Glossary
T
112 terms.
- T.140
An ITU-T standard that defines how text conversation sessions work, including how to encode text, control elements, and handle character sequences.
Like I'm five The official rules for how real-time text messages should be sent and received.
- T.38
An ITU-T international standard that defines procedures for sending real-time facsimile (fax) documents between Group 3 fax machines over IP networks, using either TCP or UDP as the transport protocol.
Like I'm five A standard for sending faxes over the internet in real-time.
- TACACS+
A protocol for authentication, authorization and accounting (AAA) used to administer routers, network access servers and similar devices from central servers.
Like I'm five A central guard who decides who may log into network equipment and keeps a record of what they do.
- Tag-length-value
A way of packing data as a code (the tag), a count of bytes (the length) and then the bytes themselves (the value). A reader can skip any item it does not understand by using the length.
Like I'm five Each item says what it is, how long it is, and then gives the thing, so you can skip the ones you do not need.
Used in RFC 1395 RFC 2131 RFC 2132 RFC 2516 RFC 2868 RFC 2910 RFC 3212 RFC 3331 RFC 3784 RFC 3847 RFC 4171 RFC 4430 RFC 4446 RFC 5061 RFC 5130 RFC 5410 RFC 5857 RFC 6320 RFC 6395 RFC 6839 RFC 7035 RFC 7271 RFC 7401 RFC 7552 and 32 more
- Tail drop
A queue management discipline that accepts packets until a maximum queue length is reached and then drops each newly arriving packet until the queue has room again.
Like I'm five When the line is full, the newest person to arrive is turned away.
- Target list
The ordered list of targeted field names a cache uses for its caching policy, from most to least applicable. The cache uses the first listed field that is valid and non-empty.
Like I'm five The list of notes a helper listens to, in the order it checks them.
- TCP
The Transmission Control Protocol. It provides a reliable, ordered, full-duplex byte stream between two programs on top of IP, using sequence numbers, acknowledgments, retransmission and a window.
Like I'm five A mail service that numbers every page, checks they all arrived and puts them back in order.
Used in RFC 42 RFC 60 RFC 87 RFC 238 RFC 270 RFC 298 RFC 661 RFC 675 RFC 761 RFC 766 RFC 771 RFC 772 RFC 773 RFC 774 RFC 776 RFC 781 RFC 782 RFC 784 RFC 788 RFC 793 RFC 794 RFC 800 RFC 801 RFC 813 and 598 more
- TCP Control Block
The data structure that holds the state and parameters of a TCP connection, including sequence numbers, window sizes, and connection state. Deleting it terminates the connection.
Like I'm five The information your computer keeps about one conversation.
- TCP Friendly Rate Control (TFRC)
A congestion control mechanism that adjusts sending rate more smoothly than TCP does, reducing data loss while maintaining fairness with TCP flows.
Like I'm five A way to slow down that's nicer to the network and applications than TCP's abrupt stop-and-go.
- TCP segment
The unit of data TCP sends: a TCP header followed by some bytes of the application's stream, carried inside one IP datagram.
Like I'm five One envelope in a long series of envelopes that together carry your whole story.
Used in RFC 793 RFC 879 RFC 983 RFC 1323 RFC 1337 RFC 2018 RFC 2351 RFC 2385 RFC 2415 RFC 2488 RFC 2581 RFC 2647 RFC 2883 RFC 3042 RFC 3390 RFC 3649 RFC 4022 RFC 5044 RFC 5482 RFC 5681 RFC 5926 RFC 5961 RFC 6191 RFC 6349 and 15 more
- TCP Urgent notification
A TCP facility that signals the receiver ahead of the normal flow of data that something special is in the stream. Telnet combines it with the Data Mark command to make the Synch signal.
Like I'm five A tap on the shoulder that gets through even when a long queue is waiting.
Used in RFC 764 RFC 793 RFC 854 RFC 1282 RFC 2147 RFC 2675 RFC 4413 RFC 6897 RFC 7414 RFC 7560
- TCP/UDP port
A 16-bit number that tells the receiving host which application or conversation a TCP or UDP packet belongs to. NAPT rewrites these numbers to tell sessions apart.
Like I'm five A room number that tells the mail which person in the house it is for.
Used in RFC 783 RFC 854 RFC 1204 RFC 1288 RFC 1340 RFC 1413 RFC 1906 RFC 2722 RFC 2746 RFC 2818 RFC 2940 RFC 3022 RFC 3195 RFC 3261 RFC 3912 RFC 4171 RFC 4707 RFC 4992 RFC 4993 RFC 5097 RFC 5428 RFC 5440 RFC 5460 RFC 6057 and 16 more
- TE link
A traffic engineering link is a subinterface capable of carrying MPLS traffic engineered traffic. It abstracts the properties of a link for routing and signaling.
