Access drives a need for 10G compact aggregation boxes

Infinera has unveiled a platform to aggregate multiple 10-gigabit traffic streams originating in the access network. 

The 1.6-terabit HDEA 1600G platform is designed to aggregate 80, 10-gigabit wavelengths. The use of ten-gigabit wavelengths in access continues to grow with the advent of 5G mobile backhaul and developments in cable and passive optical networking (PON).

A distributed access architecture being embraced by cable operators. Shown are the remote PHY devices (RPD) or remote MAC-PHY devices (RMD), functionality moved out of the secondary hub and closer to the end user. Also shown is how DWDM technology is moved closer to the edge of the network. Source: Infinera.

Infinera has adopted a novel mechanical design for its 1 rack unit (1RU) HDEA 1600G that uses the sides of the platform to fit 80 SFP+ optical modules. 

The platform also features a 1.6-terabit Ethernet switch chip that aggregates the traffic from the 10-gigabit streams to fill 100-gigabit wavelengths that are passed to other switching or transport platforms for transmission into the network.  

Distributed access architecture

Jon Baldry, metro marketing director at Infinera, cites the adoption of a distributed access architecture (DAA) by cable operators as an example of 10-gigabit links that are set to proliferate in the access network.

DAA is being adopted by cable operators to compete with the telecom operators’ rollout of fibre-to-the-home (FTTH) broadband access technology. 

A recent report by market research firm, Ovum, addressing DAA in the North American market, discusses how the architectural approach will free up space in cable headends, reduce the operators’ operational costs, and allow the delivery of greater bandwidth to subscribers.

Implementing DAA involves bringing fibre as well as cable network functionality closer to the user. Such functionality includes remote PHY devices and remote MAC-PHY devices. It is these devices that will use a 10-gigabit interface, says Baldry: “The traffic they will be running at first will be two or three gigabits over that 10-gigabit link.” 

Julie Kunstler, principal analyst at Ovum’s Network Infrastructure and Software group, says the choice whether to deploy a remote PHY or a remote MAC-PHY architecture is a issue of an operator's ‘religion’.  What is important, she says, is that both options exploit the existing hybrid fibre coax (HFC) architecture to boost the speed tiers delivered to users.   

The current, pre-DAA, cable network architecture. Source: Infinera.

In the current pre-DAA architecture, the cable network comprises cable headends and secondary distribution hubs (see diagram above). It is at the secondary hub that the dense wavelength-division multiplexing (DWDM) network terminates. From there, RF over fibre is carried over the hybrid fibre-coax (HFC) plant. The HFC plant also requires amplifier chains to overcome cable attenuation and the losses resulting from the cable splits that deliver the RF signals to the homes. 

Typically, an HFC node in the cable network serves up to 500 homes. With the adoption of DAA and the use of remote PHYs, the amplifier chains can be removed with each PHY serving 50 homes (see diagram top).  

“Basically DWDM is being pushed out to the remote PHY devices,” says Baldry. The remote PHYs can be as far as 60km from the secondary hub. 

“DAA is a classic example where you will have dense 10-gigabit links all coming together at one location,” says Baldry. “Worst case, you can have 600-700 remote PHY devices terminating at a secondary hub.”

The same applies to cellular.

At present 4G networks use 1-gigabit links for mobile backhaul but 5G will use 10-gigabit and 25-gigabit links in a year or two. “So the edge of the WDM network has really jumped from 1 gigabit to 10 gigabit,” says Baldry. 

It is the aggregation of large numbers of 10-gigabit links that the HDEA 1600G platform is designed to address.

HDEA 1600G 

Only a certain number of pluggable interfaces can fit on the front panel of a 1RH box. To accommodate 80, 10-gigabit streams, the two sides of the platform are used for the interfaces. Using the HDEA’s sides creates much more space for the 1RU’s input-output (I/O) compared to traditional transport kit, says Baldry.

The 40 SFP+ modules on each side of the platform are accessed by pulling the shelf out and this can be done while it is operational (see photo below). Such an approach is used for supercomputing but Baldry believes Infinera is the first to adopt it for a transport product.

Infinera has also adopted MPO connectors to simplify the fibre management involved in connected 80 SFP+, each module requiring a fibre pair. 

The HDEA 1600 has two groups of four MPO connectors on the front panel. Each MPO cluster connects 40 modules on each side, with each MPO cable having 20 fibres to connect 10 SFP+ modules. 

A site terminating 400 remote PHYs, for example, requires the connection of 40 MPO cables instead of 800 individual fibres, says Baldry, simplifying installation greatly.

DAA is a classic example where you will have dense 10-gigabit links all coming together at one location. Worst case, you can have 600-700 remote PHY devices terminating at a secondary hub.

The other end of the MPO cable connects to a dense multiplexer-demultiplexer (mux-demux) unit that separates the individual 10-gigabit access wavelengths received over the DWDM link.  

