3.1.4.8.2 Connectivity Checks Phase

An application triggers the start of the connectivity checks phase after the completion of the offer and answer exchange of candidates, as specified in sections 3.1.4.2, 3.1.4.3, and 3.1.4.4. The connectivity checks phase MUST have an overall worst case timeout, as specified in section 3.1.6.2. When a connectivity check request and a connectivity check response packet have been received from the peer, the timeout for the connectivity check MUST be reduced to the value specified in section 3.1.6.2.

During the connectivity checks phase, whenever a connectivity check request or response is sent, an additional connectivity check request or response SHOULD<11> be sent along with it. This additional request or response is identical to the original request or response, except that the fingerprint for these additional messages MUST be computed through a cyclic redundancy check (CRC) using the following lookup table of hexadecimal values. This is done to interoperate with implementations that used the CRC lookup table.

Column 0	Column 1	Column 2	Column 3	Column 4	Column 5	Column 6	Column 7
00000000	77073096	EE0E612C	990951BA	076DC419	706AF48F	E963A535	9E6495A3
0EDB8832	79DCB8A4	E0D5E91E	97D2D988	09B64C2B	7EB17CBD	E7B82D07	90BF1D91
1DB71064	6AB020F2	F3B97148	84BE41DE	1ADAD47D	6DDDE4EB	F4D4B551	83D385C7
136C9856	646BA8C0	FD62F97A	8A65C9EC	14015C4F	63066CD9	FA0F3D63	8D080DF5
3B6E20C8	4C69105E	D56041E4	A2677172	3C03E4D1	4B04D447	D20D85FD	A50AB56B
35B5A8FA	42B2986C	DBBBC9D6	ACBCF940	32D86CE3	45DF5C75	DCD60DCF	ABD13D59
26D930AC	51DE003A	C8D75180	BFD06116	21B4F4B5	56B3C423	CFBA9599	B8BDA50F
2802B89E	5F058808	C60CD9B2	B10BE924	2F6F7C87	58684C11	C1611DAB	B6662D3D
76DC4190	01DB7106	98D220BC	EFD5102A	71B18589	06B6B51F	9FBFE4A5	E8B8D433
7807C9A2	0F00F934	9609A88E	E10E9818	7F6A0DBB	086D3D2D	91646C97	E6635C01
6B6B51F4	1C6C6162	856530D8	F262004E	6C0695ED	1B01A57B	8208F4C1	F50FC457
65B0D9C6	12B7E950	8BBE8EA	FCB9887C	62DD1DDF	15DA2D49	8CD37CF3	FBD44C65
4DB26158	3AB551CE	A3BC0074	D4BB30E2	4ADFA541	3DD895D7	A4D1C46D	D3D6F4FB
4369E96A	346ED9FC	AD678846	DA60B8D0	44042D73	33031DE5	AA0A4C5F	DD0D7CC9
5005713C	270241AA	BE0B1010	C90C2086	5768B525	206F85B3	B966D409	CE61E49F
5EDEF90E	29D9C998	B0D09822	C7D7A8B4	59B33D17	2EB40D81	B7BD5C3B	C0BA6CAD
EDB88320	9ABFB3B6	03B6E20C	74B1D29A	EAD54739	9DD277AF	04DB2615	73DC1683
E3630B12	94643B84	0D6D6A3E	7A6A5AA8	E40ECF0B	9309FF9D	0A00AE27	7D079EB1
F00F9344	8708A3D2	1E01F268	6906C2FE	F762575D	806567CB	196C3671	6E6B06E7
FED41B76	89D32BE0	10DA7A5A	67DD4ACC	F9B9DF6F	8EBEEFF9	17B7BE43	60B08ED5
D6D6A3E8	A1D1937E	38D8C2C4	4FDFF252	D1BB67F1	A6BC5767	3FB506DD	48B2364B
D80D2BDA	AF0A1B4C	36034AF6	41047A60	DF60EFC3	A867DF55	316E8EEF	4669BE79
CB61B38C	BC66831A	256FD2A0	5268E236	CC0C7795	BB0B4703	220216B9	5505262F
C5BA3BBE	B2BD0B28	2BB45A92	5CB36A04	C2D7FFA7	B5D0CF31	2CD99E8B	5BDEAE1D
9B64C2B0	EC63F226	756AA39C	026D930A	9C0906A9	EB0E363F	72076785	05005713
95BF4A82	E2B87A14	7BB12BAE	0CB61B38	92D28E9B	E5D5BE0D	7CDCEFB7	0BDBDF21
86D3D2D4	F1D4E242	68DDB3F8	1FDA836E	81BE16CD	F6B9265B	6FB077E1	18B74777
88085AE6	FF0F6A70	66063BCA	11010B5C	8F659EFF	F862AE69	616BFFD3	166CCF45
A00AE278	D70DD2EE	4E048354	3903B3C2	A7672661	D06016F7	4969474D	3E6E77DB
AED16A4A	D9D65ADC	40DF0B66	37D83BF0	A9BCAE53	DEBB9EC5	47B2CF7F	30B5FFE9
BDBDF21C	CABAC28A	53B39330	24B4A3A6	BAD03605	CDD70693	54DE5729	23D967BF
B3667A2E	C4614AB8	5D681B02	2A6F2B94	B40BBE37	C30C8EA1	5A05DF1B	2D02EF8D

The transmission of this additional connectivity check packet SHOULD be stopped on receiving a connectivity check request or response from the peer endpoint with the IMPLEMENTATION-VERSION attribute as specified in section 2.2.2.2. The additional messages MUST NOT be sent for ICE keep-alive messages. When a connectivity request or response is received, the fingerprint checks MUST use the fingerprint mechanism specified in [IETFDRAFT-ICENAT-19] section 7.1.1. If the fingerprint checks fail and the connectivity check request or response does not have the IMPLEMENTATION-VERSION attribute, the fingerprint checks SHOULD<12> be tried by using the CRC table shown earlier in this section. If the fingerprint checks succeed with the CRC table, the packet SHOULD<13> be considered a valid packet, and processed as such.