Copper Media and the ATM Network. Version 2.0

Transcription

1 Copper Media and the ATM Network Version 2.0

2 ATM TO THE DESKTOP The first implementations of ATM, deployed in pilot environments, used fiber optic cable and optical transceivers as the physical medium-dependent interface. Commercial acceptance of ATM has moved the technology out of the controlled environments where a variety of media is available. In addition, the advent of ATM for the PC environment has pushed the technology all the way to the desktop. These events, coupled with advances in physical layer transmission technology, have made ATM over Category 5 unshielded twisted pair (UTP) and Type 1 shielded twisted pair (STP) a reality. Summary: This white paper describes the different types of copper media and offers guidelines for their proper use. The technical details of using copper cabling to install ATM equipment in the LAN environment include information on wire type, impedance, capacitance, attenuation, and distance limitations. Information is also provided on the types of connectors and pin assignments available. Copper Media Types UTP and STP wiring are the most commonly used media types in the LAN environment. Although early implementations of ATM technology were primarily laboratory environments and used fiber optic cable, the commercial acceptance of ATM technology requires compatibility with more widely-used cabling schemes. UTP consists of two or more pairs of insulated wire twisted together and bundled within an insulating jacket. The twists and the insulation provide better performance in two ways. First, they reduce emissions the radiation of the signal into the atmosphere as noise. Second, they reduce susceptibility the ability of the cable to withstand interference from external sources of noise. Two types are typically used in LANs: Category 3 (CAT-3) and Category 5 (CAT-5). CAT-3 UTP is often called telephone wire and is the minimum grade suitable for use in a LAN. CAT-5 UTP is a higher grade and provides better performance at LAN operating speeds. CAT-5 uses better insulation and specifies a minimum of eight twists per foot. CAT-3 has no minimum number of twists per foot. To further improve performance, CAT-5 is also available in a screened version. This is an extra layer of shielding that provides even better emissions and susceptibility characteristics. CAT-5 is quickly becoming the media of choice for LANs operating at speeds ranging from 10 Mbps to 155 Mbps. STP adds a metal shield around the common insulation jacket of the twisted pair. Type 1 STP (IBM Token Ring) cable is the highest grade of twisted pair copper cabling and most common type of STP in use today. 1 Copper Media and the ATM Network

3 Both CAT-5 UTP and Type 1 STP support ATM transmissions at speeds up to 155 Mbps. The following chart summarizes these three types of copper media. A WG C ap ac ita nc e (p F/ ft m ax ) Impedance (ohm s) A ttenua tion (d B/ ft m ax ) N EXT wo rs t p ai r (db min) C at 3 UTP ±1 5% 4 0d 1 6MH z 2 3d 1 6MH z C at 5 UTP ±1 5% 1 00 ±1 5% 1 00 ±1 5% 2 5d 1 6MH z 5 2d MH z 4 0d 1 00 MHz 4 4d 1 6MH z 3 5d MH z 3 2d 1 00 MHz Ty pe 1 STP ±1 5% 3 9d MH z 4 0d 1 6MH z Figure 1: Summary of Cable Specifications Structured Wiring Schemes and ATM Networks The most commonly used wiring scheme, or cabling topology, is known as huband-spoke, or star, topology. ATM networks are also star topology networks. The ATM switch is centrally-located and each desktop is wired directly to the switch. ATM Backbone ForeRunner ASX-200 ATM Switch Figure 2: Typical Hub-and-Spoke (Star) Wiring Configuration WIRING STANDARDS AND SPECIFICATIONS Two sets of standards apply to UTP ATM applications: generic EIA/TIA and ISO standards and ATM Forum physical medium dependent (PMD) specifications. The EIA/TIA 568A Commercial Building Wiring Specification provides guidelines for implementing structured wiring that uses CAT-5 cabling. It also specifies the maximum distance for cable runs to the desktop. 2

