Connection to the Internet these days has become so easy and user-friendly that we tend to forget the technical aspects of things like page loads and file downloads. Such operations still take place, even though the average user doesn’t give them a second thought.

One such overlooked set of operations is TCP/IP. This often used but little understood set of operations stands for Transmission Control Protocol/Internet Protocol. TCP/IP is the combination of the two and describes the set of protocols that allows hosts to connect to the Internet. In actuality, TCP/IP is a combination of more than those two protocols, but the TCP and IP parts of TCP/IP are the main ones and the only ones to become part of the acronym that describes the operations involved.

TCP/IP doesn’t just happen. It is an active process; a set of constant communications between private computers and Internet servers. When a computer attempts to log on to the Internet, that computer’s TCP/IP operations send a series of signals to Internet servers looking for a connection. In nearly all cases, access is successful. Some exceptions would keep access from being granted, but these exceptions are rare.

The two layers of TCP/IP are defined by the separate spelled-out versions. Transmission Control Protocol is the top layer; the one that converts messages or files into data packets that are transmitted over the network connection to the destination computer and then reassembled into messages or files that can be read by the destination user. The lower layer of TCP/IP, Internet Protocol, provides the transmitting operation, configuring the connection’s address so that the information gets to the right place. IP could function without TCP, although it would be idle, but the reverse is not possible.

Despite the very evident presence of the word Internet in the spelled-out version of TCP/IP, the set of protocols can be used for internal use as well. Company intranets utilize TCP/IP protocols in order to set up a network within the company’s computer framework. No outside connection develops, but connections are made between the company’s servers and/or mainframes and individual computers. This sort of connectivity mimics the connection functionality of TCP/IP as used for Internet connections.

source: http://www.wisegeek.com/what-is-tcpip.htm

A passphrase is a series of letters, characters, or words that can be combined like a password. They are used for many computer programs, to gain access to systems, data, or messages. It is similar to shorter passwords in use, but a passphrase can be as long as 100 characters and offer extra protection when needed. They can be used as a digital signature or to encrypt messages, and are often employed by important systems vulnerable to outside hackers.

Whereas a password is generally 4-16 characters, a passphrase is typically at least 20-40. The common passphrase should be known only to the user, should be long enough to remain difficult, hard to guess, easy to remember, and easy to type quickly and accurately. The passphrase should not be a common phrase or one from literature or culture. It should not be something with obvious meaning to the user or something that can be easily identified, even by people who know the user.

Different passphrases, just like different passwords, possess varying passphrase strengths. This is determined by the length of the phrase, the randomness of the phrase, and its use of characters available in the common lexicon. A phrase such as “IAmTheKingOfTheWorld” would not be good because it is not particularly original or uncommon. Replace the vowels with numbers, or a word with an anagram or a nonsensical string of words, and the phrase becomes more difficult. “I4m7heK1ng0fTheW0r1d,” for example, would be much more difficult.

A passphrase can be easy or difficult to remember, and can be written down. Certain passphrase are made of random groupings of numbers and letters, though a sense of structure makes them easier to remember. One method of formulating a passphrase is called Diceware. This tool is comprised of a list of 7776 short English words, and is determined by rolling dice. With a certain number of corresponding letters for each number on the die, different combinations of letters make different words. These different words can be combined into a phrase with more than 2,000,000,000,000,000,000 possibilities.

The modern idea of the passphrase was invented by Sigmund N. Porter in 1982 as a means of extra protection as computer systems began to enter mainstream culture. Pretty Good Privacy, a popular passphrase method, revolutionized the practice in 1991. Created by Phil Zimmerman in the United States, it was used to encrypt e-mails, and features a public and a private passphrase encryption key. A private key is used to open and send messages personally, and the public key of someone else is used to receive or send messages to them.

source: http://www.wisegeek.com/what-is-a-passphrase.htm

The maximum transmission unit, or MTU, is the single largest frame or packet of data that can be transmitted across a network. The exact nature of the maximum transmission unit will be determined by the configuration of the network and what type of protocols is in place for the transmission of data. Generally, a maximum transmission unit is composed of eight-bit bytes of information.

The size of the frame or packet is very important to the process of transmitting data through any network. For this reason, there are usually specific rules that govern the size of data packets that can be transmitted without creating some sort of bottleneck within the network. In the case of the Internet, a set of standards referred to as the Transmission Control Protocol is utilized to define what constitutes a functional size of data packet.

When transmitting information, the size of the maximum transmission unit is very important. In the event that the packet or frame is too large, the end result could be a router that is unable to process the packet properly and the data transmission will fail, or the router will go into a series of continual attempts to process the packet. This can lead to failure of the router to handle other transmissions.

At the same time, if the maximum transmission unit is rather small, that leaves more room for headers and other types of overhead that may be processed as part of the data packet. This can also mean more that it is necessary to send and process more acknowledgements as well. While a smaller packet is less likely to cause a bottleneck, it does leave room for resources to be wasted.

MTUs have been around for a number of years. As technology has continued to progress, the desirable size of a given maximum transmission unit has grown accordingly. Operating systems located on hard drives usually are preset with an MTU range that is in accordance with most common applications. Generally, the setting reflects a general range, as what is standard for one type of network may be high or low for another network. Internet service providers tend to make recommendations about settings for MTU reception as well, based on the type of connectivity that is in place and the operating system employed by the end user.

source: http://www.wisegeek.com/what-is-a-maximum-transmission-unit.htm

Network access control or NAC is one of the strategies that is employed to enhance the security protocols associated with a private or proprietary network. This is accomplished by setting restrictions on the ability to access various programs and functions that are available on the network. The creation of the authorizations required to allow access to any given database, software, or function on the network remains in the control of a network administrator or other persons who are granted that level of management by the administrator.

