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DETNET WG                                                  CJ. Bernardos
Internet-Draft                                            A. de la Oliva
Intended status: Informational                                      UC3M
Expires: May 4, 2017                                        L. Cominardi
                                                           LM. Contreras
                                                        October 31, 2016

                    DETNET crosshauling requirements


   Future 5G networks will not make a clear distinction between
   fronthaul and backhaul transport networks, because varying portions
   of radio access network functionality might be moved toward the
   network as required for cost reduction and performance increase.
   This will pose additional challenges on the transport network,
   driving for a new design of integrated fronthaul and backhaul,
   usually referred to as crosshaul.

   This document present the crosshaul architecture framework being
   developed by the EU 5G-Crosshaul project, as well as identifies
   several key requirements for the transport network, with the goal of
   fostering discussion at the DETNET WG.

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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   This Internet-Draft will expire on May 4, 2017.

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Copyright Notice

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   document authors.  All rights reserved.

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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  5G-Crosshaul architecture . . . . . . . . . . . . . . . . . .   4
     3.1.  Data plane architecture . . . . . . . . . . . . . . . . .   6
   4.  Crosshaul requirements  . . . . . . . . . . . . . . . . . . .   6
   5.  Summary . . . . . . . . . . . . . . . . . . . . . . . . . . .   8
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   8
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   According to recent predictions, mobile data traffic will increase
   11-fold between 2013 and 2018.  Fifth generation (5G) radio access
   network (RAN) technologies serving this mobile data tsunami will
   require fronthaul and backhaul solutions between the RAN and packet
   core to deal with this increased traffic load.  Furthermore, there
   will be a sizeable growth in the capillarity of the network since
   traffic load increase in the 5G RAN is expected to stem from an
   increased number of base stations with reduced coverage (i.e., mobile
   network densification).  To support the increased density of the
   mobile network (e.g., in terms of interference coordination) and
   achieve the required 5G capacity, extensive support for novel air
   interface technologies such as cooperative multipoint (CoMP), carrier
   aggregation (CA), and massive multiple-input multiple-output (MIMO)
   will be needed.  Such technologies require processing of information
   from multiple base stations simultaneously at a common centralized

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   entity and also tight synchronization of different radio sites.
   Hence, backhaul and fronthaul will have to meet more stringent
   requirements not only in terms of data rate but also in terms of
   latency, jitter, and bit error rate.

   In this upcoming 5G network environment, the distinction between
   fronthaul and backhaul transport networks will blur as varying
   portions of functionality of 5G points of attachment might be moved
   toward the network as required for cost efficiency reasons.  The
   traditional capacity over provisioning approach on the transport
   infrastructure will no longer be possible with 5G.  Hence, a new
   generation of integrated fronthaul and backhaul technologies will be
   needed to bring capital expenditure (CAPEX) and operational
   expenditure (OPEX) to a reasonable return on investment (ROI) range.
   Current transport networks cannot cope with the amount of bandwidth
   required for 5G.  Next generation radio interfaces, using 100 MHz
   channels and squeezing the bit-per-megahertz ratio through massive
   MIMO or even fullduplex radios, requires a 10-fold increase in
   capacity on the integrated fronthaul and backhaul (crosshaul)
   segment, which cannot be achieved just through the evolution of
   current technologies [crosshaul_magazine].

   Current trend is moving towards defining an integrated fronthaul and
   backhaul into a common packet-based network, as supported by the
   works working towards the definition of a Next Generation Fronthaul
   Interface (NGFI, IEEE 1914), the packetization and encapsulation on
   Ethernet frames of this newly interface (IEEE 1914.1) or the
   extensions to bridging for Time Sensitive Networking (IEEE 802.1TSN)
   and their profiling for frontal traffic (IEEE 802.1CM).  The design
   of the crosshaul poses new challenges that need to be tackled.
   Different project and initiatives are looking at the design of the
   crosshaul, among which we present here the one by the 5G-Crosshaul EU
   project (summarized in Section 3).  [I-D.ietf-detnet-use-cases]
   introduces and describes several use cases for DETNET.  While there
   are some documents analyzing DETNET requirements for backhaul and
   fronthaul, such as [I-D.huang-detnet-xhaul], in this document
   (Section 4) we derive identify some requirements relevant for the
   DETNET WG posed by the 5G-Crosshaul design.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

   While [RFC2119] describes interpretations of these key words in terms
   of protocol specifications and implementations, they are used in this

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   document to describe requirements for DETNET mechanisms regarding
   support for integrated backhaul and crosshaul.

   The following terms are used in this document:

      Backhaul: the network or links between radio base station sites
      (or digital units) and network controller/gateway sites.

      Common Public Radio Interface (CPRI): industry cooperation aimed
      at defining a publicly available specification for the key
      internal interface of radio base stations between the Radio
      Equipment Control (REC) and the Radio Equipment (RE), which are
      the two basic building blocks into which a radio base station can
      be decomposed in order to provide flexible radio base station
      system architectures for mobile networks.

