Data transmission method and communication system using the same

A data transmission method, suitable for a communication system, wherein the communication system comprises a plurality of first stations which uses an 802.11 protocol and a plurality of second stations which uses an 802.11e protocol and supports Quality of Service (QoS), the data transmission method comprising:

• using one of the second stations as a Contention AssisTance (CAT) station to obtain a medium access right with a first access category (AC), wherein the method of using one of the second stations as the CAT station comprises voluntarily issuing the first AC after counting a second predetermined time by using a CAT timer in the second stations connected to a QoS access point (QAP) which uses the 802.11e protocol and supports QoS, and obtaining the medium access right by using one of the second stations connected to the QAP;
• and
• broadcasting a CAT packet to all the first stations and the other second stations, wherein the other second stations stop contending for the medium access right for a first predetermined time according to the CAT packet, and the first stations transmit a packet with a QoS requirement according to the CAT packet.