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Matthew Fredrickson matt at fredricknet.netIs the data dump output from /dev/dahdi/1 the output of a single timeslot (bchan=1), or this in clear channel mode with all timeslots bonded together in DAHDI (clear=1-31)? Matthew Fredrickson On Tue, Feb 8, 2011 at 12:02 PM, Harald Welte <laforge at gnumonks.org> wrote: > Hi all, > > Some people have been working together in order to finally start with > support of the Ericsson RBS2308 (and similar models) in OpenBSC. > > The biggest issue so far is bringing up the actualy LAPD on the E1/T1 link. > It seems Ericsson is using some dynamic timeslot configuration between BSC > and BTS, so unlike e.g. Siemens, you cannot explicitly configure the OML E1 > timeslot on the BTS using local configuration tools. > > The current working assumption is: Somehow the BSC produces bit-patterns on the > E1 link and uses them to let the BTS know where to start LAPD for OML. > > One contributor was friendly enough to do raw bit-traces of a Racal 6113 > connected to the Ericsson RBS, and they look like this: > > Racal to BTS > > Initialization > > openbsc:/etc/dahdi# cat /dev/dahdi/1 | hexdump > 0000000 aaaa aaaa aaaa aaaa aaaa aaaa aaaa aaaa > * > 00092e0 aaaa aaaa aaaa aaaa aaaa aaaa aaaa 55aa > 00092f0 ffff ffff ffff ffff ffff ffff ffff ffff > * > 0009600 ffff ffff ffff ffff ffff ffff ffff 7e7e > 0009610 7e7e 7e7e 7e7e 7e7e 7e7e 7e7e 7e7e 7e7e > * > 00096b0 7e7e 7e7e 7e7e 7e7e 7e7e 7e7e 7e7e 5f7e > 00096c0 3e5f 49ce cfef cfcf cfcf cfcf cfcf cfcf > 00096d0 cfcf cfcf cfcf cfcf cfcf cfcf cfcf cfcf > * > > > I've written a small C program to do soft-hdlc decode. > > * a pattern of alternating bits (0xaa) > * a pattern of all-1 bits(0xff) > * a sequence of FLAG symbols (01111110) > * a HDLC message FA 7D 7F 4E F2, which is a TEI=62/SAPI=62 SABME > (SAPI 62 / TEI62 is configured for OML on the BTS) > > The interesting part is: > > 1) this is a SABME from BSC to BTS, whereas GSM 08.56 > specifically says the BTS is the TE and the BSC the NT > 2) we have not seen any TEI manager related messages(L2ML) > > > Keep alives afterwards, about every 8 seconds > > 001d5e0 cfcf cfcf cfcf ebcb 04e4 a805 f323 f3f3 > 001d5f0 f3f3 f3f3 f3f3 f3f3 f3f3 f3f3 f3f3 f3f3 > * > 0031630 f3f3 f2f3 f9fa 0101 086a fcfc fcfc fcfc > 0031640 fcfc fcfc fcfc fcfc fcfc fcfc fcfc fcfc > * > 0045680 fcfc fcfc fcfc fcfc fcfc fcfc bebe 4040 > 0045690 825a 3f3f 3f3f 3f3f 3f3f 3f3f 3f3f 3f3f > 00456a0 3f3f 3f3f 3f3f 3f3f 3f3f 3f3f 3f3f 3f3f > * > 00596e0 3f3f 2f3f 90af 1610 8fa0 cfcf cfcf cfcf > 00596f0 cfcf cfcf cfcf cfcf cfcf