An acronym for intellectual property, a created right (granted by government) as opposed to the natural rights which are easy enough to understand. In recent times, IP is getting to be more important than physical property in some circles.

IP is based on the principle of getting from point A to point B. It is an unreliable, connectionless protocol, meaning that no attempt is made to keep the packet from getting lost, and no packet is set up to go through the same set of routers (which is commonly known as a circuit or a virtual circuit) but is bounced through each router in turn (known as next-hop) and may be reassembled at the destination out of order.

The real meat of the IP address is a set of four numbers. You have the source IP address and port number, and the destination IP address and port number. You know from the IP addresses that they exist on a certain network through the subnet mask, so you don't have to keep track of every host individually. If you're a router and you get a packet, you check it against a table of hosts you know about, and if so, send it to that host. If not, then you check networks you know about, and forward the packet to that network. If no tables match, you send it to a default router and let THAT worry about it.

That's it.... everything else is just a small matter of programming.

IP used to mean Information Provider in the days of the Prestel Viewdata service. IIRC, this was as opposed to a service provider, who published a particular collection of frames.

Baseball statistical abbreviation for "innings pitched".

The career record for innings pitched is 7354 2/3, held by Cy Young, and will likely never be broken. Second place all-time (Pud Galvin) had less than 6000. By comparison, the active leader (Roger Clemens) had less than 4000, entering the 2001 season. Pitchers don't pitch as many innings as in the past for a variety of reasons (rule changes, rise of relief pitchers, and changes in pitching techniques, among others).

Will White of the Cincinnati Redlegs holds the single-season record with 680(!!) IP in 1879. By comparison, Jon Lieber led the majors in 2000, with a "mere" 251 IP.

In linguistics, IP stands for "Inflectional Phrase", in other words, a sentence.

In the mid-level Chomskyan theory known as "X-bar syntax", which has since come to be disfavoured/replaced by more current syntax theories such as minimalism, it was believed that any syntactical group had a number of features in common. An "XP" or "X-phrase" was the shorthand used to refer to such groups in general, using the common mathematics/science practice of "X" representing an unspecified or unknown quantity/factor/etc. This could be specified in ways such as "NP" (noun phrase), "VP" (verb phrase), etc.

As stated, any XP had a number of features in common, including a hierarchical structure, and of course, a root. The root of XP was always an X, and the root was the only totally necessary component of an XP. (For example, the root of an NP, a noun phrase, is of course a noun! Examples of NPs include "John" and "the tall man with auburn hair"... these show the varying levels of inclusion within a possible XP. A noun phrase such as "John" contains only the root, a proper noun, whereas a noun phrase such as "the tall man with auburn hair" contains a root noun, "man", a determiner, "the", an adjective {actually, an AP {{afjectival phrase}} "tall"}, and an adjunct PP (prepositional phrase) "with auburn hair" which itself includes another noun phrase, "auburn hair". This exemplifies the possible complexities and hierarchy that an XP can have.})

The following tree diagram shows the "basic" format of any XP. X' is called "X-bar" by the way, and is the source of the name of the theory:

      
             XP
             /\
            /  \
           /    \
          /      \
         /        \
        Det       X'
    (determiner)  /\
                 /  \
                /    \
               /      \
               X     Complement
             (root)

The problem with X-bar syntax theory, then, became, what kind of XP is a sentence, exactly? A sentence in its simplest form includes at least a noun and a verb, or more acurately, a noun phrase and a verb phrase. Can an NP+VP combination be seen in and of itself to be some sort of XP? But if so, what is the root X of such an XP?

The solution to this problem was arrived at in theorizing that a sentence is itself a type of XP... an IP, or inflectional phrase. According to this theory, the root of an IP is the inflectional information that "maps on" to the verb... this information is "hidden" (or located in the "deep structure", to use the technical parlance) and only manifests on the verb in the "surface structure".

So, within X-bar theory, a simple sentence such as "John saw the sunset", can be seen as an IP with a hierarchical structure along these lines:
{IP{NPJohn} {I' {I (inflectional information: past tense, third person, singular)} {VPsee {NPthe sunset}}}}

In a slightly more clear tree diagram format:

                  IP
                  /\
                 /  \
                /    \
               /      \
              /        \
             NP        I'
              |        /\
           John       /  \
                     /    \
                    /      \
                   I       VP
                 (past,    /\
                  3rd,    /  \
                  sg.)   /    \
                        /      \
                       /        \
                       V        NP
                       |        |
                      see    the sunset

IP is sometimes used as an abbreviation for "in-patient" as in one that is a patient in a hospital that does not go home at night.

