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TCP/IP is short forÂ TransmissionÂ ControlÂ Protocol/InternetÂ Protocol,Â which is a suite ofÂ communications protocolsÂ used to connectÂ hostsÂ on theÂ Internet. TCP/IP uses severalÂ protocols with the two main ones beingÂ TCPÂ andÂ IP. TCP/IP is built into theÂ UNIXÂ operating systemÂ and is used by theÂ Internet, making it theÂ de facto standardÂ for transmittingÂ dataÂ overÂ networks. EvenÂ network operating systemsÂ that have their own protocols, such asÂ Netware, alsoÂ supportÂ TCP/IP.
Abbreviation ofÂ Transmission Control Protocol,Â and pronounced as separate letters. TCP is one of the mainÂ protocolsÂ inÂ TCP/IPÂ networks. Whereas theÂ IPÂ protocol deals only withÂ packets, TCP enables twoÂ hostsÂ to establish a connection and exchange streams of data. TCP guarantees delivery of data and also guarantees that packets will be delivered in the same order in which they were sent.
(Pronounced as separate letters); short forÂ InternetÂ Protocol.Â IP specifies the format ofÂ packets, also calledÂ datagram's,Â and the addressing scheme. MostÂ networksÂ combine IP with a higher-levelÂ protocolÂ calledÂ Transmission Control Protocol (TCP), which establishes a virtual connection between a destination and a source.
IP by itself is something like the postal system. It allows you to address a package and drop it in the system, but there's no direct link between you and the recipient. TCP/IP, on the other hand, establishes a connection between twoÂ hostsÂ so that they can send messages back and forth for a period of time.
The current version of IP isÂ IPv4.Â AÂ newÂ version, calledÂ IPv6Â orÂ IPng, is under development.
History & Introduction:
TCP and IP were developed by a Department of Defense (DOD) research project to connect a number different networks designed by different vendors into a network of networks (the "Internet"). It was initially successful because it delivered a few basic services that everyone needs (file transfer, electronic mail, remote logon) across a very large number of client and server systems. Several computers in a small department can use TCP/IP (along with other protocols) on a single LAN. The IP component provides routing from the department to the enterprise network, then to regional networks, and finally to the global Internet. On the battlefield a communications network will sustain damage, so the DOD designed TCP/IP to be robust and automatically recover from any node or phone line failure. This design allows the construction of very large networks with less central management. However, because of the automatic recovery, network problems can go undiagnosed and uncorrected for long periods of time.
The following timeline shows, the origins of TCP/IP began inÂ 1969, when the U.S. Department of Defense (DoD) commissioned the Advanced Research Projects Agency Network (ARPANET).
The ARPANET was the result of a resource-sharing experiment. The purpose was to provide high-speed network communication links between various supercomputers located at various regional sites within the United States.
Early protocols such as Telnet (for virtual terminal emulation) and File Transfer Protocol (FTP) were first developed to specify basic utilities needed for sharing information across the ARPANET. As the ARPANET grew in size and scope, two other important protocols appeared:
In 1974, Transmission Control Protocol (TCP) was introduced as a draft specification that described how to build a reliable, host-to-host data transfer service over a network.
In 1981, Internet Protocol (IP) was introduced in draft form and described how to implement an addressing standard and route packets between interconnected networks.
On January 1, 1983, ARPANET began to require standard use of the TCP and IP protocols for all network traffic and essential communication. From this date forward, ARPANET started to become more widely known as the Internet and its required protocols started to become more widely known as theÂ TCP/IP protocol suite.
The TCP/IP protocol suite is implemented in a variety of TCP/IP software offerings available for use with many computing platforms. Today, TCP/IP software remains widely in use on the Internet and is used often for building large routed private internetworks.
As with all other communications protocol, TCP/IP is composed of layers:
IPÂ - is responsible for moving packet of data from node to node. IP forwards each packet based on a four byte destination address (the IP number). The Internet authorities assign ranges of numbers to different organizations. The organizations assign groups of their numbers to departments. IP operates on gateway machines that move data from department to organization to region and then around the world.
TCPÂ - is responsible for verifying the correct delivery of data from client to server. Data can be lost in the intermediate network. TCP adds support to detect errors or lost data and to trigger retransmission until the data is correctly and completely received.
Sockets -Â is a name given to the package of subroutines that provide access to TCP/IP on most systems.
