cobranet_cntraining2[1]

Audio Networks An Overview

Peak Audio, a division of Cirrus Logic, Inc.

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Table of Contents:DETERMINING WHEN AN AUDIO NETWORK IS THE RIGHT SOLUTION ........................... 6 INTRODUCTION ......................................................................................................................................... 6 FACILITY OVERVIEW ................................................................................................................................ 8 DISTANCE AND CHANNEL COUNT ............................................................................................................ 9 OTHER NETWORK REQUIREMENTS AND EXISTING INFRASTRUCTURE .................................................... 10 FLEXIBILITY REQUIREMENTS ................................................................................................................. 11 CONTROL AND MONITORING .................................................................................................................. 12 REDUNDANCY AND RELIABILITY REQUIREMENTS .................................................................................. 13 FUTURE EXPANSION ............................................................................................................................... 14 MATERIAL AND LABOR COSTS ............................................................................................................... 15 STADIUM EXAMPLE:............................................................................................................................... 16 CONVENTION CENTER EXAMPLE:........................................................................................................... 17 ETHERNET: HISTORY AND BACKGROUND................................................................................ 19 INTRODUCTION ....................................................................................................................................... 19 THE FIRST ETHERNET............................................................................................................................. 19 CSMA/CD.......................................................................................................................................... 19 ETHERNET PACKET STRUCTURE ............................................................................................................. 20 THE ETHERNET STANDARD .................................................................................................................... 21 10BASE-T .......................................................................................................................................... 22 100BASE ETHERNET ............................................................................................................................. 23 Fast Ethernet Variations ................................................................................................................... 23 GIGABIT ETHERNET................................................................................................................................ 24 Gigabit Ethernet Variations .............................................................................................................. 24 THE FUTURE........................................................................................................................................... 25 SELECTING THE CORRECT CABLE FOR A PROJECT ............................................................. 26 INTRODUCTION ....................................................................................................................................... 26 THE CABLE PLANT ................................................................................................................................. 26 CAT5..................................................................................................................................................... 26 Distance Limitations ......................................................................................................................... 27 Connectors ........................................................................................................................................ 27 Twists and Terminations ................................................................................................................... 28 Straight-Through vs. Crossover Cables ............................................................................................ 29 Crossover Cables and Uplink Ports.................................................................................................. 30 FIBER OPTIC CABLE ............................................................................................................................... 30 Connectors ........................................................................................................................................ 31 CABLING AND NETWORK PERFORMANCE ............................................................................................... 31 CAT5 and Cable Ties ........................................................................................................................ 32 Pull Force and Bend Radius ............................................................................................................. 32 SOURCES FOR MORE INFORMATION ....................................................................................................... 34 SELECTING THE CORRECT HARDWARE FOR A PROJECT................................................... 35 INTRODUCTION ....................................................................................................................................... 35 DATA TERMINAL EQUIPMENT ................................................................................................................ 35 2001 Cirrus Logic, Inc. 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DATA COMMUNICATIONS EQUIPMENT AND ETHERNET HARDWARE ...................................................... 35 Network Interface Card..................................................................................................................... 35 Repeater Hubs ................................................................................................................................... 36 Switching Hubs.................................................................................................................................. 38 Hubs vs. Switches .............................................................................................................................. 41 Bridges and Routers .......................................................................................................................... 41 ESTABLISHING LINK ............................................................................................................................... 42 10Mbps networks............................................................................................................................... 42 100Mbps Devices .............................................................................................................................. 43 Auto-negotiating Devices .................................................................................................................. 43 Auto-negotiation Examples ............................................................................................................... 44 Media Converters.............................................................................................................................. 44 NETWORK ADDRESSING ......................................................................................................................... 45 IP Address ......................................................................................................................................... 46 Subnets and Subnet Masks ................................................................................................................ 47 Classless Addressing ......................................................................................................................... 48 IP Addresses and Audio Networks .................................................................................................... 48 DESIGNING AND BUILDING A NETWORK ................................................................................................ 48 Assign IP Addresses to PCs .............................................................................................................. 49 Configuring the Switch...................................................................................................................... 49 Test Connectivity ............................................................................................................................... 50 RECOMMENDED READING ...................................................................................................................... 51 ROUTING AUDIO ON A NETWORK ................................................................................................ 52 INTRODUCTION ....................................................................................................................................... 52 FILE TRANSFER THEN PLAY ................................................................................................................... 52 Advantages ........................................................................................................................................ 53 Disadvantages ................................................................................................................................... 53 Applications....................................................................................................................................... 54 PLAY OVER NETWORK - PULL MODEL................................................................................................... 54 Advantages ........................................................................................................................................ 55 Disadvantages ................................................................................................................................... 55 Applications....................................................................................................................................... 55 PLAY OVER NETWORKS - PUSH MODEL................................................................................................. 55 Advantages ........................................................................................................................................ 56 Disadvantages ................................................................................................................................... 56 SYNCHRONOUS STREAMING ................................................................................................................... 57 Advantages ........................................................................................................................................ 57 Disadvantages ................................................................................................................................... 58 ISOCHRONOUS STREAMING .................................................................................................................... 58 Isochronous Transmitters and Receivers .......................................................................................... 59 Advantages ........................................................................................................................................ 59 Disadvantages ................................................................................................................................... 60 COBRANET............................................................................................................................................. 60 COBRANET TERMINOLOGY .................................................................................................................... 61 COBRANET INTERFACE .......................................................................................................................... 62 THE ISOCHRONOUS CYCLE ..................................................................................................................... 63 2001 Cirrus Logic, Inc. 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CONDUCTOR........................................................................................................................................... 63 CONDUCTOR ARBITRATION .................................................................................................................... 63 COBRANET PROTOCOL........................................................................................................................... 64 Beat Packet........................................................................................................................................ 64 Reservation Packet............................................................................................................................ 65 Audio Data Packet ............................................................................................................................ 66 NETWORK MANAGEMENT AND CONTROL ............................................................................... 67 INTRODUCTION ....................................................................................................................................... 67 WHAT IS NETWORK MANAGEMENT?...................................................................................................... 67 TELNET, HTTP AND FTP....................................................................................................................... 68 Telnet................................................................................................................................................. 69 HTTP ................................................................................................................................................. 69 TFTP.................................................................................................................................................. 70 MANAGEMENT USING SNMP ................................................................................................................ 70 AGENTS MANAGERS AND MIBS ............................................................................................................. 71 Agent.................................................................................................................................................. 71 MIB.................................................................................................................................................... 72 Manager ............................................................................................................................................ 72 SNMP Message ................................................................................................................................. 73 MANAGEMENT SOFTWARE ..................................................................................................................... 75 Polling and Network Topology ......................................................................................................... 75 Drill Down Capability....................................................................................................................... 75 Event Logs and Performance ............................................................................................................ 76 RECOMMENDED READING ...................................................................................................................... 77 SNMP MANAGEMENT APPLICATION REFERENCE .................................................................................. 77 DESIGNING A NETWORK TO ACCOMMODATE SPECIAL NEEDS........................................ 78 HIGH AVAILABILITY .............................................................................................................................. 78 High Availability Design................................................................................................................... 78 Quality Components.......................................................................................................................... 78 Cold Spares ....................................................................................................................................... 79 Hot Swap ........................................................................................................................................... 79 Fail-over............................................................................................................................................ 79 Fault Tolerance ................................................................................................................................. 79 ENVIRONMENTAL FACTORS ................................................................................................................... 80 MONITORING .......................................................................................................................................... 80 LIFE SAFETY .......................................................................................................................................... 81 NETWORK AVAILABILITY ...................................................................................................................... 81 Link Aggregation (Trunking) ............................................................................................................ 81 Spanning Tree Protocol .................................................................................................................... 82 Meshing ............................................................................................................................................. 83 AUDIO INTERFACE AVAILABILITY .......................................................................................................... 84 Pairing Interface Devices.................................................................................................................. 84 Buddylink........................................................................................................................................... 84 DuaLink............................................................................................................................................. 85 MIXED USE NETWORKS ......................................................................................................................... 85 2001 Cirrus Logic, Inc. 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NON-BLOCKING SWITCHED NETWORK DESIGN ..................................................................................... 86 VIRTUAL LOCAL AREA NETWORKS ....................................................................................................... 86 QUALITY OF SERVICE ............................................................................................................................. 87 LARGE INSTALLATIONS .......................................................................................................................... 87 CORE SWITCHING ................................................................................................................................... 88 AUDIO VLANS ...................................................................................................................................... 88 LAYER 3 ROUTING ................................................................................................................................. 89 DISTANCE AND SWITCH HOPS ................................................................................................................ 89 Forwarding Delay ............................................................................................................................. 89 Delay Variation ................................................................................................................................. 91 TROUBLESHOOTING AUDIO NETWORKS................................................................................... 92 INTRODUCTION ....................................................................................................................................... 92 CHECK THE OBVIOUS!............................................................................................................................ 92 VERIFY LINK .......................................................................................................................................... 92 MANAGED SWITCH CONFIGURATION ..................................................................................................... 93 ARE LEDS INDICATING ERRORS? .......................................................................................................... 94 CHECK THE AUDIO ................................................................................................................................. 94 Signal Presence ................................................................................................................................. 94 Audio quality ..................................................................................................................................... 94

