This read-only value (Unsigned32, bytes) reports the maximum Service Data Unit (SDU) size actually negotiated for this UMTS QoS profile, ranging from 1 to 1520 bytes, with 0 meaning the subscribed maximum applies. An admin monitoring a 3G WAN router checks this to confirm the carrier granted the packet-size ceiling the device requested, since a smaller negotiated SDU size than expected can limit throughput for that PDP context. For example, if the device requested a 1500-byte SDU to match its Ethernet MTU but this object reads 1024, the admin knows the carrier trimmed the negotiated size and may need to adjust local MTU settings to avoid fragmentation.