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trailer A section of a data packet that contains error-checking information.

transceiver A device that allows the network interface card (NIC) to connect to the network.

transmission Sending packets from the PC to the server. The transmission can occur over a network cable, wireless connection, or other medium.

Transmission Control Protocol (TCP) The protocol found at the Host-to-Host layer of the Department of Defense (DoD) model. This protocol breaks data packets into segments, numbers them, and sends them in order. The receiving computer reassembles the data so that the information is readable for the user. In the process, the sender and the receiver confirm that all data has been received; if not, it’s resent. TCP is a connection-oriented protocol. See also connection-oriented.

Transmission Control Protocol/Internet Protocol (TCP/IP) The protocol suite developed by the Department of Defense (DoD) in conjunction with the Internet. It was designed as an internetworking protocol suite that could route information around network failures. Today it’s the de facto standard for communications on the Internet.

transmission media Physical cables and/or wireless technology across which computers are able to communicate.

Transport layer The fourth layer of the OSI model. It’s responsible for checking that the data packet created in the Session layer was received. If necessary, it also changes the length of messages for transport up or down the remaining layers. See also Open Systems Interconnection (OSI) model.

Transport Layer Security (TLS) A protocol whose purpose is to verify that secure communications between a server and a client remain secure. Defined in RFC 2246.

Triple-DES (3DES) A symmetric block cipher algorithm used for encryption.

Trivial File Transfer Protocol (TFTP) A UDP-based protocol similar to FTP that doesn’t provide the security or error-checking features of FTP. See also File Transfer Protocol (FTP).

Trojan horse Any application that masquerades as one thing in order to get past scrutiny and then does something malicious. One of the major differences between Trojan horses and viruses is that Trojan horses tend not to replicate themselves.

Trust List A list of objects signed by a trusted entity. Also known as a Certificate Trust List (CTL).

Trusted Platform Module (TPM) A method of utilizing encryption and storing the passwords on a chip. The hardware holding the chip is then needed to unencrypt the data and make it readable.

TTL See time to live (TTL).

tunneling The act of sending data across a public network by encapsulating it into other packets.

two-factor authentication Using two access methods as a part of the authentication process.

two-tier model A model in which the client PC or system runs an application that communicates with a database that is running on a different server.

U

UDP See User Datagram Protocol (UDP).

Uniform Resource Locator (URL) A way of identifying a document on the Internet. It consists of the protocol used to access the document and the domain name or IP address of the host that holds the document; for example, http://www.sybex.com.

uninterruptible power supply (UPS) A device that can provide short-term power, usually by using batteries.

Unshielded Twisted Pair (UTP) The most common networking cable currently in use; Unshielded Twisted Pair (UTP) is 8-wire cabling used with Ethernet.

uptime The amount of time a particular computer or network component has been functional.

URL See Uniform Resource Locator (URL).

usage policies Defined policies governing computer usage.

user The person who is using a computer or network or a resource.

User Datagram Protocol (UDP) The protocol at the Host-to-Host layer of the TCP/IP Department of Defense (DoD) model, which corresponds to the Transport layer of the OSI model. Packets are divided into datagrams, given numbers, sent, and put back together at the receiving end. UDP is a connectionless protocol. See also connectionless,