2001 Cirrus Logic, Inc.

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DETERMINING WHEN AN AUDIO NETWORK IS THE RIGHT SOLUTION IntroductionNetworks have had a major impact on technical systems of all types. Most commercial buildings include a network infrastructure. These networks can carry many types of data including lighting, security, point-of sale information, as well as general office computer data. The world has indeed become a networked world. Until recently, the audio system has not been a part of the building data infrastructure. Rather, it was always a separate, typically analog wiring system. Having to install a completely separate wiring infrastructure can result in a great increase in costs of materials, labor and time. In certain types of projects, the savings can be very significant. In addition to the cost factors, there are of course, many technical advantages to distributing audio over a network. Flexibility is greatly increased. In a properly designed system any audio input can be routed to any audio output without having to physically move wires or make use of patchbays. This routing capability allows for different system configurations and for future changes to be accommodated without having to make hardware or wiring changes. Redundancy and fault tolerant designs can be implemented using audio networks. A system can be designed so that if any piece of equipment or wire on the network should fail, an automatic switchover can take place. In a traditional analog system, if a wire is cut someone has to discover this through troubleshooting and then it has to be either repaired, replaced or patched around. Through network management a centrally located computer can monitor all network


When a Network is the Right Solution

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products and alert the system operator if a fault should occur anywhere in the system. Networked systems can result in a significant reduction in cable and infrastructure requirements. A single CAT-5 or fiber optic cable can replace many cables. The same cable that transports the audio can carry control and monitoring data as well. In deciding whether an audio network is right for your project, you must expand your thinking beyond the traditional cabling means. Networks provide many new capabilities that were heretofore not possible. You must be willing to learn about these new capabilities and then use your system design skills and knowledge to think of ways where these new possibilities can provide better systems. Just the fact that you can now have any channel appear at any output results in the necessity of thinking in an entirely new way. Those contractors and consultants who do not learn how to take advantage of the world of networking will be left behind. It is also just as necessary to not become so enamored with the new technology that you use it when a simple analog point-to-point connection is the best solution. By the end of this class you should have the knowledge tools necessary to move forward and lead this industry into the networked world. While there are many benefits to using a design that distributes audio over a network, it is not always the right solution. In this section we will examine audio system needs and learn how to determine whether an audio network is of benefit for a particular project.



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Facility OverviewThere are several criteria that must be judged when determining whether a network is appropriate for a project. These include: Overall scope of the project Equipment locations Routing needs Distances Channel counts Other network infrastructure and existing infrastructure Flexibility requirements Control and monitoring requirements Redundancy and reliability requirements Future expansion requirements Material costs Labor costs The first step in determining if a networked approach is appropriate is to look at the big picture. How many physical locations have audio inputs, audio outputs or audio processing equipment? What locations require system control? How physically large is the system? What are the distances between locations? Is the client technology oriented? If all of the equipment is located in one small equipment closet, a network may not be a good solution as one of the benefits of networks is the ability to transport audio and data over long distances. The first step is to locate all of the equipment locations, input locations, output locations and control locations. Typically, as the number of locations goes up so does the convenience of utilizing an audio network.



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Next, determine the audio routing requirements. Does all audio need to matrixed between all locations, or are the needs simply point-to point? Is there a need to change routing depending upon the needs of a particular event? An example of this is a convention center where the needs change on an hourly basis. One day a meeting room may be associated with a particular ballroom and the next day it may be tied into the audio feed from an adjacent large hall. Will the needs change over time? The needs of legislative facilities often change after an election, especially if the majority or chairmanships have changed. Will the actual routing needs be determined after the system design must be complete? An example of this is in a theme park. The infrastructure must be designed well ahead of the show itself. The show designer often does not determine his or her actual needs until the very end of the project. The flexibility of being able to change the routing at the end of the project makes a network a very attractive solution. If the project simply has a control room and a single amplifier closet where routing changes are never needed, an analog solution may be appropriate

Distance and Channel CountThe distances between locations are an important factor in determining when a network is appropriate. Typically longer distances lend themselves to networks, although short distance situations may also benefit from a network when other factors such as routing requirements are considered. A single CAT-5 cable can carry 64 channels in each direction (a total of 128 channels) up to 100 meters using CobraNet technology. This same data can be carried up to 2 kilometers using multimode fiber optic cable. It is possible to carry over a thousand channels over Gigabit switched Ethernet. These design rules will be covered in a later part of the class.



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As part of the design process you should determine how many input and output channels are required at each device and location. It is also useful to know how many channels need to be transported between locations.

Other Network Requirements and Existing InfrastructureIt is useful to determine what other data will be transported around a facility. If it is a new facility you should make the effort to learn what the data distribution needs are for other disciplines. You may learn that the M&E engineering firm has designed in an Ethernet network for the lighting and security and that this network has excess capacity. If this bandwidth can be made available to you, there could be a huge cost savings on the sound system. Or perhaps you will find that the IT department is designing a facility network and your needs can be included in this, thus reducing the cost impact on your design, perhaps freeing up funds for other areas of the sound system. Is there another discipline that is designing a data network for their purposes within the same facility? Perhaps you can coordinate efforts with them and share in the infrastructure costs. Remember, if your data is being transmitted over Ethernet, and the network utilizes switching technology, you can share the network and your data can travel down the exact same wires as the data being distributed for other purposes. If the project is being installed into an existing facility you should find out what network infrastructure is already in place. If the infrastructure exists, does it have excess capacity? Does it have drops in locations that are useful to you? You should also determine if there is an infrastructure in place that could prove to be of benefit in a design that uses traditional analog distribution. Perhaps there are a number of empty conduits available for your use that could be utilized. Does a cable tray system exist? 2001 Cirrus Logic, Inc. When a Network is the Right Solution

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Flexibility RequirementsTraditional wiring is of the point-to-point variety. This means that the signal always goes from one known location to another, and the connection is hard-wired in place. This is true of both analog and digital wiring. Even though an AES/EBU signal is digital, it still only connects from one specific point to another. This type of hard-wired condition is very limited, as it only operates in one manner. It is not flexible or configurable. The method that is normally used to add some level of flexibility is to incorporate patchbays into the system. Although, this allows you to change the routing of the audio, it is still very limited. Each location that the audio goes to must have a dedicated cable that is home run to the patchbay. Patchbays are themselves limited to the signal paths that are available at the patchbay and are not very flexible. Also, patchbays must be operated by a technically competent person. They can create problems such as hum, loud pops, noise, etc. In a network, all of the audio channels can appear anywhere on the network (depending upon the particular network design). This greatly increases flexibility, as the designer did not have to home run dedicated wires (with a dedicated pair for each channel.) The network can be easily configured on site. Channel routing can be stored into presets allowing the functional wiring to completely change to meet the needs of a particular event. It can also be changed in the future to meet the changing needs that may occur down the road. You can design your network so that you have enough capacity and nodes so that you do not actually design the routing ahead of time, but rather do so in the field as the exact needs unfold. As mentioned earlier, this capability can prove very useful in a theme park where the show designer works with you to fine tune the needs long after the basic design had to be completed. This is highly flexible. Is this type of flexibility and configurability desirable for your project? 2001 Cirrus Logic, Inc. When a Network is the Right Solution

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Since this opportunity was not previously available, you must think about the potential benefits of having these new capabilities. While designing the system using traditional point-topoint wiring may work, these new capabilities may prove to be beneficial to your project. On the other hand, you may not need any of these capabilities. By attending this class, you are equipping yourself with the knowledge to learn how to make that determination.

