ulticast packets and relays them to the already active TEIDs. These TEIDs are those of MSs that have joined a multicast group. There are two states in which each PDP context can exist: the active state and inactive state. The PDP state indicates whether data transfer is enabled for that PDP address or not. In case all PDP contexts associated with the same PDP address are deactivated, data transfer for that PDP address is disabled. Inactive PDP Context In this state, data service for a certain PDP address of the subscriber is not activated. The PDP context contains no routing or mapping information to process PDP PDUs related to that PDP address. No data can be transferred. A changing location of a subscriber causes no update for the PDP context in the inactive state, even if the subscriber is GPRS attached. If a GGSN receives a data packet destined for an MS in the inactive state, it will generate error and the packet will be discarded. An Internet Control Message Protocol (ICMP) packet (error notification) will be sent to the originator. The PDP context activation procedure is always initiated by the mobile station for it to move from the inactive to the active state. Active PDP Context In this state, the PDP context for the PDP address is activated in the MS, SGSN and GGSN. The PDP context contains mapping and routing information for transferring PDP Units for that particular PDP address between the MS and the GGSN. An active PDP context for an MS is moved to the inactive state when the deactivation procedure is initiated. All active PDP contexts for an MS are moved to the inactive state when the handset moves to the IDLE state. A GPRS-attached mobile station can at any time activate and de-activate the PDP context in the MS, SGSN and GGSN. A GGSN can de-activate a PDP context. When the SGSN receives an activate PDP context request message, it initiates a procedure to set up the PDP context. It performs subscription checking and APN selection. If the request is to activate a secondary PDP context (a primary PDP