Glossary
A
AAL
ATM adaptation layer. A series of protocols enabling various types of traffic, including voice, data, image, and video, to run over an ATM network.
ADM
Add/drop multiplexer. SONET functionality that allows lower-level signals to be dropped from a high-speed optical connection.
ANSI
American National Standards Institute. The United States' representative to the ISO.
ARP
Address Resolution Protocol. Protocol for mapping IP addresses to MAC addresses.
AS
Autonomous system. Set of routers under a single technical administration. Each AS normally uses a single interior gateway protocol (IGP) and metrics to propagate routing information within the set of routers. Also called routing domain.
ASIC
Application-specific integrated circuit. Specialized processors that perform specific functions on the router.
ATM
Asynchronous Transfer Mode. A high-speed multiplexing and switching method utilizing fixed-length cells of 53 octets to support multiple types of traffic.
autonomous system
B
backplane
Forms the rear of the FPC card cage. Provides data transfer, power distribution, and signal connectivity.
bandwidth
The range of transmission frequencies a network can use, expressed as the difference between the highest and lowest frequencies of a transmission channel. In computer networks, greater bandwidth indicates faster data-transfer rate capacity.
Bellcore
Bell Communications Research. Research and development organization created after the divestiture of the Bell System. It is supported by the regional Bell holding companies (RBHCs), which own the regional Bell operating companies (RBOCs).
BERT
Bit error rate test. A test that can be run on a T3 interface to determine whether it is operating properly.
BGP
Border Gateway Protocol. Exterior gateway protocol used to exchange routing information among routers in different autonomous systems.
bit error rate test
BITS
Building Integrated Timing Source. Dedicated timing source that synchronizes all equipment in a particular building.
Border Gateway Protocol
broadcast
Operation of sending network traffic from one network node to all other network nodes.
bundle
Collection of software that makes up a JUNOS software release.
C
CE device
Customer edge device. Router or switch in the customer's network that is connected to a service provider's provider edge (PE) router and participates in a Layer 3 VPN.
CFM
Cubic feet per minute. Measure of air flow in volume per minute.
channel service unit
CIDR
Classless interdomain routing. A method of specifying Internet addresses in which you explicitly specify the bits of the address to represent the network address instead of determining this information from the first octet of the address.
class of service
CLEC
(Pronounced "see-lek") Competitive Local Exchange Carrier. Company that competes with the already established local telecommunications business by providing its own network and switching.
CLEI
Common language equipment identifier. Inventory code used to identify and track telecommunications equipment.
CLI
Command-line interface. Interface provided for configuring and monitoring the routing protocol software.
community
In BGP, a group of destinations that share a common property. Community information is included as one of the path attributes in BGP update messages.
confederation
In BGP, a group of systems that appears to external autonomous systems to be a single autonomous system.
constrained path
In traffic engineering, a path determined using RSVP signaling and constrained using CSPF. The ERO carried in the packets contains the constrained path information.
core
The central backbone of the network.
CoS
Class of service. A group of privileges and features assigned to a particular service.
CPE
Customer premises equipment. Telephone or other service provider equipment located at a customer site.
craft interface
Mechanisms used by a Communication Workers of America craftsperson to operate, administer, and maintain equipment or provision data communications. On a Juniper Networks router, the craft interface allows you to view status and troubleshooting information and perform system control functions.
CSU/DSU
Channel service unit/data service unit. Channel service unit connects a digital phone line to a multiplexer or other digital signal device. Data service unit connects a DTE to a digital phone line.
customer edge device
D
daemon
Background process that performs operations on behalf of the system software and hardware. Daemons normally start when the system software is booted, and they run as long as the software is running. In the JUNOS software, daemons are also referred to as processes.
data circuit-terminating equipment
data-link connection identifier
data service unit
Data Terminal Equipment
dcd
The JUNOS software interface process (daemon).
DCE
Data circuit-terminating equipment. RS-232-C device, typically used for a modem or printer, or a network access and packet switching node.
default address
Router address that is used as the source address on unnumbered interfaces.
denial of service
dense wavelength-division multiplexing
DHCP
Dynamic Host Configuration Protocol. Allocates IP addresses dynamically so that they can be reused when they are no longer needed.
Dijkstra algorithm
DIMM
Dual inline memory module. 168-pin memory module that supports 64-bit data transfer.
direct routes
DLCI
Data-link connection identifier. Identifier for a Frame Relay virtual connection (also called a logical interface).
DoS
Denial of service. System security breach in which network services become unavailable to users.
