[*لانا*]

لو سمحتوا اللي يفهم في موضوع الشبكات يوضح لي الموضوع ( مطلوب مني شرح وأنا مو فاهمه)
وهل الانواع دي من انواع الشبكات السلكية والا لا

The most well-known wired LAN types are CSMA/CD bus, token ring and token bus.
I - CSMA/CD bus

CSMA/CD bus networks are also known as Ethernet. It is normally implemented as 10Mbps base band coaxial cable or twisted-pair cable network. When there is a problem, the transceiver may send too much unwanted random data(jabber) on the cable and hinders the usage of the network. The transceiver unit is connected to the DTE with 5 sets of twisted-pair wires. One is for power, two is for data and the other two is for control purposes. In a twisted pair and a hub configuration, the collision detection function is on the interface board in the DTE. The hub just receives and repeats electrical signals. two twisted pair cables connect each DTE to the hub. One is for transmitting and the other is for receiving. To help the collision detection electronics function, the hub retransmits the signal on an input pair to all output pairs. The repeater electronics ensures that the retransmitted signal on output pairs does not interfere with the received

signal on the input pair which is weaker. This is known as near-end crosstalk. Adaptive crosstalk cancellation circuits are used for reliable operation at 10Mbps with 100m wire lengths. Independent of the transmission media being used, the controller card within each DTE includes
- A MAC unit, which performs functions like encapsulation, de-encapsulation of frames for transmission and reception on the cable, error detection and implementation of the MAC algorithm.

- A dual port RAM that allows the MAC unit to receive and transmit frames at high speeds and allows the computer to read
.and write the information content of frames

Token Ring

In token ring networks, only the DTE that possesses the token can send data on the network. The frame sent is repeated by each DTE on the ring until it reaches back to the sender DTE. When the frame comes to the recipient DTE, besides being repeated, a copy of the frame is retained and response bits at the end of the frame is set. Depending on the speed of the ring, the token is either released after the response bits have been received, like in 4 Mbps ring networks, or after transmitting the last bit of a frame, like in 16 Mbps rings. The latter is also known as the early token release. The cable medium (trunk) is normally a screened twisted-pair operating at a bit rate between 4-16 Mbps. The DTEs can be connected either directly to the ring or through a concentrator. The concentrator is connected directly to the trunk and provides direct drop connections for DTEs. Normally it is located where the cable enters an office.