T3 Line

What does T3 Line mean?

A T3 line is a dedicated physical circuit that uses high-speed media to transmit data, voice and video at the rate of 45 Mbps. It offers a broadband connection consisting of 672 individual channels of 64 kilobits each.

They are commonly used in applications requiring high bandwidth, such as in research centers and big organizations, to provide uninterrupted data transmission, and other multi-channel services such as email and Internet. Other applications include Internet telephony, large file transfers, telemedicine, video conferencing, credit card processing and more.

A T3 line is also known as digital signal level 3 (DS3).

T3 refers to the trunk line level 3, and is sometimes used interchangeably with DS3 (digital signal level 3). In practice, the DS3 signal is transmitted over a T3 physical line, consisting of a fiber optic cable or coaxial cable. The T3 lines, which are symmetrical and duplex, have equal speeds on both upload and download, and therefore allow simultaneous transmissions without clogging the data lines.

A T3 line is an ideal connection for big business, however, small businesses that cannot afford the full 45 Mb or who may not need such a high capacity, have an option of buying a fraction of the full T3 line. The fractional T3 has some of the 28 lines turned off, and has a lower capacity such as 10 or 20 Mbps.

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Referential Integrity

What does Referential Integrity (RI) mean?

Referential integrity is a relational database concept, which states that table relationships must always be consistent. In other words, any foreign key field must agree with the primary key that is referenced by the foreign key. Thus, any primary key field changes must be applied to all foreign keys, or not at all. The same restriction also applies to foreign keys in that any updates (but not necessarily deletions) must be propagated to the primary parent key.

Consider a bank database, which contains two tables:

  • CUSTOMER_MASTER Table: This holds basic customer/account holder data such as name, social security number, address, gender and date of birth.
  • ACCOUNTS_MASTER Table: This stores basic bank account data such as account type, account creation date, account holder and withdrawal limits.

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