Ethereal-users: Re: [Ethereal-users] RTCP for VoIP QoS

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From: "Aisling O'Driscoll" <ashling.odriscoll@xxxxxx>
Date: Sat, 25 Mar 2006 16:20:53 -0000
Hello Martin,

My name is Aisling and I am helping David Grau with his project (his
project as part of an undergraduate degree but this also interests me
as part of my postgraduate degree).

I have read rfc 3550 with particular emphasis on the part detailing
how the round trip time (RTT) should be calculated.  The formula
"A-DLSR-LSR" is provided and an example "46864.500 - 5.250 -
46853.125 = 6.125 seconds" is given. We are working from a tethereal
capture file - This was running on the same pc as one of the
softphones involved in the call but as the two softphones calling
each other are on the same LAN segment we should have captured all
the necessary RTCP sender and receiver reports anyway.I have attached
the sample capture file.

Myself and David are not clear on a few things:

1) The A field is when the receiver report block is received. Is this
referring to the NTP timestamp? I am struggling to identify this from
the tethereal capture (perhaps the capture format is slightly
non-standard?)and if you could point this out from the attached
capture file we would greatly appreciate it.
2)The LSR field is said to be the middle 32 bits of the NTP timestamp
and the NTP timestamp is made up of the MSW and LSW. So if the
figures are MSW=3350115113 and LSW=493921239 I still fail to
understand why the LSR=3005816176...this is based on the figures from
the attach capture file.
3)the DLSR does appear to be 1 for all captures but as you said this
could be for the reasons that you described before.
4)Based on the above points and the attached capture file could you
give an example with figures (from the file) of using A-DLSR-LSR?

Your replies and time so far are much appreciated(the same for
everone else who has helped),
Many thanks,
Aisling.


---- Original Message ----
From: martin.mathieson@xxxxxxxxxxxx
To: ethereal-users@xxxxxxxxxxxx
Subject: Re: [Ethereal-users] RTCP for VoIP QoS
Date: Fri, 24 Mar 2006 16:47:45 +0000

