Hybrid Access Networks

Hybrid Access Networks refer to a special architecture for broadband access networks where two different network technologies are combined to improve bandwidth. A frequent motivation for such Hybrid Access Networks is to combine one xDSL network with a wireless network such as LTE. The technology is generic and can be applied to combine different types of access networks such as DOCSIS, WiMAX, 5G or satellite networks. The Broadband Forum has specified an architecture[1] for the deployment of such networks.

Use cases

One of the main motivations for such Hybrid Access Networks is to provide faster Internet services in rural areas where it is not always cost effective to deploy faster xDSL technologies such as G.Fast or VDSL2 that cannot cover long distances between the street cabinet and the home. Several governments, notably in Europe, require network operators to provide fast Internet services to all inhabitants with a minimum of 30 Mbps by 2020.[2]

A second use case is to improve the reliability of the access link given that it is unlikely that both the xDSL network and the wireless network will fail at the same time.

A third motivation is the fast service turnup. The customer can immediately install the hybrid network access and use the wireless leg while the network operator is installing the wired part.

Technology

Several techniques are defined by the Broadband Forum to create Hybrid Access Networks. To illustrate them, we assume that the enduser has an hybrid CPE router that is attached to both a wired access network such as xDSL and a wireless on such as LTE. Other deployments are possible, e.g. the enduser might have two different access routers that are linked together by a cable instead of a single hybrid CPE router.

The first deployment scenario is where the network operator provides a hybrid CPE router to each subscriber but no specialised equipment in the operator's network. There are two possible configurations for IP addresses. A first deployment scenario is to allocate different IP addresses to the wired and wireless interfaces. In this case, the hybrid CPE router needs to load-balance intelligently the packets over the two networks. In particular, it must ensure that all packets belonging to a given TCP connection are sent over the same interface. A second deployment scenario is to allocate the same IP address to both the wired and the wireless networks and configure the routing in these networks to ensure that packets are correctly routed.

The second deployment scenario is where the network operator provides a hybrid CPE router to each subscriber and installs a Hybrid Aggregation Gateway inside its access networks. The Hybrid Aggregation Gateway plays an important role in balancing the packets sent by and destined to the hybrid CPE router over the two access networks. Two technologies have been defined and deployed to enable hybrid CPE routers to interact with Hybrid Aggregation Gateways. The main objective of these technologies is to efficiently use the two access links even if they have different delay and bandwidth. One technical difficulty that occurs when distributing packets over such heterogeneous links is to accurately detect congestion, notably on the wireless network whose bandwidth can vary quickly, and cope with the reordering which is caused by the delay difference. One approach uses GRE tunnels [3] to hide the two links to the upper layer protocol. Both the hybrid CPE and the HAG need to reorder the received packets to ensure that TCP receives in-sequence packets. The second approach uses Multipath TCP, a recent TCP extension that has been designed to enable the transmission of the packets that belong to a single session across different links. This approach leverages the ability of MPTCP to efficiently handle congestion and cope with reordering on the heterogeneous access links. MPTCP needs support in both the host and the server[4]. Two approaches have been defined for the interactions between the hybrid CPE router and the Hybrid Aggregation Gateway. The transparent mode [5] is used when the Hybrid Aggregation Gateway is placed on the path of all packets sent by the hybrid CPE router. Otherwise, the Hybrid Aggregation Gateway includes a TCP converter as defined in [6]. Additional details on Hybrid Access Networks and their deployment are described in [7]

Hybrid Access Network

Deployments

The first commercial deployments started in 2015 [8] Several deployments of Hybrid Access Networks have already been documented.

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References
  1. Broadband Forum (2016-07-01). "TR-348 Hybrid Access Broadband Network Architecture" (PDF). Retrieved 2018-07-01.
  2. "Broadband Europe". 2013-03-25.
  3. Leiman, N. (May 2017). Huawei's GRE Tunnel Bonding Protocol. IETF. doi:10.17487/RFC8157. RFC 8157.
  4. {{cite IETF |title=TCP Extensions for Multipath Operation with Multiple Addresses |date=Jan 2013|autolink=yes |publisher=IETF|rfc=rfc6824}
  5. Peirens, Bart; Detal, Gregory; Barre, Sebastien; Bonaventure, Olivier (July 2016). Link bonding with transparent Multipath TCP. IETF. I-D draft-peirens-mptcp-transparent-00.
  6. Bonaventure, Olivier; Boucadair, Mohammed; Gundavelli, Sri; Seo, SungHoon; Hesmans, Benjamin (March 2020). 0-RTT TCP Convert Protocol. IETF. I-D draft-ietf-tcpm-converters-19.
  7. Keukeleire, Nicolas; Hesmans, Benjamin; Bonaventure, Olivier (2020). "Increasing Broadband Reach with Hybrid Access Networks". IEEE Communications Standards Magazine,. 4 (1): 43–49. doi:10.1109/MCOMSTD.001.1900036.CS1 maint: extra punctuation (link)
  8. Armita Satari (2019-05-10). "Hybrid broadband offers fibre alternative for rural Europe".
  9. N. Leyman (2017). "Hybrid Access deployment @ DT" (PDF).
  10. Proximus Press release (2017-05-16). "Tessares-Proximus' Access Bonding - offering faster Internet in large, sparsely populated rural areas – now successfully qualified to move to a countrywide deployment phase". Archived from the original on 2018-07-05. Retrieved 2018-07-05.
  11. KPN (2018-03-10). "Fast internet delivered in rural areas by KPN & Tessares".
  12. Ian Scales (2019-05-10). "Wire in the mud: Dutch rural users offered LTE boost for slow copper".
  13. "Telia's innovations: the hybrid-type Internet and cloud computing". 2017-03-02.
  14. "Telia intros hybrid fixed-mobile broadband service in Finland". 2018-08-17.
  15. "Press Release Freebox Delta" (PDF). www.iliad.fr. Retrieved 2018-12-10.
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