Like I'm five A road lane group that the traffic planners treat as one unit.
- TE-Class
A pair of a Class-Type and a preemption priority allowed for that Class-Type. A router can be configured with up to 8 of them.
Like I'm five A team plus how important that team is allowed to be.
- Telepresence
A kind of video conferencing in which rooms with several cameras, screens and microphones try to make remote participants feel present together.
Like I'm five A video call set up so well it feels like everyone is in the same room.
- Telnet
A protocol for remote login that carries a user's keyboard and screen to a command interpreter on another host over one TCP connection.
Like I'm five A long extension cord for your keyboard and screen, so you can use another computer from far away.
Used in RFC 15 RFC 33 RFC 96 RFC 97 RFC 98 RFC 100 RFC 106 RFC 110 RFC 111 RFC 112 RFC 123 RFC 130 RFC 131 RFC 137 RFC 138 RFC 139 RFC 140 RFC 146 RFC 158 RFC 165 RFC 166 RFC 176 RFC 183 RFC 189 and 260 more
- Template
An ordered list of field types and lengths that tells a receiver how to read the data records that follow. Each template is identified by a Template ID.
Like I'm five The column headings that tell you what each number in a row means.
- Template Record
A description of the ordered fields that make up a data record. Collectors need it to read the records that follow.
Like I'm five A form that says which boxes are on the sheet and in what order.
- Temporal scalability
Encoding a video stream in layers so that frames of higher layers can be dropped, leaving a lower frame rate that still decodes properly.
Like I'm five Making a video so you can skip some pictures and it still plays, only less smoothly.
- Temporary address
An IPv6 address meant to be used for a short time, to address privacy concerns. It contrasts with a public address, which is stable.
Like I'm five A throwaway nickname you use for a while so people cannot easily follow you around.
- Teredo
A tunneling protocol that lets a node behind one or more IPv4 NATs obtain IPv6 connectivity by carrying IPv6 packets over UDP. It uses Teredo servers as helpers.
Like I'm five A way to send new-style internet mail through the old-style postal system, even from behind a router.
- Teredo bubble
A minimal IPv6 packet with no payload (next header 59) that Teredo clients and relays send to create a mapping in a NAT.
Like I'm five A tiny empty message sent just to prop open a door in the router.
- Termination
A logical entity on a Media Gateway that sources and/or sinks media or control streams, such as a telephone line or an RTP flow. Terminations are placed into Contexts to be connected to each other.
Like I'm five One end of a call, like a single phone line or a single internet audio stream.
- Test vector
A set of inputs and expected outputs used to verify that an implementation of a cryptographic algorithm is correct.
Like I'm five A known correct answer you use to check if your code works.
- Textual convention
A named data type defined once in a MIB module so that many objects, in that module or others, can reuse the same syntax and meaning.
Like I'm five A shared label with a fixed meaning that everyone agrees to use, like the same traffic light colors everywhere.
Used in RFC 1213 RFC 1903 RFC 2465 RFC 2579 RFC 2851 RFC 3291 RFC 3419 RFC 3595 RFC 3705 RFC 3796 RFC 3805 RFC 3808 RFC 3811 RFC 4001 RFC 4181 RFC 4268 RFC 4706 RFC 4780 RFC 4836 RFC 5017 RFC 5131 RFC 5542 RFC 6340 RFC 6643 and 2 more
- TFTP
The Trivial File Transfer Protocol. A very small file-transfer protocol over UDP that is simple enough to fit in a boot ROM, so diskless machines use it to download a boot image.
Like I'm five A tiny delivery service that can only fetch one file at a time but is easy to carry around.
Used in RFC 783 RFC 840 RFC 906 RFC 913 RFC 951 RFC 1123 RFC 1350 RFC 1497 RFC 1782 RFC 1783 RFC 1784 RFC 1785 RFC 2021 RFC 2090 RFC 2132 RFC 2347 RFC 2348 RFC 2349 RFC 3617 RFC 4639 RFC 5859 RFC 5970 RFC 7440
- Third-party call control (3pcc)
A SIP technique in which one party sets up and controls a media session between other parties, for example connecting a user agent to a transcoder.
Like I'm five One person arranges a call between two others and stays in charge of setting it up.
A cookie set by a server other than the site the user is visiting, for example by an ad network whose content is embedded in the page. It lets that server recognize the same user across different sites.
>Like I'm five A ticket handed out by a stranger whose picture is on the page you are looking at.
