?? ppp中使用hdlc幀.htm
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<P align=justify>0x2942, 0x38cb, 0x0a50, 0x1bd9, 0x6f66, 0x7eef, 0x4c74,
0x5dfd,</P>
<P align=justify>0xb58b, 0xa402, 0x9699, 0x8710, 0xf3af, 0xe226, 0xd0bd,
0xc134,</P>
<P align=justify>0x39c3, 0x284a, 0x1ad1, 0x0b58, 0x7fe7, 0x6e6e, 0x5cf5,
0x4d7c,</P>
<P align=justify>0xc60c, 0xd785, 0xe51e, 0xf497, 0x8028, 0x91a1, 0xa33a,
0xb2b3,</P>
<P align=justify>0x4a44, 0x5bcd, 0x6956, 0x78df, 0x0c60, 0x1de9, 0x2f72,
0x3efb,</P>
<P align=justify>0xd68d, 0xc704, 0xf59f, 0xe416, 0x90a9, 0x8120, 0xb3bb,
0xa232,</P>
<P align=justify>0x5ac5, 0x4b4c, 0x79d7, 0x685e, 0x1ce1, 0x0d68, 0x3ff3,
0x2e7a,</P>
<P align=justify>0xe70e, 0xf687, 0xc41c, 0xd595, 0xa12a, 0xb0a3, 0x8238,
0x93b1,</P>
<P align=justify>0x6b46, 0x7acf, 0x4854, 0x59dd, 0x2d62, 0x3ceb, 0x0e70,
0x1ff9,</P>
<P align=justify>0xf78f, 0xe606, 0xd49d, 0xc514, 0xb1ab, 0xa022, 0x92b9,
0x8330,</P>
<P align=justify>0x7bc7, 0x6a4e, 0x58d5, 0x495c, 0x3de3, 0x2c6a, 0x1ef1,
0x0f78</P>
<P align=justify>};</P>
<P align=justify> </P>
<P align=justify>#define PPPINITFCS16 0xffff /* Initial FCS value */</P>
<P align=justify>#define PPPGOODFCS16 0xf0b8 /* Good final FCS value
*/</P>
<P align=justify> </P>
<P align=justify>/*</P>
<P align=justify>* 由給定的當前FCS值和新數據計算新的FCS數值</P>
<P align=justify>*/</P>
<P align=justify>u16 pppfcs16(fcs, cp, len)</P>
<P align=justify>register u16 fcs;</P>
<P align=justify>register unsigned char *cp;</P>
<P align=justify>register int len;</P>
<P align=justify>{</P>
<P align=justify>ASSERT(sizeof (u16) == 2);</P>
<P align=justify>ASSERT(((u16) -1) > 0);</P>
<P align=justify>while (len--)</P>
<P align=justify>fcs = (fcs >> 8) ^ fcstab[(fcs ^ *cp++) &
0xff];</P>
<P align=justify> </P>
<P align=justify>return (fcs);</P>
<P align=justify>}</P>
<P align=justify> </P>
<P align=justify>/*</P>
<P align=justify>* 如何使用FCS</P>
<P align=justify>*/</P>
<P align=justify>tryfcs16(cp, len)</P>
<P align=justify>register unsigned char *cp;</P>
<P align=justify>register int len;</P>
<P align=justify>{</P>
<P align=justify>u16 trialfcs;</P>
<P align=justify> </P>
<P align=justify>/* add on output */</P>
<P align=justify>trialfcs = pppfcs16( PPPINITFCS16, cp, len );</P>
<P align=justify>trialfcs ^= 0xffff; /* 取反 */</P>
<P align=justify>cp[len] = (trialfcs & 0x00ff); /* 最低位優先 */</P>
<P align=justify>cp[len+1] = ((trialfcs >> 8) & 0x00ff);</P>
<P align=justify> </P>
<P align=justify>/* check on input */</P>
<P align=justify>trialfcs = pppfcs16( PPPINITFCS16, cp, len + 2 );</P>
<P align=justify>if ( trialfcs == PPPGOODFCS16 )</P>
<P align=justify>printf("Good FCS\n");</P>
<P align=justify>}</P>
<P align=justify> </P>
<P align=justify>C.3. 32位FCS計算方法</P>
<P align=justify> </P>
<P align=justify>下面例子的功能：當數據到達時，由一個查找表計算32位的幀檢查序列。</P>
<P align=justify> </P>
<P align=justify>/*</P>
<P align=justify>* FCS-32產生子多項式：x**0 + x**1 + x**2 + x**4 + x**5</P>
<P align=justify>* + x**7 + x**8 + x**10 + x**11 + x**12 + x**16</P>
<P align=justify>* + x**22 + x**23 + x**26 + x**32.</P>
<P align=justify>*/</P>
<P align=justify> </P>
<P align=justify>/*</P>
<P align=justify>* u32代表無符號的32位數</P>
<P align=justify>*/</P>
<P align=justify>typedef unsigned long u32;</P>
<P align=justify> </P>
<P align=justify>static u32 fcstab_32[256] =</P>
