u-blox Multiplexer User Manual
UBX-13001887 - R12
C1-Public www.u-blox.com
Multiplexer
3GPP 27.010 Mux implementation in cellular modules
Application note
Abstract
This document provides basic multiplexer information and a short description of how to implement
a multiplexer driver according to 3GPP TS 27.010. This document serves as a reference to customers
developing proprietary multiplexer drivers for communication with u-blox cellular modules using
several virtual channels simultaneously.
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Document information
Title
Multiplexer
Subtitle
3GPP 27.010 Mux implementation in cellular modules
Document type
Application note
Document number
UBX-13001887
Revision and date
R12
26-Oct-2020
Disclosure restriction
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This document applies to the following products:
Product name
LEON-G1 series
LISA-U2 series
SARA-G3 series
SARA-G4 series
SARA-U2 series
LISA-C2 series
TOBY-L2 series
TOBY-R2 series
LARA-R2 series
SARA-R5 series
u-blox or third parties may hold intellectual property rights in the products, names, logos and designs included in this
document. Copying, reproduction, modification or disclosure to third parties of this document or any part thereof is only
permitted with the express written permission of u-blox.
The information contained herein is provided “as is” and u-blox assumes no liability for its use. No warranty, either express or
implied, is given, including but not limited to, with respect to the accuracy, correctness, reliability and fitness for a particular
purpose of the information. This document may be revised by u-blox at any time without notice. For the most recent
documents, visit www.u-blox.com.
Copyright © u-blox AG.
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Contents
Document information ................................................................................................................................ 2
Contents .......................................................................................................................................................... 3
1 Introduction ............................................................................................................................................. 5
1.1 Features and implementations ................................................................................................................ 6
1.1.1 TOBY-L2, TOBY-R2, LARA-R2, SARA-R5, SARA-U2, LISA-U2, SARA-G3, SARA-G4,
LEON-G1 series ................................................................................................................................................. 6
1.1.2 LISA-C2 series ..................................................................................................................................... 7
2 System parameters .............................................................................................................................. 8
2.1 Acknowledgement timer (T1).................................................................................................................... 8
2.2 Maximum frame size (N1) .......................................................................................................................... 9
2.3 Maximum number of retransmissions (N2) .......................................................................................... 9
2.4 Window size (k) ............................................................................................................................................ 9
2.5 Response timer for multiplexer control channel (T2) .......................................................................... 9
2.6 Response timer for wake-up procedure (T3) ....................................................................................... 10
2.7 Multiplexer control channel setup mode (subset) ............................................................................. 10
3 Multiplexer packet format for basic option ................................................................................. 11
3.1 Flag ................................................................................................................................................................ 11
3.2 Address ........................................................................................................................................................ 11
3.3 Control .......................................................................................................................................................... 11
3.3.1 Set Asynchronous Balanced Mode (SABM) command ..............................................................12
3.3.2 Unnumbered Acknowledgement (UA) response .........................................................................12
3.3.3 Disconnected Mode (DM) response ...............................................................................................12
3.3.4 Disconnect (DISC) command ..........................................................................................................12
3.3.5 Unnumbered Information with Header check (UIH) and unnumbered Information (UI)
frames ...............................................................................................................................................................12
3.4 Length indicator ........................................................................................................................................ 13
3.5 Information field ........................................................................................................................................ 13
3.6 Frame checking sequence field (FCS) .................................................................................................. 13
4 AT command / data interface .......................................................................................................... 14
4.1 AT command profiles ............................................................................................................................... 14
4.2 UART lines state during MUX protocol execution .............................................................................. 14
4.2.1 Exceptions for RING and DCD lines on UART. ............................................................................. 15
4.2.2 Break signal in a MSC command packet from TE ...................................................................... 15
5 Linux reference driver ........................................................................................................................ 16
5.1 Gsm0710.c .................................................................................................................................................. 16
5.1.1 Main ..................................................................................................................................................... 16
5.1.2 openDevicesAndMuxMode .............................................................................................................. 17
5.2 Buffer ............................................................................................................................................................ 17
6 Notes for developers .......................................................................................................................... 18
6.1 Enabling multiplexer trace messages .................................................................................................. 18
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6.2 Frame size .................................................................................................................................................. 18
6.3 Flow control on virtual channels ............................................................................................................ 18
6.4 Multiplexer start-up procedure .............................................................................................................. 19
6.5 Multiplexer close-down procedure......................................................................................................... 19
Appendix ....................................................................................................................................................... 20
A Glossary ................................................................................................................................................. 20
B Multiplexer transactions example ................................................................................................. 21
B.1 Multiplexer protocol establishment .......................................................................................................21
B.2 Multiplexer protocol AT command communication .......................................................................... 22
B.3 Multiplexer protocol close-down ............................................................................................................ 22
C Multiplexer debug command .......................................................................................................... 23
C.1 Debug command +UMUX ........................................................................................................................ 23
C.1.1 Defined values ................................................................................................................................... 24
C.2 Debug command +XL1SET="muxtron:<value>" ................................................................................. 24
C.2.1 Defined values ................................................................................................................................... 24
C.3 Debug with +TRACE AT command ....................................................................................................... 25
C.3.1 Defined values ................................................................................................................................... 25
Related documents ....................................................................................................................................26
Revision history ...........................................................................................................................................26
Contact ........................................................................................................................................................... 27
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1 Introduction
☞ The multiplexer protocol is not supported by TOBY-L2 "00" product versions.
