RRC State Overview
RRC stands for Radio Resource Control. I personally define RRC as a common language that should be understood by both Network and UE. As you know, UE and Network is communicating via radio channel. Every parties participating in the communication should exchange a lot of information to make the real data exchange possible. In other words, the final goal of communication is to exchange the data (user data) between communicating parties, but to make this happen there are a lot of things (especially a lot of lower layer issues) that need to be configured in common. In case of low end communication system, those common configuration is done before the product is released into market and once they are released, those configuration would not change. However, in many high end communication system (e.g, cellular communication) these configuration should change dynamically for optimal configuration at the time of communication. Then the question is how both parties in the communication reach agreement on those common configuration. To do this, we need a special control mechanism to exchange informations on those configurations between communicating parties. The resulting implementation of this control mechanism is called RRC (Radio Resource Control).
Another central role of RRC within each communicating party (i.e, within UE and Network) is to work as a control center for all of the lower layers within each system. The collection of all the lower layers within UE or basestation is called 'Radio Resource' (i.e, resources required to make radio communication possible). The major role of RRC is to control(configure) all the Radio Resources (PHY, MAC, RLC, PDCP) to make it possible to communicate between UE and the base station (e.g, gNB, eNB, NB, BTS etc).
In this page, I will give you the brief introduction to RRC in NR. In fact, RRC is a huge topic because it eventually get involved in whole protocol stack. So it would be difficult to describe the wholes details of RRC in single page. So I would just talk about overall RRC structure / functions in this page and for further details I will write many separate pages and put the links in this page.
When you think of RRC in NR only, it can be illustrated as shown below. Do you see any difference from LTE RRC ? Yes, you might have noticed that a new block (state) are introduced in NR. It is 'NR RRC INACTIVE'. Full details of this new state is not fully defined in the specification yet, but my first impression of the function and purpose of this new state would be similar to the combined functionality of CELL PACH and CELL/URA PCH in UMTS RRC State Change process.
< TR 38.804- Figure 5.5.2-1 : UE state machine and state transitions in NR >
Unlike LTE, in NR there is a addition RRC states between RRC Connected and Idle and Network/UE can optionally stay in INACTIVE state without completely releasing the RRC when there is no traffic and quickly switch back to CONNECTED states when necessary. To me, RRC INACTIVE state is similar to the combination of FACH and PCH in UMTS. Actually Use case of INACTIVE state is almost same as FACH/PCH in UMTS.
The switching between RRC CONNECTED and RRC INACTIVE state happens as shown below.
The details of this transition is described in a separate note : RRC INACTIVE
NR RRC does not only involved in NR but also in other radio access technology as well. The interaction of NR RRC and LTE RRC can be illustrated as follows. Things to be noticed here are
< 36.331 v16.5-Figure 4.2.1-6: Mobility procedures between E-UTRA/EPC, E-UTRA/5GC and NR >
The interaction of NR RRC and UMTS / GSM RRC can be illustrated as follows. Things to be noticed here are
< TR 38.804 - Figure 10.2-3:UE state machine and state transitions between NR and UTRAN/GERAN>
