Cellular Network Infrastructure

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h1. Configuring the ip.access nano3G

h2. IP address

The ip.access nano3G will obtain an IP address from the DHCP server in your network. Ways to find out:

* Run @abisip-find@ (currently in the osmo-bsc.git repository), which should find the nano3G (despite no Abis interface being present). Find the @abisip-find@ output matching the MAC address printed on the sticker next to the power jack.

* Watch wireshark, filtering on 'BOOTP' while the nano3G starts up.

* Look it up in your DHCP server's list of leases.

For this text, let's assume the IP address it obtained is 192.168.0.124.

h2. Initial Config

Once off, configure:

* the MCC + MNC,

* the UARFCN (i.e. the frequencies to transceive on) and

* the LAC and RAC (max. 256)

* the Cell ID composed by RNC (12 bits) and HNB C-ID (16 bits)

You can do this on the _dmi_ console reachable by telnet:

<pre>

telnet 192.168.0.124 8090

dmi>

</pre>

On the dmi, enter commands like these:

<pre>

# PLMN Id == MCC + MNC

set mcc="901"

set mnc="98"

# [uarfcnDownlink, 1900 MHz band], [scramblingCode], [dummyCellId]

set rfParamsCandidateList=({9800, 401, 1})

# [lac], [rac]

set lacRacCandidateList=({10422, (99)})

# cellid == RNCID<<16+HNBCID

set hnbCId=1

set rncIdentity=0

</pre>

These settings persist across nano3G power down.

*All of the above settings require a reboot of the nano3G to take effect.*

h2. After Every Boot: Starting Operation

Every time you boot the nano3G, you need to

* set the IP address the nano3G will find the HNB-GW at.

* 2061 = set cell parameters

* 1216 = unlock ap

* activate HNB-GW connection

* set csg to open access so that any IMSI can register

Enter the _dmi_...

<pre>

telnet 192.168.0.124 8090

dmi>

</pre>

...and issue commands like:

<pre>

set hnbGwAddress="192.168.0.132" 

action 2061

action 1216

action establishPermanentHnbGwConnection

set csgAccessMode=CSG_ACCESS_MODE_OPEN_ACCESS

</pre>

If the telnet interface for dmi is closed (after you quit it), you can still issue commands using the [[Configuring_the_ipaccess_nano3G#SSH-Access|console]] (here to close the connection to the HNB-GW)

<pre>

/opt/ipaccess/DMI/ipa-dmi -c 'action terminatePermanentHnbGwConnection'

</pre>

h2. SSH Access

The nano3G come with a root password of 'newsys':

<pre>

ssh root@192.168.0.124

password: newsys

</pre>

In case you are using a recent version of the OpenSSH-client you'll get the following error message while trying to connect:

_Unable to negotiate with 192.168.0.124 port 22: no matching key exchange method found. Their offer: diffie-hellman-group1-sha1_

Starting with OpenSSH version 7.0 support for the 1024-bit diffie-hellman-group1-sha1 key exchange was disabled by default at run-time.

Furthermore, the ciphers supported by the nano3G may be disabled by default. To enable both manually:

<pre>

ssh -o KexAlgorithms=+diffie-hellman-group1-sha1 -c aes128-cbc root@192.168.0.124

</pre>

h2. NTP

Be sure that the nano3G is able to resolve the DNS record _0.ipaccess.pool.ntp.org_ and can connect the the corresponding NTP servers.

Without syncronized NTP the nano3G does not bring up the TRX and it even do not try to connect to the hnbGw.

A workaround is to edit the @/etc/hosts@ file on the nano3G (via SSH) and add an entry to resolve 0.ipaccess.pool.ntp.org to your local NTP server's IP address (which requires re-mounting the root file system in read-write mode...).

h2. Logging

When logged in via SSH, you can view the live logging here:

<pre>

ls /tmp/iapclogs/trace_*.log

</pre>

h2. Closed Mode

You can also set csgAccessMode to closed and allow only specific IMSIs:

<pre>

set csgAccessMode=CSG_ACCESS_MODE_CLOSED_ACCESS

# IMSI, 1:allowed/2:not allowed, phone number (only for "Closed Access")

set accessControlList = ({"001010123456015",  1, "81084"},{"001010123456025", 2, "81025"})

</pre>

(The phone number is actually not relevant)

h2. Neighbour Cells

If you have multiple cells running you can add the other to the neighbouring cell list over dmi.

