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NASLTEUE to MME3GPP TS 24.301
LTE PDN Connectivity Request
PDN Connectivity Request is the EPS session-management message the UE sends when it wants connectivity to a PDN, either during attach or later as a standalone LTE NAS session request.
Message Fact Sheet
Protocol
nas
Network
lte
Spec
3GPP TS 24.301
Spec Section
6.5.1.2, 8.3.20
Direction
UE to MME
Message Type
ESM signaling
Full message name
LTE PDN Connectivity Request
Protocol
NAS
Technology
LTE
Direction
UE to MME
Interface
N1 over LTE access / S1-MME control path
Signaling bearer / channel
NAS signaling / Commonly carried inside Attach Request as the ESM message container during initial attach, or later in uplink NAS transport when PDN connectivity is requested after registration.
Typical trigger
Sent when the UE needs default PDN connectivity for internet, IMS, enterprise, or another APN and the corresponding EPS bearer does not already exist.
Main purpose
Requests default EPS bearer establishment for a PDN, carrying request type, PDN type, and optional APN and protocol configuration information so the EPC can create PDN connectivity.
What is LTE PDN Connectivity Request in simple terms?
PDN Connectivity Request is the EPS session-management message the UE sends when it wants connectivity to a PDN, either during attach or later as a standalone LTE NAS session request.
Requests default EPS bearer establishment for a PDN, carrying request type, PDN type, and optional APN and protocol configuration information so the EPC can create PDN connectivity.
Why this message matters
PDN Connectivity Request is the LTE NAS session-management message the UE uses to ask for PDN connectivity and default bearer setup.
Where this message appears in the call flow
Initial attach default PDN request
In the initial attach path, PDN Connectivity Request is usually embedded in Attach Request and drives the default bearer setup branch that follows attach continuation.
Call flow position: Embedded ESM request carried inside Attach Request when the UE asks for default PDN connectivity as part of initial EPS registration.
Typical state: The UE is not yet fully attached and is asking the network to create the first PDN connection as part of attach completion.
Preconditions:
The UE is starting the LTE attach procedure.
The UE needs default PDN connectivity for the attach path.
Next likely message: Authentication Request, Attach Accept with embedded bearer handling, or Attach Reject
Standalone PDN connectivity after attach
After EPS registration already exists, PDN Connectivity Request can be sent as a standalone ESM procedure to request a new PDN connection.
Call flow position: Standalone ESM request sent after the UE already has EPS registration and wants a new default bearer toward a PDN.
Typical state: The UE is already attached and is adding or restoring PDN connectivity outside the initial attach branch.
Preconditions:
The UE already has usable EPS registration.
The UE needs new PDN connectivity and sends the request as a standalone ESM procedure.
Next likely message: Activate Default EPS Bearer Context Request or PDN Connectivity Reject
Additional APN or IMS PDN request
For IMS or another APN, PDN Connectivity Request shows the UE explicitly asking the EPC for another PDN connection outside the initial attach branch.
Call flow position: Standalone ESM request used when the UE asks for another PDN connection, often toward IMS or a dedicated APN.
Typical state: The UE already has one EPS context but needs another PDN connection for a different service path.
Preconditions:
Existing EPS registration is healthy.
The UE needs connectivity for another APN or service context.
Next likely message: Activate Default EPS Bearer Context Request or PDN Connectivity Reject
Interface: N1 over LTE access / S1-MME control path
Domain: Core-side EPS session management signaling for PDN connectivity and default bearer creation.
Signaling bearer: NAS signaling
Logical channel: Commonly carried inside Attach Request as the ESM message container during initial attach, or later in uplink NAS transport when PDN connectivity is requested after registration.
Transport / encapsulation: EPS NAS ESM message sent by the UE and delivered to the MME through the eNodeB during PDN connectivity establishment.
Security context: PDN Connectivity Request rides inside NAS signaling, so its protection depends on whether it is embedded in an early attach branch or sent later after NAS security is active.
Message Structure Overview
PDN Connectivity Request is an EPS session-management message rather than an ASN.1 LTE RRC structure.
The practical reading path starts with Request type, PDN type, and whether the message is embedded in Attach Request or sent later as standalone ESM signaling.
In real traces, this message explains why the network started default bearer establishment or why a bearer setup branch moved into reject handling.
ASN.1 Message Syntax for LTE PDN Connectivity Request
PDN Connectivity Request
Request type
PDN type
ESM information transfer flag OPTIONAL
Access point name OPTIONAL
Protocol configuration options OPTIONAL
Device properties OPTIONAL
NBIFOM container OPTIONAL
Header compression configuration OPTIONAL
Extended protocol configuration options OPTIONAL
How to read this message syntax
PDN Connectivity Request is a NAS layer-3 ESM message, not an ASN.1 LTE RRC message. Read it first from the procedure context: embedded during attach or standalone after attach.
Start by deciding whether the message is inside Attach Request or sent later as a standalone ESM procedure.