>You can't do the calculation using just one frame.  And bear in mind 
>that the calculation Ethereal does is relative to the point of
>capture 
>(although in many cases you may be capturing on the same machine as
>the 
>client).
>
>Look below, the following line is present:
>"MSW and LSW as NTP timestamp: Feb 24, 2036 17:42:56,0000 UTC "
>
>This is done by the function ntp_fmt_ts() in packet-ntp.c.
>
>However, this isn't important for calculating the rountrip, as it is 
>relative.  We are comparing:
>- the observed difference between the current SR and the one the DLSR
>
>refers to
>- the time in the DLSR (which is the number of 1/65536 ths of a
>second)
>
>Martin
>
>David Grau Serra wrote:
>
>> Hi,
>>
>>>>
>>>> The softphone is X-Lite.
>>>
>> And now I show you one capture:
>>
>> Real-time Transport Control Protocol (Sender Report)
>>    Stream setup by SDP (frame 32)
>>        Setup frame: 32
>>        Setup Method: SDP
>>    10.. .... = Version: RFC 1889 Version (2)
>>    ..0. .... = Padding: False
>>    ...0 0001 = Reception report count: 1
>>    Packet type: Sender Report (200)
>>    Length: 12
>>    Sender SSRC: 2307084394
>>    Timestamp, MSW: 3351350040
>>    Timestamp, LSW: 2280627634
>>    MSW and LSW as NTP timestamp: Feb 24, 2036 17:42:56,0000 UTC
>>    RTP timestamp: 1509280
>>    Sender's packet count: 5291
>>    Sender's octet count: 846560
>>    Source 1
>>        Identifier: 2307084394
>>        SSRC contents
>>            Fraction lost: 0 / 256
>>            Cumulative number of packets lost: 0
>>        Extended highest sequence number received: 346756267
>>            Sequence number cycles count: 5291
>>            Highest sequence number received: 5291
>>        Interarrival jitter: 0
>>        Last SR timestamp: 2333640687
>>        Delay since last SR timestamp: 1
>> Real-time Transport Control Protocol (Receiver Report)
>>    Stream setup by SDP (frame 32)
>>        Setup frame: 32
>>        Setup Method: SDP
>>    10.. .... = Version: RFC 1889 Version (2)
>>    ..0. .... = Padding: False
>>    ...0 0001 = Reception report count: 1
>>    Packet type: Receiver Report (201)
>>    Length: 7
>>    Sender SSRC: 2307084394
>>    Source 1
>>        Identifier: 428529494
>>        SSRC contents
>>            Fraction lost: 0 / 256
>>            Cumulative number of packets lost: 50
>>        Extended highest sequence number received: 65535
>>            Sequence number cycles count: 0
>>            Highest sequence number received: 65535
>>        Interarrival jitter: 7787
>>        Last SR timestamp: 2333640687
>>        Delay since last SR timestamp: 1
>>
>>
>>>>
>>>> I know how can I calculate jitter and the packet loss rate.
>>>>
>>>> My problem now is how can I calculate delay (round trip delay).
>>>> I don't understand why the "Delay since last SR timestamp" is
>always 1.
>>>> I don't know how it works the "MSW" and "LSW" (Timestamp).
>>>>
>>> These fields and the way the calculation should be done, is
>described 
>>> in RFC 3550, section 6.4.1.
>>
>>
>> I have read but I am still confuse, I will read again.
>>
>>>
>>> Ethereal already does this calculation for you (if the preference
>is 
>>> turned on).  There have been fixes made to this calculation, the
>last 
>>> of which I believe was made after the last (0.10.14) release.
>>
>>
>> I am using 0.10.14, but I use tethreal command line.
>>
>>>
>>> DLSR is defined as:
>>>
>>>      "The delay, expressed in units of 1/65536 seconds, between
>>>      receiving the last SR packet from source SSRC_n and sending
>this
>>>      reception report block.  If no SR packet has been received
>yet
>>>      from SSRC_n, the DLSR field is set to zero."
>>>
>>>
>>>
>>> If the DLSR is always 1, that indicates that either:
>>> - the RTCP stack isn't filling the value in properly, OR
>>> - it really is replying almost instantly after receiving a report 
>>> from the other side.  This could be because:
>>>    - both clients are sending reports at the same rate and they
>are 
>>> almost exactly in sync
>>>    - they are sending reports in response to an incoming SR rather
>
>>> than on a timer (or some other trigger)
>>
>>
>> I was thinking as well if it could be the softphone X-Lite....
>>
>>>
>>> Note that the Last SR timestamp is formed by taking the middle 32 
>>> bits from the MSW and LSW fields.  Taken together they are the
>Most 
>>> Significant Word and Least Significant Word or an NTP timestamp.
>>
>>
>> I would like to know how can I translate the NTP timestamp a human
>and 
>> readable time?
>>
>> Many thanks,
>>
>> David
>>
>> _______________________________________________
>> Ethereal-users mailing list
>> Ethereal-users@xxxxxxxxxxxx
>> http://www.ethereal.com/mailman/listinfo/ethereal-users
>>
>
>_______________________________________________
>Ethereal-users mailing list
>Ethereal-users@xxxxxxxxxxxx
>http://www.ethereal.com/mailman/listinfo/ethereal-users
>
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-------------------Legal  Disclaimer---------------------------------------

The above electronic mail transmission is confidential and intended only for the person to whom it is addressed. Its contents may be protected by legal and/or professional privilege. Should it be received by you in error please contact the sender at the above quoted email address. Any unauthorised form of reproduction of this message is strictly prohibited. The Institute does not guarantee the security of any information electronically transmitted and is not liable if the information contained in this communication is not a proper and complete record of the message as transmitted by the sender nor for any delay in its receipt.