DRAM
Dynamic random-access memory. Storage source on the router that can be accessed quickly by a process.
drop profile
Drop probabilities for different levels of buffer fullness that are used by RED to determine from which queue to drop packets.
DSU
Data service unit. A device used to connect a DTE to a digital phone line. Converts digital data from a router to voltages and encoding required by the phone line. See also CSU/DSU.
DTE
Data Terminal Equipment. RS-232-C interface that a computer uses to exchange information with a serial device.
DVMRP
Distance Vector Multicast Routing Protocol. Distributed multicast routing protocol that dynamically generates IP multicast delivery trees using a technique called reverse path multicasting (RPM) to forward multicast traffic to downstream interfaces.
DWDM
Dense wavelength-division multiplexing. Technology that enables data from different sources to be carried together on an optical fiber, with each signal carried on its own separate wavelength.
Dynamic Host Configuration Protocol
E
ECSA
Exchange Carriers Standards Association. A standards organization created after the divestiture of the Bell System to represent the interests of interexchange carriers.
EGP
Exterior gateway protocol, such as BGP.
EIA
Electronic Industries Association. A United States trade group that represents manufacturers of electronics devices and sets standards and specifications.
EMI
Electromagnetic interference. Any electromagnetic disturbance that interrupts, obstructs, or otherwise degrades or limits the effective performance of electronics or electrical equipment.
explicit path
export
To place routes from the routing table into a routing protocol.
F
FEAC
Far-end alarm and control. T3 signal used to send alarm or status information from the far-end terminal back to the near-end terminal and to initiate T3 loopbacks at the far-end terminal from the near-end terminal.
Flexible PIC Concentrator
forwarding information base
forwarding table
JUNOS software forwarding information base (FIB). The JUNOS routing protocol process installs active routes from its routing tables into the Routing Engine forwarding table. The kernel copies this forwarding table into the Packet Forwarding Engine, which is responsible for determining which interface transmits the packets.
FPC
Flexible PIC Concentrator. An interface concentrator on which PICs are mounted. An FPC inserts into a slot in a Juniper Networks router. See also PIC.
FRU
Field-replaceable unit. Router component that customers can replace onsite.
H
HDLC
High-level data link control. An International Telecommunication Union (ITU) standard for a bit-oriented data link layer protocol on which most other bit-oriented protocols are based.
hold time
Maximum number of seconds allowed to elapse between the time a BGP system receives successive keepalive or update messages from a peer.
host subsystem
Provides routing and system-management functions of the router. Consists of a Routing Engine and an adjacent Control Board (CB).
I
IANA
Internet Assigned Numbers Authority. Regulatory group that maintains all assigned and registered Internet numbers, such as IP and multicast addresses. See also NIC.
ICMP
Internet Control Message Protocol. Used in router discovery, ICMP allows router advertisements that enable a host to discover addresses of operating routers on the subnet.
IDE
Integrated Drive Electronics. Type of hard disk on the Routing Engine.
IEC
International Electrotechnical Commission. See ISO.
IEEE
Institute of Electronic and Electrical Engineers. International professional society for electrical engineers.
IETF
Internet Engineering Task Force. International community of network designers, operators, vendors, and researchers concerned with the evolution of the Internet architecture and the smooth operation of the Internet.
IGMP
Internet Group Membership Protocol. Used with multicast protocols to determine whether group members are present.
IGP
Interior gateway protocol, such as IS-IS, OSPF, and RIP.
import
To install routes from the routing protocols into a routing table.
interface routes
Routes that are in the routing table because an interface has been configured with an IP address. Also called direct routes.
IP
Internet Protocol. The protocol used for sending data from one point to another on the Internet.
IS-IS
Intermediate System-to-Intermediate System protocol. Link-state, interior gateway routing protocol for IP networks that also uses the shortest-path first (SPF) algorithm to determine routes.
ISO
International Organization for Standardization. Worldwide federation of standards bodies that promotes international standardization and publishes international agreements as International Standards.
ISP
Internet service provider. Company that provides access to the Internet and related services.
ITU
International Telecommunications Union (formerly known as the CCITT). Group supported by the United Nations that makes recommendations and coordinates the development of telecommunications standards for the entire world.
J
jitter
Small random variation introduced into the value of a timer to prevent multiple timer expirations from becoming synchronized.
K
kernel forwarding table
L
label-switched path (LSP)
Sequence of routers that cooperatively perform MPLS operations for a packet stream. The first router in an LSP is called the ingress router, and the last router in the path is called the egress router. An LSP is a point-to-point, half-duplex connection from the ingress router to the egress router. (The ingress and egress routers cannot be the same router.)
label switching
label-switching router
link
Communication path between two neighbors. A link is up when communication is possible between the two end points.
link-state PDU (LSP)
Packets that contain information about the state of adjacencies to neighboring systems.
