I want to know proper standard for transport streams,Some of my doubts are:
If size of PES packet is > 65536 then pes_packet_length filed should be zero ?
If PES packet size more than 65536 then do we require PES header for over flow packets ?
1) PES Length should always be 0 for the video stream, and always set to real values for any other stream. 2) no, only video streams are aloud to have packets larger than 65535.
It depends about the information carried by your PES packet: cf this very good poster by Tektronix for PES packet format.
Related
I have a traffic dump in csv file containing packet arrival time, frame length and boolean values for multiple flags.
Can someone please explain how to calculate packet size from the traffic dump.
I further want to generate distribution of the packet size in python.
What will be the bitrate of 320x200 video at 25 fps, which is compressed by a videocodec with a compression ratio of 1: 150? Write with a formula.
I have some PCAPNG file, one UDP packet has Frame length 187 Bytes (1496 bits) and Data length 472 Bytes. All other packets fame length is greater than data length.
Please correct me if I'm wrong. My basic understanding is Frame length should be greater than data length because frame length includes data length.
1) Whether this packet is captured correctly ?
2) In which case this could happen ?
I found its related to fragmented packet. This case occurs when packet reassembled.
I'm using python and cryptography.io to sign and verify messages. I can get a DER-encoded bytes representation of a signature with:
cryptography_priv_key.sign(message, hash_function)
...per this document: https://cryptography.io/en/latest/hazmat/primitives/asymmetric/ec/
A DER-encoded ECDSA Signature from a 256-bit curve is, at most, 72 bytes; see: ECDSA signature length
However, depending on the values of r and s, it can also be 70 or 71 bytes. Indeed, if I examine length of the output of this function, it varies from 70-72. Do I have that right so far?
I can decode the signature to ints r and s. These are both apparently 32 bytes, but it's not clear to me whether that will always be so.
Is it safe to cast these two ints to bytes and send them over the wire, with the intention of encoding them again on the other side?
The simple answer is, yes, they will always be 32 bytes.
The more complete answer is that it depends on the curve. For example, a 256-bit curve has an order of 256-bits. Similarly, a 128-bit curve only has an order of 128-bits.
You can divide this number by eight to find the size of r and s.
It gets more complicated when curves aren't divisible by eight, like secp521r1 where the order is a 521-bit number.
In this case, we round up. 521 / 8 is 65.125, thus it requires that we free 66 bytes of memory to fit this number.
It is safe to send them over the wire and encode them again as long as you keep track of which is r and s.
after ARP protocol in a frame, there are many 0 bytes. Does anyone know the reason for the existence of these 0 bytes?
Check the Ethernet II accordion, all the 0 are labelled as padding.
Ethernet requires that all packets be at least 60 bytes long (64 bytes if you include the Frame Check Sequence at the end), so if a packet is less than 60 bytes long (including the 14-byte Ethernet header), additional padding bytes have to be added to the end of the packet.
(Those padding bytes will not show up on packets sent by the machine running Wireshark; the padding is added by the Ethernet hardware, and packets being sent by the machine capturing the traffic are given to the program before being handed to the hardware, so they haven't been padded.)