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1. Discuss RAB overview?

RAB Overview

 

If you are in this area (Wireless communication) for at least about a year, you would

be familiar with the ping-pongs of the messages between the two parties in thecommunication(e.g, messages between a mobile phone and Network). You can eendo some troubleshootings based on the ping-pong rule. !or e"ample, if you see #$$%

%onnection &etup# being sent from Network log and you haen#t seen #$$%%onnection %omplete# in the network log, you would say 'his may be * issue

because it doesn#t seem to send proper reply#.Then you would go to UE log and found 'RRC Connection Complete'

message were sent from RRC layer. hen there going to be long argumentbetween the two party, +ust memoriing the message seuence would not help

much. o handle this kind of situation, you should know e"actly what is supposed tohappen when a Network or * receied a message and what is supposed to

happened before they send any specific message.

ne of the key things to do after receiing a message or before sending a messageis to establish a specific channel (signal path or data path). hese data path orsignaling path is called #$adio /earer# and the process of setting up these data path

is called #$adio /earer &etup#.his is one of the most critical part and tricky part to understand in any kind of

communication mainly because you hae to know the ery details from physicallayer to higher layer.

!rom your e"perience you would realie that understanding a little bit of eerythingwould be relatiely easy, obtaining in-depth knowledge in a specific0narrow area

would be a little tough, but not impossible to achiee. 1oweer, mastering the whole

area to a ery detailed leel and getting a clear picture both on high leel and indetail would be ery, ery difficult.

his is why it is difficult to hae complete understanding of $adio /earer &etup. his

page and seeral other pages are for trying to help you hae better picture on thisprocess.

 

• erall %hannel 2apping

• 2a+or steps and $$% messages 2apping the channels

• $adio /earer &etup - &pecification able

• $adio /earer &etup - 2essage &tructure

• $adio /earer &etup - $3% &ie ype

• $adio /earer &etup - !%& to !%I %onersion

 

Overall Channel Mapping

 

he critical part of $adio /earer &etup procedure is to establish the signaling0data

path as shown below. You don#t hae to set up all the possible path at once,but youhae to make it sure that the data path for a specific message0data has already

established before they are getting transmitted. !or e"ample, you hae to make itsure that %%%1 - $4%1 - 5$4%1 channel has been established before receiing $$%

%onnection $euest and %%%1 - !4%1 - &%%5%1 before sending $$% %onnection

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&etup.

ry marking the path for each signaling message and user data. 6et your selffamiliar so that your finger draw the path on its own as soon as hear the name of

the signaling message.

 

Maor steps and RRC messages Mapping the channels

 

!ollowing is the oerall steps of $adio /earer *stablishment during the registration

and call setup.i) *stablish /%%1 - /%1 - 5%%5%1

ii) 2I/0&I/ ransmission0$eception

iii) *stablish %%%1-$4%1-5$4%1 (%onfigured in &I/7)i) *stablish %%%1-!4%1-&-&%%5%1 (%onfigured in &I/7)

) $$% %onnection $euesti) $$% %onnection &etup

ii) *stablish 8%%1-8%1-858%1085%%1 (%onfigured in $$% %onnection&etup)

iii) 6o through to the end of registrationi") 9 Idle :

") 2ake a call"i) *stablish %%%1-$4%1-5$4%1 (%onfigured in &I/7)

"ii) *stablish %%%1-!4%1-&-&%%5%1 (%onfigured in &I/7)

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"iii) $$% %onnection $euest

"i) $$% %onnection &etup") *stablish 8%%1-8%1-858%1085%%1 (%onfigured in $$% %onnection

&etup)"i) 6o through signaling for call connection

"ii) $adio /earer &etup

"iii) *stablish 8%1-8%1-858%1085%%1 (%onfigured in $adio /earer &etup)"i") 8ata ransmission0$eception

 

!ollwing diagram would help you isualie which channel path is establish by which

$$% messages.

 

Radio Bearer !etup " !pecification Ta#le

 

Attribute Conversational

conversational 64

Interactive Background

 Trafc class es es es esRAB as!!etricindicator

"!etric "!etric "!#As! "!#As!

$a%i!u! bitrate

1&&'' 64''' ()*64k+D)*64+1&,+-,4

 

uaranteed bitrate

1&&'' 64''' ignored ignored

Deliver order deliverorder

deliverorder

deliver order notre/uested

deliverorder not

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re/uested re/uested re/uested

$a%i!u! "D(si0e

&44 64' 1&'16 1&'16

"D( error ratio %1'23 1'2

Residual bit err

ratio

1'25 1'2 1'25

Deliver oerroneous "D(s

es es 7o 7o

"D( or!atinor!ation

64' bits 64' bits ignored ignored

 Tafc 8anding9riorit

ignored ignored :es Ignored

 Transer dela ,' 1'' ignored ignoredAllocation#Retention 9riorit

de9ends onsubscri9tion

de9ends onsubscri9tion

de9ends onsubscri9tion

de9endsonsubscri9tion

relocation

re/uire!ent

ignored ignored

"ource statisticsdescri9tor

"9eec8 unknown ignored ignored

 

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Radio Bearer !etup " Message !tructure

 

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Radio Bearer !etup " R$C !i%e Type

 

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Radio Bearer !etup " T&C! to T&C Conversion

 

When I started looking into $adio /earer &etup ($$% %onnection &etup, &I/7) andtry to create some test cases, the most confusing thing was about this.

4s you may noticed, the most confusing things about 2& radio bearer setup is toobig difference between how ;655 $adio /earer &pecification document (;<.=>?)

represents and how $$% messages(e.g, $$% %onnection &etup,$adio /earer &etup,&I/7) represents. 4mong those confusing things, the most confusing thing to me

was to represent the !%& table in ;655 document into ctfc information elements in$$% messages.

 

3et me gie you one e"ample case and show you how the !%& table in ;655

document is conerted into ctfc information elements. I will illustrate this conersionprocess into multiple steps. (In real protocol stack implementation, they would not

use these multiple steps, but I think the multi-step representation would be easierand clearer to most of readers).

 

9 &tep = :

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!irst step is to constructs !& table for each subflow from the ;655 !%& table asillustrated below. In this illustration, you would see an intermediate steps to

rearrange the !%& list into a tabular format. In reality, nobody would really drawthis intermediate procedure, but I introduced the procedure +ust for clarity.

 

9 &tep @ :

 

nce you get the table that shows all the possible ! for each subflow, ne"t step is

to figure out all the permutations of !%(ransport !ormat %ombination) out of thetable as shown below.

 

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9 &tep ; :

 nce you get the permutation table, the ne"t step is to find the number of row

(inde" of !%) to which each item in !%& table corresponds. hese correspondingrow number (the row number starts from >) is the !%I (ransport !ormat

%ombination Inde") which will be specified in $$% message in ne"t step.

 

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9 &tep < :

 

nce you got the !%I that matches each of the items in!%& table. he last step is +ust to specify those inde" number in ctfc information elements as shown below.

 

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&. ;8at are t8e <=I>s t8at needed to be c8ecked?

-. "8ow t8e co!9lete diagra! o t8e co!!unication taking 9art between (and R7C?

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RNC-Oriented Directed Retry Decision (DRD) algorithm parameters.