Network Design & Control

              


Ethernet Definitions


10Base-2:
The implementation of the 802.3 standard also known as thinnet. 10Base-2 networks operate over thin coaxial cable at 10 Megabits per second baseband.
10Base-5:
The implementation of the 802.3 standard also known as standard Ethernet or thicknet. 10Base-5 networks run on thick coaxial cable at 10 Megabits per second baseband.
10Base-FL:
The implementation of the 802.3 standard designed to operate over fiber optic cable at 10 Megabits per second baseband.
10Base-T:
The implementation of the 802.3 standard designed to operate over Unshielded Twisted Pair (UTP) cable at 10 Megabits per second baseband.
100Base-X:
The IEEE standard for Fast Ethernet (100 Mbps CSMA/CD).
100Base-TX:
The IEEE Fast Ethernet standard for 100 Mbps Ethernet over category 5 UTP/STP.
100Base-T4:
The IEEE Fast Ethernet standard for 100 Mbps Ethernet over category 3 UTP/STP (N.B. All four pairs must be available for T4 to operate correctly).
100Base-FX:
The IEEE Fast Ethernet standard for 100 Mbps Ethernet over fiber optic cabling.
802.3:
The numerical designation for the IEEE standard governing the use of the CSMA/CD media-access method.
802.3u:
Supplement to the IEEE 802.3 standard which defines 100 Mbps Fast Ethernet.
802.3x:
A draft to 802.3 for Full-Duplex Ethernet (FDX).
802.3y:
A draft supplement to the IEEE 802.3 standard for the operation of 100 Mbps Fast Ethernet over two pairs of category 3 UTP/STP.
802.3z:
A draft to 802.3 for gigabit Ethernet.
Agent:
Refers to all software components running within a manageable device (e.g.: the SNMP tasks, TCP/IP tasks).
ASN.1:
Abstract Syntax Notation One - An OSI programming/ description language used by SNMP to define managed objects.
Attenuation:
The weakening of the signal being transmitted. It is a crucial factor in LAN design and the lengths of cable being used.
Authentication:
A "message" is authentified. For example: Is the community string, and, optionally, the IP address, correct? If one or both is incorrect, an Authentication Failure occurs.
Backbone:
The primary connectivity mechanism of a hierarchical distributed system.
Backplane:
The bus in the back of a hub chassis that connects interface modules.
Bandwidth:
The data-carrying capacity of a transmission medium measured in bits per second (bps) or in cycles per second or Hertz (Hz).
Baseband:
A data-transmission technique that uses the entire bandwidth of a media without modulating a digital signal. Ethernet, Token Ring and ARCnet use baseband transmission. As opposed to broadband.
BNC:
A bayonet-locking connector used on 10Base-2 thinnet coaxial cabling. BNC is an acronym for Bayonet-Neill-Concelman.
Bit Budget:
The "span" of an Ethernet collision domain (i.e. length of cabling, number of repeaters), is limited by Ethernet's bit budget. The bit budget is directly related to the minimum Ethernet frame size (64 bytes or 512 bits), if a device transmits a frame and a collision does not take place within 512 bits, errors may appear on the network (late collisions and fragments). Although the network will continue to operate, performance will be reduced and workstations will timeout. All devices on a network (PC's, repeaters, cabling) take a certain number of bits away from the bit budget.
Bridge:
A networking device, often referred to as MAC level bridges, that connects local or wide area networks using the same or different data-link layer, or Layer 2 of the OSI model, protocol. Two LANs connected in this manner effectively become one LAN.
Broadband:
A data-transmission technique that allows multiple signals to share the bandwidth of a transmission media. Cable TV is a broadband transmission in that signals for multiple TV stations are carried over separate channels. As opposed to baseband.
Bus Topology:
A network architecture in which all the nodes are connected to a single cable which is terminated at each end.
Cascading:
The term used to describe the connection of twisted pair hubs by running twisted pair cable from one hub to another.
Category 3 & 5 Cabling:
Category 3 is a type of UTP/STP cable that can handle signaling up to 16Mhz (16 Mbps). Category 5 can handle signaling up to 100 MHz (100 Mbps). Both Category 3 and Category 5 have been standardized by the EIA/TIA. N.B. If Category 5 is in use, all components (i.e. patch panels, wall boxes, patch cables, etc.) must be Category 5 certified.
Collision:
The term used when the electrical signals from two network devices run into each other triggering a retransmission. When this is detected retransmission is timed so a second collision is not likely.
