A.2 False Z sequence detection
08.203GPPRate Adaptation on the Base Station System - Mobile Service Switching Centre (BSS-MSC) InterfaceTS
The Framing Pattern Substitution algorithm presented in subclause 10.2 ensures sure that all the Z sequences found in the original sub frame are removed, but it shall be checked that the transformations performed do not introduce new unwanted Z sequences.
The goal of this subclause is to show that the transformed sub frame does not contain new Z sequences introduced by the algorithm itself.
The coding of the ZSP is the key point to avoid such an emulation. The different cases are considered below.
1 : Sequence ZSP
The worst case is when the address is equal to 1 :
1 | C | A0 | A1 | A2 | A3 | A4 | 1 |
1 | 0 | 0 | 0 | 0 | 0 | 1 | 1 |
There is a maximum of 5 zeroes.
2 : Sequence Di / ZSP.
By definition, a data block always ends up with a one (except the last one of the message) and the ZSP always starts with a 1.
3 : Sequence ZSP / Di
ZSP always ends up with a 1 and Di has a maximum of 7 zeroes : it is not possible to find 16 zeroes in a row.
4 : Sequence Di / Dj
Di is not the last data block of the message.
As already mentioned, Di ends up with a one (except the last one) : this is the same case as 3.
5 : Sequence Zi / D or D / Zi
This case only occurs when there is no substitution. In this case, the Zi bit close to the D field is always a one: this does not change the number of zeroes in sequence.
6 : Sequence last Di / new framing pattern
The last D sequence can end up with up to 7 zeroes, followed by the 16 zeroes of the next frame.
There is anyhow no ambiguity, when considering that the framing pattern is made up of 16 zeroes followed by a one.
7 : Sequence last Di / Z bit of the next sub frame
The last D sequence can end up with up to 7 zeroes, followed in the worst case by Z=0 and then a ZSP. As a ZSP starts with a one, this makes a maximum of 8 zeroes in a row.
8 : Sequence ZSP / ZSP (not shown on the figure)
This case arrives when the original message has at least 16 zeroes in a row.
As the ZSP element always starts and ends up with a one, this always induces two consecutive ones.
Annex B (informative):
Change History
Change history | |||||||
Date | TSG # | TSG Doc. | CR | Rev | Subject/Comment | Old | New |
s27 | A005 | Synchronisation | 5.3.0 | 7.0.0 | |||
s29 | A006 | Introduction of EDGE channel codings into the specifications | 7.0.0 | 8.0.0 | |||
s30 | A007 | Asymmetric channel coding | 8.0.0 | 8.1.0 | |||
09-2000 | TSG#09 | NP-000551 | A008 | 1 | 32 kbit/s UDI/RDI multimedia in GSM | 8.1.0 | 8.2.0 |
12-2000 | TSG#10 | NP-000604 | A009 | Removal of 1200/75 bit/s data rate and clean-up | 8.2.0 | 8.3.0 | |
03-2001 | TSG#11 | NP-010040 | A013 | Correction of downgrading procedure for HSCSD | 8.3.0 | 8.4.0 |