When a BM-SC server starts a MBMS bearer service, it also tells where to multicast/broadcast.
A group of cells may be part of one MBMS service area.
MBMS service area is a group AVP and type is OctetString.
1. First Octet - tell # of MBMS area's
2. Second Octet onwards list of MBMS area code.
Each MBMS area code occupies 2 octets.