<P align=justify>{</P>
<P align=justify>0x00000000, 0x77073096, 0xee0e612c, 0x990951ba,</P>
<P align=justify>0x076dc419, 0x706af48f, 0xe963a535, 0x9e6495a3,</P>
<P align=justify>0x0edb8832, 0x79dcb8a4, 0xe0d5e91e, 0x97d2d988,</P>
<P align=justify>0x09b64c2b, 0x7eb17cbd, 0xe7b82d07, 0x90bf1d91,</P>
<P align=justify>0x1db71064, 0x6ab020f2, 0xf3b97148, 0x84be41de,</P>
<P align=justify>0x1adad47d, 0x6ddde4eb, 0xf4d4b551, 0x83d385c7,</P>
<P align=justify>0x136c9856, 0x646ba8c0, 0xfd62f97a, 0x8a65c9ec,</P>
<P align=justify>0x14015c4f, 0x63066cd9, 0xfa0f3d63, 0x8d080df5,</P>
<P align=justify>0x3b6e20c8, 0x4c69105e, 0xd56041e4, 0xa2677172,</P>
<P align=justify>0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b,</P>
<P align=justify>0x35b5a8fa, 0x42b2986c, 0xdbbbc9d6, 0xacbcf940,</P>
<P align=justify>0x32d86ce3, 0x45df5c75, 0xdcd60dcf, 0xabd13d59,</P>
<P align=justify>0x26d930ac, 0x51de003a, 0xc8d75180, 0xbfd06116,</P>
<P align=justify>0x21b4f4b5, 0x56b3c423, 0xcfba9599, 0xb8bda50f,</P>
<P align=justify>0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924,</P>
<P align=justify>0x2f6f7c87, 0x58684c11, 0xc1611dab, 0xb6662d3d,</P>
<P align=justify>0x76dc4190, 0x01db7106, 0x98d220bc, 0xefd5102a,</P>
<P align=justify>0x71b18589, 0x06b6b51f, 0x9fbfe4a5, 0xe8b8d433,</P>
<P align=justify>0x7807c9a2, 0x0f00f934, 0x9609a88e, 0xe10e9818,</P>
<P align=justify>0x7f6a0dbb, 0x086d3d2d, 0x91646c97, 0xe6635c01,</P>
<P align=justify>0x6b6b51f4, 0x1c6c6162, 0x856530d8, 0xf262004e,</P>
<P align=justify>0x6c0695ed, 0x1b01a57b, 0x8208f4c1, 0xf50fc457,</P>
<P align=justify>0x65b0d9c6, 0x12b7e950, 0x8bbeb8ea, 0xfcb9887c,</P>
<P align=justify>0x62dd1ddf, 0x15da2d49, 0x8cd37cf3, 0xfbd44c65,</P>
<P align=justify>0x4db26158, 0x3ab551ce, 0xa3bc0074, 0xd4bb30e2,</P>
<P align=justify>0x4adfa541, 0x3dd895d7, 0xa4d1c46d, 0xd3d6f4fb,</P>
<P align=justify>0x4369e96a, 0x346ed9fc, 0xad678846, 0xda60b8d0,</P>
<P align=justify>0x44042d73, 0x33031de5, 0xaa0a4c5f, 0xdd0d7cc9,</P>
<P align=justify>0x5005713c, 0x270241aa, 0xbe0b1010, 0xc90c2086,</P>
<P align=justify>0x5768b525, 0x206f85b3, 0xb966d409, 0xce61e49f,</P>
<P align=justify>0x5edef90e, 0x29d9c998, 0xb0d09822, 0xc7d7a8b4,</P>
<P align=justify>0x59b33d17, 0x2eb40d81, 0xb7bd5c3b, 0xc0ba6cad,</P>
<P align=justify>0xedb88320, 0x9abfb3b6, 0x03b6e20c, 0x74b1d29a,</P>
<P align=justify>0xead54739, 0x9dd277af, 0x04db2615, 0x73dc1683,</P>
<P align=justify>0xe3630b12, 0x94643b84, 0x0d6d6a3e, 0x7a6a5aa8,</P>
<P align=justify>0xe40ecf0b, 0x9309ff9d, 0x0a00ae27, 0x7d079eb1,</P>
<P align=justify>0xf00f9344, 0x8708a3d2, 0x1e01f268, 0x6906c2fe,</P>
<P align=justify>0xf762575d, 0x806567cb, 0x196c3671, 0x6e6b06e7,</P>
<P align=justify>0xfed41b76, 0x89d32be0, 0x10da7a5a, 0x67dd4acc,</P>
<P align=justify>0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5,</P>
<P align=justify>0xd6d6a3e8, 0xa1d1937e, 0x38d8c2c4, 0x4fdff252,</P>
<P align=justify>0xd1bb67f1, 0xa6bc5767, 0x3fb506dd, 0x48b2364b,</P>
<P align=justify>0xd80d2bda, 0xaf0a1b4c, 0x36034af6, 0x41047a60,</P>
<P align=justify>0xdf60efc3, 0xa867df55, 0x316e8eef, 0x4669be79,</P>
<P align=justify>0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236,</P>
<P align=justify>0xcc0c7795, 0xbb0b4703, 0x220216b9, 0x5505262f,</P>