There are several common ways that network access control is achieved. The most common approach is to set up a process for authenticating each valid user for the network. This may be accomplished by employing a simplistic user name and password combination, or involve additional clearances that are necessary, such as a test question or proper identification of an image that is associated with the login credentials.

Typically, the administrator sets the structure for the credentials, although users may or may not be granted the privilege of changing passwords from time to time. This level of network admission control (which is also identified as NAC) is usually the foundational tool in making sure a network is secure. However, it rarely is the only security measure utilized.

Along with setting login credentials and procedures, network access control also usually involves setting rights and privileges associated with each user. For example, salespersons are likely to have access rights to a general sales database, but be limited to the type of information that may be accessed and viewed from the accounting software program that also resides on the network access server or NAS. Privileges are usually determined based on the perimeters of the job or position held by each user. However, administrators can grant users additional rights and privileges if the need arises.

Other tools help to provide general enhancement to these basic network access control protocols. The addition of a firewall can help to minimize attacks from outside the network. In like manner, the presence of spyware detection programs and antivirus protection software can also be a great help if users make regular use of Internet access.

While a network administrator can purchase and load individual tools to assist in network access control, several vendors now offer software packages that include a wide range of different network access control features and options. Several of the packages allow the administrator to pick and choose from available options, making it possible to customize the type and level of network security that is required.

source: http://www.wisegeek.com/what-is-network-access-control.htm

What are the network setting required for a computer to join a domain?

In order to be able to join a Windows 2000 or Windows Server 2003 domain you must properly configure your XP/W2K computer.

Note: XP Home Edition is not designed to join domains; only workgroups. To join domains, use XP Professional version or above.
Required Settings

A network Interface Card (NIC) – Duh, but unless you have one (or a wireless connection) how do you expect to connect to the server?

Physically be connected to the LAN – Windows XP (and 2000) has an LAN auto sensing feature. Whenever you disconnect from the network, a balloon appears in the task bar area notifying you of the disconnection status. Without a physically connected network the NIC looses it’s IP settings, thus preventing you from connecting to the network (which was disconnected in the first place) or viewing your IP configuration.

A valid IP address – Valid for the network you’re connected to. You can either configure one manually, receive one from a local DHCP Server, or leave it as is and receive an APIPA address. If it’s an APIPA address you’re asking for potential problems, as APIPA and AD do not go together hand-in-hand.

All-time connectivity to the Domain Controller – Or at least one of them. The IP address you’ve configured (or leased) should be good enough to enable you to connect to one of the Domain Controllers on your Domain. Test your connectivity with PING.

A properly configured DNS server – Without a properly configured DNS server your workstation will not be able to connect to the domain. Even if it did (for example you had a working DNS server but you somehow messed it up or shut it down) it will take a lot of time to actually log-on, and many AD related administration tasks will not work.

The DNS server must hold a zone with the exact name of the AD domain you’re trying to join. It also must hold 4 SRV folders (you can tell by the “_” in their name). If it doesn’t, you either misspelled the domain name or DNS zone, or the zone is not configured to accept dynamic registrations, or it’s not a Windows 2000 DNS server, or the Domain Controller does not have a working connection with the DNS server (firewall problems, improper IP configuration, IPSec etc.)

All-time connectivity to the DNS server – Test your connection to the DNS server by PINGing it and performing an NSLOOKUP query.

Local Administrative power – A simple user won’t do. You must be the local Administrator.

Correct domain name, Administrator’s name and password – Misspelled your domain name? You won’t get to the Username and Password prompt!

Got your domain name right? You’ll be asked for a valid username and password. To be safe, enter one that has Domain Admins rights, although you could get away with less, depending on your AD configuration.

No Internet Connection Sharing please – ICS will mess up your network. Do not use it. Use RRAS and NAT instead. It will work if it has to, but ICS and AD do not go together hand-in-hand. You are warned.

source:
http://www.petri.co.il/requirements_when_joining_a_domain.htm

Introduction

Over the past number of years processor performance has doubled approximately every 18 months. This increase in processor performance, combined with multi-core technologies has driven the demand for higher data transfer rates. This data transfer needs to happen between an I/O device, memory, and between processors. In many of today’s computers the data transfer capability is the limiting factor for overall system performance. In this article I will highlight the details of one solution to this performance issue.

One solution for higher data transfer rates is called HyperTransport. Most users will recognize this from some AMD products. In fact, HyperTransport was invented at AMD (with help from some industry partners) although it is now managed and promoted by an independent group called the HyperTransport Consortium.

HyperTransport is a point-to-point interconnecting system focused on chip-to-chip communications. From its inception it has been designed to offer high speeds and low latency. This is a requirement today and into the future as CPU clock speeds continue to increase. Chip-to-chip communication especially demands low latency and high performance.

Being a point-to-point interconnect technology, as opposed to a bus system, offers many advantages for chip-to-chip communication. One advantage is that the communication signals do not require multiplexing. Also, these communication signals experience less interference and therefore experience less noise and can be transmitted with less power. This all combines for faster, and cleaner, communications.

Another advantage of a point-to-point technology is that it does not suffer from degraded performance, as PCI buses do, as the number of devices connected increases. HyperTransport utilizes a direct connection between two devices only. More devices can be connected only by utilizing a daisy chain method. This means that the performance is the same as more devices are connected.