Control and MonitoringWhen we discuss control and monitoring, we are talking about two types of control and monitoring. One is the control and monitoring of the network itself. This includes all cables, network products such as switches, and the actual products producing and consuming data on the network. As an example, you may have a power amplifier on the network that has a network interface built into the amplifier itself. You may want to monitor the status of the network interface in the amplifier to be certain that it is operating properly. This can be done from a remote location over the network. There are commercially available products that perform these functions. If a fault should occur anywhere on the network you can be alerted to that fact and easily diagnose the problem. This type of monitoring increases the reliability and ability to diagnose a network. These capabilities must be weighed in deciding if an audio network fits your particular project. The other type of control and monitoring, in our amplifier example would be performing functions such as remotely observing the clip lights on the amplifier and adjusting the levels from that same remote location. CobraNet networks can transport many types of control and monitoring data. While the network carries this data, the equipment manufacturer supplies the control data. Examples of this include QSControl, MediaMatrix, IQ, RaneWare, Nexsys, etc. The important thing to consider is the fact that if you are going to be using these 2001 Cirrus Logic, Inc. When a Network is the Right Solution

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types of control and monitoring software in many cases, when using CobraNet, they can be carried over the same wire or fiber that the audio is carried on. This can greatly reduce the complexity and cost of the cabling infrastructure by eliminating an entirely separate infrastructure. Installation and troubleshooting are also greatly reduced when there is only one cable infrastructure. This can be a very significant factor if you are using these types of control or monitoring systems. If your system does not use these technologies, then this audio network advantage would not apply to your project.

Redundancy and Reliability RequirementsEthernet networks are used in a very large number of mission critical applications throughout the world in many different disciplines. The need for redundancy and faulttolerance has been around for a long time and there are many different solutions available depending upon the needs of the project. One of the benefits of utilizing well established technologies is that these needs have already been addressed. When an entirely new technology is invented, the problems must first be discovered, then the solutions must be developed and finally they must be tested and refined. This takes a lot of time and being involved in this process at the beginning can often be a time consuming and frustrating experience. As mentioned previously, managed products such as managed switches can be purchased that have the ability to be remotely monitored. Using network management software an operator can monitor the operation of the entire network. This greatly improves reliability.



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By taking advantage of redundancy schemes it is possible to design many different levels of redundancy including a network that is fully redundant. This means that every cable and device is duplicated in a redundant, parallel system. If any piece of equipment or cable should fail on the network, the failure will be automatically detected and the faulty item or network will be bypassed and replaced with the redundant option. This can all occur without any human intervention and is quite seamless. Any cable can be cut without affecting the continued audible presence of audio over the system. For projects that need a lesser amount of redundancy or fault tolerance other schemes, typically at a lower cost, can be implemented. With traditional cables, if a wire is cut, or if a connector fails, or a product breaks, it will require a person to troubleshoot the problem and manually correct it. In a well designed system with a patchbay this can possibly be easily accommodated. In other systems, it may take a long time, however there are projects where that is acceptable. One other benefit of digital audio, especially when it is transmitted over fiber optic cable is the low susceptibility to RFI (radio frequency interference). All audio networks are digital and thus enjoy this added benefit.

Future ExpansionAny well thought out system can be designed to accommodate future expansion. A networked system offers the benefit of an infrastructure that is readily expanded. It is fairly easy to add more nodes or products onto an existing network. With an analog system new locations often require additional cable, conduit etc. Of course, if the future expansion simply requires a larger mixing console, or adding some new equipment into a new rack, then a network may be of no benefit at all. If the future expansion involves new locations, more channels being distributed, or the ability to change routing in the future, then audio networks can provide a real benefit. 2001 Cirrus Logic, Inc. When a Network is the Right Solution

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Material and Labor CostsThe materials required for a networked audio system differ from those required for a traditional analog or digital system. A networked system has the added cost of network specific products such as Ethernet switches and management software (if the network is of the managed variety). But a network it greatly reduces other infrastructure costs. In a typical large facility there are numerous runs of multichannel cables through conduits. The ends of these cables are typically connected via large multi-pin connectors. The material cost for these items can be very high, especially when there are long runs in conduit. Connectorizing these cables can take a lot of time, therefore the labor costs are high. The installation of the conduit is also a very labor intensive process with a high cost. And troubleshooting these systems adds further to the labor costs. Of course in a smaller facility such as a restaurant or bar, there may not be very much wiring and therefore the materials and labor costs are not very high. Over a thousand channels can be carried over a pair of fiber optic cables using Gigabit switched Ethernet. This data cable does not need to be run in conduit and results in a significant reduction in both material and labor costs. Even a standard CobraNet signal over CAT-5 cable can carry a total of 128 channels. The connectors are simple crimp type or fiber optic types. These do not require soldering and are very easy to install. They do not require the specialized skills needed when working with the more typical audio connector varieties. Depending upon the system requirements there can be a huge cost savings incurred when using an audio network in a system. Sample cost and design comparisons are shown below.



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Stadium Example:There is a total of 4600 of cable used in this analog design example, and most of the conduit is 3". With cable and conduit costs estimated at $44,700, and a labor estimate of $1,500, the total infrastructure cost for this analog system if $46,200.ANALOG PROCESSING EQUIPMENT 2-32 PAIR CABLESPA-1

2-32 PAIR CABLES

PA-1

1-32 PAIR (SPARE)

PA-2

1-32 PAIR (SPARE)

PA-2

PA-3

PA-3

PA-N

PA-N

EQUIPMENT RM 1

EQUIPMENT RM 3

2-32 PAIR CABLES

PA-1

3 C. (TYP.)

1-32 PAIR (SPARE)

PA-2

PA-3

CENTRAL CONTROL LOCATION EQUIPMENT RM 2

PA-N

Traditional Analog SystemWhile the network design may look more complex, its actually much simpler from an infrastructure perspective, and much less costly. Networks can carry more channels over fewer wires, and using fiber in the existing cable tray reduces the infrastructure cost to under $3,000.ANALOG PROCESSING EQUIPMENT

COBRANET INTERFACE (TYP) CN CN CN 100BASE -FX SWITCH

PA-1

PA-1

PA-2

CN 100BASE -FX SWITCH

PA-2

CN

PA-3

CN

PA-3

PA-N PA-N

CN CN 100BASE -FX SWITCH

EQUIPMENT RM 1 CABLE RACEWAY

EQUIPMENT RM 3

PA-1

CN CN

3/4 C. FIBER OPTIC CABLE (TYP)

CN 100BASE -FX SWITCH

PA-2

CN

PA-3

CENTRAL CONTROL LOCATION EQUIPMENT RM 2

PA-N


CobraNet System


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Convention Center Example:An 8 pair cable and a 4 pair cable are run to a remote equipment closet from each of 4 meeting rooms in a 100 ft. long 1-1/2" conduit. A 3" conduit is home run from each remote equipment closet to the equipment room. These conduits carry four 8-pair and four 4-pair cables each. In this example, well look at the costs for the Meeting Rooms only. The conduit and cable cost is almost $160,000, while the labor to install the cable is a little over $8,000. This results in a total infrastructure cost of $163,000.

