efficiency and the flexibility of coping with different
traffic demands is never out of date.
This document describes a data center interconnect with SDN control
which can support both finer and coarse granularity switching
requirements. By implementing traffic monitoring into SDN-based data
center network to allocate appropriate bandwidth to either fixed or
flexible grid channel, spectrum efficiency is optimized and bandwidth
utilization is greatly increased. To realize both fixed grid and
flexible grid transmission, multiple Small Form-Factor Pluggable
(SFPs) and Single-Carrier Frequency-Division-Multiplexed (SCFDM)
transceivers are attached to the cascaded (Micro-Electro-Mechanical
System) MEMS which is in charge of the communication between ToRs in
different clusters. We also proposed a module named MUX/DEMUX&SSS
module using optical components to provide the flexible switching
functionality.
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].
This document makes use of the following acronyms:
SDN: Software Defined Network
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WDM: Wavelength Division Multiplexing
MEMS: Micro-Electro-Mechanical System
ToRs: Top-of-Racks
SFP: Small Form-Factor Pluggable
SCFDM: Single-Carrier Frequency-Division-Multiplexed
SSS: Spectrum Selective Switches
AWG: Arrayed Waveguide Grating
MIMO: Multi-Input Multi-Output
3. Required Technology
With the wide deployment of cloud computing and other kinds of
applications, traffic switching inter or intra data center networks
is drawing more and more attention. Nevertheless, despite the
commercial employment of SDN technology in the data centers,
architecture of current data centers network is still far from being
ideal.
On one hand, in conventional WDM optical networks, a traffic demand
is supported by a wavelength channel which occupies a 50GHz spectrum.
In this case, when the traffic demand between the end nodes is no
more than the capacity of the wavelength channel, the spectrum is
waste because of the fixed and coarse granularity. To address this
issue, scenario where flexible and fixed grid transceivers can be
adopted in the data center networks. On the other hand, with the
advantage of open interfaces and programming, the SDN-enabled network
can be implemented to realize required control methods to optimize
the bandwidth efficiency.
To satisfy the requirement of fast speed switching as well as
improving bandwidth efficiency in data center networks, traffic
monitor is embedded in the ToR to monitor the bandwidth that might
require to modulate the traffic to either fixed or flexible grid
channel. Monitoring the traffic before it comes, mice or elephant
flow can be severed by allocating appropriate flexible or fixed grid
bandwidth rather than allocating uniform fixed 50GHz bandwidth. Thus,
the spectrum is optimized and the bandwidth utilizing is improved.
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4. Data center interconnect
As shown in Fig.1, we employ the cascaded MEMS-switches. The inter-
cluster MEMS in the core is in charge of the communication between
ToRs in different clusters. Multiple SFPs and SCFDM transceivers are
implemented to realize the mixed transmission whose bandwidth demand
is either fixed grid or flexible grid. To provide flexible switching
functionality, we proposed the module named Mux/Demux & SSS which is
illustrated in Fig.2. Optical components such as coupler, Spectrum
Selective Switches (SSS), Arrayed Waveguide Grating (AWG), and
circulator are attached to a backplane to further increase the
flexibility of coping with different traffic demands. In Fig.2, the
symbol "@" represents a circulator which is a passive non-reciprocal
three-port device, and an optical signal entering any port is
transmitted to the next port in rotation(only). The coupler is a
passive device which is used to split and combine signals in the
optical network and can have multiple inputs and outputs. The SSS is
typical an 1xN optical component that can partition the spectrum of
input signal to different ports. The AWG is a passive data-rate
independent optical device that route each wavelength of an input to
a different output. Using this module, traffic can be deliberately
added and dropped through these components, and can be merged and
switched to the same destination together through AWG or coupler, and
also can be separated by SSS and switched to the different output
ports for purpose of realizing Multi-Input Multi-Output(MIMO)
switching. At the same time, each ToR has both SFP and SCFDM
transceivers which can realize fixed or flexible grid traffic
switching. Thus, each rack can communicate with multiple racks
simultaneous and high interconnect efficiency can be achieved as
arbitrary traffic inter or intra ToRs can be switched using fine
bandwidth rather than fixed grid bandwidth.
+----------------+ +----------------+ +----------------+
|Mux/Demux &SSS 1| |Mux/Demux &SSS 2| |Mux/Demux &SSS 3| ...
+----------------+ +----------------+ +----------------+
| | | | | | | | |
| | | | | | | | |
+----------------------------------------------------------------+
| Optical OXC |
+----------------------------------------------------------------+
| | | | | |
| | | | | |
+--------------+ +--------------+ +--------------+
| SFP|BV-TX/RX | | SFP|BV-TX/RX | | SFP|BV-TX/RX |
| ToR 1 | | ToR 2 | | ToR 3 |
+--------------+ +--------------+ +--------------+
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Figure 1: Schematic of architecture in data center
+------------------------------------------------------------------+
| |
+------------------------------------------------------------------+
A A A A | | | |
+---|---------------------|--------|------|--------|--|--|-----|--+
| | V | | | | | | |
| | +--------------@ V | +---------+ | |
| | | +----------A--------@ V | AWG | | |
| | | | +-----|---------A------@ +---------+ | |
| | | | | | | A | | |
| | V V V | | | +--------+ |
| | +---------+ +---------------------+ |
| +-----| Coupler | | SSS | |
| +---------+ +---------------------+ |
+-----------------------------------------------------------------+
Figure 2: Mux/Demux &&& SSS
5. Traffic-Monitor based routing in data center networks
The proposed architecture which is based on SDN technology is shown
in Fig.3. Resource Computation Element (RCE) is responsible for
allocating available port resource to configure the backplane to
sever the new coming request based on the resource information
provided by the Resource Management Element (RME).RME storages all of
the port and spectrum information. Both RCE and RME are controlled by
a SDN controller. In particular, RCE can be implemented with certain
algorithm for routing and allocating spectrum optimally and RME can
also be configured by the SDN controller.
