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Trivial File Transport Protocol - TFTP

Posted in Network Protocols

Trivial File Transport Protocol - TFTP - 3.7 out of 5 based on 7 votes

TFTP is a file transport protocol and its name suggests it's something close to the FTP protocol (File Transfer Protocol), which is true .. to a degree. TFTP isn't very popular because it's not really used on the Internet because of its limitations which we'll explore next.


The Protocol

TFTP's main difference from FTP is the transport protocol it uses and the lack of any authentication mechanisim. Where FTP uses the robust TCP protocol to establish connections and complete the file transfers, TFTP uses the UDP protocol which is unsecure and has no error checking built in to it (unless they have implemented some type of error checking in the program you are using to transfer files), this also explains why you are more likely to find TFTP in a LAN, rather than a WAN (Wide Area Network) or on the Internet.

IPSec - Internet Protocol Security

Posted in Network Protocols

IPSec - Internet Protocol Security - 4.5 out of 5 based on 45 votes

IPSec is one of the new buzz words these days in the networking security area. It's becoming very popular and also a standard in most operating systems. Windows 2000 fully supports IPSec and that's most probably where you are likely to find it. Routers these days also support IPSec to establish secure links and to ensure that no-one can view or read the data they are exchanging.

When the original IP (Internet Protocol) specification was created, it didn't really include much of a security mechanisim to protect it from potential hackers. There were 2 reasons they didn't give IP some kind of security. First was because back then (we are talking around 30 years ago) most people thought that users and administrators would continue to behave fairly well and not make any serious attempts to compromise other people's traffic. Second reason was because the cryptographic technology needed to provide adequate security simply wasn't widely available and in most cases not even known about!

USB Direct Cable Connection, USB Versions, Specifications and Speeds

Posted in Network Cabling

USB Direct Cable Connection, USB Versions, Specifications and Speeds - 3.6 out of 5 based on 7 votes

USB Ports, specifications, power output, speeds and moreToday, Serial and Parallel Direct Cable Connections are considered obsolete methods of transferring data between computers. The fact is that even USB Direct Cable Connection (DCC), is not all that popular, but is still used mostly by home users because of its easy setup and fast transfer speeds.  

USB DCC has been around for well over a decade but has failed to become a popular method of transferring data because of the rapid growth of networks and their significant speeds. In most cases, users with Gigabit Ethernet ports on their workstations simply require a standard UTP straight-thru cable to begin transferring data at double the rate of a USB DCC.

Let’s now take a closer look at USB interfaces and how they work.

About USB

USB stands for Universal Serial Bus and it’s the standard interface for all computer peripherals (printers, faxes, CDROMs, mice, joysticks etc) and mobile devices today.

The Universal Serial Bus gives you a single, standardized, easy-to-use way to connect multiple devices to a computer. The USB port is also capable of providing power to the connected devices, but it should be noted that each USB port has a limit of delivering a maximum amount of power, depending on the USB version. !

The initial specification of USB v1.1 was designed to deliver a maximum of 150mA (0.75 watts) at 5Volts. USB 2.0 specification increased the maximum power to an impressive 500mA (2,5 watts). USB 3.0 specification next came along and further increased the maximum power to 1,5Amps (7,5 watts) at 5Volts, allowing more power demanding peripherals to connect and be powered by USB.

Finally, the latest USB specification v3.1, jumped from 7,5 watts to a whopping 100 watts, but at the same time providing support for 5Volts, 12Volts and 20Volts.

USB Ports on a PC motherboard

Figure 1. USB Ports on a PC motherboard

As mentioned previously, there are 4 different versions of USB specifications: v1.1, v2, v3.0 and v3.1. Most USB ports today on computers and laptops support USB v3.0 specification while peripheral devices with USB v3.0 interfaces are already available in the market.

USB v3.1 and v3.0 are fully backwards compatible with USB v2.0 and v1.1 peripherals, ensuring full compatibility with any USB device.

The table below compares the different USB versions currently available, along with their most important technical specifications:

USB Specifications, different versions, Names, Data rates and power capabilities

Figure 2. USB Specifications, different versions, Names, Data rates and power capabilities

Keep in mind that when you're using a USB DCC cable, you won't get such great speeds, but somewhere around the 500 Kbps. This also depends on the type of CPU, O/S, the quality of the cable and electronic components and protocols running on your system.

When transferring data between two computers, the effective throughput (speed) achieved will depend on a variety of factors such as USB port version on both ends, USB Direct Cable version, CPU and HDD speed, how busy both systems are more. A USBv2.0 cable connected to two USBv2 ports is expected to achieve a 480Mbps transfer rate, however if the HDD on either side is unable to keep a sustained transfer speed, its likely the throughput will dramatically decrease.