This term is often used to refer to staying at a psychiatric or mental hospital, a place that no one actually wants to go, but sometimes agree to go until they are more "stable." One can also be forced into IP if they are a danger to themself or others or unable to care for themselves. The alternative is "out-patient" in which one goes to group and other forms of therapy usually for 5-8 hours and then goes home.

Used online more often than in verbal conversation.

The specifications (as we know them today) for the Internet Protocol (known as IP) were set down in January 1980 by Jon Postel and several others in the document known as RFC760. IP was based upon earlier protocols for the ARPA net and drew heavily from their successes.

The motivation for IP comes from the creation of packet switching communications networks where were called at the time "catenet" coined by the Defense Advanced Research Projects Agency in July 1978. With IP blocks of data (known as datagrams) are sent from machine to machine that are identified by an IP Address. One of the key points here is that the IP Address is a fixed size (4 bytes properly called octets). Another significant advance was the ability for datagrams to be fragmented to be sent through networks that only allowed small packets.

At the IP level, things are simple - IP implements two features:

Addressing
Within the Internet, there are three concepts: names (what is sought), address (where what is sought is found), and routes (how to get to where what is sought). Internet Protocol deals with the addresses. These addresses are a fixed length of 32 bits. It is possible that a single host may have multiple addresses (and quite common today).
Fragmentation
Fragmentation occurs when datagrams are sent from a network that allows large packet sizes to a network that requires smaller sizes. It is possible to mark a datagram "don't fragment" which will cause it to never be fragmented. However, if it reaches a network where it would be invalid, the unfragmentable datagram will be discarded.

Fragmentation allows for a datagram to be broken into an arbitrary number of smaller datagrams that can be reassembled at a later point. To do this, the identification field of the options is used to mark the fragments and make certain that they are not reassembled with the wrong datagram.

When fragmentation occurs, new Internet datagrams are created with the same Internet header. The data is fragmented and attached to the new headers. Several fields are set in each header:

  • NFB (Number of Fragment Blocks) - how many fragments are there?
  • more-fragments - are there any fragments after this?
  • length - the length of the data
  • offset - how far from the start is this data (the first fragment is '0')
For a datagram to be reassembled, it must have the same identification, source, destination, and protocol.
The IP level does not deal with data reliability, flow control, sequencing and other such features. These are left to other protocols that are implemented on top of IP (such as TCP/IP or UDP).

Each packet within the Internet Protocol is independent and unrelated to any other packet that may be out there on the network or yet to be sent.

There are 4 parts to the IP service:

  • Type of service
  • Time to Live
  • Options
  • Header Checksum

Type of Service
This is a selector of the quality of service. The example given in the RFC provides "Interactive", "Bulk", and "Real Time". This feature is used by the gateways and routers from network to network to select the parameters for transmission on the network. More on this below.
Time to Live
Often abbreviated TTL, the time to live is set by the sender. As the datagram proceeds through the network, each place it is processed re-evaluates the time to live. If the time to live reaches zero before the packet gets to the destination, it is destroyed.

While this may come as a surprise to some it makes perfect sense. Consider playing a network game, such as Diablo. If for some reason, some packets get delayed from the server to your machine, it would be unfortunate for them to later catch up when they are no-longer needed. While the program could probably deal with them (I'm on update #100, this packet is update #70, thus I will discard it) it just clutters the network to be sending data that has to get there in 5 seconds to make any sense before it should be thrown away after those 5 seconds have gone by.

Options
These are common control functions that are needed for most communication protocols. The options include
  • Timestamps
  • Error reports
  • Special Routing
Header Checksum
This checksum acts as a verification that the datagram has been sent correctly. The checksum is a simple "Yes/No" indicator if any errors have occurred during transmission. This does not provide for correcting those errors. At any point where the checksum fails to match the data, the packet may be discarded.

An example of how IP works. Picture two hosts, each on a separate Local Area Network that are connected via the Internet.

  1. The sender application prepares its data and calls on its network code to send a datagram to the receiver.
  2. The network library looks at the destination for the datagram. It prepares an IP header and attaches the data to it.
  3. Because these machines are on separate networks, this IP packet must be sent the gateway via the LAN (this could be via Novell, Token Ring, Apple Talk, what have you...). The IP datagram is attached as data to a local network header. The resulting datagram is sent out on the local network.
  4. The datagram arrives at the gateway. The gateway unwraps the local network header from the IP datagram. The gateway then once again determines the Internet address that it should be sent to and sends the datagram to the second gateway.
  5. Gateway to gateway, this is repeated until the datagram reaches the last gateway which is connected to the LAN of the destination machine.
  6. The gateway examines the header, determines the local network address for the destination machine, creates the local network header and sends the datagram onto the local network.
  7. The destination machine receives the datagram, unwraps the local net header, examines the IP header and passes the data to the appropriate application along with other information such as the source address.