cfcf cfcf cfcf > * > 006d730 cfcf cfcf cfcf cfcf cbcf e4eb 0504 23a8 > 006d740 f3f3 f3f3 f3f3 f3f3 f3f3 f3f3 f3f3 f3f3 > * > 0081790 faf2 01f9 6a01 fc08 fcfc fcfc fcfc fcfc > 00817a0 fcfc fcfc fcfc fcfc fcfc fcfc fcfc fcfc > * > 00957e0 fcfc fcfc fcfc befc 40be 5a40 3f82 3f3f > 00957f0 3f3f 3f3f 3f3f 3f3f 3f3f 3f3f 3f3f 3f3f > > If you decode this, you get > > FA 7D 01 01 AD 20 (LAPD RR) > FA 7D 01 01 21 AC (LAPD RR) > FA 7D 01 01 AD 20 (LAPD RR) > FA 7D 01 01 AD 20 (LAPD RR) > FA 7D 01 01 AD 20 (LAPD RR) > FA 7D 01 01 AD 20 (LAPD RR) > FA 7D 01 01 AD 20 (LAPD RR) > > > If we look at the BTS to Racal 6113 side: > > Initialization > > openbsc:/etc/dahdi# cat /dev/dahdi/1 | hexdump > 0000000 e7e7 e7e7 e7e7 e7e7 e7e7 e7e7 e7e7 e7e7 > * > 000fe00 e7e7 e7e7 e7e7 e7e7 e7e7 e7e7 e5e7 f3f5 > 000fe10 1039 f971 f9f9 f9f9 f9f9 f9f9 f9f9 f9f9 > 000fe20 f9f9 f9f9 f9f9 f9f9 f9f9 f9f9 f9f9 f9f9 > * > > > Keep Alives, every 8 seconds > > > 0023e40 f9f9 f9f9 f9f9 f9f9 f9f9 7c7d 8080 04b5 > 0023e50 7e7e 7e7e 7e7e 7e7e 7e7e 7e7e 7e7e 7e7e > * > 0037ea0 5f5f 2020 412d 9f1f 9f9f 9f9f 9f9f 9f9f > 0037eb0 9f9f 9f9f 9f9f 9f9f 9f9f 9f9f 9f9f 9f9f > * > 004bef0 9f9f 9f9f 9f9f 9f9f 979f c8d7 0b08 4750 > 004bf00 e7e7 e7e7 e7e7 e7e7 e7e7 e7e7 e7e7 e7e7 > * > 005ff40 e7e7 e7e7 e7e7 e7e7 e7e7 e7e7 e7e7 f5e5 > 005ff50 02f2 d402 f911 f9f9 f9f9 f9f9 f9f9 f9f9 > 005ff60 f9f9 f9f9 f9f9 f9f9 f9f9 f9f9 f9f9 f9f9 > * > 0073fa0 f9f9 f9f9 f9f9 7c7d 8080 04b5 7e7e 7e7e > 0073fb0 7e7e 7e7e 7e7e 7e7e 7e7e 7e7e 7e7e 7e7e > * > 0087ff0 7e7e 7e7e 7e7e 7e7e 7e7e 7e7e 5f7e 205f > 0088000 2d20 1f41 9f9f 9f9f 9f9f 9f9f 9f9f 9f9f > 0088010 9f9f 9f9f 9f9f 9f9f 9f9f 9f9f 9f9f 9f9f > * > 009c050 9f9f 9f9f 979f c8d7 0b08 4750 e7e7 e7e7 > 009c060 e7e7 e7e7 e7e7 e7e7 e7e7 e7e7 e7e7 e7e7 > * > > Decoded, we get: > > FA 7D 73 60 3A (LAPD UA) > FA 7D 01 01 AD 20 (LAPD RR) > FA 7D 25 25 AD 20 (LAPD unknown??) > FA 7D 01 01 AD 20 (LAPD RR) > FA 7D 01 01 AD 20 (LAPD RR) > FA 7D 01 01 AD 20 (LAPD RR) > FA 7D 01 01 AD 20 (LAPD RR) > FA 7D 01 01 AD 20 (LAPD RR) > > So as a summary, it seems that > > 1) the BSC applies some magic pattern (0xaa / 0xff) > 2) the BSC establishes the LAPD session for OML TEI/SAPI > 3) there is no L2ML, contrary to lots of Ericsson Abis documentation > that you can find online. > > We'll continue our attempts and see if we can get the OML up... > > -- > - Harald Welte <laforge at gnumonks.org> http://laforge.gnumonks.org/ > ============================================================================ > "Privacy in residential applications is a desirable marketing option." > (ETSI EN 300 175-7 Ch. A6) > >