      Fronthaul: the connection from a radio base station site (or
      digital unit) to a remote radio unit.  The fronthaul is therefore
      the transport connection between the functional building blocks of
      a cellular radio base station.  The fronthaul has traditionally
      been implemented with point-to-point connections based on the
      Common Public Radio Interface (CPRI) standard.

      In-Phase and Quadrature (IQ): User plane data between the REC and
      RE is transported in the form of one or many In-Phase and
      Quadrature (IQ) data flows.  Each IQ data flow reflects the radio
      signal, sampled and digitised of one carrier at one independent
      antenna element, the so- called Antenna Carrier (AxC).

3.  5G-Crosshaul architecture

   The 5G-Crosshaul project is developing an architecture for the next
   generation of 5G integrated backhaul and fronthaul networks enabling
   a flexible and software-defined reconfiguration of all networking
   elements in a multi-tenant and service-oriented unified management
   environment.  The envisioned crosshaul transport network will consist
   of high-capacity switches and heterogeneous transmission links (e.g.,
   fiber or wireless optics, high-capacity copper, or millimeter-wave)
   interconnecting remote radio heads, 5G wireless points of attachment
   (e.g., macro and small cells), pooled-processing units (mini data
   centers), and points of presence (PoPs) of the core networks of one
   or multiple service providers.

   The 5G-Crosshaul architecture is based on a novel unified data plane
   protocol able to transport both backhaul and fronthaul traffic,
   regardless of the functional RAN split.  Major challenges for such a
   protocol are the big amount of data to handle, the synchronization of
   user data, and reflection of the channel structure of RAN protocols.

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   A unified data plane is adopted, supporting future RAN evolutions (as
   they may happen on shorter timescales than transport network
   upgrades).  This new data plane allows CPRI data to be transported in
   a packetized form over the unified crosshaul data plane.

   5G-Crosshaul is also developing a unified control and management
   plane (network model and interface primitives) to simplify network
   operations across heterogeneous technologies.  Co-existance with
   legacy infrastructure and support for smooth migration are considered
   as key requirements for operators.

   Three main novel building blocks are considered in 5G-Crosshaul

   o  A control infrastructure using a unified, abstract network model
      for control plane integration (Crosshaul Control Infrastructure,
      XCI).  The XCI is based on existing software defined network (SDN)
      controllers, to provide the services for novel northbound and
      southbound interfaces (NBI and SBI), and enable multi-tenancy
      support in trusted environments.  A key aspect of the XCI is the
      development of new mechanisms to abstract the mobile transport
      network and aggregate measured contextual information.

   o  A unified data plane encompassing innovative high-capacity
      transmission technologies and novel latency-deterministic switch
      architectures (Crosshaul Forwarding Element, XFE).  This element
      is the central part of the Xhaul infrastructure, integrating the
      different physical technologies used for fronthaul and backhaul
      through a common data frame and forwarding behavior.  Developing a
      flexible frame format is a key aspect of fronthaul/backhaul
      integration, allowing the transport of fronthaul/backhaul traffic
      on the same physical link, replacing different technologies by a
      uniform transport technology for both network segments.

   o  A set of computing capabilities distributed across the network
      (Crosshaul Processing Units, XPUs).

   5G-Crosshaul follows a unique approach towards the integration of the
   different network segments (fronthaul and backhaul) into a common
   transport stratum.  In order to integrate the different nature of the
   fronthaul and backhaul traffic (with their very disparate
   requirements) and the different technologies that can be used to
   transport them, a new common transport framing format is defined (the
   XCF, Crosshaul Common Frame) which is used to perform the forwarding
   within the Crosshaul.  This XCF is based on MAC-in-MAC Ethernet, and
   all traffic going into a Crosshaul area is adapted to this frame
   format.  In this way, 5G-Crosshaul can leverage all the work
   performed in IEEE 802.1 (IEEE 802.1TSN and IEEE802.1CM) to transport
   flows with stringent delay requirements in Ethernet-based networks.

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3.1.  Data plane architecture

   Essentially, the XFE is modeled as a modular multi-layer switch, that
   can support single or multiple link technologies (mmWave, microwave,
   Ethernet, copper, fiber, etc.).  The XFE is mainly made up of a
   packet switch (5GCrosshaul Packet Forwarding Element, XPFE) and a
   circuit switch (5G-Crosshaul Circuit Switching Element, XCSE).  The
   packet switching path is the primary path for the transport of most
   delay-tolerant fronthaul and backhaul traffic, whereas the circuit
   switching path is there to complement the packet switching path for
   those particular traffic profiles that are not suited for packet-
   based transporting (e.g., legacy CPRI or traffic with extremely low
   delay tolerance) or just for capacity offloading.  The packet switch
   is controlled by a unified Common Frame (XCF).  The circuit switch
   can have an optical cross-connection component (based on wavelength
   selective switches) and a TDM part, based on OTN, a new cost
   effective approach for deterministic delay switching.  Note that in
   this draft we focus on the packet switch only.