- Three-way handshake
The SYN, SYN-ACK, ACK exchange that opens a TCP connection and lets both sides agree on their initial sequence numbers.
Like I'm five Hello, hello back, and OK, before you start talking.
Used in RFC 675 RFC 761 RFC 793 RFC 827 RFC 908 RFC 916 RFC 964 RFC 1337 RFC 1379 RFC 1948 RFC 2140 RFC 2267 RFC 2678 RFC 3038 RFC 3360 RFC 3373 RFC 3390 RFC 3540 RFC 4101 RFC 4340 RFC 4614 RFC 5303 RFC 5382 RFC 5596 and 21 more
- Threshold signature
A digital signature scheme where a private key is split into shares, and a minimum number of shares (the threshold) must be combined to create a valid signature.
Like I'm five A signature that requires multiple keys to work, like a safe that needs two different keys turned at the same time.
- Throughput
The amount of data a system can handle per unit of time. In device benchmarking it is the highest rate at which no frames are dropped.
Like I'm five How much stuff can get through in one go without anything being lost.
- Ticket
An encrypted Kerberos credential that a client presents to a service. It contains the client's identity and a session key, sealed in the service's key so the client cannot read or alter it.
Like I'm five A sealed envelope that only the ride operator can open.
Used in RFC 1235 RFC 1507 RFC 1731 RFC 1964 RFC 2350 RFC 2712 RFC 2942 RFC 4120 RFC 4121 RFC 4153 RFC 4430 RFC 4537 RFC 4556 RFC 4757 RFC 4777 RFC 5077 RFC 5896 RFC 6043 RFC 6111 RFC 6112 RFC 6448 RFC 6806 RFC 6880 RFC 7751 and 2 more
- Ticket-granting ticket (TGT)
The ticket a client gets from the Authentication Service at login. It is presented to the Ticket-Granting Service to obtain tickets for other services without using the password again.
Like I'm five The wristband you get at the gate that lets you ask for ride tickets.
Used in RFC 3820 RFC 4120 RFC 4430 RFC 5896 RFC 6113 RFC 6806 RFC 8070
- TIFF
Tag Image File Format, a file format for storing raster images together with tagged fields that describe them, such as size, resolution and compression.
Like I'm five A picture file with a built-in set of labels that say how to show it.
- Time offset
The difference between a local time and UTC, written as a sign, hours and minutes such as -08:00, calculated as local time minus UTC.
Like I'm five How many hours your clock is ahead of or behind the world's main clock.
Used in RFC 1589 RFC 3339 RFC 4833 RFC 9557 RFC 9636 RFC 9769 RFC 9922
A service that issues a cryptographically secure confirmation, called a timestamp, that certain data existed at a given time.
Like I'm five A trusted helper who stamps a paper with the date so nobody can argue about when it was made.
Used in RFC 3126 RFC 4810 RFC 4998 RFC 5126 RFC 5544 RFC 6283 RFC 9921
- Time step
The length in seconds (X) of the window during which one TOTP value stays the same. RFC 6238 recommends a default of 30 seconds.
Like I'm five How long one code lasts before the next one takes over.
- Time-division multiplexing
A way to share one line among several channels by giving each a fixed, repeating time slot. E1 and T1 lines work this way.
Like I'm five Taking turns on one phone line, with each person getting a fixed slice of time.
- Time-Sensitive Networking
A set of IEEE 802.1 standards that provide zero congestion loss and bounded latency in bridged networks, so that traffic is delivered predictably.
Like I'm five Network rules that make messages arrive within a set time and never get lost to traffic jams.
- Time-Slotted Channel Hopping
A medium access mode of IEEE 802.15.4 in which time is divided into slots and each transmission happens in a scheduled slot on a scheduled channel offset. Communication follows a schedule of such cells.
Like I'm five Everyone gets assigned a time and a radio channel for talking, like a school timetable.
- TIME-WAIT
The state in which the endpoint that closed first waits for twice the maximum segment lifetime before deleting a connection, so the final ACK is not lost and stray old segments expire.
Like I'm five Waiting a little after saying goodbye, in case your last wave was missed.
Used in RFC 793 RFC 916 RFC 1337 RFC 1379 RFC 1644 RFC 3102 RFC 4340 RFC 5382 RFC 6056 RFC 6191 RFC 6269 RFC 7413 RFC 9210 RFC 9293
- Timestamp
An unambiguous written representation of one instant in time, as used to record when a protocol event happened.
Like I'm five A note saying exactly when something happened.
