Small Cell Backhaul

Delivering faster Enterprise Small Cell backhaul over CAT5e Cables

NBASE TData rates are getting faster all the time. Enterprise Wi-Fi and Small Cells typically use 1Gbps Ethernet backhaul over standard Cat5e cable, but that's insufficient for the latest 802.11ac Wi-Fi and LTE-U small cells. Aquantia has designed chips that achieve up to 5Gbps over existing cable, using a new technology called NBASE-T which should be more than enough to meet demand. Commercial products are already available although standards have still to catch up.

 

Copper, copper everywhere

About 99% of the 1Gbps connections in data centres and enterprise buildings run over copper wires. In recent years, there has been a transition to 10Gbps speeds, uprating many servers, switches and interface boards inside data centres. Chip vendor Aquantia dominates market share and has been looking for related markets to expand into.

They studied the enterprise market and realised that 802.11ac Wave 2 wireless access points (and Small Cells) would also be a strong driver for faster speeds. Theoretical maximum RF peak throughput of a Wi-Fi access point alone could exceed 6Gbps, although real-world rates are likely to be somewhat lower.

While their existing chip provides 10Gbps, legacy Cat5e and Cat6 cabling won't support those speeds up to the desired 100m distance. Around 90% of the worldwide installed Ethernet cabling is Cat5e or Cat6 today – although this varies a lot between regions. There are still around 20 million ports of Cat5e being installed annually. Very few buildings have installed Cat6A (A = Augmented, with wider separation between wires to reduce crosstalk) which is much thicker, costly and slightly more difficult to install.

Reuse is almost always cheaper than pulling through new cable except for brand new buildings.

The NBASE-T™ Specification: A new protocol

So Aquantia went on to design a new protocol that achieves up to 5Gbps at up to 100 metres over standard Cat5e or Cat6 copper cable and presented it as a contribution to the NBASE-T Alliance, forming the foundation for the alliance's Physical Layer (PHY) Spec 1.0.

Key objectives of the spec are:

  1. Data rates of 2.5Gbps and 5Gbps over Cat5e and 5Gbps over Cat6
  2. Support Power over Ethernet (PoE) and UPoE up to 60W per port
  3. Vendor Interoperability

The NBASE-T Alliance was launched in October 2014, providing a forum to build consensus around specifications and interoperability for the proposed 2.5Gbps and 5Gbps data rates. The alliance has secured participation from big names including Cisco, Ruckus, Intel, Cavium, Freescale, Microsemi, Brocade, Xilinx – 32 companies in all to date. There is also a competing alliance, called MGBASE-T supported by Broadcom and Freescale – 18 companies are listed on their website. 

The NBASE-T Alliance has released NBASE-T 1.0, the PHY specification to its members. In addition, individuals from NBASE-T Alliance member companies are working to formalise a standard through IEEE 802.3. A study group has been formed and the specification will be called 802.3bz. The Alliance does not directly participate or contribute to the final spec.

Multi-Gigabit Product available Q2 2015

Cisco was the first to announce commercial IP switches with NBASE-T, which they term MultiGigabit Ethernet (See their FAQ for details). This is available in their Catalyst 4500, 3850 and C3560-CX product families. These are understood to be based on the Aquantia chipset (AQrate product line).

The ports autoconfigure for best achievable speeds depending on capability of the connected equipment and cabling. They are backward compatible with existing 1Gbps ports and use the same RJ45 plug and socket physical connections.

Cisco policy is normally to introduce this into their higher level premium products first and then trickle down to lower cost products in due course. Although not announced, it seems likely to me that it would be incorporated into their Aironet Wireless Access points since this is a key driver for the technology.

Peter Jones, Cisco Principal Engineer and Chairman of the NBASE-T Alliance, introduced NBASE-T and Cisco Multigigabit Ethernet and discussed the technical challenges to adoption in a workshop which was recorded and posted online.

He indicated that customers are typically looking for 75% efficiency – i.e. the backhaul link should have at least 75% of the theoretical RF peak data rate supported by wireless access point.

I would expect 2.5Gbps to be more than adequate in most cases but would think that 1Gbps could become insufficient in the long term.

Related technology for remote radio heads using CPRI

Enterprise small cell architectures that centralise the baseband processing require much higher data rates to the remote radio heads. These are typically connected using CPRI (Common Packet Radio Interface) which requires at least 2Gbps and up to 10Gbps per link.

Aquantia has developed a specific chipset for point-to-point CPRI links over copper, called AQcell. The specs are similar to AQrate and support up to 10Gbps (CPRI Level 7) over 100 metres, SyncE and PTP 1588 timing synchronisation.

Products were announced in February 2015 and are already available in production quantities.

Summary

Silicon vendors have to place some very large bets when investing in new products. Those investments are a good indication of industry direction, and it is clear that in-building wireless data is a growing opportunity.

NBASE-T solutions are already commercially available and offer up to 5Gbps data rates over existing Cat5e and Cat6 cabling. This should be more than enough even for combined Wi-Fi 802.11ac Wave 2 and LTE Small Cells.

A variant of this technology is also available for C-RAN in-building architectures using CPRI.

This approach will reduce the cost of installing and upgrading in-building wireless systems by reusing and extending the life of existing Ethernet building wiring.

Our thanks to Phil Delansay, Co-Founder and Senior VP Business Development at Aquantia, for his insights during the preparation of this article.

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