<P align=justify>0xc5ba3bbe, 0xb2bd0b28, 0x2bb45a92, 0x5cb36a04,</P>
<P align=justify>0xc2d7ffa7, 0xb5d0cf31, 0x2cd99e8b, 0x5bdeae1d,</P>
<P align=justify>0x9b64c2b0, 0xec63f226, 0x756aa39c, 0x026d930a,</P>
<P align=justify>0x9c0906a9, 0xeb0e363f, 0x72076785, 0x05005713,</P>
<P align=justify>0x95bf4a82, 0xe2b87a14, 0x7bb12bae, 0x0cb61b38,</P>
<P align=justify>0x92d28e9b, 0xe5d5be0d, 0x7cdcefb7, 0x0bdbdf21,</P>
<P align=justify>0x86d3d2d4, 0xf1d4e242, 0x68ddb3f8, 0x1fda836e,</P>
<P align=justify>0x81be16cd, 0xf6b9265b, 0x6fb077e1, 0x18b74777,</P>
<P align=justify>0x88085ae6, 0xff0f6a70, 0x66063bca, 0x11010b5c,</P>
<P align=justify>0x8f659eff, 0xf862ae69, 0x616bffd3, 0x166ccf45,</P>
<P align=justify>0xa00ae278, 0xd70dd2ee, 0x4e048354, 0x3903b3c2,</P>
<P align=justify>0xa7672661, 0xd06016f7, 0x4969474d, 0x3e6e77db,</P>
<P align=justify>0xaed16a4a, 0xd9d65adc, 0x40df0b66, 0x37d83bf0,</P>
<P align=justify>0xa9bcae53, 0xdebb9ec5, 0x47b2cf7f, 0x30b5ffe9,</P>
<P align=justify>0xbdbdf21c, 0xcabac28a, 0x53b39330, 0x24b4a3a6,</P>
<P align=justify>0xbad03605, 0xcdd70693, 0x54de5729, 0x23d967bf,</P>
<P align=justify>0xb3667a2e, 0xc4614ab8, 0x5d681b02, 0x2a6f2b94,</P>
<P align=justify>0xb40bbe37, 0xc30c8ea1, 0x5a05df1b, 0x2d02ef8d</P>
<P align=justify>};</P>
<P align=justify> </P>
<P align=justify>#define PPPINITFCS32 0xffffffff /* 初始化FCS值 */</P>
<P align=justify>#define PPPGOODFCS32 0xdebb20e3 /* 好的最終FCS值 */</P>
<P align=justify>/*</P>
<P align=justify>* 由給定的當前FCS值和新數據計算新的FCS數值</P>
<P align=justify>*/</P>
<P align=justify>u32 pppfcs32(fcs, cp, len)</P>
<P align=justify>register u32 fcs;</P>
<P align=justify>register unsigned char *cp;</P>
<P align=justify>register int len;</P>
<P align=justify>{</P>
<P align=justify>ASSERT(sizeof (u32) == 4);</P>
<P align=justify>ASSERT(((u32) -1) > 0);</P>
<P align=justify>while (len--)</P>
<P align=justify>fcs = (((fcs) >> 8) ^ fcstab_32[((fcs) ^ (*cp++))
& 0xff]);</P>
<P align=justify> </P>
<P align=justify>return (fcs);</P>
<P align=justify>}</P>
<P align=justify> </P>
<P align=justify>/*</P>
<P align=justify>* How to use the fcs</P>
<P align=justify>*/</P>
<P align=justify>tryfcs32(cp, len)</P>
<P align=justify>register unsigned char *cp;</P>
<P align=justify>register int len;</P>
<P align=justify>{</P>
<P align=justify>u32 trialfcs;</P>
<P align=justify> </P>
<P align=justify>/* add on output */</P>
<P align=justify>trialfcs = pppfcs32( PPPINITFCS32, cp, len );</P>
<P align=justify>trialfcs ^= 0xffffffff; /* 取反 */</P>
<P align=justify>cp[len] = (trialfcs & 0x00ff); /* 最低位優先 */</P>
<P align=justify>cp[len+1] = ((trialfcs >>= 8) & 0x00ff);</P>
<P align=justify>cp[len+2] = ((trialfcs >>= 8) & 0x00ff);</P>
<P align=justify>cp[len+3] = ((trialfcs >> 8) & 0x00ff);</P>
<P align=justify> </P>
<P align=justify>/* check on input */</P>
<P align=justify>trialfcs = pppfcs32( PPPINITFCS32, cp, len + 4 );</P>
<P align=justify>if ( trialfcs == PPPGOODFCS32 )</P>
<P align=justify>printf("Good FCS\n");</P>
<P align=justify>}</P>
<P align=justify> </P>
<P align=justify>安全問題</P>
<P align=justify> </P>
<P
align=justify>正如在物理層要求中提到的，鏈路層在物理層發生變化時可能不清楚這一變化。這是因為過分信賴轉發系統的安全和一致性而導致安全上的問題。這可能導致對系統的攻擊，使系統身份驗證失效。</FONT></P></TD></TR></TBODY></TABLE></BODY></HTML>
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