Used in RFC 28 RFC 32 RFC 34 RFC 41 RFC 738 RFC 868 RFC 1057 RFC 1071 RFC 1128 RFC 1165 RFC 1361 RFC 1507 RFC 1510 RFC 1761 RFC 1769 RFC 1889 RFC 1890 RFC 2006 RFC 2029 RFC 2198 RFC 2250 RFC 2330 RFC 2435 RFC 2562 and 133 more
- TIP
Terminal Interface Processor; specialized hardware that allowed user terminals to connect directly to the ARPANET without an intermediate host computer.
Like I'm five A box that let people's terminals plug into the network directly.
- TLS (Transport Layer Security)
The protocol that encrypts and authenticates a connection between two programs, most visibly in HTTPS. RFC 6066 works with version 1.2, defined in RFC 5246.
Like I'm five A secret tunnel two computers build before they start talking, so nobody in between can listen in.
Used in RFC 2179 RFC 2222 RFC 2246 RFC 2255 RFC 2316 RFC 2371 RFC 2487 RFC 2565 RFC 2566 RFC 2567 RFC 2568 RFC 2595 RFC 2653 RFC 2712 RFC 2716 RFC 2719 RFC 2728 RFC 2748 RFC 2801 RFC 2813 RFC 2817 RFC 2818 RFC 2829 RFC 2830 and 610 more
- TLS extension
An optional block of data added to the client hello or server hello to offer or accept an extra feature. Peers that do not know an extension ignore it.
Like I'm five A sticky note attached to the first message that asks for something extra.
Used in RFC 2487 RFC 4366 RFC 4492 RFC 4642 RFC 4680 RFC 4681 RFC 5019 RFC 5054 RFC 5077 RFC 5705 RFC 5746 RFC 5764 RFC 5878 RFC 6042 RFC 6066 RFC 6091 RFC 6176 RFC 6460 RFC 6520 RFC 6962 RFC 7151 RFC 7250 RFC 7301 RFC 7366 and 31 more
- TLS handshake
The opening exchange in which a TLS client and server agree on settings, check certificates and set up keys before any application data is sent.
Like I'm five The secret handshake two friends do to prove who they are before talking.
Used in RFC 2246 RFC 2712 RFC 2716 RFC 2817 RFC 2830 RFC 3207 RFC 3436 RFC 3546 RFC 3943 RFC 4217 RFC 4261 RFC 4279 RFC 4346 RFC 4366 RFC 4492 RFC 4507 RFC 4572 RFC 4642 RFC 4680 RFC 4681 RFC 4851 RFC 5054 RFC 5077 RFC 5216 and 63 more
- TLSA record
A DNS record type that ties a TLS server's certificate or public key to its service name. It carries a certificate usage, a selector, a matching type and the certificate association data.
Like I'm five A line in the internet phone book that says which key a website should show when you visit.
- TLV
A Type-Length-Value element, a common way to pack data in a protocol message. A sub-TLV is a TLV nested inside another.
Like I'm five A labeled box that says what is inside, how big it is, and then holds the contents.
Used in RFC 3103 RFC 3359 RFC 3475 RFC 3476 RFC 3630 RFC 4970 RFC 4972 RFC 5029 RFC 5036 RFC 5073 RFC 5089 RFC 5120 RFC 5252 RFC 5301 RFC 5304 RFC 5305 RFC 5307 RFC 5310 RFC 5354 RFC 5420 RFC 5497 RFC 5561 RFC 5578 RFC 5642 and 86 more
- Token bucket
A rate-limiting method that adds tokens to a bucket at a steady rate and spends one per message. It allows short bursts up to the bucket size while keeping the long-term average under the limit, and RFC 4443 recommends it for ICMPv6 errors.
Like I'm five A jar that fills with one coin a second. Each note costs a coin, so you can send a few quickly but not forever.
Used in RFC 1363 RFC 1633 RFC 2206 RFC 2210 RFC 2211 RFC 2212 RFC 2215 RFC 2381 RFC 2475 RFC 2597 RFC 2638 RFC 2688 RFC 2697 RFC 2698 RFC 2724 RFC 2963 RFC 2996 RFC 3006 RFC 3175 RFC 3208 RFC 3212 RFC 3246 RFC 3247 RFC 3289 and 15 more
- Token introspection
The act of asking an OAuth 2.0 authorization server about the current state of a token, such as whether it is active and what it allows. It is done by calling the server's introspection endpoint.
Like I'm five Phoning the office to ask if a visitor's pass is still good.
- Token Ring
A local network technology (IEEE 802.5) in which a station may transmit only while it holds a token. The maximum frame size is set by how long a node may hold the token.
Like I'm five A circle of computers passing a baton, where only the one holding the baton may talk.