    The Internet header is thus:

     0                   1                   2                   3   
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |Version|  IHL  |Type of Service|          Total Length         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |         Identification        |Flags|      Fragment Offset    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Time to Live |    Protocol   |         Header Checksum       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                       Source Address                          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                    Destination Address                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                    Options                    |    Padding    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    
    Version - 4 bits
    What version of the Internet Protocol is this? The above describes IPv4 (thus the number is 4). There is work being done on IPv6, though it is not accepted universally yet.
    IHL - 4 bits
    Internet Header Length in 32 bit words. In the above diagram, each 32 bit word is one line. For IPv4, the correct minium value is '5'.
    Type of Service - 8 bits
    This information shows the quality of service and type of service provided. While this is not standardized, some networks do regard different types of service in different ways (voice data being more important than routine data for example). This field can be expanded to:
       0     1     2     3     4     5     6     7
    +-----+-----+-----+-----+-----+-----+-----+-----+
    |   PRECEDENCE    | STRM|RELIABILITY| S/R |SPEED|
    +-----+-----+-----+-----+-----+-----+-----+-----+
    
    • Precedence
      • 111 - Flash Override
      • 110 - Flash
      • 11X - Immediate
      • 01X - Priority
      • 00X - Routine
    • STRM (Streaming) - This is used to indicate if the gateways should expect more packets from this source to this destination at regular and frequent intervals.
      • 1 - Streaming Data
      • 0 - Datagram
    • Reliability
      • 11 - Highest
      • 10 - Higher
      • 01 - Lower
      • 00 - Lowest
    • Speed or Reliability? If there is a choice between speed and reliability and a conflict between them - which is more important?
      • 1 - Speed
      • 0 - Reliability
    • Speed
      • 1 - High
      • 0 - Low
    Some examples include:
    • Telnet - Streaming, Normal Reliability, S/R: speed, Fast
    • FTP - Streaming, Normal Reliability, S/R: reliable, Normal
    • Speech - Streaming, Least Reliability, S/R: speed, ASAP
    Total Length - 16 bits
    The total length of the datagram, in octets (bytes) including the header. The maximum length of a datagram is 64kB. It should be noted that packets of maximum length are rather impractical for most networks. The recommendation (from 1980) is to send packets no larger than 576 octets unless there is a guarantee that the destination network and host is able to handle larger packets. The number 576 comes from a 512 byte packet plus 64 bytes for the header.
    Identification - 16 bits
    This is sent by the sender to allow for assembling fragments of a datagram.
    Flags - 3 bits
    Bit 0: Reserved, must be 0.
    Bit 1: Don't Fragment
    Bit 2: More Fragments
    Fragment Offset - 13 bits
    This indicates where the datagram belongs when fragmented in the larger datagram. This is measured in 8 octet units. The first fragment of a fragmented datagram has the offset of zero.
    Time to Live (TTL) - 8 bits
    The time to live for a datagram in the network. This value is measured in seconds. This provides a means for undeliverable packets to be discarded along with those that have time sensitive information that have lost their meaning. (This field worries me if Star Trek like transporters ever work via IP)
    Protocol - 8 bits
    The protocol is the next level of the protocol. It would be a waist of space to list all 256 possibilities. The two most important ones are TCP (decimal 6) and UDP (decimal 17). The current listing of the assigned protocols can be found in RFC1700.
    Header Checksum - 16 bits
    A checksum of the header only. Because some fields may change (such as the Time to Live) as the datagram moves from gateway to gateway, this checksum needs to be recomputed at each point. For the purposes of calculating the checksum, the checksum field itself is considered to be nulls.
    Source Address - 32 bits
    The IP address of the host that sent the datagram
    Destination Address
    The IP address of the host that the datagram is intended for
    Options - variable
    The options field contains many possibilities for information to be added. Of those, the most amusing includes that of "Security" for the DOD to send information that may be "top secret" through the network and it is believed that other machines would honor this. Of more practical use is the ability to suggest and record routing information, identification of streaming data, returning error codes, and time stamps.


For more information on IP see http://www.faqs.org/rfcs/rfc760.html and any other RFCS that may follow it. Much of the information above can be found stated in more concise and technical terms within these documents. Diagrams where copied from the above URL.

In the possessive case, IP is typically used as an informal abbreviated form of IP address. Example: His IP is 1.2.3.4.

This usage is typically found on IRC and similar real-time, textual chat media, where such abbreviations are used to save typing, and references to IP addresses are common. This usage could conceivably be used in vocal communication as well (e.g. on a telephone or face to face), but in this case, the means of communication does not typically involve IP addresses (with the notable exception of voice over IP), so the concept is not usually relevant.

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