CENTRAL CONTROL LOCATIONREMOTE EQUIP RM 1ANALOG PROCESSING EQUIPMENT

REMOTE EQUIP RM 2 TO RMS 3-5

3 C. 4-4 PR 4-8 PR

ELECTRICAL PULL-BOX

1-1/2 C. 1-8 PR CABLE 1-4 PR CABLE MTG RM 3 MTG RM 4 REMOTE EQUIP RM 6

ELECTRICAL PULL-BOX

MTG RM 1 MTG RM 2

MTG 5 MTG 6

MTG 7 MTG 8

REMOTE EQUIP RM 7

TO RMS 8-10

3 C. 4-4 PR 4-8 PR

ELECTRICAL PULL-BOX

ELECTRICAL PULL-BOX

MTG 21 MTG 22

MTG 23 MTG 24

MTG 25 MTG 26

MTG 27 MTG 28 TO HALLS 4/3

2-1/2 C. 1-16 PR 2-4 PR

ELECTRICAL PULL-BOX

PANEL 1 PANEL 2

ELECTRICAL PULL-BOX

PNL 4 PNL 5

1-1/2 C. 1-12 PR 1-4 PR

EXHIBIT HALL 1

PANEL 3

EXHIBIT HALL 2

TO BALLROOMS 1-4

Traditional Analog System



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Again, theres a bit more equipment involved, but a much simpler infrastructure. With a CobraNet system, one 1000 ft. long " conduit connects the North remote equipment closets together and another connects the South equipment closets. This is a total of 2000 of " conduit plus 4000 ft. of 1-1/2" conduit to connect the I/O panels to the remote equipment closets. Conduit and cable costs total $30,000. With the addition of labor, the total infrastructure cost is $36,700.CENTRAL CONTROL LOCATIONANALOG PROCESSING EQUIPMENT

REMOTE EQUIP RM 1

REMOTE EQUIP RM 2

CN CN

100BASE -FX SWITCH3/4C. (TYP) 4 STRAND FIBRE

100BASE -FX SWITCH1-1/2C. 1-8 PR 1-4 PR MTG 1

CN CN

100BASE -FX SWITCH

CN CN

TO RMS 3-5

MTG 3 MTG 4

MTG 5 MTG 6

MTG 7 MTG 8 TO RMS 9/10

ANALOG AUDIO LINES (TYP)

MTG 2

CN CN

100BASE -FX SWITCH

100BASE -FX SWITCH

CN CN

100BASE -FX SWITCH

CN CN

EQUIP RM 6

EQUIP RM 7 MTG 3 MTG 4

CN CN

100BASE -FX SWITCH

MTG RM 1 MTG RM 2

MTG 5 MTG 6

MTG 7 MTG 8 TO HALLS 3/44

100BASE -FX SWITCH CN CN 100BASE -FX SWITCH

CN CN

P1 P2 P3

100BASE -FX SWITCH

CN CN

P4

EXHIBIT HALL EQUIP RM 1 TO BALLROOMS 1-4

EXHIBIT HALL EQUIP RM 2

P5 2-1/2C. 1-16 PR 1-8 PR

CobraNet System



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ETHERNET: HISTORY AND BACKGROUND IntroductionIn 1972 Robert Metcalfe and his Xerox Palo Alto Research Center (PARC) colleagues developed the first experimental Ethernet system to interconnect the Xerox Altos. This was initially called the Alto Aloha Network, but in 1973 Metcalfe changed the name to "Ethernet.

The First EthernetThe first Ethernet functioned as shared media, with the available bandwidth shared amongst all of the stations connected to the network. Although the transmissions from any one station are received by all stations, only one station may transmit at a time. A collision is a situation that occurs when two or more devices on the network attempt to send a signal along the same wire at the same time. The result of a collision is generally a garbled message. Collisions are a fact of life in a shared media Ethernet network, and under most circumstances should not be considered a problem. As a result, the network requires a mechanism to both manage access to the network, and to prevent or recover from collisions. CSMA/CD Carrier Sense, Multiple Access with Collision Detection, or CSMA/CD, is the media access method used by Ethernet. Carrier Sense means that network stations with data to transmit should first listen to determine if another station is sending data. If another station is talking, this station will wait until there is no carrier signal present. Multiple Access means that Ethernet provides a number of stations the opportunity to transmit on the single cable. When a station has completed its transmission it is allowed to immediately make another access to the medium. Collision Detection refers to the process by which stations detect simultaneous transmissions. 2001 Peak Audio, Inc.

Fig. 2.1: The First Ethernet

Ethernet History and Background

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T

T

node

node

node

node

2km

Fig. 2.2: Network Diameter

If the distance between the two end stations, known as the network diameter, is very large (greater than 2000 meters) there is a possibility that data received at one of those stations may be corrupted. If both devices begin to transmit at the same time, small data packets (the entire packet is already on the transmission line) collide in the middle of the line and get sent on to the other station as corrupted data. The transmitting station will never realize that a collision has occurred because the transmission was completed prior to the collision. As a result of this potential for problems, the minimum frame size in Ethernet is specified such that, based on the speed of propagation of electrical signals in copper media, an Ethernet device is guaranteed to remain in transmit mode, and therefore detecting collisions, long enough for a collision to propagate back to it from the farthest point on the wire from it. Ethernet standards do not allow data packets smaller than 512 bits to be transmitted. (This is standard for both huband switch-based networks, and for both 10BASE and 100BASE networks). Any data packets smaller than 512 bits are automatically padded to equal 512 bits.

Ethernet Packet StructureDestination Address (6 Bytes) Source Address (6 Bytes) Protocol (2 Bytes) Payload (46-1500 Bytes) FCS (4 Bytes)

Fig. 2.3: Ethernet Packet

The figure to the left shows a standard Ethernet packet. The destination address is the MAC address of the receiving station, while the source address is the MAC address of the transmitting device. (MAC addresses will be discussed in a later section.) The protocol is a publicly registered numeric identifier issued by IEEE that signifies what kind of payload the receiver should expect. For example, the ID for CobraNet is 8819; and the ID for the Internet is 801.

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The FCS or frame check sequence provides a 99.9% probability that if 1 bit of data is corrupted, the frame check will detect the error This is sometimes referred to as a CRC, or Cyclical Redundancy Check.

The Ethernet StandardEthernet was standardized by the IEEE in 1980, as IEEE 802.3. The initial standard was based on 10mm 50 ohm coax, but this was followed quickly by many different variations: 10BASE-5: the original coax cable Ethernet 10BASE-2: used a thinner (5mm) 50-ohm coaxial cable instead of the 10mm used in 10BASE-5. Hence the name Thin Ethernet. The transmission rate is also 10Mbps. Maximum cable segment length is 185 meters. A standard T-type BNC connector (barrel connector) is typically used to attach two cable segments directly to the network interface card (NIC), thus allowing a daisy chain configuration in connecting the stations. A 10BASE-2 network supports a maximum of 30 stations per cable segment. 1BASE-2: the same as 10BASE-2, but running at only 1Mbps 10BROAD-36: a broadband implementation of Ethernet.

Out of all of these incarnations, only 10BASE-5 and 10BASE-2 saw much wide use. Both are uncommon now.




