40G ATCA Meets LTE – Speeding from Backplanes to Broadband

With 10 Gigabit Ethernet already well established, the huge increase in mobile communications is demanding yet more speed and bandwidth with a path beyond. Long Term Evolution (LTE) is ready to take this to 40G and to serve as a network architecture for the future well after that.


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How much is a Yottabyte? Well if you don’t instantly know the answer let me tell you it’s extremely big, 1024 or 1,000,000,000,000,000,000,000,000 bytes to be exact. That’s a Lottabytes—sorry couldn’t resist. One step down in the hierarchy is the zettabyte, (a mere 1021 bytes = 1 billion terabytes), and according to the Cisco VNI Forecast, “Annual global IP traffic will exceed three-quarters of a zettabyte (767 exabytes) in four years.” One step under the zettabyte is the exabyte, and looking at Cisco’s forecast for mobile traffic, by 2014 our mobile networks will be transporting 3.6 exabytes of data/month—OMG!

We are already seeing tremendous increases in the data traffic carried in the mobile network as there is a massive shift in content and usage models. With Android-based phones adding to the market boom kicked off by the iPhone, and a wide range of new tablets about to join the iPad for our mobile delectation, mobile broadband subscriptions are going through the roof. According to ABI Research, “At the end of 2009, there were 181 million HSxPA subscriptions, with overall mobile broadband subscriptions growing to 271 million, representing a year over year growth rate of 43%.” With sales of data and Internet-enabled mobile devices on a similar growth curve, we can easily see what will be filling that zettabyte.

New Infrastructure for a New Network

This dramatic increase in mobile broadband subscriptions will have a dramatic impact on the network infrastructure as data traffic continues to grow. A shift to a new generation of equipment and architecture is being put in place to manage this data expansion. It is known as Long Term Evolution (LTE) and is the brainchild of 3rd Generation Partnership Project (3GPP).

The 3GPP was established late in 1998 as key telecommunications standards bodies recognized the need for a unified approach. An evolution of the General System for Mobile Communication (GSM) was the initial focus for 3GPP as they worked to produce Technical Specifications and Technical Reports that would lead to new radio access and core developments. 3GPP’s scope grew as they helped create specifications for General Packet Radio Service (GPRS) and edge. They then went on to lead the development of standards including—High Speed Packet Downlink Access (HSDPA), High Speed Packet Uplink Access (HSUPA) and finally LTE, where work began as early as 2004. The core standards work for LTE went on through 2007, and in early 2008 the first signs of adoption were seen as several vendors began shipping LTE test equipment. Late in 2009 the first LTE services became available in Oslo and Stockholm provided by the Swedish-based operator TeliaSonera AB.

Any mobile network requires two primary components, a Radio Access Network (RAN) that connects to and manages subscriber devices and a core network that will route and switch voice and data traffic to the desired destination. The LTE architecture primarily describes the evolved RAN while the broader packet interconnect system is known as System Architecture Evolution (SAE). The starting point for SAE was the GPRS core network. Building on that, 3GPP worked to greatly simplify the architecture and create an all-IP network (AIPN) that would be capable of supporting a RAN that had significantly higher throughput and lower latency. Another key goal of SAE is to create an infrastructure where multiple heterogeneous RANs can coexist and work together (Figure 1).

Figure 1
LTE network architecture.

The all-IP network is built out as the Evolved Packet Core (EPC). The EPC is constructed from three components: The Packet Data Network Gateway (P-GW), Serving Gateway (SGW) and Mobility Management Entity (MME). The division of labor and roles within the EPC are:

- The MME has significant responsibility as it is the primary control-node for the LTE RAN. The MME’s responsibilities include:

   — User authentication through interaction with the HSS (Home Subscriber Server)
   — Selection of the SGW and P-GW
   — Idle mode User Equipment (UE) tracking and paging procedure including retransmissions 
   — A significant part of the bearer activation/deactivation process
   — Replication of the user traffic for lawful interception applications
   — Mobility and interaction between the LTE and 2G/3G access networks

- The P-GW manages end devices or UE and their connectivity to external Packet Data Networks. An end device may connect with more than one PGW simultaneously while gaining access to multiple PDNs. Policy enforcement, packet filtering, charging support, lawful Interception and packet screening are some of the functions handled by the PGW.
- The SGW is the foundation for mobility between eNodeBs as well as linkages to other 3GPP technologies. All user data packets are routed and forwarded by the SGW.

The EPC is surrounded by the LTE RAN or evolved UTRAN (eUTRAN). One way the 3GPP simplified the overall architecture and improved core efficiency is by keeping traffic out that doesn’t need to be there. The RAN therefore has the ability to route traffic within the same or adjacent cells. In contrast to current architectures where a combination of two elements (NodeB and RNC) control the RAN, LTE has a single element called the eNodeB. Responsibilities of the eNodeB include: connection mobility control, dynamic allocation of the uplink and downlink, radio admission control, radio bearer control and radio resource management. 