LSP
See label-switched path (LSP) and link-state PDU (LSP).
LSR
Label-switching router. A router on which MPLS and RSVP are enabled and is thus capable of processing label-switched packets.
M
mask
MBone
Internet multicast backbone. An interconnected set of subnetworks and routers that support the delivery of IP multicast traffic. The MBone is a virtual network that is layered on top of sections of the physical Internet.
MED
Multiple exit discriminator. Optional BGP path attribute consisting of a metric value that is used to determine the exit point to a destination when all other factors in determining the exit point are equal.
mesh
Network topology in which devices are organized in a manageable, segmented manner with many, often redundant, interconnections between network nodes.
MIB
Management Information Base. Definition of an object that can be managed by SNMP.
MPLS
Multiprotocol Label Switching. Mechanism for engineering network traffic patterns that functions by assigning to network packets short labels that describe how to forward them through the network. Also called label switching. See also traffic engineering.
MTBF
Mean time between failure. Measure of hardware component reliability.
MTU
Maximum transfer unit. Limit on packet size for a network.
multicast
Operation of sending network traffic from one network node to multiple network nodes.
Multiprotocol Label Switching
N
neighbor
Adjacent system reachable by traversing a single subnetwork. An immediately adjacent router. Also called a peer.
NET
Network entity title. Network address defined by the ISO network architecture and used in CLNS-based networks.
Network Time Protocol
NIC
Network Information Center. Internet authority responsible for assigning Internet-related numbers, such as IP addresses and autonomous system numbers. See also IANA.
NSAP
Network service access point. Connection to a network that is identified by a network address.
n-selector
Last byte of a nonclient peer address.
NTP
Network Time Protocol. Protocol used to synchronize computer clock times on a network.
O
OC
Optical Carrier. In SONET, Optical Carrier levels indicate the transmission rate of digital signals on optical fiber.
OSI
Open System Interconnection. Standard reference model for how messages are transmitted between two points on a network.
OSPF
Open Shortest Path First. A link-state IGP that makes routing decisions based on the shortest-path-first (SPF) algorithm (also referred to as the Dijkstra algorithm).
P
package
A collection of files that make up a JUNOS software component.
Packet Forwarding Engine
The architectural portion of the router that processes packets by forwarding them between input and output interfaces.
PCI
Peripheral Component Interconnect. Standard, high-speed bus for connecting computer peripherals. Used on the Routing Engine.
PCMCIA
Personal Computer Memory Card International Association. Industry group that promotes standards for credit card-size memory or I/O devices.
PDU
Protocol data unit. IS-IS packets.
PE router
Provider edge router. A router in the service provider's network that is connected to a customer edge (CE) device and that participates in a Virtual Private Network (VPN).
peer
An immediately adjacent router with which a protocol relationship has been established. Also called a neighbor.
PFE
Physical Interface Card
PIC
Physical Interface Card. A network interface-specific card that can be installed on an FPC in the router.
PIM
Protocol Independent Multicast. A protocol-independent multicast routing protocol. PIM Sparse Mode routes to multicast groups that might span wide-area and interdomain internets. PIM Dense Mode is a flood-and-prune protocol.
PLP
policing
Applying rate limits on bandwidth and burst size for traffic on a particular interface.
PPP
Point-to-Point Protocol. Link-layer protocol that provides multiprotocol encapsulation. It is used for link-layer and network-layer configuration.
preference
Desirability of a route to become the active route. A route with a lower preference value is more likely to become the active route. The preference is an arbitrary value in the range 0 through 255 that the routing protocol process uses to rank routes received from different protocols, interfaces, or remote systems.
primary interface
Router interface that packets go out when no interface name is specified and when the destination address does not imply a particular outgoing interface.
Protocol-Independent Multicast
provider edge router
provider router
Router in the service provider's network that does not attach to a customer edge (CE) device.
Q
QoS
Quality of service. Performance, such as transmission rates and error rates, of a communications channel or system.
quality of service
R
RADIUS
Remote Authentication Dial-In User Service. Authentication method for validating users who attempt to access the router using Telnet.
Random Early Detection
rate limiting
RBOC
(Pronounced "are-bock") Regional Bell operating company. Regional telephone companies formed as a result of the divestiture of the Bell System.
RDRAM
RAMBUS dynamic random access memory.
RED
(Pronounced "red") Random Early Detection. Gradual drop profile for a given class that is used for congestion avoidance. RED tries to anticipate incipient congestion and reacts by dropping a small percentage of packets from the head of the queue to ensure that a queue never actually becomes congested.
