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The composite data load is a reasonable estimate of He data load that must be accommodated at the TOCs and on backbone links. Table A.2.5-3 summarizes anticipated ITS link loads. It should be noted that the CCTV camera at 3 Mbps represents Be dominant data load. CCTV is an emerging ITS requirement that significantly increases We llS communication infrastructure requirements. Table A.2.5~3 Anticipated AS Link Loads I Link I Data Rate I Local Links Data 2400- 9600 bps Digital Video 3 - 8 Mbps Digital Voice ~ Backbone Links ~ ~ ~ 000 Mbps (Node-to-Node) Center-to-Center Links 155.2 Mbps District-to-Region Links 15~ Region-to-National Links 9~ eel A.2.6 ITS Network Architecture and Topology Architecture refers to technology, fault tolerant redundancy, TOC backup, security, and standard requirements. Topology refers to geographic placement of field equipment, communication nodes and hubs, and interconnecting communication links (i.e., mediums) to implement He communication infrastructure. The Communications Handboolfor Traffic Control Systems, April 1993, presented several representative legacy traffic control communication architecture classifications (Figure 5.2 of Handbook). These are represented in Figure A.2.6-~. These communication architectures were conceived for a single application (traffic control) and for data (not multimedia). Additionally, they have typically been implement why He proprietary non-open standards of He controller manufacturers. L;`NCHRE~\ NCHRP3-51 · Phase2FmalReport A2-22
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As video requirements emerged, traditional ITS-related communication systems have employed an overlay of analog video circuits and digital data circuits, as depicted in Figure A.2.6-2. It is necessary to note ~at: I. The legacy signal systems are on a data network with 1200/2400 bps and mulddrop modems, usually on a private TWO cable plant. 2. Later emerging CCTV video requirements have often been addressed by parapet analog po~nt-to-point (CCTV camera to TOC) fiber circuits or analog fiber frequency division multiplexed 0:DM) network. a. In some larger system deployments, fiercer analog FDM of data has been deployed in hub- to-TOC links to achieve cost-effec~ve multiplexing of data where longer fiber-based links are required. It should also be noted that these FDM systems have been mostly non-standard proprietary systems from a particular multiplexer vendor. This overlay approach has been cost effective as He data network was already installed. Fortunately, legacy lTS-related systems have not required significant integration and sharing of data across applications and jurisdictions, which would be difficult on these overlay networks because Hey are usually implemented using incompatible propnetary multi-vendor products. Several impor~t considerations will create a need in future ITS systems for integrated ITS multimedia communication (sub) systems: 1. The ITS goal of integrated ITS services consisting of multiple applications (or services), data sharing by multiple jurisdictions, and the possibility of shared communication infrastructures. This requires open standards Hat are most efficiently supported on a multimedia network. t;`NCH~Phase~p'` NCHRP3-51 · Phase2F'nalReport A2-2S
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2. Many jurisdictions are upgrading or adding systems Nat include new video and data infrastructure. Usually, except for small systems or where existing facilities are expanded, the most cost-effec~ve commun~cadons options are integrated voice, data, and video networks. Video signals should maintain end-to-end 45-60 dB SIN (signal-to-noise) for acceptable video quality. Analog video signal gracefully degrades SIN over distance which cannot be restored at amplifiers. Digital video signals are completely restored at repeaters (assuming proper link designs) and suffer essentially no degradation over distance. ITS has a requirement for video shanug with multiple, often distant, ITS service providers and junsdictions. 