Basic Network question

zeBes used Ask the Experts™
I'm damn regret now because i never pay attention to my networking class.. so, i need experts here to tell me in detail what it means by:

1. RS 232
2. parallel interface
3. serial interface
4. usb interface
5. hub
6. router
7. how to differentiate usb, parallel and serial port?

i allocate 50pts for each topic..

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i don't want an answer with link(s) only.. please explain in your words, and provide the link(s) as additional reference only.
1) RS 232 is a serial cable that normally connects a router WAN interface to the WAN link. It connects the DTE device (a router) to a DCE device (CSU/DSU).  RS 232 port is a serial port

2) Parallel interface/port is the printer port at the back of your PC

3) serial port/interface is the serial ports (Com1 and Com2) at the back of a PC

4) USB ports/interface you'll also find at the back of a PC. Connects USB devices like external CD writers/USB   printers/keyboard/mouse  etc. etc.

5) A hub is a device where you plug PC's/printers/servers in to network them. You would still have to configure the IP addresses of the devices that plugs into the hub to make them communicate on the network. In todays modern networks, hubs are being replaced by swtiches because of the switch's ability to learn MAC addresses.

6) a router is a device that routes IP, or other layer 3 protocol packets between networks that are interconnected. Example: You have an office in New York and one in London and one in Sydney connected with a WAN links. You will have a router at each office that decide where packets should go so that packets destined for new York reach the destination address.

7) USB/Parellel/serial connecters/ports look different. See the links I provided above.


NicBrey> ok, just tell me one last thing: what does P/S 2 means?? like ps2 mouse and keyboard.. let me know and i give u my pts straight away!
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First came the serial mouse that plugged into COM1 / COM2. That was replaced with the PS2 mouse with the small round plug. Nowadays you get USB mice that plugs into the USB ports.  Essentially, the PS2 is also a serial port.
PS2 is another name for the mini-DIN connector, which was first introduced by IBM with their PS/2 PC systems. The PS/2 keyboard connector is mini-DIN 6 (has 6 pins inside the DIN shell) while the old AT-standard keyboard connector is DIN-5 (5 pins inside the shell) and the PS/2 mouse uses the exact same mini-DIN 6 connector as the PS/2 keyboard.  A PS/2 mouse also uses the reserved IRQ 12 instead of a serial-port IRQ.
RS232 *is* a serial cable, using the RS232 standard.  There are other serial interfaces besides RS232. The standard defines the pin assignments.

RS232 can be a 25-pin D-shell type connection or a 9-pin D-shell type connection, usually male on one end and female on the other.  You can also get "null-modem" RS232 cables that can connect devices directly without a modem.

RS232, as I just indicated, is usually used with a modem, and very few people use modems for WAN connections.

A parallel interface has the communications occuring in parallel, meaning multiple signals can travel at the same time.  The most frequent use for parallel interfaces are for printers.  The interface can be a 25-pin D-shell connector or a Centronix connector.  Often, a parallel cable will have one of each type connector - the D-shell connector for the PC interface and the Centronix for the printer interface.  

A serial interface has the communications occurring in series, meaning one signal follows the other.  Serial communications can be synchronous or asynchronous, meaning communications in both directions at the same time (synchronous) or communications from one direction waiting for communications from the other direction to complete before sending (asynchronous)

USB is Universal Serial Bus, which takes the serial interface to the next step.  In a way, it is similar to firewire and has some similarities to SCSI, in that it is a bus topology, meaning you can hook up more than one device in a string.  It has higher bandwidth capabilities than the old serial interface.  It also isn't tied down to specific IRQ and port assignments like the old serial - it dynamically assigns them.  Many USB devices are "hot" plug-and-play, meaning you don't have to shut down the system to add them like you had to do with  the old serial.

Another word for a hub is a repeater.  Essentially, a hub connects multiple lines in a "star" configuration for a bus-type topology.  An Ethernet hub, for example, lets you individually connect each Ethernet device on it's own wire to the hub, as opposed to having a bus-type coaxial cable Ethernet configuration where they all connect one to the other in series.  A USB hub does the same thing - you can hook up multiple USB devices to the central hub device directly, rather than stringing them one to the other (which you can't do with many USB devices anyway, so you're pretty much stuck with buying a hub...)

A router connects different networks together, routing only the traffic intended for the other network to the other network.  A router can be used to connect to the Internet, or to connect different sites in a corporate WAN, or to segregate sections of a LAN from each other.  A switch is a low-level router.  A router often can do protocol translation and rudimentary firewall functions while a switch usually only works at the transport or network level of the OSI stack.

Thanx for the points.

A couple more tidbits - free of charge ;>)

A router usually connects to the Internet using a device similar to a modem, called a dsu/csu or tsu (depending on the brand.)

Modem stands for what it does: MODulator/DEModulator. It translates a digital signal into an analog signal (modulate) to make it transferable over a standard, or POTS, phone line, then translates it back to digital (demodulate) on the other end.  There are major limitations to this type of communication, and MODEMs usually max out at about 56,000 bits per second downstream, and 33,600 bits per second upstream.  Although they are digital, the similar devices that connect ISDN, DSL and Cable data connections are also referred to as modems.  Don't ask me why - they aren't the same thing - they don't modulate and demodulate over analog.  Whatever... ;)

DSU stands for Digital Service Unit.  CSU stands for Channel Service Unit.  TSU is another acronym for DSU but it refers specifically to a T1 digital connection.

The DSU/TSU connects with a T1 or fractional T1.  Each digital channel (hence the "channel service unit" part,) depending on the T1 frame type, provides either 56Kbits/second synchronous or 64Kbits/second synchronous bandwidth.  Synchronous bandwidth means that the same data volume can travel in both directions at the same time.  A full T1 will give up to 1.55 Mbit/s synchronous data flow.  T3, OC1, OC3 and other digital transport media types have higher bandwidth, more channels, and higher cost.

In a WAN, you usually have a point-to-point or frame-relay connection, both of which are dedicated digital connections.  More frequently you are seeing non-dedicated digital connections, lile DSL and Cable being used for WAN connections in conjunction with a VPN (virtual private network.)  Although the device is called a "DSL/Cable Modem" it really is a form of DSU/CSU because the signal is not translated from digital to analog and back, but stays digital.  A DSL/Cable router connects to a DSL/Cable Modem using an Ethernet-standard RJ-45 UTP cable.  The only thing a DSL/Cable router is good for, IMHO, is allowing multiple devices to access the Internet concurrently through your DSL/Cable connection.  Explaining VPN is for another TA... :)

A TSU or DSU/CSU will usually connect to a router for a WAN connection using a V.35 connection, which is a specific standard for digital information transmission.  Sometimes, a V.35 connection can be made using a 25-pin D-sub connector rather than the standard Winchester block used in V.35.  That does not make it an RS-232 connection, however, simply because the cable is using a 25-pin D-sub connector.  The pinouts do not match, and the purpose and type of signals on those pins is different.

Some DSU/CSU or Digital Access Products also have POTS dial-up backup capability (with a built-in modem), and some actually do have an RS/232 connection, but those are specific to the devices and applications and have nothing to do with what the cable looks like.


Thanks ShineOn ;) You're so nice!

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