一种改进的STUN协议方案

在基于对STUN协议方案分析研究的基础上,本文提出一种更灵活的基于SIP的NAT穿越方案——S-STUN,该方案通过简化和改进现有协议STUN,实现了SIP对各类型NAT的穿越,解决了原STUN无法穿越对称型NAT的问题。

STUN技术通信问题的研究

采用NAT设备后,可以缓解公网IP地址紧张问题。但是采用了NAT设备后,改变了局域网中计算机与外网的拓扑结构,使得计算机与外网中计算机通信问题变得复杂。目前STUN是解决NAT穿越问题的技术之一。STUN技术是利用计算机网络通信技术,解决了NAT穿越问题。本文提出在原来的STUN技术基础上,使用数据库技术解决发送信息方与接收信息方之间的通信。通过实验证明了改进后的STUN技术在信息传输的速度上有所改善。

STUN技术深入分析

本文对STUN技术进行了深入分析,总结了各种NAT路由器的可穿越性,对STUN提出的识别NAT类型的方法进行了详细阐述并作了有效改进,提高了识别的效率,并指出了STUN技术的优点和不足。

基于STUN协议的NAT路由器穿越算法设计与实现

NAT穿越是多媒体传输技术中的一个重要研究课题,STUN解决方案能解决部分NAT的穿越问题,但是还有一定的弊端。在STUN技术的基础上,介绍了NAT路由器的识别方法,详细分析并设计一种解决NAT路由器穿越问题的算法,并对处于不同NAT路由器环境下的直接通信给出一种解决方案。既提高了NAT路由器的识别效率,也改善了通信质量。

STUN协议的实现原理及测试方法研究

由于IPV4地址十分紧缺,人们在组建网络时部署了大量的NAT路由设备。而NAT设备会影响SIP协议RTP媒体流的穿越。STUN协议由于具有实现简单、对媒体流消息不产生影响,对现有网络环境改动较小的特点,可以有效解决SIP协议的NAT穿越问题。

基于STUN技术的网络多协议互联

多协议并存的复杂网络必须要妥善地解决协议互联问题．阐述了ＳＴＵＮ技术的原理及实现方法，介绍了基于ＳＴＵＮ的几种联接方式，给出了一个具体应用的实现．

基于STUN和STUNT协议的M2M通信方案的设计与研究

物联网是目前我国发展最快,应用范围最广的一种新型网络,其本质属于M2M系统。由于物联网的异构性较强,因此导致各种通信协议、组网方式和数据类型呈现出多样化的特点,这对数据的快速传输造成了极大的障碍。该文在分析了M2M系统工作原理和运行机制的基础上,采用网络地址转换NAT技术与物联网技术相结合,提出了一种基于STUN和STUNT协议的通信方案。在保持网络拓扑结构不变的条件下,通过添加两个客户端模块即可实现数据的跨网传输,具有一定的实用价值。

针对SIP的STUN解决方案的设计与实现

SIP是一个基于文本的应用层协议,但SIP协议本身无法实现让SIP消息安全地穿过NAT和防火墙。从SIP消息的特点出发,提出一种无需扩展SIP协议的应用层解决方案,引入STUN协议,取得IP地址和端口的映射关系,修改SIP和SDP消息的内容来保证通信连接,从而实现对NAT的穿越。

UPnP和STUN相结合的NAT穿越技术研究

NAT穿越是P2P(Peer-to-Peer)流媒体应用必须要解决的问题,目前已有的单一穿越方法由于各自的局限性造成穿越成功率不高。为此提出UPUN方法,将UPnP和STUN有效结合以提高穿越成功率;同时针对对称NAT的穿越以及通信节点都位于NAT后情况下的穿越提出端口添加样本估计算法PASE和外网节点辅助中继算法PAR,以改进现有算法的不足。实验证明了方法的有效性。

一种带STUN功能的高性价比以太网SIP话机的设计与实现

提出了一种带STUN功能的高性价比以太网SIP话机的设计方案,主控单元采用SDA80D51芯片,网络接口采用RTL8019AS芯片.根据嵌入式系统资源有限的特点,设计并实现了适合于嵌入式系统的SIP协议栈结构及STUN实现算法,并提出了一系列对代码和数据存储区占用的优化方法和技巧.

