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Direct Cable Connection

Posted in Network Cabling

Direct Cable Connection - 3.7 out of 5 based on 3 votes

network direct cable connection and Data transferFrom the early PC days, Direct Cable Connection (DCC) was the most popular way to transfer data from one PC to another. Of course, it might seem a bit of an "old fashioned" way to transfer data these days but remember that back then most PC's were running Dos 6.22 or Windows for Workgroups 3.11 if you were lucky!

Today, all computers are equipped with a network card and using straight-thru or cross-over network cables, we are able to quickly transfer data at speeds much greater than a serial or parallel cable. However , there are still times where we require a transfer via the serial or parallel port, and that's what this page is about.

Transferring data between computers via direct cable connections can be performed using the following methods:

  • Serial Cross-over cable
  • Parallel cable – also known as ‘LapLink’ cables
  • USB Transfer or Data Link cable
  • UTP Cross-over or Straight-thru cable

Serial Direct Cable Connection, DB9, DB25, COM Ports and Pinouts

Posted in Network Cabling

Serial Direct Cable Connection, DB9, DB25, COM Ports and Pinouts - 4.3 out of 5 based on 8 votes

This article covers the popular serial ports on workstations, servers and laptop computers. We cover serial data transfer, port pinouts, port speeds, serial interface types (DB9 & DB25), null modem cables and much more.

The Serial Direct Connection is the one which utilizes the COM ports of your computers. Every computer has at least two COM ports, COM1 and COM2. The "COM" stands for "Communications". Its pinouts are a lot simpler when compared to the parallel port, but the speed is also a lot slower.

To give you an idea of how fast (or slow) a serial port is, at its best you will get around 12 to 14 KB per second. That's pretty slow when you're used to a network connection, but let me show you how serial data is transferred so you can also understand why it's a lot slower:

Transfer of data via serial port

Figure 1. Transfer of data via serial port

 

The above picture gives you an idea on how serial data is transferred. Each colored block that is numbered is sent from PC 1 to PC 2. PC 2 will receive the data in the same order it was sent, in other words it will receive data block 1 first and then 2, all the way to block 7. This is a pretty good representation of data flow in a serial cable. Serial ports transmit data sequentially over one pair of wires (the rest of the wires are used to control the transfer).

Another way you can think of it is like a one lane road where the road is wide enough to only fit one car at a time (one data block at a time in our example above) so you would imagine that the road cannot process several cars at one time.

The Serial Port

Most new computers have two COM ports with 9 pins each; these are DB-9 male connectors. Older computers would have one DB-9 male connector and one DB-25 male connector. The 25 pin male connector is pretty much the same as the 9 pin, it's just bigger.

Let's have a look at a serial port to see what we are talking about:

Physical Serial interface - DB-9 (usually COM1) and DB-25 (usually COM2)

Figure 2. Physical Serial interface - DB-9 (usually COM1) and DB-25 (usually COM2)

Different pinouts are used for the DB-9 and DB-25 connectors and we will have a look at them in a moment. Let's just have another quick look at the COM ports of a new computer:

cabling_dcc3

Figure 3. Serial ports (COM1 & COM2)

Notice the COM ports, they are both DB-9 connectors, there is no more DB-25! The connector above the two blue COM ports is an LPT or Parallel port.

LPT Ports - Parallel Direct Cable Connection - Pinouts - Transfer speeds

Posted in Network Cabling

LPT Ports - Parallel Direct Cable Connection - Pinouts - Transfer speeds - 4.1 out of 5 based on 8 votes

LPT Ports - Parallel Direct Cable Connection - Pinouts - Transfer speedsThe Parallel Direct Connection is the second solution covering the transfer of data from one computer to another. The cable required is slightly more complicated as it has more wires that need to be connected, but the transfer speeds achieved make it well worth the time and effort required to make the cable. We'll also take a look at physical LPT ports, LPT modes (SPP, EPP, ECP), LPT port Pintouts, LPT direct connection cable and more.

Users interested in transferring files using parallel direct cables can visit the following Microsoft support page which explains How to Install and Configure the Direct Cable Connection Feature (https://support.microsoft.com/en-us/kb/298446).

As we’ll see further below, there are three different type of LPT ports, SPP, EPP and ECP, each supporting different speeds and features, but all use the same direct cable connection.

A standard LPT port will provide speeds of 40Kb/s to 60Kb/s while the faster ECP ports will deliver up to 1.1 Mb/sec or 8.8 Mbps.

To better understand why parallel links are much faster than serial links, we’ll need to analyze the way data is transferred. This is clearly shown and explained in the diagram below:

Transfer of Data via Parallel (LPT) Port

Figure 1. Transfer of Data via Parallel (LPT) Port

This diagram shows data transfer via parallel ports and we can see multiple data blocks being simultaneously transferred from one host to another, increasing significantly the overall throughput. Serial ports are capable of transferring one data block per time, therefore unable to match speeds of parallel ports.

What does the parallel port (LPT) look like?

Introduction To Protocols

Posted in Network Protocols

Introduction To Protocols - 3.6 out of 5 based on 22 votes

In the networking and communications area, a protocol is the formal specification that defines the procedures that must be followed when transmitting or receiving data. Protocols define the format, timing, sequence, and error checking used on the network.

In plain english, the above means that if you have 2 or more devices e.g computers which want to communicate, then they need a common "Protocol" which is a set of rules that guide the computers on how and when to talk to each other.

The way this "defenition" happens in computer land is by the RFC's (Requests For Comments) where the IETF (a group of enginners with no life) make up the new standards and protocols and then the major vendors (IBM, Cisco, Microsoft, Novell) follow these standards and implement them in their products to make more money and try to take over this world !

There are hundreads of protocols out there and it is impossible to list them all here, but instead we have included some of the most popular protocols around so you can read up on them and learn more about them.

The table below shows the most popular TCP/IP protocols. The OSI model is there for you to see which layer each of these protocols work at.

One thing which you should keep in mind is that as you move from the lower layers (Physical) to the upper layers (Applications), more processing time is needed by the device that's dealing with the protocol.

          osi-tcp-ip     protocols-osi

Following are the protocols analysed on Firewall.cx:

UDP Protocol - Header

Posted in Network Protocols

UDP Protocol - Header - 4.1 out of 5 based on 15 votes

This article covers the UDP protocol. We examine the structure of the UDP header, the protocols that use UDP as a transport plus a lot more.

Some common protocols which use UDP are: DNS, TFTP, ARP, RARP and SNMP.

When people refer to "TCP/IP" remember that they are talking about a suite of protocols, and not just one (as most people think). TCP/IP is NOT one protocol. Please see the Protocols section for more information.

The User Datagram Protocol (UDP) is defined by IETF RFC768

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