RRC (Radio Resource Control) ni kifupi cha neno la Kiingereza RRC (Radio Resource Control). Mimi binafsi kufafanua RRC kama lugha ya kawaida ambayo inapaswa kueleweka na wote Network na UE. Kama unavyojua, U.S. na U.S. na U.S. na U.S. na U.S. na U.S. na U.S. na U.S. na U.S. na U.S. na U.S. na U.S. na U.S. na U.S. na U.S. na U.S. na U.S. na U.S. na U.S. na U.S. na U.S. na U.S. na U.S. na U.S. na U.S. na U.S. na U.S. na U.S. na U.S. na U.S. na U.S. na U.S. na U.S. na U.S. na U.S. na U.S. na U.S. na U.S. na U.S. Kila chama kushiriki katika mawasiliano inapaswa kubadilishana mengi ya habari ili kufanya kubadilishana data halisi inawezekana. Kwa maneno mengine, lengo la mwisho la mawasiliano ni kubadilishana data (data ya mtumiaji) kati ya pande zinazohusiana, lakini ili kufanya hivyo kutokea kuna mambo mengi (haswa masuala mengi ya safu ya chini) ambayo yanahitaji kuwa umeboreshwa kwa pamoja. Katika kesi ya mfumo wa mawasiliano wa mwisho wa chini, usanidi huo wa kawaida hufanywa kabla ya bidhaa kutolewa kwenye soko na mara tu zinapotolewa, usanidi huo haubadiliki. Hata hivyo, katika wengi high mwisho mfumo wa mawasiliano (kwa mfano, mawasiliano ya kiini) hizi Configuration lazima kubadilisha dynamically kwa ajili ya Configuration bora wakati wa mawasiliano. Kisha swali ni jinsi pande zote mbili katika mawasiliano kufikia makubaliano juu ya wale muundo wa kawaida. Kufanya hili, tunahitaji utaratibu maalum wa kudhibiti kubadilishana habari juu ya miundo hiyo kati ya vyama vya mawasiliano. Utekelezaji unaotokana na utaratibu huu wa kudhibiti unaitwa RRC (Radio Resource Control). Kazi nyingine ya RRC ndani ya kila chama cha mawasiliano (yaani, ndani ya UE na Mtandao) ni kufanya kazi kama kituo cha kudhibiti kwa tabaka zote za chini ndani ya kila mfumo. Mkusanyiko wa tabaka zote za chini ndani ya UE au kituo cha msingi inaitwa 'Radio Resource' (yaani, rasilimali zinazohitajika kufanya mawasiliano ya redio iwezekanavyo). RRC ni uwezo wa kuongoza (kuweka) rasilimali zote za redio (PHY, MAC, RLC, PDCP) ili kuwezesha mawasiliano kati ya UE na kituo cha msingi (kwa mfano, GNB, NBN, NBN, etc.). Katika ukurasa huu, nitakupa utangulizi mfupi wa RRC katika NR. Kwa kweli, RRC ni mada kubwa kwa sababu hatimaye kushiriki katika stack nzima itifaki. Ni vigumu kuelezea mambo yote ya RCC katika ukurasa mmoja. Kwa hivyo, kwa sasa, ninaweza kuelezea kwa ufupi jinsi RFCs zinavyofanya kazi, na kwa maelezo zaidi, nitaandika kurasa nyingi tofauti na kuweka viungo katika ukurasa huu. Ikiwa unafikiria RRC katika NR tu, inaweza kuonyeshwa kama inavyoonyeshwa hapa chini. Je, unaona tofauti yoyote na LTE RRC? Ndio, unaweza kuwa umegundua kwamba block mpya (hali) ni kuletwa katika NR. Ni 'NR RRC INACTIVE'. Maelezo kamili ya hali hii mpya bado hayajafafanuliwa katika vipimo, lakini hisia yangu ya kwanza ya kazi na kusudi la hali hii mpya itakuwa sawa na utendaji wa pamoja wa CELL PACH na CELL URA PCH katika mchakato wa UMTS RRC State Change. "Kama ilivyoelezwa katika kipengele cha 5.5.2-1 cha ""Mashine ya hali ya RRC na mabadiliko ya hali katika NR"" (kwa Kiingereza: State Machine and State Transitions in NR) - ""Kinyume cha LTE, katika NR kuna hali ya RRC ya ziada kati ya RRC iliyounganishwa na idle na Network-UE inaweza kuchagua kukaa katika hali ya INACTIVE bila kuachilia kabisa RRC wakati hakuna trafiki na haraka kubadilisha nyuma kwa hali ya CONNECTED wakati inahitajika." RRC inactive ni sawa na mchanganyiko wa FACH na PCH katika UMTS. Kwa kweli matumizi ya hali INACTIVE ni karibu sawa na FACH / PCH katika UMTS. Kubadilisha kati ya RRC CONNECTED na RRC INACTIVE hali hutokea kama inavyoonyeshwa hapa chini. "Kama ilivyoelezwa katika maelezo ya awali, ""Radio Access Technology"" ni moja ya teknolojia za mawasiliano ya redio ambazo zinahusika katika uendeshaji wa huduma za redio." Mwingiliano wa NR RRC na LTE RRC unaweza kuonyeshwa kama ifuatavyo. "Kama ilivyoelezwa katika makala ya kwanza ya ""Ufunuo wa Utafiti wa Utafiti wa Utafiti wa Utafiti wa Utafiti wa Utafiti wa Utafiti wa Utafiti wa Utafiti wa Utafiti wa Utafiti wa Utafiti wa Utafiti wa Utafiti wa Utafiti wa Utafiti wa Utafiti wa Utafiti wa Utafiti wa Utafiti wa Utafiti wa Utafiti wa Utafiti wa Utafiti wa Utafiti wa Utafiti wa Utafiti wa Utafiti wa Utafiti wa Utafiti wa Utafiti.""" "Kama ilivyoelezwa katika makala ya kwanza ya ""Utrans"" (Third edition) ya Toleo la Toleo la Toleo la Toleo la Toleo la Toleo la Toleo la Toleo la Toleo la Toleo la Toleo la Toleo la Toleo la Toleo la Toleo la Toleo la Toleo la Toleo la Toleo la Toleo la Toleo la Toleo la Toleo la Toleo la Toleo la Toleo la Toleo la Toleo la Toleo la Toleo la Toleo la Toleo la Toleo la Toleo la Toleo la Toleo la Toleo la Toleo la Toleo la Toleo la Toleo la Toleo la Toleo la Toleo la Toleo la Toleo."