Collision Domain:
A LAN is a network which spans a limited geographical area. It is further described by the IEEE as a collision domain. A collision domain is a single CSMA/CD network which may consist of two or more Medium-Access Control (MAC) sublayers. MAC sublayers separated by a repeater are within the same collision domain. MAC sublayers separated by a bridge are within different collision domains. Splitting a hub or repeater into separate or multiple collision domains is often incorrectly referred to as "segmentation".
Community Strings:
SNMP's "security". A community string is normally associated with a group of managed objects.
Concentrator:
See Repeater.
Connection-less mode (CL):
A transport service which includes ALL information required. (e.g.: addressing, data transfer and control [error checking]). CL is often termed "robust".
Connection-orientated (CO):
A transport protocol with 3 distinct phases: Establish session, Transfer data, Release session.
Converter:
A device which converts one media type to another (BNC to twisted pair, for example). These devices do not retime data as required by the IEEE 802.3 standard for repeater performance. Use of these devices on a heavy traffic LAN may result in excessive collisions.
CRC:
Cyclical Redundancy Check - The mathematical calculation for checking the number of errors in a message.
Crossover Wiring:
A special twisted pair cable with the transmit and receive functions of the two twisted pairs transposed on one end for connecting (cascading) twisted pair hubs through RJ-45 ports without the ability to disable the internal crossover function.
CSMA/CD:
Carrier-Sense Multiple Access with Collision Detection - The network-access method used by Ethernet networks.
DCE:
Data Communications Equipment - The equipment that sits between end devices (DTE) and the network, establishing, maintaining and terminating the connection in a data conversation. It also provides any encoding or conversion necessary via transceiver/MAU.
Default Gateway:
The IP address of a gateway (usually a router) on the network.
DTE:
Data Terminal Equipment - The end point of a communications link (e.g., workstations, repeater, fileservers, printers). A DTE must connect with a DCE for data conversation.
EIA/TIA:
Electronic Industry Association/Telecommunications Industry Association. A body involved in the setting of various industry standards including those applicable to cabling.
EMI:
Electromagnetic Frequency Interference - Unwanted "noise" created by current-producing devices such as electric motors and fluorescent lights. EMI effects the quality of the signal passing through data transmission medium.
Ethernet:
A 10 megabit per second (Mbps) baseband-type network that uses the contention-based CSMA/CD media access method. Invented by Robert Metcalfe (Now 3COM) at Xerox's Palo Alto Research Center in the mid-1970s.
Ethernet II Frame:
An Ethernet frame format defined by the IEEE. Ethernet II frames are usually associated with the TCP/IP protocol.
Fast Ethernet:
A 100 megabit per second (Mbps) baseband-type network that uses the contention-based CSMA/CD media access method. The new method was presented to the IEEE committee for review in 1994.
Fault Tolerance:
A method of making a LAN resistant to cable or hardware problems. In reference to a LAN, fault tolerance is accomplished with the use of a transceiver/MAU, hub or multiport repeater where each segment can be isolated from others and the rest of the LAN remains up and running with no loss of data.
FDX
Full-Duplex Ethernet. Ethernet (both 10 Mbps and 100 Mbps), without collisions. Since no collisions take place the bit budget of Ethernet is not applicable. Extended distances (when using Single-Mode fiber) can be achieved if Full-Duplex Ethernet is used.
FOIRL:
Fiber Optic Inter Repeater Link - An early implementation of a subset of the 802.3 10Base-FL standard designed to connect fiber optic repeaters at 10 Mbps. This specification has been used by various Ethernet manufacturers to produce network and port interface cards and MAUs/transceivers.
Frame:
A term applied to an Ethernet packet.
Gateway:
An historically INCORRECT term used by the Internet. In reality, a gateway is really a router or bridge which allows connection onto the Internet.
Hot-swapping:
The ability to remove and replace a network device interface without taking the network out of service or powering down the network device.
Heartbeat:
Also known as SQE (Signal Quality Error), a test between the transceiver/MAU and the DTE to ensure that the collision detection circuit in the transceiver/MAU is working. The heartbeat function must be disabled when a transceiver/MAU is attached to a repeater. Every time a transceiver/MAU has successfully completed a transmission, it must send the SQE to the DTE to which it is connected to confirm that the collision detect circuit is functioning properly. This continual "pulsing" is referred to as heartbeat.
Hub:
A wiring concentrator or repeater that brings together the connections from multiple network nodes in a star topology. See also Repeater.
IAB:
Internet Architecture Board - The "top" committee of the Internet. Responsible for overseeing the IETF and IESG.
IANA:
Internet Assigned Numbers Authority - A committee responsible for assigning "numbers" for the Internet suit of protocol (IP addresses, enterprise specific MIBs, etc).
ICMP:
Internet Control Message Protocol - A reporting protocol for the IP component of TCP/IP. ICMP relays messages as to the status of an IP connection.
