Next-Generation Wireless Backhauling Requires Sophisticated Silicon Support
Moving from a Sonet/SDH and PDH infrastructure to Ethernet is probably one of the most important evolutions in wireless backhauling in this decade. It also introduced the most difficult challenges to overcome.
The significant growth in mobile subscribers with new applications and bandwidth requirements, as well as the migration from 2G to 3G and the coming Long-Term Evolution (LTE) standard, have created major challenges for service providers.
In most cases, the existing mobile backhauling network is a mixture of microwave and wireline infrastructure.
Typically, the wireline infrastructure comprises a combination of plesynchronous digital hierarchy (PDH) links such as DS1, E1, and DS3 lines and Sonet/SDH (synchronous digital hierarchy). The protocol over these lines depends on the generation and the network functionality, and it may well include carrying time domain multiplexing (TDM), voice and native circuits, point-to-point protocol (PPP), high-level data-link control (HDLC), frame relay (FR), asynchronous transfer mode (ATM), and Ethernet.
As a result, one of the major challenges that carriers and service providers face is the migration from this heterogeneous, inefficient, and complex infrastructure toward a simple and cost-effective Ethernet-based transport network. One solution, though, can enable this migration to happen in a controlled, flexible, efficient, and smooth way based upon on new technology.
Figure 1 shows a high-level abstraction of a typical 3G wireless network. Node Bs are connected to the radio network controllers (RNCs) via some sort of transport network (the UTRAN), while the RNCs are connected to the other systems in a 3G network (SGSN, GGSN, and media gateway) via the core network. The same picture can be used to illustrate a 2G or a 2.5G network, with some trivial changes such as replacing the term UTRAN with a radio access network (RAN) and then replacing Node B with a b ases tation and the RNC with a b ases tation c ontroller (BSC).
There are many differences between the systems used in the various generations (2G, 2.5G, 3G, and 3.5G), and the underlying communication technologies change from generation to generation. This introduces significant complexity and a major interoperability challenge.
For example, 2G networks dealt only with TDM and circuit switching, while 2.5G networks also dealt with packet switching and added new protocols such as FR, PPP, multilink frame relay, and multilink PPP to the arsenal of underlying protocols.
When 3G was introduced, it included ATM cell switching techniques along with a new bundling technology (IMA) and various segmentation and reassembly standards (SAR, AAL2, AAL5), not forgetting some flavors of circuit emulation (CES, AAL1).
There weren’t too many alternatives for 2G networks, since they only dealt with and supported TDM and circuit switching. For these networks, the only functionality required was to deliver T1s and E1s from/to the basestation to/from the BSC and then some multiplexing of circuits into the rest of the network. Any normal transport network supporting PDH and Sonet/SDH would have been optimized for this, and there was no need to change or improve it.
This all changed when packet switching and cell switching became the underlying switching technologies. Now the backhauling network could have continued to deliver T1s and E1s and be based solely on circuit switching. However, new and more efficient alternatives became possible.
These alternatives included performing additional functionality, such as grooming, aggregation, local switching, statistical multiplexing, eliminating deep channelization, and moving to larger pipes. Carriers were given the choice of basing their networks on any mixture of these alternatives, which kept changing with more and more options available when the world migrated from 2.5G to 3G and now to LTE. These options resulted in different networks using different systems and equipment, each optimizing certain aspects of the network.
Despite all of these changes, one thing wasn’t touched—the physical underlying infrastructure, which continued to be PDH and Sonet/SDH. While this can continue forever, it is very inefficient. Replacing it with a Carrier Ethernet transport-based infrastructure can achieve major savings in capital and operational expenditures.
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© 2013 Penton Media Inc.
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