Frame 167 (126 bytes on wire, 126 bytes captured)
    Arrival Time: Feb 28, 2006 11:31:53.118888000
    Time delta from previous packet: 0.013927000 seconds
    Time since reference or first frame: 3.950678000 seconds
    Frame Number: 167
    Packet Length: 126 bytes
    Capture Length: 126 bytes
Ethernet II, Src: 00:0d:56:72:f2:26, Dst: 00:0b:82:02:6d:48
    Destination: 00:0b:82:02:6d:48 (Grandstr_02:6d:48)
    Source: 00:0d:56:72:f2:26 (DellPcba_72:f2:26)
    Type: IP (0x0800)
Internet Protocol, Src Addr: 157.190.74.153 (157.190.74.153), Dst Addr: 157.190.74.101 (157.190.74.101)
    Version: 4
    Header length: 20 bytes
    Differentiated Services Field: 0x00 (DSCP 0x00: Default; ECN: 0x00)
        0000 00.. = Differentiated Services Codepoint: Default (0x00)
        .... ..0. = ECN-Capable Transport (ECT): 0
        .... ...0 = ECN-CE: 0
    Total Length: 112
    Identification: 0x7f0d (32525)
    Flags: 0x00
        0... = Reserved bit: Not set
        .0.. = Don't fragment: Not set
        ..0. = More fragments: Not set
    Fragment offset: 0
    Time to live: 128
    Protocol: UDP (0x11)
    Header checksum: 0xeaf4 (correct)
    Source: 157.190.74.153 (157.190.74.153)
    Destination: 157.190.74.101 (157.190.74.101)
User Datagram Protocol, Src Port: 8001 (8001), Dst Port: 8563 (8563)
    Source port: 8001 (8001)
    Destination port: 8563 (8563)
    Length: 92
    Checksum: 0x296c (correct)
Real-time Transport Control Protocol
    Stream setup by SDP (frame 159)
        Setup frame: 159
        Setup Method: SDP
    10.. .... = Version: RFC 1889 Version (2)
    ..0. .... = Padding: False
    ...0 0001 = Reception report count: 1
    Packet type: Sender Report (200)
    Length: 12
    Sender SSRC: 469084700
    Timestamp, MSW: 3350115113
    Timestamp, LSW: 493921239
    RTP timestamp: 12960
    Sender's packet count: 2
    Sender's octet count: 320
    Source 1
        Identifier: 469084700
        SSRC contents
            Fraction lost: 0 / 256
            Cumulative number of packets lost: 0
        Extended highest sequence number received: 131074
            Sequence number cycles count: 2
            Highest sequence number received: 2
        Interarrival jitter: 0
        Last SR timestamp: 3005816176
        Delay since last SR timestamp: 1
Real-time Transport Control Protocol
    Stream setup by SDP (frame 159)
        Setup frame: 159
        Setup Method: SDP
    10.. .... = Version: RFC 1889 Version (2)
    ..0. .... = Padding: False
    ...0 0001 = Reception report count: 1
    Packet type: Receiver Report (201)
    Length: 7
    Sender SSRC: 469084700
    Source 1
        Identifier: 2233234561
        SSRC contents
            Fraction lost: 0 / 256
            Cumulative number of packets lost: 10
        Extended highest sequence number received: 61209
            Sequence number cycles count: 0
            Highest sequence number received: 25574
        Interarrival jitter: 0
        Last SR timestamp: 3005816176
        Delay since last SR timestamp: 1

Frame 174 (160 bytes on wire, 160 bytes captured)
    Arrival Time: Feb 28, 2006 11:31:53.179109000
    Time delta from previous packet: 0.014144000 seconds
    Time since reference or first frame: 4.010899000 seconds
    Frame Number: 174
    Packet Length: 160 bytes
    Capture Length: 160 bytes
Ethernet II, Src: 00:0d:56:72:f2:26, Dst: 00:0b:82:02:6d:48
    Destination: 00:0b:82:02:6d:48 (Grandstr_02:6d:48)
    Source: 00:0d:56:72:f2:26 (DellPcba_72:f2:26)
    Type: IP (0x0800)
Internet Protocol, Src Addr: 157.190.74.153 (157.190.74.153), Dst Addr: 157.190.74.101 (157.190.74.101)
    Version: 4
    Header length: 20 bytes
    Differentiated Services Field: 0x00 (DSCP 0x00: Default; ECN: 0x00)
        0000 00.. = Differentiated Services Codepoint: Default (0x00)
        .... ..0. = ECN-Capable Transport (ECT): 0
        .... ...0 = ECN-CE: 0
    Total Length: 146
    Identification: 0x7f11 (32529)
    Flags: 0x00
        0... = Reserved bit: Not set
        .0.. = Don't fragment: Not set
        ..0. = More fragments: Not set
    Fragment offset: 0
    Time to live: 128
    Protocol: UDP (0x11)
    Header checksum: 0xeace (correct)
    Source: 157.190.74.153 (157.190.74.153)
    Destination: 157.190.74.101 (157.190.74.101)
User Datagram Protocol, Src Port: 8001 (8001), Dst Port: 8563 (8563)
    Source port: 8001 (8001)
    Destination port: 8563 (8563)
    Length: 126
    Checksum: 0x6260 (correct)
Real-time Transport Control Protocol
    Stream setup by SDP (frame 159)
        Setup frame: 159
        Setup Method: SDP
    10.. .... = Version: RFC 1889 Version (2)
    ..0. .... = Padding: False
    ...0 0001 = Reception report count: 1
    Packet type: Sender Report (200)
    Length: 12
    Sender SSRC: 469084700
    Timestamp, MSW: 3350115113
    Timestamp, LSW: 751619277
    RTP timestamp: 13440
    Sender's packet count: 5
    Sender's octet count: 800
    Source 1
        Identifier: 469084700
        SSRC contents
            Fraction lost: 0 / 256
            Cumulative number of packets lost: 0
        Extended highest sequence number received: 327685
            Sequence number cycles count: 5
            Highest sequence number received: 5
        Interarrival jitter: 0
        Last SR timestamp: 3005820108
        Delay since last SR timestamp: 1
Real-time Transport Control Protocol
    Stream setup by SDP (frame 159)
        Setup frame: 159
        Setup Method: SDP
    10.. .... = Version: RFC 1889 Version (2)
    ..0. .... = Padding: False
    ...0 0001 = Reception report count: 1
    Packet type: Receiver Report (201)
    Length: 7
    Sender SSRC: 469084700
    Source 1
        Identifier: 2233234561
        SSRC contents
            Fraction lost: 0 / 256
            Cumulative number of packets lost: 15
        Extended highest sequence number received: 61413
            Sequence number cycles count: 0
            Highest sequence number received: 25577
        Interarrival jitter: 0
        Last SR timestamp: 3005820108
        Delay since last SR timestamp: 1
Real-time Transport Control Protocol
    Stream setup by SDP (frame 159)
        Setup frame: 159
        Setup Method: SDP
    10.. .... = Version: RFC 1889 Version (2)
    ..0. .... = Padding: False
    ...0 0001 = Source count: 1
    Packet type: Source description (202)
    Length: 7
    Chunk 1, SSRC/CSRC 469084700
        Identifier: 469084700
        SDES items
            Type: CNAME (user and domain) (1)
            Length: 22
            Text: unknown@157.190.74.153

