he method of transmission can be similar that from BTS to BSC, or BSC to MSC, or it can be sent by the frame-relay method. If there is no frame-relay network, then the ATM network could also be used to transfer frame relay. Even dedicated PCM links (also known as frame-relay links) could be used to send packet data from the BSC to the SGSN. The main result of frame-relay dimensioning is to find the number of time slots that are needed to send the packet data traffic from the BSC to the SGSN. GPRS: NETWORK PLANNING AND OPTIMISATION The Gn interface The interface connecting all the GPRS network elements (SGSN-SGSN, SGSN-GGSN, etc.) is the Gn interface. Dimensioning of this interface is based on the amount of data flow during peak hours, the number of subscribers, the number of Gb interfaces, information about the IP network, etc. The core planning engineers classify the GPRS network based on this information. Generally the GPRS network could be one of a number of types. It could be a GSM network in which the GPRS network elements are introduced to launch the packet data services, or it could be an advanced network that focuses on issues like coverage and quality. The main difference between these two types of GPRS network is in the GPRS network elements that would be used. In an advanced network, the number of SGSNs or GGSNs would be increased, thereby increasing the number of Gb or Gn interfaces. An Ethernet LAN connection is the GPRS IP backbone. All the network elements inside the GPRS packet core network - such as NMS, firewalls, DNS, SGSN, GGSN, etc. - are connected through this switch. Thus, it becomes necessary to not only use a good-quality switch but also keep a redundant switch. The Gi interface The core network planning engineers have also to look into the interface between the GPRS network and any external network (i.e. the interface between the GGSN and the external network). Since a different type of data will be flowing through this network, Gi is not a standard interface but acts as a reference poin