Another important detail is the operating system used. Today, all Windows and Linux operating systems fully support USB ports, however older operating systems are not completely compatible. The table below shows which operating systems provide full support for USB ports, regardless of their specification version:

USB support by Microsoft Windows operating system

Figure 3. USB support by Microsoft Windows operating system

The Standard USB Cable

The USB standard uses A and B connectors to avoid confusion. "A" connectors head "upstream" toward the computer, while "B" connectors head "downstream" and connect to individual devices. This might seem confusing to some, but it was designed to avoid confusion between consumers because it would be more complicated for most people to try and figure out which end goes where.

This is what the USB cable and connectors look like:

                    USB 'A' and 'B' type connectors         USB 'A' and 'B' type connectors

Figure 4. USB 'A' and 'B' type connectors

As mentioned earlier, the USB port can power certain devices and also transfer data at the same time. For this to happen, the USB port must have at least four cables or two pairs,of which one pair is used to power the USB device (e.g hdd) and the second pair is used for data transfer between the device and computer.

The diagram below shows a standard USB cable with its internal 4 wires and their function. The shielding located at the far left is used to protect the cable from electromagnetic interference:

USB Cable - Wires inside the USB cable

Figure 5. USB Cable - Wires inside the USB cable

The USB Direct Connection Cable (DCC)

As previously mentioned, transferring data between two computers using the USB ports, requires the purchase of a USB Direct Connection Cable. (DCC). This cable is also known as a USB Transfer or Data Link cable. The DCC cable is not a simple cross-over cable, but contains electronic circuits that make it possible to use it to transfer data between computers.

                                   USB Transfer or Data Link cable  USB Transfer or Data Link cable

Figure 6. USB Transfer or Data Link cable

Searching for USB DCC cables will reveal a number of manufactures however almost all offer only USB 2.0 DCC cables, which means that the maximum transfer speed expected would be 480Mbps.

In addition, DCC cables are plug-and-play, not requiring additional drivers and are powered directly from the USB port. In most cases, when the USB cable is plugged into the computer, it will see it as an external drive, containing a special executable application that needs to be run on each computer to begin transferring files between them. This completes the discussion on USB Direct Cable Connection & port specifications. More information on Data transfer methods, Serial & Parallel ports, Ethernet (Fast/Gigabit/10Gigabit) and Fiber optic can be found in our Network Cabling Section.

 Back to Network Cabling Section

Important Direct Cable Connection Notes

Posted in Network Cabling

Important Direct Cable Connection Notes - 3.0 out of 5 based on 2 votes

Direct Cable Transfer NotesThis page was designed to provide some notes on Direct Cable Connection (File-transfer) of Win9x/ME/2000 with LAPLINK (Printer port) Cable or Null-Modem (serial port) Cable. We've already analysed extensively Serial Direct Transfer, Parallel Direct Transfer , Network (Cross-over) Transfer and USB Transfer methods in previous articles. For more information on Network cabling, transfer methods, speeds, specifications and more, visit our Network Cabling section.

I've successfully used Laplink cable to link two PCs for FILE TRANSFER only (not playing Games), with WIN95 and Direct Cable Connection program using the NetBeui protocol on each computer. You can quickly check to see if the protocol is installed by doubleclicking on the "Network Section" in Control Panel of your Windows operating system.

In addition to the above, you must have installed "Client for Microsoft Networks", "File and Printer Sharing for Microsoft Networks" and optionally the TCP/IP protocol, which will require some configuration. Providing a simply IP Address and subnetmask will be enough for our purposes, the rest of the fields can be ignored. If you would like to allow users to access your files and printer, then ensure both the options in "File and Print Sharing" are selected.

Once you have completed the above steps, you should have the following listed in the "Network Selection" window::

  • Client for Microsoft Networks
  • TCP/IP
  • Netbeui
  • File and Printer Sharing for Microsoft Networks

Fibre Optic Cables - Single-Mode Multi-Mode - Advantages, Construction and Elements

Posted in Network Cabling

Fibre Optic Cables - Single-Mode Multi-Mode - Advantages, Construction and Elements - 4.1 out of 5 based on 9 votes

Fibre Optic Cables - Single-Mode Multi-Mode - Advantages, Construction and ElementsIn this article, we'll talk about Fiber optic cables and how it has changed the design and implementation of network infrastructures, providing high Gigabit speeds, increased security, flexibility and complete immunization from electromagnetic interference.

