RAD Helps Mobile Operators and Broadcasters to Clock on to IP

According to tests carried out by the industry-leading test house Chronos, classic problems such as data loss and errors that are deterring fixed and mobile operators and broadcasters from migrating traffic from TDM (telephone) to IP (Internet Protocol) networks can be eliminated by deploying RAD Data Communications' IPmux pseudowire gateways.

In addressing accurate clock synchronization over IP networks, the IPmux allows companies, including mobile operators, to switch over to low-cost IP networks without fear of sacrificing core functionality that can be lost as a result of timing issues.

Delivering carrier-class TDM services requires sophisticated clock recovery technology in addition to pseudowire technology. RAD has solved this problem by developing an Application-Specific Integrated Circuit (ASIC) that incorporates an advanced adaptive clock recovery mechanism that conforms to the latest industry standards.

Fixed and mobile operators, as well as IPTV, mobile TV and digital broadcasters often rely on time dependent processes and require accurate clock synchronization to run their network and for functions such as monitoring and SCADA. Chronos confirmed that the advanced algorithms that RAD has incorporated into its IPmux pseudowire gateways overcome the major clock accuracy barrier posed by migration to packet switched Ethernet, IP and MPLS networks. This has been a daunting problem because while TDM networks inherently deliver timing along with their data, packet switched networks (PSNs) don't transfer any timing information whatsoever.

Convergence Towards a Single Packet based Infrastructure "In the TDM networks of old, synchronization was always part of the furniture and enterprise networks, as well as the applications they supported, didn't need to consider synchronization," says Martin Kingston, Senior Designer for Transport Networks at Orange UK.

"However, networks now are converging towards a single packet based infrastructure supporting all applications," Kingston continues. "This implies emulation of TDM services, and so synchronization must also be supported," he notes. "Synchronization's low profile has meant that the importance of this hasn't always hit home."

Mobile operators with 2G and 3G frequency division duplex (FDD) networks use frequency synchronization at base stations so that mobile phones are able to handover seamlessly as they move from the coverage of one base station to the next. Without this synchronization the mobile phone would be unable to "see" the next base station.

Kingston concludes: "It's the applications at the edge of the packet network that need synch such as pure IP telephony and video conferencing. For other applications like interworking or circuit emulation for PBX, clock synchronization is vital."

Timing is Everything

"In business timing is everything," states Gaby Junowicz, Director of Business Development for Cellular and Wireless Networks at RAD Data Communications. "Many mobile operators have been offered the carrot of GSM and 3G cellular backhaul over low-cost IP but have been unable to migrate because it means losing vital time-dependent services," he explains. "In delivering accurate clock synchronization in IP networks, organizations can be assured that the benefits of IP won't be gained at the expense of time sensitive services."

Strategic Sync Testing

Chronos offers Strategic Sync Testing Consultancy to evaluate products and services to ensure that they're fit for purpose or perform to network requirements. Chronos' industry-respected Next Generation Network Sync Testing Consultancy is aimed at manufacturers, users and network operators that provide or connect equipment or services impacted by poor sync to the next generation of packet-based telecom networks.

RAD's patented TDM over IP (TDMoIP(r)) technology enables transport of TDM traffic over Ethernet, IP and MPLS PSNs. It segments and encapsulates TDM bit-streams and then transports packets containing TDM payloads across the PSN. At the remote end of this "pseudowire" the TDM signal is reconstructed, emulating the original TDM transport.

GSM/3G Mobile Base Stations

The tests were proposed to evaluate the suitability of RAD's IPmux solutions to provide synchronization to telecom network applications - for example, GSM/3G mobile base stations. A number of different scenarios were proposed to include ideal conditions, conditions representing normal network operation and performance during network failure scenarios.

Testing was carried out on two systems, one used as a transmitter representing the network end and the other used as a receiver representing the customer end (e.g. base station case).

Conforms to G.823 and ITU-T G.8261 Standards In the Chronos test, the IPmux pseudowire gateways provided TDM equivalent performance by conforming to G.823 jitter and wander requirements. The solutions demonstrated conformance when tested under ITU-T G.8261, a standard defining testing methodology and accuracy criteria for clock transport over packet networks.

G.8261 includes network impairment scenarios to simulate more realistic network conditions. The IPmux also demonstrated its ability to provide very high frequency accuracy - much better than the required 50 ppb. The tests performed show that given the requirement to prioritize the TDMoIP traffic, stable synchronization signals were transported across the test network.