计算机网络第七版谢希仁课后答案8-10章

living standards, poor farmers in less t han complete elimination of 4600 Yuan, 8949, 19008. "Five waters rule": the County inve sted 2.169 bi llion yuan, similar counties line the city's first complete t he 42 km of sewage pipe netw ork construction, completi on rate ranked first in the city, won the pr ovincial rural sewage treatment w ork better; key polluti on sour ces such as ele ctroplati ng, pa permaki ng, chemical i ndustry management t hroug h verification and accepta nce of the muni cipa l governme nt, the County removed Black a nd odorous River, River waste, beginning of river ecologi cal restora tion effects. "Three modified a split" aspects: County total demolition illegal area up 2.759 milli on square meters, com pleted City issued annual task of 153%, split against area ranking city se cond; complete d "three modified" area 4.846 million square meters, complete d City issued a nnual t ask of 403%, ranki ng city thir d, whi ch vi llage in the a target complete d total city ranki ng first; County Governme nt

was named city level "three modified a split" work advanced. The se achievement s are hard w on a nd should be a ppre ciated. Howeve r, we are fully aware, t he ne w peri od, a nd w ork in the countrysi de and the e nvironment facing higher sta ndar ds and requirements, provi ncial party Comm ittee offered to hig h level build a compre he nsive well -off society goal re quires "no filth, dirty environment illegal buil dings, into a w ell-off"; municipal party Committee also pr oposes t o build int o the well -off be nchmark goals of the city. Com pared wit h the superi or claim, "South Gate of XX beautif ul" goal, my County "San Nong" a nd envir onme nt there are a number of weaknesses a nd gaps, hig hlighted i n the foll owing five aspect s: first, agriculture remaine d "low" pattern. "Low" is reflecte d in the quality and l ow; short, value added of the industry chain is low; 123 fusion yield l ow empl oyee age, l ow qualit y. "Small" is reflected in small er, specialized cooperatives t hroughout the County there were 3,396, but on

the scal e of too little. "San" is refle cted in producti on, ma nagement, service s, de centralize d, centralize d, standardized, brand, information and organizati onal l evel is not high. Second, the countryside is still i n "dirty" phase. "Dirty" is dirty of rural sanitati on sit uation has not cha nged. "Chaos" is a village in rural housing construction planning, construction of di sorder, no drawi ngs, no constructi on, no vetting "four no" phenomenon, heap lyi ng there. " Bad" is the weak rural ba se, village g overna nce i s poor. T hirdly, farmers continued t o be "persistent" look. "Ol d" is aging, rural la bor for ce accounted for 70% over the age of 50. "Big" is that the reform measures ground resistance, such as the transa ctions of property rights, l and re pla cement; public service supply gap, r ural education, health car e, pe nsi ons a nd other services can not meet the demand still difficult for poverty alleviati on, w ith empha sis on poverty alleviation and 191. "Har d" is a "peasa nts, pea sants. Four water effects still la cks

ompell ing." Althoug h the "five water treatment" a lot, work very hard, but t he flood of sci entific e nough, before the treatment a nd water quality improveme nt after the treatment effect is not obvi ous, county-wide focus on river st ill largely inferior five water, swimming the River coul d not be found. Five i s "three to split" task still lies a head. Noti ce of stock there, new constructi on did not receiv e timely treatment every year (such a s ancestral hall a s unauthorise d repeate d), contrary to the create d work i s very different from the provi ncial a nd m uni cipal sta ndar ds. Me anw hile, w hen im ple mentation is not in place, generally only focus on ill egal construction dem olished, failing t hat split that is clea r, combined demolition, insufficie nt attention t o reconstr uction of ol d residential areas, urban village s, sha nty tow ns and prom ote poor. o solve t hese pr oblems, we must e nha nce t he sense of responsi bility and urge ncy, insi st on problem-oriente d, to take strong measures, efforts to make up the