Request type and PDN type are the highest-value fields because they explain what kind of PDN setup the UE is asking for.
If APN is absent during attach, that can be expected because attach handling may rely on default APN selection.
Important Information Elements
IE
Required
Description
Request type
Yes
Indicates whether the UE is asking for an initial request, handover-related request, or another allowed PDN-connectivity request type.
PDN type
Yes
Tells the network whether the requested PDN connection is IPv4, IPv6, IPv4v6, or another supported PDN type.
ESM information transfer flag
Optional
Tells the network whether a later ESM information exchange is needed before completing PDN connectivity handling.
Access point name
Optional
Carries the requested APN when the UE explicitly identifies the PDN it wants to reach.
Protocol configuration options
Optional
Carries UE requests related to protocol configuration, such as DNS or other PDN setup parameters.
Detailed field explanation
Request type
Indicates whether the UE is asking for an initial request, handover-related request, or another allowed PDN-connectivity request type.
Presence: Required
In practice: In practice, compare this field with the original request and with any later release-dependent optional fields so you can see whether the network accepted the same service model the UE asked for.
PDN type
Tells the network whether the requested PDN connection is IPv4, IPv6, IPv4v6, or another supported PDN type.
Presence: Required
In practice: In practice, compare this field with the original request and with any later release-dependent optional fields so you can see whether the network accepted the same service model the UE asked for.
ESM information transfer flag
Tells the network whether a later ESM information exchange is needed before completing PDN connectivity handling.
Presence: Optional
In practice: In practice, compare this field with the original request and with any later release-dependent optional fields so you can see whether the network accepted the same service model the UE asked for.
Access point name
Carries the requested APN when the UE explicitly identifies the PDN it wants to reach.
Presence: Optional
In practice: In practice, compare this field with the original request and with any later release-dependent optional fields so you can see whether the network accepted the same service model the UE asked for.
Protocol configuration options
Carries UE requests related to protocol configuration, such as DNS or other PDN setup parameters.
Presence: Optional
In practice: In practice, compare this field with the original request and with any later release-dependent optional fields so you can see whether the network accepted the same service model the UE asked for.
What to check in logs and traces
Confirm whether the PDN Connectivity Request is embedded in Attach Request or sent later as a standalone ESM message.
Check the request type first.
Inspect the PDN type and requested APN.
Check whether ESM information transfer flag is present.
Follow the trace into Activate Default EPS Bearer Context Request, reject handling, or later attach continuation.
Common Issues and Troubleshooting
Attach starts but default bearer setup never completes cleanly.
Likely cause: The embedded PDN Connectivity Request may not match the network's expected APN, PDN type, or session policy.
What to inspect: Check Attach Request, the ESM message container, request type, PDN type, and any APN-related fields.
Next step: Read the attach branch as mobility plus session setup instead of treating bearer establishment as a separate later issue.
The UE is attached but cannot bring up IMS or another additional PDN.
Likely cause: The standalone PDN Connectivity Request may be asking for an APN, PDN type, or configuration the network does not accept.
What to inspect: Check the APN, PDN type, protocol configuration options, and the next bearer-activation or reject message.
Next step: Decide first whether the issue is APN policy, PDN type mismatch, or a broader EPC session-management problem.
The UE keeps retrying PDN setup after a standalone request.
Likely cause: The request may be supervised by T3482 and the network may not be accepting the requested PDN connectivity.
What to inspect: Check whether the request is standalone, whether T3482 behavior is visible, and whether the branch ends in bearer activation or reject handling.
Next step: Treat repeated retries as an ESM procedure issue before blaming lower-layer radio behavior.
LTE / 5G / Variant Comparison
Compared with Attach Request
Attach Request starts EPS mobility registration. PDN Connectivity Request is the ESM payload that asks for PDN connectivity and default bearer setup.
Compared with Service Request
Service Request restores service using existing EPS context. PDN Connectivity Request asks for PDN setup or another PDN connection.
Compared with Activate Default EPS Bearer Context Request
PDN Connectivity Request is the UE asking for PDN connectivity. Activate Default EPS Bearer Context Request is the network side starting the bearer activation response.
FAQ
What is PDN Connectivity Request in LTE?
It is the EPS NAS session-management message the UE sends to ask for PDN connectivity and default bearer establishment.
Is PDN Connectivity Request always sent by itself?
No. During initial attach it is often embedded inside Attach Request as the ESM message container. Later it can be sent as a standalone ESM procedure.
What should I inspect first in PDN Connectivity Request?
Start with the procedure context, then check Request type, PDN type, APN, and protocol configuration options.
Why is PDN Connectivity Request important in troubleshooting?
Because it shows what PDN or APN the UE actually asked for and whether the session setup problem started in the request itself.
Decode this message with the 3GPP Decoder, inspect the related message database, or open the matching call flow to see where this signaling step fits in the full procedure.
