RIM procedures provide a generic mechanism for the exchange of arbitrary information between RAN nodes. The RAN information is transferred via the SGSN core network node(s). In order to make the RAN information transparent for the core network, the RAN information is included in a RIM container that shall not be interpreted by the core network nodes.

The RAN information is transferred in RIM containers from the source RAN node to the destination RAN node by use of messages. The SGSN independently routes and relays each message carrying the RIM container.

In pre-15.0 releases, the SGSN supported RIM messages from BSS/RNC to another BSS/RNC belonging to a different or the same SGSNover GTPv1 protocol. Now, the SGSN also supports transfer of RIM messages to/from an MME (eNodeB) via GTPv1 protocol.

The SGSN uses existing CLI to enable the RIM transfer functionality. Whether or not the RIM message goes from/to BSC/RNC to/from BSC/RNC or to/from eNodeB is determined by the addressing. To transfer RIM messages to the MME (eNodeB),

OR

For this feature to work properly, the peer-MME for the eNodeB must also support RIM message handling.

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).

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.

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.

The following call flow illustrates how the SGSN behaves as the transmitter of GTP RIM messages.

In the above illustration, the RIM message is transferred to the peer SGSN as follows:

The following call flow illustrates how the SGSN behaves as the receiver of GTP RIM messages.

In this case, the SGSN has to decode the incoming GTP message correctly and forward the RIM message to the destination RNC/BSS.

The RIM application processes the decoded RIM PDU from the access application. The routing area identifier (RAI) -- comprised of the mcc, mnc, rac -- is extracted from the destination address and is used to decide if the target routing area (RA) is local. If the RAI is locally available, the PDU is forwarded to either the RANAP or BSSGP stack based on the RIM routing address discriminator field.

The SGSN has a global list of local RAs. Each RA in turn has a list of RNCs and NSEIs that control it. If the destination RA is local, the list of NSEIs which serve the RAI is fetched. Each NSEI is searched for a matching cell id in the cellid-list. The PDU is then forwarded to the NSEI when signaling the BVCI.

If the RNC Id is in the destination cell identifier, then the IuPS service serving the local RAI is identified. The PDU is encoded in a RIM container and forwarded to the corresponding RANAP stack instance of that IuPS service.

If the eNodeB Id is in the destination cell identifier, then the PDU will be sent to the GTP app using the appropriate event.

The peer-MME address is resolved using the SGSN's local configuration or a DNS query for the TAI present in the destination address. For a successful DNS response, the PDU is encoded in a GTP RIM container and forwarded to the peer-MME. The SGTP service used will be the default SGTP service associated with the GPRS service or the SGSN service under which the source BSS/RNC was present. The RIM app drops a PDU if the DNS response fails. There will no retransmission or state-maintenance for the RIM PDU at the GTP-app.

The SGSN's RIM message transfer from/to eNodeB functionality complies with the following standards:

The following command sequences are used to enable RAN information management (RIM) functionality on the SGSN. The order in which these two configurations are performed is not significant.

The first command sequence enables RIM for the entire SGSN (global level).

configure 
   sgsn-global 
     ran-information-management 
     end 

The second command sequence associates the RNC configuration, the part of the IuPS service configuration governing the SGSN communication with any RNC, needs to have the RIM functionality enabled.

configure 
   context context_name 
     iups-service service_name 
        rnc id rnc_id 
           ran-information-management 
           end 

The SGTP service configuration is a mandatory part of the SGSN's setup (refer to Configuring an SGTP Service in the SGSN Administration Guide), so an SGTP service configuration must already exist. The SGTP service is needed to send and/or receive GTPv1 protocol messages.

It is also a good idea to associate the IuPS service for the SGSN service to use for communication with the RAN.

The following illustrates the minimum configuration required to associate the SGTP and IuPS services for the RIM message transfers:

configure 
  context context_name 
     sgsn-service service_name 
        associate sgtp-service service_name context context_name 
        ran-protocol iups-service service_name 
        end 

Use the Call Control Profile to define the peer-MME address.

Use the tac keyword to configure the tracking area code (TAC) of the target eNodeB that maps to the peer-MME address. For RIM message transfer, you also need to configure the Gn interface. The following is an example of the configuration to use:

configure 
  call-control-profile profile_name 
     peer-mme tac tac_value prefer local address ip_address interface gn 
     end 

Where:

If using a DNS query to determine the peer-MME RIM address, then the DNS server must be pre-configured to respond to a TAI-based DNS query in the following format: tac-lb<TAC-low-byte>.tac-hb<TAC-high-byte>.tac.epc.mnc<MNC>.mcc<MCC>.3gppnetwork.org

show gmm-sm statistics verbose 
... 
Ranap Procedures: 
  Direct Transfer Sent:   0     Direct Transfer Rcvd:   0 
 

show gmm-sm statistics verbose | grep RIM 
... 
RIM Message Statistics: 
RIM Messages dropped: 
  due to RIM disabled in SGSN:             0     due to RNC not Capable:     0 
  due to RIM Routing Address not present:   0     due to RNC does not exist:   0 

show sgtpc statistics verbose 
... 
RAN info Relay Msg: 
Total messages received:         0  Total messages sent:  0 
Total messages dropped:          0 
  due to DNS failure:            0 
  due to RIM disabled in SGSN:   0 
  due to Invalid Routing Addr:   0 

show bssgp statistics verbose 
... 
RIM Messages 
  RAN Information messages received 
  RAN Information messages transmitted 
  RAN Information Request messages received 
  RAN Information Request messages transmitted 
  RAN Information ACK messages received 
  RAN Information ACK messages transmitted 
  RAN Information Error messages received 
  RAN Information Error messages transmitted 
  RAN Information Appln Error messages received 
  RAN Information Appln Error messages transmitted 
  RIM messages dropped 
    due to RIM disabled in SGSN 
    due to destination BSC not RIM capable 
    due to destination cell does not exist 
     due to invalid destination address