This document describes the implementation of the multiplexer protocol for cellular modules. The
following symbols are used to highlight important information within the document:
☞ An index finger points out key information pertaining to integration and performance.
⚠ A warning symbol indicates actions that could negatively impact performance or damage the
device.
u-blox cellular modules support the 3GPP TS 27.010 multiplexer protocol [3]. It is possible to emulate
several virtual connection channels on a single physical interface to access the module concurrently
(e.g. it is possible to read phonebook contacts while receiving GPRS data).
Each channel between the TE and UE is called a Data Link Connection (DLC) and is separately and
sequentially established.
The multiplexer has three operating options:
• basic
• advanced without error recovery
• advanced with error recovery
u-blox cellular modules only support the basic mode.
Module
Control channel
AT commands /
data connection
GNSS
tunneling
SAP (SIM
Access Profile)
Remarks
TOBY-L2
Channel 0 (DLC0)
Channel 1 - 5
Multiplexer control channel as described in
3GPP TS 27.010 [3]
TOBY-R2
Channel 0 (DLC0)
Channel 1 - 5
LARA-R2
Channel 0 (DLC0)
Channel 1 - 5
Channel 61
SARA-R5
Channel 0 (DLC0)
Channel 1 - 32
Channel 43
LEON-G1
Channel 0 (DLC0)
Channel 1 - 5
Channel 6
SARA-G300
Channel 0 (DLC0)
Channel 1 -2
Channel 6
SARA-G310
Channel 0 (DLC0)
Channel 1 - 2
Channel 6
SARA-G340
Channel 0 (DLC0)
Channel 1 - 5
Channel 6
SARA-G350
Channel 0 (DLC0)
Channel 1 - 5
Channel 6
SARA-G4
Channel 0 (DLC0)
Channel 1 - 5
Channel 64
SARA-U2
Channel 0 (DLC0)
Channel 1 - 5
Channel 6
Channel 7
LISA-U2
Channel 0 (DLC0)
Channel 1 - 5
Channel 6
Channel 75
LISA-C2
Channel 0 (DLCI)
Channel 1 (DLCI1)
as AT channel
Channel 2 (DLCI2)
as data channel
Channel 3
(DLCI3)
AT channel is used for all AT commands
except the ATD#777 command, which sets
up a data call. Data channel is used for
data calls; it is only set up by ATD#777.
Table 1: Multiplexer configuration on u-blox cellular modules
1
Not supported by LARA-R204-02B and LARA-R211-02B-00
2
Channel 3 only available in case of single UART configuration or in case the AUX UART is not configured as AT interface
3
Channel 4 only available in case of single UART configuration or in case the AUX UART is not configured as GNSS tunneling
interface
4
Not supported by SARA-G450-00C
5
Not supported by LISA-U200-00S
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1.1 Features and implementations
1.1.1 TOBY-L2, TOBY-R2, LARA-R2, SARA-R5, SARA-U2, LISA-U2,
SARA-G3, SARA-G4, LEON-G1 series
• Multiplexer Basic Option compliant to 3GPP TS 27.010 [3] is supported. All the required features
are supported, within the limits identified in this document. If not specified in the document, the
optional features described in 3GPP technical specification are not supported.