IEA:
Electronic Industries Association - A professional organization that formulates computer and communications standards in the U.S.
IEEE:
Institute of Electrical and Electronics Engineers - A professional organization that formulates computer and communications standards in the U.S. and works with other standards-setting bodies including the International Standards Organization (ISO).
IEEE 802.3 Repeater MIB:
The IEEE MIB for repeaters and hubs.
IESG:
Internet Engineering Steering Group - The coordinators of IETF and standard setters for the Internet.
IETF:
Internet Engineering Task Force - A task force under supervision of the IAB responsible for answering the "short term" needs of the Internet.
In-band:
The technique of transmitting controlling information over the same LAN the information is controlling.
Internet:
A collection of computer networks all running the Internet suite of protocols. The Internet is the basic foundation for the "information super-highway".
internet:
(with a small "I") A term applied to a group of interconnected networks.
Inter-Repeater Link:
See Link Segment.
IP:
Internet Protocol - A connectionless orientated protocol offering network services.
IP Address:
A unique address assigned to ANY device running TCP/IP.
ISO:
International Standards Organization - An internationally recognized standards body.
Jabber:
An error condition that occurs when an Ethernet network device transmits packets that are larger than the maximum allowable size.
LAN:
See Local Area Network - Collision Domain.
Link Segment:
Electronically continuous piece of a bus consisting of the same cable with only two devices in a point-to-point configuration.
MAC:
Medium Access Control - The lower half of OSI Layer 2 that governs access to the transmission media (e.g.: coaxial, fiber optic or twisted pair cable); the method of determining which device has access to the Ethernet collision domain at any given time.
MAC Interface:
The Ethernet interface used by the intelligence (specifically the SNMP agent) in the network device for communications to/from another device.
Managed Object:
A term applied to a unit of management information (e.g.: the status of Board 1 Port 1 is a managed object).
MAU
Medium Attachment Unit - Also known as a transceiver and not to be confused with a Token Ring MAU (Media Access Unit). An Ethernet device for transmitting and receiving data that often provides data packet collision detection as well. It can either be an internal or external feature of a network device such as network interface card, repeater, hub or concentrator. Internal MAUs are built into the network device; external MAUs usually plug directly onto the AUI port of the device. A multi-port MAU, or transceiver, allows a number of computers/workstations to be attached to a single connection on the Ethernet bus and each port performs the standard transceiver functions.
MIB:
Management Information Base - The general term for a database of objects managed within a network.
MIB Variable:
See Managed Object.
Multi-Mode Fiber:
The most common type of fiber optic cabling used in network installations. Typically, multi-mode has a core diameter of 62.5 microns and an outer cladding diameter of 125 microns. Nearly all fiber based networking hardware (repeaters, switches, LAN cards etc.) are multi-mode.
Netmask:
Used by the TCP/IP protocol to decide how the network is broken up into sub-networks.
Network Interface Card
- An adapter card providing the physical connection between a computer and the network medium.
NMS:
Network Management Software - A term applied to ANY SNMP compliant management software. Not to be confused with NetWare Management Services from Novell.
Node:
A point in a network where service is provided, service is used, or communications channels are interconnected (e.g.: a workstation, a fileserver, etc.).
Non-volatile RAM:
Memory which holds its information even when main power is turned off. Usually, non-volatile RAM is backed up via a battery.
Octet:
Eight bits make an octet. Many MIBs have a managed object for counting the number of octets received by the MAC, the port or the index.
Out-of-band:
The technique of transmitting controlling information over a separate channel to the LAN the information is controlling. This allows access to network devices even when the network is not functioning.
Packet:
A collection of bits comprising data and control information including source and destination node addresses, formatted for transmission from one node to another.
PDS:
Packet Driver Specification - A defined driver structure usually used in conjunction with a higher level protocol (e.g.: TCP/IP)
PDU:
Protocol Data Unit - A term applied to the user data and control information transmitted by an SNMP manageable device or SNMP management station.
Port:
The entrance and exit point for information going into and out of a network device.
Promiscuous Mode:
The MAC interface on the device that will record/capture ALL packets on the collision domain, regardless to the fact that the packet may NOT be destined to this MAC.
Protocol:
A standardized set of rules specifying the packet format, timing, sequencing and/or error checking for data transmission.
Protocol Stack:
Several protocols that are stacked on top of each other to form a layered structure in which each protocol utilizes the services provided by the layer below and provides services to the layer above.
Repeater
A device that regenerates and amplifies signals to extend transmission distance. It also links multiple segments of an Ethernet network in either a bus or star topology. Fully 802.3 compliant repeaters regenerate and retime the signal of each packet of information and automatically partition and isolate faulty segments when collisions occur on the network. Repeaters, hubs and concentrators all technically perform the same basic function.