In the 1950s, more research and development into the transmission of visible images through optical fibers led to some success in the medical world where it was being used in remote illumination and viewing instruments. In 1966 Charles Kao and George Hockham proposed the transmission of information over glass fiber and realized that to make it a practical proposition, much lower losses in the cables were essential.

This was the driving force behind the developments to improve the optical losses in fiber manufacturing and today optical losses are significantly lower than the original target set by Charles Kao and George Hockham.

The Advantages of Using Fiber Optics

Because of the low loss, high bandwidth properties of fiber cables they can be used over greater distances than copper cables. In data networks this can be as much as 2 km without the use of repeaters. Their light weight and small size also make them ideal for applications where running copper cables would be impractical and, by using multiplexers, one fiber could replace hundreds of copper cables. This is pretty impressive for a tiny glass filament, but the real benefit in the data industry is its immunity to Electro Magnetic Interference (EMI), and the fact that glass is not an electrical conductor

Fiber Optic Cable

Figure 1. A Fiber Optic Cable

Because fiber is non-conductive it can be used where electrical isolation is needed, for instance, between buildings where copper cables would require cross bonding to eliminate differences in earth potentials. Fibers also pose no threat in dangerous environments such as chemical plants where a spark could trigger an explosion. Last but not least is the security aspect; it is very, very difficult to tap into a fiber cable to read data signals.

Fiber Construction

There are many different types of fiber cable, but for the purposes of this explanation we will deal with one of the most common types -- 62.5/125 micron loose tube. The numbers represent the diameters of the fiber core and cladding, these are measured in microns which are millionths of a meter.

Construction of Fiber Optic Cable - Components

Figure 2. Construction of Fiber Optic Cable - Components

Loose tube fiber cable can be indoor or outdoor, or both. Outdoor cables usually have the tube filled with gel to act as a moisture barrier to the ingress of water. The number of cores in one cable can be anywhere from 4 to 144.

Over the years a variety of core sizes have been produced but these days there are three main sizes that are used in data communications, these are 50/125, 62.5/125 and 8.3/125. The 50/125 and 62.5/125 micron multi-mode cables are the most widely used in data networks, although recently the 62.5 has become the more popular choice. This is rather unfortunate because the 50/125 has been found to be the better option for Gigabit Ethernet applications.

ST Duplex Patch Lead

Figure 3. ST Duplex Patch Lead

The 8.3/125 micron is a single-mode cable which until now hasn't been widely used in data networking due to the high cost of single mode hardware. Things are beginning to change because the length limits for Gigabit Ethernet over 62.5/125 fiber has been reduced to around 220m and now using 8.3/125 may be the only choice for some campus size networks.

What's the Difference Between Single-Mode and Multi-Mode?

With copper cables larger size means less resistance and therefore more current, but with fiber the opposite is true. To explain this we first need to understand how the light propagates within the fiber core.

Light propagation

Light travels along a fiber cable by a process called 'Total Internal Reflection' (TIR); this is made possible by using two types of glass which have different refractive indexes. The inner core has a high refractive index and the outer cladding has a low index. This is the same principle as the reflection you see when you look into a pond. The water in the pond has a higher refractive index than the air and if you look at it from a shallow angle you will see a reflection of the surrounding area, however, if you look straight down at the water you can see the bottom of the pond


Figure 4. Light transmitted through a Fiber Optic cable

At some specific angle between these two views points the light stops reflecting off the surface of the water and passes through the air/water interface allowing you to see the bottom of the pond. In multi-mode fibers, as the name suggests, there are multiple modes of propagation for the rays of light. These range from low order modes, which take the most direct route straight down the middle, to high order modes, which take the longest route as they bounce from one side to the other all the way down the fiber.

Light bouncing while it travels inside a Fiber Optic cable

Figure 5. Light bouncing while it travels inside a Fiber Optic cable

This has the effect of scattering the signal because the rays from one pulse of light arrive at the far end at different times; this is known as Intermodal Dispersion (sometimes referred to as Differential Mode Delay, DMD). To ease the problem, graded index fibers were developed. Unlike the examples above which have a definite barrier between core and cladding, these have a high refractive index at the centre which gradually reduces to a low refractive index at the circumference. This slows down the lower order modes allowing the rays to arrive at the far end closer together, thereby reducing intermodal dispersion and improving the shape of the signal.

So what about the single-mode fiber?

Well, what's the best way to get rid of Intermodal Dispersion? Easy, only allow one mode of propagation. So a smaller core size means higher bandwidth and greater distances. Simple as that!

 Back to Network Cabling Section


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