VoIP: UDP Packet compression to save bandwidth...

Discussion in 'Cisco' started by groobo, Oct 13, 2005.

  1. groobo

    groobo Guest

    I am running VoIP services on 1.2Mb realtime link (anything above the
    bandwidth will be dropped). The voip protocol is proprietary (by Etrali
    telecom), not anywhere close to other industry standards. These are not
    the typical VoIP phones either; specialized broker 'turrets', that can
    handle 2 handsets and 6 so-called open broadcasts (OBs), which are
    audio channels 'assigned' directly to the device. Should trader hit the
    button on the other end, voice will be heard on the OB channel.
    Otherwise, it's quiet. To make things more complicated, there is
    bandwidth used, no matter if there is audio present on the OBs. It's
    like they transmit 'empty' data. Etrali does not use any voice
    compression (why?), which results 80Kbps per channel with overhead.
    I have done some dumps with Ethereal to analyze the UDP packets (that's
    how the voice is being sent). The size of a typical packet is 302 bytes
    total (260 data) 75% of the time, the remaining 25% is 542 bytes (500
    data). I believe, the difference in size depends on how many OBs has
    been placed on the client's turret; important to say is, that the
    packets sizes should not exceed 600 bytes.
    A typical small-size packet looks like this: (i have marked the start
    of the data part by ***), there were concurrent 2/3 conversations
    active at the time of the probe.

    0000 00 11 93 bc 28 43 00 06 47 30 03 39 08 00 45 b8 ....(C..
    G0.9..E.
    0010 01 20 f1 bf 00 00 40 11 28 4d c0 a8 04 84 42 09 . ....@.
    (M....B.
    0020 57 d3 10 00 10 e0 01 0c 00 00***90 17 3c 8f 3f ec W.......
    .....<.?.
    0030 dc 16 5e 59 5f ff 01 81 00 01 02 00 00 00 d7 d7 ..^Y_...
    .........
    0040 d6 d7 d7 d4 55 55 54 54 54 54 54 55 d5 d4 d4 d4 ....UUTT
    TTTU....
    0050 d4 d5 55 55 55 55 55 d5 d4 d4 d4 d4 d4 d4 d4 d4 ..UUUUU.
    .........
    0060 d5 d4 d4 d4 d4 d4 d5 55 54 55 54 55 55 d5 55 d5 .......U
    TUTUU.U.
    0070 d4 d5 d4 d4 d5 d5 55 55 55 55 d5 d4 d5 d4 d4 d4 ......UU
    UU......
    0080 d7 d4 d5 55 d5 d5 d5 d4 d5 d4 d4 d4 d7 d7 d4 55 ...U....
    ........U
    0090 55 55 54 55 d5 d5 d5 d4 d5 d5 d5 d5 d5 d5 d5 d5 UUTU....
    .........
    00a0 d5 55 d5 d5 d5 d5 d4 d4 d5 d5 d5 d5 d5 d5 d4 d5 .U......
    .........
    00b0 d5 55 54 55 d5 d5 d5 d4 d5 d4 d4 d4 d4 d4 d4 d5 .UTU....
    .........
    00c0 d4 d5 d5 d4 d4 d5 55 d5 55 55 55 d5 d5 d5 d5 d5 ......U.
    UUU.....
    00d0 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d4 d4 d7 d7 d7 d4 ........
    .........
    00e0 d5 55 54 57 54 54 55 d5 d4 d7 d7 d4 d5 d5 55 55 .UTWTTU.
    .......UU
    00f0 55 d5 d4 d4 d7 d7 d4 d4 d5 54 54 54 54 55 d5 d5 U.......
    ..TTTTU..
    0100 d4 d4 d4 d4 d4 d5 d5 d5 55 55 d5 d4 d4 d4 d4 d5 ........
    UU......
    0110 d5 55 55 d5 d5 d4 d4 d7 d7 d4 d5 55 55 55 55 55 .UU.....
    ....UUUUU
    0120 55 55 d5 d5 d4 d5 d5 d5 d5 d5 55 d5 d5 d5 UU......
    ...U...