- Top-Level Domain
The rightmost part of a domain name, such as .COM, .ORG, .UK, or .FR. Top-level domains are either generic (gTLDs like .COM) or country-code domains (ccTLDs like .UK).
Like I'm five The ending of a web address, like .COM or .UK.
- Top-Level Domain (TLD)
The highest level in the domain name hierarchy, such as .com, .org, or .edu in the Domain Name System.
Like I'm five The rightmost part of a web address, like .com or .org in example.com.
Used in RFC 920 RFC 2352 RFC 3375 RFC 4931 RFC 7485 RFC 8023
- TOTP
Time-Based One-Time Password. An algorithm, defined in RFC 6238, that turns a shared secret and the current time into a short numeric code that is valid for only a brief window, usually 30 seconds.
Like I'm five A secret code that changes every half minute, so an old one is useless.
- TPKT
A small header that wraps one ISO transport message so it can be sent over a TCP byte stream. It carries a version number and the total length of the packet.
Like I'm five A label on each message saying how long it is, so the receiver knows where it ends.
- Traceroute
A tool that discovers the path to a host by sending datagrams with small time-to-live values and listening for the ICMP Time Exceeded messages that gateways send back.
Like I'm five Finding the stops along a road by asking each stop to wave back.
Used in RFC 791 RFC 792 RFC 1470 RFC 1574 RFC 1578 RFC 1739 RFC 1879 RFC 2004 RFC 2151 RFC 2745 RFC 2925 RFC 2991 RFC 3542 RFC 3609 RFC 4379 RFC 4560 RFC 4884 RFC 4950 RFC 5388 RFC 5508 RFC 5837 RFC 5884 RFC 6045 RFC 6424 and 40 more
- Traffic class
An 8-bit IPv6 header field used to identify and distinguish classes or priorities of packets.
Like I'm five A label saying how urgent a packet is.
Used in RFC 1455 RFC 2123 RFC 2430 RFC 2460 RFC 2514 RFC 2597 RFC 2751 RFC 2814 RFC 2815 RFC 2816 RFC 2836 RFC 2859 RFC 3168 RFC 3290 RFC 3334 RFC 3542 RFC 3564 RFC 3644 RFC 4127 RFC 4363 RFC 4689 RFC 5316 RFC 5455 RFC 5462 and 29 more
- Traffic Conditioning
The process of classifying, metering, marking, shaping, and policing traffic at a router to enforce traffic profiles and service-level agreements.
Like I'm five The work of sorting traffic, checking rates, and applying rules to make sure traffic behaves according to agreements.
- Traffic Encryption Key
The symmetric key used to encrypt and decrypt group data traffic (for example, IPsec ESP packets), distributed by the GCKS to all group members.
Like I'm five The actual secret password members use to encrypt their messages to each other.
- Traffic engineering
Steering traffic along chosen paths through a network, using information such as link bandwidth, instead of only taking the shortest route.
Like I'm five Choosing which roads cars should take so no road gets jammed.
Used in RFC 2340 RFC 2702 RFC 3209 RFC 3272 RFC 3630 RFC 4128 RFC 4206 RFC 4216 RFC 5146 RFC 5305 RFC 5543 RFC 6119 RFC 6373 RFC 6827 RFC 6882 RFC 7823 RFC 7855 RFC 8051 RFC 8195 RFC 8776 RFC 9346 RFC 9479 RFC 9492 RFC 9522 and 3 more
- Traffic Engineering Database
The collection of all traffic engineering information about the nodes and links in a network, used as the basis for computing TE paths.
Like I'm five The big notebook that lists every town and road and how much each can carry.
Used in RFC 4655 RFC 5152 RFC 6825 RFC 7399 RFC 8233 RFC 8426 RFC 8795 RFC 9730
- Traffic Flow
A sequence of packets sharing the same source and destination addresses at one or more layers of the network stack, identified for the purpose of measurement and accounting.
Like I'm five A stream of network messages from one place to another, identified by where they come from and where they are going.
- Traffic Flow Confidentiality
Hiding the size and frequency of traffic so that observers cannot learn information from its patterns, even though the data is already encrypted.
Like I'm five Hiding how much you send and when, not just what you say.
- Traffic selector
A description of which packets a Child SA applies to: an address range, a port range and an IP protocol. IKE exchanges them as TSi and TSr payloads.
Like I'm five A rule that says which packets go through the locked pipe.