"three agricult ure" and "five water treatment", "three to split a" short Board, construction of comprehensive saf eguards, "Sout h Gate of XX bea utiful" goal of realizi ng. II, and preci sion Shi policy, a nd manpow er playing good "thre e agricultural" work pr otracted "three agri cult ural" work is do economic soci al devel opme nt the work of base d, county level s the sector t o accordi ng to "base d agricultural, a nd and manpow er rural, a nd development farmers" of requirement s, insisted agri cultural r ural base d status not shake, i nsisted hui nong kulak poli cy not weake ned, insi sted reform innovation test not stop, effort s created new era "three agri cultural" w ork new situation. (A) to make agriculture m ore. To establi sh the concept of agriculture ar ound the people demand, and com prehe nsively promote the supply side of agricultur e struct ural reform, strive to enhance the qua lity and efficiency of agriculture a nd competitiveness. Focus i s on doi ng the four articles. One is the stea dy increase of grain

article. Always tighte n the stri ng for food security, "rice bag" catch in hand, to hold la nd i n the adjustment of agricult ural planti ng structure i n the "red line." Accelerating the construction of grain ribbons, impr oving agri cultural i nfrastruct ure, enhance food pr oducti on ca pacit y, improv e the quality of agricultural product s, effectively "steady increase of grain" and maintai n "tongue." Second, i ndustry convergence arti cle. Enhance the level of concentration, inte nsificati on of agriculture , creating producti on, processi ng, distribution, sale s and service in one of the agri cultural industrial chai n, to break down the value chai n, improve a dde d value. Pushi ng forward "the Internet + agricultural" model to improv e agricult ural production, manageme nt, and servi ce level, i nnovating the mode of e -commer ce marketing of agricultural pr oducts, solve the difficult probl em of sales of agri cultural product s. Agriculture a nd tourism, educati on, cult ure, hea lth, pensi on a nd other deep i ntegration, devel op lei sure,

travel

第八章 因特网上的音频 / 视频服务

8-1 音频 / 视频数据和普通文件数据都有哪些主要区别？这些区别对音频 / 视频数据在因特

影响

如果利用 TCP协议对这些出错或丢失的分组进行重传，那么时延就会大大增加。因此

实时数据的传输在传输层就应采用用户数据报协议 UDP而不使用 TCP协议。

电信网的通信质量主要由通话双方端到端的时延和时延抖动以及通话分组的丢失率决

定。这两个因素都是不确定的， 因而取决于当时网上的通信量， 有网络上的通信量非常大以

至于发生了网络拥塞， 那么端到端的网络时延和时延抖动以及分组丢失率都会很高， 这就导

致电信网的通信质量下降。

8-2 端到端时延与时延抖动有什么区别？产生时延抖动的原因时什么？为什么说在传送音

频/ 视频数据时对时延和时延抖动都有较高的要求？

答：端到端的时延是指按照固定长度打包进 IP 分组送入网络中进行传送；接收端再从收到

把传播时延选择的越大，就可以消除更大的时延抖动，但所要分组经受的平均时延也

增大了， 而对某些实时应用是很不利的。 如果传播时延太小， 那么消除时延抖动的效果就较

差。因此播放时延必须折中考虑。

8-3 目前有哪几种方案改造因特网使因特网能够适合于传送 / 音频视频数据？

答： 1. 大量使用光缆， 是网络的时延和时延抖动减小， 使用具有大量高速缓存的高数路

由器，在网上传送实时数据就不会有问题。

2. 将因特网改造为能够对端到端的带宽实现预留， 从而根本改变因特网的协议栈—

从无连接的网络变为面向连接的网络。

3. 部分改动因特网的协议，也能够使多媒体信息在因特网上的传输质量得到改进。

8-4 实时数据和等时数据是一样的意思吗？为什么说因特网是不等时的？实时数据都有哪

living standards, poor farmers in less t han complete elimination of 4600 Yuan, 8949, 19008. "Five waters rule": the County inve sted 2.169 bi llion yuan, similar counties line the city's first complete t he 42 km of sewage pipe netw ork construction, completi on rate r anked first in the city, won the pr ovincial rural sewage treatment w ork better; key polluti on sour ces such as ele ctroplati ng, pa permaki ng, chemical i ndustry management t hroug h verification and accepta nce of the muni cipa l governme nt, the County removed Black a nd odorous River, River waste, beginning of river ecologi cal restora tion effects. "Three modified a split" aspects: County total demolition illegal area up 2.759 milli on square meters, com pleted City issued annual task of 153%, split against area ranking city se cond; complete d "three modified" area 4.846 million square meters, complete d City issued a nnual t ask of 403%, r anki ng city thir d, whi ch vi llage in the a target complete d total city ranki ng first; County Governme nt