Packet Based

HyperTransport is packet-based. This allows HyperTransport to play the interconnect role for many different purposes. This technology can be used to interconnect processing cores, RAM and CPU, or even external memory equipment. For more information on these memory types, see my previous articles on computer memory here, here, and here. Since the HyperTransport technology is packet-based, the hardware that is interconnected forms what most would consider a network. In the case of a super-computer having a network of processors interconnected with a point-to-point technology can be very beneficial.

Low Packet Overhead

Like most networks, a HyperTransport network will have performance characteristics. HyperTransport happens to measure up very well when its performance is compared against other interconnect technologies such as PCI Express. One reason that HyperTransport compares favorably to its peers is the low packet overhead designed into the technology.

HyperTransport required an 8 byte read request control packet for read operations. For write operations, HyperTransport uses an 8 byte write request control packet with and a 4 byte read response packet. This is it. That is all the overhead; 8 bytes for a read operation and 12 bytes for a write operation. PCI Express requires 20 to 24 bytes of overhead for its read and write operations. This is obviously a major advantage for HyperTransport.

But all is not perfect for HyperTransport. I need to be fair to the PCI Express technology here. With HyperTransport, the data packet which follows the control packet(s) can only be from 4 to 64 bytes. The data packet for PCI Express can be up to 4096 bytes. So, in some instances PCI Express can have a lower packet overhead than HyperTransport. However, in my opinion, and I don’t have any data to back this up, most read/write operations will require relatively small data packets; thus giving the advantage to HyperTransport. This is especially the case when we are talking about data transfers between processors.

Figure 1: A diagram of packet overhead for HyperTransport and PCI Express.

Bandwidth

HyperTransport was originally designed to offer significantly higher bandwidth than other competing technologies. One way it does this is to provide a Double Data Rate (DDR). Normally when data is digitally transmitted between two points, data is read as either high or low which represents either a 1 or 0. This data is read whenever the clock produces a high signal. With DDR, data can be read on the rising and falling edges of a clock signal. This means that in one full clock cycle a DDR capable transmission data can be read twice, producing twice the data rate.

Low Latency

Low Latency is a design parameter which has been a focus of the HyperTransport technology since the beginning. HyperTransport can achieve this in part by having a single clock signal per set of 8 data bit paths. This is significant because other technologies, such as PCI Express, have their clocks embedded in a complicated encoding/decoding scheme at both ends of the data link. The method used by HyperTransport is effective in reducing the latency when compared to other technologies because the transmitting device does not need to spend time encoding the clock and the receiving device does not need to spend time decoding the clock.

Priority Request Interleaving

Another aspect of HyperTransport which contributes to its high performance is what they call Priority Request Interleaving (PRI). This is a really cool idea. Figure 2 below shows how PRI works. The problem PRI solves is this: When the CPU is in the midst of a long communication sequence with peripheral device B and peripheral device A needs to communicate with the CPU device A will normally need to wait until device B is finished communicating in order to proceed with its own communication; this can take quite some time and obviously reduce the overall performance.

PRI technology allows peripheral device A to insert a PRI packet into the data stream of device B. This PRI packet is read by the CPU which can then commence a communication sequence with device A on a different link channel.

Figure 2: Diagram explaining PRI. Courtesy of www.hypertransport.org

The HyperTransport technology has been designed from the beginning to provide board level interconnects which allow for high communication speeds with low latency, high bandwidth, and high scalability. By all accounts it has achieved these goals. HyperTransport is used in many applications from the embedded market, consumer electronics, home computers, enterprise level networking equipment, carrier grade networking equipment, and even super-computers.

However, not all of these applications use HyperTransport in the same way. Some processors include HyperTransport technology right in the processor. Such processors include many offerings from AMD, Transmetta, Broadcom, and PMC Sierra. Other processors, PowerMac’s old G5 for instance, use HyperTransport as a high performance I/O bus that pipes data from PCI, PCI Express, USB, and other technologies through the system. HyperTransport provides excellent performance in both use case scenarios.

Conclusion

Although HyperTransport is an excellent technology with many performance benefits there is still a place in the market for other technologies. Engineers need to consider their needs carefully to choose the technology that is right for a specific application. In upcoming articles I will go into more detail on some of these other interconnect technologies.

source:
http://www.windowsnetworking.com/articles_tutorials/HyperTransport.html

Once, home networks were primarily the realm of technophiles — most families either didn’t need or couldn’t afford more than one computer. But now, in addition to using computers for e-mail, people use them for schoolwork, shopping, instant messaging, downloading music and videos, and playing games. For many families, one computer is no longer enough to go around. In a household with multiple computers, a home network often becomes a necessity rather than a technical toy.
A home network is simply a method of allowing computers to communicate with one another. If you have two or more computers in your home, a network can let them share:

* Files and documents
* An Internet connection
* Printers, print servers and scanners
* Stereos, TVs and game systems
* CD burners

The different network types use different hardware, but they all have the same essential components:

* More than one computer
* Hardware (such as a router) and software (either built in to the operating system or as a separate application) to coordinate the exchange of information
* A path for the information to follow from one computer to another

If you’re thinking of networking the computers in your home, you have several options to explore. In this article, you’ll learn about the different types of home computer networks, how they work and what to keep in mind if you’re considering creating one.

Building a Home Network

The two most popular home network types are wireless and Ethernet networks. In both of these types, the router does most of the work by directing the traffic between the connected devices. By connecting a router to your dial-up, DSL or cable modem, you can also allow multiple computers to share one connection to the Internet.

