Two weeks a go I was in a meeting – the issue was about CC error , since no one really knew what is "cc error" , I was asked to figure out what is CC error , well … this was a task with no real information in hand , actually I knew its something to do with video multicasting , so I was looking for some clue about cc error in UDP/RTP header , but ,,, found basically nothing , the problem was I did not know what 'cc' stands for . Then I assumed that may be CC error is related to the MPEG-2 frame - ..ha ha … yha I was correct , cc = 'continuity counter' …. so the cc error is "continuity counter error" , this is used for keeping a track of the sequence of the MPEG-2 frames , and if you are seeing "cc error" at the clients end when you are using some video stream analyzer like "IQmedia" , the error can be mainly due to ,
1) one packet repeat more than twice
2) packets out of sequence
3) packet loss
each UDP packet of 1316 bytes carry 7 MPEG-2 frames of 188bytes each – each MPEG-2 frames has 4 byte header and the last byte is for continuity counter .
| ETH | IP | UDP | FR-1 | FR-2 | FR-3 | FR-4 | FR-5 | FR-6 | FR-7 | Eth… |
Frame – 1 (FR-1)
| SYN(8) | TEI(1) | PUSI(1) | TP(1) | PID(13) | TSC(2) | AF(2) | CC (4) | Video |
Found something interesting , This happened with Many major DOCSIS 2.0 cable modem brands. The problems is if you set the DHCP lease time to infinite – that is the 32-bits in the DHCP header (option-51) that defines the DHCP lease time is set to
FF FF FF FF
if it is set to the maximum value , the cable modem will fail to register with the CMTS , the maximum value you can use is 7F FF FF FF , yha the most significant bit is made zero ,
| 0111 | 1111 | 1111 | 1111 | 1111 | 1111 | 1111 | 1111 |
| 7 | F | F | F | F | F | F | F |
I used the DHCP-turbo server where there is an option to set an infinite lease .
DHCP infinite lease ,
I wrote a small MATLAB code to calculate how many Days , hours , minutes and seconds is 7F FF FF FF
--------------------------------------------
format long
x=hex2dec('7fffffff');
days = fix(x/(3600*24))
y = x - days*3600*24;
hours = fix(y/3600)
z = y - hours*3600;
minutes = fix(z/60)
seconds = z - minutes*60
---------------------------------------------
answer :
>> dhcplease
days = 24855
hours = 3
minutes = 14
seconds = 7
the first problem I faced - how can I initiate an Active FTP session because all FTP clients use passive FTP by default !!! .... after lot of search I figuredout that its not that difficult ,
open linux shell , tupe "ftp" and then type "passive" - then u will see the message "passive mode is off"
shell> ftp
ftp> passive
Passive mode off
ftp>
then just use get command to download some file !!! u have ur self an ACTIVE FTP connetion !!!
ftp> get test.txt
and use "etheral to capture pkts " ... then u can see for sure that it was an Active FTP session !!!