4 Generic Cabling Standards EIA/TIA 568A defines three grades of performance for cabling systems. The highest of these grades is Category 5 intended for high speed network applications (e.g., Fast Ethernet or ATM). Most new structured cabling systems are designed to meet CAT-5 performance standards. The ISO specification defines grades of performance classes B, C, and D. Class D is intended for high speed network application support and is similar to CAT-5. ATM Forum Specification for CAT-5 Implementations AF-PHY is the ATM Forum standard for 155 Mbps ATM application support over CAT-5 UTP. It defines the PMD requirements for both 100 ohm CAT-5 UTP and 150 ohm STP support. The equipment signaling methods specifically defined are: transmitter and receiver characteristics, and minimum requirements for cabling to assure robust operation (i.e., bit error rates) for ATM applications. AF-PHY also defines the data rate and line coding technique as Mbps and binary non-return to zero (NRZ). This refers to the data rate transmitted through the PMD interface and the technique used to map the binary data bits to analog signals for transmission over the cable. Connectors Three types of connectors are associated with these cable types: 1) RJ-45 Connectors: These are commonly found on networks that use UTP wiring. Both shielded and unshielded RJ-45 connectors are available. But a shielded RJ-45 connector will work with any type of UTP cabling. Figure 3: RJ-45 Plug and Jack 3 Copper Media and the ATM Network

5 2) DB-9: These are commonly found on networks that use Type 1 STP cabling and are used in conjunction with four-position connectors in Token Ring LAN cabling. The DB- 9 is used on the host adapter because of size constraints on the cutout for the host computer's interface. They support Type 1 STP cabling up to 155 Mbps. Figure 4: DB-9 Plug and Receptacle 3) Four-Position Data Connectors: These are also commonly found on networks that use Type 1 STP cabling. Four position data connectors are used in conjunction with DB-9 connectors in Token Ring LAN cabling. The Data Connectors are commonly used at the wall jack, patch panel, and concentrator end of the Type 1 cable. They can also support Type 1 STP cabling up to 155 Mbps. Guidelines for CAT-5 UTP Installation for ATM Networks 1) Insist on conformance to EIA/TIA 568A specifications. 2) Verify that all components (i.e., cable plant) comply with CAT-5 ratings. This includes connectors, punch down blocks, wall jacks, and patch cords. 3) Cable length should be no more than 100 meters at 155 Mbps. This includes the total length of the first patch cord from the switch to the first patch panel or punch down block, the distance to the wall jack, and the patch cord to the host computer. The maximum horizontal run length is 90 meters, leaving 10 meters (five at each end) for patch cables. (See Figure 5.) Equipment Rack Patch Panel or Punch Down Block End Station Wall Jack 90 Meters 100 Meters 4

6 Figure 5: Copper Media Distance Specifications 4) A maximum of two connections per 100 meters is permitted. This means one punch down block in the wiring closet and one wall jack in the office (or cubicle). The term, "home run cabling," describes cabling that extends from the host connection to the wiring closet equipment rack with no intermediate connections. 5) CAT-5 UTP usually comes with a minimum of four pair per cable. Cabling for 155 Mbps ATM over UTP requires two twisted pairs per connection and no other signals are permitted on unused pairs within the cable. Signals on other pairs can disrupt the data transmissions. 6) Transmissions at 155 Mbps using ATM over CAT-5 UTP meet FCC Class A emissions and susceptibility ratings. The FCC Class A rating is required for commercial installations. The more stringent Class B rating refers to residential installations. Exceptions include businesses located in a residential transition zone or hospital facilities where Class A emissions may interfere with other electronic equipment. In these instances, Type 1 STP or optical fiber may be needed. 7) Insist on end-to-end channel performance testing from your cable installer. FORE Delivers ATM Over CAT-5 UTP FORE provided the industry's first ATM Forum-compliant, CAT-5 UTP interface on both the ForeRunner ASX-200 switch and ForeRunner 200 series host adapters in the first quarter of CAT-5 UTP interfaces are available for FORE s entire line of ATM adapters. The ForeRunner CAT-5 UTP network module provides up to 96 ports of UTP connectivity within the same switch. The ForeRunner ATM switch family s modular design supports a mixture of UTP and fiber interfaces within the same chassis, allowing desktop runs of UTP or fiber and backbone/riser runs of fiber optic cable. 5 Copper Media and the ATM Network

7 APPENDIX RJ-45 Connector Pin Signal Assignments User Device-to-Host Adapter Pin # 1 Transmit + 2 Transmit Not used 7 Receive + 8 Receive - Network Equipment-to-Switch Network Modules Pin# 1 Receive + 2 Receive Not used 7 Transmit + 8 Transmit - DB-9 Connector Pin Signal Assignments User Device-to-Host Adapter Pin # 1 Transmit Not used 5 Receive + 6 Transmit Not used 9 Receive - Shell chassis Network Equipment-to-Switch Network Module Pin# 1 Receive Not used 5 Transmit + 6 Receive Not used 9 Transmit - Shell chassis 6

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