white paper Maintaining Service Continuity During DCS Migration A universal truth in network design is that all active equipment will require upgrades and replacement. Software patches can be required as soon as 30 days after installation. Upgrades to an existing platform, changes often required to maintain vendor support, will certainly follow over the years. Complete replacement due to new technologies or discontinued support can occur within 10 years of commissioning. Every project for active equipment includes a detailed installation plan. Yet given the certainty of replacement for all active equipment and given the prospects for service disruption in a forklift upgrade, an exit plan for active equipment is just as important as the installation plan. The latest example illustrating the importance of planning for the entire life cycle of active equipment is seen with digital cross-connect systems, or DCS. Due to manufacturer discontinued DCS and new DCS platforms required to support advanced network capabilities, service providers face wholesale replacement of DCS equipment. DS1 DS3 DS3 DS3 DS3 DS3 DS3 DS3 DS3 DS3 DS3 DS3 DS3 DS1 DS1 DS1 DS1 DS1 DS1 DS1 DS1 DS1 DS1 DS1 VT1.5 Compressed Video Packet Switching Hi Cap Service Circuit Grooming Fractional T1 SS7 DS1 POTS/PANS Video ASYNC SONET FAA Data Services ISDN Medical Sevices Switched Services Government Services Collocation 911 Emergency DS3 B-ISDN Internet Services 64 kb Alarm Services 50 kb VF Fiber Distribution Frame NARROWBAND WIDEBAND ATM BROADBAND 3/3 DCS 3/1/0 DCS 1/0 DCS 1/0 DCS 3/1/0 DCS Special Service T1 T1 VT1.5 T1 T1 T1 E1 T1 E1 T1 E1 OC-192 OC-N OC-48 2.4 GB 1.2 GB 560 MB 180 MB 90 MB 45 MB M13 OC-12 OC-3 3/1 DCS Digital Distribution Frame (Twisted Pair) Digital Distribution Frame (Coaxial) 2 Migrating Hard-Wired DCS Will Disrupt Service Considering that a single DCS grooms and intertwines thousands of circuits, DCS replacement is not a trivial undertaking. Embedded in each DS3 are 28 DS1 circuits. In turn, each DS1 carries 24 DS0 circuits. This equates to 672 sub-channels on one DS3 – each of which may be destined for a different path in the network through the DCS matrix. Some current DCS models claim to handle up to 2,048 DS3s in the matrix. This can mean over 1.3 million DS0-equivalent circuits intertwined in one DCS. Fortunately for service providers and their customers, an estimated 80% to 90% of existing DCS are cabled to cross-connect distribution frames, making the change to new equipment a classic patch and roll procedure that transitions service to next generation DCS without disruption of service. For those service providers who cabled DCS equipment to cross-connect distribution frames, transition to next generation DCS will be relatively painless. However, the story is not so bright for owners of the 10% to 20% of existing DCS that are cabled directly to network elements. For these service providers, transition to next generation DCS will be a nightmare for operations and customers alike, because without an exit plan, service interruptions are guaranteed. In fact, work-around solutions are not viable. Alternatively, the existing DCS could be capped with new services deployed only on the new DCS. However, given the large of number of circuits intertwined on one DCS, waiting for natural circuit attrition to gradually shut down service on the old DCS could take years to complete. During this lengthy transition, expensive DCS ports are idle and floor space is wasted. In addition, the old DCS continues to require administration and regular maintenance. Moreover, even with one circuit active, the DCS requires significant power to operate which, in turn, requires cooling and lighting. Again, this DCS transition plan is neither practical nor cost-effective. Without an exit plan, transitioning to next generation DCS from hard-wired DCS has only one outcome – service will shut down. It could be for 5 minutes, 5 hours, or 5 days per circuit, a problem that becomes magnified for customers with multiple circuits. An Exit Plan Ensures a Smooth Transition to Next Generation DCS Proper installation of DCS requires not only an installation plan, but also an exit plan. Cabling DCS equipment to a modular distribution frame that provides cross-connect points for each circuit offers the most flexibility for managing the life cycle of DCS from installation to exit. As compared to direct connect and interconnect methods of cabling DCS equipment, cross-connect offers the most advantages because you can selectively direct any circuit into the DCS. With DCS that are directly cabled to network elements, in-service circuits are constantly exposed to damage. All moves/adds/changes are done on sensitive back planes and on live equipment cables where just a dropped wrench can take out service on multiple circuits. To make matters worse, network elements that are directly cabled to DCS create such a tangle of cables crisscrossing the central office that circuit identification and tracing is difficult, at best. With direct connect, rerouting is virtually impossible and any transition of circuits will interrupt service. Interconnect cabling for DCS is somewhat better than direct connect. Some interconnect solutions do offer jack access, making an in-service patch and roll of circuits possible with several steps. Yet whether the interconnect frame features jack access or not, transitioning from one DCS to another still requires disconnecting, rerouting, and even complete re-cabling of permanent equipment cables. For transition to next generation DCS, a centralized cross-connect distribution frame is the solution that is craft-friendly, cost-effective, and not service-affecting. Cross-connect frames support day-to-day management, mid-life upgrades and configurations, and final replacement of DCS. In this architecture, equipment cables have dedicated termination points on the distribution frame. Once equipment cables 3 from DCS and other network elements are