The following information was obtained from a product catalog from South Hills Datacomm. Ethernet -------- The Ethernet Local Area Network was co-developed by Digital Equipment Corp. (DEC), Intel and Xerox in the early 1980's. In 1983, the IEEE committee adopted the original specification, creating the 802.3 standard. It is by far the most widely installed and supported network to date. The 802.3 standard defines how a device accesses the network and the speed at which the network operates. The accessing scheme dictated by the IEEE 802.3 is the Carrier Sense Multiple Access with Collision Detection (CSMA/CD) method. CSMA/CD is defined as: Carrier Sense (CS) A device listens for a clear channel before transmittion. If the channel is in use (or a carrier is sensed), then the device will delay its transmission. Multiple Access (MA) Many pieces of equipment can be interconnected to a single or common cable, and all have equal access to the cable when a channel is clear. Collision Detection (CD) Since it is possible for more than one device to sense a clear channel and begin transmission at the same time, data collision will occur. When a collision does occur, the devices sense this and stop their transmissions. At this point, each device waits a random length of time and then attempts to retransmit. Also dictated under the 802.3 standard are the types of cabling which should be used. 10 Base 5 - RG-8 type coax, 50 ohm impedance (a.k.a., "Thick Ethernet") 10 Base 2 - RG-58 type coax, 50 ohm impedance (a.k.a., "Thin-wire") 10 Base T - Ethernet over unshielded twisted pair 10 Base F - (Proposed) Ethernet over optical fiber Standard Thick Ethernet: o A standard Ethernet cable can have a maximum length of 500m (1640ft) o Up to 100 transceivers can be attached to a 500m cable length. o Transceivers must be at least 2.5m (8.2ft) apart. Note: To ensure proper spacing, a standard Ethernet cable is premarked every 2.5m. o A transceiver cable is required for each transceiver on the network. o A standard transceiver drop cable can have a maximum length of 50m (165ft). Be advised that some devices have an internal cable equivalency and this should be taken into consideration. To find this internal equivalency, it would be best to consult your user's manual. o When using the more flexible office transceiver cabling, the maximum cable length is 12.5m. o In a standard Ethernet network, you are limited to 101 segments (1 backbone plus 100 branch segments). o The maximum number of stations on a standard Ethernet network is 1024. o Both ends of a standard Ethernet cable segment must be terminated by 50 ohm terminator. o Repeaters are used to continue the signal from one segment to another. This allows the overall cable segment length to be increased. However, data should not pass through more than two repeaters before reaching its final destination. Thin Ethernet: o ThinWire cabling is RG-58 type coax cable. o A ThinWire cable segment should not exceed 185m (606ft). o External transceivers must be at least .5m (16ft) apart. o Both ends of a ThinWire cable segment must be terminated with a 50 ohm terminator. o When directly attached to a station rather than using a transceiver, it is imperative that the "T" connector be used at the workstation. o Up to 30 devices can be attached directly to a 185m cable segment. o A local repeater may be attached to the ThinWire cable to extend the distance. o Data may not pass through more than 2 repeaters, multi-port repeaters or in combination before it reaches its destination. o Each ThinWire cable segment should have at least one end grounded. Never configure the cable in a closed loop. Twisted pair Ethernet: o Twisted pair cabling is unsheilded twised pair (UTP). o Since 10 Base T is wired as a star topology, an active concentrator or hub must be employed. To ensure compatibility with existing or future equipment, be certain your hub complies fully with the 10 Base T and other IEEE 802.3 standards. o Typically you can attach your hub to the network devices in one of two ways: a). Via a 10 Base T media access unit (MAU), also referred to as a 10 Base T transceiver. The 10 Base T transceiver has an RJ-45 jack and a DB-15 male connection for attachment to the AUI port on a standard Ethernet device. b). Direct connection with a 10 Base T patch cord, provided your network device has a built-in 10 Base T transceiver. o 10 Base T requires 4 pair 22-24 AWG solid UTP cable. When selectin new cable, be certain it can handle a maximum data rate of 10 Mbps. Likewise, if you are planning to use existing telephone cabling, verify that it can handle the 10 Mbps maximum data rate. o Although twisted pair cabling is a reliable transmission medium, there are factors that must be considered when using it, such as: a). UTP cabling is inherently sensitive to electromagnetic and radio frequency interference (EMI/RFI), so try to install it as far away as possible from flourescent lights. b). To avoid the possibility of induced spikes or noise, do not install UTP in a consuit with electrical wiring. o 10 Base T is wired according to the AT&T 258A cabling specification; however, only pins 1 & 2 and pins 3 & 6 are used. As a general rule, never try to operate more than one station on any cable drop. Also, it is not recommended to pass voice and data on any single cable drop. o 10 Base T cable drops can be a maximum of 100m (330ft). o No flat satin telephone cable should be used anywhere in the network configuration. o Concentrators or hubs may be daisy chained together via UTP cabling. They may also be attached to optical fiber or standard thick or ThinWire coax backbones.