active optical cable

Nokia's FP4 p-chip. The multi-chip module shows five packages: the p-chip die surrounded by four memory stacks. Each stack has five memory die. The p-chip and memory stacks are interconnected using an interposer.

• Nokia has unveiled the FP4, a 2.4 terabit-per-second network processor that has 6x the throughput of its existing FP3. 
• The FP4 is a four-IC chipset implemented using 16nm CMOS FinFET technology. Two of the four devices in the chipset are multi-chip modules.
• The FP4 uses 56 gigabit-per-second serial-deserialiser (serdes) technology from Broadcom, implemented using PAM-4 modulation. It also supports terabit flows.
• Nokia announced IP edge and core router platforms that will use the FP4, the largest configuration being a 0.58 petabit switching capacity router. 

Much can happen in an internet minute. In that time, 4.1 million YouTube videos are viewed, compared to 2.8 million views a minute only last year. Meanwhile, new internet uses continue to emerge. Take voice-activated devices, for example. Amazon ships 50 of its Echo devices every minute, almost one a second.

Given all that happens each minute, predicting where the internet will be in a decade’s time is challenging. But that is the task Alcatel-Lucent’s (now Nokia’s) chip designers set themselves in 2011 after the launch of its FP3 network processor chipset that powers its IP-router platforms.

Six years on and its successor - the FP4 - has just been announced. The FP4 is the industry’s first multi-terabit network processor that will be the mainstay of Nokia’s IP router platforms for years to come.

Cloud-scale routing

At the FP4’s launch, Nokia’s CEO, Rajeev Suri, discussed the ‘next chapter’ of the internet that includes smart cities, new higher-definition video formats and the growing number of connected devices.

IP traffic is growing at a compound annual growth rate (CAGR) of 25 percent through to 2022, according to Nokia Bell Labs, while peak data rates are growing at a 39 percent CAGR. Nokia Bell Labs also forecasts that the number of connected devices will grow from 12 billion this year to 100 billion by 2025. 

Basil Alwan, Nokia’s president of IP and optical networks, said the internet has entered the era of cloud-scale routeing. When delivering a cloud service, rarely is the request fulfilled by one data centre. Rather, several data centres are involved in fulfilling the tasks. “One transaction to the cloud is multiplied,” said Alwan.

IP traffic is also becoming more dynamic, while the Internet of Things presents a massive security challenge. 

Alwan also mentioned how internet content providers have much greater visibility into their traffic whereas the telcos’ view of what flows in their networks is limited. Hence their interest in analytics to understand and manage their networks better. 

These are the trends that influenced the design of the FP4.

We put a big emphasis on making sure we had a high degree of telemetry coming out at the chip level

FP4 goals

Telemetry, the sending of measurement data for monitoring purposes, and network security were two key design goals for the FP4.

Steve Vogelsang“We put a big emphasis on making sure we had a high degree of telemetry coming out at the chip level,” said Steve Vogelsang, CTO for Nokia's IP and optical business.

Tasks include counters, collecting statistics and packet copying. “This is to make sure we have the instrumentation coming off these systems that we can use to drive the [network] analytics platform,” said Vogelsang.

Being able to see the applications flowing in the network benefits security. Distributed Denial-of-Service (DDoS) attacks are handled by diverting traffic to a ‘scrubbing centre’ where sophisticated equipment separates legitimate IP packets from attack traffic that needs scrubbing.

The FP4 supports the deeper inspection of packets. “Once we identify a threat, we can scrub that traffic directly in the network,” said Vogelsang. Nokia claims that that the FP4 can deal with over 90 percent of the traffic that would normally go to a scrubbing centre.

Chipset architecture

Nokia’s current FP3 network processor chipset comprises three devices: the p-chip network processor, the q-chip traffic manager and the t-chip fabric interface device. 

The p-chip network processor inspects packets and performs table look-ups using fast-access memory to determine where packets should be forwarded. The q-chip is the traffic manager that oversees the packet flows and decides how packets should be dealt with, especially when congestion occurs. The third FP3 chip is the t-chip that interfaces to the router fabric.

The FP4 retains the three chips and adds a fourth: the e-chip - a media access controller (MAC) that parcels data from the router’s client-side pluggable optical modules for the p-chip. However, while the FP4 retains the same nomenclature for the chips as the FP3, the CMOS process, chip architecture and packaging used to implement the FP4 are significantly more advanced. 

The FP4 can deal with over 90 percent of the traffic that would normally go to a scrubbing centre

Nokia is not providing much detail regarding FP4 chipset's architecture, unlike the launch of the FP3. “We wanted to focus on the re-architecture we have gone through,” said Vogelsang. But looking at the FP3 design, insight can be gained as to how the FP4 has likely changed.

The FP3’s p-chip uses 288 programmable cores. Each programmable core can process two instructions each clock cycle and is clocked at 1GHz.

The 288 cores are arranged as a 32-row-by-9-column array. Each row of cores can be viewed as a packet-processing pipeline. A row pipeline can also be segmented to perform independent tasks. The array’s columns are associated with table look-ups. The resulting FP3 p-chip is a 400-gigabit network processor.