If you’re going to connect your network to the Internet, you’ll need a firewall. A firewall is simply a hardware device or software program that protects your network from malicious users and offensive Web sites, keeping hackers from accessing or destroying your data. Although they’re essential for businesses looking to protect large amounts of information, they’re just as necessary for someone setting up a home network, since a firewall will secure transactions that might include Social Security numbers, addresses, phone numbers and credit card numbers. Most routers combine wireless and Ethernet technology and also include a hardware firewall.

Many software firewalls installed onto your computer block all incoming information by default and prompt you for permission to allow the information to pass. In this way, a software firewall can learn which types of information you want to allow into your network. Symantec, McAfee and ZoneAlarm are popular companies that produce software-based firewalls. These companies usually offer some free firewall protection as well as advanced security that you can buy.

Wired Networks

Ethernet and wireless networks each have advantages and disadvantages; depending on your needs, one may serve you better than the other. Wired networks provide users with plenty of security and the ability to move lots of data very quickly. Wired networks are typically faster than wireless networks, and they can be very affordable. However, the cost of Ethernet cable can add up — the more computers on your network and the farther apart they are, the more expensive your network will be. In addition, unless you’re building a new house and installing Ethernet cable in the walls, you’ll be able to see the cables running from place to place around your home, and wires can greatly limit your mobility. A laptop owner, for example, won’t be able to move around easily if his computer is tethered to the wall.

There are three basic systems people use to set up wired networks. An Ethernet system uses either a twisted copper-pair or coaxial-based transport system. The most commonly used cable for Ethernet is a category 5 unshielded twisted pair (UTP) cable — it’s useful for businesses who want to connect several devices together, such as computers and printers, but it’s bulky and expensive, making it less practical for home use. A phone line, on the other hand, simply uses existing phone wiring found in most homes, and can provide fast services such as DSL. Finally, broadband systems provide cable Internet and use the same type of coaxial cable that gives us cable television.

If you plan to connect only two computers, all you’ll need is a network interface card (NIC) in each computer and a cable to run between them. If you want to connect several computers or other devices, you’ll need an additional piece of equipment: an Ethernet router. You’ll also need a cable to connect each computer or device to the router.

Once you have all of your equipment, all you need to do is install it and configure your computers so they can talk to one another. Exactly what you need to do depends on the type of network and your existing hardware. For example, if your computers came with network cards already installed, all you’ll need to do is buy a router and cables and configure your computers to use them. Regardless of which type you select, the routers, adapters and other hardware you buy should come with complete setup instructions.

The steps you’ll need to take to configure your computers will also vary based on your hardware and your operating system. User manuals usually provide the necessary information, and Web sites dedicated to specific operating systems often have helpful tips on getting several different computers to talk to each other.

Wireless Networks

The easiest, least expensive way to connect the computers in your home is to use a wireless network, which uses radio waves instead of wires. The absence of physical wires makes this kind of network very flexible. For example, you can move a laptop from room to room without fiddling with network cables and without losing your connection. The downside is that wireless connections are generally slower than Ethernet connections and they are less secure unless you take measures to protect your network.

Faster Wireless
Most home wireless networks use 802.11g wireless networking, which transmits data at 2.4 GHz with a speed of 54 megabits. A newer wireless standard is 802.11n, which is designed to be faster and offer a longer range than 802.11g. However, the 802.11n standard isn’t yet final, and early 802.11n hardware has failed to meet expectations in tests. The ratification date by the Institute of Electrical and Electronics Engineers (IEEE) is expected to be in March 2009.

If you want to build a wireless network, you’ll need a wireless router. Signals from a wireless router extend about 100 feet (30.5 meters) in all directions, but walls can interrupt the signal. Depending on the size and shape of your home and the range of the router, you may need to purchase a range extender or repeater to get enough coverage.

You’ll also need a wireless adapter in each computer you plan to connect to the network. You can add printers and other devices to the network as well. Some new models have built-in wireless communication capabilities, and you can use a wireless Ethernet bridge to add wireless capabilities to devices that don’t. Any devices that use the Bluetooth standard can also connect easily to each other within a range of about 10 meters (32 feet), and most computers, printers, cell phones, home entertainment systems and other gadgets come installed with the technology.

If you decide to build a wireless network, you’ll need to take steps to protect it — you don’t want your neighbors hitchhiking on your wireless signal. Wireless security options include:

* Wired Equivalency Privacy (WEP)
* WiFi Protected Access (WPA)
* Media Access Control (MAC) address filtering

You can choose which method (or combination of methods) you want to use when you set up your wireless router. The IEEE has approved each of these security standards, but studies have proven that WEP can be broken into very easily. If you use WEP, you may consider adding Temporal Key Integrity Protocol (TKIP) to your operating system. TKIP is a wrapper with backward compatibility, which means you can add it to your existing security option without interfering with its activity. Think of it like wrapping a bandage around a cut finger — the bandage protects the finger without preventing it from carrying out its normal functions.

New Home Network Technology

New developments in home networks affect more than just home offices and entertainment systems. Some of the most exciting advances are in healthcare and housing.

In healthcare, Wireless Sensor Networks (WSNs) let doctors monitor patients wirelessly. Patients wear wireless sensors that transmit data through specialized channels. These signals contain information about vital signs, body functions, patient behavior and their environments. In the case of an unusual data transmission — like a sudden spike in blood pressure or a report that an active patient has become suddenly still — an emergency channel picks up the signal and sends medical services to the patient’s home.

The housing industry is another important field for home network technology development. Bill Gates owns one of the few smart houses in existence, but someday, we might all live in one. A smart house is a fully networked structure with functions that can be controlled from a central computer, making it an ideal technology for homeowners who travel frequently or for homeowners who simply want it all.

