Chapter 2
GSM Call Mode Operation
GSM tests
4460 GSM System Option and 4468 EDGE System Option
Version 12.20
63
Fast BER Live Display
The Fast BER is similar to a BER measurement on the class II bits. The main differ-
ence is, that in Fast BER, there are only ‘class II bits’ and all 456 bits of a voice
block are used for the measurement, while there are only 78 class II bits in a
standard voice block.
How to read the Fast BER results display
Round-trip
delay
The round-trip delay is the number of TDMA frames
between the reception of the first burst of a particular
voice block at the mobile and the transmission of the first
burst of the same voice block on the uplink. According to
GSM/ETSI recommendations, the round-trip delay should
be less than 26 TDMA frames.
The round-trip delay is a measure of how fast the mobile
can receive, decode and encode data.
Notes:
– Using a full-rate TCH, a voice block is spread out on
eight TDMA frames. Consequently, the mobile has to
gather those eight TDMA frames in order to be able to
decode the voice block sent initially. After the voice
block has been decoded, the mobile must encode it
again and send it back to the 4400. Therefore, the
minimum round-trip delay will be 8 TDMA frames on
a full-rate TCH.
If there are SACCH frames or idle frames between the
single blocks, the typical round-trip delay is 9 or 13
frames.
– A round-trip delay of 26 TDMA frames equals roughly
120 ms.
– More details on speech frames and diagonal inter-
leaving can be found in section
“Voice coding”
.
Counter
Channel
In the current software release, this display field has no
meaning. Therefore, six hyphens ---
---
are displayed.