With reference to EPC (Evolved Packet Core), what are some of the MME and eNodeB specific DNS queries, give examples where possible?
In the context of an Evolved Packet Core (EPC), the Mobility Management Entity (MME) and eNodeB perform specific DNS queries to ensure proper routing and connection establishment within the LTE network. Here are some examples:
(i) – What MME(s) can serve a given tracking area (TA)?
The eNodeB may query the DNS to find an MME when a User Equipment (UE) initially attaches to the network. The query typically includes the Tracking Area Identity (TAI), which is composed of the Tracking Area Code (TAC) and the Mobile Country Code (Mobile Network Code (MCC/MNC). An example of a TAI Fully Qualified Domain Name (FQDN) might look like this: tac-lb.tac-hb.tac.epc.mnc.mcc.3gppnetwork.org. This FQDN is used to discover the MME that serves the UE’s location.
(ii) – What SGW(s) can serve a given tracking area (TA)?
The eNodeB can perform a DNS query to find the Serving Gateway (SGW) that can serve a given tracking area. This is particularly important for setting up the user plane connectivity for a User Equipment (UE). The eNodeB uses the Tracking Area Code (TAC) associated with the UE’s location to form the DNS query. The eNodeB constructs a Service Selection (S-NAPTR) DNS query using the TAC. The DNS query might look something like this: sgw.tac.epc.mnc<MNC>.mcc<MCC>.3gppnetwork.org, where <MNC> is the Mobile Network Code and <MCC> is the Mobile Country Code associated with the tracking area. For example; if the TAC is 1234, the MNC is 01, and the MCC is 001, the eNodeB would send a DNS query for sgw.tac1234.epc.mnc01.mcc001.3gppnetwork.org. The DNS server would then respond with the IP address of the SGW that can serve the UE in the tracking area identified by the TAC. This allows the eNodeB to route the UE’s data traffic to the correct SGW for further processing and forwarding to the Packet Data Network Gateway (PDN-GW).
• MME DNS Queries:
(i) – What PGW(s) can serve an APN requested by UE?
(ii) – What SGW(s) can serve a tracking area (TA) reference by an eNodeB? The MME may perform DNS queries to select a Serving Gateway (S-GW) based on the UE’s location. This is part of the S1-MME interface setup between the MME and the eNodeB for the UE’s session.
(iii) – What SGW(s) and PGW(s) are compatible with each other? For example; when it makes sense to pair a specific SGW with a PGW.
(iv) – How can i reach the PGW identified by the HSS for a UE?
(v) – Where can i get security information for a UE, when i know its S-TMSI?
These DNS queries are crucial for the dynamic nature of the LTE network, allowing for flexibility and mobility management as UEs move across different eNodeBs and geographical locations. The specific DNS queries and configurations can vary based on the network setup and the equipment manufacturers’ implementations.