Builders are beginning to offer home network options for their customers that range from the primitive — installing Ethernet cables in the walls — to the cutting-edge — managing the ambient temperature from a laptop hundreds of miles from home. In one trial experiment called Laundry Time, Microsoft, Hewlett Packard, Panasonic, Proctor & Gamble and Whirlpool demonstrated the power of interfacing home appliances. The experiment networked a washing machine and clothes dryer with a TV, PC and cell phone. This unheard-of combination of networked devices let homeowners know when their laundry loads were finished washing or drying by sending alerts to their TV screens, instant messaging systems or cell phones. Research and development also continues for systems that perform a wide variety of functions — data and voice recognition might change the way we enter, exit and secure our homes, while service appliances could prepare our food, control indoor temperatures and keep our homes clean.

This technology is promising, but it’s not quite ready for the consumer market yet. The average consumer can’t afford a WSN or a smart house, and if he could, there’s a good chance he or she wouldn’t be able to operate these sophisticated systems. Another issue is security — until developers find a way to secure these networks, consumers risk sharing medical information and leaving their homes open to attack.

source: http://www.howstuffworks.com/home-network.htm

This tutorial will help you understand the practical differences between DSL and cable modem networking. While similar in many respects, DSL and cable Internet services differ in several fundamental ways.
DSL and Cable – Comparison and Contrast
When evaluating cable and DSL services, you should consider the following:

* Speed (advantage – Cable): Cable boasts faster speed than DSL Internet in theory. However, cable does not always deliver on the promise in everyday practical use.

Read more – DSL vs Cable – Speed Comparison

* Popularity (advantage – Both): In the U.S., cable Internet enjoys significantly greater popularity than DSL, although DSL has been closing the gap recently. Outside the U.S., DSL continues to hold the edge. Both dominate the rest of the competition with millions of subscribers to each.

Read more – DSL and Cable Modem Subscribers – U.S.

* Customer Satisfaction (advantage – DSL): Even if a technology is popular, customers may be unhappy with it whether due to cost, reliability or other factors. Indeed, in the U.S. cable services generally rate lower than DSL in customer surveys.

Read more – DSL vs Cable Customer Satisfaction – U.S.

* Security (advantage – Both): Cable and DSL implement different network security models. Historically, more concerns have existed with cable security, although cable providers have definitely taken steps to improve security over the past few years. It’s likely both DSL and cable are “secure enough” for most people’s needs.

Read more – Cable and DSL Security Compared.

Finally, over the years, readers have contributed their opinions on this topic to our message board. Be sure to consider their suggestions, too:

* Community Opinion: What Is the General Consensus – Cable or DSL?

A Note About DSL and Cable Service Providers

Both DSL and cable high-speed Internet services are available to millions of residential and business consumers worldwide. In some areas, only one service is available. Others have a choice.

Some of the differences between DSL and cable modem originate not with the technology itself but rather with the service provider. All other things being equal, factors like cost, reliability and quality of customer support for installation and maintenance issues can vary significantly from one provider to the next.

Both DSL and cable speeds exceed those of competing Internet services. Are DSL or cable any faster than each other? More importantly, are you getting all of the performance you should from your Internet connection? Follow along as we explain the speed difference between DSL and cable and offer tips for maximizing your performance.
DSL and Cable Speed – Bottom Line
Cable modem Internet services on average promise higher levels of bandwidth than DSL Internet services, and this bandwidth roughly translates to raw speed. However, while cable Internet will theoretically run faster than DSL, several technical and business reasons can reduce or even eliminate this advantage.
DSL vs Cable Raw Speed – Advantage Cable
In terms of theoretical peak performance, cable modem runs faster than DSL. Cable technology supports approximately 30 Mbps of bandwidth, whereas most forms of DSL cannot reach 10 Mbps.

One type of DSL technology, VDSL, can match cable’s performance, also supporting 30 Mbps. However, Internet service providers generally do not offer VDSL, but rather the cheaper and slower ADSL or SDSL services.

DSL vs Cable – Real-World Speed

In practice, cable’s speed advantage over DSL is much less than the theoretical numbers suggest. Why?

* Cable modem services can slow down significantly if many people in your neighborhood access the Internet simultaenously.
* Both cable modem and DSL performance vary from one minute to the next depending on the pattern of use and traffic congestion on the Internet.
* DSL and cable Internet providers often implement so-called “speed caps” that limit the bandwidth of their services.
* Some home networks cannot match the speed of the Internet connection, lowering your performance

DSL and Cable Speed Caps
Both cable and DSL service providers commonly employ bandwidth / speed caps for residential customers. Bandwidth caps place an artificial limit on the maximum speed a customer can achieve by monitoring their individual traffic flow and throttling network packets if necessary. Bandwidth caps can reduce a 30 Mbps service down to 3 Mbps or even lower.

Service providers may have several motivations for imposing speed caps including the following:

1. Providers concerned about the capacity limits of their network may implement a cap so that they can accomodate more customers.

2. Providers may believe that the vast majority of customers do not actually need any more bandwidth than that allowed under the cap.

3. Providers may want to create a fair-and-equal distribution of bandwidth of customers. Without a cap, for example, some DSL subscribers would enjoy much higher bandwidth levels than others in the same neighborhood.

4. Providers may be want to charge higher or lower rates for greater or lesser bandwidth levels.

Cable Speed – How Fast Is Cable Modem Internet?