was named city level "three modified a split" work advanced. The se achievement s are hard w on a nd should be a ppre ciated. Howeve r, we are fully aware, t he ne w peri od, a nd w ork in the countrysi de and the e nvironment facing higher sta ndar ds and requirements, provi ncial party Committee of fered to hig h level build a compre he nsive well -off society goal re quires "no filth, dirty environment illegal buil dings, into a w ell-off"; municipal party Committee also pr oposes t o build int o the well -off be nchmark goals of the city. Com pared wit h the superi or claim, "South Gate of XX beautif ul" goal, my County "San Nong" a nd envir onme nt there are a number of weaknesses a nd gaps, hig hlighted i n the foll owing five aspect s: first, agriculture remaine d "low" pattern. "Low" is reflecte d in the quality and l ow; short, value added of the industry chain is low; 123 fusion yield l ow empl oyee age, l ow qualit y. "Small" is reflected in small er, specialized cooperatives t hroughout the County there were 3,396, but on

the scal e of too little. "San" is refle cted in producti on, ma nagement, service s, de centralize d, centralize d, standardized, brand, information and organizati onal l evel is not high. Second, the countryside is still i n "dirty" phase. "Dirty" is dirty of rural sanitati on sit uation has not cha nged. "Chaos" is a v illage in rural housing construction planning, construction of di sorder, no drawi ngs, no constructi on, no vetting "four no" p henomenon, heap lyi ng there. " Bad" is the weak rural ba se, village g overna nce i s poor. T hirdly, farmers continued t o be "persistent " look. "Ol d" is aging, rural la bor for ce accounted for 70% over the age of 50. "Big" is that the reform measures ground resistance, such as the transa ctions of property rights, l and re pla cement; public service supply gap, r ural education, health car e, pe nsi ons a nd other services can not meet the demand still difficult for poverty alleviati on, w ith empha sis on poverty alleviatio n and 191. "Har d" is a "peasa nts, peasants. Four water effects still la cks

ompell ing." Althoug h the "five water treatment" a lot, work very hard, but t he flood of sci entific e nough, before the treatm ent a nd water quality improveme nt after the treatment effect is not obvi ous, county-wide focus on river st ill largely inferior five water, swimming the River coul d not be found. Five i s "three to split" task still lies a head. Noti ce of stock there, new constructi on did not receiv e timely treatment every year (such a s ancestral hall a s unauthorise d repeate d), contrary to the create d work i s very different from the provi ncial a nd m uni cipal sta ndar ds. Me anw hile, w hen im ple mentation is not in place, generally only focus on ill egal construction dem olished, failing t hat split that is clea r, combined demolition, insufficie nt attention t o reconstr uction of ol d residential areas, urban village s, sha nty tow ns and prom ote poor. o solve the se pr oblems, we must e nha nce t he sense of responsi bility and urge ncy, insi st on problem-oriente d, to take strong measures, efforts to make up the

"three agricult ure" and "five water treatment", "three to split a" short Board, construction of comprehensive safeguards, "Sout h Gate of XX bea utiful" goal of realizi ng. II, and preci sion Shi policy, a nd manpow er playing good "thre e agricultural" work pr otracted "three agri cult ural" work is do economic soci al devel opme nt the work of base d, county level s the sector t o accordi ng to "base d agricultural, a nd and manpow er rural, a nd development farmers" of requirement s, insisted agri cultural r ural base d status not shake, i nsisted hui nong kulak poli cy not weake ned, insi sted reform innovation test not stop, efforts created new era "three agri cultural" w ork new situatio n. (A) to make agriculture m ore. To establi sh the concept of agriculture ar ound the people demand, and com prehe nsively promote the supply side of agricultur e struct ural reform, strive to enhance the qua lity and efficiency of agriculture a nd competitiveness. Focus i s on doi ng the four articles. One is the stea dy increase of grain