It is LTE that promises significant enhancements in the area of speed/bandwidth and latency. Definitions allow for peak bit rates of more than 100 Mbit/s in the downlink and greater than 50 Mbit/s in the uplink, while latency, measured in terms of Round Trip Times (RTT) should be less than 10 ms. Frequency division duplexing (FDD) and time division duplexing (TDD) modes are both supported with LTE along with a scalable range of operating frequencies in bandwidths from 1.25 MHz to 20 MHz.

As one looks at everything that is required to build out these new LTE-SAE networks one can see how the design challenges for equipment vendors will be extensive. As the service providers migrate to these new all-IP networks, the equipment created by the TEMs will need to improve in terms of capacity, coverage and cost metrics. The rate of adoption and deployment continues to accelerate so “time-to-market” issues have become even more acute. Taking all this into account, plus the fact that LTE calls for significant improvements in the areas of bandwidth and latency, an outsourced solution that can hit all the requirements would be extremely attractive. Creating an LTE network element requires that the hardware platform must provide certain specific features.

These include a backplane like the one in Figure 2 that can provide more than 10GbE to support high-bandwidth network processing along with low-latency packet switching capabilities. It should be standards-based for time-to-market advantage, provide scalability and extensibility and be designed for resiliency, reliability and high-availability functionality. It is also essential that such a platform provide support for IPv6, MPLS and IPsec protection as well as Sync. E and IEEE1588 support.

Figure 2
Multi-functional 40G ATCA system with SyncE and IEEE-1588 support.

AdvancedTCA (ATCA) technologies have been growing in popularity as they meet all the open standards requirements for telecommunications platforms. PICMG, the standards body that is responsible for ATCA, is taking steps to enhance the specification with respect to the specific requirements for LTE. One of the most exciting changes that vendors across the ecosystem have been following closely is the move to faster backplanes. In this case that means backplanes that will be capable of delivering 40 Gbit per second.

New PICMG 40G Standards

Having evolved from first generation 1 Gbit/s versions, 10G fabrics have been available in ATCA backplanes and systems for some time now. With the IEEE Ethernet standard (802.3) at its core, option 9 of the PICMG 3.1 standard provides the definitions for today’s switched Ethernet backplanes. A single 10 Gbit/s interface is created through the aggregation of 4 x 2.5 Gbit/s links each using 10GBASE-KX4 PHYs. Even though there are four lanes involved, a single MAC is presented to the application and a similar strategy will be used to deliver 40G backplanes.

Thanks to the work of the IEEE Higher Speed Study Group, a new revision (802.3ba) of Ethernet was approved earlier this year. It is this new “ba” version that provides the foundation on which PICMG will base R2 of the 3.1 standard. R2 will set the rules for how ATCA backplanes, switches and enabled blades can support 40G speeds. Following the same aggregation strategy as its 10G predecessor, the new 40GBASE-KR4 PHY will be used. In this case four lanes of 10G will be combined and presented at the MAC layer as one 40G stream. Given the architectural similarity to the current 10G solution, the leading ATCA companies already have products close to being finalized. Kontron is one of those companies and they have laid a clear migration path to 40G such that their customers can get development projects started now rather than having to wait, thus speeding time-to-market further.

40G-Ready AdvancedTCA Platforms

For Telecom Equipment Manufacturers who are developing LTE solutions, there is a full range of ATCA blade and application-ready platforms already using 10G technologies. These will soon be augmented with the addition of 40G capabilities. Already field proven in 10GbE applications, the 14-slot OM9140 carrier-grade platform uses the AT8904 10GbE Switch. Fully supported in this platform are the AT8404 10GbE Carrier Blade, and the AT8050 10GbE AdvancedTCA processor blade, which supports both Intel Xeon 5500 and 5600 Series Processors. Various combinations can be created using this modular platform and each will come pre-integrated, validated and tested to accelerate new application designs for faster market deployment.

A 40G-ready ATCA platform already has been created comprising a 40G chassis, 40G backplane and advanced cooling. This is suitable for TEMs preparing for 40G-based LTE platforms since development can begin immediately. Using the fully compatible 10G internal infrastructure, platforms can be fully deployed, and as the 40G elements become available starting in early 2011, they can easily be updated with new switching and multicore processing blades.

With an easy and “in-situ” upgrade strategy and no “forklifting” required, there is no need to introduce unnecessary delay. With the holiday season nearly upon us we know one thing for sure, and that is there are lots more mobile devices hitting the network and taking us one step closer to reaching that Yottabyte. 

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