In case of SRVCC, the home network application server viz., SCC-AS anchors the call. This anchoring by home network tends to increase the handover delay in case a home subscriber roams to a distant network and latches on to a roaming partner. The roaming network now awaits signalling from home network before the call can be handed from LTE to 2G/3G and this could result in handover delay exceeding minimum acceptable limits – causing degraded quality of experience for the end subscriber.
In order to avoid this problem, eSRVCC is proposed, wherein when a subscriber roams to a roaming partner network, the call is anchored at the roaming network itself by a new entity called ATCF/ATGW – which results in substantial reduction in delay. Roaming partner’s ATCF/ATGW coordinates with the home network SCC-AS to complete necessary SIP updates without impacting handover time.
Original Source: http://lteuniversity.com/ask_the_expert/f/59/t/5672.aspx