Resource Reservation Protocol
RFC
Request for Comments. Internet standard specifications published by the Internet Engineering Task Force.
RFI
Radio frequency interference. Interference from high-frequency electromagnetic waves emanating from electronic devices.
RIP
Routing Information Protocol. Distance-vector interior gateway protocol that makes routing decisions based on hop count.
routing domain
Routing Engine
Architectural portion of the router that handles all routing protocol processes, as well as other software processes that control the router's interfaces, some of the chassis components, system management, and user access to the router.
routing table
Common database of routes learned from one or more routing protocols. All routes are maintained by the JUNOS routing protocol process.
rpd
JUNOS software routing protocol process (daemon). User-level background process responsible for starting, managing, and stopping the routing protocols on a Juniper Networks router.
RPM
Reverse path multicasting. Routing algorithm used by DVMRP to forward multicast traffic.
RSVP
Resource Reservation Protocol. Resource reservation setup protocol designed to interact with integrated services on the Internet.
S
SAP
Session Announcement Protocol. Used with multicast protocols to handle session conference announcements.
SAR
Segmentation and reassembly. Buffering used with ATM.
SDH
Synchronous Digital Hierarchy. CCITT variation of SONET standard.
SDP
Session Description Protocol. Used with multicast protocols to handle session conference announcements.
SDRAM
Synchronous dynamic random access memory.
secure shell
shortest-path-first algorithm
simplex interface
An interface that assumes that packets it receives from itself are the result of a software loopback process. The interface does not consider these packets when determining whether the interface is functional.
SNMP
Simple Network Management Protocol. Protocol governing network management and the monitoring of network devices and their functions.
SONET
Synchronous Optical Network. High-speed (up to 2.5 Gbps) synchronous network specification developed by Bellcore and designed to run on optical fiber. STS-1 is the basic building block of SONET. Approved as an international standard in 1988. See also SDH.
SPF
Shortest-path first, an algorithm used by IS-IS and OSPF to make routing decisions based on the state of network links. Also called the Dijkstra algorithm.
SSH
Secure shell. Software that provides a secured method of logging in to a remote network system.
SSRAM
Synchronous Static Random Access Memory.
STM
Synchronous Transport Module. CCITT specification for SONET at 155.52 Mbps.
STS
Synchronous Transport Signal. Synchronous Transport Signal level 1. Basic building block signal of SONET, operating at 51.84 Mbps. Faster SONET rates are defined as STS-n, where n is a multiple of 51.84 Mbps. See also SONET.
subnet mask
Number of bits of the network address used for host portion of a Class A, Class B, or Class C IP address.
Switch Interface Board
sysid
System identifier. Portion of the ISO nonclient peer. The sysid can be any 6 bytes that are unique throughout a domain.
T
TCP
Transmission Control Protocol. Works in conjunction with Internet Protocol (IP) to send data over the Internet. Divides a message into packets and tracks the packets from point of origin to destination.
ToS
traffic engineering
Process of selecting the paths chosen by data traffic in order to balance the traffic load on the various links, routers, and switches in the network. (Definition from http://www.ietf.org/internet-drafts/draft-ietf-mpls-framework-04.txt.) See also MPLS.
tunnel
Private, secure path through an otherwise public network.
type of service
U
unicast
Operation of sending network traffic from one network node to another individual network node.
UPS
Uninterruptible power supply. Device that sits between a power supply and a router (or other piece of equipment) the prevents undesired power-source events, such as outages and surges, from affecting or damaging the device.
V
vapor corrosion inhibitor
VCI
Vapor corrosion inhibitor. Small cylinder packed with the router that prevents corrosion of the chassis and components during shipment.
VCI
Virtual circuit identifier. 16-bit field in the header of an ATM cell that indicates the particular virtual circuit the cell takes through a virtual path. Also called a logical interface. See also VPI.
virtual circuit identifier
virtual path identifier
Virtual Router Redundancy Protocol
VPI
virtual path identifier. 8-bit field in the header of an ATM cell that indicates the virtual path the cell takes. See also VCI.
VRRP
Virtual Router Redundancy Protocol. On Fast Ethernet and Gigabit Ethernet interfaces, allows you to configure virtual default routers.
W
wavelength-division multiplexing
WDM
Wavelength-division multiplexing. Technique for transmitting a mix of voice, data, and video over various wavelengths (colors) of light.
weighted round-robin
WRR
Weighted round-robin. Scheme used to decide the queue from which the next packet should be transmitted.