In order to ensure that the current and future ITS projects in Topeka-Shawnee County follow the common communications and infrastructure protocol, it is important to establish some guidelines for C2F communications and interconnection requirements for each center. The following presents some specific C2F communications network requirements that Topeka-Shawnee County agencies should consider for their current and future ITS projects.
I. Data Requirements
There are several types of ITS devices that have been or will be deployed in the Topeka-Shawnee County Region. The specific data requirements for each type of devices are presented below.
1. Traffic Signals
a. Support NTCIP Class B standards.
b. Support once per second communications with traffic signal controllers.
c. The minimum baud rate for signal communications is assumed to be 9,600 bits per second (bps) and preferably 19.2 kbps.
d. Traffic signal data can be multi-dropped.
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e. The maximum number of traffic signal controllers on a 9.6 kbps channelshould be four, and on a 19.2 kbps channel should be eight.
f. In a digital system, each traffic signal controller should have its own IP-address.
2. CCTV Cameras
a. The communications network should support the transmission of National Television System Committee (NTSC) full motion video as well as camera control and status data. There should be 30 frames per second for full motion video.
b. For IP NTSC full motion video, MPEG 2 or MPEG 4 compression standards should be used.
c. At a minimum, CCTV camera control data should be transmitted on a 9.6 kbps channel.
d. For analog transmission, each CCTV video should be transmitted on a dedicated communication channel.
e. CCTV camera control data can be multi-dropped.
f. In a digital system, each CCTV camera should have its own IP-address.
g. The latency of a digital CCTV camera system should be less than one second.
3. Dynamic Message Signs (DMS)
a. The communications network should support the transmission of DMS messages and control and status data.
b. At a minimum, DMS signals should be transmitted on a 9.6 kbps or higher baud rate channel.
c. DMS messages and control and status data can be multi-dropped.
d. The maximum number of DMS on a 9.6 kbps or higher baud rate channel should be six.
e. In a digital system, each DMS should have its own IP-address.
4. Other ITS Elements
a. At a minimum, all other ITS elements should be transmitted on a 9.6 kbps or higher baud rate channel.
II. Connectivity Requirements
1. C2F communications should be continuously available to the owner.
2. C2F communications and interface should be able to make use of an open architecture and industry standards.
3. C2F communications should be able to recover from communications failure automatically.
III. Bandwidth Requirements
1. At a minimum, all data should be transmitted on 9.6 kbps baud rate channels and all video should be transmitted on Integrated Digital Service Network (ISDN) or equivalent channels.
IV. Design Requirements
1. In order to avoid duplication of investments in infrastructure, all field devices should utilize as much existing communications infrastructure as possible.
2. A desired, but not required ability for each field element is to have at least one alternate routing option to ensure uninterrupted operations during communications failure or down time on one path.
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4.0 COMMUNICATIONS ALTERNATIVE ANALYSISThis analysis will discuss the various network architecture alternatives. Based on the recommended alternative, applicable communication technologies and media will be presented and analyzed. The final Topeka-Shawnee County ITS Communications Network will be presented in terms of recommended network architecture and communication technologies and media.
4.1 Network Architecture
Network architecture consists of the configuration which is used to design and construct a communications network. Configuration is an arrangement of functional units of a communications network according to their number and nature and can be represented by a schematic description showing how those functional units are connected together.
Network architecture can be described in both physical and logical ways. The physical architecture of a communications network shows the actual geometric layout of its elements and how those elements are connected together physically. Logical architecture describes the communications paths between elements of the network. In fact, logical links and connections can also be implemented as physical links and connections.
The physical architecture of a communications network is usually based on the identification of the number and geographical locations of the connecting field elements. Such information is usually available during the conceptual or preliminary design stage. For the purpose of ITS communications in Topeka-Shawnee County, this analysis will focus on developing logical architecture
alternatives for Center to Center (C2C) communications only.
Strategies for Center to Field (C2F) communications should be
The most common types of network configuration are star, tree, ring, and mesh. A star network is designed with the communication links emanating from the central point of communications concentration, such as a center. Each communication
link will be directly connected to the network elements, for example a device or a center.
Figure 4.1 illustrates the concept of a star network.
TYPE 1
Figure 4.1: Star Network (Example)
The tree configuration is a variation of the star network. It works similar to the star configuration
or aggregated. Figure 4.2 illustrates the concept of a tree network.
