networkZONE Products for the week of November 10, 2003
Transwitch Says…
Evolutionary Force -- TranSwitch and RAD Data Enable
Voice/Data Convergence Over IP/MPLS Networks With TDM-over-IP Packet Trunking
Device
TranSwitch Corporation and RAD Data Communications Ltd.have announced
the PacketTrunk-4 (TXC-05870), the first TDM over IP (TDMoIP) device developed
as a result of the strategic technology partnership and OEM agreement between the two companies announced earlier
this year. PacketTrunk-4 ushers in a new family of VLSI products that can
be used to develop TDMoIP-capable network equipment. These advanced devices
enable transparent transport of legacy TDM and serial data over IP/MPLS
networks.
PacketTrunk-4 is an internetworking gateway device that efficiently transports TDM trunks over packet-switched networks (PSNs) using DMoIP, the world's most popular protocol for circuit emulation over IP/MPLS. This single-chip solution incorporates robust clock recovery, encapsulation, jitter compensation, Layer 2/3/4 QoS support, and standards-based support for transport of structured and unstructured TDM signals over a PSN. The device serves as a building block for TDM over IP, TDM over MPLS, or TDM over switched Ethernet networks. Typical applications include:
PacketTrunk-4 provides a scalable solution in single-chip to multi-chip configurations. It is a highly integrated VLSI device designed to meet a wide variety of network access and edge requirements. In combination with other TranSwitch products such as QT1F+, QE1F+, T1Fx8, and E1Fx8 framers, the TEPro" channelized T1/E1/T3 access solution, the Envoy"-8FE octal FE-to-POS/SPI controller, and the EtherMap"-3 mapper, PacketTrunk-4 enables rapid development of TDMoIP equipment.
PacketTrunk-4's versatile features were chosen for fast, easy TDMoIP system design. The product's TDM-side interface can accommodate four separate T1/E1 serial ports, each with a dedicated T1/E1 Channel Associated Signaling (CAS) interface, or one T3/E3/STS-1. A DPLL-based quad adaptive clock recovery block provides fast frequency lock and highly accurate phase tracking for each TDM port. The block achieves G.823/G.824-compliant jitter and wander performance under real-world PSN conditions by reconstructing the TDM clock based solely on inter-packet arrival time and jitter buffer fill level. During phase tracking, the chip optimizes jitter buffer levels to minimize latency and prevent buffer overflow or underflow.
PacketTrunk-4's payload processing block implements Constant Bit Rate (CBR) static allocation for circuit emulation, Variable Bit Rate (VBR) dynamic allocation for loop emulation, and HDLC for efficient transfer or termination of frame-based traffic. Payload size is selectable over a wide range, giving end users maximum tradeoff flexibility between latency and overhead.
Supported PSNs and encapsulation types include UDP/IP, MPLS, and switched Ethernet. VLAN tagging, priority labeling, and stacking per IEEE 802.1p and Q are also supported. PacketTrunk-4's PSN-side interface is an 802.3 Ethernet HDX/FDX MAC with a choice of MII, RMII, SMII, or SSMII interfaces.
TranSwitch recognizes enormous potential in developing solutions for evolutionary convergence," stated Brian Stroehlein, TranSwitch Product Marketing Manager. "Evolutionary convergence involves transporting legacy services over next generation networks, as with PacketTrunk-4, and next generation services over legacy infrastructure, as with our EtherMap and Envoy products. PacketTrunk-4 is a key addition to our portfolio of evolutionary convergence products for access and edge networks."
Packet-switched networks are not designed to provide TDM services, explained Tal Gilad, TDMoIP Product Manager at RAD Data Communications. TDMoIP enables transmission of TDM traffic over asynchronous networks while overcoming packet loss and delay variations introduced by those networks. TDMoIP, developed by RAD and introduced to the industry at Telecom Geneva in 1999, is now an established technology that has been successfully deployed in over 15,000 ports worldwide to carry TDM over the packet-switched networks of carriers, Metropolitan Area Networks and enterprises.