The Army puts out a bid on a computer and DEC wins the bid. The Air Force puts out a bid and IBM wins. The Navy bid is won by Unisys. Then the President decides to invade Grenada and the armed forces discover that their computers cannot talk to each other. The DOD must build a "network" out of systems each of which, by law, was delivered by the lowest bidder on a single contract.
Figure 1: Network A group of two or more computer systems linked together.
The Internet Protocol was developed to create a Network of Networks (the "Internet"). Individual machines are first connected to a LAN (Ethernet or Token Ring). TCP/IP shares the LAN with other uses (a Novell file server, Windows for Workgroups peer systems). One device provides the TCP/IP connection between the LAN and the rest of the world.
To insure that all types of systems from all vendors can communicate, TCP/IP is absolutely standardized on the LAN. However, larger networks based on long distances and phone lines are more volatile. In the US, many large corporations would wish to reuse large internal networks based on IBM's SNA. In Europe, the national phone companies traditionally standardize on X.25. However, the sudden explosion of high speed microprocessors, fiber optics, and digital phone systems has created a burst of new options: ISDN, frame relay, FDDI, Asynchronous Transfer Mode (ATM). New technologies arise and become obsolete within a few years. With cable TV and phone companies competing to build the National Information Superhighway, no single standard can govern citywide, nationwide, or worldwide communications.
The original design of TCP/IP as a Network of Networks fits nicely within the current technological uncertainty. TCP/IP data can be sent across a LAN, or it can be carried within an internal corporate SNA network, or it can piggyback on the cable TV service. Furthermore, machines connected to any of these networks can communicate to any other network through gateways supplied by the network vendor.
There are three levels of TCP/IP knowledge. Those who administer a regional or national network must design a system of long distance phone lines, dedicated routing devices, and very large configuration files. They must know the IP numbers and physical locations of thousands of subscriber networks. They must also have a formal network monitor strategy to detect problems and respond quickly.
Each large company or university that subscribes to the Internet must have an intermediate level of network organization and expertise. A half dozen routers might be configured to connect several dozen departmental LANs in several buildings. All traffic outside the organization would typically be routed to a single connection to a regional network provider.
However, the end user can install TCP/IP on a personal computer without any knowledge of either the corporate or regional network. Three pieces of information are required:
The IP address assigned to this personal computer
The part of the IP address (the subnet mask) that distinguishes other machines on the same LAN (messages can be sent to them directly) from machines in other departments or elsewhere in the world (which are sent to a router machine)
The IP address of the router machine that connects this LAN to the rest of the world.
In the case of the PCLT server, the IP address is 220.127.116.11. Since the first three bytes designate this department, a "subnet mask" is defined as 255.255.255.0 (255 is the largest byte value and represents the number with all bits turned on). It is a Yale convention (which we recommend to everyone) that the router for each department have station number 1 within the department network. Thus the PCLT router is 18.104.22.168. Thus the PCLT server is configured with the values:
My IP address: 22.214.171.124
Subnet mask: 255.255.255.0
Default router: 126.96.36.199
The subnet mask tells the server that any other machine with an IP address beginning 130.132.59.* is on the same department LAN, so messages are sent to it directly. Any IP address beginning with a different value is accessed indirectly by sending the message through the router at 188.8.131.52 (which is on the departmental LAN).
Explanation & Overview:
Each technology has its own convention for transmitting messages between two machines within the same network. On a LAN, messages are sent between machines by supplying the six byte unique identifier (the "MAC" address). In an SNA network, every machine has Logical Units with their own network address. DECNET, Appletalk, and Novell IPX all have a scheme for assigning numbers to each local network and to each workstation attached to the network.
On top of these local or vendor specific network addresses, TCP/IP assigns a unique number to every workstation in the world. This "IP number" is a four byte value that, by convention, is expressed by converting each byte into a decimal number (0 to 255) and separating the bytes with a period. For example, the PC Lube and Tune server is 184.108.40.206.
Figure 2 : On TCP/IP networks, subnets are defined as all devices whose IP addresses have the same prefix.
The enterprise network is built using commercially available TCP/IP router boxes. Each router has small tables with 255 entries to translate the one byte department number into selection of a destination Ethernet connected to one of the routers.