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T

T

node

node

node

node

Fig. 2.4: Backbone Topology

These early Ethernet networks were implemented in what is called a backbone topology. Although it looks simple and distributed, the backbone is the weak point in these networks. The problem is that a missing terminator or a faulty connection between a node and the cable can take down the whole network. This could be described as a distributed single point of failure, a worst case scenario in that not only is the cable a single point of failure, but when it fails, the location of the failure can be very difficult to find. The solution was to collapse the backbone. The resultant collapsed backbone topology is referred to as a star topology. And thus, 10BASE-T was born

node

node

hub

node

nodeFig. 2.5: Star Topology

10BASE-T 10BASE-T was introduced in 1990. It uses durable and inexpensive twisted pair cable and a repeater hub as a substitute for the coax backbone. This incarnation of Ethernet is still a shared media with the same maximum network diameter limitations. The packet structure also remained the same. Two pairs are required for each station: one pair for incoming traffic and one for outgoing. Home runs from each station to a central concentrator carry data to and from each station. With 10BASE-T, the vulnerable shared media portion of the network is now safely hidden in the closet and is not strewn across the office. In a 10BASE-T system, a wiring fault typically takes out network service only to a single station. Using this topology, stars may be connected to other stars to create much larger networks. In the star of stars figure to the left, note that there are no loops in the network. If a loop was introduced in the network, data would endlessly re-circulate, completely bringing down the network.

Fig. 2.6: Star of Stars




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The CAT3 cable is restricted to a maximum distance of 100m. To grow the network to the maximum 2km size supported, fiber is used. This is known as 10BASE-F.

node

node

hub

node

100BASE Ethernet100BASE Ethernet supports data transfer rates of up to 100 Mbps (100 Megabits per second). Because it is 10 times faster than Ethernet, it is often referred to as Fast Ethernet. Like Ethernet, Fast Ethernet is based on the CSMA/CD media access method, it has the same packet size, and also the same format as the 10Base-X variety. In moving from 10BASE to Fast Ethernet, only the bit rate was increased. Therefore 10 times the number of bits may now fit on the transmission line. Rather than changing the minimum packet size requirements, the maximum allowed diameter was decreased in order to maintain accurate collision detection. This limits Fast Ethernet repeater networks to a 200 meter network diameter. FAST ETHERNET VARIATIONS Like Ethernet, Fast Ethernet also has a number of variations: 100BASE-T4: Fast Ethernet using all 4 pairs of a Category 3 cable. 100BASE-TX: Fast Ethernet using only 2 pairs in a Category 5 cable. This is the most common Fast Ethernet. 100BASE-FX: Fast Ethernet over multimode fiber.node

node

node

hub

node

node

Fig. 2.7: 10BASE-F




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Gigabit EthernetThe latest incarnation of Ethernet is Gigabit Ethernet or 1000BASE Ethernet. It also has the same packet format as the 10 and 100BASE varieties, but a larger minimum packet size. This allows the network diameter limitation to remain at 200 meters. The mechanism that makes a 200-meter network diameter possible is known as carrier extension. Whenever a gigabit network adapter transmits a frame less than 512 bytes long, the gigabit MAC sends out a special signal called a carrier extension (all the while continuing to monitor for collisions). The Ethernet frame and carrier extension will last for a minimum of 512 bytes, which is equivalent in time to transmitting 64 bytes at 100 Mbps. If the gigabit MAC detects a collision during this period, it reacts just like its conventional counterparts, sending a jam signal and telling the offending stations to back off and try again. GIGABIT ETHERNET VARIATIONS 1000BASE-SX: (S is for short wavelength) defines optical transceivers or physical layer devices for laser fiber cabling. Targeted for multimode fiber only, 1000BASE-SX transceivers are less costly than those found in products implementing the long wavelength specification 1000Base-LX: (L for long wavelength) also defines optical transceivers or physical layer devices for laser fiber cabling. 1000BASE-LX is specified for use on either multimode or single-mode fiber. 1000BASE-LH: (LH for long haul) is a multi-vendor specification where each vendor has a set of transceivers covering different distances. Although it is not an IEEE standard, many vendors are working toEthernet History and Background



Page 25

interoperate with IEEE 1000BASELX equipment. 1000BASE-T: Gigabit Ethernet over Category 5 cable. It uses all 4 pairs, and can be up to 100 meters long.

The FutureWireless Ethernet or IEEE 802.11 is gaining popularity and is becoming more widely used. It is also a shared media and has a bandwidth of 11Mbps. 50 Mbps versions are in the works and should be available shortly. Powering Fast Ethernet devices over CAT5 cable has been accomplished by a number of manufacturers. Work is underway to standardize how this is done so that equipment from different manufacturers may interoperate. One application will be telephones which communicate over Ethernet using Voice over Internet Protocol (Voice/IP).



Audio Networks

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SELECTING THE CORRECT CABLE FOR A PROJECT IntroductionThis section will provide information about designing and installing network cable plants. It will present a general overview of cable plant considerations that will help lead to a highquality network installation.

The Cable PlantA typical Ethernet network cable path is shown in the figure to the right. The items that make up the cable plant include: cabling connecting nodes this can be CAT5 or fiber optic cable Wiring closet patch panels Station cables - the cable that runs from node to wall plate Wall plates - the data or information outlet close to the nodeDCE Patch Cord - Store Bought, Stranded CAT5 Main Run - Field Terminated, Solid Core CAT5 Patch Panel or Wall Plate DTE Patch Panel or Wall Plate

It is considered good design practice to include the intermediate patch points as shown. This gives the cable plant operator flexibility in accommodating expansion and configuration changes. There are two main types of cables used in audio networks: CAT5 cable and fiber optic cable. The following sections will describe these cable types, as well as the issues associated with each.

Fig.3.1: Typical Cable Plant

CAT5CAT5 is inexpensive unshielded twisted pair (UTP) data grade cable. It is very similar to ubiquitous telephone cable but the pairs are more tightly twisted. It should be noted that not all CAT5 cable is UTP. Shielded CAT5 also exists but is rare due to its greater cost and a much shorter distance limitations than UTP CAT5. 2001 Peak Audio, Inc. Selecting the Correct Cable


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DISTANCE LIMITATIONS On Fast Ethernet systems, CAT5 cable runs are limited to 100 meters due to signal radiation and attenuation considerations. A CAT5 run in excess of 100 meters may be overly sensitive to electromagnetic interference (EMI). CONNECTORS CAT5 cable is terminated with an RJ-45 connector. There are two different types of RJ-45s. There is the "bent tyne" connector, intended for use with solid core CAT5, and then there is the "aligned tyne" connector used with stranded CAT5 cable. Errors can occur when using incorrect cable/connector combinations. The diagrams to the left show an end on view of a single contact in a modular connector. The aligned tyne contact (far left) must be able to pierce through the center of the wire, therefore it can only be used on stranded wire. The bent tyne contact has the 2 or 3 tynes offset from each other to straddle the conductor; therefore, it can be used on solid or stranded wire. Cable openings in modular connectors can be shaped for flat, oval or round cable. CAT5 cable does not usually fit properly into connectors made specifically for flat cable. Cheap modular connectors may not have proper gold plating on the contacts, but instead only have a gold flash. Without proper plating, the connectors may quickly wear and corrode, causing unreliable connections. AMP makes quality modular connectors, but the secondary crimp point is located in a different position from everyone elses connectors. Figure 3.4 shows a standard crimper and an AMP plug. Point A is the primary crimp point, and should fold the primary strain relief tab in the plug down so that it locks against the cable jacket. At the opposite end of the plug, the contacts are pressed down into the individual conductors. The B secondary crimp point secures the 2001 Peak Audio, Inc. Selecting the Correct Cable

