Default Eps Bearer Activation

The purpose of the default bearer context activation procedure is to establish a default EPS bearer context between the UE and the EPC. The default EPS bearer context activation procedure is initiated by the network as a response to the PDN CONNECTIVITY REQUEST message from the UE. The default bearer is a non-Guaranteed Bit Rate GBR bearer. A dedicated bearer can be either a GBR or a non-GBR bearer. The default bearer remains established throughout the lifetime of the PDN connection to provide the UE with IP connectivity to the PDN The default bearer context activation procedure can be part of the Attach procedure, and if the attach procedure fails, the UE shall consider that the default bearer activation has implicitly failed Once the UE is successfully attached, the UE can request the MME to set up connections to additional PDNs. For each additional connection, the MME will activate a separate default EPS bearer context The MME shall initiate the default bearer context activation procedure by sending an ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST message When the default bearer is activated as part of the attach procedure, the MME shall send the ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST message together with ATTACH ACCEPT

When the default bearer is activated as the response to a stand-alone PDN CONNECTIVITY REQUEST message apart from the attach procedure, the MME shall send the ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST message alone, and start the timer T3485 The MME shall assign and include an EPS bearer identity in the ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST message. The MME shall retrieve the PTI Procedure Transaction Identity from the PDN CONNECTIVITY REQUEST message and include it in the ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST message Typical IEs in  ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST message include EPS bearer identity, Procedure transaction identity PTI, EPS QoS, Access point name APN, PDN address, Negotiated QoS, Negotiated LLC SAPI, Packet flow Identifier, APN-AMBR APN aggregate maximum bit rate, ESM cause, and Protocol configuration options etc The network shall include the IE ESM cause, if the network allocated a PDN address of a PDN type which is different from the PDN type requested by the UEExample: ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST with Attach Accept message.

Bearers in LTE e-RAB transports the establish an EPS Bearer is called EPS Bearer Activation up and the second will be done using Activate default EPS.

The following diagram describes the steps the messages follow during the dedicated bearer activation EPS Bearer QoS, PCO, EPS Bearer Identity and default EPS.

• LTE: Default vs. Dedicated Bearer. One of the big changes brought about by LTE is that when the mobile device connects This is called Default EPS Bearer Activation.
• Hi, the spec says that : 24.301 The default EPS bearer context does not have any TFT assigned during the activation procedure. This corresponds to using a match-all.
• The EPS session management messages for the default EPS bearer context activation are transmitted in an information element in the EPS mobility management messages.
• Dec 01, 2009  Dedicated bearer activation in combination with the default bearer activation at attach or UE requested PDN connectivity.

One of the big changes brought about by LTE is that when the mobile device connects to the network it also implicitly gets an IP address. This is called Default EPS Bearer Activation. What seems to be a trivial change at first is actually a whole new way of thinking compared GSM and UMTS.

In 2G and 3G systems, the mobile registers to the network first and in order to get an IP address, a PDP context activation procedure has to follow. This is also what is known as establishing a packet call. I never very much liked the term packet call which was probably created because of the still mainly circuit switched thinking at the time. So with the default bearer activated right from the start, the packet call and all the legacy behind it has become history.

To build on the default bearer there is also a procedure in LTE called Dedicated EPS Bearer Activation which is initiated for the network. But what is it needed for, most people ask at first, the mobile already has an IP address.. True, the mobile already has an IP address but the default bearer comes without any quality of service guarantees. For VoIP, IMS, VoLGA and other real time streaming applications, it would be good to have some QoS, especially on the air interface. This ensures that the base station and other network components deliver IP packets for those applications with a higher priority. Also on the mobile side, such IP packets should get a higher priority than other packets, especially when the bandwidth is limited. And that s what is done with a dedicated bearer.

In the network, the dedicated bearer is connected to a Traffic Flow Template TFT, a concept that already exists in GSM and UMTS. In this template, think of it as a list of ip addresses and tcp/udp port combinations, describes which IP packets should be given a higher priority. The TFT is also forwarded to the mobile during the dedicated bearer activation and it helps the protocol stack to put the IP packets to or from a specific TCP/UDP port and/or IP addresses into a special QoS queue that is treated with a higher priority.

No need for the mobile to have an extra IP address for this higher priority traffic, as the protocol stack uses the Traffic Flow Template information to decide what to do with each IP packet. In other words for those who are familiar with GSM and UMTS, a dedicated bearer activation is pretty similar to a Secondary PDP context activation in 2G and 3G that can be used by the IMS for example to ensure real time data is delivered promptly.

For the details have a look at 3GPP TS 24.301, chapter 6.4 and table 8.3.3.1 a bit further down for the message details.

Default Bearer, Dedicated Bearer the LTE Attach/Default EPS Bearer will be equivalent to the UMTS The Secondary PDP Context Activation is similar to the.

LTE Quick Reference Go Back To Index Home : www.sharetechnote.com EPS Bearer Bearer in the dictionary means Is linked to a specified default EPS bearer;.

Bearer Dedicated EPS bearer dedicated EPS bearer context activation procedure The rule is that you must have one and only one default EPS bearer per.

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