Ang ethernet technology ang karaniwang technology or standard na ginagamit for LAN (local area network). Ito ang nagde-define ng wiring and signaling for the physical layer of the OSI model(network access layer in TCP/IP).
Ethernet technology is describe as IEEE 802.3 standard.
Gumagamit ito ng Carrier Sense Multiple Access with Collision Detection (CSMA/CD) method at kaya nitong i-support ang speed na up to 100 Gbps.
It can use coaxial, twisted pair and fiber optic cables. Ang ethernet technology din ay gumagamit ng frames (layer 2 information) with source and destination mac-addresses to deliver data.
As you can see in our illustration above, ethernet revolves around many different protocols and standards in our LAN(local area network). Kumbaga, standards are also within standards.
Sa madaling salita mga idol, ang ethernet ay isa lamang “paraan” or standard kung paano nakakapag-communicate ang mga networking devices within local area network. Nagtatakda din ito ng mga standards and “codes” or protocols kung papaano makaka-pag-usap usap ang mga magkaka-ibang networking devices specifically in local area connection.
Ito ang concern kung papaano mag-tratravel ang data from one PC to another device or another PC. Or kung papaano magno-notify ang isang PC na magse-send siya ng data at papaano naman mag-aadvise ang isang PC na magre-receive siya ng data.
For example, before kasi talagang maging advance ang ethernet technology, sa isang network or group of computers noon, hindi pwedeng sabay-sabay mag-send or mag-receive ang mga network devices.
Ang mga computers ay connected lamang sa isang “line of connection” usually called “single shared physical bus” then may limit ang haba ng wire(before it was coaxial cable).
Bago makapag-send ng data ang isang device, mag-aadvise muna siya or mag-checheck kung walang ibang device ang nag-papadala ng data or information. Ganun din sa pag-receive.
Think of it like crossroad, bago ka tumawid, you have to check and look left or right kung merong sasakyan. Ngayon, with the help of Ethernet technology, let say sabihin natin na meron tayong “overpass” para pwede ka nang tumawid kahit may dumadaan man na sasakyan or wala(just for the sake of explanation).
Or para mas madali natin maintindihan, dahil nga sa CSMA/CD na ginagamit ng ethernet technology, naiiwasan ang collision at nagiging smooth ang network communication.
Pero since advance at marami ng natuklasan technology ngayon, it can happen na pwede ng mag-send at mag-receive ng data ang isang device simultaneously. Idi-discuss natin ang mga ito sa susunod.
Kagaya nga ng nabanggit natin sa taas, meron itong collision detection para maiwasan ang collision or “pagru-rumble” ng mga frames. Na-oorganize ang pag-send at pag-receive ng information or data sa pamamagitan ng ethernet technology using CSMA/CD.
Duplex and Half-duplex
This is very basic. But I can assure you na kailangan din natin itong daanan para mas madali natin maintindihan how network works and how it evolves through the years.
Kapag sinabi nating half-duplex, it’s only a one-way of communication. It cannot send and receive at the same time. Kung send, sending lang. Kung receive, receiving lang. Pero hindi sabay. Ibig sabihin, no simultaneous communication can happen.
Take for example, a walkie-talkie. A traditional walkie-talkie operates in half-duplex mode. Hindi pwedeng mag-receive and mag-send ng “signal”. It’s either you talk or listen. Kung nakasakay ka na ng mga fx, you probably heard and see how these drivers used walkie-talkie.
Ginagamit nila ito para makapag-communicate sila about traffic at maka-iwas sa mga nanghuhuli. Right?
If you ever observed, hindi sila pwedeng mag-salita ng kausap niya. It’s always the first one talk and the other listen. Kapag tapos nang mag-salita yung isa, that’s the time na pwede na sumagot yung kausap niya. Kaya lagi silang meron confirmation, “do you copy? over”.
That’s how half-duplex operates in a sense.