Used in RFC 2401 RFC 4301 RFC 4306 RFC 4555 RFC 4877 RFC 5324 RFC 5406 RFC 5660 RFC 6088 RFC 6089 RFC 7222 RFC 7296 RFC 7619 RFC 7674 RFC 7815 RFC 9061 RFC 9478 RFC 9611 RFC 10053
- Traffic Shaping
A traffic management function that smooths bursty traffic by buffering packets and controlling the output rate to match a configured limit.
Like I'm five Storing packets and letting them out at a controlled speed to avoid bursts.
- Trajectory sampling
Consistently selecting a packet at either all measurement points along its path or none of them. This lets a collector rebuild the route the packet took.
Like I'm five Following the same few travellers at every stop so you can see their whole journey.
- Transaction ID (xid)
A random number a client puts in a request so it can match the reply to it. In BOOTP the client discards replies whose transaction ID does not match its own.
Like I'm five A ticket number you hold so you know which answer is yours.
Used in RFC 951 RFC 1002 RFC 1050 RFC 1831 RFC 2371 RFC 2372 RFC 2741 RFC 3435 RFC 4993 RFC 5389 RFC 5452 RFC 6926 RFC 6977 RFC 7653 RFC 7675 RFC 7846 RFC 7877 RFC 7878 RFC 7982 RFC 9811 RFC 9915
- Transcoding
The process of converting audio or video from one codec to another, which typically degrades quality and adds latency.
Like I'm five Converting a recording from one format to another, like turning a MP3 into a WAV file, but for phone calls.
- Transcoding Service
A human or automated intermediary acting as a third party in a communication session, converting one type of media stream to another (for example, voice to text or text to video of sign language).
Like I'm five A service that listens to one thing and converts it to something else, like hearing voice and typing it as text.
- Transcript hash
A hash of all the handshake messages exchanged so far. TLS 1.3 mixes it into key derivation and the Finished message so that tampering is detected.
Like I'm five A fingerprint of the whole conversation so far.
- Transfer identifier (TID)
In TFTP, the port number each end picks for the duration of one transfer. The two TIDs are used as the UDP source and destination ports, and a packet with the wrong TID is rejected.
Like I'm five A table number you and your friend agree on, so you can ignore anyone shouting from a different table.
Used in RFC 1350
- Transparent Clock
A PTP device that measures how long a PTP event message takes to pass through it and updates the message with a correction for that transit time.
Like I'm five A middleman that writes down how long your message sat with it, so the time stays accurate.
- Transport Address
The combination of an IP address and a port, typically written as (IP address,port). NAT bindings map one transport address to another.
Like I'm five A building address plus the apartment number.
- Transport mode
An IPsec mode in which the security header is inserted between the original IP header and the next-layer protocol, so the original IP header is kept.
Like I'm five Sealing the letter itself and leaving the outside address as it was.
- Transport Selector
An opaque string of octets used in OSI networks to demultiplex incoming data to the correct service or process, analogous to port numbers in TCP/IP.
Like I'm five A name or identifier that tells OSI where to send incoming messages, similar to port numbers in the Internet.
- Traversal Using Relays around NAT (TURN)
An extension to STUN that provides a relay server which forwards media traffic when direct paths through NATs are not available.
Like I'm five A backup service that relays your audio through a server when direct paths do not work.
Used in RFC 5245 RFC 5767 RFC 6062 RFC 6156 RFC 6314 RFC 7350 RFC 7983 RFC 8016 RFC 8445 RFC 8835 RFC 9443
- Treat-as-withdraw
An error-handling approach for a malformed BGP UPDATE message, in which the routes in that message are treated as withdrawn instead of resetting the session.
Like I'm five If a note is broken, you act as if the route was taken back instead of hanging up the phone.
- Treatment Aggregate
A group of Diffserv classes whose traffic is forwarded together, for example in a single MPLS TC value. It lets a network offer several behaviors without using many TC values.
Like I'm five A bundle of similar kinds of traffic that all get the same treatment.
- Tributary slot
One of the equal-sized time slots inside a higher-order optical container. Smaller signals are multiplexed into one or more of these slots.
Like I'm five One numbered seat inside a big container that a smaller package can sit in.
- Trickle algorithm
A timer-based method in which nodes share information by repeating it at growing intervals. A node stays quiet when it has already heard enough consistent messages from its neighbors.
Like I'm five Everyone repeats the news, but stays quiet if they hear enough others already saying it.
- Trickle ICE
An extension to ICE that lets candidate gathering and connectivity checks run in parallel, so candidates can be sent a few at a time instead of all at once.
Like I'm five Sharing meeting spots one by one instead of waiting to have the full list.
- Trickle Timer
A timer algorithm that spaces out message transmissions and suppresses a message when neighbors already sent consistent ones. RPL uses it to control how often DIO messages are sent.