Frame 851 (126 bytes on wire, 126 bytes captured)
    Arrival Time: Feb 28, 2006 11:31:58.154942000
    Time delta from previous packet: 0.010746000 seconds
    Time since reference or first frame: 8.986732000 seconds
    Frame Number: 851
    Packet Length: 126 bytes
    Capture Length: 126 bytes
Ethernet II, Src: 00:0d:56:72:f2:26, Dst: 00:0b:82:02:6d:48
    Destination: 00:0b:82:02:6d:48 (Grandstr_02:6d:48)
    Source: 00:0d:56:72:f2:26 (DellPcba_72:f2:26)
    Type: IP (0x0800)
Internet Protocol, Src Addr: 157.190.74.153 (157.190.74.153), Dst Addr: 157.190.74.101 (157.190.74.101)
    Version: 4
    Header length: 20 bytes
    Differentiated Services Field: 0x00 (DSCP 0x00: Default; ECN: 0x00)
        0000 00.. = Differentiated Services Codepoint: Default (0x00)
        .... ..0. = ECN-Capable Transport (ECT): 0
        .... ...0 = ECN-CE: 0
    Total Length: 112
    Identification: 0x805a (32858)
    Flags: 0x00
        0... = Reserved bit: Not set
        .0.. = Don't fragment: Not set
        ..0. = More fragments: Not set
    Fragment offset: 0
    Time to live: 128
    Protocol: UDP (0x11)
    Header checksum: 0xe9a7 (correct)
    Source: 157.190.74.153 (157.190.74.153)
    Destination: 157.190.74.101 (157.190.74.101)
User Datagram Protocol, Src Port: 8001 (8001), Dst Port: 8563 (8563)
    Source port: 8001 (8001)
    Destination port: 8563 (8563)
    Length: 92
    Checksum: 0xf537 (correct)
Real-time Transport Control Protocol
    Stream setup by SDP (frame 159)
        Setup frame: 159
        Setup Method: SDP
    10.. .... = Version: RFC 1889 Version (2)
    ..0. .... = Padding: False
    ...0 0001 = Reception report count: 1
    Packet type: Sender Report (200)
    Length: 12
    Sender SSRC: 469084700
    Timestamp, MSW: 3350115118
    Timestamp, LSW: 652835029
    RTP timestamp: 53760
    Sender's packet count: 257
    Sender's octet count: 41120
    Source 1
        Identifier: 469084700
        SSRC contents
            Fraction lost: 0 / 256
            Cumulative number of packets lost: 0
        Extended highest sequence number received: 16843009
            Sequence number cycles count: 257
            Highest sequence number received: 257
        Interarrival jitter: 0
        Last SR timestamp: 3006146281
        Delay since last SR timestamp: 1
Real-time Transport Control Protocol
    Stream setup by SDP (frame 159)
        Setup frame: 159
        Setup Method: SDP
    10.. .... = Version: RFC 1889 Version (2)
    ..0. .... = Padding: False
    ...0 0001 = Reception report count: 1
    Packet type: Receiver Report (201)
    Length: 7
    Sender SSRC: 469084700
    Source 1
        Identifier: 2233234561
        SSRC contents
            Fraction lost: 0 / 256
            Cumulative number of packets lost: 0
        Extended highest sequence number received: 25826
            Sequence number cycles count: 0
            Highest sequence number received: 25826
        Interarrival jitter: 2
        Last SR timestamp: 3006146281
        Delay since last SR timestamp: 1

