Encryption - Ericsson CME 20 R6.1 Reference Manual

12

Encryption

"Encryption" is used for ciphering and deciphering of information to
and from an MS over a dedicated resource. The RBS supports two
encryption modes, either using no encryption or using a GSM
encryption algorithm. The BSC controls which encryption mode is used.
There are two product variants with different encryption algorithms
implemented:
•
•
12.1 References
/GSM:04.08/
/GSM:08.58/
12.2 Functions
12.2.1 Start Encryption at Channel Activation
By means of the CHANNEL ACTIVATION procedure /
GSM:08.58:4.1/, the BSC controls initiation of encryption mode.
Fundamentals regarding channel activation are described in chapter Call
Control.
Supported channel numbers:
•
•
•
The function is initiated when a CHANNEL_ACTIVATION message /
GSM:08.58:8.4.1/ indicating start of encryption, is received from the
BSC.
Access bursts, which are received from the MS at handover access, are
not deciphered.
12.2.2 Encryption Mode Change
By means of the START OF ENCRYPTION procedure /GSM:08.58:-
4.4/, the BSC controls initiation and change of encryption mode.
Channel numbers supported are described in the section above.
The function is initiated when an ENCRYPTION_COMMAND
message /GSM: 08.58:8.4.6/ is received from the BSC for an active
dedicated channel.
Encryption mode change is carried out according to /GSM:04.08:3.4.7/.
When encryption is active and a new ciphering key is to be loaded,
there is a period of time where the old key is used for ciphering and the
new key is used for deciphering simultaneously. Consequently, the RBS
supports independent key update for ciphering and deciphering.
EN/LZT 123 2697 R5A
1998-08-13
No encryption — GSM encryption algorithm version 1 (A5/1)
No encryption — GSM encryption algorithm version 2 (A5/2)
Bm + ACCH
SDCCH/8 + ACCH
SDCCH/4 + ACCH (and TN = 0)
© Ericsson Radio Systems AB
— All Rights Reserved —
GSM 04.08 (phase 2)
GSM 08.58 (phase 2)
Encryption
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