access. SIP trunks generally offer fewer features than PRIs, and even where they offer equivalent features, the features might work differently or be less consistent than on a PRI. This is simply an indication of the immaturity of the SIP trunk market. As time passes, the expectation is that SIP trunk services will mature, closing the gap in features with PRIs and then surpass them with features that are not, and never will be, available on PRIs. Table 11-1 summarizes some of the current, important differences between SIP trunk and PRI services. Determine Geographic Coverage Depending on the countries, or regions within a country, where your network has sites targeted to connect to a SIP trunk, you may have to do several evaluations and select sev- eral different providers to cover the different geographic areas where you operate. Assess DID Porting Realities Routing outbound calls over SIP trunks is often easier than routing inbound calls to the enterprise. And for this reason, it is sometimes where a SIP trunk trial starts-with out- bound calls only. If you target inbound calls to arrive via the SIP trunk, you must determine which DIDs in your organization are affected, which current provider these DIDs belong to, and whether the DID numbers can be reassigned to the SIP trunk. If the DID number belongs to the same provider you are considering for a SIP trunk, this might be eminently achievable, but if they belong to different providers, it will be more difficult. For a SIP trunk trial, a few new numbers are usually assigned and porting existing DID numbers typically does not take place until you are ready to roll out production services. 250 SIP Trunking Table 11-1 Current SP SIP Trunk Services Compared to TDM Services Consideration SIP Trunk Services Services Basic call completion. Well defined Well defined Supplementary services (Caller ID, Call Waiting, Requires validation Well defined Transfer, Forward, Hold, Conference). testing Fault monitoring and isolation. Options PING Yellow/Red monitoring Alarms Emer