RFC:
Request For Comment - A document describing an Internet protocol (e.g.: RFC1155 is the "core" document for SNMP).
RFC1155 SMI:
Structure and identification of Management Information. The core RFC for SNMP compliant devices.
RFC1157 SNMP:
Definition of the SNMP command set and PDU.
RFC1212 Concise MIB definition:
The RFC outlining how MIBs should be structured.
RFC1213 Management Information Base II:
The Internet Standard MIB. The minimum MIB requirement in order to be called SNMP compatible.
RFC1271 RMON MIB:
Remote MONitor MIB. A MIB designed for monitoring and diagnosing traffic on a collision domain.
RFC1398:
MIB for "Ether-like" interfaces.
RFI:
Radio Frequency Interference - Unwanted "noise" created by current-producing devices such as electric motors and fluorescent lights. RFI effects the quality of the signal passing through some data transmission medium.
RMON:
Remote MONitor - The specification for gathering SNMP information from an RMON compliant network device.
Router:
A device which provides intelligent connections between networks. Routers operate at the network layer (Layer 3) of the OSI model and are responsible for making decisions about which paths through a network the transmitted data will use.
RS232-C:
An IEA standard definition for the 25-pin interface linking DTEs and DCEs. RS232-C is suitable for both synchronous and asynchronous communications.
RS422:
An IEA recommended standard definition for extending an RS232C interface beyond the 50 foot limit.
RS485:
Similar to RS422 but is used in multi-point application where up to 64 network devices may be interconnected.
Segment:
An electronically continuous portion of a network, usually consisting of the same coaxial cable with multiple devices attached.
Single-Mode Fiber: (SMF)
A type of fiber that uses a single path for light transmission (i.e. the light is not reflected within the core). Single-Mode supports greater distances than multi-mode. Typically, Single-Mode fiber may support distances from between 2Km up to 20Km. The distance supported is a factor of the loss budget of the cable vs. the power budget of the Single-Mode transmitter.
SGMP:
Simple Gateway Monitoring Protocol - The forerunner of SNMP. SGMP was developed by the Internet community to manage the gateways which provide access to the Internet.
SNMP:
Simple Network Management Protocol - The protocol governing network management and monitoring of network devices and their functions.
SNMPv2:
Version 2 of the SNMP Protocol. The next release of SNMPv2 adds extra security, commands and statistics.
Socket:
A unique number defined by the TCP/IP protocol indicating what type of services or packet the frame is composed of. (e.g.: socket 161 is a UDP/SNMP socket)
SQE :
Signal Quality Error - Also know as heartbeat, a test between the transceiver/MAU and the DTE to ensure that the collision detection circuit in the transceiver/MAU is working. The heartbeat function must be disabled when a transceiver/MAU is attached to a repeater. If a transceiver/MAU, while transmitting, detects a collision, the transceiver/MAU sends the SQE signal to the repeater, or node, to which it is connected. Also see Heartbeat
Star Topology:
A network architecture in which nodes are connected to a central device such as a hub or concentrator.
STP:
Shielded Twisted Pair - Cabling with metal-backed mylar, plastic or PVC covering to protect it from EMI and RFI. STP cable offers better noise protection than UTP (Unshielded Twisted Pair) cabling.
Subnet:
A physically distinct network identified by its IP address.
Subnet-mask:
A 32-bit number used by IP to identify subnets.
Subnet-number:
The part of the IP address which identifies a certain subnet.
TCP:
Transmission Control Protocol - A connection orientation transport protocol.
TCP/IP:
Transmission Control Program/Internet Protocol - A general term applied to the transport suite developed by the Internet.
Transceiver:
Also known as a MAU and not to be confused with a Token Ring MAU (Media Access Unit). An Ethernet device for transmitting and receiving data that provides data packet collision detection as well. It can either be an internal or external feature of a network device such as network interface card, repeater, hub or concentrator. Internal MAUs are built into the device; external MAUs usually plug directly onto the AUI port of the device. A multi-port MAU, or transceiver, allows a number of computers/workstations to be attached to a single connection on the Ethernet bus and each port performs the standard transceiver functions.
UDP:
User Datagram Protocol - A connectionless orientated transport protocol. UDP is the transport protocol used by SNMP.
UTP:
Unshielded Twisted Pair - Cabling with insulation material like that commonly used with telephone cabling but without a covering to protect it from EMI and RFI. The cable consists of at least two conductors twisted together six twists per inch to minimize the effects of electromagnetic radiation.
Wiring Closet:
Central location for terminating and routing onsite wiring systems.