Elements of a ring network are connected together by a uni-directional communication link to form a closed loop. As a result, data will travel from one element in the loop to the next in a single direction around
Figure 4.2: Tree Network (Example)
TYPE 1
Figure 4.3: Unprotected Ring Network (Example)
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An unprotected ring can be configured as a protected ring by adding another unprotected ring whereby data is able to travel in the opposite direction. During the normal operation of the network, only the primary ring will be activated. When the medium between two elements is cut or not available, the primary data flow is blocked and the secondary ring will be activated automatically.Then, data will travel in the reverse direction around the loop to its destination. This allows each element on the the others. In the partial mesh configuration, some elements are connected to all the others, and some are connected only to those other elements with which they exchange the most data. Figure 4.5 illustrates the concept of a partial mesh network.
Since the recommendation for the Topeka-Shawnee County communications is to utilize the City of Topeka IT network where available, particularly for the Type 1 centers, and establish direct communications to the Topeka TMC for Type 2 centers, the network architecture for the Topeka-Shawnee County Region will be a combination of Mesh Network and Star Network (point-to-point communications). The City of Topeka IT network is comprised of a Mesh Network, and the communications between the Topeka TMC and the Type 2 centers will likely be a combination of fiber optic cable, leased line, or dial up using point to point communications. The following data and video communications alternatives are based on a combination of star, tree, ring, and mesh configurations.
TYPE 1
Figure 4.4: Protected Ring Network (Example)
TYPE 1
Figure 4.5: Mesh Network (Example)
4.2 Communications Approach
Based on the recommendation above to utilize the City of Topeka IT network to support communications between the Type 1 centers, this section presents the detailed approach to implementing the communications network.
4.2.1 Communication Approach – Type 1 Centers
The development of the Topeka-Shawnee County communications system to support communications between the Type 1 centers will be based on the following list of assumptions.
1. The TMC will act as the central point of data communication concentration.
2. Each Type 1 Center will receive a regional server to perform the following functions:
a. Interface with the Type 1 agency’s existing system. Such systems can be a traffic control system, DMS system, CCTV camera control system, or a combination of these individual subsystems.
b. Collect data from the existing system.
c. Convert collected data into a standard format that will be recognized by the regional server.
d. Receive data from other regional servers.
3. The City of Topeka’s Pyramids signal system software will serve as the regional signal software system.
a. The server application will reside on the server at the Topeka TMC.
b. Each Type 1 Center will receive a client application to support a Topeka-Shawnee County ITS workstation(s) at each Type 1 Center.
c. The Pyramids system will interface with the field devices including traffic signal controllers, CCTV, DMS and system detectors.
4. Each Type 1 Center will receive a network switch / router that will interface with the City of Topeka IT network.
5. The communication network will be Ethernet-based to support IP communications to the field devices.
a. Ethernet communications to the traffic signal controllers, requiring 1B modules on the 2070 controllers, an Ethernet module for Type 170E controllers or a serial to Ethernet converter (SLIP) for other Type 170 controllers.
b. IP video and data from CCTV cameras utilizing MPEG2 or MPEG4 compression algorithms.
c. Ethernet communications to other field devices such as DMS or system detectors.
The communication link between a Type 1 Center and the field devices can utilize various media and technologies, such as Ethernet on fiber, analog video and data that is converted to Ethernet-based communications at a hub, dedicated leased line, spread spectrum or broadband wireless, such at the planned Wi-Fi network to be implemented by the City of Topeka IT.
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This approach should be relatively easy and inexpensive to deploy because the Type 1 Centers will utilize the existing City of Topeka IT network and only require slight modification of the network to support the Type 1 Centers, including the installation of a regional server, workstation and network switch/router. Figure 4.6 illustrates the concept of communications approach for Type 1 Centers.4.2.2 Communication Approach – Type 2 Centers
The Type 2 centers will be connected to the City of Topeka regional server to transmit or receive information. Again, the communication link between those centers and the network switch or router can utilize the same or different media and technologies as the backbone, being the City of Topeka IT network, fiber optic cable, leased line, phone drop or private internet website.
The development of the Topeka-Shawnee County communications system to support communications between the Type 2 centers will be based on the following list of assumptions.