Fig. 3.2: Aligned and Bent Tyne Contacts

Fig. 3.3: Flat and Oval Cable Openings

Fig. 3.4: Standard Crimper and AMP Plug


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individual conductors so that they do not pull out of the contacts. AMP puts this crimp in a different location from all other manufacturers. If AMP connectors are used in a standard crimper they will either jam, bend or break the crimp die. If standard connectors are used in an AMP crimper, the die will usually break. Once either type of plug is properly crimped onto the wire, they are interchangeable and will work properly in any mating jack. Some plugs are made with inserts which guide the wires. These can make the job of properly assembling the connector easier. Some connectors made with inserts may also provide better performance than CAT5.Fig. 3.5: Plug with Insert

TWISTS AND TERMINATIONS CAT5 cable consists of 4 twisted pairs of wires. One pair is used to transmit (pins 1 and 2) and another pair is used to receive (pins 3 and 6). The remaining two pairs are terminated but unused. Although only 2 of the 4 twisted pairs are used for Ethernet, it is important that all pairs be terminated, and that the proper wires be twisted together. Standards set forth by EIA/TIA 568A/568B and AT&T 258A define the acceptable wiring and color-coding schemes for CAT5 cables. These are different from the USOC wiring Standards used in telecommunications. When terminating CAT5 UTP cable, it is important that the natural twist of each pair be carried through as close as possible to the point of termination. EIA/TIA standard 568B requires no more than 1/2 inch be left untwisted for Category 5. More than 1/2 inch of untwisted cable will affect performance at high bit rates.

Pin 1 2 3 4 5 6 7 8

Signal

EIA/TIA 568A

EIA/TIA 568B

Ethernet X X X Not Used* Not Used* X Not Used* Not Used*

Transmit White/Green White/Orange + Transmit Green/White Orange/White or Green or Orange Receive White/Orange White/Green + N/A N/A Blue/White or Blue/White or Blue Blue White/Blue White/Blue

Receive Orange/White Green/White or Orange or Green N/A N/A White/Brown White/Brown Brown/White Brown/White or Brown or Brown

*These connections must still be terminated Table 3.1: Wiring/Color Coding for CAT5 Cable


Selecting the Correct Cable


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STRAIGHT-THROUGH VS. CROSSOVER CABLES Two types of CAT5 cables are typically used in a network: the straight-through cable and the crossover cable. The difference between the two has to do with how the conductors terminate to the RJ-45 connector at each end of the cable. The tables to the right show the RJ-45 connector "pin-outs" for CAT5 crossover and straight-through cables. A straight-through cable is used to connect a network device (or DTE), to a switch. DTEs, switches and other networking devices will be discussed in the next section. The transmit pins on the network device connect directly to the receive pins on the switch and vice versa (i.e., pin 1 to pin 1, pin 2 to pin 2, pin 3 to pin 3, etc. as shown in the graphic). Crossover cables are used to connect switches to other switches. In crossover cables, the pins are "swapped" at one end (i.e., pin 1 to pin 3, pin 2 to pin 6, pin 3 to pin1, and pin 6 to pin 2) to allow the transmit of one switch to connect to the receive of the other. It is very easy to tell the difference between a crossover cable and a straight-through cable by looking at the conductors in the RJ-45 connectors. If the wiring is identical at both ends, you are holding a straight-through cable, if it is different, you most likely have a crossover cable. Some switches employ an auto-select crossover feature. This allows the use of either a straight-through or a crossover cable in any port. The switch automatically senses which cable type is in use and adjusts the electronics to suit the cable.

Crossover Cable RJ-45 Pin RJ-45 Pin 1 RX+ 3 TX+ 2 RX6 TX3 TX+ 1 RX+ 6 TX2 RXPin 1

Straight-through Cable RJ-45 Pin RJ-45 Pin 1 TX+ 1 RX+ 2 TX2 RX3 RX+ 3 TX+ 6 RX6 TX-

Fig. 3.6: RJ-45 Connector Pin-outs




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62.5m Core

125m Cladding

CROSSOVER CABLES AND UPLINK PORTS Some hubs and switches contain uplink ports. These ports are intended to serve as a connection to another switch or hub. As such, the uplink port is wired to use a straight-through instead of requiring a crossover cable. On some switches and hubs uplink ports share their connection with an adjacent port, so be sure to read the manufacturers instructions for proper use.

Fiber Optic CableThere are two varieties of fiber: single-mode and multimode, and both may be used in Ethernet network designs. Two fibers are needed to make an Ethernet connection: 1 fiber for transmit, and 1 for receive. Multimode fiber is built of two types of glass arranged in a concentric manner. Multi-mode fiber allows many "modes", or paths, of light to propagate down the fiber optic path. The relatively large core of a multi-mode fiber allows good coupling from inexpensive LEDs light sources, and the use of inexpensive couplers and connectors. Two sizes of multimode fiber are available. 62.5/125m is used primarily in data communications, and 50/100m is used primarily in telecommunications applications. The standard for transmission of 100Mbit Ethernet over 62.5/125m multimode fiber is called 100BASE-FX. 100BASE-FX has a 2 kilometer distance limitation. Single-mode fiber optic cable is built from a single type of glass. The cores ranges from 8-10 m, with 8/125m being the most commonly used. There is only a single path of light through the fiber. While single-mode fiber cable costs approximately the same as a multimode cable, the cost of the optical transmitters and receivers is significantly more for a single-mode installation than multimode. Single-mode fiber has a core diameter that is so small that only a 2001 Peak Audio, Inc. Selecting the Correct Cable

Fig. 3.7: Multimode Fiber

Fig. 3.8: Light Path Through Multimode Fiber

Fig. 3.9: Light Path Through Single-mode Fiber


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single mode of light is propagated. This eliminates the main limitation to bandwidth, but makes coupling light into the fiber more difficult. Although multi-mode fiber has a specific distance limitation of 2km, distance limitations of single-mode fiber vary according to the proprietary system in use. All are in excess of 2km. There is currently no Ethernet standard for single-mode fiber. CONNECTORS There are two common types of fiber optic connectors: SC and ST. The ST or "straight tip" connector is the most common connector used with fiber optic cable, although this is no longer the case for use with Ethernet. It is barrel shaped, similar to a BNC connector, and was developed by AT&T. A newer connector, the SC, is becoming more and more popular. It has a squared face and is thought to be easier to connect in a confined space. The SC is the connector type found on most Ethernet switch fiber modules and is the connector of choice for 100Mbit and Gigabit Ethernet. A duplex version of the SC connector is also available, which is keyed to prevent the TX and RX fibers being incorrectly connected. There are two more fiber connectors that we may see more of in the future. These are the MTRJ and MTP. They are both duplex connectors and are approximately the size of an RJ-45 connector.

Duplex SCFig. 3.10: Fiber Connector Types

Condition

5kVA

Unshielded power lines or electrical 5 in. (12.7 equipment in proximity cm) to open or non-metal pathways Unshielded power lines or electrical 2.5 in. (6.4 equipment in proximity cm) to grounded metal conduit pathway Power lines enclosed in a grounded metal conduit (or equivalent N/A shielding) in proximity to grounded metal conduit pathway Transformers and electric motors Fluorescent lighting

12 in. (30.5 cm) 24 in. (61 cm)

6 in. (15.2 cm)

12 in. (30.5 cm)

Cabling and Network PerformanceA number of factors can degrade the performance of your Ethernet network, and among these is a poor cable plant. Cabling problems and a susceptibility to EMI can actually lead to packet loss. The following sections present cabling considerations that will help to ensure a high-quality cable plant installation.

