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[Didier Barvaux <didier@xxxxxxxxxxx>]

Hello,

>                 I have just got the test-bed for rohc setup and was
> wondering whether anyone can answer a couple of questions for me as
> it would be of great help.

My answers below.


> 1.) I set the tunnel up as specified in faq#639 with a slight
> variation, ³sudo rohctunnel rohc0 remote <ip_address> local
> <ip_address> port 5000
> 3>comp_stats 4>decomp_stats dir unidirectional²
> I execute the same rohctunnel command just reversing the ip_addresses
> on system A and system B. When I look on system A (from where packets
> are being sent), I can see comp_stats file for info but on system B
> (where packets are received) I cannot see any info in the
> decomp_stats file. If anyone can shed some light on this it would be
> great.

What version of the ROHC library do you use? I tested with the trunk
version and I get data written in the decomp_stats file.

Here is exactly what I did:
 1/ On machine A as root on shell 1:
    # rohctunnel rohc0 remote 192.168.0.200 local 192.168.0.1 \
      port 5000 dir unidirectional \
      1>lib_output 2>tunnel_output \
      3>comp_stats 4>decomp_stats 
 2/ On machine A as root on shell 2:
    # ip link set rohc0 up
    # ip -4 addr add 10.1.0.1/24 dev rohc0
    # tail -f comp_stats
 3/ On machine B as root on shell 1:
    # rohctunnel rohc0 remote 192.168.0.1 local 192.168.0.2 \
      port 5000 dir unidirectional \
      1>lib_output 2>tunnel_output \
      3>comp_stats 4>decomp_stats 
 4/ On machine B as root on shell 2:
    # ip link set rohc0 up
    # ip -4 addr add 10.1.0.2/24 dev rohc0
    # tail -f decomp_stats
 5/ On machine A as root on shell 3:
    # ping -c 1 10.1.0.2

The ping is successful. On machine A shell 2, the following line was
printed:
  1	U-mode	IR	84	20	85	21	0

On machine B shell 2, the following line was
printed:
  1	0	0	0

If you do not have the same result, send me the 8 files generated by
the 2 rohctunnel instances.


> 2.) What do the columns in the output files represent?

The columns of the comp_stats file are:
 - the sequence number of the packet sent through the ROHC/UDP
   tunnel,
 - the ROHC mode in which the compressor is,
 - the ROHC state in which the compressor is,
 - the size (in bytes) of the uncompressed IP packet,
 - the size (in bytes) of the header of the uncompressed IP packet,
 - the size (in bytes) of the compressed ROHC packet,
 - the size (in bytes) of the header of the compressed ROHC packet.

The columns of the decomp_stats file are:
 - the sequence number of the packet received through the ROHC/UDP
   tunnel,
 - the total number of the packets that were not present at the output
   of the tunnel (= the sum of the 2 next columns, ie. lost packets
   plus the decompression failures), 
 - the number of packets lost in the tunnel (it may be real losses or
   losses due to error emulation),
 - the number of packets the decompressor failed to decompress.

I have just updated the FAQ #639 to describe them.

Regards,
Didier

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