Cable modem has long been recognized for its superior speed compared to other forms of Internet service. Is cable modem speed really that much better than alternatives? If so, how much faster?
Answer: Cable modem speeds vary widely. While cable modem technology can theoretically support up to about 30 Mbps, most providers offer service with between 1 Mbps and 6 Mbps bandwidth for downloads, and bandwidth between 128 Kbps and 768 Kbps for uploads.

Cable Speed Considerations
Did you know your cable speed will vary depending on the usage pattern of your neighbors? Cable modem services share bandwidth among subscribers in a locality. The same cable line connects to many households. If many of your neighbors access the Internet simulataneously, it is a distinct possibility that cable speeds for you (and them) will decrease significantly during those times.

The causes of cable modem speed problems are similar to those of DSL or other high-speed Internet services:

* Service glitches. Cable speed can suddendly drop if the service provider has technical difficulty with their network. Speeds should return to normal after a few minutes or hours.

* Spyware on computer(s). Even when your network may be functioning at full speed, spyware programs may be consuming the modem bandwidth, lowering your cable speed.

* Mis-configured wired or wireless router. Routers sit between your computers and the Internet connection. If not functioning properly, a router can greatly limit the cable speed achievable on all computers.

* Slow wireless network connection. In some cases, a very slow Wi-Fi connection between a computer and a wireless home network will not keep pace with the speed of the cable Internet connection.

* Old computer(s). Very old computers lacking sufficient processing power or memory cannot keep pace with a high-speed Internet connection.

As with DSL services, some cable modem services are symmetric (providing equal bandwidth for both uploading and downloading), but most offer much higher download bandwidth to match the typical needs of residential customers. Check with your service provider to determine the typical bandwidth levels associated with your subscription.

DSL Speed – How Fast Is DSL Internet Service?

Compared to the performance of cable Internet service, DSL speed has historically been slower. However, the speed of DSL Internet is increasing as the technology improves and service providers upgrade their network infrastructure. The exact DSL speed you will enjoy varies depending on several factors. How fast, then, is DSL?
Answer: Service providers advertise DSL speed in terms of bandwidth ratings. Bandwidth numbers advertised for residential DSL service range from 128 Kbps to 3 Mbps (3000 Kbps).

Because these DSL speed ratings vary so widely, its best to check first with your service provider to determine the bandwidth levels associated with your subscription. Many providers offer a choice of DSL services with different bandwidth ratings.

DSL Speed of Downloading and Uploading

Your DSL speed can change depending on how you use the network.

DSL providers often advertise speed of their service using a combination of two bandwidth numbers; for example, “1.5 Mbps / 128 Kbps:”

* The first number, 1.5 Mbps in this case, refers to the maximum bandwidth available for downloads. Examples of network download activities include browsing Web sites, receiving files from P2P networks, and receiving emails.

* The second number, 128 Kbps in this case, corresponds to the bandwidth available for uploads. Example of network upload activities include publishing to Web sites, sending files over a P2P network, and sending emails.

Residential DSL services often provide higher bandwidth for downloads than for uploads, as most customers spend more time in network downloading activities. These are sometimes called asymmetric DSL (ADSL) services. In ADSL, the first bandwidth number will be much higher than the second as in the example above. With symmetric DSL (SDSL), both numbers will be the same. Many business-class DSL services utilize SDSL, as business customers often spend significant time uploading over their networks.

DSL Speed Differences Between Households

The rated maximum bandwidth of a DSL connection often cannot be reached. Additionally, actual DSL speeds vary between households. Factors affecting DSL speed include:

* Quality of the phone line at your residence. Neighborhoods with better copper wiring can achieve somewhat faster DSL speeds.

* Length of the phone line between the residence and the phone company hub (often called “central office”). DSL technology is “distance sensitive” because its performance decreases significantly as you get further away from this hub.

* Service glitches. While normally a constant, DSL speed can suddendly drop if the service provider has technical difficulty with their network. Speeds should return to normal after a few minutes or hours.

Short of rewiring their residence, customers can do little about changing these factors. Other factors you can more directly control include:

* Spyware on computer(s). Even when the DSL network may be functioning at full speed, spyware programs may be consuming the bandwidth, robbing your DSL speed. Anti-spyware programs should be run regularly on networks to prevent this problem.

* Mis-configured wired or wireless router. Routers sit between your computers and the Internet connection. If not functioning properly, a router can greatly limit the DSL speed achievable on all computers. Temporarily connecting a computer directly to the Internet can help diagnose this situation.

* Slow wireless network connection. In extreme cases, a very slow Wi-Fi connection between a computer and a wireless home network will not keep pace with the speed of the DSL Internet connection. Improving the quality of the Wi-Fi connection will solve this problem.

* Old computer(s). Very old computers lacking sufficient processing power or memory cannot keep pace with a high-speed DSL connection. You can verify this problem by comparing the DSL speed between computers at the residence.

DSL vs. Cable Modem Comparison – Security
Is One Really Any Safer Than the Other?

When debating the relative merits of cable modem and DSL service, network security might be the most controversial item on the comparison chart. At first glance it appears one clearly wins the security battle over the other, but does this commonly-held opinion stand up to closer scrutiny?

DSL’s Leg Up

A few years ago, conventional wisdom held that DSL service inherently offers better security than cable modem service. Some proponents of this view happened to be DSL providers. One might dismiss such claims as a sales gimmick from over-exuberant DSL networking companies. Yet one finds the same sentiment among some non-commercial organizations as well.

No matter their origins, the claims of superior security for DSL all relate more to a perceived weakness in cable modem security than to any unique advantage DSL might hold.
Cable’s Network Neighborhood

Cable modem service uses a shared cable line to provide service to an entire neighborhood. Essentially, all cable customers in the region belong to the same local area network (LAN). Without any security measures in place, anybody in the neighborhood might technically be able to click on their Windows Network Neighborhood icon and actually see the computer names and addresses of their neighbors on the service. If a customer enables file sharing on any drives, neighbors could even download copies of their data!