6 in. (15.2 cm)

12 in. (30.5 cm)

40 in. (1.02 40 in. (1.02 m) m)

40 in. (1.02 m)

12 in. (30.5 12 in. (30.5 cm) 12 in. (30.5 cm) cm)

Table 3.2: Proximity Specifications




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Similar to audio cabling, there are certain proximity specifications to be aware of when designing your network cable routes. The adjoining chart lists some CAT5 proximity guidelines. For fiber optic cable runs, proximity is not a concern due to fiber's inherent immunity to EMI and RFI. CAT5 AND CABLE TIES Another factor that can degrade the installation quality is snug cable ties. Ties should never be pulled tight enough to deform the outer jacket of the UTP cable. Doing so produces a slight change in the cable impedance at the point under the tie, which could lead to poor network performance. If tight ties are used at even intervals down the cable length, the performance degradation is even worse. PULL FORCE AND BEND RADIUS A common myth is that fiber optic cable is fragile. In fact, an optical fiber has greater tensile strength than copper or steel fibers of the same diameter. It is flexible, bends easily and resists most of the corrosive elements that attack copper cable. Some optical cables can withstand pulling forces of more than 150 pounds! The fact is, Category 5 cable may be more fragile than optical cables: tight cable ties, excessive untwisting at the connector, and sharp bends can all degrade the cables performance until it no longer meets Category 5 performance requirements. While fiber may have a reputation for being more fragile than it really is, it still has limitations, and as such, care should be taken when installing both CAT5 and fiber optic cables. Here are some guidelines for CAT5 and fiber optic bend radius and pull force limitations: For CAT5 Cable: All UTP cables have pull force limitations much lower than those tolerated in the audio industry. If more than 25 pounds of force is applied to CAT5 cable during installation, it 2001 Peak Audio, Inc. Selecting the Correct Cable


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may no longer meet specification. Like most audio cables, UTP cables also have minimum bend radius limitations. Generic CAT5 allows a minimum bend radius of 4 times the cable diameter or 1" for a 1/4" diameter cable. Unless specified otherwise by the manufacturer, it is fairly safe to use this as a guideline. Note that this is a minimum bend radius and not a minimum bend diameter. For Fiber Optic Cable: The bend radius and pull force limitations of fiber vary greatly based on the type and number of fibers used. If no minimum bend radius is specified, one is usually safe in assuming a minimum radius of 10 times the outside diameter of the cable. For pulling force, limitations begin at around 50 lbs and can exceed a more than 150 pounds. In general, it is recommended that you check with the fiber manufacturer for specifications on the specific cable used in your installation.




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Sources for More InformationOne good way to keep up with current happenings in the field of cabling is to subscribe to Cabling Installation & Maintenance magazine. They are also a good source for training videos and reference books.cim.pennwellnet.com/home/home.cfm

BiCSi (pronounced bic-see) publishes a Telecommunications Distribution Methods Manual which serves as the reference for their Registered Communications Distribution Designer Certification exam. They also Certify 3 levels of Installers. They offer training courses, videos, and books, and hold an annual convention.www.bicsi.org/

This paper by Belden shows why a "neat" installation may not be a good idea, and defines some of the important tests done on UTP data cabling. It also shows that neatly bundling cables together (as is considered good practice in the audio industry) may actually degrade the performance of UTP cables.http://bwcecom.belden.com/college/ Techpprs/ieacectp.htm

While it's not your typical FAQ page, the Data Communications Cabling FAQ provides a good source for technical information on cabling, connectors, standards and testing. It also provides a thorough listing of contact information for manufacturers and standards organizations.alpha.mhpcc.edu/net_class/net_lan/ faq.html



Audio Networks

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SELECTING THE CORRECT HARDWARE FOR A PROJECT IntroductionThere are 3 classes of items that make up a network. These are: cable plant data terminal equipment (DTE) data communications equipment (DCE) In the graphic to the right, dashed lines indicate the network cable plant, and shading represents DTEs. The DCEs in this case are made up entirely of Ethernet switches. Although this section will introduce data terminal equipment, it will focus primarily on data communications equipment.Switch Switch

Fig. 4.1: Audio Network

Data Terminal EquipmentData terminal equipment refers to any devices that produce and/or consume data on a network. DTEs are sometimes referred to as network nodes, and include things like PCs and network printers, just to name a few. CobraNet devices and other networked audio devices are also data terminal equipment. Well discuss audio networking devices in greater detail in a later unit.

Data Communications Equipment and Ethernet HardwareTypically, data communications equipment is classified as either Workgroup Equipment or Interconnect components. Workgroup equipment includes devices such as hubs and switches, while interconnect components include routers, bridges and core switches. NETWORK INTERFACE CARD A network interface card, or NIC, is used to enable a PC to connect to and access a network. NICs are network physical layer specific, meaning that a PC containing an 2001 Peak Audio, Inc. Selecting the Correct Hardware


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AppleTalk NIC cannot function on an Ethernet network. REPEATER HUBS A repeater hub is a multi-port Ethernet device that receives a signal, re-clocks it, boosts it and sends it out all ports. A loose audio analogy to a simple repeater hub would be a mix minus system. A data signal arriving at the receive pair of any port is electrically regenerated and reproduced out all other ports on the hub via the transmit pairs. As a result, hub networks may only be wired in a star topology. If a ring topology were used, the data would continue circulating endlessly! Because the data received by a repeater hub is simply transmitted to all devices on the network, repeater networks must share bandwidth. Bandwidth is the amount of data that can be transmitted within a fixed period of time, and is typically expressed in Megabits per second or Mbps. On a Fast Ethernet network, this means that there is 100Mbps of bandwidth available network-wide when using repeaters. Repeater hubs operate in half-duplex mode. They cannot transmit and receive data simultaneously. A repeater hub network is considered to be a collision domain. A collision domain is a half-duplex Ethernet system whose elements are all part of the same timing domain. This means that if two or more devices on a repeater network attempt to transmit at the same time, a collision occurs. When this happens both devices cease transmission, wait a random period of time and then attempt to retransmit the data.

Port 1

Port 2

Port 3

Fig. 4.2: Repeater Hub

Hub

Fig. 4.3: Star Topology


Selecting the Correct Hardware


Page 37

A protocol is required to enable each device in the collision domain to: share the available network bandwidth detect when another device is transmitting detect when a collision has occurred The protocol used is known as CSMA/CD or Carrier Sense Multiple Access with Collision Detect. Because there is no designated control station on an Ethernet network, each device must operate independently. The CSMA/CD protocol equips each device on the network with the same set of rules, allowing all stations connected to the shared media to cooperate. Even though signals travel very quickly on an Ethernet network, they still require a finite amount of time to propagate over the entire network. The longer the cables, the longer the time it takes the signals to travel from one end of the system to another. For CSMA/CD to work properly, maximum cable lengths and overall network diameter limitations must be observed. Network diameter is defined as the longest cable distance between any two DTEs on the network. With allowances for propagation times through up to two hubs and the receiver, Fast Ethernet typically supports a maximum network diameter of just over 200 meters on a repeater hub network. Network designers and administrators are quickly abandoning the use of repeaters. This is due primarily to the dramatic decrease in the cost of Ethernet switching hubs. For this reason, the rest of this course will focus primarily on networks utilizing switching hubs.

