Communication Mediums for Signal, ITS, and Freeway Surveillance Systems Final Report (1996) / Chapter Skim
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A.1.5 Communication Networks and Protocols
A.1.5 Communication Networks and Protocols
Pages 204-245
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2) TOC computer networks employ packet-switched techniques (e.g., L`ANS)
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setup for short bursty data messages creates significant inefficiencies in c~rcu~t-sw~tched networks which are best suited for voice cans urge durations of minutes as opposed to fractions of seconds. Packet technologies handle this more efficiently.
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Figure A.~.5.~-2 illustrates how packet links and networks generally perform by plotting average delay versus percent throughput capacity. As We figure illustrates, if a network is lightly loaded, Me average delay is largely fixed and a function of propagation time and processing delays.
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' ca ~ ~ 0 5? c#o Q cent CD x al o ._ 3 _ U
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Although each layer is often referred to as a protocol, application protocol stacks, or profiles, such as NEMA's NICIP Signal System protocol, require definitions of Be individual layer protocols, services, and interfaces. With the OST reference model, Me assignment of funchonality to individual layers has achieved significantly better standardization.
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the physical layer, (2) He link layer, and (3)
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Modern communication links are less error prone and can operate efficiency win these overhead error control functions on He periphery of the communications infrastructure. Lower overhead in layers I, 2, and 3 of He infrastructure is essential for higher link bit rates.
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A bridge works at Be link (2) layer and converts one link layer protocol (e.g., Ethernet)
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/ l L I 1- 1 1 1' ~1 , 1~ ~ ~1 1 ~ _ 1 1 ~ 1 1 1 1 1 1 I I I T -ad- I I r .
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The NTCIP standards suite is being developed in the NTCIP Subcommittee of Me 'transportation Management System and Control Section Committee" of National Electrical Manufacturers Association (NEMA)
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Advanced Mediums - Wireless, fiber, high speed modems · Local, Regional, State and Nationwide Interjurisdictional Communication · Provide Interoperability & Integration Guidelines and Standards Support interoperability with commercial standards applicable to ITS Provide ITS-specific protocol stacks and layer protocols where required Promote Competitive Procurement · Initial procurement . Upgrades and expansions Promote Multiple Application Integration on Common Communication Infrastructure .
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- reduced protocol for operation on installed base of 1200 bps, FSK modems in multidrop configuration Class C - Connection oriented services · Class E - High speed connection oriented services I SmallTransportationManagementProtocol(STMP) -networkmanagement l Flexibility in configuration, plus other benefits ~ More flexible OSI stack to accommodate evolution Class B Operation The OST reference mode]
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the lindc layer, network layer, and application layer. Thlls, in addition to employing proprietary protocols and message sets, historical signal system protocols are not well suited to muldapplication communication infrastructures, efficient data sharing, multimedia network, or integration of modern network management capabilities.
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Significantly expanded and complete application message sets. The Class A protocol stack is intended for rrS-related systems which support: I)
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The NEMA standards subcommittee has selected a derivative of the widely deployed Single Network Management Protocol (SNMP)
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Its MIB defines the message fields, data types, etc. Using As, controller message sets of multiple vendors can be defined to TOC computers by the simple loading of He FIB definition data base (usually from floppy disks)
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~ ~ ~ o as o · En in 46 41 o o He in cO ~ In a, ~ em o [L, cL a, En c.
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Get - next request Enables sequential retrieval of variables Get - response Returns results of above operations , Trap Reports event occurrence The use of SNMP in ITS-related applications is straight forward, but requires specific ITS definitions and some fine tuning in NTCIP to define simp~iBed message set types and protocol for Me low bit rate modem circuits. NTCIP defines a Simple Transportation Management Framework (STMFi)
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. , · Reduces system operation and maintenance costs · Supports integration with widely-deployed SNMP-based implementations Essential tool for supporting multiple field devices at TOCs Provides for configuration of Application Message Sets according to local requirements, vendor capabilities, and architectural / equipment capabilities · Streamlines and supports interoperability of equipment from different vendors Supports self-test and centralized monitoring - Supports computerized configuration management L:`NCHRPPhase2.rp ~NCHRP3-51.
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Ramp Meter Controllers Camera Controllers Sensors Highway Advisory Radio (MAR) Global Objects Philosophy: All application (layer)
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Because of the connection-or~ented nature of this profile and He resuldng overhead, this profile is not wed suited for low speed lines, although Here is nothing to preclude its use on such facilities. Its pnncipal application is in communicating win devices which need to exchange relatively large files, such as Highway Advisory Radio controllers, or Variable Message Signs.
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. Both of these application layer protocols provide a degree of security through user authentication procedures.
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NEMA Standards Publication TS3.5 - 1996 National Transportation Communication for ITS Protocol Object Definition for actuated Traffic Signal Controller Units 6) National Electrical Manufacturers Association, Draft Standard - NTCIP Object Definitions for Ramp Meter Controllers 7)
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layer protocols. The physical layer specifies a medium (e.g., TWP, coaxial cable, fiber, etc.~.
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cn cn os e~ cn eQe Q cn _ O e~ O C~ ~_ e~.
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LAN ong~naDy used a 10 Mbps bit rate on a shared coaxial cable bus with ad devices employing Catner Sense Multiple Access wad Collision Detect (CSMA/CD)
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The overall features and capabilities of FDDI are summarized in Table A.~.5.4-~. Frame relay is a fast packet switching technology that provides end users a high-speed virtual private network (VPN)
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c`i o Q A no _ ~ ~ _ ?
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c~ o c~ Q o ~ ~ ° s ., cn ° ce o o o o C~ o cn o ~q ~ ' a)
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. Fiber channel networking transparently supports several LAN protocols plus TCP/IP.
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