layer3 work / issues

Harald Welte laforge at
Tue Mar 30 01:37:53 UTC 2010

On Mon, Mar 29, 2010 at 01:39:21PM +0200, Andreas.Eversberg wrote:
> hi harald,
> >> must random value in chan_request change on every resend or only on
> >> every RR establishment? (currently it changes on every RR
> >> establishment only.)
> >
> >as far as I know, it has to change on every retransmission.  Dieter is
> >probably the person who knows all RACH aspects in detail, maybe he can
> >comment on this.
> from the specs it is quite clear that every access burst has different
> random number when resending. but how does the network know if the burst
> is from the same phone but retransmitted? 

it does not know, and I think according to the spec it should not know.

The rationale might be that if two phones chose the same random value
and keep retransmitting it, they will never get out of their collision.

> in case of poor uplink many bursts may be resent. will the network
> allocate a channel for every burst received and waits for timeout? (if
> this is the case, emergency calls could quickly 'evacuate' the cell.)

yes, this is the case.  however, RACH retransmissions are spaced large
enough that a phone will detect the immediate assignment on the downlink
before sending the next RACH burst.

- Harald Welte <laforge at> 
"Privacy in residential applications is a desirable marketing option."
                                                  (ETSI EN 300 175-7 Ch. A6)

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