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SDNRG                                                         Q. Kong
Internet Draft                                                 T. Gao
Intended status: Informational                                   BUPT
Expires: April 2019                                           D. Wang
                                                              Z. Wang
                                                              J. Wang
                                                                  ZTE
                                                               B. Guo
                                                             S. Huang
                                                                 BUPT
                                                     October 05, 2018



           Routing Optimization with SDN in Data Center Networks
             draft-kong-sdnrg-routing-optimization-sdn-in-dc-05


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   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.

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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