Frame 1540 (126 bytes on wire, 126 bytes captured)
    Arrival Time: Feb 28, 2006 11:32:03.191066000
    Time delta from previous packet: 0.007661000 seconds
    Time since reference or first frame: 14.022856000 seconds
    Frame Number: 1540
    Packet Length: 126 bytes
    Capture Length: 126 bytes
Ethernet II, Src: 00:0d:56:72:f2:26, Dst: 00:0b:82:02:6d:48
    Destination: 00:0b:82:02:6d:48 (Grandstr_02:6d:48)
    Source: 00:0d:56:72:f2:26 (DellPcba_72:f2:26)
    Type: IP (0x0800)
Internet Protocol, Src Addr: 157.190.74.153 (157.190.74.153), Dst Addr: 157.190.74.101 (157.190.74.101)
    Version: 4
    Header length: 20 bytes
    Differentiated Services Field: 0x00 (DSCP 0x00: Default; ECN: 0x00)
        0000 00.. = Differentiated Services Codepoint: Default (0x00)
        .... ..0. = ECN-Capable Transport (ECT): 0
        .... ...0 = ECN-CE: 0
    Total Length: 112
    Identification: 0x81a9 (33193)
    Flags: 0x00
        0... = Reserved bit: Not set
        .0.. = Don't fragment: Not set
        ..0. = More fragments: Not set
    Fragment offset: 0
    Time to live: 128
    Protocol: UDP (0x11)
    Header checksum: 0xe858 (correct)
    Source: 157.190.74.153 (157.190.74.153)
    Destination: 157.190.74.101 (157.190.74.101)
User Datagram Protocol, Src Port: 8001 (8001), Dst Port: 8563 (8563)
    Source port: 8001 (8001)
    Destination port: 8563 (8563)
    Length: 92
    Checksum: 0xc104 (correct)
Real-time Transport Control Protocol
    Stream setup by SDP (frame 159)
        Setup frame: 159
        Setup Method: SDP
    10.. .... = Version: RFC 1889 Version (2)
    ..0. .... = Padding: False
    ...0 0001 = Reception report count: 1
    Packet type: Sender Report (200)
    Length: 12
    Sender SSRC: 469084700
    Timestamp, MSW: 3350115123
    Timestamp, LSW: 811748819
    RTP timestamp: 94560
    Sender's packet count: 512
    Sender's octet count: 81920
    Source 1
        Identifier: 469084700
        SSRC contents
            Fraction lost: 0 / 256
            Cumulative number of packets lost: 0
        Extended highest sequence number received: 33554944
            Sequence number cycles count: 512
            Highest sequence number received: 512
        Interarrival jitter: 0
        Last SR timestamp: 3006476386
        Delay since last SR timestamp: 1
Real-time Transport Control Protocol
    Stream setup by SDP (frame 159)
        Setup frame: 159
        Setup Method: SDP
    10.. .... = Version: RFC 1889 Version (2)
    ..0. .... = Padding: False
    ...0 0001 = Reception report count: 1
    Packet type: Receiver Report (201)
    Length: 7
    Sender SSRC: 469084700
    Source 1
        Identifier: 2233234561
        SSRC contents
            Fraction lost: 0 / 256
            Cumulative number of packets lost: 0
        Extended highest sequence number received: 26078
            Sequence number cycles count: 0
            Highest sequence number received: 26078
        Interarrival jitter: 3
        Last SR timestamp: 3006476386
        Delay since last SR timestamp: 1