If the size of the network grows, then the complexity of the routing updates will increase as will the cost of transmitting them. Building a single network that covers the entire US would be unreasonably complicated. Fortunately, the Internet is designed as a Network of Networks. This means that loops and redundancy are built into each regional carrier. The regional network handles its own problems and reroutes messages internally. Its Router Protocol updates the tables in its own routers, but no routing updates need to propagate from a regional carrier to the NSF spine or to the other regions (unless, of course, a subscriber switches permanently from one region to another).
IBM designs its Systems Network Architecture (SNA) to be centrally managed. If any error occurs, it is reported to the network authorities. By design, any error is a problem that should be corrected or repaired. IP networks, however, were designed to be robust. In battlefield conditions, the loss of a node or line is a normal circumstance. Casualties can be sorted out later on, but the network must stay up. So IP networks are robust. They automatically (and silently) reconfigure themselves when something goes wrong. If there is enough redundancy built into the system, then communication is maintained.
Data traffic is frequently organized around "hubs," much like airline traffic. The problem is that data arrives without a reservation. Airline companies experience the problem around major events, like the Super Bowl. Just before the game, everyone wants to fly into the city. After the game, everyone wants to fly out. Imbalance occurs on the network when something new gets advertised.
Occasionally a snow storm cancels flights and airports fill up with stranded passengers. Many go off to hotels in town. When data arrives at a congested router, there is no place to send the overflow. Excess packets are simply discarded. It becomes the responsibility of the sender to retry the data a few seconds later and to persist until it finally gets through. This recovery is provided by the TCP component of the Internet protocol.
TCP was designed to recover from node or line failures where the network propagates routing table changes to all router nodes. Since the update takes some time, TCP is slow to initiate recovery. The TCP algorithms are not tuned to optimally handle packet loss due to traffic congestion. Instead, the traditional Internet response to traffic problems has been to increase the speed of lines and equipment in order to stay ahead of growth in demand.
TCP treats the data as a stream of bytes. It logically assigns a sequence number to each byte. The TCP packet has a header that says, in effect, "This packet starts with byte 379642 and contains 200 bytes of data." The receiver can detect missing or incorrectly sequenced packets. TCP acknowledges data that has been received and retransmits data that has been lost. The TCP design means that error recovery is done end-to-end between the Client and Server machine. There is no formal standard for tracking problems in the middle of the network, though each network has adopted some ad hoc tools.
Figure 3: The types of services performed and protocols used at each layer within the TCP/IP model are described in more detail in the following table.
Defines TCP/IP application protocols and how host programs interface with transport layer services to use the network.
HTTP, Telnet, FTP, TFTP, SNMP, DNS, SMTP, XÂ Windows, other application protocols
Provides communication session management between host computers. Defines the level of service and status of the connection used when transporting data.
TCP, UDP, RTP
Packages data into IP datagrams, which contain source and destination address information that is used to forward the datagrams between hosts and across networks. Performs routing of IP datagrams.
IP, ICMP, ARP, RARP
Specifies details of how data is physically sent through the network, including how bits are electrically signaled by hardware devices that interface directly with a network medium, such as coaxial cable, optical fiber, or twisted-pair copper wire.
Ethernet, Token Ring, FDDI, X.25, Frame Relay, RS-232, v.35
Table 1: TCP/IP Model
The wordÂ wirelessÂ is dictionary defined as "having no wires". InÂ networkingÂ terminology, wireless is the term used to describe anyÂ computerÂ network where there is no physical wired connection between sender and receiver, but rather the network is connected by radio waves and/or microwaves to maintain communications. Wireless networkingÂ utilizes specific equipment such asÂ NICs,Â APs andÂ routersÂ in place of wires (copperÂ orÂ optical fiber) for connectivity.
AÂ wirelessÂ network orÂ WirelessÂ LocalÂ AreaÂ NetworkÂ (WLAN) serves the same purpose as a wired one - to link a group ofÂ computers. Because "wireless" doesn't require costly wiring, the main benefit is that it's generally easier, faster and cheaper to set up.
By comparison, creating a network by pulling wires throughout the walls and ceilings of an office can be labor-intensive and thus expensive. But even when you have a wired network already in place, a wireless network can be a cost-effective way to expand or augment it. In fact, there's really no such thing as a purely wireless network, because most link back to a wired network at some point.
