سؤال للمتعمقين في الشبكات

[En.Khaled Alfaiomi]

حبيب قلبي عمور شوف إذا حتجت شي خبرنا نحنة جاهزين

[king-of-nothing]

Wireless fundamentals.
802.11

ورح احكي عن السيزما سيدي معاها وطرقة شغلها




IEEE 802.3 & 802.11 is 2 of the most important protocols technologies for data communication that we are using these days, 802.3 is for the Ethernet communication & 802.11 is for the wireless communication and for using any technology we need physical devices to have the ability to communication such as:

- For Ethernet: Network Card – Network Cable – Ethernet device such as Router, Hub Switch …

- For Wireless: Wireless adapter or Mobile has the ability to work with IEEE 802.11 – Station to work as communication point for transferring the data – Wave or frequency to carry the data of course it’s noun physical.

Each technology got its own way of interaction 802.3 got no authentication because we are dealing with broadcasting devices once u connected the physical layers to the devices and set up the IPs for them you are good to go, unlike the 802.11 because it need authentication and for having a successful authentication we need for 3 way handshake technique (Sending Synchronization - Receiving Synchronization – Acknowledgment the Synchronization).

The 802.11 protocol that used for the communication is build on the main protocols of the 802.3 technology

When we deal with media in consisting 2 frames for the minimal MAC frame exchange protocol (one sent from the source to the destination and acknowledgment from the destination to the source and that reduces the inherent error rate of the medium, at the expense of additional bandwidth consumption without needing higher layer protocols, Physical Layer functionality The PHY provides three levels of functionality:

- First, the PHY layer provides a frame exchange between the MAC and PHY under the control of the physical layer convergence procedure (PLCP) SubLayer.

- Secondly, the PHY uses signal carrier and spread spectrum modulation to transmit data frames over the media under the control of the physical medium dependent (PMD) SUB layer.

- Thirdly, the PHY provides a carrier sense indication back to the MAC to verify activity on the media.







IEEE 802.11 had a problem called Hidden Node Problem, hidden node problem occurs when a node is visible from a wireless access point (AP), but not from other nodes communicating with said AP. This leads to difficulties in media access control and this problem A problem that does not occur on a wired LAN.

IEEE 802.11 MAC frame exchange protocol address this created by adding two additional frames to minimal frame exchange protocol described so far. The two frames are a request to send the RTS frame and a clear to send the CTS frame. Source sends RTS and destination replies with CTS and nodes when here RTS and CTS suspend transmission for a specific time indicated in the RTS/CTS frames. frames are atomic unit of the MAC protocol. Stations that hear RTS delay transmitting until CTS frame. That does not hear CTS, it transmits and the stations that here CTS suspend transmission until they get the acknowledgement .In the source station, a failure of the frame exchange protocol causes the frame to be retransmitted. That’s treated as a collision, and the rules for scheduling the retransmission are described in the section on the basic access mechanism. To prevent the MAC from being monopolized attempting to deliver a single frame, there are retry counters and timers to limit the lifetime of a frame

Two retry counters associated with every frame the MAC attempts to transmit: a short retry counter and along retry counter. There is also a lifetime timer associated with every frame the MAC attempts to transmit .Between these counters and the timer, the MAC may determine that it may cancel the frame‘s transmission and discard the frame. Then MAC indicates to the MAC user through the MAC service interface. Fewer tries for the shorter frames as compared to longer frames which is determined from the value of an Attribute in the MIB, dot11RTSThreshold. These counters are incremented in each unsuccessful transmission.

CSMA/CA (Carrier sense multiple access with collision avoidance) & CSMA/CD (Carrier sense multiple access with collision detection), played part in the IEE802.11 and the way they fixed the Hidden Node Problem,

In the end each protocol can be protected by setting your own security of course 802.3 as long as you are counting your clients and how many are connected to your devices physically you know the number of the clients. But regarding for the 802.11 they made a privacy *** encryption to secure your network.


King of Nothing

[En.Khaled Alfaiomi]

ياغالي أنطرني دقائق و رح أعطيك الحل الشافي ..

واسف على التأخر لأنوا الصراحة أول مرة بشوف الموضوع

[salwaieh]

مرحبا يا king



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