LoopStar® 700 Circuit Emulation Technology Extends TDM Services Over Packet Networks

ApplicAtion note
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LoopStar
®
700
Circuit Emulation Technology Extends TDM Services Over Packet Networks
Overview
Traditional voice and private leased-line traffic continues to provide significant revenues for
metro service providers, while at the same time, packet-based traffic is growing exponentially.
This incongruity ultimately requires metro networks to determine the most cost-effective and
strategic way to serve two masters: the traditional time-division multiplex (TDM) world, or the
emerging packet world that represents the revenue future.
In many cases, the right solution is the one that extends the patented “circuit-over-IP” technology
value of existing TDM services while optimizing the network for new revenues from packet
services. It is the solution that supports a complete array of new and existing services across a
unified, easy-to-manage infrastructure. And in today’s lean economy, the right solution is the
one that offers very low cost of entry yet scales gracefully in services and bandwidth, whenever
the business case warrants.
Carrier-class Voice and Private Line TDM Services Over a Packet Infrastructure
ADC responded to these market requirements by providing a solution that allows packet-based
networks to carry both Ethernet and TDM traffic. Our solution bridges the diverse requirements
between TDM traffic, with its requirements for timing and synchronization, and packet
networking, which tolerates all manner of delay, inconsistency and impairment. The LoopStar
700 product suite uses breakthrough circuit emulation technology to extend carrier-class TDM
services over today’s packet networks. The LoopStar 700 delivers traditional T1 (E1 or J1)
circuit-based voice/data/video services over Ethernet/IP with the same no compromise
quality and robustness as a circuit delivered in native TDM over SONET/SDH.
Using this cost-effective device at the carrier edge, one efficient Ethernet/IP network can carry a full
range of services to customer locations, such as voice trunks from private branch exchange (PBX)
systems and Frame Relay leased lines, alongside Ethernet traffic.
SONET/SDH or

Optical Ethernet
Metro Network
Data
Video
Voice
Ethernet
TDM
TDM

PBX
LS
700
The LoopStar 700 delivers carrier-class TDM and Ethernet
circuits over a carrier-grade packet network
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LoopStar
®
700 Circuit Emulation
LoopStar
®
700
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Reduce CAPEX and OPEX While Growing Services and Revenues
Converging TDM traffic onto a packet infrastructure provides compelling benefits. It allows enterprise
customers to receive a full range of services, whether Ethernet or TDM-based, from one provider, and
enjoy the advantages of one monthly bill, attractive service bundles, and a single point of contact for
all their communication needs.
For metro service providers, the ability to offer premium TDM services over packet networks while also
adding new revenues from Ethernet services enhances all facets of the cost/revenue/quality equation.

With circuit emulation service on the LoopStar 700 family, providers can:
• Attract new customers by offering more services on existing networks.
• Increase revenues by extending valued TDM services to areas covered only by packet networks,
without having to deploy overlay networks or rely on alternative carriers.
• Reduce CAPEX by providing multiple services without multiple networks, devices or links. A single
LoopStar 700 can support any combination of Ethernet and TDM bandwidth, up to the payload
rate of the uplink. Because all traffic is packetized, there’s no need to aggregate circuit and packet
traffic separately, either at the customer edge, in the transport network or back at the central office.
Providers can cap investment in expensive TDM edge devices as the transition to cost-effective,
multi-service platforms based on IP occurs.
• Significantly reduce OPEX by capitalizing on the efficiencies of packet processing, consolidating
packet and TDM services over shared links, and provisioning end-to-end services.
To provision a T1 circuit, for example, an operator simply specifies the destination IP address and port
of the circuit. Unlike TDM systems, there are no intermediate nodes to configure. There also are no
SONET ADMs to configure, digital cross-connects to program or wires to cross up. New customers
and services can be turned up easily and quickly.
Preserve Timing Across Packet Networks
The LoopStar 700 products can synchronize the timing of the emulated signal in any of the
following ways:
• From an external timing source, such as a BITS clock or GPS source.
• From a direct incoming link from the central office or Point of Presence (PoP). For example, if the
link is a T1 from a digital cross-connect or Class 5 switch, the LoopStar 700 can take the timing
from that link.
• Using adaptive timing, the timing of the signal is reconstructed based on the average arrival rate
of incoming packets carrying TDM traffic. The LoopStar 700 applies a patented adaptive timing
technique that uses advanced algorithms to meet circuit jitter specifications – even in the face
of high packet delay variation and packet impairments.
This flexibility in timing options enable providers to design synchronization solutions that best suit
their networks.
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LoopStar
®
700 Circuit Emulation
LoopStar
®
700
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Ethernet / IP Network
Circuits In
(T1, E1, J1)
Circuits Out
(T1, E1, J1)
Transmit
Packets
Receive
Packets
LS
700
LS
700
The LoopStar 700 delivers carrier-quality TDM circuits over a packet network
Transparently Handle Packet Impairments and Delay Variation
The LoopStar 700 has an auto-optimizing jitter buffer that intelligently absorbs packet delay variation,
recovers from out-of-order packets, and minimizes the effects of lost packets. As packets are received,
the buffer holds them only as long as necessary to smooth out the effects of a packet transport and
deliver accurate, ordered TDM bits at consistent intervals.
Other vendors use a fixed buffer for this purpose. However with fixed buffers, the size of a buffer must
generally be set for anticipated worst-case delay, and all traffic receives the same buffer treatment,
regardless of current network performance. When the buffer is set high, packets that arrive with