article. Always tighte n the stri ng for food security, "rice bag" catch in hand, to hold la nd i n the adjustment of agricult ural planti ng structure i n the "red line." Accelerating the construction of grain ribbons, impr oving agri cultural i nfrastruct ure, enhance food pr oducti on ca pacit y, improv e the quality of ag ricultural product s, effectively "steady increase of grain" and maintai n "tongue." Second, i ndustry convergence arti cle. Enhance the level of concentration, inte nsificati on of agriculture , creating producti on, processi ng, distribution, sale s and service in one of the agri cultural industrial chai n, to break down the value chai n, improve a dde d value. Pushi ng forward "the Internet + agricultural" model to improv e agricult ural production, manageme nt, and servi ce level, i nnovating the mode of e -commer ce marketing of agricultural pr oducts, solve the difficult probl em of sales of agri cultural product s. Agriculture a nd t ourism, educati on, cult ure, hea lth, pensi on a nd other deep i ntegration, devel op lei sure,

travel

消除时延的抖动。

8-5 流式存储音频 / 视频，流式实况音频 / 视频和交互式音频 / 视频都有何区别？

务器？

答： 媒体播放器的主要功能是： 管理用户界面，解压缩， 消除时延抖动和处理传输带来

的差错。

媒体服务器的主要功能是使用元文件的 URL接入到媒体服务器， 请求下载浏览器所

请求的音频 / 视频文件，给出响应把该音频 / 视频文件发送给媒体播放器。

8-7 实时流式协议 RTSP的功能是什么？为什么说它是个带外协议？

答： RTSP 是 IETF 的 MMUSIC工作组开发的协议，功能是为了给流式过程增加更多的功能

而设计的协议。

RTSP 本身并不传送数据， 而仅仅是使媒体播放器能够控制多媒体的传送， 因此 RTSP

又称为外带协议。

8-09 IP 电话的通话质量与那些因素有关？影响 IP 电话话音质量的主要因素有哪些？为什

么 IP 电话的通话质量是不确定的？

答： IP 电话的通话质量主要由两个因素决定。一是通话双方端到端的时延和时延抖动，另

一个是话音分组的丢失率。影响 IP 电话话音质量主要因素有：语音编解码技术、包丢失以

及时延和时延抖动等。 若网络上的通信量非常大以致发生了网络拥堵， 那么端到端时延和时

延抖动以及分组丢失率都会很高，这就导致 IP 电话的通信质量下降。因此，一个用户使用

IP 电话的通信质量取决于当时其他的许多用户的行为。

8-10 为什么 RTP协议同时具有运输层和应用层的特点？

答：从开发者的角度看， RTP应当是应用层的一部分。在应用程序的发送端，开发者必须编

写用 RTP封装分组的程序代码，然后把 RTP分组交给 UDP套接字接口。在接受端， RTP分组

living standards, poor farmers in less t han complete elimination of 4600 Yuan, 8949, 19008. "Five waters rule": the County inve sted 2.169 bi llion yuan, similar counties line the city's first complete t he 42 km of sewage pipe netw ork construction, completi on rate ranked first in the city, won the pr ovincial rur al sewage treatment w ork better; key polluti on sour ces such as ele ctroplati ng, pa permaki ng, chemical i ndustry management t hroug h verification and accepta nce of the muni cipa l governme nt, the County removed Black a nd odorous River, River waste, beginning of river ecologi cal restora tion effects. "Three modified a split" aspects: County total demolition illegal area up 2.759 milli on square meters, com pleted City issued annual task of 153%, split against area ranking city se cond; complete d "three modified" area 4.846 million square meters, complete d City issued a nnual t ask of 403%, ranki ng city thir d, whi ch vi llage in the a target complete d total city ranki ng first; County Governme nt

was named city level "three modified a split" work advanced. The se achievement s are hard w on a nd should be a ppre ciated. Howeve r, we are fully aware, t he ne w peri od, a nd w ork in the countrysi de and the e nvironment facing higher sta ndar ds and requirements, provi ncial party Committee offered to hig h level build a compre he nsive well -off society goal re quires "no filth, dirty environment illegal buil dings, into a w ell-off"; municipal party Committee also pr oposes t o build int o the well -off be nchmark goals of the city. Com pared wit h the superi or claim, "South Gate of XX beautif ul" goal, my County "San Nong" a nd envir onme nt there are a number of weaknesses a nd gaps, hig hlighted i n the foll owing five aspect s: first, agriculture remaine d "low" pattern. "Low" is reflecte d in the quality and l ow; short, value added of the industry chain is lo w; 123 fusion yield l ow empl oyee age, l ow qualit y. "Small" is reflected in small er, specialized cooperatives t hroughout the County there were 3,396, but on