terminated and tested, they are never touched again. Replacing a DCS is a matter of moving jumpers on the centralized cross-connect field – not moving equipment cables. Cabling DCS through a distribution frame using the cross-connect method provides the necessary physical access point to other network elements and creates an exit plan that allows logical transition for thousands of circuits without disrupting service. For those facing transition of hard-wired DCS, they know the reality of their situation – their only choice is service interruption on many circuits involving critical high cap service. Even with this stark reality, there are people who persist with the idea that transitioning intertwined circuits from one DCS to another can be done in software with just some keystrokes, an argument often offered to cost-justify a new DCS project by deleting cross-connect equipment from the installation plan. This notion is false, at least if one of the objectives is no disruption of service to customers. A physical access point outside of the DCS is required to complete the migration of circuits to next generation DCS. Cross-Connect Architecture Enables DCS Migration For the majority of DCS installed today, transitioning to the next generation DCS can be accomplished through the familiar "in-service patch and roll" of circuits. This craft-friendly procedure is possible because most DCS are cabled to a cross-connect distribution frame. The transition procedure is not complicated. It is, however, a precise activity because complex sub-channel grooming of circuits and multiple distribution paths for thousands of circuits within the DCS matrix must be replicated in the next generation DCS. A step-by-step manual entitled “Migration Strategy to New 3/1 DCS: Operational Procedures” documents the circuit-by-circuit procedure for migration to next generation DCS. Available from ADC, the manual details cutover procedures for DCS cabled to cross-connect distribution frames. In the procedure, moving circuits is an “in-service patch and roll” of moving jumpers and changing circuit assignments on the DCS. There is no capital outlay because ports in the old DCS are reassigned during the transition, not added. As the procedure is followed circuit-by-circuit, 50% of traffic soon travels via reassigned tie pairs as traffic is increased on the new DCS and decreased on the old DCS. The procedure is similar to siphoning water from one glass into another – as one glass empties, the other fills up. This synchronization of physical path routing, patching through the cross-connect distribution frame, and software commands to map service to the new DCS results in complete offload of traffic from the old DCS without disruption of service. Summary Service providers who cabled last generation DCS to cross-connect distribution frames are breathing a sigh of relief, especially where DCS replacements involve critical 911, SS7, business, government, and military circuits. That’s because these service providers have an exit plan for transition to next generation equipment. Yet even with the lessons learned with the first wave of DCS installations in the 1980s – that managing upgrades, rearrangements, and decommissioning of DCS requires physical access points on a distribution frame – there are still network planners today being asked to cable DCS directly to network elements. The good intentions of trimming minor costs by omitting cross-connect distribution frames for DCS hides the relatively enormous costs not only of managing normal rearrangements and upgrades in the short-term but also complete replacement in the long-term. Trimming costs from a DCS installation project by eliminating the distribution frame pales in comparison to increased operations costs to manage hard-wired DCS and lost revenue due to service disruptions. 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 or features contained herein may be covered by one or more U.S. or foreign patents. An Equal Opportunity Employer 1276558 11/03 Original © 2003 ADC Telecommunications, Inc. All Rights Reserved 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. As options are reviewed for replacing DCS equipment, the following holds true: • Every DCS has a limited service life and will need replacement. • Cabling DCS to a cross-connect distribution frame offers the only viable exit strategy for transition of circuits with complete service integrity. • DCS that are directly cabled to other network elements will result in service outages not only during replacement but also normal rearrangements and upgrades. • ADC offers a manual, “Migration Strategy to New 3/1 DCS: Operational Procedures” (ADCP-80- 425), which outlines the process for migration to next generation DCS where cross-connect distribution frames are used. • ADC is the market leader in fiber, coax and twisted pair distribution frames for active network equipment. For today’s planners doomed to repeat what now plagues the owners of the 10% to 20% of DCS equipment that are hard wired to network elements, there is an old saying that is relevant: Every time history repeats itself, the price goes up. In this case, the short-term goal of saving just a few dollars by excluding distribution frames on installation will result in significant costs during the entire life cycle of a DCS. Given the complexity and number of intertwined circuits managed by a single DCS, and certain replacement in the future, an elegant exit is more than a bonus – it is a necessity. For more information about creating an exit plan for DCS and for the DCS transition guide,” Migration Strategy to New 3/1 DCS: Operational Procedures” (ADCP-80-425), contact your ADC account manager or call 1-800-366-3891. . Cap Service Circuit Grooming Fractional T1 SS7 DS1 POTS/PANS Video ASYNC SONET FAA Data Services ISDN Medical Sevices Switched Services Government Services. white paper Maintaining Service Continuity During DCS Migration A universal truth in network design