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framing,errordetection.
InTCP:
framing,reliabledeliverybetweenadjacentnodes,errordetection,half-duplexandfull-duplex.
2.IfallthelinksintheInternetweretoprovidereliabledeliveryservice,wouldtheTCPreliabledeliveryserviceberedundant?
Whyorwhynot?
不会多余,因为TCP保证的是传输层的数据传送,而link提供稳定可靠传输保证链路层的传输稳定,二者不完全重叠,所以TCP可靠传输也不会多余。
3.InSection5.3,welistedfourdesirablecharacteristicsofabroadcastchannel.WhichofthesecharacteristicsdoesslottedALOHAhave?
Whichofthesecharacteristicsdoestokenpassinghave?
4.SupposetwonodesstarttotransmitatthesametimeapacketoflengthLoverabroadcastchannelofrateR.Denotethepropagationdelaybetweenthetwonodesasdprop.Willtherebeacollisionifdprop<
L/R?
因为L/R=包传递的时间,如果dprop<
L/R,也就意味着A的信号跑到B的时候B的最后一个分组还没离开B,所以发生碰撞。
7.SupposenodesA,B,andCeachattachtothesamebroadcastLAN(throughtheiradapters).IfAsendsthousandsofIPdatagramstoBwitheachencapsulatingframeaddressedtotheMACaddressofB,willC’sadapterprocesstheseframes?
Ifso,willC’sadapterpasstheIPdatagramsintheseframestothenetworklayerC?
HowwouldyouranswerschangeifAsendsframeswiththeMACbroadcastaddress?
不会,C会拆封帧从而读取报头的MAC,因为每一个host的MAC都唯一,C读取到数据报中的MAC和自己的不一样就不会继续拆封数据报,不会投递给C。
当使用LAN口广播地址的时候,C的适配器就会拆封帧,向C传递数据。
8.HowbigistheMACaddressspace?
TheIPv4addressspace?
TheIPv6addressspace?
2^48,2^32,2^128.
9.WhyisanARPquerysentwithinabroadcastframe?
WhyisanARPresponsesentwithinaframewithaspecificdestinationMACaddress?
因为新加入网络的主机是不知道路由器的IP的,自己也没有IP,所以只能广播才能得到IP。
因为每个主机的MAC地址都是唯一的,而ARP建立转发表的时候会带上MAC地址。
12.InCSMA/CD,afterthefifthcollision,whatistheprobabilitythatanodechoosesK=4?
TheresultK=4correspondstoadelayofhowmanysecondsona10MbpsEthernet?
可能,因为第五次K的取值范围是0-(2^5-1)即0-31。
Bittime=1bit/R=1bit/10Mbps=1msec,K=4,waittime=4*512*1msec=2048msec。
Problems:
1.Supposetheinformationcontentofapacketisthebitpattern1110110010001010andanevenparityschemeisbeingused.Whatwouldthevalueofthefieldcontainingtheparitybitsbeforthecaseofatwo-dimensionalparityscheme?
Youranswershouldbesuchthataminimum-lengthchecksumfieldisused.假设一个数据包的信息含量是XXX,使用偶校验方案。
采用二位奇偶校验方案的字段包含的奇偶校验位的字段的值是多少?
答案要使用最小长度校验。
10100
10111
00011
2.Supposetheinformationportionofapacket(DinFigure5.4)contains10bytesconsistingofthe8-bitunsignedbinaryASCIIrepresentationoftheintegers0through9.ComputetheInternetchecksumforthisdata.假设一个包的信息的一部分包括10bytes组成的8-bit无符号二进制码表示的整数0-9,计算该数据的网络校验。
算校验码先把0-9加起来
0000000000000001
0000001000000011
0000010000000101
0000011000000111
0000100000001001
0001010000011001
→→→→取反可得
校验码为1110101111100110
3.Considerthepreviousproblem,butinsteadofcontainingthebinaryofthenumbers0through9supposethese10bytescontain.ComputetheInternetchecksumforthisdata.
a.thebinaryrepresentationofthenumbers1through10.
0000000100000010
0000001100000100
0000010100000110
0000011100001000
0000100100010100
0001101100011110
1110010011100001
b.theASCIIrepresentationofthelettersAthroughJ(uppercase).
0100000101000010
0100001101000100
0100010101000110
0100011101001000
0100100101001010
0101100001011111
1010011110100000
c.theASCIIrepresentationofthelettersathroughj(lowercase).小写字母表示
0110000101100010
0110001101100100
0110010101100110
0110011101101000
0110100101101010
1111100111111101
0000011000000010
6.Considerthepreviousproblem,butsupposethatDhasthevalue
a.10010001.
b.10100011.
c.01010101.
前一题题目:
Considerthe7-bitgenerator,G=10011,andsupposethatDhasthevalue1010101010.WhatisthevalueofR?
求余而已,记住不要做减法而是做与运算就好。
a.R=001
b.R=101
c.R=101
12.ConsiderthreeLANsinterconnectedbytworouters,asshowninFigure5.38.
a.Redrawthediagramtoincludeadapters.重新画图
b.AssignIPaddressestoalloftheinterfaces.ForSubnet1useaddressesoftheform111.111.111.xxx;
forSubnet2usesaddressesoftheform122.122.122.xxx;
andforSubnet3useaddressesoftheform133.133.133.xxx.所有的接口分配IP地址。
c.AssignMACaddressestoalloftheadapters.
a.b.c如图
e.Repeat(d),nowassumingthattheARPtableinthesendinghostisempty(andtheothertablesareuptodate).
发送方的ARP