Like I'm five A rule that tells you to stay quiet if your neighbors have already said the same thing.
- Triggered update
A routing update sent soon after a route changes instead of waiting for the next regular timer. RIP rate-limits them to one every 1 to 5 seconds.
Like I'm five Shouting news right away instead of waiting for the next meeting.
Used in RFC 1058 RFC 1581 RFC 1582 RFC 2080 RFC 2091 RFC 2453 RFC 4783
- TRILL
Transparent Interconnection of Lots of Links, a protocol that forwards Ethernet frames between switches using IS-IS link-state routing and a header with a hop count.
Like I'm five A way for switches to find the best path for each message, like a map app for network cables.
Used in RFC 7172 RFC 7174 RFC 7177 RFC 7379 RFC 7782 RFC 7783 RFC 8243 RFC 8564
- TRILL nickname
A 16-bit identifier for an RBridge in TRILL. It is used in the ingress and egress fields of the TRILL header.
Like I'm five A short name tag that tells the network which switch is which.
- Triple-DES
A cipher that applies the DES algorithm three times, here as encrypt, decrypt, encrypt, using three independent keys. It enlarges the effective key to 168 bits.
Like I'm five Locking a box with three different locks one after another.
- Truechimer
A time source whose answer agrees with a majority of other sources in NTP's selection algorithm. Sources that disagree are called falsetickers and are not used.
Like I'm five A clock that tells the same time as most of the others, so you can believe it.
Used in RFC 5905
- Trunk group
A set of trunks that are traffic engineered as a unit for making connections within or between switching systems. All of the paths in it are interchangeable except where subgrouped.
Like I'm five A bundle of phone lines that are treated as one big pipe.
- Trunking
A situation in which several network addresses are connected to the same server, so a client can reach it over multiple paths.
Like I'm five Having several roads that all lead to the same town.
- Trust anchor
A configured DNSKEY, or a hash of one, that a validating resolver treats as its starting point for building an authentication chain. It must be obtained by means outside the DNS.
Like I'm five The one stamp you already trust, so you can check all the others.
Used in RFC 1422 RFC 1507 RFC 2065 RFC 2704 RFC 2906 RFC 3125 RFC 3280 RFC 3379 RFC 3658 RFC 3779 RFC 3788 RFC 3971 RFC 4033 RFC 4035 RFC 4108 RFC 4158 RFC 4261 RFC 4431 RFC 4806 RFC 4945 RFC 4986 RFC 5011 RFC 5055 RFC 5074 and 101 more
- Trust Anchor Locator
A small file that tells a relying party where to fetch a trust anchor's CA certificate and which public key to expect, so it can start validating RPKI data.
Like I'm five A card that says where to find the top boss's ID and what it should look like.
- Trust anchor store
The secure storage on a device that holds its trust anchors, along with related data such as community identifiers and sequence numbers.
Like I'm five The locked drawer where a device keeps its list of keys it trusts.
- Trust boundary
The line around the systems that a service provider owns or controls. Information may flow freely inside it, but private data must be removed before anything crosses to an untrusted party.
Like I'm five The edge of the staff-only area, where private notes must be left behind.
- Trust Domain
A set of SIP nodes that are explicitly trusted by all users and systems within a domain to assert identity and service information. All nodes in a trust domain must agree on service definitions and policies.
Like I'm five A private network where all the servers trust each other.
- Trust on first use
Accepting and storing a public key or credential for an identity the first time it is seen, without authenticating it. Later contact is checked against the stored key.
Like I'm five Believing someone's name the first time you meet and checking it matches afterwards.
- Trusted Platform Module
A hardware cryptoprocessor that stores keys that never leave it, holds measurement registers, and signs reports about them. Defined by the Trusted Computing Group.
Like I'm five A tiny locked safe chip inside the device that keeps secrets and signs reports.
- Trusted zone
A part of a network, such as one VPN or the provider core, whose members trust each other and whose security is judged against breaches from outside it.
Like I'm five A fenced yard where everyone inside is allowed in and everyone outside has to stay out.
- TSIG
A way to authenticate DNS messages using a secret key shared by both parties and a keyed hash code. It is defined in RFC 2845.
Like I'm five A secret handshake that only two friends who share the secret can do.
Used in RFC 2845 RFC 2931 RFC 3007 RFC 3645 RFC 4635 RFC 5625 RFC 8945
- TSpec
A traffic specification: a description of the traffic a flow will send, given as a token bucket plus a peak rate, a minimum policed unit and a maximum packet size.
Like I'm five A short form that says how much and how fast you plan to send.