the scal e of too little. "San" is refle cted in producti on, ma nagement, service s, de centralize d, centralize d, standardized, brand, information and organizati onal l evel is not high. Second, the countryside is still i n "dirty" phase. "Dirty" is dirty of rural sanitati on sit uation has not cha nged. "Chaos" is a village in rural housing construction planning, construction of di sorder, no drawi ngs, no constructi on, no vetting "four no" phenomenon, heap lyi ng there. " Bad" is the weak rural ba se, village g overna nce i s poor. T hirdly, farmers continued t o be "persistent" look. "Ol d" is aging, rural la bor for ce accounted for 70% over the age of 50. "Big" is that the reform measures ground resistance, such as the transa ctions of property rights, l and re pla cement; public service supply gap, r ural education, health car e, pe nsi ons a nd other services can not meet the deman d still difficult for poverty alleviati on, w ith empha sis on poverty alleviation and 191. "Har d" is a "peasa nts, pea sants. Four water effects still la cks

ompell ing." Althoug h the "five water treatment" a lot, work very hard, but t he flood of sci entific e nough, before the treatment a nd water quality improveme nt after the treatment effect is not obvi ous, county-wide focus on river st ill largely inferior five water, swimming the River coul d not be found. Five i s "three to split" task still lies a head. Noti ce of stock there, new constructi on did not receiv e timely treatment every year (such a s ancestral hall a s unauthorise d repeate d), contrary to the create d work i s very different from the provi ncial a nd m uni cipal sta ndar ds. Me anw hile, w hen im ple mentation is not in place, generally only focus on ill egal construction dem olished, failing t hat split that is clea r, combined demolition, insufficie nt attention t o reconstr uction of ol d residential areas, urban village s, sha nty tow ns and prom ote poor. o solve the se pr oblems, we must e nha nce t he sense of responsi bility and urge ncy, insi st on problem-oriente d, to take strong measures, efforts to make up the

"three agricult ure" and "five water treatment", "three to split a" short Board, construction of comprehensive safeguards, "Sout h Gate of XX bea utiful" goal of realizi ng. II, and preci sion Shi policy, a nd manpow er playing good "thre e agricultural" work pr otracted "three agri cult ural" work is do economic soci al devel opme nt the work of base d, county level s the sector t o accordi ng to "base d agricultural, a nd and manpow er rural, a nd development farmers" of requirement s, insisted agri cultural r ural base d status not shake, i nsisted hui nong kulak poli cy not weake ned, insi sted reform innovation test not stop, efforts created new era "three agri cultural" w ork new situation. (A) to make agriculture m ore. To establi sh the concept of agriculture ar ound the people demand, and com prehe nsively promote the supply side of agricultur e struct ural reform, strive to enhance the qua lity and efficiency of agriculture a nd competitiveness. Focus i s on doi ng the four articles. One is the stea dy increase of grain

article. Always tighte n the stri ng for food security, "rice bag" catch in hand, to hold la nd i n the adjustment of agricult ural planti ng structure i n the "red line." Accelerating the construction of grain ribbons, impr oving agri cultural i nfrastruct ure, enhance f ood pr oducti on ca pacit y, improv e the quality of agricultural product s, effectively "steady increase of grain" and maintai n "tongue." Second, i ndustry convergence arti cle. Enhance the level of concentration, inte nsificati on of agriculture , creating producti on, processi ng, distribution, sale s and service in one of the agri cult ural industrial chai n, to break down the value chai n, improve a dde d value. Pushi ng forward "the Internet + agricultural" model to improv e agricult ural production, manageme nt, and servi ce level, i nnovating the mode of e -commer ce marketing of agricultural pr oducts, solve the difficult probl em of sales of agri cultural product s. Agriculture a nd tourism, educati on, cult ure, hea lth, pensi on a nd other deep i ntegration, devel op lei sure,