4. Standard interfaces are required for rRs data sharing and Me emerging MPEG-2 digital video standard web defined interfaces to Me T] digital hierarchy and SONET are wed suited for this purpose. 5. The emerging trend toward greater distributed intelligence in field controllers due to Me deployment of modern 16/32 bit microprocessor technology, such as the 2070 controller. Local T~me-of-Day (TOD) plans convert real hme second-by-second control commun~cadon to less demanding communication consisting of monitoring, TOD plan activation, and plan downloading. These microprocessors have Me processing power to support modem high speed communication links and associated protocols as weD as required transportation functions. These ITS requirements and communication industry trends favor the communication architecture of Figure A.2.6~03) as expanded in Figure A.2.6-3 to illustrate Me concept of a modem integrated multimedia digital communications network. In this integrated network, Distribution Links (DL) connect field devices to communication nodes. At nodes, the various digitized voice, data, and video signals are multiplexed for communication over Me higher bit rate Backbone Links (BL) for communication to Me TOC. ~ large networks, a hierarchy of nodes and hubs may be employed with hubs providing more multiplexing and still higher bit rates. These nodes, hubs, backbone links, and distribution links are referred to as Be communication infrastructure. L;wCHRP\Phase2~p'\ NCHRP3-51 · Phase2FmalReport A2-28
A cost trade-off always exists when multiplexing is employed. Single Mode Fiber Optic (SMFO) cable and installation costs are marginally more expensive with additional fiber per cable. SMFO has repeaterless distances of 50 to 100 miles and bit rate capacities over 10 Gbps. Thus, a system architecture could employ short links to many multiplexers or longer links to fewer multiplexers. This is a cost trade-off involving system geographic topology, number of field dences, interconnecting link distances, tnstaBed fiber costs and multiplexer terminal costs. Small systems may be most cost effective win no field multiplexing. Multiplexing is often used to provide interfaces for data sharing among ITS services, which should be considered in design. Similar tracie-offs exist for revere and wireless ~mplementabons, but with less flexibility due to lower bit rates and shorter repeaterless distances. This trade-off should be considered in system design. Because MPEG-2 Video encoders are still expensive, near-term video should perhaps be maintained as analog from camera equipment cabinet to a communication node where it is digitized and switched for transmission to Me TOC and/or over ITS jurisdictions or services. It should be noted Mat uncompressed video requires approximately 45 Mbps bit rates (DS-3 rate), while Me MPEG-2 requires 3-6 Mbps. As technology is evolving rapidly, ITS communication system designs should accommodate an anticipated rapid cost-effec~ve evolution to Me 3-6 Mbps, MPEG-2, encoders In Me camera equipment cabinets or Me camera itself. A.2.6.1 Recommended ITS Communication Infrastructure Standards As discussed in Section A.0.2, ITS will be an evolutionary process. Thus, no nerd set of communication architectures or standards will be suitable for all implementations. Flexibility must be prowded to accommodate: 1. A multitude of ITS services as described in A.0.2 that Will have evolutionary deployment. 2. Local agency/jur~sdicdonal operational requirements that are unique In terms of services deployed and exact feature sets. L;`NCHR~rp'` NCHRP 3-51 · Phase 2 Fmal Report A2-29