Gas stunning with CO_2 affected meat color,lipid peroxidation, oxidative stress, and gene expression of mitogen-activated protein kinases, glutathione S-transferases,and Cu/Zn-superoxide dismutase in the skeletal muscles of broilers

Background: Meat color and lipid peroxidation are important traits related to meat quality. CO_2 concentration is a critical factor that can affect meat quality in the commercial use of gas stunning(GS). However, the effect and mechanism of CO_2 stunning on meat color and lipid peroxidation during long-term storage remain poorly studied. We aimed to study the effects of GS methods, especial y CO_2 concentration, on meat color and meat lipid peroxidation in broilers during long-term storage at 4 °C and to explore the potential mechanism of meat color change via lipid peroxidation and the inner lipid peroxide scavenging system.Methods: Eighteen broilers were sacrificed after exposure to one of the following gas mixtures for 90 s: 40% CO_2+21% O_2+ 39% N2(G40%), 79% CO_2+ 21% O_2(G79%), or no stunning(0% CO_2, control). Meat color, serum variables,enzyme activities, and the gene expression of mitogen-activated protein kinase(MAPK), nuclear factor-erythroid2-related factor 2(Nrf2), glutathione S-transferase(GST) and superoxide dismutase(SOD) were determined.(Continued on next page)Results: The concentrations of serum triiodothyronine(T3, P = 0.03) and the ratio of serum free triiodothyronine/free thyroxine(FT3/FT4, P < 0.01) were decreased, whereas levels of serum cortisol(P < 0.01) were increased in the 40%CO_2 group compared with the control group. Additionally, the thiobarbituric acid-reactive substances(TBARS)3 d(P < 0.01) and TBARS6 d(P = 0.01) in breast meat and the TBARS3 din thigh meat(P < 0.01) were increased in the40% CO_2 group compared with the control group. Serum T3 was negatively correlated with TBARS6 dboth in the breast and thigh meat(r =-0.63, P < 0.01 and r =-0.47, P = 0.05 respectively). T3/T4 was negatively correlated with TBARS6 din the breast meat and in the thigh meat(r =-0.57, P = 0.01; and r =-0.53, P = 0.03 respectively). Compared with the control group, Lightness(L*)1 d(P = 0.03) and L*9 d(P < 0.01) were increased, whereas total chromatic aberration(E*)1 d(P = 0.05) and E*3 d(P < 0.01) were decreased in the breast meat of both the G40% and G79% groups. The values of yel owness(b*)3 d(P = 0.01), b*6 d(P < 0.01) and E*6 d(P < 0.01) in the thigh meat were lower in both the G40% and G79% groups than in the control group. In the breast muscle, the m RNA levels of c-Jun N-terminal kinase 2(JNK2, P = 0.03),GSTT1(P = 0.04), and SOD1(P = 0.05) were decreased, and the m RNA levels of JNK1(P = 0.07), Nrf2(P = 0.09), and GSTA3(P = 0.06) were slightly lower in both the G40% and G79% groups compared with the control group. However, among these genes, only the m RNA level of JNK1 was decreased in the G40% group compared with the control group and the G79% group(P = 0.03) in the thigh muscle.Conclusions: Compared with the control group, meat color quality in the breast meat was decreased, and the expression of genes in the MAPK/Nrf2/ARE(antioxidant responsive element) antioxidant pathway in breast muscle was partly suppressed by GS of both 40% and 79% CO_2. However, oxidative stress and meat lipid peroxidation during storage were aggravated by GS with 40% CO_2 compared to GS with 79% CO_2 and no GS.

