3.10.2.2. General 
There is substantial difference between SRS for HFA and SIP/UFIP:
- HFA: Once the WAN Settings of the SoftGate are activated, a HFA Proxy will be used to query any HG3530 vSTMI boards when a phone tries to logon (meaning the HG3530 vSTMI doesn’t need any special configuration for this feature).
- SIP/UFIP: Dedicated SIP vSTMI must be configured for SRS and all remote subscribers must be configured on this board.
- Only one endpoint (phone or soft client) and a DSL router are required at the remote office location (e.g. Netgear, D-Link, FRITZ!Box, etc.). OpenStage, DPIP & CPx00 HFA terminals and the OpenScape Personal Edition Software Clients are supported as endpoints for HFA SRS (Info: OpenScape Personal Edition Software Clients additionally need to connect to DLS - see Section 14.2.3, “Restrictions”). OpenScape SIP terminals and wide scale of VoIP soft clients are supported for SIP/UFIP SRS.
- The solution is NAT aware and is suitable for a number of HFA devices behind one NAT router. Since V7R2 the solution supports also a so called near-end Destination NAT (DNAT) on the SoftGate Server Side. Hereby the SoftGate can be used also behind a DMZ firewall with port forwarding configuration.
- The OpenScape 4000 SoftGate offers a dedicated Ethernet port (WAN interface) for Internet connectivity including the necessary firewall configuration.
- OpenScape 4000 SoftGate administration including this feature is performed fully via the Intranet/enterprise IP connectivity to the OpenScape 4000 host system/OpenScape 4000 Assistant. External access over the Internet is not necessary.
- Centralized deployment via DLS is optional.
- Bandwidth requirement considerations
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Due to the best effort characteristic of the public Internet, a reliable bandwidth for RTP traffic between the user in the remote office and OpenScape 4000 SoftGate WAN access cannot be guaranteed.Based on our experiences during testing, we can make the following recommendations.
- Subscriber side connection
The minimum recommended DSL speed for a user with home Internet access is a DSL 6000 (max. download 6016 kbit/s - max. upload 512 kbit/s), assuming that this Internet Service Provider access is used in parallel for standard office working tasks (e.g. e-mail and "normal" Web browsing).- OpenScape 4000 SoftGate WAN interface
The dimensioning of the bandwidth of the OpenScape 4000 SoftGate for Internet access must be considered carefully. Because the user's devices in the remote office cannot use DMC functionality, all calls (payload voice streams) are terminated in the OpenScape 4000 SoftGate. For the bandwidth calculation a payload voice channel (b/d channel in classical PBX wording) with the corresponding codec parameters based on the existing bandwidth tables (see Gateways HG 3500 and HG 3575 > Section 2.5, “Bandwidth Requirements”) and traffic model calculation (http://intranet.mch4.global-intra.net/syseng/perfeng/tools/nert/index.htm) must be considered for each device.Sample calculation for dimensioning OpenScape 4000 SoftGate WAN access with G./11 (without VAD, 20 ms):- SDSL 1000 kbit/s (Note: symmetric connection, uplink speed/bandwidth= downlink speed/bandwidth)
- User in remote office uses G.711 without VAD and with 30 ms sampling time => 85 kbit/s
- This results in (1000/85 = 11.7 -> rounded down by ~5% for signaling and non-media, e.g. DLS, Picture CLIP) a maximum of 11 parallel channels
- 11 channels with 1 % probability of blocking results according to Erlang calculator in 5.1599 Erlang (see also Gateways HG 3500 and HG 3575 > Section 2.7, “Traffic Considerations”)
- For 0.15 Erlang per user, this results in (5.1599/0.15 =>) a maximum of 34 users in the remote office.
Sample calculation for dimensioning OpenScape 4000 SoftGate WAN access with G.729 (without VAD, 20ms):- SDSL 1000 KBit/s (Note: symmetric connection, uplink speed/bandwidth= downlink speed/bandwidth)
- User in remote office uses G.729 without VAD and with 20 ms sampling time => 40 KBit/s
- This results in (1000/40 = 25 -> rounded down for ~5% for signaling and non-media, e.g. DLS, Picture CLIP) a maximum of 24 parallel channels
- 24 channels with 1 % probability of blocking results according to Erlang calculator in 15,2950 Erlang (see also Gateways HG 3500 and HG 3575 > Section 2.7, “Traffic Considerations”)
- For 0.15 Erlang per user, this results in (5.1599/0.15 =>) a maximum of 102 users in the remote office.
Mixing of regular users and call center agents via the same WAN interface is possible. However, in order to guarantee connection availability to call center agents at all times, these users will be trafficked at 1 Erlang (36 C.C.S.). The WAN interface is subject to the same traffic model calculations like other communication models.
- Notes
- OpenScape 4000 SoftGate has its own voice firewall based on HFA. It therefore behaves like a voice firewall. If customers require additional protection of the OpenScape 4000 SoftGate server and the corporate IT network, however, this can be achieved by setting up a DMZ. See also Section 14.2.4, “DMZ”.
- Most providers of standard home (user) Internet connections perform a forced disconnect after 24 hours. The time of this forced disconnect can be controlled with many of the IADs (e.g. 03:00h). This disconnect leads to loss of any active calls and reregistration of the phone. This process corresponds to a "normal" L1 error.
- Where mobile HFA is used, the disconnect described in Note 2 leads to the logging off of the mobile HFA.