1. Type 2 centers will be connected to the regional server at the Topeka TMC.
2. The Topeka TMC will act as the central point of data communication concentration.
3. Each Type 2 Center will receive a remote workstation to perform the following functions:
a. Transmit or receive information from the Topeka-Shawnee County regional server.
b. View Topeka-Shawnee County regional information map.
4. The communication interface between the Type 2 Centers and the Topeka TMC will vary by center.
a. Communication may be implemented via the City of Topeka IT network for Type 2 Centers with access to the network.
b. Direct fiber optic cable connection can be implemented.
c. Leased line or dial up communications for Type 2 Centers outside of the City of Topeka-Shawnee County Region.
d. Internet-based connection via private network connection.
The level of complexity to complete each Type 2 Center connection will vary based on means of communication utilized as noted above. This information will need to be determined as part of this project based on discussions with the project stakeholders.
Figure 4.7 illustrates the concept of communications approach for Type 2 Centers. Type 1 Centers are shown for completeness.
Figure 4.6: Communications Approach – Type 1 Centers
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Figure 4.7: Communications Approach – Type 2 Centers
5.0 COMMUNICATIONS MEDIA AND TECHNOLOGIES ASSESSMENT
This section presents a discussion and assessment of communication media and technologies that are applicable to the communication network and approach discussions presented in Section 4. The possible communication solutions can be categorized into the following land-line and wireless solutions:
• Land-Line Solutions
- Synchronous Optical Network (SONET) on fiber - Asynchronous Transfer Mode (ATM) on Fiber - Ethernet on fiber
- Leased Line - Internet
• Wireless Solutions
These solutions are applicable to both the Type 1 Center and Type 2 Center communications links. The City of Topeka’s IT network is currently a combination of Synchronous Optical Network (SONET) and Gigabit Ethernet, so both of these technologies are included in the discussion. Asynchronous Transfer Mode (ATM) is also included in the discussion, but is not considered as a viable alternative for the Topeka-Shawnee County Region.
Because the assessment of communication media and technologies for center to center communications can be applied to center to field communications, recommendations for center to field communication solutions will be provided in this section as well.
5.1 Land-Line Solutions
Land-line communications refer to the use of wires or cables for connection purposes in a communications system. These cables or services can be leased or owned. The major land-line mediums used for ITS communications include the following:
• Twisted Pair Copper Wire
• Coaxial Cable
• Fiber Optic Cable
• Leased Line
• Internet
Twisted pair copper wire is not a feasible solution for regional communications because it provides limited bandwidth and has a high maintenance cost. However, it can be a very economic solution for signal control applications. Although coaxial cable can provide much higher bandwidth than twisted pair copper wire, it is not a feasible solution because of its high cost of terminations and splicing and the requirement of highly-skilled maintenance personnel.
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5.1.1 Fiber Optic
Fiber optic technology is the communication medium of choice for ITS applications because of its virtually unlimited bandwidth, electromagnetic and Radio Frequency (RF) interference immunity, long life expectancy, long-range transmission capability, and ease of installation.
SONET, ATM, and Ethernet are the most widely used ITS communications technologies which take advantage of the bandwidth characteristics of fiber optic cable, with Ethernet becoming the technology of choice. The following paragraphs discuss and evaluate each of the two other technologies.
5.1.1.1 SONET on Fiber
SONET is an internationally applicable standard endorsed by both ANSI (American Network Standards Institute) and ITU (International Telecommunications Union). It has been a very reliable standard since 1988. It offers transmission speeds of up to 10 Gbps. Its high-speed backbone transport function provides reliable and economical long-distance transport. The robustness of this protocol has reduced the requirements in equipment and therefore increased the network reliability.
A SONET system will provide a significantly less-expensive system if more bandwidth is needed. Some vendors’ products support plug-and-play installation and most SONET equipment interface modules are hot swappable, so that they can be replaced without interrupting network traffic. The configuration of deployed modules can be provided in a database so that new modules can be configured with minimal downtime. SONET allows optical interconnection between networks regardless of the make of equipment. Next generation SONET equipment are equipped with security capabilities that ensure secure networking, safe from intruders and hacking tools.
However, SONET is a significantly more complicated protocol than Ethernet. Although it has substantial overhead information to allow quicker troubleshooting and detection of failures, installation, operations, and maintenance of SONET are not familiar to many Local Area Network (LAN) professionals. Most SONET equipment can meet all NEMA environmental specifications. Some of the SONET equipment manufacturers include CISCO, Intelect, Tektronix, and Lightriver Technologies.
