On Fri, Oct 30, 2020 at 3:21 PM Xie He <xie.he.0...@gmail.com> wrote: > > On Fri, Oct 30, 2020 at 9:31 AM Willem de Bruijn > <willemdebruijn.ker...@gmail.com> wrote: > > > > > Add an fh->ea2 check to the initial checks in fr_rx. fh->ea2 == 1 means > > > the second address byte is the final address byte. We only support the > > > case where the address length is 2 bytes. > > > > Can you elaborate a bit for readers not intimately familiar with the > > codebase? > > > > Is there something in the following code that has this implicit > > assumption on 2-byte address lengths? > > Yes, the address length must be 2 bytes, otherwise the 3rd and 4th > bytes would not be the control and protocol fields as we assumed in > the code. > > The frame format is specified in RFC 2427 > (https://tools.ietf.org/html/rfc2427). We can see the overall frame > format on Page 3. If the address length is longer than 2 bytes, all > the following fields will be shifted behind.
Thanks for that context. If it's not captured in the code, it would be great to include in the commit message. >From a quick scan, RFC 2427 does not appear to actually define the Q.922 address. For that I ended up reading ITU-T doc "Q.922 : ISDN data link layer specification for frame mode bearer services", section 3.2.
