RNTI — Radio network temporary identifier — the address that is not a field

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Procedures over time

Where it sits

Sits atLevel 7 of the hierarchy · Procedures over time · explained
The 9 of them
C-RNTI — the device's own identity while it is connected
CS-RNTI — configured-scheduling grants — semi-persistent, no DCI each time
SI-RNTI — system information
P-RNTI — paging
RA-RNTI — the random-access response
TC-RNTI — temporary, held during random access until a C-RNTI is issued
G-RNTI — group — multicast and broadcast services
MCS-C-RNTI — the same device, told to read the low-spectral-efficiency MCS table
MSGB-RNTI — message B of two-step random access
Learn firstCRC — 7 concepts in the full chain, see the paths
UnlocksScrambling · DCI · Search space · Initial access
Primary clauseTS 38.321 §7.1
Used innr-pdsch 9 · ref-channels 5 · index 1 · ref-modulation 1 · ref-ue-identity 1
Scanned from the notes at page load and joined with terms.json; nothing on this card is typed by hand.

What it is

What it is. A 16-bit radio network temporary identifier, scrambled into the parity bits of a DCI's CRC rather than transmitted as an address. TS 38.212 clause 7.3.2 gives the mechanism, and ref-modulation §6 quotes it.

One device holds several at once, and which one is used says what the message is:

RNTIAddressesWhat it changes
C-RNTIOne connected deviceThe ordinary case. Scrambling uses dataScramblingIdentityPDSCH if configured (PDSCH §6.1).
MCS-C-RNTIThe same deviceSelects a different MCS table — the low-spectral-efficiency one, for URLLC.
CS-RNTIThe same deviceConfigured scheduling: activates, reactivates or releases a semi-persistent allocation.
SI-RNTIEveryone in the cellSystem information on PDSCH. xOverhead is forced to 0 and the transport block may not exceed 2 976 bits (TS 38.214 §5.1.3.2).
P-RNTIEveryonePaging. The TBS gets a scaling factor from Table 5.1.3.2-2.
RA-RNTI / MSGB-RNTIWhoever sent a preambleThe random-access response, addressed by when and where the preamble arrived.
TC-RNTIA device mid-random-accessTemporary, until contention is resolved.
G-RNTI / G-CS-RNTIA groupMulticast on PDSCH — the Release 17 job that LTE gave to PMCH.
Table 1: The RNTIs a device may be addressed by on PDCCH, as used across TS 38.211 clause 7.3.1.1, TS 38.212 clause 7.3.1.2 and TS 38.214 clauses 5.1.3 and 5.1.4. The right-hand column is what changes when the CRC is scrambled with that value rather than another - which is why the RNTI is not merely an address but a mode selector.

Read the third column. The RNTI does not only say who; it changes the MCS table, the overhead assumption, the scrambling seed and the size limit. It is a mode selector that costs zero bits, because it rides in parity that had to be sent anyway.

Read on

This concept was first written up in ref-channels, which reads the whole group as one argument.

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Before this concept, the hierarchy says to learn the following — the full chain, in order:

To understand RNTI (level 7) you first need 7 other concepts. Read them in this order — everything on one line can be read in any order, but no line before the one above it:
Level Learn these
0 Subcarrier
1 OFDM
2 OFDM symbol
3 Resource element
4 Physical layer
5 Transport block
6 CRC
Immediately before RNTI: CRC.
Keep going — where this sits on the route
◀Beamformingstep 77 · level 7
Step 78 of 118level 7 · Procedures over time
Carrier aggregationstep 79 · level 7▶
Level 7 → 8 · this unlocks
Scrambling · DCI level 9 · Initial access level 9 · Search space level 9
↳ all 8 concepts at level 8 · level 7 in full · the whole route
The route is every concept in the folder ordered by level, so nothing here needs anything after it. Computed at page load from terms.json; the same numbering as the route page.
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