This article analyses some of the main technical architectures, features and SLAs of a selection of SIP trunking providers active in Western Europe, including both large international providers targeting mainly large enterprises (around 11 such providers) as well as local providers targeting mainly SMBs (a further 15 providers). The article ends with an analysis of the main drivers and obstacles for SIP trunking in order to reach a conclusion regarding its potential.
Mainly because of the general trend towards IP, SIP trunking will prevail in the long term and eventually replace ISDN. Furthermore, SIP trunking offers some advantages: granularity, centralisation and thus cost savings, although only large enterprises with many distributed offices can really benefit from these (i.e. aggregating the number of channels onto a few sites, instead of ISDN at all sites). But for single-site SMBs there are currently hardly any real advantages to SIP trunking. However, there are also some obstacles and IP migrations (which typically include LAN, WAN, UC / PBX teams, possibly across several countries) usually take a (very) long time for the companies most likely to benefit from it, i.e. large enterprises with many offices. Besides, the still large number of installed TDM/ISDN PBX as well as the compatibility and security obstacles slow these migration processes further down. We therefore overall expect only a gradual constant growth over several years for SIP trunking, but no exponential growth and no swift demise of ISDN or analogue connections.