Although some cable customers encountered this problem in the past, many providers avoid this problem today by bundling security features in the cable modem hardware. In particular, basic network firewall capabilities will prevent files from being viewed or downloaded. Most cable modems today also implement the Data Over Cable Service Interface Specification (DOCSIS). DOCSIS includes support for cable network security features including authentication and packet filtering.

DSL uses dedicated rather than shared cabling, and DSL customers in a given neighborhood do not appear as nodes on a LAN. From this, many have concluded DSL service provides better security. However, this argument is at best an oversimplified one.

Considerations for Both DSL and Cable

Both DSL and cable provide always-on connection capability. By design, DSL and cable customers can stay logged into the Net indefinitely if they choose. This feature provides great convenience but also creates a security risk. First, the “law of averages” means simply being online longer increases the likelihood of attack proportionately. But more importantly, the always-on feature typically means the customer will be using the same network address — a static IP address — for the duration of their online session.

Static IP addresses provide network attackers with a fixed target. The analogy to baseball and other sports applies: a moving target will generally be harder to “hit.” Many DSL and cable providers offer DHCP address assignment, that causes one’s address to change each time they sign on. However, this feature helps only slightly if this address stays the same throughout the days and weeks one remains online.

How do attackers actually penetrate a home or small office network? In general, they exploit weaknesses in applications or in the underlying operating system. Typically vulnerable applications include email, databases, and instant messaging and conferencing tools. Operating systems contain many potentially vulnerable network services like FTP that utilize specific network ports.

Many DSL and cable modem customers choose to purchase routers to protect their internal systems. A DSL or cable router enhances the functionality of the basic modem with security features such as packet filtering and network address translation (NAT). One can usually build an equivalent security system with the basic modem and proxy software installed on the computer directly connected to the modem. Broadband routers simply provide a convenient and operating system-independent packaging of security features.
Summary

Both DSL and cable provide reasonably safe Internet access as long as one follows reasonable security precautions. Considering the numerous security holes found in operating systems and applications in the past, these precautions should be followed regardless of the form of Net access one uses.

Customers of DSL or cable can choose from a number of possible precautions including use of a broadband router, firewall software, or proxy server software. When possible, one should also disable network file sharing on the internal LAN. Anytime one signs up for new Internet service, or changes providers, one should immediately perform vulnerability tests. A number of different security testing tools exist for popular operating systems.

Finally, when evaluating cable modem service providers, consider the technology they offer. Does their modem implement DOCSIS, for example, and if so, what security options have been enabled? Does the provider offer dynamic IP assignment, and does one’s IP address change at a periodic interval, or only when one first goes online?

The growing popularity of DSL and cable is helping to raise awareness of private network security issues, but these services really add very little in the way of new security holes themselves. Home networkers who haven’t yet studied the security of their LAN should do so immediately whether they use DSL, cable, ISDN, or traditional dial-up access.

Q1: “Although DSL is ‘dedicated,’ isn’t it still only as good as the local service provider’s connection to the Internet backbone?”

A: Yes, this is generally true, and it creates several potential disadvantages for DSL relative to cable modem.

1. First is the issue of reach. With its “shared neighborhood” style of connection, cable companies reach hundreds of people in a local neighborhood with a single pre-qualified line. DSL customers, on the other hand, each require their own line, and the provider incurs extra expense in managing each of these individually.

True, most households already have telephone lines, but these require some form of testing or “qualification” as some lines (especially older ones) might not be of sufficient quality to support data traffic.

2. DSL technology also is distance sensitive. Essentially, the longer one’s telephone line runs from their house to the phone company, the less performance they can achieve with DSL compared to neighbors who might live closer to the public exchange. This creates a marketing problem for DSL providers, who must convince customers that the variation in performance isn’t a serious or “unfair” limitation.

3. With cable modem, customers find it very convenient that the same company they use for cable TV service provides them Internet access (usually on a single monthly bill). Unless a person signs up for DSL with their local telephone company, DSL customers do not enjoy this same convenience.

Q2: “Some people claim that their cable modem performance drops between the hours of 5 PM and 11 PM. Why?”

A: A now-famous 1999 cable/DSL study by Keynote Systems designated the 5 PM to 11 PM timeframe as “Peak Personal Hours”

The study was made to test the hypothesis that cable modem performance would degrade in a busy neighborhood as people came home from work and logged onto the Internet.

Generally speaking, data from the study backed up this claim.

The Keynote study is frequently quoted on the Web, but it is just one data point in the cable vs. DSL performance debate. Overall, performance of broadband depends on many factors besides time of day, including the quality of the service provider and the destination(s) a person visits.

Q3: “Do any cable Internet providers provide a firewall to protect their customers?”

A: Yes. Cable companies all generally include firewall support nowadays, so that it is no longer possible to simply open “Network Neighborhood” and see all of the computers of people on your street.

Whether using cable or DSL, a person should never rely on someone else’s firewall, though. At the very least, a home user should consider installing one of the several personal firewall products available, such as ZoneAlarm or BlackICE.

Q4: “Friends tell me that wireless Internet service could be an option, just that it’s still off in the future. Is it true that a third high-speed competitor could emerge, or is it technically difficult to deliver high-speed wireless?”

