OEB913309 EPC Session Management Troubleshooting(MME) ISSUE1.00

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Huawei Proprietary and Confidential

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A bearer context can be seen an information list, which stores the signaling control

data mandatory for performing data services. After the UE and the network have

finished the negotiation of the signaling data, the network allocates service channels

for the bearer context according to the negotiated signaling. Then, the bearer context

is activated, and the user plane data can be transmitted between the UE and the

network. Both the UE and the network can modify the signaling data of the bearer

context to improve or reduce the QoS and deactivate the bearer context to terminate

the connection service for the application layer.

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PDN connection

The EPS provides the UE with an IP connection between the UE and the PDN

through the E-UTRAN network and the EPC network. This IP connection is called a

PDN connection. Each PDN connection consists of an EPS bearer and an IP

connection. When the UE is connected to the PDN, an EPS bearer is established.

This bearer is called the default bearer, which is not released during PDN connection

so that a permanent connection to the PDN is provided. All additional EPS bearers to

the PDN are called dedicated bearers.

UE request pdn connectivity

The UE requests a PDN connection to establish a bearer to the PDN. The UE request

PDN connectivity procedure involves the following two cases: One is the PDN

connection establishment procedure initiated when the UE includes a PDN

connection request message in an initial attach message during attach, and the other

is the PDN connection establishment procedure initiated independently by the UE for

establishing a new PDN connection after the UE attaches.

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1. The UE sends a resource modification request message to the MME. The message

can be used to trigger the bearer establishment procedure, bearer modification

procedure, and bearer deletion procedure independently. The specific procedure is

determined by the traffic flow aggregate description (TAD).

2. The MME sends the request message to the S-GW through a Bearer Resource

Command message, and the S-GW forwards the message to the P-GW.

3. In a resource adding procedure, the UE sends an Update Bearer Request

message carrying QoS and APN-AMBR to the MME.

4. The MME sends a request message carrying QoS to the eNodeB/UE for creating a

bearer.

5. The eNodeB/UE returns the bearer modification result to the MME.

6. The MME sends the bearer modification result to the P-GW/PCRF.

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According to the invalidation mode, the fault may be triggered by the handling on the

local NE.

As the MME rejects the PDN connection request immediately, check whether the

handling on the local NE is abnormal.

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Analysis thinking

According to the cause value Request service option not subscribed, the

fault is related to the subscription data on the UE.

According to the internal handling mechanism for the subscription data on the

MME, the subscription data on the UE and the HSS must be checked,

especially the APN, PDP type, and PDP address.

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According to the invalidation mode, the fault may be triggered by the handling on the

local NE.

As the MME rejects the PDN connection request immediately, check whether the

handling on the local NE is abnormal.

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According to the symptom, the MME has sent the rejection message. Therefore, the

handling on the MME may trigger the fault. View the Dns Query RSP message. The

DNS server provides the cause value Missing or unknown APN. Therefore, the

output of the peer NE triggers the fault.

Perform the next-step analysis according to the internal message procedure of the

MME.

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DNS query is considered as a step of UE resource allocation.

Before the MME queries the IP addresses from the DNS server, the FQDN must be

created. That is, the MME generates a FQDN related to the APN based on the IMSI

of the UE and the APN NI in the subscription data.

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An APN consists of two parts:

APN NI is the mandatory part of the APN. It specifies the type of the external

data network to be accessed. The APN NI must be subscribed on the HLR. To

use it, activate it first.

APN OI is the optional part of the APN. It specifies the type of the operator.

Example 1

If the APN is internet.mnc015.mcc234.gprs, the FQDN of the APN is

internet.apn.epc.mnc015.mcc234.3gppnetwork.org.

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A TAI consists of the mobile country code (MCC), mobile network code (MNC), and

tracking area code (TAC).

A TAC is a 16-bit binary integer. is the most significant

hexadecimal byte, and is the least significant hexadecimal byte.

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The ADD DNSH command is used for configuring IP addresses for NE interfaces.

Precautions

Multiple groups of IP addresses exist in each DNSH. If the priorities and

weights of the IP addresses are the same, IP addresses are selected

randomly.

Multiple groups of IP addresses exist in each DNSH. If the priorities of the IP

addresses are different, the IP addresses of high priorities will be selected.

Multiple groups of IP addresses exist in each DNSH. If their priorities are the

same but their weights are different, the IP addresses will be selected

randomly, but the IP addresses of heavier weights are more likely to be

selected.

Parameter description

HSINDEX indicates the host name index.

HOSTNAME indicates the host name.

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The ADD DNSN command is used for configuring the mapping between the FQDNs

and NE interfaces.

Parameter description

FQDN is the short form of fully qualified domain name.

HSINDEX indicates the host name index.

ENTITY indicates the NE type.

INTYPE indicates the interface type.

WEIGHT indicates weight.

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According to the B3FA analysis, the faulty module may be tunnel negotiation or

access bearer establishment.

As the eNodeB returns the cause value Unavailable Resource, the peer NE triggers

the fault.

Perform the next-step analysis according to the related cause value in the messages.

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According to the symptom, the fault is not triggered by the QoS negotiation failure.

The cause values 2, 4, 5, and 6 cannot be analyzed at the core network side.

Therefore, focus on the cause value 3: The eNodeB fails to allocate the S1-U

resource.

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Observe the key information elements (IEs) in the Bearer Setup message. The user

plane information assigned by the MME is not configured on the eNodeB.

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Documents

OEB913309 EPC Session Management Troubleshooting(MME) ISSUE1.00