sergeant dude: Internet Protocols

Wednesday, April 25, 2007

Internet Protocols

In this context, there are three layers of protocols:

• At the lowest level is IP (Internet Protocol), which defines the datagrams or packets that carry blocks of data from one node to another. The huge majority of today's Internet uses version four of the IP protocol (i.e. IPv4), and although IPv6 is uniform, it exists only as "islands" of connectivity, and there are many ISPs without any IPv6 connectivity. [1]

• Next come TCP (Transmission Control Protocol), UDP (User Datagram Protocol), and ICMP (Internet Control Message Protocol) - the protocols by which data is transmitted. TCP makes a virtual 'connection', which gives some level of assurance of reliability. UDP is a best-effort, connectionless transport, in which data packets that are lost in transit will not be re-sent. ICMP is connectionless, it is used for control and signaling purposes.

• On top comes the application protocols. This defines the specific messages and data formats sent and understood by the applications running at each end of the communication.

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Difference Between Which and That

Which or That?

While both which and that can be used in other constructions, the confusion usually arises when they are being used as relative pronouns to introduce adjective (or relative) clauses. In the examples below, we have bracketed the adjective clauses. (Remember that a clause is simply a group of words containing a subject and a verb):

1. Our house [that has a red door and green shutters] needs painting.

2. Our house, [which has a red door and green shutters], needs painting.

3. The classrooms [that were painted over the summer] are bright and cheerful.

4. The classrooms, [which were painted over the summer], are bright and cheerful.

In all four cases, the adjective clause tells us something about either the house or the classrooms, but the choice of which or that changes the way we should read each sentence.

The rule of thumb, then, is that which clauses are nonrestrictive (nonessential) while that clauses are restrictive (essential). Nonrestrictive clauses and phrases are set off from the rest of a sentence by a pair of commas (as in our examples above) or by a single comma if they come at the end of the sentence. (Example: "I took a vacation day on my birthday, which happened to fall on a Monday this year.")

TEST YOURSELF:

Which pronoun--which or that--belongs in each blank below?

1. Carlos gave Maria a study guide for material ________ was going to be on the test.

2. Carlos gave Maria notes from chapters 3 through 7 _________ were going to be on the test.

3. Mark and Sarah took their children on every vacation _________ they took to the coast.

4. The teachers gave awards to all paintings ________ showed originality.

ANSWERS:(that,which,that,that)