3. A growing complement of field sensor/equipment types that include We traditional signal systems (loops), VMS, ramp meters, weather, HAR, etc. Each has unique message sets to support unique data content. 4. Diverse geographical areas ranging from sparse rural area, to small cities, to dense urban metropolitan areas wad system scope scaled appropriately. 5. Need for multimodal operations and shared data. Often multiple TOCs are required at multiple jurisdiction locations, but often why emergency and after hour back-up capabilities. 6. Different jurisdictional budget resources and procurement procedures. 7. Legacy ITS-related system that must be integrated. The deployed ITS communication architectures must be based on standards Cat are modular, scalable, and extensible. Fortunately, as depicted in Figure A.2.6-4, He communication industry supports a set of physical layer standards based on hierarchial multiplexed data rate capabilities: Multiplexed RS-232 (below 64 kbps); 2. Subrate Multiplexing (64 kbps and below); 3. The digital hierarchy (i.e., DS-0, DS-l, DS-3, etch; and 4. The SONET Standards (i.e., OC-l, OC-3, etc.; above 51.84 Mbps). These standards provide a wed conceived and tested framework for commun~cadng data by multiplexing for transmission and switching, routing, or bridging at nodes. The key capability is to identify cost-effective opportunities for multiplexing using techniques, equipment, and standards employed for years in He LAN/MAN/WAN and telecommunication industries. The hierarchy has data rates from the traditional 1200 bps deployable over IMP up to 10 Gbps at SONET OC-192 rate. L;\Nc}~Ph~pr\ NCHRP3-51 · Phase2FmalReport A2-30
- ~n o z o I z U] INTERFACE ~ \~7 I NTERFACE C~L 4876 Mbps 2 OC 48 / INTERFACE OC 48 2488 Mbps l \ 2 OC 24 INTERFACE OC 24 1244 Mbps 1 \ 2 OC-1~7 INTERFACE OC 1 2 L _ 622.08 Mbps \ 40C 3/ INTERFACE OC-3 . 1 55.52 Mbps_ - l ~1 INTERFACE 3C-1 51.84 Mbps _ _ \ 1 DS 3 INTERFACE DS 3 . _ \ 28 DS- 1 / u: o z 0 I INTERFACE DS 1 L~- ~7 INTERFACE DS O SERIAL LINK _ 64 kbps FIBER / \ WIRE / \ WIRELESS S~ERIAL LINK ~OC-1 92 | INTERFACE FIBER _ S:3 f3f; ~ M hn~ SERIAL LINK O C-9 6 INTERFACE _ _ F~BER 4876 Mbos SERIAL LINK _ _ FIBER SERIAL LINK FIBER , l ~ OC-48 INTERFACE - 2488 Mbps . \ 2 OC 24 / I ~ , ~ O C-2 4 INTERFACE _ _ 1 244 Mbps I 1 \ 2 OC-12/ SERIAL LINK OC 12 INTERFACE _ _ _ _ . __ FIBER 622.08 Mbp~ \ 4 OC 3 / SERIAL LINK OC 3 | INTERFAcE FIBER 1 55.5 2 M b p sl WIRELESS ~1 SERIAL LINK IV~ INTERFACE . _ _ _ _ _ _ FIBER WIRELESS J 1 51.84 Mbps| DS 3 SERIAL LINK | D S 3 1 INTERFACE _ . FIBER | 45 M bps I WIRE \ 28 DS- ~ / D S ~ ~ INTERFACE 1.544 Mbps ~ DS O | INTERFACE L~ · ~ ''X~\ 1200 bps WI RELESS 2400 bps 4800 bps 9 600 bps 1 9,200 bps 38, 400 bps 1 200 bps 2400 bps 4800 bps 9600 bps 1 9,200 bps 38,400 bps , 1 INTERFACE | 21 STANDARDS BASED DIGITAL MULTIPLEXED I DATA RATE HIERARCHY ~FIGUREA.2.6-4 -~n
~ reality, communication systems are designed to standard interfaces, as depicted on Figure A.2.6-S, and We commun~cabon infrastructure is designed and implemented as necessary to cost effectively support current and anticipated future composite multiplexed system data loads as geographically distributed. Since industry standard interfaces are employed, private networks and/or commercial communication service networks can be employed, based on cost or over factors. This hierarchy of data rates and interfaces supports the required interfaces for current and anticipated ITS field devices and related interfaces: I. Full-motion video is supported by ~ to 4 DS-Is for MPEG-2 compressed digital video, while DS-3 is available for uncompressed digital video 2. DS-O for voice; 3. Subrate multiplexing for ElA-232/4227485 for controller network interfaces; 4. Wireline modem technology supportable win TWP or T1 networks (via DS-0 channels and channel banks); 5. T} and SONET interfaces for TOC and intequr~dictional communications; and 6. T! and SONET interfaces for developing a modular, scalable, and extensible communication infrastructure that is well suited for integrates} services goals of rRs. Up to the limit of bit rate capacity, these interfaces can be implemented using wire, wireless, or fiber media These interfaces are, in fact, the most common and available interfaces provided by equipment vendors. u~NCHRPPh~.rpr\ NCHRP3-51 · Phase2F~nalReport A2-32
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