A CCESS P OINTS O N N ARROWBAND D ATA C IRCUITS IN M ODERN C ARRIER E NVIRONMENTS N ETWORK T ECH C ONTROL W HITE P APER Today’s transmission methods and equipment are robust and reliable and feature integrated network monitoring, troubleshooting, maintenance, and provisioning systems. However, public carriers and most major private networks have historically engineered their network’s physical plant to include access points at which they can gain quick and organized “hard-contact” access to any particular circuit path. Typically, these access points were comprised of analog jackfields with “line-drop-monitor” access capability. With these jackfields, craftpersons could passively monitor and/or intrusively test circuits, or perform circuit reconfigurations to bypass faulty paths or accommodate changes in traffic patterns. With the transition to the modern digital network hierarchy with increased bandwidth, these analog jackfield bays gave way to more functional DSX-1 and DSX-3 systems. A typical DSX-1 bay is shown in Figure 1. Today we also see this “hard contact” access philosophy extending into our emerging optical network transmission systems. The reasons for this philosophy, as evidenced in virtually every telephone office and even many outside plant (OSP) locations, are simple. While networks are increasingly sophisticated and “self healing”, the simple fact remains that physical things will break and require physical intervention, and thus the way to restore or reroute service is to change the physical arrangement of the circuit path. As a result, providing easy access to networks continues to be a popular practice. Increasingly, carrier networks are being invaded with types of circuits on media different from the traditional telco circuit physical plant. A rapidly growing share of office cabling are low speed data circuits on RS232, V.35, and ANSI/EIA-530 interfaces. Figure 1 210/97 440 Network Tech Control White Paper Applications The first significant application to bring these new interfaces to the central office was the changeover to Signaling System #7 (SS7). In the past the telephone system consisted only of the wires that carried our conversations. Switching instructions created by dialing were sent on the same lines that carry voice conversations, as was information for long distance billing. Thus, all signaling was in-band. In the late 1970s, a new system was created to provide out-of-band signaling. Basically, a separate data network was created between switching offices to work in conjunction with the voice networks. Phone com- pany computers could use the signaling system to check and make sure a call could be completed before actually switching the call all the way to the local loop only to find a busy line. Later enhancements of the system allowed for information to be sent to specific locations in the telephone network, and allowed for a way to send information from the data line over the local loop in a short in-band burst of information. How SS7 Works There are three elements of the SS7 network: • Service Switching Point (SSP) - A central office switch • Signal Transfer Point (STP) - Packet switched data network • Service Control Point (SCP) - A shared data base Service Switching Points (SSP) are central office switches that originate or terminate telephone calls. Signaling messages are sent between SSPs to set up, manage, and release voice circuits required to complete a call. An SSP may also send a query message to a centralized database to determine how to route a call, for example the routing of a toll-free 1-800/888 call in North America. A Service Control Point (SCP) sends a response to the originating SSP which contains the routing number(s) associated with the dialed number. An alternate routing number may be used by the SSP if the primary number is busy or the call is unanswered within a specified time. Network traffic between signaling points is routed via a packet switch called a Signal Transfer Point (STP). An STP routes each incoming message to an outgoing signaling link based on the routing information contained in the SS7 message. Because it acts as a network hub, an STP provides improved utilization of the SS7 network by eliminating the need for direct links between signaling points. SCPs and STPs are usually shared between multiple SSPs, thus it is typical to find only one of two sets in a particular LATA. Because the SS7 network is critical to call processing, SCPs and STPs are usually deployed in mated pair configurations in separate physical locations to ensure network-wide service in the event of an isolated failure. The SS7 data links, generally 56kbps V.35 circuits, are also duplicated, and frequently protected by Network Tech Control facilities such as ADC’s PatchMate product line to ensure reliable service on the SS7 network. SS7 Links SS7 Links SSP SCP SCP SSP STP STP 3 10/97 440 Network Tech Control White Paper Signaling System #7 (SS7), the linking of the phone system with computers for switch- ing purposes through the data link has allowed the phone system to become intelligent by linking SS7 with databases. SS7 works as a packet switched digital transmission medium. The digital circuits between the switching offices operate at 56kbps. Informa- tion from the common databases controls the switching of calls and allows the transfer of messages within the system. SS7 paved the way for a variety of new services referred to as custom calling services. These include call blocking, call forwarding, caller ID and similar service enhancements, many of which generate additional revenue for the local phone company. SS7 will continue to enhance traditional basic telecommunication services as well as improve the interconnection and inter-working of separate networks. In addition to the inside network support applications such as SS7, the public networks are also increasingly involved in providing narrowband data transport services such as ATM and ISDN. While these services are usually “bundled up” into more traditional wideband transport paths, at the individual customer interface point, they commonly exist as narrowband (generally sub-56kbps rate) RS232, V.35, or ANSI/EIA-530 signal interfaces on CSU’s, ATM switches, and other similar devices. Clearly a means of gaining rapid and organized physical access to these circuits is needed. They are simply too important to ignore. Because of their physical complexity, these circuits cannot be