minimal latency and delay variation sit for a long time in the buffer, adding unnecessarily to overall
latency. Yet, when a fixed buffer is set too low, it can only correct for small amounts of packet delay
variation, and the provider risks disruptions from out-of-spec traffic. Under the best circumstances, a
fixed buffer is never optimized; it always adds more latency than necessary.
The LoopStar 700 constantly measures packet delay variation (PDV) and automatically resizes the buffer
in response to actual traffic conditions:
• If the network is efficient (or traffic is local) and packet delay variation is low, the LoopStar 700
reduces the buffer size and minimizes incremental buffer delay.
• If the network is inefficient, congested (or traffic traverses long distances or multiple networks), and
packet delay variation is high, the LoopStar 700 automatically increases buffer size to absorb the
greater variation. This enables the system to continue to deliver bits at the consistent interval
required by TDM.
These changes in buffer size take place without operator intervention and without affecting transported
traffic. Auto-optimizing buffer capability not only enables the system to respond dynamically to network
events, it simplifies set-up and installation. There’s no need to calculate or guess possible packet delay
variation and pre-configure buffer sizes on all edge devices.
Quality of Service (QoS) Required by TDM Traffic
The LoopStar 700 uses several mechanisms to provide the QoS required by voice traffic, including
marking packets with up to seven levels of priority treatment using 802.1D (p) priority bits. By default,
the LoopStar 700 always grants highest priority to circuit emulation traffic.
Even if the packet transport network delivers disappointing performance, the LoopStar 700 continues
to deliver no compromise circuit emulation service. Robust packet-handling mechanisms ensure that
mis-ordered packets are properly reordered, and prevent lost packets from causing frequency errors.
The auto-optimizing jitter buffer can accommodate more than 100 milliseconds of packet delay variation
(PDV). Since business-class IP networks typically are designed to produce no more than 50 milliseconds
of PDV, providers know they can consistently deliver carrier-quality TDM services to their customers.
In contrast, some alternative systems can only operate within very small tolerances, leaving the
emulated service vulnerable to degradation or disruption.
Web Site: www.adc.com
From North America, Call Toll Free: 1-800-366-3891 • Outside of North America: +1-952-938-8080

Fax: +1-952-917-3237 • For a listing of ADC’s global sales office locations, please refer to our web site.
ADC Telecommunications, Inc., P.O. Box 1101, Minneapolis, Minnesota USA 55440-1101
Specifications published here are current as of the date of publication of this document. Because we are continuously
improving our products, ADC reserves the right to change specifications without prior notice. At any time, you may
verify product specifications by contacting our headquarters office in Minneapolis. ADC Telecommunications, Inc.
views its patent portfolio as an important corporate asset and vigorously enforces its patents. Products orfeatures
contained herein may be covered by one or more U.S. or foreign patents. An Equal Opportunity Employer
102316AE 4/06 Original © 2006 ADC Telecommunications, Inc. All Rights Reserved
ApplicAtion note
Boston Metro
Atlanta Metro
LAN
PBX
LAN
Data
PSTN
Class 5
Class 5
IP MPLS Core
PSTN
Switch
Switch
Router
Router
LAN
PBX
LS
700
LS
700

LS
700
LS
700
LS
700
Transport Circuit Emulation Traffic Across a Multi-vendor Network
The LoopStar 700 maps circuits to standard IP packets that are carried over standard Ethernet frames,
with or without VLAN (Virtual Local Area Network) tags. As a result, circuit emulation traffic generated by
the LoopStar 700 can be switched or routed through any vendor’s equipment. The service provider can
build a best-of-breed open system with switches, routers and other components from
multiple vendors.
Leadership in Circuit Emulation
Our product design engineers are playing a leadership role in the IETF working group that addresses
mapping and transport of non-IP services (such as TDM, SONET, Frame Relay and ATM) over IP and
MPLS. This Pseudo-Wire Emulation Edge-to-Edge (PWE3) working group is developing standards that
enable services on packet networks to look, feel and perform like dedicated, private circuits.
ADC strongly believes that emulated circuits must support the same service quality, testing mechanisms,
alarms and alerts found in traditional transport systems. Anything less is unacceptable for today’s
competitive metro carrier markets.
The LoopStar 700 product suite is optimized to provide this service along with Ethernet services in
high-density, metropolitan area networks serving single enterprise customers, multi-tenant units and
campus environments.
With true, IP-centric circuit emulation, traffic can pass through multiple
networks and switches and routers from multiple vendors