PacketTrunk-4 is furnished with an RTOS-independent, hardware-abstracting,
API-based device driver, evaluation kit, TDMoIP calculator spreadsheet,
BSDL and IBIS models, and extensive documentation.
analogZONE Says . . .
TranSwitch has already done a great job in supporting the growing movement to Ethernet-based access services with its EtherMap Ethernet over TDM products. Now with the introduction of their PacketTrunk-4 internetworking gateway chip, they are throwing their weight behind the TDM over IP (TDMoIP) protocol, MPLS, or switched Ethernet. The device trunks four T1/E1 (or freeform serial) channels onto a 10/100 Ethernet MAC which is intended as a metro Ethernet-based WAN connection (see block diagram). If your application requires it, you can also use the chip to bridge a single T3/E3/STS-1 connection. Depending on how it's configured, the chip provides TDM trunking services for circuit or loop emulation, and can also support HDLC payloads for transporting SS7 over IP networks.
Because TranSwitch's press release (above) provides an excellent description of its product, I'll only give you a few of the basic facts behind the chip, and spend most of the review talking about why I think TransSwitch's vision is so powerful.
When trying to understand why the PacketTrunk-4 is such a significant product, you have to sort of invert the thinking you use with VoIP. The device employs the TDM over IP (TDMoIP) protocol developed by RAD Data to encapsulate traditional TDM services within IP packets. Now this sounds a lot like VoIP, but here's the difference: While VoIP digitizes and compresses an analog voice channel before encapsulating it into an IP-based format, TDMoIP lets the telephony traffic remain in its "native" TDM format. The packetized TDM is then trunked along with data traffic and passed out to an IP-based WAN connection.
While both VoIP and TDMoIP deliver traditional services using Ethernet or IP-based access services, TDMoIP allows a subscriber to easily transition from T1/T3-based access services. This is because IP-based loop and circuit emulation allows you to "hollow-out" a PSTN leaving a "PSTN-flavored wrapper" around an IP network. When done properly, you can replace your T1/T3 connection by plugging most of your existing equipment into a relatively inexpensive trunking box before it heads off to the metro Ethernet connection.
RAD Data and other companies have been producing TDMoIP equipment like this for several years, but until now they used costly custom circuits. Equipment manufacturers should be able to significantly cut both costs and development time when they replace the ASICs and FPGAs with the PacketTrunk-4 device.
While it's relatively simple in the abstract, actually getting such a device to work across such dissimilar environments was a significant challenge. In developing the PacketTrunk-4, one of the biggest challenges RAD and TranSwitch faced was to keep the data synchronized while flowing between two completely different timing environments that had no direct way of relating to each other.
This is accomplished using some very clever latency management techniques on the IP side of the chip. Part of their secret is an adaptive clock recovery block that monitors buffer fill and inter-packet arrival time to manage arrival times and buffers inter-packet jitter. RAD has found that solid clock recovery and good network design can eliminate the need for the overhead associated with the RTP protocol normally used to guarantee quality of voice over IP connections.
By preserving most customer side equipment, and simplifying the provisioning requirements, a PacketTrunk-4-powered TDMoIP device makes the transition to last-mile Ethernet a whole bunch less disruptive. It should also find a home replacing expensive T1-based backhaul lines in cellular base stations, as well as IP-CENTREX units, IP-based DSLAMs or other multi-service access equipment.
Rather than compete head-on with networking powerhouses like Agere, Cypress, Conexant, and PMC, for its SONET/SDH products, TranSwitch is artfully crafting its own niche in the emerging multi-service broadband market space. And with the introduction of the PacketTrunk-4, they are addressing one of the previously-invisible stumbling blocks that hampers the migration of voice services to lower-cost IP-based carrier technologies.
The TranSwitch PacketTrunk-4 will sample in December 2003, is packaged in a 27 x 27 mm PBGA-256, and will be priced at $70 in volume. Power supply voltages are 2.5-V core and 3.3-V I/O.
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