• The multiplexer can operate only at a fixed baud rate. Once the +CMUX AT command is sent and
the autobauding is active (AT+IPR=0, where applicable), a switch to fixed rate is performed as soon
as the multiplexer protocol is successfully activated. It is strongly recommended to enable the
highest baud rate supported by the UE.
• Every instance has its own user profile. For additional information, see section 4.
• Every instance has its own independent flow control, implemented by means of MSC packets (for
more details, 3GPP TS 27.010 [3]).
• Software flow control (XOn/XOff) on the DLCs is not supported and should be disabled.
• The response to only one test command (as specified in 3GPP TS 27.010 [3], section 5.4.6.3.4) is
supported, since it is presumed that, when the connection UE-TE is established, it will not be lost.
This behavior prevents from looping TEST traffic.
• It is recommended to use Hardware Flow Control (RTS/CTS) on the multiplexer physical port. If the
ME power saving is enabled (e.g. AT+UPSV=1) and the UART interface is used this configuration
is mandatory.
• The flow control configuration of the multiplexer physical port is not changed when the multiplexer
protocol is established (the configuration previously selected via the &K or +IFC AT commands is
retained).
• Multiplexer timers and retransmission (T1, T2, T3, and N2, see 3GPP TS 27.010 [3]) have limited
support. For more details, see section 2.
• The multiplexer protocol can be activated over SPI interface (where available).
• No need to use multiplexer protocol with USB interface (where available). USB multiplexing
capability based on multiple CDCs should be used.
• The multiplexer is supported only on UART and SPI interfaces. Only one interface can be used at a
time.
1.1.1.1 Multiplexer Control Channel messages (as specified in 3GPP TS
27.010 [3], section 5.4.6.3)
• Parameter Negotiation (PN) command is not supported.
• Multiplexer Power control and wake-up mechanism via power saving control (PSC) command (as
described in the 3GPP TS 27.010 [3]) is not supported. If power saving is enabled, power saving
information towards the TE is indicated by the module CTS line (module output).
• Flow Control On Command (FCon) is not supported.
• Flow Control Off Command (FCoff) is not supported.
• Remote Port Negotiation (RPN) command is not supported.
• Remote Line Status (RLS) command is not supported.
• Service Negotiation Command (SNC) is not supported.
☞ On LISA-U2 / SARA-G3 / LEON-G1 series, the Hardware Flow Control is forced active on the
multiplexer physical port, when the multiplexer protocol is established. This configuration cannot
be subsequently changed.
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1.1.2 LISA-C2 series
The multiplexer implementation has the following limitations:
• When an AT command is sent on Channel 1, the application must wait for a response prior to
sending the ATD#777 command on Channel 2 and vice versa.
• When a data call is active on Channel 2, the application cannot use any AT commands that require
data services on Channel 1. This includes FTP, UHTTP, and sockets. For more details, see u-blox
C200 AT commands manual [4].
• The +CMUX AT command cannot be used again once the multiplexer has been enabled.
• The UART baud rate cannot be changed after the multiplexer enabling, so the +IPR command
should be used to set the desired baud rate prior to using the +CMUX AT command.
• The multiplexer frame size, N1, must typically be greater than 64; below this size there may be
issues with the host to modem PPP data transfers.
• Multiplexer timers and retransmission (T1, T2, T3, and N2, see 3GPP TS 27.010 [3]) have limited
support.
• Software Flow control (XOn/XOff) on the DLCs is not supported and should be disabled.
• Multiplexer Power Control and wake-up mechanism (as described in the 3GPP 27.010 Technical
Specification) is not supported.
• It is recommended to use Hardware Flow Control (RTS/CTS) on the multiplexer physical port.
• No need to use the multiplexer protocol with USB interface (where available). USB multiplexing
capability based on multiple CDCs should be used.
• The multiplexer is supported only on UART and SPI interfaces. Only one interface can be used at a
time.
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2 System parameters
The +CMUX AT command starts the multiplexer operation. This command enables the multiplexer to
start up the multiplexer control channel. The TE multiplexer initiates this by sending an SABM frame
on DLCI 0.