travel

一个协议框架因为它只包含了实时应用的一些共同功能。 RTP并不对多媒体数据块做任何处

理而只是向应用层提供一些附加的信息，让应用层知道应当如何进行处理。

8-13 RTCP 协议使用在什么场合？它们各有何主要特点？

答： RTP协议分别使用在：结束分组 BYE表示关闭一个数据流；特定应用分组 APP时应用

程序能够定义新的分组类型；接收端报告分组 RR用来使接收端周期性地向所有的点用多播

方式进行报告；发送端报告分组 SR用来使发送端周期性地向所有接收端用多播方式进行报

告；远点描述分组 SDES给出会话中参加者的描述。

8-14 IP 电话的两个主要标准各有何特点？

解： IP 电话的两个标准分别为： ITU-T 定义的 H.323 协议和 IETF 提出的绘画发起协议 SIP.

H.323 协议的特点：以已有的电路交换电话网为基础，增加了 IP 电话的功能。 H.323

的指令沿用原有电话网的信令模式，与原有电话网的连接比较容易。

（1）用图表示出这些分组发出时间和到达时间。

（2）若在接收端还原时的端到端时延为 75ms，试求出每个分组经受的时延。

（3）画出接收端缓存中的分组数与时间的关系。

解： （1）下图（ a）的纵横坐标表示这些分组的发出时间和到达时间

living standards, poor farmers in less t han complete elimination of 4600 Yuan, 8949, 19008. "Five waters rule": the County inve sted 2.169 bi llion yuan, similar counties line the city's first complete t he 42 km of sewage pipe netw ork construction, completi on rate r anked first in the city, won the pr ovincial rural sewage treatment w ork better; key polluti on sour ces such as ele ctroplati ng, pa permaki ng, chemical i ndustry management t hroug h verification and accepta nce of the muni cipa l governme nt, the County removed Black a nd odorous River, River waste, beginning of river ecologi cal restora tion effects. "Three modified a split" aspects: County total demolition illegal area up 2.759 milli on square meters, com pleted City issued annual task of 153%, split against area ranking city se cond; complete d "three modified" area 4.846 million square meters, complete d City issued a nnual t ask of 403%, r anki ng city thir d, whi ch vi llage in the a target complete d total city ranki ng first; County Governme nt

was named city level "three modified a split" work advanced. The se achievement s are hard w on a nd should be a ppre ciated. Howeve r, we are fully aware, t he ne w peri od, a nd w ork in the countrysi de and the e nvironment facing higher sta ndar ds and requirements, provi ncial party Committee of fered to hig h level build a compre he nsive well -off society goal re quires "no filth, dirty environment illegal buil dings, into a w ell-off"; municipal party Committee also pr oposes t o build int o the well -off be nchmark goals of the city. Com pared wit h the superi or claim, "South Gate of XX beautif ul" goal, my County "San Nong" a nd envir onme nt there are a number of weaknesses a nd gaps, hig hlighted i n the foll owing five aspect s: first, agriculture remaine d "low" pattern. "Low" is reflecte d in the quality and l ow; short, value added of the industry chain is low; 123 fusion yield l ow empl oyee age, l ow qualit y. "Small" is reflected in small er, specialized cooperatives t hroughout the County there were 3,396, but on

the scal e of too little. "San" is refle cted in producti on, ma nagement, service s, de centralize d, centralize d, standardized, brand, information and organizati onal l evel is not high. Second, the countryside is still i n "dirty" phase. "Dirty" is dirty of rural sanitati on sit uation has not cha nged. "Chaos" is a v illage in rural housing construction planning, construction of di sorder, no drawi ngs, no constructi on, no vetting "four no" p henomenon, heap lyi ng there. " Bad" is the weak rural ba se, village g overna nce i s poor. T hirdly, farmers continued t o be "persistent " look. "Ol d" is aging, rural la bor for ce accounted for 70% over the age of 50. "Big" is that the reform measures ground resistance, such as the transa ctions of property rights, l and re pla cement; public service supply gap, r ural education, health car e, pe nsi ons a nd other services can not meet the demand still difficult for poverty alleviati on, w ith empha sis on poverty alleviatio n and 191. "Har d" is a "peasa nts, peasants. Four water effects still la cks

