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