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Is Broadcom’s chip powering Juniper’s Stratus?

Briefing:  Data centre switching

Part 1: Single-layer switch architectures

Juniper Networks’ Stratus switch architecture, designed for next-generation data centres, is several months away from trials. First detailed in 2009, Stratus is being engineered as a single-layer switch with an architecture that will scale to support tens of thousands of 10 Gigabit-per-second (Gbps) ports.


Stratus will be in customer trials in early 2011.

Andy Ingram, Juniper Networks






Data centres use a switch hierarchy, made up of three layers commonly. Multiple servers are connected to access switches, such as top-of-rack designs, which are connected to aggregation switches whose role is to funnel traffic to large, core data centre switches.

Moving to a single-layer design promises several advantages. Not only does a single-layer architecture reduce the overall number of managed platforms, bringing capital and operational expense savings, it also reduces switch latency.


Broadcom’s IC for Stratus?

The Stratus architecture has yet to be detailed by Juniper. But the company has said that the design will be based on a 64x10Gbps ASIC building block dubbed a path-forwarding engine (PFE).

“The building block – the PFE – that can have that kind of density (64x10Gbps) gives us the ability to build out the network fabric in a very economical way,” says Andy Ingram, vice president of product marketing and business development of the fabric and switching technologies business group at Juniper Networks.

Stratus is being designed to provide any-to-any connectivity and operate at wire speed. “You have a very dense, very high-cross-sectional bandwidth fabric,” says Ingram. “The only way to make it economical is to use dense ASICs.”

Broadcom’s latest StrataXGS Ethernet switch family - the BCM56840 series - comprises three devices to date, the largest of which - the BCM56845 – also has 64x10Gbps ports.

Juniper will not disclose whether it is using its own ASIC or a third-party device for Stratus.

Broadcom, however, has said that its BCM56840 series is being used by vendors developing flat, single-layer switch architectures. “Anyone using merchant Ethernet switching silicon to build a single-stage environment is probably using our technology,” says Nick Ilyadis, chief technical officer for Broadcom’s infrastructure networking group.

Stratus will be in customer trials in early 2011. “In a lot less than 6 months”, says Ingram. “We have some customers that have some very difficult networking challenges that are signed up to be our early field trials and we will work with them extensively.”

The timeline aligns with Broadcom’s claim that samples of the BCM56840 ICs have been available for months and will be in production by year-end.

According to Broadcom, only a handful of switch vendors have the resources to design such a complex switch ASIC and also expect to recoup their investment. Moreover, a switch vendor using Broadcom's IC has plenty of scope to differentiate their design using software, and even FPGA hardware if needed. It is software that brings out the many features of the BCM56845, says Broadcom.


The BCM56845

Broadcom’s BCM56840 ICs share a common feature set but differ in their switching capacity. The largest, the BCM56845, has a switching capacity of 640Gbps. The device’s 64x10 Gigabit Ethernet (GbE) ports can also be configured as 16x40 GbE ports. 

The BCM56845 supports data center bridging (DCB), the Ethernet protocol enhancement that enables lossless transmission of storage and high-performance computing traffic. It also supports the Fibre Channel over Ethernet (FCoE) protocol that frames Fibre Channel storage traffic over DCB-enhanced Ethernet.

Besides DCB Ethernet, the series switch includes layer 3 packet processing and routeing.  There is also a multi-stage content-aware engine that allows higher layer, more complex packet inspection (layer 4 to 7 of the Open Systems Interconnection model) and policy management.

The content-aware functional block can also be used for packet cut-through; a technique to reduce switch latency by inspecting header information and forwarding all the while the packet’s payload is arriving. Broadcom says the switch’s latency is less than one microsecond.

Most importantly, the BCM56845 addresses the move to a flatter switching architecture in the data centre.

It supports the Transparent Interconnection of Lots of Links (TRILL) standard ratified by the Internet Engineering Task Force (IETF) in July. Ethernet uses a spanning tree technique to avoid the creation of loops within a network. However the spanning tree becomes unwieldy as the Ethernet network size grows and works only at the expense of halving the available networking bandwidth. TRILL is designed to allow much larger Ethernet networks while using all available bandwidth.

Broadcom has its own protocol know as HiGig that adds tags to packets. Using HiGig, a very large logical switch can be created and managed, made up of multiple interconnected switches. Any port of the IC can be configured as a HiGig port.

So has Broadcom’s BCM56845 been chosen by Juniper Networks for Stratus?  “I really can’t comment on which customers are using this,” says Ilyadis.



Click here for Part 2: Ethernet switch chips

Click here for Part 3: Networking developments


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