Vogelsang said there is limited scope to increase the clock speed of the FP4 p-chip beyond 1GHz. Accordingly, the bulk of the FP4’s sixfold throughput improvement is the result of a combination of programmable core enhancements, possible a larger core array and, most importantly, system improvements. In particular, the memory architecture is now packaged within the p-chip for fast look-ups, while the chipset’s input-output lanes have been boosted from 10 gigabits-per-second (Gbps) to 50Gbps.

Nokia has sought to reuse as much of the existing microcode to program the cores for the FP4 p-chip but has added new instructions to take advantage of changes in the pipeline.

Software compatibility already exists at the router operating system level. The same SROS router operating system runs on Nokia’s network processors, merchant hardware from the like of Broadcom and on x86 instruction-set microprocessors in servers using virtualisation technology.

Such compatibility is achieved using a hardware abstraction layer that sits between the operating system and the underlying hardware. “The majority of the software we write has no idea what the underlying hardware is,” said Vogelsang.

Nokia has a small team of software engineers focussed on the FP4’s microcode changes but, due to the hardware abstraction layer, such changes are transparent to the main software developers.

The FP3’s traffic manager, the q-chip, comprises four reduced instruction set computer (RISC) cores clocked at 900MHz. This too has been scaled up for the FP4 but Nokia has not given details.

The t-chip interfaces to the switch fabric that sits on a separate card. In previous generations of router products, a mid-plane is used, said Nokia. This has been scrapped with the new router products being announced. Instead, the switch cards are held horizontally in the chassis and the line cards are vertical. “A bunch of metal guides are used to guide the two cards and they directly connect to each other,” said Vogelsang. “The t-chips are what interface to these connectors inside the system.”

The MAC e-chip interfaces to the line card’s pluggable modules and support up to a terabit flow. Indeed, the MAC will support integer multiples of 100 Gigabit Ethernet from 100 gigabit to 1 terabit. Nokia has a pre-standard implementation of FlexMAC that allows it to combine lanes across multiple transceivers into a single interface.

Nokia will have line cards that support 24 or 36 QSFP-DD pluggable modules, with each module able to support 400 Gigabit Ethernet.

The FP4 is also twice as power efficient, consuming 4 gigabit/W.

We wanted to make sure we used a high-volume chip-packaging technology that was being driven by other industries and we found that in the gaming industry

Design choices

One significance difference between the two network processor generations is the CMOS process used. Nokia skipped 28nm and 22nm CMOS nodes to go from 40nm CMOS for the FP3 to 16nm FinFET for the FP4. “We looked at that and we did not see all the technologies we would need coming together to get the step-function in performance that we wanted,” said Vogelsang.   

Nokia also designed its own memory for the FP4.

“A challenge we face with each generation of network processor is finding memories and memory suppliers that can offer the performance we need,” said Vogelsang. The memory Nokia designed is described as intelligent: instructions can effectively be implemented during memory access and the memory can be allocated to do different types of look-up and buffering, depending on requirements.

Another key area associated with maximising the performance of the memory is the packaging. Nokia has adopted multi-chip module technology for the p-chip and the q-chip.

“We wanted to make sure we used a high-volume chip-packaging technology that was being driven by other industries and we found that in the gaming industry,” said Vogelsang, pointing out that the graphics processing unit (GPU) has similar requirements to those of a network processor. GPUs are highly memory intensive while manipulating bits on a screen is similar to manipulating headers and packets.

The resulting 2.5D packaged p-chip comprises the packet processor die and stacks of memory. Each memory stack comprises 5 memory die. All sit on an interposer substrate - itself a die that is used for dense interconnect of devices. The resulting FP4 p-chip is thus a 22-die multi-chip module.

“Our memory stacks are connected at the die edges and do not use through-silicon vias,” said Vogelsang. “Hence it is technically a 2.5D package [rather than 3D].”

The q-chip is also implemented as a multi-chip module containing RISC processors and buffering memory, whereas the router fabric t-chip and MAC e-chip are single-die ICs.

The FP4’s more advanced CMOS process also enables significantly faster interfaces. The FP4 uses PAM-4 modulation to implement 56Gbps interfaces. “You really need to run those bit rates much much higher to get the traffic into and out of the chip,” said Vogelsang.

Nokia says it is using embedded serialiser-deserialiser interface technology from Broadcom.

Next-gen routers

Nokia has also detailed the IP edge and core routers that will use the FP4 network processor.

The 7750 Service Router (SR-s) edge router family will support up to 144 terabits in a single shelf. This highest capacity configuration is the 7750 SR-14. It is a 24-rack-unit-plus-the-power-supply high chassis and supports a dozen line cards, each 12Tbps when using 100-gigabit modules, or 24x400GbE when using QSFP-DD modules.

Another new platform is the huge 7950 Extensible Routing System (XRS-XC) IP core router which can be scaled to 576 terabits - over half a petabit - when used in a six-chassis configuration. Combining the six chassis does not make require the use of front-panel client-side interfaces. Instead, dedicated interfaces are used with active optical cables to interlink the chassis.

The first router products will be shipped to customers at the year end with general availability expected from the first quarter of 2018.