Investigation of Myocardial Stunning after Cardiopulmonary Resuscitation in Pigs

Objective To investigate cardiac function and myocardial perfusion during 48 h after cardiopulmonary resuscitation （CPR）, further to test myocardial stunning and seek indicators for long‐term survival after CPR. Methods After 4 min of untreated ventricular fibrillation, fifteen anesthetized pigs were studied at baseline and 2 h, 4 h, 24 h, and 48 h after restoration of spontaneous circulation （ROSC）. Hemodynamic data, echocardiography and gated‐single photon emission computed tomography myocardial perfusion images were carried out. Results Mean arterial pressure （MAP）, coronary perfusion pressure （CPP） and cardiac troponin I （CTNI） showed significant differences between eventual survival animals and non‐survival animals at 4 h after ROSC （109.2±10.7 mmHg vs. 94.8±12.3 mmHg, P=0.048; 100.8±6.9 mmHg vs. 84.4±12.6 mmHg, P=0.011; 1.60±0.13 ug/L vs. 1.75±0.10 ug/L, P=0.046）. Mitral valve early‐to‐late diastolic peak velocity ratio, mitral valve deceleration time recovered 24 h; ejection faction and the summed rest score recovered 48 h after ROSC. Conclusion Cardiac systolic and early active relaxation dysfunctions were reversible within survival animals; cardiac stunning might be potentially adaptive and protective after CPR. The recovery of MAP, CPP, and CTNI could be the indicators for long‐term survival after CPR.

一种基于NAT穿越的优化STUN算法

针对目前用户数据报协议(user datagram protocol,UDP)简单穿越NAT(simple traversal of UDP over NATs,STUN)的过程中,时延较长导致建立peer-to-peer(P2P)连接较慢的问题,提出了一种优化穿越性能的STUN算法。该算法根据客户端向STUN服务器发送UDP绑定请求的返回信息,计算出端口分配间距,然后利用分配间距提前计算出需要分配的实际传输的端口号,从而实现NAT穿越。搭建系统的服务器和客户端模块,并对算法的NAT穿越进行模拟测试。结果表明,与传统的STUN算法相比,通信双方使用优化的STUN算法建立P2P连接所需的时延较短,数据传输的吞吐量较高。

利用SBC作为STUN实现NAT穿越

本文针对VoIP应用如何穿越NAT的问题,研究了利用SBC作为STUN来实现NAT穿越的方案。设计了基于SBC作为STUN服务器实现穿越NAT的工作原理,并讨论了实现过程与SIP信息流传递过程,具有一定的应用价值。

内网搜索与UPNP STUN整合实现NAT网关数据通道

由于IPV4在数量与安全上的局限性等因素,大量企业采取了NAT网关来扩展IP数量,满足IPV4不足的现象。但又由于NAT的固有特点,如何可以高效,稳定突破NAT网关,实现对内部计算机的连接,显得尤其重要。本文对3种NAT网关突破技术进行重新整合,即内网搜索技术,UPNP,STUN保障了NAT数据通道的稳定性与高效性。

Intactness of membranous structure in canine stunned myocardium shown with colloidal lanthanum nitrate

A comparative study was performed of the permeability of cell membranous structures in canine stunned myocardium and that of infarct myocardium by using colloidal lanthanum nitrate as an ultrastructure probe. Stunned myocardium was characterized by mitochondrial swelling, vacuolar formation, a few lanthanum granules deposrting inside cells and intact structure of such membranes as cell membrane, mitochondrial membrane and lysosome membrane.Infarct myocardium was characterized by a large number of lanthanum granules passing through ruptured cell membrane and depositing in the cytoplasm and mitochondria. These results suggest that membranous structure remained intact during the occurrence of stunned myocardium.

The effect of stunned myocardium on heart function and the protection of fructose－1，6－diphosphate on it

Ｔｈｅｅｆｆｅｃｔｏｆｓｔｕｎｎｅｄｍｙｏｃａｒｄｉｕｍｏｎｈｅａｒｔｆｕｎｃｔｉｏｎａｎｄｔｈｅｐｒｏｔｅｃｔｉｏｎｏｆｆｒｕｃｔｏｓｅ－１，６－ｄｉｐｈｏｓｐｈａｔｅｏｎｉｔ￥ＣｈｅｎＡｉｈｕａ（陈爱华）；ＱｉａｎＸｕｅｘｉａｎ（钱学贤）；ＷｕＨ...