A portion of the Topeka IT network is supported by a SONET ring.
5.1.1.2 ATM on Fiber
ATM is a cell oriented switching and multiplexing communication technology that can be viewed as an evolution of packet switching, which is a fundamental communication technology for the telecommunication industry.
ATM network is scalable in both speed and network size. It offers dynamic bandwidth for
“bursty” data traffic. It shares a common architecture for both LAN and Wide Area Network (WAN). In addition, ATM allows all types of Ethernet LAN traffic to be multiplexed over a single ATM WAN and ATM equipment operate with direct SONET interface cards.
However, like SONET, ATM is a more complicated protocol than Ethernet and its installation, operations, and maintenance are not familiar to many LAN professionals. In addition, an ATM network is less secure than a SONET because hackers can bypass the
firewall. A wide range of ATM equipment is available in ruggedized format that meet NEMA environmental specifications. Some of the ATM equipment manufacturers include Teleste, Cellstack, and Marconi.
5.1.1.3 Ethernet on fiber
Ethernet has traditionally been the technology for the LAN. In the past few years, Gigabit Ethernet (GigE), in particular is becoming popular as a LAN system due to its deployment over Cat 5 copper cabling. When GigE over fiber was approved by IEEE in 1998, many agencies began looking into applying a GigE system to their traffic communication system.
Although GigE is an emerging system for traffic applications (readily available NEMA-hardened equipment emerged in 2002/2003), there has been substantial implementation by private companies in other market sectors which demand high communication bandwidth.
Many cities throughout the country are employing either partial or full deployments of GigE technology for their communication systems. In the past few years, several vendors began offering hardened GigE equipment, accelerating the use of GigE for transportation applications.
Ethernet was not originally designed to provide redundancy and to handle real-time voice and video. However, GigE has incorporated enhancements that the same ring protection in SONET provides. Resilient Packet Ring (RPR) aims to give Ethernet the SONET-level protection and reliability with a data link layer optimized for packet traffic in both LAN and WAN environment. In addition, QoS functionality is available in GigE to prioritize voice and video traffic across networks.
GigE or Ethernet is a familiar technology to the information system (IS) and LAN professional. A GigE network is easily understood and configured. A GigE system is highly scalable. While ATM can reach a capacity of 622 Mbps, hardened GigE has the higher ultimate bandwidth, 1,000 Mbps. However, SONET still has the highest ultimate bandwidth (in excess of 1.6 Gbps) – at the price of complexity.
Due to the fact that Ethernet was developed for LANs primarily utilized in the air-conditioned environment of corporate and campus networks; heat and humidity were never issues.
NEMA specifications, however, for outdoor traffic signal cabinets are 70oC (165 oF). This limits the choices for hardened network equipment. However, there are an increasing number of traffic equipment vendors supporting Ethernet communication, such as IP-addressable CCTV cameras (or encoder/camera combinations) and signal controllers.
When used in a GigE system, the IP-addressable devices can be accessed by their IP address from any standard Web browser or TCP/IP commands. Some GigE equipment manufacturers include Extreme Network, Cisco, Etherwan, GarretCom, Cisco and RuggedCom. Note that to date, hardened Ethernet equipment is available in speeds up to Gigabit bandwidth. Hardware is available in higher bandwidths, such as 10 Gigabit, but not in hardened configuration. Lastly, it should be noted that like ATM, a GigE network is less secure than a SONET network, but again, at the price of complexity.
A portion of the Topeka IT network is supported by a GigE ring.
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5.1.2 Leased Line
Obtaining communication links from a 3rd party provider (telecom utility) is a valid method of quickly obtaining communications connectivity to individual locations and/or complete networked implementations. This option is especially attractive to Topeka-Shawnee County because the cost and time to implement the full infrastructure to support some of the remote locations that may be cost-prohibitive to the overall implementation of the system.
Obtaining communication links from a 3rd party provider (telecom utility) is a valid method of quickly obtaining communications connectivity to individual locations and/or complete networked implementations. This option is especially attractive to Topeka-Shawnee County because the cost and time to implement the full infrastructure to support some of the remote locations that may be cost-prohibitive to the overall implementation of the system.