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Hi all, I'm new to SIPp and came
across it via Wireshark. We have a small network and have an issue with a VoIP
deployment. I am looking to SIPp to see if it can help with Quality assessment
of the network to look at things like jitter, packet loss and latency and
report back with easy to understand quality rating such as a MOS score. We have the following scenario: - Scenario. There are three remote sites in There is one
site that is the head office and the other two are branches. All calls are
received via PSTN (ISDN 30) at the head office and are then transferred using a
SIP trunk to the remote branch offices (Alcatel PBX to Alcatel PBX) via the
VPN. Known limitations. The system has been specified so
that no more than 8 simultaneous calls from the head office to the branch
office would be allowed. The Alcatel PBX’s only support a limited number
of Codecs – namely G711, G723.1, G729a. Call quality is an issue with
anything other than G711. This codec gives 64kbps per call, but with TCP
overheads we are looking at around 80-90kbps. 8 calls then equates to around
720kbps – which is close to the upper limit of our bandwidth. IPSEC VPN
translation will also add a bandwidth consideration and could push this to 115
kpbs. This would flood the network. In addition, although the Bandwidth is
managed by the edge of network routers and VoIP traffic is prioritised across
the VPN, the actual VPN packet is not marked for QoS as it travels across the
Internet. Caveats. It is unlikely that 8 calls will
be placed at any one time. In fact the issues that are being seen with just one
call in place. Bandwidth limitation are know and potentially being addressed. A
second DSL line maybe installed at the main office so that one circuit will
carry voice and the other will carry data. The ZyWALL 35 will handle this
segregation through its dual WAN ports. However, we may still find bandwidth
issues if the pipe is not sufficiently large considering the amount of
concurrent calls required. This may require a limitation of the number of
concurrent calls. SNMP logs have been taken to look various router parameters
(such as bandwidth usage, CPU utilisation etc) on the ZyWALL’s,
particularly looking at the managed bandwidth OUT of the router on the egress
to the WAN. These show that maximum bandwidth usage can spike to the managed
level occasionally, although VoIP issues also appear to not necessarily
coincide with these spikes, Internet connectivity at all sites is handled through
one ISP ( Areas of Concern. The users are experiencing what
they describe as a “buzzing” on the line. This appears to be only
in one directly (i.e. callers cannot hear a noise but the workers in the office
can). It also appears to be intermittent and of differing magnitude –
sometimes it is bearable, other times it makes the call inaudible. Users have
also reported a number of dropped calls. Plan of action. First and foremost, we need to
identify the area/s that is causing call quality issues and to do that we need
to identify what is the exact nature of the problem (i.e. what is this
“buzzing”). Is this purely a bandwidth issue, or is there
some other issue and where does this issue lay? Once the problem is identified
we need to put forward a resolution then retest once this has been implemented. I do not know if the issue is codec or network related.
What I need to do now is a packet trace and run some VoIP call simulations.
Ideally I would like to get a packet dump from the ZyWALL itself but I have not
managed to do this. Failing that I will insert a hub before the ZyWALL and plug
the network and PBX into that, then hook the hub up to the ZyWALL. I should
then be able to plug into the hub with a sniffer and monitor all traffic going
to the ZyWALL. I can’t monitor upstream of the ZyWALL as this packets
will be encrypted within IPSEC packets. Ideally I need a piece of software that can give my
quality scores (MOS), potential issues (jitter, packet loss) and suggested
resolutions. We’ve looked at Observer Suite from NI but this is a hefty
£4000. I am looking at the combination Wireshark/Ethereal and SIPp but
I’m not sure if they will do all that is needed – or at least my
skills set may not be able to get the required info. Can SIPp be used to get the necessary information
required? If not, are there any developer add-ons or other utilities at low
cost that could help in my quest? Many thanks Chris |
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