To put xhaul (also known as crosshaul or X-haul) into a context, let's start from the domains of a mobile network. These include [5GPPP-1]:
Xhaul is a concept related to the second domain on the list above, that is, the 5G transport network. The transport network consists of the backhaul of radio base stations and fronthaul of remote radio units (a.k.a., Remote Radio Heads, RRHs). In the case of LTE, fronthaul refers to the high-bandwidth (optical [EX]) transport links that connect the RRHs to a BaseBand Unit (BBU) pool in the LTE C-RAN (Centralized Radio Access Network) architecture. Backhaul is the IP (IP/MPLS [EX]) network from the centralized BBUs to the LTE Evolved Packet Core (EPC). Finally, xhaul could be defined as a common flexible transport solution for future 5G networks, which integrates the fronthaul and backhaul networks with all their wired and wireless technologies into a common packet-based network that is under SDN (Software Defined Networking) based and NFV (Network Functions Virtualization) enabled common control [ER].
This SDN-controlled integrated backhaul and fronthaul transport network (i.e., xhaul) aims to enable a flexible and software-defined reconfiguration of all network functions in a multi-tenant and service-oriented manner [5GPPP-2]. The xhaul transport network is envisioned to consist of high-capacity software-defined switches and heterogeneous transmission links (e.g., fiber or wireless optics, high-capacity copper, and wireless millimeter wave links). These links will interconnect RRHs, macro and small cells, and distributed physical and virtual 5G RAN and core network functions (i.e., Physical Network Functions (PNFs) and Virtual Network Functions (VNFs)) hosted on in-network cloud nodes.
The vision is that Xhaul will turn the fronthaul and backhaul into a unified IP network [Cisco]. The unified approach will provide support for key timing issues like phase and frequency, and increases in network scale. The xhaul transport network needs to be application-aware and automated. Xhaul will be a key enabler for network slicing. Slicing will construct xhaul network resources based on SLAs (Service Level Agreements) and the needs of the application. The xhaul resources will be automated, model-driven and programmable (i.e., SDN-based) to be able to deal with real-time service transition and specific latency demands.
[5GPPP-1] 5G PPP Architecture Working Group, View on 5G Architecture, https://5g-ppp.eu/wp-content/uploads/2014/02/5G-PPP-5G-Architecture-WP-For-public-consultation.pdf
[5GPPP-2] 5G Crosshaul, the integrated fronthaul/backhaul, https://5g-ppp.eu/xhaul/
[Cisco] Are you ready for 5G xHaul? http://blogs.cisco.com/sp/are-you-ready-for-5g-xhaul
[ER] X-haul, fronthaul and backhaul network research, https://www.ericsson.com/research-blog/5g/x-haul-fronthaul-and-backhaul-network-research/
[EX] Overcoming Network Failures in C-RAN for 5G-Readiness, http://www.exfo.com/corporate/blog/2017/overcoming-network-failures-in-c-ran-for-5g-readiness
[NM] LTE Network Architecture: Basic, http://www.netmanias.com/en/post/techdocs/5904/lte-network-architecture/lte-network-architecture-basic
- Radio Access Network (RAN) domain
- Transport network domain
- Core Network (CN) domain
- Other domains, like the OSS/BSS domain for supporting telecommunication services and application domain for providing services [NM]
Xhaul is a concept related to the second domain on the list above, that is, the 5G transport network. The transport network consists of the backhaul of radio base stations and fronthaul of remote radio units (a.k.a., Remote Radio Heads, RRHs). In the case of LTE, fronthaul refers to the high-bandwidth (optical [EX]) transport links that connect the RRHs to a BaseBand Unit (BBU) pool in the LTE C-RAN (Centralized Radio Access Network) architecture. Backhaul is the IP (IP/MPLS [EX]) network from the centralized BBUs to the LTE Evolved Packet Core (EPC). Finally, xhaul could be defined as a common flexible transport solution for future 5G networks, which integrates the fronthaul and backhaul networks with all their wired and wireless technologies into a common packet-based network that is under SDN (Software Defined Networking) based and NFV (Network Functions Virtualization) enabled common control [ER].
This SDN-controlled integrated backhaul and fronthaul transport network (i.e., xhaul) aims to enable a flexible and software-defined reconfiguration of all network functions in a multi-tenant and service-oriented manner [5GPPP-2]. The xhaul transport network is envisioned to consist of high-capacity software-defined switches and heterogeneous transmission links (e.g., fiber or wireless optics, high-capacity copper, and wireless millimeter wave links). These links will interconnect RRHs, macro and small cells, and distributed physical and virtual 5G RAN and core network functions (i.e., Physical Network Functions (PNFs) and Virtual Network Functions (VNFs)) hosted on in-network cloud nodes.
The vision is that Xhaul will turn the fronthaul and backhaul into a unified IP network [Cisco]. The unified approach will provide support for key timing issues like phase and frequency, and increases in network scale. The xhaul transport network needs to be application-aware and automated. Xhaul will be a key enabler for network slicing. Slicing will construct xhaul network resources based on SLAs (Service Level Agreements) and the needs of the application. The xhaul resources will be automated, model-driven and programmable (i.e., SDN-based) to be able to deal with real-time service transition and specific latency demands.
References
[5GPPP-1] 5G PPP Architecture Working Group, View on 5G Architecture, https://5g-ppp.eu/wp-content/uploads/2014/02/5G-PPP-5G-Architecture-WP-For-public-consultation.pdf
[5GPPP-2] 5G Crosshaul, the integrated fronthaul/backhaul, https://5g-ppp.eu/xhaul/
[Cisco] Are you ready for 5G xHaul? http://blogs.cisco.com/sp/are-you-ready-for-5g-xhaul
[ER] X-haul, fronthaul and backhaul network research, https://www.ericsson.com/research-blog/5g/x-haul-fronthaul-and-backhaul-network-research/
[EX] Overcoming Network Failures in C-RAN for 5G-Readiness, http://www.exfo.com/corporate/blog/2017/overcoming-network-failures-in-c-ran-for-5g-readiness
[NM] LTE Network Architecture: Basic, http://www.netmanias.com/en/post/techdocs/5904/lte-network-architecture/lte-network-architecture-basic
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