# **蔡瀚興-讀書會-21/07/10**

## 推薦連結
- [What is DNS](https://aws.amazon.com/tw/route53/what-is-dns/)

## <font color="#FF0000">LTE NE IDs:</font>
They can be divided into two group
1. **With PLMN ID**
2. **Without PLMN ID**

## <font color="#FF0000">IDs to Identify MME:</font>
MMEs serve as brain for the LTE network,and usually operate as MME groups.

- **MMEGI:** MME Group Identifier
- **MMEC:** MME Code that represents an MME within the MME group
- **MMEI:** MMEGI + MMEC
- **GUMMEI:** PLMN + MMEI

## <font color="#FF0000">IDs to Identify eNB:</font>
- Global eNB ID: PLMN ID +　ｅNB ID
- Cell ID: To identify a cell belonging to an eNB
### Notes
- eNB IDs and cell IDs are allocated when an eNB is installed
- When eNB requests the MME for S1 link ,it reports its **Global eNB ID** and supported TAs and a **CSG ID** if CSGs are supported.
- **Closed Subscriber Group(CSG)**: is a cell open to only a certain group of subscribers

## <font color="#FF0000">IDs to Identify P-GW:</font>
MME has to know the PDN to connect the UE and the P-GW to attach the UE through.
- **P-GW IDs:** IP address or **FQDN(Fully Qualified Domain name)**
There are two ways to allocate P-GW ID:
1. **Fixed allocation:** Network operator provisions a P-GW ID as a subscrubed profile in the HSS.
2. **Dynamic allocation:** MME selects a P-GW according to the P-GW selection policy set by the operator.
### Notes
- **Fixed allocation policy**
- **Dynamic allocation pilicy:** MME obtains a P-GW IP address list through **DNS query**.

## <font color="FF0000">Identifiers for UE Location</font>
MME has to updated information on the UE's location
- **UE is active state:** Location of UE is known at **cell level**
- **UE is idle state:** Location of UE is known at **TA level**

## <font color="FF0000">IDs to identify the location of a UE(TAC and TAI):</font>
A UE is registered to a network at TA level.
- **Trackin Area Code(TAC):** Used to identify a TA
- **Tracking Area Identifier(TAI):** PLMN + TAC
### Notes
- MME allocates a TAI list to the UE and keeps the UE location updated.
- UE does not have to request update TAI list if traveling to a TA in the list.
- If UE is in active state ,MME can simply forward the data.
- If UE is in idle state ,MME sends a **Paging message**
### Paging procedure
1. MME sends a **Paging message** to all the eNBs belong to the TA announcing there is data for the UE
2. UE in idle state wakes up at certain periods to check for any **Paging message**.
3. If UE finds it has been paged ,it responds to the message to recieve the data

## <font color="#FF0000">*Closing*</font>