Table 1. Key parameters for Broadcom’s StrataXGS enterprise-switch chips. Although the two chips share many features, the BCM56340 has the lowest price. (Source: Broadcom)

Unlike the 56340, the 56547 supports one 40GbE uplink as an alternative to 4x10GbE uplinks. Although a single uplink may appear deficient for redundancy, another switch in the stack can provide a second 40GbE uplink for failover. The HiGig[42] stacking port delivers adequate bandwidth for 40GbE uplinks.

One feature borrowed from Trident II is flexible L2/L3 table management, which Broadcom calls Smart-Table. Most Ethernet switch chips implement fixed-size tables for MAC addresses, IP host and multicast addresses, IP routes (longest-prefix match), and ARP entries. By contrast, Broadcom’s Smart-Table design unifies these tables in a single memory structure that can be configured with balanced, L2-heavy, or L3-heavy profiles. Depending on the selected profile, the 56547 enables more than 64K MAC addresses or more than 64K IPv4 entries. The 56340 implements a smaller table memory, but Broadcom has withheld its capacity. Similarly, the company has not disclosed the size of the 56340’s or 56547’s TCAMs, which hold access-control-list (ACL) entries.

Another 56340 optimization for cost and power is the chip’s 4MB shared-memory packet buffer, which is smaller than that of the 56547; Broadcom has not revealed the size of the latter. Both chips integrate a processor complex consisting of dual 1.0GHz ARM Cortex-A9 CPUs, 512KB of shared L2 cache, a 32-bit DDR3 SDRAM controller with ECC, and a PCI Express interface. For typical enterprise-switch designs, the integrated dual-core processor should eliminate a separate host processor, reducing cost and board space. Built in 40nm technology, the 56340 and 56547 are pin compatible.

Broadcom complements its silicon with two distinct software levels. For OEMs that develop their own software, the company supplies drivers that provide a common API across all StrataXGS products. This API hides hardware-specific details such as register configurations, allowing OEMs to easily port their software across different StrataXGS devices.

For ODMs or OEMs that need turnkey software, Broadcom supplies its production-quality FastPath solutions at added cost. The standard FastPath offering supports a comprehensive feature set including stacking, L2 switching, TRILL, IPv4/v6 routing, multicast, ECMP, and SNMP. For unified wireless switching, FastPath UWS adds Wi-Fi configuration and management features including automatic access-point detection, RF management, client authentication (WEP/WPA), rogue AP and client detection, and a single point of management for multiple switches.

The Unwiring Closet

The 56340’s major feature additions are not new to the StrataXGS line. That is, the BCM56540 was first to implement both CAPWAP and App-IQ. By introducing these features in the 56340, however, Broadcom is moving them down the LAN hierarchy from the aggregation layer to the access layer. As more clients use Wi-Fi instead of GbE as their connection to the enterprise LAN, network performance will suffer if too much wireless traffic must be forwarded to a centralized controller. This is particularly true as 802.11ac pushes Wi-Fi rates to the gigabit level. (Broadcom’s brand name for 802.11ac is “5G Wi-Fi” because it’s the fifth-generation Wi-Fi standard.)

The 56340 and 56547 support 8,192 wireless clients and can terminate up to 1,024 CAPWAP tunnels, which are transported over UDP. The switch classifies incoming packets using an L3 tunnel table to see if CAPWAP processing is needed. It differentiates between CAPWAP data messages and control messages using their UDP ports. The processing pipeline decapsulates tunneled data messages by stripping the IP header, UDP header, and CAPWAP header, leaving an L2 frame for forwarding. Control messages are forwarded to the control plane for processing in firmware running on the embedded ARM CPUs. The 56340 and 56547 also support L2-over-GRE, which is an alternative tunneling protocol that some wireless switches use.

Whereas CAPWAP is a standardized protocol, App-IQ is a proprietary feature unique to StrataXGS. App-IQ is essentially a distributed DPI implementation, which enables application visibility and control throughout the network. This feature adds Layer 7 classification, building on Broadcom’s proven ContentAware engine for Layer 2–4 packet classification. The existing ContentAware engine classifies flows using TCAMs and then applies actions such as mark or drop (deny), which is how StrataXGS implements ACLs.