Effects of Berberineon Cardiac Function and ATPase Activity of Postischemic Myocardial Stunned Rat Hearts

This is a report of a study on the protective effect of berberine(Ber) on postischemic myocardial stunning and the role it plays in ATPase activity. Isolated working rat hearts were used with global ischemia for 30 min followed by reperfusing for 40 min. Both systolic and diastolic functions of stunned myocardium were significantly decreased. The recovery of LVSP×HR and CO was 52%±8% and 40%±8% respectively; LVEDP and T were elevated; while both Na +, K +ATPase activity and Ca 2+ , Mg 2+ ATPase activity of myocardial membrane and mitochondria were depressed. Berberine(25 mg·kg -1 ·d -1 , ip, 3 d, and 10 μmol L -1 for isolated heart perfusion) was able to enhance the percent recovery of LVSP×HR and CO to 85%±12% and 75%±11%, respectively, and reduce LVEDP from 298%±64% to 166%±44%, with an improvement in myocardial membrane Na +, K +ATPase activity and mitochondria Ca 2+ , Mg 2+ ATPase activity. This study suggested that berberine can protect cardiac function from ischemia reperfusion stunning injury by preserving ATPase activity in ischemic myocardium.

Effects of inhibition of glycolysis on calcium homeostasis and functional recovery of stunned myocardium

Objective:To observe the effects of inhibition of glycolysis with iodoacetate (IAA) on calcium homeostasis and functional recovery of stunned myocardium in anesthetized dogs. Methods: Atomic absorption spectrophotometry was employed to measure myocyte calcium and magnesium contents. Hemodynamics were monitored with a multichannel electrophysiologic recorder. Results: In nonischemic canine hearts (control), IAA's inhibition of glycolysis failed to change the [Ca2+] and [Mg2+] levels and cardiac functional conditions, whereas in hearts subjected to 15-minute ischemia , [Ca2+] increased from nonischemic 1.40±0. 20μmol/g to ischemic 1.80±0.17 μmol/g (P<0. 05), while [Mg2+] decreased. After 30 min of reperfusion,[Ca2+] continued to increase from 1.57±0.21 μmol/g (nonischemic area)to 2. 26±0. 09 μmol/g (abnormal area) and 60 min of reperfusion saw a slight restoration (1.54±0. 16 μmol/g in nonischemic area and 2. 21±0.20 μmol/g in abnormal area). In the glycolysis-inhibiting group, the calcium level registered a significant rise after 30 min of reperfusion: 1.57±0.07 μmol/g in nonischemic area and 2. 90? 0.25 μmol/g in abnormal area (P<0. 01).There was a significant difference between the glycolysis-inhibiting group and the group to which IAA was not applied. [Mg2+] maintained at a relatively low level and registered a more remarkable drop during inhibition of glycolysis, P<0.01 in comparison with the non IAA-administered group,suggesting that inhibition of glycolysis could cause severe calcium overload to sustain, in addition to an obvious harm to cardiac function. Left ventricular end-diastolic pressure and diastolic factor T were augmented andp/dt(max)declined. Conclusion: Since in vivo inhibition of glycolysis seemed to lead to severe calcium overload and hemodynamics changes,it might indicate that glycolysis played an importent role in the restoration of calcium homeostasis in postischemic myocardium,and that ATP derived from glycolysis took a significant part in myocardial ion transport both at the stage of ischemia and the early stage of reperfusion and in cardiac functional recovery.

Mechanisms of Myocardial Stunning in Stress-Induced Cardiomyopathy

Stress-induced cardiomyopathy,in contrast to acute myocardial infarction,is a type of acute heart failure characterized by reversible left ventricular dysfunction.Cardiac imaging primarily reveals left ventricle myocardial stunning,81.7%of which is apical type.Emotional or psychological stress usually precedes the onset of stress-induced cardiomyopathy,which is increasingly being recognized as a unique neurogenic myocardial stunning disease.To distinguish between acute myocardial infarction and acute viral or auto-immune myocarditis,this review summarizes specific mechanisms of myocardial stunning in stress-induced cardiomyopathy,such as calcium disorders,metabolic alterations,anatomical and histological variations in different parts of the left ventricle,and microvascular dysfunction.