r*n
2 楼
研究这个的说哈,谢谢了。
z*y
3 楼
为什么UDP header里有length field,而TCP header却没有?
s*s
4 楼
【 以下文字转载自 Hardware 讨论区 】
发信人: shakuras (doskey), 信区: Hardware
标 题: ATI显卡如何设置双显示器
发信站: BBS 未名空间站 (Sun Nov 9 00:09:07 2008), 转信
用自带的软件设置播放视频的时候自动在TV上最大化, 现在只有用WMP的时候是
成功的, 用影音风暴或者pplive的时候就不会, 请问应该怎样设置.
发信人: shakuras (doskey), 信区: Hardware
标 题: ATI显卡如何设置双显示器
发信站: BBS 未名空间站 (Sun Nov 9 00:09:07 2008), 转信
用自带的软件设置播放视频的时候自动在TV上最大化, 现在只有用WMP的时候是
成功的, 用影音风暴或者pplive的时候就不会, 请问应该怎样设置.
z*r
11 楼
did a quick search
http://stackoverflow.com/questions/281606/why-does-udp-have-a-l
There is a 96 bit pseudo header conceptually prefixed to the TCP header that
contains the information already.
The checksum field description from this source gives the answer:
Checksum: 16 bits
The checksum field is the 16 bit one's complement of the one's complemen
t sum of all 16 bit words in the header and text. If a segment contains an o
dd number of header and text octets to be checksummed, the last octet is pad
ded on the right with zeros to form a 16 bit word for checksum purposes. The
pad is not transmitted as part of the segment. While computing the checksum
, the checksum field itself is replaced with zeros.
The checksum also covers a 96 bit pseudo header conceptually prefixed to
the TCP header. This pseudo header contains the Source Address, the Destina
tion Address, the Protocol, and TCP length. This gives the TCP protection ag
ainst misrouted segments. This information is carried in the Internet Protoc
ol and is transferred across the TCP/Network interface in the arguments or r
esults of calls by the TCP on the IP.
+--------+--------+--------+--------+
| Source Address |
+--------+--------+--------+--------+
| Destination Address |
+--------+--------+--------+--------+
| zero | PTCL | TCP Length |
+--------+--------+--------+--------+
The information is not needed at the TCP level since TCP is a stream based p
rotocol.
【在 z**r 的大作中提到】
: agree, and TCP UDP were designed by different groups
http://stackoverflow.com/questions/281606/why-does-udp-have-a-l
There is a 96 bit pseudo header conceptually prefixed to the TCP header that
contains the information already.
The checksum field description from this source gives the answer:
Checksum: 16 bits
The checksum field is the 16 bit one's complement of the one's complemen
t sum of all 16 bit words in the header and text. If a segment contains an o
dd number of header and text octets to be checksummed, the last octet is pad
ded on the right with zeros to form a 16 bit word for checksum purposes. The
pad is not transmitted as part of the segment. While computing the checksum
, the checksum field itself is replaced with zeros.
The checksum also covers a 96 bit pseudo header conceptually prefixed to
the TCP header. This pseudo header contains the Source Address, the Destina
tion Address, the Protocol, and TCP length. This gives the TCP protection ag
ainst misrouted segments. This information is carried in the Internet Protoc
ol and is transferred across the TCP/Network interface in the arguments or r
esults of calls by the TCP on the IP.
+--------+--------+--------+--------+
| Source Address |
+--------+--------+--------+--------+
| Destination Address |
+--------+--------+--------+--------+
| zero | PTCL | TCP Length |
+--------+--------+--------+--------+
The information is not needed at the TCP level since TCP is a stream based p
rotocol.
【在 z**r 的大作中提到】
: agree, and TCP UDP were designed by different groups
B*R
12 楼
赫赫,面试时没词儿了我就喜欢问UDP CHECKSUM怎么算的
field-in-the-header-and-tcp-does-not
that
complemen
an o
pad
The
【在 z**r 的大作中提到】
: did a quick search
: http://stackoverflow.com/questions/281606/why-does-udp-have-a-l
: There is a 96 bit pseudo header conceptually prefixed to the TCP header that
: contains the information already.
: The checksum field description from this source gives the answer:
: Checksum: 16 bits
: The checksum field is the 16 bit one's complement of the one's complemen
: t sum of all 16 bit words in the header and text. If a segment contains an o
: dd number of header and text octets to be checksummed, the last octet is pad
: ded on the right with zeros to form a 16 bit word for checksum purposes. The
field-in-the-header-and-tcp-does-not
that
complemen
an o
pad
The
【在 z**r 的大作中提到】
: did a quick search
: http://stackoverflow.com/questions/281606/why-does-udp-have-a-l
: There is a 96 bit pseudo header conceptually prefixed to the TCP header that
: contains the information already.
: The checksum field description from this source gives the answer:
: Checksum: 16 bits
: The checksum field is the 16 bit one's complement of the one's complemen
: t sum of all 16 bit words in the header and text. If a segment contains an o
: dd number of header and text octets to be checksummed, the last octet is pad
: ded on the right with zeros to form a 16 bit word for checksum purposes. The
f*n
15 楼
UDP里的length看来是多余的, stevens那本书里也这么说
但是TCP要length有啥用? 本来就是stream oriented protocol, length这个概念就不
适合TCP
that
complemen
o
pad
The
【在 z**r 的大作中提到】
: did a quick search
: http://stackoverflow.com/questions/281606/why-does-udp-have-a-l
: There is a 96 bit pseudo header conceptually prefixed to the TCP header that
: contains the information already.
: The checksum field description from this source gives the answer:
: Checksum: 16 bits
: The checksum field is the 16 bit one's complement of the one's complemen
: t sum of all 16 bit words in the header and text. If a segment contains an o
: dd number of header and text octets to be checksummed, the last octet is pad
: ded on the right with zeros to form a 16 bit word for checksum purposes. The
但是TCP要length有啥用? 本来就是stream oriented protocol, length这个概念就不
适合TCP
that
complemen
o
pad
The
【在 z**r 的大作中提到】
: did a quick search
: http://stackoverflow.com/questions/281606/why-does-udp-have-a-l
: There is a 96 bit pseudo header conceptually prefixed to the TCP header that
: contains the information already.
: The checksum field description from this source gives the answer:
: Checksum: 16 bits
: The checksum field is the 16 bit one's complement of the one's complemen
: t sum of all 16 bit words in the header and text. If a segment contains an o
: dd number of header and text octets to be checksummed, the last octet is pad
: ded on the right with zeros to form a 16 bit word for checksum purposes. The
m*t
17 楼
There is an offset field to contain the option header length though
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