Component

Round Trip Propagation Bit Periods

Optical Fiber (single mode and multimode) CAT5 cable Receiver Class I Hub Class II Hub

1.000/meter 1.112/meter >=100 >=140 >=92

Table 4.1: Propagation time for selected network components




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node

node Collision Domain

hub

node

SWITCHING HUBS Based on Ethernet bridging technology, a switching hub (or switch) is a multi-port device that filters and forwards data packets between devices on a network. Unlike a standard repeater hub, a switch is able to read the destination address of each data packet and then forward the packet to the correct port. This intelligence in the switch means that a given device receives only those packets addressed to it. Another benefit is that switches can transmit and receive data simultaneously. Switches are full-duplex devices, and each port operates independently. For example, if the network operates at 100Mbps, each switch port can handle 100Mbps of data in each direction simultaneously. This provides a total bandwidth of 200Mbps over a single link! While each link between switches still has a bandwidth limit, the total bandwidth available in the network is much larger in a switched network. The overall network bandwidth can be easily increased by simply adding more switches to the network. Because each switch port operates independently in a full-duplex configuration, collisions do not occur on switched networks. Therefore, the CSMA/CD protocol used for repeater hubs is not required. This lifts the network diameter limitation, allowing the construction of larger networks. When used with repeaters, switches enable the creation of separate collision domains. Although the propagation of the collision is interrupted, switches are still able to pass data from one collision domain to another. Switches enable the connection of LANs that operate at different speeds, as well as other networking technologies such as Gigabit Ethernet and ATM.

node

switch

switch

node

node

hub

node Collision Domain

node

Fig. 4.4: Full Duplex




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How does a switch accomplish all of this? A switch is made up of four main parts: ports a lookup table (LUT) FIFO queues switch fabric The ports on a switch can each operate in fullduplex mode, and multiple ports can be carrying on conversations simultaneously. This not only increases the amount of bandwidth available on the network, but makes a switch much more efficient than a repeater hub. The lookup table (LUT) is what gives a switch the ability to send packets out to selective ports. The LUT contains a list of each switch port and the MAC address of the device(s) attached to each port. The MAC address or media access control address is an IEEE issued hardware address that uniquely identifies each node on a network. As network nodes send packets, the switch reads each incoming packets source MAC address. If the address is not contained in the lookup table, it is added so that the switch will later know where to send data addressed to that device. Over time, the switch learns the MAC addresses of all the devices attached to each of its ports. Switches can also unlearn. If no packets are received from a particular source address after a period of time (typically five minutes), or it is suddenly found on a different port, the source address is deleted from the LUT. This allows the flexibility to move nodes to different segments of the network without the worry that the lookup table may contain inaccurate information.

LUT

Switch Cloud

1 Tx Rx Tx

2 Rx

3 Tx Rx

Fig. 4.5: Switching Hub




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node

node

switch

node

node

node

Switches also have the ability to distinguish between different types of addresses: If an incoming packets destination address is a unicast address (point-topoint), the packet is only sent out the port to which the destination device is connected. If an incoming packets destination address is a multicast address (one-tomany), the packet is sent out all ports.node

node

switch

node

Fig. 4.6: Unicast Address

If the destination address is not contained in the LUT, the packet is sent out all ports. This is known as flooding, and guarantees that the packet with the unknown destination address will reach the correct node. The first-in-first-out (FIFO) queue provides short-term buffer memory for each port. Each packet is queued here prior to transmission, which allows the switch to handle the transmission of multiple packets to the same destination device. The switch fabric is the means used to move packet data from the input of one port on the switch to the output of one or more ports. The LUT and switch fabric work together to route packets through the switch. The LUT knows where the packets need to go and the switch fabric gets them there. Managed vs. Unmanaged Switches

node

node

switch

node

node

node

node

switch

node

node

Fig. 4.7: Multicast Address

Switches can be managed or unmanaged. Unmanaged switches are plug and play, and contain few, if any, configuration options. Typically, any configuration on an unmanaged switched is performed through the use of dipswitches. Managed switches offer a great deal of configurability options, as well as several fault tolerance options such as Spanning Tree Protocol, Link Aggregation and Meshing. Managed switches also provide network administrators with information about the operation of the switch itself, including traffic reports, bandwidth utilization and port




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configuration information that can be used for analysis and troubleshooting. The interface for switch configuration is typically a web browser or a telnet interface. Many of the advanced networking topics we will discuss later, are only available with the use of managed switches. Switched Network Topologies Switched networks may be wired in a star topology similar to repeater networks. Simply replacing the hub with a switch automatically increases the available bandwidth from 100Mbps network wide to 100Mbps per link in each direction. Switches may also be wired in a ring, as long as the switches participating in the ring support protocols that prevent loop conditions. These include Spanning Tree Protocol, aggregation, or Hewlett Packards proprietary Meshing technology, which are only available on managed switches. HUBS VS. SWITCHES Because the cost of Ethernet switching hubs has decreased dramatically over the last few years, there really is no reason not to use switches! Switches allow the construction of large networks with great distances between the nodes, they allow fault tolerance to be incorporated into the network design, can provide great channel capacity and even greater channel capacity, like Gigabit. BRIDGES AND ROUTERS Although this course focuses primarily on the use of switches for audio network design, some background information on interconnect components is worthwhile. Routers connect LANs. Although they are protocol dependent, meaning they can only be used to connect LANs using the same Layer 3 networking protocol, routers are independent of Layer 2 and often contain a combination of physical port types (i.e., Ethernet, token-ring, ISDN, etc.). A router first strips the Layer 2 2001 Peak Audio, Inc.

Switch

Switch

Switch

Switch

Fig. 4.8: Ring Topology



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headers off of all packets it receives, and examines the Layer 3 header to determine how to route the packet. It then generates a new Layer 2 header as appropriate for the destination physical layer and sends the packet. A bridge is two-port device that is also used to connect LANs. Bridges are protocol independent, and work only at Layer 2. For example, an Ethernet bridge only sees Ethernet packets and doesnt care about the Layer 3 protocol carried within the packet. Bridges do not analyze packets - they simply forward the data, and as such, they perform faster than routers. Ethernet switches, which are based on bridging technology, used to be referred to as multi-port bridges. But because switching technology has advanced tremendously in recent years, bridges arent so common anymore. In fact, bridges are now sometimes referred to as two-port switches.

Establishing LinkWhether it be for sending audio signals over long distances, providing immunity from EMI, or due to a lack of cable space in existing conduits, many network designs require the use of fiber. To produce a successful design, it is important to understand how network devices such as switches, hubs and media converters interact with one another.Normal Link Pulses 10Mbps Hub 10/100 NIC

Fig. 4.9: Normal Link Pulses

10MBPS NETWORKS When 10Mbps network devices are not transmitting data, the transmission line becomes idle. If data transmissions are not resumed within a certain period of time, the device begins transmitting Normal Link Pulses (NLPs). These pulses allow the presence of a non-transmitting 10Mbit device to be recognized by other devices on the network (i.e., enables link), and also serve to distinguish a 10Mbps device from 100Mbps or 10/100 devices.




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100MBPS DEVICES Unlike their 10Mbps counterparts, 100Mbps devices exhibit activity even when no data is being transmitted. This activity is called a carrier, and is a distinguishing characteristic of a 100Mbps network device. AUTO-NEGOTIATING DEVICES CobraNet devices and many other 10/100 network devices go through a process called auto-negotiation before establishing link. Auto-negotiation is a low bit rate form of communication during which one device tells another device if it is capable of full- or halfduplex operation and whether to connect at 10Mbps, 100Mbps or Gigabit rates. This information is conveyed using Fast Link Pulses (FLPs), which are simply a sequence of Normal Link Pulses that come together to form a message. If the auto-negotiation process results in a 10Mbit connection, the network devices transmit NLPs when idle. If a 100Mbps connection was negotiated, carrier signals are transmitted. Any device capable of auto-negotiation also implements parallel detection. Parallel detection enables link to be established with a non-negotiating, fixed speed network device prior to the detection of Fast Link Pulses. The state diagram below shows how network connections between devices of differing capabilities are established. Notice that a device can never parallel detect to a fullduplex link. This is important, as autonegotiation does not take place over fiber optic cable. Over fiber, carrier signals are used to establish link, which means that if a fullduplex connection over fiber is required, this must be manually configured.

100Mbps Hub

Carrier

10/100 NIC

Fig. 4.10: Carrier

10/100 Switch

Fast Link Pulses

10/100 NIC

Fig. 4.11: Auto-negotiation

no link Carrier FLP LP

100 HD

10 HD 100 FD

negotiating

10 FD

Parallel Detect Key to Abbreviations: 100: 10: HD: FD: 100Mbit 10Mbit Half Duplex Full Duplex

Fig. 4.12: Link State Diagram




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cobranet_cntraining2[1]

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base ethernet

ethernet standard

gigabit ethernet variations

fast ethernet variations

ethernet packet structure

network requirements

audio networks page

overview peak audio