<pre>

set neighbourListPopulation=STATIC_ONLY

# ({band:ENUM, dlUarfcn:INT, scramblingCode:INT, mcc:STRING, mnc:STRING, lac:INT, rac:INT, rncId:INT, cellId:INT, qQualMin:INT, qRxlevMin:INT, txDiversityIndicator:ENUM, primaryCpichTxPower:INT, hcsPriority:INT, qHcs:INT, deltaQhcs:INT}, ...)

set staticUmtsNeighbourList_001=({UMTS_BAND_2, 9800, 401, "262", "42", 10422, 99, 0, 1, -24, -119, TX_DIVERSITY_DISABLED, -10, 0, 0, -5},)

</pre>

h1. Peculiarities and Tips

h2. Exiting the dmi while keeping it alive

When you exit the dmi telnet by hitting Ctrl-C, it will not be available anymore until you reboot the nano3G.

Every connection attempt will then end in

<pre>

dmi> Connection closed by foreign host.

</pre>

However, if you end your session by the telnet escape character and quitting, the dmi remains open for further connections. Usually that means: hit Ctrl-] (Ctrl and closing square brace) and then enter 'quit':

<pre>

dmi> ^]

telnet> quit

</pre>

h2. UE Register

The nano3G apparently passes the same identity received from the UE through to

the HNBAP UE Register Request message. This means that when the UE sends a

TMSI, the UE Register Request received by osmo-hnbgw contains no IMSI.

In this scenario, the problem is that Paging apparently does not (always) work.

So even though we have working code that allows HNBAP registration with

a TMSI, that means that you can't (always) reach the UE from the CN.

This is not always the case, sometimes the nano3G can well page UEs that have

registered by TMSI. Vague idea: it may be that it needs to have seen the IMSI

once after power-cycling, e.g. after a closed-mode registration, and then

TMSI registration will not harm Paging. (TODO: clarify this)

The VTY configuration option to allow TMSI-only attaching to HNBGW, which

possibly helps to shorten your dev cycle but may harm paging, is:

<pre>

hnbgw

 iuh

  hnbap-allow-tmsi 1

</pre>

Legacy workaround: connect the phone to a different network between retries (being

rejected suffices). That causes the UE to discard its TMSI and then use the IMSI

for the next registration.

A [[Configuring the ipaccess nano3G#Closed-Mode|closed csgAccess]] with explicit IMSIs could help here to enforce that a UE

indeed sends its IMSI to the nano3G and hence Paging should work.

See also #1924.

h2. id-Reset

The nano3G seems to *not* send an id-Reset message upon connecting to the HNB-GW.

h2. Location Update failure due to timeout

If a UE seems to connect successfully at first but fails by timeout because the final

"TMSI Reallocation Complete" message is missing, this might be due to misconfiguration:

the CN is sending the wrong LAC or the PLMN-ID (NCC/MNC) is configured wrongly.

This might be confusing in the sense that a complete LU worked once but not after that;

GMM Attach may be successful; Security Mode Commands succeed; and so forth.

Still the solution might be simply to fix the mobile network code in the osmo-msc.cfg.

h2. RAB Assignment needs IuUP ACK Initialization

IuCS uses UP encapsulated in RTP. The UP starts off by sending an Initialization, replied

upon by an ACK Initialization.

The nano3G seems to not reply with an ACK when it receives an IuUP Initialization frame.

Thus it is not possible to merely echo its own RTP packets back to itself; instead, the

first RTP frame received from the nano3G (that is an IuUP Initialization) can be changed

to an ACK Initialization by writing 0xe4 to the first payload byte. Sending this back to

the nano3G then results in successful RAB Assignment.

(With the SysmoCell5000, echoing its own Initialization back to itself results in an ACK

being sent, which we can also echo back to itself, so mere echoing works there.)

A hack to make the nano3G work is currently on the "3G master" (the vlr_3G branch),

because it does not seem to harm other femto cells: the commit's summary is

"mgcp: hack RAB success from nano3G: patch first RTP payload", see "cgit":http://git.osmocom.org/openbsc/log/?h=vlr_3G.

See also #1712#note-21 and the following two comments.