Transport block — The opaque block MAC hands to layer 1

5G Systems Notes · Concept map · Transport block Route · Hierarchy · Index · All concepts · Hub

The protocol stack

Where it sits

Sits atLevel 5 of the hierarchy · The protocol stack · explained
Also writtenTB
Learn firstPhysical layer — 5 concepts in the full chain, see the paths
UnlocksMAC · Transport channel · CRC · Code block · Scrambling · HARQ
Primary clauseTS 38.202 §4.1
Used innr-pdsch 33 · index 3 · ref-stack 3 · nr-srs 1
Scanned from the notes at page load and joined with terms.json; nothing on this card is typed by hand.

What it is

A transport block is the data MAC delivers to the physical layer — an opaque bag of bits with a length, and nothing more.

"A transport block is defined as the data delivered by MAC layer to the physical layer and vice versa" — TS 38.202 clause 4.1.

Its opacity is what makes the design scale. The physical layer never learns whether a block holds a video frame or a signalling message, so a new service can be added above without any change below. Every step of the coding chain operates on this bag.

Read on

The full treatment is in nr-pdsch — this page is the definition and the map reference; that note is where the subject is actually developed.

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

To understand Transport block (level 5) you first need 5 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
Immediately before Transport block: Physical layer.
Keep going — where this sits on the route
◀REG and CCEstep 46 · level 5
Step 47 of 118level 5 · The protocol stack
SS/PBCH blockstep 48 · level 5▶
Level 5 → 6 · this unlocks
Transport channel · CRC · MAC · Code block level 7 · Scrambling level 8 · HARQ level 10
↳ all 11 concepts at level 6 · level 5 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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