Skype for Business unifies voice and video calls, Skype for Business Meetings, presence, and instant messaging (IM) in one easy-to-use client, making it simple to choose and switch between different forms of communication. Clients are available for Enhanced Experience for Meetings Hosted on Skype for Business On-premisesBut I have not been able to figure out how to connect a number (phone number). Guests can also join using the Skype for Business apps for Android or iOS, but they may not have access to all interactive features.I have recently been troubleshooting an issue a customer had been facing since installing a SIP trunk from a UK Provider in preparation for a migration away from older ISDN circuits. In the network capture we saw that the Skype for Business Front End Server was trying to connect to a.config.skype.com (13.107.3.128), but this connection failed because it was blocked by the firewall.Please note that the IP address range 13.107.3.0/24 is part of the Office 365 IP address list:We added a new firewall rule that allow connections to 13.107.3. So there is an Object reference library in VBA which we need to use for reference. The three business platforms contributed.For further reading, the following are good references:The customer has decided to strictly define the endpoints presented to them by the ITSP, in the static route table using a /32 notation and therefore would need to explicitly define each of the endpoints required for communication to ensure correct routing. The invite was a routable IP address in our signalling group and SIP server table (ITSP IP) coming in to our internal IP interface for this SIP trunk……but then looking at the SDP negotiation, I noticed that for the media endpoint being offered within the SDP (referred to as ITSP IP2 below), the SBC did not have a static route back available to it, and all traffic to this IP address would be sent to the default route 0.0.0.0, pointing to an internal gateway (and therefore no way of reaching the ITSP):The SDP negotiation provides valuable information, from the media processing endpoint, to the codecs and capabilities of the call. Media lists were in place, the provider used G711 and the appropriate TLS media list was in place for SfBUsing the Sonus logging tool, LX, from a bird’s eye view of the call, I could see the invite being accepted, call being setup and teared down correctly:The next step for me was to review the invite, from the outside in (inbound call), firstly reviewing the SIP invite and SDP negotiation between the provider and our SBC appliance. SIP server tables which were all defined for both SIP provider and SfB Signalling groups which were configured correctly (inbound/outbound calls were OK) Whenever a call was made to these numbers, the calls would establish, but no audio was being sent from the Conferencing Auto Attendant, greeting a callee and offering meeting ID and pin entry options.As I hadn’t configured the SIP trunk myself I did the usual checks and reviewed the configuration of:
![]() Skype For Business Cannot Join Meetings How To Connect AThis post, won’t go into the depths of the initial configuration of the gateway and SIP circuit, but will focus on what is needed that is different to the typical SIP trunk configuration.From here, I assume you have deployed the following: The local gateway being provisioned was a Ribbon SBC1000, very familiar technology.Our SIP circuit was a registration mode trunk, meaning that a registration process must be completed with the trunk to authenticate and then subsequently, each outbound call would also need to respond to a challenge request.This was the first trunk I had encountered using this mode so I thought it would make a good blog entry. Each of the local site gateways was provisioned with SBA functionality. Eset nod32 antivirus for mac aI have seen references to configuration guides that state, that only the Contact Registrant table is required, certainly in my instance I had to configure both tables.The Contact Registrant contains information in relation the Realm and User ID used when registering on the trunk and the Remote Authorisation table contains the credentials. Call transformation tables have been createdIf you do need some advice on the above, the following blog article but my friend Mark Vale is a great multi-part walk-through:So assuming the above is all in place, the very first thing to configure are the Contact Registrant and Remote Authorisation tables which can be found under the SIP configuration node. A signalling group has been created representing an SfB Pool / SBA / STD Edition server To overcome this, within the ITSP SIP Profile, we set the following:I have been very fortunate to have been given the opportunity to attend Ignite 2017 in sunny Orlando Florida, its my first time at ignite and all I can say is WOW.It’s a great opportunity to network, meet those faces you see everyday online and just get a much better understanding of all products at a deep dive level. It can be found correctly formatted in the image below:Confirmation of this theory became apparent when I found the following errors in the SBC log:No tag value in FROM header, it then goes on to fail to find a suitable signalling group.Taking a step back reviewing my options I decided to revert the FROM manipulation and not implement it using SIP Message Manipulation, and use the more simplified SIP profile options to set a static FQDN for both TO and FROM fields:This did the trick, my call was correctly presenting ALL required ITSP information, calls were not permitted inbound and outbound!! SIp Message Manipulation could have achieved what we needed in this point, but the SIP profile is easier configuration for anyone to pickup and read so we opted for this method.We were using EXT prefix in a user Line URI and this was affecting the presentation of the P-Asserted Identity field. From: (for example PAI: (for example is significant information needed on the trunk for the correct presentation of the call, to the provider before they will accept the call.To manipulate the FROM header, I initially did a literal replacement of the entire FROM field, resulting in being presented using SIP Message Manipulation.I also did the same for the HOST portion of the PAI field and replaced it with SIPPROVIDER.comSo now, my invites outbound, to the best of my knowledge, should be presented in a format that the provider accepts – boy was I wrong.Upon sending an invite now, the provider was sending a 401 Challenge Request which was expected, now the issue was that our SBC was simply not responding to the challenge request and re-inviting without any authenticationAllow: INVITE, ACK, CANCEL, BYE, NOTIFY, OPTIONS, REFER, REGISTER, INFO, UPDATE, PRACKThis one had me stumbled for a couple of hours, I started looking at the logs, line by line and then noticed that the FROM: field, did not contain a tag=xxxx sgid=x, this tag information is what a UAS uses to determine that a call is not a duplication session (if you want to dig a little deeper ), and which signalling group should manage the connection and without this our SBC was not responding as we would expect it to. They responded this time with an internal configuration guide, that, would have been useful at the very start!Within this guide, the provider stipulated the following: Now depending on your trunk, these calls may be OK, my test calls were failing and upon viewing an LX trace from the gateway, our provider was immediately responding with 404 User Not Found for a valid local HK telephone number:I went back to the provider and requested additional configuration information. Any failures at this point are likely to be due to the realm, user ID or password across the tables.Once the trunk is registered, like me you will be tempted to make a test call (in my instance I actually believed I had the configuration ready).
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