    And the big-size:

    0000 00 06 47 30 03 39 00 11 93 bc 28 43 08 00 45 b8 ..G0.9..
    ...(C..E.
    0010 02 10 db 28 00 00 3c 11 41 f4 42 09 57 d3 c0 a8 ...(..<.
    A.B.W...
    0020 04 84 10 06 10 28 01 fc 00 00***90 17 36 13 1f 08 .....(..
    .....6...
    0030 87 be c3 a9 9d f4 83 82 00 01 06 07 00 00 d5 d5 ........
    .........
    0040 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 ........
    .........
    0050 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 ........
    .........
    0060 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 ........
    .........
    0070 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 ........
    .........
    0080 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 ........
    .........
    0090 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 ........
    .........
    00a0 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 ........
    .........
    00b0 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 ........
    .........
    00c0 d5 54 d5 d5 d5 d5 d5 d5 d5 d5 d5 54 d7 d5 51 d5 .T......
    ....T..Q.
    00d0 d5 d4 54 d5 d7 51 d4 d5 d5 d4 56 d5 56 d5 d5 54 ..T..Q..
    ...V.V..T
    00e0 d5 53 d6 d5 51 d4 d5 d5 d5 d4 d5 d5 d5 d5 d5 54 .S..Q...
    ........T
    00f0 d5 d5 54 d5 d5 d5 d5 54 d5 d5 d5 d5 d5 d5 d5 d5 ..T....T
    .........
    0100 d5 d5 d5 d5 d5 d5 57 56 d5 d5 d5 d5 d5 54 54 d5 ......WV
    ......TT.
    0110 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 ........
    .........
    0120 57 54 d5 54 57 d5 d5 d5 d5 d5 d5 54 d5 d5 d5 d5 WT.TW...
    ....T....
    0130 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 ........
    .........
    0140 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 ........
    .........
    0150 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 ........
    .........
    0160 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 ........
    .........
    0170 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 ........
    .........
    0180 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 ........
    .........
    0190 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 ........
    .........
    01a0 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 ........
    .........
    01b0 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 ........
    .........
    01c0 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 ........
    .........
    01d0 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 ........
    .........
    01e0 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 ........
    .........
    01f0 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 ........
    .........
    0200 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 ........
    .........
    0210 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 d5 ........
    .......

    It appears to me, that the data part of the packet would compress
    pretty well, even with simplest and fastest compression algorithms.
    However, knowing nothing about packet compression, my questions are:
    1. Is UDP packet compression possible at all?
    2. I am talking compression the data part?
    3. What are the recommended methods and delays associated with it?
    4. I have 2 catalysts 2950 with Enhanced Image on both ends, 2801
    router on the host side and - that's important - 1721 on the remote
    side with NO ACCESS to it (provider's). So, is it possible to set up
    the compression/decompression on the switch level only? Looking around,
    I have seen solution for packet compression on the routers (3600 and
    7200, 7250 series), both hardware and software.
    5. If so, are there any special settings on the routers to be made to
    handle 'compressed' packets going from the switch?
    6. Any tools to 'evaluate' the tcpdump?
    groobo, Oct 13, 2005
    #1
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  2. groobo

    Guest

    I doubt very much that the 2950's have compression facilities.

    Compression is very CPU intensive and the high packet
    rate typical of voice will put quite a load on a small router.

    Compression itself ads latency (jitter too?) which is often
    detrimental to voice. If you had the equipment I would say
    give it a try.

    A very common voice scheme is to use 64kbps of voice data
    in the form of 256 level (8 bit) samples at 8kbps. This is
    quite possibly what they have used.

    It is very close to RTP with a header extension.
    You have 240 bytes of voice data, one sample I have has
    160.

    Some analysis. Sorry for the long lines, hope you can fix it.
    I took out most of the ASCII since it is meaningless in this context.



    0000 00 11 93 bc 28 43 00 06 47 30 03 39 08 00 is
    IP
    45 b8 ....(C.. IP
    DSCP=b8
    0010 01 20 f1 bf 00 00 40 11 28 4d c0 a8 04 84 42 09 . ....@. IP
    len 288 11=UDP

    0020 57 d3
    10 00 10 e0 01 0c 00 00
    UDPsrc 4096 dst 4320 len 268
    ***90 17 3c 8f 3f ec W.......
    ***90 = RTP with Header Extension
    0030 dc 16 5e 59 5f ff If
    RTP
    01 81 00 01 02 00 00 00 RTP
    extension??? 2 x 32 bits

    d7 d7
    0040 d6 d7 d7 d4 55 55 54 54 54 54 54 55 d5 d4 d4 d4
    , Oct 13, 2005
    #2
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  3. groobo

    stephen Guest

    <> wrote in message
    news:...
    > I doubt very much that the 2950's have compression facilities.
    >
    > Compression is very CPU intensive and the high packet
    > rate typical of voice will put quite a load on a small router.