Wireless networks operate usingÂ radioÂ frequencyÂ (RF)Â technology, a frequency within the electromagnetic spectrum associated with radio wave propagation. When an RF current is supplied to an antenna, an electromagnetic field is created that then is able to propagate through space.
The cornerstone of a wireless network is a device known as anÂ accessÂ pointÂ (AP). The primary job of anÂ accessÂ pointÂ is to broadcast a wireless signal that computersÂ can detect and "tune" into. Since wireless networks are usually connected to wired ones, an access point also often serves as a link to the resources available on the a wired network, such as an Internet connection.
In order to connect to an access point and join a wireless network, computers must be equipped with wirelessÂ network adapters. These are often built right into the computer, but if not, just about any computer or notebook can be made wireless-capable through the use of an add-onÂ adapterÂ plugged into an empty expansion slot,Â USBÂ port, or in the case ofÂ notebooks, aÂ PC CardÂ slot.
Wireless Technology Standards
Because there are multiple technology standards for wireless networking, it pays to do your homework before buying any equipment. The most commonÂ wireless technology standardsÂ include the following:
802.11b: The first widely used wireless networking technology, known as 802.11b (more commonly called Wi-Fi), first debuted almost a decade ago, but is still in use.
802.11g: In 2003, a follow-on version called 802.11g appeared offering greater performance (that is, speed and range) and remains today's most common wireless networking technology.
802.11n:Â Another improved standard called 802.11n is currently underÂ developmentÂ and is scheduled to be complete in 2009. But even though the 802.11n standard has yet to be finalized, you can still buy products based on the draft 802.11n standard, which you will be able to upgrade later to the final standard.
All of the Wi-Fi variants (802.11b, g and n products) use the same 2.4 GHz radio frequency, and as a result are designed to be compatible with each other, so you can usually use devices based on the different standards within the same wireless network. The catch is that doing so often requires special configuration to accommodate the earlier devices, which in turn can reduce the overall performance of the network. In an ideal scenario you'll want all your wireless devices, the access point and all wireless-capable computers, to be using the same technology standard and to be from the same vendor whenever possible.
Wireless Speed & Range
When you buy a piece of wireless network hardware, it will often quote performance figures (i.e., how fast it can transmit data) based on the type of wireless networking standard it uses, plus any added technological enhancements.Â In truth, these performance figures are almost always wildly optimistic.
While the official speeds ofÂ 802.11b,Â 802.11g, andÂ 802.11nÂ networks are 11, 54, and 270Â megabitsÂ perÂ secondÂ (Mbps) respectively, these figures represent a scenario that's simply not attainable in the real world. As a general rule, you should assume that in a best-case scenario you will get roughly one-third of the advertised performance.Â
It's also worth noting that a wireless network is by definition a shared network, so the more computers you have connected to a wireless access point the less data each will be able to send and receive. Just as a wireless network's speed can vary greatly, so too can the range. For example, 802.11b and g officially work over a distance of up to 328 feet indoors or 1,312 feet outdoors, but the key term there is "up to". Chances are you won't see anywhere close to those numbers.Â
As you might expect, the closer you are to an access point, the stronger the signal and the faster the connection speed. The range and speed you get out of wireless network will also depend on the kind of environment in which it operates. And that brings us to the subject of interference.
Interference is an issue with any form of radio communication, and a wireless network is no exception. The potential for interference is especially great indoors, where different types of building materials (concrete, wood, drywall, metal, glass and so on) can absorb or reflect radio waves, affecting the strength and consistency of a wireless network's signal. Similarly, devices like microwave ovens and some cordless phones can cause interference because they operate in the same 2.4 frequency range as 802.11b/g/n networks. You can't avoid interference entirely, but in most cases it's not significant enough to affect the usability of the network. When it does, you can usually minimize the interference by relocating wireless networking hardware or using specializedÂ antennas.
Data Security on Wireless Networks
In the same way that all you need to pick up a local radio station is a radio, all anyone needs to detect a wireless network within nearby range is a wireless-equipped computer. There's no way to selectively hide the presence of your network from strangers, but you can prevent unauthorized people from connecting to it, and you can protect the data traveling across the network from prying eyes. By turning on a wireless network's encryption feature, you can scramble the data and control access to the network.Â
Wireless network hardware supports several standard encryption schemes, but the most common areÂ WiredÂ EquivalentÂ Privacy(WEP),Â Wi-FiÂ ProtectedÂ AccessÂ (WPA), andÂ Wi-FiÂ ProtectedÂ AccessÂ 2Â (WPA2). WEP is the oldest and least secure method and should be avoided. WPA and WPA2 are good choices, but provide better protection when you use longer and more complex passwords (all devices on a wireless network must use the same kind of encryption and be configured with the same password).
