Understanding SDU and PDU and their application in UMTS

network

By Stefan Dolapchiev

PDU vs. SDU in IP network

4

3

2

1

4

3

2

1

Layer 4 PDU (TCP Segment)

Upper Layer SDU (Data)

L4 (TCP) Header

Layer 1 transmission

Layer 2 PDU (Ethernet Frame)

L2 SDU = L3 PDUL3 SDU = L4 PDU

Upper Layer SDU (Data)

L4 (TCP) Header

L3 (IP) Header

L2 (Ethernet)

Header

L2 (Ethernet)

Footer

Layer 3 PDU (IP Datagram)L3 SDU = L4 PDU

Upper Layer SDU (Data)

L4 (TCP) Header

L3 (IP) Header

In general, LnSDU = Ln+1PDU

UMTS Uu Interface Protocol Stack

Coding, Rate Matching, Spreading, Modiulation

AMR Voice

CS Data

PS Data

Network Control(CC/MM/GMM, etc.)

Radio Resource Control (RRC)

Medium Access Control (MAC)

Radio Link Control (RLC)

Packet Data Convergence

Protocol (PDCP)

Layer 1

Layer 2

Layer 3

Non Access Stratum

(NAS)

Access Stratum

Control Plane User Plane

Radio Access Bearers (RAB)

Radio Bearers (RB)

Logical Channels (DCCH, CCCH, PCCH,

BCCH, DTCH)

Transport Channels (DCH, PCH, BCH, RACH, FACH)

Physical Channels (DPCH, P-CCPCH, PRACH, SCCPCH, AICH, PICH)