Briefly, a method and apparatus to a channel access parameter to mobile units of a wireless communication network. After a user uses a mobile device to activate a PTT call, the mobile device checks the network condition before transmitting a PTT call origination request to a PTT server. Such measures are defined as new extensions in the PSS Base Vocabulary, PSS Quality of Experience and RTPAVPF. With the coupling of the receiving member and the fixing member, the supporting wall and the supporting housing can be tightly connected together, therefore the shake of the magnetic rack or the sample vials inserted in the magnetic rack can be significantly avoided. During expansion, the escape of the gas produced is limited to increase the state of compression of the elastomer in the gap by means of confining any free surfaces or by including a platy filler such as nanoclay in the composition. A pincher assembly is supported by the upper bagger arms and the lower bagger arms.