Basic physical layer protocol used by the Digital Signal level 1 (DS1) multiplexing method in North America. A T1 interface operates at a bit rate of 1.544 Mbps and can support 24 DS0 channels.


Physical layer protocol used by the Digital Signal level 3 (DS3) multiplexing method in North America. A T3 interface operates at a bit rate of 44.736 Mbps.


Terminal Access Controller Access Control System Plus. Authentication method for validating users who attempt to access the router using telnet.

tail drop

Queue management algorithm for dropping packets from the input end (tail) of the queue when the length of the queue exceeds a configured threshold. See also RED.


Generic designator for any of several digitally multiplexed telecommunications carrier systems originally developed by Bell Labs and used in North America and Japan.


Tricolor marking. Traffic policing mechanism that extends the functionality of class-of-service (CoS) traffic policing by providing three levels of drop precedence (loss priority or PLP) instead of two. There are two types of TCM: single-rate and two-rate. The JUNOS software currently supports two-rate TCM only. See also trTCM.


Transmission Control Protocol. Works in conjunction with the Internet Protocol (IP) to send data over the Internet. Divides a message into packets and tracks the packets from point of origin to destination.


UNIX packet monitoring utility used by the JUNOS software to view information about packets sent or received by the Routing Engine.

TCP port 179

Well-known port number used by BGP to establish a peering session with a neighbor.


Time-Division Multiplex Access. A type of multiplexing in which two or more channels of information are transmitted over the same link, where the channels take turns to use the link. Each link is allocated a different time interval ("slot" or "slice") for the transmission of each channel. For the receiver to distinguish one channel from the other, some kind of periodic synchronizing signal or distinguishing identifier is required. See also GSM.


Terminal Endpoint Identifier. A terminal endpoint can be any ISDN-capable device attached to an ISDN network. The TEI is a number between 0 and 127, where 0 through 63 are used for static TEI assignment, 64 through 126 are used for dynamic assignment, and 127 is used for group assignment.

Terminal Access Controller Access Control System Plus


Terminal Endpoint Identifier

See TEI.

terminating action

Action in a routing policy or firewall filter that halts the logical software processing of a policy or filter.


Used in a routing policy or firewall filter to segment the policy or filter into small match and action pairs.

Third-generation Partnership Project

See 3GPP.


JUNOS software routing policy match type representing all routes that fall between the two supplied prefixes in the route filter.

Time-Division Multiplex Access


time-division multiplexed channel

A single stream of data separated by intervals of time—signals from telephones and computers.

timeout timer

Used in a distance-vector protocol to ensure that the current route is still usable for forwarding traffic.


Trivial Network Protocol. A Juniper Networks proprietary protocol automatically configured on an internal interface by the JUNOS software. TNP is used to communicate between the Routing Engine and components of the Packet Forwarding Engine, and is critical to the operation of the router.

token-bucket algorithm

Used in a rate-policing application to enforce an average bandwidth while allowing bursts of traffic up to a configured maximum value.


Type of service. The method of handling traffic using information extracted from the fields in the ToS byte to differentiate packet flows.

totally stubby area

OSPF area type that prevents Type 3, 4, and 5 link-state advertisements (LSAs) from entering the non-backbone area.

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.

traffic engineering class

In Differentiated-Services-aware traffic engineering, a paired class type and priority.

traffic engineering class map

In Differentiated-Services-aware traffic engineering, a map among the class types, priorities, and traffic engineering classes. The traffic engineering class mapping must be consistent across the Differentiated Services domain.

traffic shaping

For class of service, a traffic regulation mechanism that controls the traffic going out of an interface in order to match its flow to the speed of the remote, target interface and to ensure that the traffic conforms to policies contracted for it. Traffic adhering to a particular profile can be shaped to meet downstream requirements, thereby eliminating bottlenecks in topologies with data-rate mismatches. A shaper typically delays excess traffic using a buffer, or queuing mechanism, to hold packets and shape the flow when the data rate of the source is higher than expected. See also shaping rate.

transient change

A commit script-generated configuration change that is loaded into the checkout configuration, but not into the candidate configuration. Transient changes are not saved in the configuration if the associated commit script is deleted or deactivated. See also persistent change.

transient interfaces

Interfaces that can be moved from one location in the router to another. All customer-facing interfaces are considered to be transient in nature.

transit area

In OSPF, an area used to pass traffic from one adjacent area to the backbone, or to another area if the backbone is more than two hops away from an area.

transit router

In MPLS, any intermediate router in the LSP between the ingress router and the egress router.

Transmission Control Protocol

See TCP.

transport mode

IPSec mode of operation in which the data payload is encrypted, but the original IP header is left untouched. The IP addresses of the source or destination can be modified if the packet is intercepted. Because of its construction, transport mode can be used only when the communication endpoint and cryptographic endpoint are the same. VPN gateways that provide encryption and decryption services for protected hosts cannot use transport mode for protected VPN communications. See also tunnel mode.

transport plane

See data plane.


Reports significant events occurring on a network device, most often errors or failures. SNMP traps are defined in either standard or enterprise-specific MIBs.

tricolor marking

See TCM.

triggered updates

Used in a distance-vector protocol to reduce the time for the network to converge. When a router has a topology change, it immediately sends the information to its neighbors instead of waiting for a timer to expire.

Triple Data Encryption Standard

See 3DES.

Trivial Network Protocol

See TNP.


Two-rate TCM polices traffic according to the color classification (loss priority) of each packet. Traffic policing is based on two rates: the committed information rate (CIR) and the peak information rate (PIR). Two-rate TCM is defined in RFC 2698, A Two Rate Three Color Marker. See also CIR and PIR.

trunk mode

Layer 2 circuit cell-relay transport mode that allows you to send ATM cells between ATM2 IQ interfaces over an MPLS core network. You use Layer 2 circuit trunk mode (as opposed to standard Layer 2 circuit cell-relay mode) to transport ATM cells over an MPLS core network that is implemented between other vendors' switches or routers. The multiple connections associated with a trunk increase bandwidth and provide failover redundancy. See also AAL5 mode, cell-relay mode, Layer 2 circuits, and standard AAL5 mode.

Tspec object

RSVP message object that contains information such as the bandwidth request of the LSP as well as the minimum and maximum packets supported.


Private, secure path through an otherwise public network.

tunnel endpoint

Last node of a tunnel where the tunnel related headers are removed from the packet, which is then passed on to the destination network.

tunneling protocol

Network protocol that encapsulates one protocol or session inside another. Protocol A is encapsulated within protocol B, such that A treats B as though it were a data-link layer. Tunneling may be used to transport a network protocol through a network which would not otherwise support it. Tunneling may also be used to provide various types of VPN functionality such as private addressing.

tunnel mode

IPSec mode of operation in which the entire IP packet, including the header, is encrypted and authenticated and a new VPN header is added, protecting the entire original packet. This mode can be used by both VPN clients and VPN gateways, and protects communications that come from or go to non-IPSec systems. See also transport mode.

Tunnel PIC

Physical interface card that allows the router to perform the encapsulation and decapsulation of IP datagrams. The Tunnel PIC supports IP-IP, GRE, and PIM register encapsulation and decapsulation. When the Tunnel PIC is installed, the router can be a PIM rendezvous point (RP) or a PIM first-hop router for a source that is directly connected to the router.

tunnel services

Provides the capability of a tunnel PIC on an AS PIC. See Tunnel PIC.

two-rate TCM

See trTCM.

type of service

See ToS.

TX Matrix platform

Routing platform that provides the centralized switching fabric of the routing matrix.