   MAC-in-MAC has been chosen as the frame format for transporting
   backhaul and fronthaul traffic within 5G-Crosshaul.  Provider
   Backbone Bridges belongs to IEEE Std 802.1Q and is a set of
   architecture and protocols for switching over a provider's network,
   allowing interconnection of multiple Provider Bridge Networks without
   losing each customer's individually defined VLANs.

4.  Crosshaul requirements

   In this section we enumerate the main requirements for the XCF packet
   technology (i.e., transport data plane architecture).  Aditional
   details will be provided in subsequent revisions of this document.

   We start listing below the main functional (qualitative)

   o  Support multiple functional splits simultaneously,

      *  Including Backhaul and CPRI-like Fronthaul.

   o  Multi-tenancy.

      *  Isolate traffic (guaranteed QoS).

      *  Separate traffic (tenant privacy).

      *  Differentiation of forwarding behavior.

      *  Multiplexing gain.

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      *  Tenant ID (identification of tenants' traffic).

   o  Coexistence, Compatibility.

      *  Ethernet (same switching equipment, for example different
         ports, etc.).

      *  Security support.

      *  Synchronization: IEEE1588, IEEE802.1AS.

   o  Transport efficiency.

      *  Short overhead.

      *  Multi-path support.

      *  Flow differentiation.

      *  Class of Service Differentiation.

   o  Management.

      *  In band control traffic (OAM info, ...).

   o  Energy efficiency.

      *  Energy usage proportional to handled traffic (e.g., sleep mode,
         reduced rate).

   o  Support of multiple data link technologies.

      *  IEEE 802.3, 802.11 (including mmWave), etc.

   o  No vendor lock-in.

   In addition to the qualitative requirements, there are performance/
   quantitative requirements:

   o  Latency: the maximum end-to-end latency for IQ data between REC
      and RE MUST be 100 us, including the propagation delay of the
      links between the devices, internal delays of the devices such as
      Bridges.  For Control and Management (C&M) there is no latency

   o  Frame loss ratio (FLR): can be caused by bit error, network
      congestion, failures, etc.  Late delivery can also imply frame

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      loss for CPRI data.  It MUST be less than 10E-7.  For C&M the FLR
      MUST be less than 10E-6.

   o  Synchronization.  Depending on the type of radio access technology
      the requirements are different:

      *  The maximum absolute time error SHOULD be less than 10ns for
         intra-band contiguous carrier aggregation radio access

      *  The maximum absolute time error MUST be less than 45ns for
         Multiple-Input and Multiple-Output (MIMO) and transmit
         diversity radio access technologies.

      *  The maximum absolute time error MUST be less than 110ns for
         intra-band non-contiguous and inter-band carrier aggregation
         radio access technologies.

      *  The maximum absolute time error MUST be less than 110ns for
         time division duplex radio access technologies.

5.  Summary

   This document presents a specific solution for the integration of
   fronthaul and backhaul (being carried out within the framework of the
   5G-Crosshaul project), to then derive some key requirements for the
   discussion and consideration of the DETNET WG.

6.  IANA Considerations


7.  Security Considerations


8.  Acknowledgments

   The authors would like to thank Akbar Rahman for his review of the

   This work is partially supported by the EU H2020 5G-Crosshaul Project
   (grant no. 671598).

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9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

9.2.  Informative References

              "Xhaul: Towards an Integrated Fronthaul/Backhaul
              Architecture in 5G Networks, IEEE Wireless Communications
              Magazine", October 2015.

              Huang, J., "Integrated Mobile Fronthaul and Backhaul",
              draft-huang-detnet-xhaul-00 (work in progress), March

              Grossman, E., Gunther, C., Thubert, P., Wetterwald, P.,
              Raymond, J., Korhonen, J., Kaneko, Y., Das, S., Zha, Y.,
              Varga, B., Farkas, J., Goetz, F., Schmitt, J., Vilajosana,
              X., Mahmoodi, T., Spirou, S., and P. Vizarreta,
              "Deterministic Networking Use Cases", draft-ietf-detnet-
              use-cases-11 (work in progress), October 2016.

Authors' Addresses

   Carlos J. Bernardos
   Universidad Carlos III de Madrid
   Av. Universidad, 30
   Leganes, Madrid  28911

   Phone: +34 91624 6236
   Email: cjbc@it.uc3m.es
   URI:   http://www.it.uc3m.es/cjbc/

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   Antonio de la Oliva
   Universidad Carlos III de Madrid
   Av. Universidad, 30
   Leganes, Madrid  28911

   Phone: +34 91624 8803
   Email: aoliva@it.uc3m.es
   URI:   http://www.it.uc3m.es/aoliva/

   Luca Cominardi
   InterDigital Europe

   Email: Luca.Cominardi@InterDigital.com
   URI:   http://www.InterDigital.com/

   Luis M. Contreras
   Telefonica I+D
   Ronda de la Comunicacion, S/N
   Madrid  28050

   Email: luismiguel.contrerasmurillo@telefonica.com

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