With App-IQ, packets are copied to a signature-match engine, which inspects the packet’s payload for up to approximately 100 signatures. The results are then fed back to the ContentAware engine, which tracks the application flow and applies actions. Although this signature set is small compared with that of dedicated DPI appliances, Broadcom’s idea is to implement basic DPI at network-access nodes using a low-cost design. The company’s example use cases include rate limiting unproductive applications such as games or P2P programs as well as blocking web sites by domain name. The combination of App-IQ and CAPWAP enable policy enforcement for wired and wireless clients throughput the enterprise.

Although enterprise LANs represent the biggest market for the 56340 and 56547, some data centers continue to connect servers using GbE rather than 10GbE. To support top-of-rack switch designs, the 56340 and 56547 implement DCB and virtualization protocols, as Table 1 shows. Relative to Broadcom’s newest 10GbE switch (Trident II), the GbE chips omit support for the VxLAN and NVGRE overlay protocols.

Dropping the BOM

Compared with their respective predecessors, the 56340 and 56547 improve system integration in several ways. As discussed above, they are the first StrataXGS chips to integrate a CPU complex, thereby eliminating one significant external component. Another major change is the use of QSGMII for GbE ports, which reduces pin count and power for both the switch chip and the external copper PHYs by multiplexing the equivalent of four SGMII signals. Whereas the 56540 already used 10Gbps serdes for uplink and stacking ports, the earlier 56330 implemented XAUI uplinks. Now, both the 56340 and 56547 directly support SFI for connecting SFP+ optical modules or direct-attach cabling.

Figure 1 shows a 48+4 stackable-switch design using the 56340 or 56547—the board design for the two devices is identical. Six octal PHYs connect with the 48 RJ45 jacks for the GbE ports. This example uses the BCM54682E, Broadcom’s newest GbE PHY optimized for copper-only ports. If an OEM wishes to enable fiber modules on some ports, it can substitute the BCM54685E dual-media PHY. Both octal PHYs are 65nm designs that implement Energy Efficient Ethernet (802.3az). No external PHYs are needed for 10GbE or 40GbE uplinks; the 56547 directly supports QSFP+ modules.

Aside from the GbE-over-copper PHYs, the board design requires few other major components. The ARM CPU complex needs one or more DDR3 SDRAM devices and a serial flash device. The integrated processor provides a GbE management port and a USB2.0 port (not shown). The switch chip requires 1.0V and 3.3V supplies; Broadcom has withheld power-dissipation figures for the 56340 and 56547.

Protecting Its Turf

With its new StrataXGS switches, Broadcom is advancing the feature set of high-volume Ethernet switch chips. In our view, the company’s primary motivation is customer retention, given it already owns about two-thirds of the merchant GbE switch market. Fully assessing the competitive environment is difficult, however, because Marvell services the enterprise segment using semicustom products from its Prestera DX and EX lines. Other GbE switch vendors, including Qualcomm Atheros, Realtek, and Vitesse, lack enterprise-class products and instead target SMB or service-provider designs.

Broadcom knows GbE switches have plenty of life left. Our most recent forecast shows GbE switch ports growing at a 13.5% compound annual growth rate (CAGR) between 2011 and 2016. Although declining per-port prices offset some of this growth, we still expect merchant GbE switch chips to break $1.3 billion in annual revenue before growth plateaus. So Broadcom is investing in a cash cow that nearly guarantees a return. There is also ongoing speculation in the financial community regarding Cisco adopting merchant switch chips. Although we see little probability of a Cisco move away from ASICs, such a change would substantially increase the size of the merchant Ethernet switch market.

The magic of Broadcom’s SoC designs is they can simultaneously reduce system costs and introduce advanced features. Using today’s process technology, the company can add new features with little impact on silicon cost. On the other hand, customers may decline to adopt an advanced feature such as App-IQ, which looks good on paper but will require a great deal of software support to enable practical deployments. By contrast, CAPWAP is an industry standard, and Broadcom already offers turnkey software for both switches and access points; ODMs can therefore easily support this protocol. In the end, the breadth and completeness of Broadcom’s offering is what makes gaining a foothold so difficult for competitors.