ompell ing." Althoug h the "five water treatment" a lot, work very hard, but t he flood of sci entific e nough, before the treatm ent a nd water quality improveme nt after the treatment effect is not obvi ous, county-wide focus on river st ill largely inferior five water, swimming the River coul d not be found. Five i s "three to split" task still lies a head. Noti ce of stock there, new constructi on did not receiv e timely treatment every year (such a s ancestral hall a s unauthorise d repeate d), contrary to the create d work i s very different from the provi ncial a nd m uni cipal sta ndar ds. Me anw hile, w hen im ple mentation is not in place, generally only focus on ill egal construction dem olished, failing t hat split that is clea r, combined demolition, insufficie nt attention t o reconstr uction of ol d residential areas, urban village s, sha nty tow ns and prom ote poor. o solve the se pr oblems, we must e nha nce t he sense of responsi bility and urge ncy, insi st on problem-oriente d, to take strong measures, efforts to make up the

"three agricult ure" and "five water treatment", "three to split a" short Board, construction of comprehensive safeguards, "Sout h Gate of XX bea utiful" goal of realizi ng. II, and preci sion Shi policy, a nd manpow er playing good "thre e agricultural" work pr otracted "three agri cult ural" work is do economic soci al devel opme nt the work of base d, county level s the sector t o accordi ng to "base d agricultural, a nd and manpow er rural, a nd development farmers" of requirement s, insisted agri cultural r ural base d status not shake, i nsisted hui nong kulak poli cy not weake ned, insi sted reform innovation test not stop, efforts created new era "three agri cultural" w ork new situatio n. (A) to make agriculture m ore. To establi sh the concept of agriculture ar ound the people demand, and com prehe nsively promote the supply side of agricultur e struct ural reform, strive to enhance the qua lity and efficiency of agriculture a nd competitiveness. Focus i s on doi ng the four articles. One is the stea dy increase of grain

article. Always tighte n the stri ng for food security, "rice bag" catch in hand, to hold la nd i n the adjustment of agricult ural planti ng structure i n the "red line." Accelerating the construction of grain ribbons, impr oving agri cultural i nfrastruct ure, enhance food pr oducti on ca pacit y, improv e the quality of ag ricultural product s, effectively "steady increase of grain" and maintai n "tongue." Second, i ndustry convergence arti cle. Enhance the level of concentration, inte nsificati on of agriculture , creating producti on, processi ng, distribution, sale s and service in one of the agri cult ural industrial chai n, to break down the value chai n, improve a dde d value. Pushi ng forward "the Internet + agricultural" model to improv e agricult ural production, manageme nt, and servi ce level, i nnovating the mode of e -commer ce marketing of agricultural pr oducts, solve the difficult probl em of sales of agri cultural product s. Agriculture a nd t ourism, educati on, cult ure, hea lth, pensi on a nd other deep i ntegration, devel op lei sure,

travel

（2）每个分组经受的时延分别为： 30，25，22，29，455，35，29，26，20 和 24ms

（3）接收端缓存中的分组数与时间的关系如下图（ b）所示。

（b）接收端缓存中的分组数语时间关系图

8-16 话音信号的采样速率为 8000HZ，每隔 10ms将已编码的话音采样装配为话音分组。每

一个话音分组在发送之前要加上一个时间戳。假定时间戳是从一个时钟得到的，该时钟每

隔△秒将计时器加 1. 试问能否将△取为 9ms？如果行，请说明理由。如果不行，你认为△

应取为多少？

越大。

8-18 什么是服务质量 QoS？为什么说“因特网根本没有服务质量可言”？

解：服务质量 QoS是服务性能的总效果， 此效果决定了一个用户对服务的满意程度。 因特网

的网络本身提供的服务是不可靠的， 它不能保证服务质量。实际上 “尽最大努力交付” 的服

务就是没有质量保证的服务，根本没有服务质量可言。

8-19 在讨论服务质量时，管制、调度、呼叫接纳表示什么意思？

解：管制：使某个数据流不影响其他正常数据流在网络中通过的一种机制。

调度：路由器的队列所采用的排队规则。

呼叫接纳： 数据流要事先声明它所需要的服务质量， 然后或者被准许进入网络， 或者被拒绝

进入网络。