When a new traffic comes from ToRs, RCE inquiries the RME for the
available port resource and other information to compute the most
suitable route and allocate appropriate spectrum. If there is no
available resource for the moment, the request will be stored in the
buffer. The traffic monitor provides all the traffic request
information both come and in the buffer in order to evaluate the type
of the traffic, and then passes the information to RME to execute the
processing scheme which we will discuss about later.
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After finishing computing the optimized route, the optical switching
module is configured through an agent to allocate appropriate
bandwidth for the request. With the implement of bandwidth variable
component and the capacity of both fixed and flexible grid switching,
the optical backplane can be ordered to allocate exactly appropriate
bandwidth for coming demands. As a consequence, the requests from the
ToRs are satisfied with the optimized route and high resource
utilizing.
+---------------------------------|-----------+
---+---+---+ | SDN controller |
+---> | | |----+-->+--------------+ +--------------+ |
| ---+---+---+ | | Resource |----->| Resource | |
| Buffer | | Computation | | Management | |
| ---+---+---+ | | Element |<-----| Element | |
| +-> | | |----+-->+--------------+ +--------------+ |
| | ---+---+---+ +----------A----------------------------------+
| | | |
| | | v
| | +--------------------+------+
| | +---------+ +----+ +-----+ | Agent|
| +--| Request |---->|ToRs|---->|Tx/Rx|-----> +------+------+------+
| +---------+ +----+ +-----+ | Optical |
| +---------+ +----+ +-----+ | Switching |
+----| Request |---->|ToRs|---->|Tx/Rx|-----> | Module |
+---------+ +----+ +-----+ +--------------------+
+------------+ A
| Traffic | |
| Monitor |----+
+------------+
Figure 3: Traffic Monitor implemented architecture
6. Dynamic traffic demand recognition scheme
With the implement of traffic monitor, the proposed architecture can
support the new switching requirements by executing dynamic traffic
demand recognition scheme through RME which is described above. We
monitor the traffic before they come, and evaluate the type of
traffic demand, and then allocate appropriate bandwidth according to
the request. When traffic comes, it is arbitrated by RME whether it
is a flexible grid signal to determine where it goes. A flexible grid
signal is transferred to the SCFDM transceiver and then arbitrated
whether it is intra-data center request. If it is, optical components
such as SSS and coupler will be placed to set or reuse connection.
Similarly, a fixed grid signal is transferred to SFP module and
arbitrated whether it is intra-cluster request to determine where it
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will be transferred next step. Thus, bandwidth with fine granularity
can be allocated to satisfy the dynamic traffic demand in data center
network. For instance, mice flow can be served directly by being
modulated to SCFDM transmitter. At the meantime, elephant flow can
also be divided into fixed and flexible grid signal. Fixed grid
signal can be switched to the WDM SFP transceivers which support
2.5 Gbps and 10 Gbps transmission. Flexible grid traffic demand can
be served by the SCFDM transceivers. Such algorithm can allocate
optimized bandwidth to potential request. Thus, both mice and
elephant flow can be served by either using the already existing
connection or setup new route to avoid frequent configuration of the
optical backplane.
7. Security Considerations
Security in the communication between ToRs through Optical Backplane
in data center network is to be addressed. While the security of the
architecture described in this document greatly depends on the
security of communication mechanism itself such as communication
protocols, processing procedure and so on. However, the architecture
that implements the traffic monitor can improve the security of
switching in data center network by evaluating the type of coming
traffic.
8. IANA Considerations
This document includes no request to IANA.
9. Conclusions and Use Cases
Data centers have received more and more attention as a result of
increasing demand for storing and switching large volumes of data.
With the advantage of open programmatic interface and privacy of
operations, SDN tends to be applied to data center so as to improve
the spectrum efficiency and bandwidth utilizing.
This document describes an architecture where a traffic monitor is
implemented and bandwidth variable components are adopted. Due to the
capacity of monitoring the traffic before they come, we can evaluate
the type of the requests and inquires RME whose function is to store
all ports information whether they are occupied or released. Based on
obtained the available resource information from RME, RCE then
allocate appropriate bandwidth for the request which may be fixed or
flexible grid. Rather than allocating the bandwidth with rigid and
coarse granularity, the new switching requirements are supported to
satisfy the dynamic traffic demand in data center networks. As a
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consequence, the spectrum efficiency is optimized and bandwidth
utilization is increased dramatically.
With the feature of switching traffic using both fixed and flexible
grid bandwidth, the proposed architecture can be well adopted in
various network structure especially in data center network. For
example, it can be accustomed to the scenario where data flow is big
and duration time is long such as data migration in the midnight, as
well as the scenario where data flow is slight and duration time is
short such as a Web request.
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
10.2. Informative References
[KT12] C. Kachris, and I. Tomkos, "A Survey on Optical Interconnects
for Data Centers," 2012.
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Authors' Addresses
Qian Kong
Beijing University of Posts and Telecommunications
Email: kongqian@bupt.edu.cn
Tao Gao
Beijing University of Posts and Telecommunications
Email: taogao@bupt.edu.cn
Dajiang Wang
ZTE Corporation
Email: wang.dajiang@zte.com.cn
Zhenyu Wang
ZTE Corporation
Email: wang.zhenyu1@zte.com.cn
Jiayu Wang
ZTE Corporation
Email: wang.jiayu1@zte.com.cn
Bingli Guo
Beijing University of Posts and Telecommunications
Email: guobingli@bupt.edu.cn
Shanguo Huang
Beijing University of Posts and Telecommunications
Email: shghuang@bupt.edu.cn
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