Each mux-demux unit uses an arrayed waveguide grating (AWG) that is tailored to the cable operators’ wavelengths needs. The 24-channel mux-demux design supports 20, 100GHz-wide channels for the 10-gigabit wavelengths and four wavelengths reserved for business services. Business services have become an important part of the cable operators’ revenues.

Infinera says the HDEA platform supports the extended C-band for a total of 96 wavelengths. 

The company says it will develop different AWG configurations tailored for the wavelengths and channel count required for the different access applications. 

In the rack, the HDEA aggregation platform takes up one shelf, while eight mux-demux units take up another 1RU. Space is left in between to house the cabling between the two.  

The HDEA 1600G pulled out of the rack, showing the MPO connectors and the space to house the cabling between the HDEA and the rack of compact AWGs. Source: Infinera.

Baldry points out that the four business service wavelengths are not touched by the HDEA platform, Rather, these are routed to separate Ethernet switches dedicated to business customers. "We break those wavelengths out and hand them over to whatever system the operator is using," he says. 

The HDEA 1600G also features eight 100-gigabit line-side interfaces that carry the aggregated cable access streams. Infinera is not revealing the supplier of the 1.6 terabit switch silicon - 800-gigabit for client-side capacity and 800-gigabit for line-side capacity - it is using for the HDEA platform. 

The platform supports all the software Infinera uses for its EMXP, a packet-optical switch tailored for access and aggregation that is part of Infinera’s XTM family of products. Features include multi-chassis link aggregation group (MC-LAG), ring protection, all the Metro Ethernet Forum services, and synchronisation for mobile networks, says Baldry   

Auto-Lambda

Infinera has developed what it calls its Auto-Lambda technology to simplify the wavelength management of the remote PHY devices. 

Here, the optics set up the connection instead of a field engineer using a spreadsheet to determine which wavelength to use for a particular remote PHY. Tunable SFP+ modules can be used at the remote PHY devices only with fixed-wavelength (grey) SFP+ modules used by the HDEA platform to save on costs, or both ends can use tunable optics. Using tunable SFP+ modules at each end may be more expensive but the operator gains flexibility and sparing benefits.  

Establishing a link when using fixed optics within the HDEA platform, the SFP+ is operated in a listening mode only. When a tunable SFP+ transceiver is plugged in at a remote PHY, which could be days later, it cycles through each wavelength. The blocking nature of the AWG means that such cycling does not disturb other wavelengths already in use. Once the tunable SFP+ reaches the required wavelength, the transmitted signal is passed through the AWG to reach the listening transceiver at the switch. On receipt of the signal, the switch SFP+ turns on its transmitter and talks to the remote transceiver to establish the link.

Jon BaldryFor the four business wavelengths, both ends of the link use auto-tunable SFP+ modules, what is referred to a duel-ended solution. That is because both end-point systems may not be Infinera platforms and may have no knowledge as to how to manage WDM wavelengths, says Baldry.

In this more complex scenario, the time taken to establish a link is theoretically much longer. The remote end module has to cycle through all the wavelengths and if no connection is made, the near end transceiver changes its transmit wavelength and the remote end’s wavelength cycling is repeated.

Given that a sweep can take two minutes or more, an 80-wavelength system could take close to three hours in the worst case to establish the link; an unacceptable delay.

Infinera is not detailing how its duel-ended scheme works but a combination of scanning and communications is used between the two ends. Infinera had shown such a duel-ended scheme set up a link in 4 minutes and believes it can halve that time.

Finisar detailed its own Flextune fast-tuning technology at ECOC 2018. However, Infinera stresses its technology is different. 

Infinera says it is talking to several pluggable optical module makers. “They are working on 25-gigabit optics which we are going to need for 5G,” says Baldry. “As soon as they come along, with the same firmware, we then have auto-tunable for 5G.”  

System benefits

Infinera says its HDEA design delivers several benefits. Using the sides of the box means that the platform supports 80 SFP+ interfaces, twice the capacity of competing designs. In turn, using MPO connectors simplifies the fibre management, benefiting operational costs. 

Infinera also believes that the platform’s overall power consumption has a competitive edge. Baldry says Infinera incorporates only the features and hardware needed. “We have deliberately not done a lot of stuff in Layer 2 to get better transport performance,” he says. The result is a more power-efficient and lower latency design. The lower latency is achieved using ‘thin buffers’ as part of the switch’s output-buffered queueing architecture, he says. 

The platform supports open application programming interfaces (APIs) such that cable operators can make use of such open framework developments as the Cloud-Optimised Remote Datacentre (CORD) initiative being developed by the Open Networking Foundation. CORD uses open-source software-defined networking (SDN) technology such as ONOS and the OpenFlow protocol to control the box. 

An operator can also choose to use Infinera’s own Digital Network Administrator (DNA) management software, SDN controller, and orchestration software that it has gained following the Coriant acquisition. 

The HDEA 1600G is generally available and in the hands of several customers.