Quality of service （QoS） support is a key attribute for multimedia traffic including video, voice, and data in wireless local area networks （LANs） but is limited in 802.11-based wireless LANs. A polling-based sche...Quality of service （QoS） support is a key attribute for multimedia traffic including video, voice, and data in wireless local area networks （LANs） but is limited in 802.11-based wireless LANs. A polling-based scheme called the point coordination function （PCF） was developed for 802.11 LANs to support the transmission of multimedia traffic. However, the PCF is not able to meet the desired practical traffic differentiation requirements for real-time data. This paper describes a QoS support polling scheme based on the IEEE 802.11 medium access control （MAC） protocol. The scheme uses a two-level polling mechanism with the QoS classes differentiated by two different access policies. Stations with higher priority traffic such as key or real-time data form the first level and can access the common channel through an exhaustive access policy. Other stations with lower priority traffic form the second level and can access the channel through a gated access policy. A system model based on imbedded Markov chain theory and a generation function were setup to explicitly analyze the mean information packet waiting time of the two-level polling scheme. Theoretical and simulation results show that the new scheme efficiently differentiates services to guarantee better QoS and system stability.展开更多
Establishing a long-term vascular access in patients exhibiting vascular access exhaustion is challenging. In this study, we reported a case of a direct catheterization in the superior vena cava of a hemodialysis pati...Establishing a long-term vascular access in patients exhibiting vascular access exhaustion is challenging. In this study, we reported a case of a direct catheterization in the superior vena cava of a hemodialysis patient with vascular access exhaustion and original dysfunctional catheter inserted via the left internal jugular vein. The direct catheterization was performed with cuffed tunnel catheter （CUFF） and guided by digital subtraction angiography （DSA） and multidetector computedtomography venography （MDCTV）. The DSA and MDCTV results revealed an occlusion in the right innominate vein and thromboses in the left innominate, right internal jugular, subclavian, and femoral veins. The distal end of the superior vena cava was localized clearly by the original CUFF under DSA. Directed at the distal end of the superior vena cava, a 0.5-cm secondary puncture was introduced below the lateral head of the sternocleidomastoid muscle via the right neck area. This study is one of the few reports regarding direct catheterization of CUFF via the superior vena cava of a patient with vascular access exhaustion and CUFF dysfunction on the left internal jugular vein. We believe that our study can provide a new alternative for inserting central venous catheter for such patient.展开更多
基金Supported by the National Natural Science Foundation of China(Nos. F0424104 and 60362001)the Natural Science Foundation of Yunnan Province of China (No. 2004F0011R)
文摘Quality of service （QoS） support is a key attribute for multimedia traffic including video, voice, and data in wireless local area networks （LANs） but is limited in 802.11-based wireless LANs. A polling-based scheme called the point coordination function （PCF） was developed for 802.11 LANs to support the transmission of multimedia traffic. However, the PCF is not able to meet the desired practical traffic differentiation requirements for real-time data. This paper describes a QoS support polling scheme based on the IEEE 802.11 medium access control （MAC） protocol. The scheme uses a two-level polling mechanism with the QoS classes differentiated by two different access policies. Stations with higher priority traffic such as key or real-time data form the first level and can access the common channel through an exhaustive access policy. Other stations with lower priority traffic form the second level and can access the channel through a gated access policy. A system model based on imbedded Markov chain theory and a generation function were setup to explicitly analyze the mean information packet waiting time of the two-level polling scheme. Theoretical and simulation results show that the new scheme efficiently differentiates services to guarantee better QoS and system stability.
文摘Establishing a long-term vascular access in patients exhibiting vascular access exhaustion is challenging. In this study, we reported a case of a direct catheterization in the superior vena cava of a hemodialysis patient with vascular access exhaustion and original dysfunctional catheter inserted via the left internal jugular vein. The direct catheterization was performed with cuffed tunnel catheter （CUFF） and guided by digital subtraction angiography （DSA） and multidetector computedtomography venography （MDCTV）. The DSA and MDCTV results revealed an occlusion in the right innominate vein and thromboses in the left innominate, right internal jugular, subclavian, and femoral veins. The distal end of the superior vena cava was localized clearly by the original CUFF under DSA. Directed at the distal end of the superior vena cava, a 0.5-cm secondary puncture was introduced below the lateral head of the sternocleidomastoid muscle via the right neck area. This study is one of the few reports regarding direct catheterization of CUFF via the superior vena cava of a patient with vascular access exhaustion and CUFF dysfunction on the left internal jugular vein. We believe that our study can provide a new alternative for inserting central venous catheter for such patient.