Once the multiplexer channel is established, other DLCs can be established. The multiplexer may
negotiate the parameters associated with each DLC prior to its establishment or use the default
values.
System parameters T1, N1, N2 and k can be configured by the multiplexer control channel, or the
default values given here can be used. T2, T3 and subset system parameters are set by means of the
+CMUX AT command.
In the basic mode, T1 is only used in case of SABM and DISC commands sent by the module. The SABM
command is never sent, because the DLC establishment procedure can only be initiated by the TE.
The DISC would only be triggered in response to a T2 timeout.
☞ For LISA-U2, SARA-U2, TOBY-R2 and LARA-R2 series, T1 and T2 timers and the retransmission
mechanism are not implemented.
☞ For SARA-R5 series, T1 timer is not implemented.
☞ For LEON-G1, SARA-G3, SARA-U2, LISA-U2, TOBY-L2, TOBY-R2, LARA-R2 and SARA-R5 series,
only the MSC command requires a response, and is therefore the only one that involves T2. On
LEON-G1 and SARA-G3 series, in case retransmission reaches the N2 number, the not responding
DLC is released (i.e. the DCE starts a DISC for the not responding DLC).
☞ In SARA-U2, LISA-U2, TOBY-R2 and LARA-R2 series, instead, T2 is not implemented to avoid
restrictions of the application response time.
☞ For all the modules, T3 is not implemented. This is because the wake-up procedure is not
supported, since the power saving control relies on the underlying hardware (UART, SPI, etc.)
power saving control mechanism.
☞ For more details about command syntax, see u-blox AT commands manual [1] or SARA-R5 series
AT commands manual [5] and AT commands examples application note [2].
2.1 Acknowledgement timer (T1)
The acknowledgement timer governs the time that a station waits for an acknowledgement before
resorting to other actions (e.g. transmitting a frame). The two stations may operate with different T1
values.
☞ For LEON-G1 and SARA-G3 series, this value is fixed at 253.
☞ For LISA-U2, SARA-U2, TOBY-L2, TOBY-R2, LARA-R2, SARA-R5 series, the T1 timer is not
implemented and the requested T1 value is not considered.
☞ For the LISA-C2 series, this timer is not implemented; if a T1 value is set then it will be ignored.
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2.2 Maximum frame size (N1)
The N1 parameter defines the maximum number of octets that may be contained in an information
field. It does not include octets added for transparency purposes.
The default value for the basic mode is 31 octets. The range is from 1 to 1509 octets.
☞ For the LISA-C2 series, this value does not include octets added for transparency purposes. The
default value for this mode is 32 octets. 0 should return error, the valid range goes from 1 to 256
octets, any other value returns error.
2.3 Maximum number of retransmissions (N2)
The N2 parameter defines the maximum number of times that a station re-attempts a procedure
requiring a response. The two stations may operate with a different value of N2.
☞ For LEON-G1, SARA-G3, TOBY-L2, SARA-R5 series, the range is 0-5, with the default value at 3.
☞ For LISA-U2, SARA-U2, TOBY-R2 and LARA-R2 series, the N2 value is not considered, since (as
previously described) the retransmission mechanism is not implemented. This could result in MSC
commands not being received (which cannot be avoided even if retransmission is implemented).
The TE must guarantee correct MSC command reception in all operating scenarios (especially if
the MSC commands are used to carry flow control information).
☞ For the LISA-C2 series, the retransmission mechanism is not implemented; if a value is requested,
then it will be ignored.
2.4 Window size (k)
The window size parameter (k) defines the maximum number of I frames that a DLC can have
outstanding. Since u-blox cellular modules support only the MUX basic mode (which does not
implement the Error Recovery Option) this parameter is not supported.
☞ For LISA-C2 series, this parameter is not supported.
2.5 Response timer for multiplexer control channel (T2)
The T2 timer is the amount of time that the multiplexer control channel waits before re-transmitting
a command.
T2 must be greater than T1.
☞ For LEON-G1, SARA-G3, TOBY-L2, SARA-R5 series, this value is fixed at 254.
☞ For LISA-U2, SARA-U2, TOBY-R2 and LARA-R2 series, the T2 timer is not implemented; the
requested T2 value is not considered.
☞ The LISA-C2 series does not support this parameter; if a value is set, it will be ignored.
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