Cisco Cisco ASR 5000
RIM Message Transfer from BSC or RNC to eNodeB
How It Works ▀
SGSN Administration Guide, StarOS Release 18 ▄
How It Works
RIM Addressing
All the messages used for the exchange of RAN information contain the addresses of the source and destination RAN
nodes. An eNodeB is addressed by tracking area identity (TAI) + eNodeB Identity (enbId).
nodes. An eNodeB is addressed by tracking area identity (TAI) + eNodeB Identity (enbId).
The source RAN node sends a message to its SGSN including the source and destination addresses. From the
destination address, the SGSN shall decide whether or not it is connected to the destination RAN node. If the destination
address is that of an eNodeB, then the SGSN uses the destination address to route the message, encapsulated in a GTPv1
message, to the correct MME via the Gn interface.
destination address, the SGSN shall decide whether or not it is connected to the destination RAN node. If the destination
address is that of an eNodeB, then the SGSN uses the destination address to route the message, encapsulated in a GTPv1
message, to the correct MME via the Gn interface.
The MME connected to the destination RAN node decides which RAN node to send the message based on the
destination address or the RIM routing address.
destination address or the RIM routing address.
Call Flows - Transmitter of GTP RIM Msg
The following call flow illustrates how the SGSN behaves as the transmitter of GTP RIM messages.
Figure 77. Transmitting RIM Message
In the above illustration, the RIM message is transferred to the peer SGSN as follows:
1. Upon receiving a RIM message from the network access BSS/RNC, the SGSN determines the RIM routing
address type. If the message indicates that the target is an eNodeB, then SGSN searches for a locally
configured MME address.
configured MME address.
2. If a locally configured MME address is not available, then a DNS-SNAPTR query will be initiated to determine
the MME address.
3. On receiving the DNS response and upon getting a valid MME address, an appropriate GTP API would be
invoked.