- TTL (Time to Live)
A counter that is decreased at each hop so a packet cannot circulate forever. In IP it is the TTL field (IPv4) or Hop Limit (IPv6); MPLS label stack entries carry their own 8-bit TTL.
Like I'm five A countdown number on a parcel that goes down by one at each stop, so lost parcels eventually stop.
Used in RFC 791 RFC 792 RFC 815 RFC 827 RFC 882 RFC 883 RFC 891 RFC 919 RFC 922 RFC 925 RFC 970 RFC 994 RFC 1002 RFC 1009 RFC 1033 RFC 1034 RFC 1035 RFC 1054 RFC 1060 RFC 1075 RFC 1118 RFC 1122 RFC 1141 RFC 1256 and 199 more
- Tunnel
A mechanism for carrying packets of one protocol through a network using another protocol, by encapsulating them inside packets of the transport protocol.
Like I'm five Putting a package inside another box so it can travel through a different route.
Used in RFC 1075 RFC 1933 RFC 2003 RFC 2341 RFC 2473 RFC 2784 RFC 2890 RFC 4087 RFC 4110 RFC 4888 RFC 5579 RFC 5944 RFC 6324 RFC 6936 RFC 8086 RFC 8190 RFC 9012 RFC 9601
- Tunnel Encapsulation
The technique of wrapping packets of one protocol (the payload) inside packets of another protocol (the carrier) to send them across incompatible networks.
Like I'm five Putting a letter inside a box so it can travel through places that don't accept letters directly.
- Tunnel mode
An IPsec mode in which the whole original IP packet is protected and wrapped in a new outer IP header. The outer header names the tunnel endpoints.
Like I'm five Putting a whole letter, address and all, inside a new envelope with a new address.
- Tunnel Router (xTR)
A LISP edge router that encapsulates packets into the tunnel (an ITR) or decapsulates them at the other end (an ETR). Many routers do both and are called xTRs.
Like I'm five A door that wraps your parcel in a bigger box to send it, or unwraps boxes that arrive.
- Tunneling
Wrapping one protocol's packets inside another protocol's headers so they can cross a network that does not understand the inner protocol.
Like I'm five Putting a letter in a different kind of envelope so a different mail service can carry it.
Used in RFC 1241 RFC 1621 RFC 2004 RFC 2764 RFC 2893 RFC 3070 RFC 4170 RFC 4213 RFC 4459 RFC 5512 RFC 6127 RFC 6180
- TWAMP
The Two-Way Active Measurement Protocol, which measures network performance by sending test packets that a reflector sends back to the sender.
Like I'm five A way to measure a network by sending a message that gets echoed back.
- Two-phase commit
A protocol for atomic commitment. In phase one every participant is asked to prepare; in phase two the coordinator tells them to commit or abort.
Like I'm five First everyone says they are ready, then the leader says go.
- Type of service
The second octet of the IPv4 header in RFC 791. It holds precedence bits plus delay, throughput and reliability bits that say how the datagram should be treated. It was later redefined as DSCP and ECN.
Like I'm five A sticker on the package saying rush it, or handle it gently.
Used in RFC 791 RFC 1017 RFC 1046 RFC 1060 RFC 1077 RFC 1126 RFC 1245 RFC 1322 RFC 1340 RFC 1455 RFC 1583 RFC 1678 RFC 1700 RFC 2003 RFC 2475 RFC 2676 RFC 2873 RFC 3260 RFC 4323 RFC 4915
- Type P
A parameterized notion in the IPPM framework representing a class of packets with specific properties like payload size, protocol type, and source/destination addresses.
Like I'm five A way to describe what kind of packets you're measuring (their size, type, where they go).
- Type-Length-Value (TLV)
A data structure with three parts: a type field identifying the kind of information, a length field for the size of the data, and a value field containing the actual data. TLVs are used in routing protocols to carry variable-length information flexibly.
Like I'm five A way to package information in a message: first you say what kind of information (type), then how big it is (length), then the actual data.
- Type-Length-Value (TLV)
A way to encode an attribute as a type, a length and a value. A parser can skip an attribute it does not recognize by using the length.
Like I'm five A labeled box that tells you what is inside and how big it is, so you can skip it if you do not need it.
Used in RFC 3036 RFC 4203 RFC 5088 RFC 5384 RFC 5444 RFC 5613 RFC 5792 RFC 7455 RFC 8489 RFC 8510 RFC 9930
- Type-Length-Value encoding
A method of encoding structured data where each field is preceded by its type identifier and length, allowing flexible and extensible message formats.
Like I'm five Each piece of information is labeled with what it is and how long it is, so the receiver knows where one piece ends and the next begins.