    Agreed. but little ciscos (26/28xxs) support a data compression AIM add on.
    >
    > Compression itself ads latency (jitter too?) which is often
    > detrimental to voice. If you had the equipment I would say
    > give it a try.


    depends - it takes time to compress / decompress the packet - true.

    but - the reduced delay to send the packet may more than offset the
    compression latency.

    (seen this on old Bay ASNs with hardware compressors, where end to end
    latency goes down with compression across a 2 Mbps link).
    >
    > A very common voice scheme is to use 64kbps of voice data
    > in the form of 256 level (8 bit) samples at 8kbps. This is
    > quite possibly what they have used.
    >
    > It is very close to RTP with a header extension.
    > You have 240 bytes of voice data, one sample I have has
    > 160.


    compression is about reducing the space used by repeatable bit strings

    thing to watch for is purely random data isnt very compressible, and pre
    compressed data is even worse - most compression schemes have a worst case
    set of data patterns where they are worse than no compression.....

    if they the app sents "silent" voice data, then that is potentially very
    compressible.
    >
    > Some analysis. Sorry for the long lines, hope you can fix it.
    > I took out most of the ASCII since it is meaningless in this context.
    >
    >
    >
    > 0000 00 11 93 bc 28 43 00 06 47 30 03 39 08 00 is
    > IP
    > 45 b8 ....(C.. IP
    > DSCP=b8
    > 0010 01 20 f1 bf 00 00 40 11 28 4d c0 a8 04 84 42 09 . ....@. IP
    > len 288 11=UDP
    >
    > 0020 57 d3
    > 10 00 10 e0 01 0c 00 00
    > UDPsrc 4096 dst 4320 len 268
    > ***90 17 3c 8f 3f ec W.......
    > ***90 = RTP with Header Extension
    > 0030 dc 16 5e 59 5f ff If
    > RTP
    > 01 81 00 01 02 00 00 00 RTP
    > extension??? 2 x 32 bits
    >
    > d7 d7
    > 0040 d6 d7 d7 d4 55 55 54 54 54 54 54 55 d5 d4 d4 d4

    --
    Regards

    - replace xyz with ntl
    stephen, Oct 14, 2005
    #3
  4. groobo

    hans m42 Guest

    hans m42, Oct 16, 2005
    #4
  5. groobo

    Guest

    > use "juniper" in former times "peribit"
    > http://www.juniper.net/welcome_peribit.html
    > it's really great. we use it with success.


    Do you use CIFS (SMB) (Windows shares) across these boxes?
    What are the results?

    May I mail you directly? My source e-mail address does not work.
    , Oct 17, 2005
    #5
  6. groobo

    hans m42 Guest

    hi

    In article <>,
    <> wrote:
    >> use "juniper" in former times "peribit"
    >> http://www.juniper.net/welcome_peribit.html
    >> it's really great. we use it with success.

    >
    >Do you use CIFS (SMB) (Windows shares) across these boxes?
    >What are the results?


    no. we use nfs. every user can access his data on every location.
    the home-server is sharing the fs, all others are mounting it.
    we user samba to access to this fileshares on every location localy.

    we are satified. we have 2 mbit leased lines. peribit ( now juniper )
    does an increasement of 2.5 till 3.3 in average. so we have
    an 6 mbit line. but without qos even a 20 mbit line wouldn't work.

    compression ( which is fantastic ) and acceleration are well things
    but qos is the best one. i think, there are no alternatives for qos
    except you have the money for dark fibre.

    >
    >May I mail you directly? My source e-mail address does not work.


    yes you can. my e-mail for newsnet is temporary and short of live, but real.

    best regards
    hans

    --
    hans m42, Oct 17, 2005
    #6
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