gracefully integrated into traditional access hardware such as jackfields or DSX systems. Fortunately, however, a concept called “network tech control” has long existed in large private data centers in the military and in data-transport-intensive industries such finance, transportation reservations and similar applications. The products that have long provided organized physical accesses to those networks are ready-made to fill the growing need in SS7, ATM, and other public network applications. In addition to referring to a family of physical products, the term network tech control also refers to a network management concept. This concept is essentially identical to the concept of a DSX installation, with a few enhancements based on the circuit-health information inherently available on most data interfaces. Network Tech Control: An old solution solves new problems 4 10/97 440 Network Tech Control White Paper In its simplest implementation, network tech control is absolutely functionally identical to the jackfield system alluded to earlier. Basically, all the data physical circuits are concentrated into patch panels that are equivalent to the familiar line-drop- monitor jackfields common in analog telco environ- ments. The familiar schematic depiction in Figure 2 is the literal heart and soul of the network tech control concept. At this simple physical access point, the following functions can be performed. Passive Monitoring The lower monitor port provides a non-intrusive access point that can accommodate a high impedance test device such as a data- scope in monitor mode. This access style allows observance of actual circuit activity without interruption of user traffic. Segmentation for Testing By use of a patch appearance, a craftperson can segment a circuit at any convenient point and perform intrusive testing with rack-mounted or portable instrumenta- tion. Circuit Rerouting By use of patch cords, circuits can be quickly rerouted to accommodate changes in traffic flow on a temporary or semi-permanent basis. Substitute Spare Equipment Quick restoration of circuit functionality is critical in these high-value traffic environments, and cannot wait for physical recabling to remove the faulty device and insert a known good device into the traffic chain. Tech control panels allow the termination of dedicated spares that can be quickly brought online with patch cords, permitting the defective device to be replaced and recabled in a more deliber- ate and less error-prone fashion. Without these patch panels, any of the above actions can only be accomplished by disconnecting interface cables and attaching instruments or spare equipment directly to the cable. Frequently these connector locations are almost impossible to reach because they are hidden deep in the back of equipment cabinets and obscured by dozens of overlying cables. Mistakes are common, and adjacent circuits are also often inadvertently disturbed in these congested areas. Figure 2 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 510/97 440 Network Tech Control White Paper These patch panels are available from ADC in a wide variety of configurations, consisting of a chassis (module shelf) and usually 16 channels of patching. Figure 3 shows a basic panel used for V.35 patching. These panels fit in 19- inch wide racks and are 5.25 inches high. Other versions are available for RS232, ANSI/EIA-530, and X.21 interface standards. Besides the “plain” patch panels described so far, ADC also has designed a series of patching equipment with extended features such as circuit activity indicators (LEDs) and a variety of alarming functions. Patching with these additional features is commonly installed on particularly high-value circuits, such as the data lines at SS7 signal transfer points (STPs) where a failure of a link could be especially disruptive. The alarm function could be programmed for an anticipated alarm circumstance, such as lack of data flow, and would alert personnel in the vicinity of the circuit problem. The activity indicators give an “at a glance” status of circuit behavior without the attachment of test equipment. A V.35 panel with these features is shown in Figure 4. Power supplies are available for AC and 48VDC environments. Patch panels that are augmented with remote control “AB” switching are also available. These panels are can be used in situations (dark sites or offices not staffed 7x24) where circuit reconfiguration must be accomplished by craftpersons at another location. These panels include the usual patching for use by on-site personnel, plus local control of the switch settings. Such a panel for RS232 circuits is shown in Figure 5. Some of these panels can also be configured as “automatic fallback” switches, switching to alternate equip- ment or routing based on pre-determined alarm conditions on the primary path. For a more complete description of this network tech control equipment, including various application examples, obtain the ADC “Network Control Products” catalog , 6 th edition, literature number 517. This information can be ordered by calling (612) 946-3434, or 1-800-366-3891, or on the internet at: http://www.adc.com/Products/PatchMate/PatchMate.html Figure 3 Figure 4 Figure 5 440 10/97 Original © 1997 ADC Telecommunications, Inc. All Rights Reserved An Equal Opportunity Employer 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. ADC Telecommunications, Inc. P.O. Box 1101 Minneapolis, Minnesota 55440-1101 FAX: (612) 946-3292 From North America, Call Toll Free: 1-800-366-3891, Ext. 3223 Outside of North America: 612-938-8080 Home Page Address: http://www.adc.com International Sales Offices: Belgium 32-2-712-6500 • United Kingdom 44-734-441955 • Montreal, Quebec (514) 677-9166 • Vancouver, BC (604) 270-1675 • Toronto, Ont. (905) 629-3104 • Ottawa, Ont. (613) 723-2171 • Singapore 65-225-8228 •Venezuela 58- 2-286-1444 • Mexico City, Mexico 525-658-4519 • Buenos Aires, Argentina (541) 449- 2669 • Sao Paulo, Brasil 55-11-3040-0666 • Sydney, Australia 61-2-9975-1499 • Melbourne, Australia 61-3-9585-3931 • Beijing, China 86-10-6500-7001 • Dusseldorf, Germany 49-211-530-6550 . (SS7). In the past the telephone system consisted only of the wires that carried our conversations. Switching instructions created by dialing were sent on. Point (STP). An STP routes each incoming message to an outgoing signaling link based on the routing information contained in the SS7 message. Because it acts