A: Third, fourth, and possibly even more competing high-speed services could emerge, but DSL and cable are currently far ahead in the race for customers

One type of wireless service available today is satellite-based Internet access, such as that offered by Starband. In the case of satellite, the equipment costs as well as monthly fees remain relatively high, as not nearly as many people possess satellite dishes as they do cable TV or telephones.

Another type of wireless service available today is microwave-based, such as that offered by Sprint. These services still are only available in limited geographic areas.

Perhaps the main hurdle the high-speed wireless services must overcome is the perception of weak security. People naturally believe that because wireless traffic travels over “open air,” their personal information will be much more open to snooping. Appropriate security technology is being developed and almost certainly will succeed in protecting the average person, but this alone may not change the public’s perception of the safety of wireless data.

Q5: “What are the typical ‘upstream’ speeds of DSL and how do they compare to cable? What exactly is ‘upstream’ anyhow?”

A: Many DSL service plans give the home customer 128 Kbps of upstream bandwidth. That’s not as bad as some people think

An ordinary “56K” modem can only perform at a maximum of 33.6 Kbps upstream — fully five times slower than basic upstream DSL.

The terms downstream and upstream refer to the direction data flows over the network connection. Most home users do not utilize upstream bandwidth nearly as heavily as their downstream bandwidth. However, as more small- and medium-sized businesses sign up for DSL, and as the use of bandwidth-heavy applications like Web serving and online gaming increase among home users, the issue of upstream vs. downstream grows in importance.

Some residental DSL services support better upstream performance: rates of 192 Kbps, 272 Kbps, or 384 Kbps are typical. So-called “business class” or “symmetric” DSL services support much better than that — usually 640 Kbps or 768 Kbps.

Like DSL, most cable providers offer asymmetric service to home customers, with less bandwidth available in the upstream direction. Modern asymmetric cable services, like DSL, start at 128 Kbps upstream and increase to over 400 Kbps and up to 1 Mbps.

Note that some older cable services (like the first generation satellite Internet services) were only capable of using a standard dial-up modem for upstream access. In these older systems, upstream access is constrained by the 56 Kbps (really 33.6 Kbps) limit.

Q6: “I have cable modem/DSL service and can’t access my email when I travel. Is there anything I can do?”

A: Both cable and DSL suffer from limited mobility compared to traditional dial-up. Generally a person can’t just move their broadband modem to a different location and expect their Internet service to function — primarily because different service providers employ different network protocols to connect to their systems.

Most cable/DSL providers recommend that their customers sign up for a traditional dial-up account for traveling access to the Internet. Some providers offer this service themselves (for an additional monthly fee), and some providers simply recommend free or low-cost dial-up services from a nation-wide service provider. After signing up for this option, be sure to test the network before embarking on a trip!

source: http://compnetworking.about.com/od/dslvscablemodem/a/dslcablecompare.htm

One way to categorize the different types of computer network designs is by their scope or scale. For historical reasons, the networking industry refers to nearly every type of design as some kind of area network. Common examples of area network types are:

* LAN – Local Area Network
* WLAN – Wireless Local Area Network
* WAN – Wide Area Network
* MAN – Metropolitan Area Network
* SAN – Storage Area Network, System Area Network, Server Area Network, or sometimes Small Area Network
* CAN – Campus Area Network, Controller Area Network, or sometimes Cluster Area Network
* PAN – Personal Area Network
* DAN – Desk Area Network

LAN and WAN were the original categories of area networks, while the others have gradually emerged over many years of technology evolution.

Note that these network types are a separate concept from network topologies such as bus, ring and star.

LAN – Local Area Network
A LAN connects network devices over a relatively short distance. A networked office building, school, or home usually contains a single LAN, though sometimes one building will contain a few small LANs (perhaps one per room), and occasionally a LAN will span a group of nearby buildings. In TCP/IP networking, a LAN is often but not always implemented as a single IP subnet.

In addition to operating in a limited space, LANs are also typically owned, controlled, and managed by a single person or organization. They also tend to use certain connectivity technologies, primarily Ethernet and Token Ring.

WAN – Wide Area Network
As the term implies, a WAN spans a large physical distance. The Internet is the largest WAN, spanning the Earth.

A WAN is a geographically-dispersed collection of LANs. A network device called a router connects LANs to a WAN. In IP networking, the router maintains both a LAN address and a WAN address.

A WAN differs from a LAN in several important ways. Most WANs (like the Internet) are not owned by any one organization but rather exist under collective or distributed ownership and management. WANs tend to use technology like ATM, Frame Relay and X.25 for connectivity over the longer distances.

LAN, WAN and Home Networking
Residences typically employ one LAN and connect to the Internet WAN via an Internet Service Provider (ISP) using a broadband modem. The ISP provides a WAN IP address to the modem, and all of the computers on the home network use LAN (so-called private) IP addresses. All computers on the home LAN can communicate directly with each other but must go through a central gateway, typically a broadband router, to reach the ISP.

Other Types of Area Networks
While LAN and WAN are by far the most popular network types mentioned, you may also commonly see references to these others:

* Wireless Local Area Network – a LAN based on WiFi wireless network technology
* Metropolitan Area Network – a network spanning a physical area larger than a LAN but smaller than a WAN, such as a city. A MAN is typically owned an operated by a single entity such as a government body or large corporation.
* Campus Area Network – a network spanning multiple LANs but smaller than a MAN, such as on a university or local business campus.
* Storage Area Network – connects servers to data storage devices through a technology like Fibre Channel.
* System Area Network – links high-performance computers with high-speed connections in a cluster configuration. Also known as Cluster Area Network.

source: http://compnetworking.about.com/od/basicnetworkingconcepts/a/network_types.htm