Unless you intend to provide public access to your wireless network - and put your business data or your own personal data at risk - you should consider encryption mandatory.
Wireless network standards:
Pros/Cons & More Info
Up to 2Mbps in the 2.4GHz band
FHSSÂ or DSSS
WEPÂ &Â WPA
This specification has been extended into 802.11b.
Up to 54Mbps in the 5GHz band
WEPÂ &Â WPA
Products that adhere to this standard are considered "Wi-Fi Certified." Eight available channels. Less potential forÂ RF interference than 802.11b and 802.11g. Better than 802.11b at supportingÂ multimediaÂ voice, video and large-imageÂ applicationsÂ in densely populated user environments. Relatively shorter range than 802.11b. Not interoperable with 802.11b.
Up to 11Mbps in the 2.4GHz band
DSSSÂ with CCK
WEPÂ &Â WPA
Products that adhere to this standard are considered "Wi-Fi Certified." Not interoperable with 802.11a. Requires fewerÂ access pointsÂ than 802.11a for coverage of large areas. Offers high-speed access to data at up to 300 feet from base station. 14 channels available in the 2.4GHz band (only 11 of which can be used in the U.S. due toÂ FCCÂ regulations) with only three non-overlapping channels.
Up to 54Mbps in the 2.4GHz band
OFDMÂ above 20Mbps,DSSSÂ with CCKÂ below 20Mbps
WEPÂ &Â WPA
Products that adhere to this standard are considered "Wi-Fi Certified." May replace 802.11b. Improved security enhancements over 802.11. Compatible with 802.11b. 14 channels available in the 2.4GHz band (only 11 of which can be used in the U.S. due to FCCÂ regulations) with only three non-overlapping channels.
Specifies WiMAX in the 10 to 66 GHz range
DES3 and AES
Commonly referred to as WiMAX or less commonly as Wireless MAN or the AirÂ InterfaceÂ Standard, IEEE 802.16 is a specification for fixed broadband wireless metropolitan access networks (MANs)
Added support for the 2 to 11 GHz range.
DES3 and AES
Commonly referred to as WiMAX or less commonly as Wireless MAN or the Air Interface Standard, IEEE 802.16 is a specification for fixed broadband wireless metropolitan access networks (MANs)
Up to 2Mbps in the 2.45GHz band
PPTP,Â SSLÂ orVPN
No native support forÂ IP, so it does not supportÂ TCP/IPÂ and wireless LAN applications well. Not originally created to support wireless LANs. Best suited for connectingÂ PDAs, cell phones and PCsÂ in short intervals.
Up to 10Mbps in the 2.4GHZ band
Independent network IP addresses for each network. Data is sent with a 56-bit encryption algorithm.
Note:Â HomeRF is no longer being supported by any vendors or working groups. Intended for use in homes, not enterprises. Range is only 150 feet from base station. Relatively inexpensive to set up and maintain. Voice quality is always good because it continuously reserves a chunk of bandwidth for voice services. Responds well to interference because of frequency-hopping modulation.
Up to 20Mbps in the 5GHz band
Per-session encryption and individual authentication.
Only in Europe. HiperLAN is totally ad-hoc, requiring no configuration and no central controller. Doesn't provide real isochronousÂ services. Relatively expensive to operate and maintain. No guarantee of bandwidth.
Up to 54Mbps in the 5GHz band
Strong security features with support for individual authentication and per-session encryption keys.
Only in Europe. Designed to carryÂ ATMÂ cells, IP packets,Â Firewire packets (IEEE 1394) and digital voice (from cellular phones). Better quality of service than HiperLAN/1 and guarantees bandwidth.
Pre-802.11 protocol, using Frequency Hopping and 0.8 and 1.6Â Mb/s bit rate
CSMA/CA withÂ MAC retransmissions
OpenAir doesn't implement any encryption at the MAC layer, but generates Network ID based on a password (Security ID)
OpenAir is the proprietary protocol from Proxim. All OpenAir products are based on Proxim's module.
Table 2: wireless networking standards