In networking, hub is a good example of device that operates in half-duplex. It cannot send and receive at the same time. So ibig sabhin, the port is either on the sending mode OR in receiving mode.
Now pagdating sa full-duplex, it a two-way communication na. Ibig sabihin, it can send AND receive at the same time. In networks, a modern switch, like a Cisco switch also operates in full-duplex mode.
Ibig sabihin, the device connected to its port can send and receive “signals” at the same time. That’s why nung una, a switch is also called “an intelligent hub”.
Now, from experience, sa troubleshooting, minsan a device can have issues connected to a switch port. You may need to check the interface setting or configuration. Minsan naka-half-duplex at yun ang nagiging problema(lalo na kapag may mga ibang devices na naka-connect doon before).
Some of the commands na pwede mong magamit are the following:
- show run interface [interface number]
- show interface [interface number]
We need to remember this kasi minsan kailangan natin ito sa troubleshooting or di kaya naman sa interview.
By now, you now understand what is half-duplex and full-duplex is.
Collision and broadcast
Let’s also talk about collision and broadcast to give us more in-depth fundamentals kung paano nagsimula ang network.
Collision domain is where a group of devices where a frame or signal can collide to each other. Now, nabanggit natin kanina, yung mga sinaunang hub is operating in a half-duplex mode right? They are also in a one “big collision domain”. Ibig sabihin, they cannot send and receive signals at the same time.
As you can see in our simple illustration above, we have a computer sending a signal on the left. Ibig sabihin, it can only send but cannot receive signal at the same time. You can also see na meron tayong mga computers on the right, although they will “try to send” a signal din, since may nag-sesend na nga, hindi ito mangyayari.
A collision happens when one or more device try to send signals at the same time. Ibig sabihin, mag-cocollide yung signals nila. Mag-babanggaan kumbaga.
That is basically what we have in an old ethernet setup lalo na nung ginagamit pa natin ang mga sina-unang hubs.
Hub is consider a big collision domain. Ibig sabihin, pwedeng mag-collide or mag-banggaan ang mga signals. Kahit pa gaanong kadaming ports or gaano kadaming devices ang naka-connect dito, it is a one big collision domain.
As you can see in our illustration above, we have two different scenario kung saan sa una, isang computer lang ang naka-connect sa ating hub. It’s a collision domain. Pero in the second one, we have multiple computers, it is still one collision domain. Kahit pa mag-dagdag tayo ng another hub, it will be consider as one big collision domain.
Does it make sense now?
Since ang hub ay isang malaking collision domain, all devices connected to it can have a collision. If you can recall, ang ginagawa lang naman ni hub ay ire-send or ire-generate yung signal na natanggap niya sa lahat ng ports “without” analying or examining(kasi wala siyang ganung capability). Unlike the switch which can analyze traffic and make a filtering decision. Pero dito pumapasok ang tinatawag natin na broadcast.
Ang broadcast domain is where group of devices can receive a broadcast. Ito yung mga devices na pwedeng-mag-communicate sa isa’t isa under layer 2 ng ating OSI model through broadcast.
If you can recall, the function of a switch is to send a broadcast to all of the devices connected to its ports(sa unang beses silang nag-communicate).
All those devices are part of a broadcast domain. Kasi ang switch ay isang malaking broadcast domain.
When switch receives a “frame”, di ba ise-send niya sa lahat ng kanyan ports(maliban sa source port) yung frame as a broadcast. This is because it needs to know kung saan port naka-connect yung destination device. Those are part of a broadcast domain.
Switch stop or minimize collision(dahil it operates in full-duplex mode). Ang isang port ng switch is consider a collision domain. But the whole switch and all devices connected to it are part of a one big broadcast domain.
I hope by this far, you now have the understanding between the difference of collision and broadcast.
Maganda na maintindihan natin ito to “solidify” our knowledge. Kasama ito sa mga fundamentals an magpapatibay ng ating pundasyon when it comes to networking.