SARA-R4/N4 series-AT Commands Manual
UBX-17003787 - R09
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13Packet switched data services
Page 119 of 307
13î™–î™–î™–î™–Packet switched data services
13.1î™–î™–î™–î™–PDP contexts and parameter definition
13.1.1î™–î™–î™–î™–Primary and secondary PDP contexts
A PDP context can be either primary or secondary. In LTE, PS data connections are referred to as EPS bearers:
EPS bearers are conceptually equivalent to the legacy PDP contexts, which are often referred to for sake of
simplicity. Similarly to a PDP context, the EPS bearer can be a default (primary) or dedicated (secondary) one.
The initial EPS bearer established during LTE attach procedure is actually a default EPS bearer. A secondary
PDP context uses the same IP address of a primary PDP context (the usual PDP context activated e.g. via
dial-up). The Traffic Flow Filters for such secondary contexts shall be specified according to 3GPP TS 23.060
[10].
The typical usage of the secondary PDP contexts is in VoIP calls, where RTP (speech) packets are conveyed on
one PDP context (e.g. the primary one) with a given QoS (e.g. low reliability) whereas SIP signalling is routed on
a different PDP context (e.g. the secondary one, with the same IP address but different port numbers) with a
more reliable QoS.
A Traffic Flow Template (i.e. a filter based on port number, specifying relative flow precedence) shall be
configured for the secondary context to instruct the GGSN to route down-link packets onto different QoS flows
towards the TE.
PDP context type Activation procedure
Primary Used to establish a logical connection through the network from the UE to the GGSN with a
specifically negotiated Quality of Service (QoS).
The UE initiates the PDP context activation: it changes the session management state to active,
creates the PDP context, obtains the IP address and reserves radio resources. After the activation,
the UE is able to send IP packets over the air interface.
Secondary Used to establish a second PDP context with the same IP address and the same APN as the
primary PDP context.
The two contexts may have different QoS profiles, which makes the feature useful for applications
that have different QoS requirements (e.g. IP multimedia); QoS is applied based on port number
addressing.
On all other modules, at most 2 secondary PDP contexts may be associated to a primary PDP context and
at most 2 secondary PDP contexts can be activated, since the maximum number of PDP contexts, both
normal and secondary, is always 3.
SARA-R4 / SARA-N4
The secondary PDP contexts are not supported.
13.1.2î™–î™–î™–î™–Multiple PDP contexts
Two PDP context types are defined:
• "external" PDP context: IP packets are built by the DTE, the MT's IP instance runs the IP relay function only;
• "internal" PDP context: the PDP context (relying on the MT's embedded TCP/IP stack) is configured,
established and handled via the data connection management AT commands.
Multiple PDP contexts are supported. The DTE can access these PDP contexts either alternatively through
the physical serial interface, or simultaneously through the virtual serial ports of the multiplexer (multiplexing
mode MUX), with the following constraints:
• Using the MT's embedded TCP/IP stack, only a internal PDP context is supported. This IP instance supports
up to 7 sockets;
• Using only external PDP contexts, it is possible to have at most 3 IP instances (with 3 different IP addresses)
simultaneously active. If in addition the internal PDP context is used, at most 2 external PDP contexts can
be activated.
SARA-R4 / SARA-N4
Multiple PDP contexts and internal PDP contexts are not supported.
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