Method and device used for wireless communication

A second node for wireless communications, comprising:

• a second transmitter, which transmits a second MAC PDU group, with a MAC Header of any MAC PDU in the second MAC PDU group comprising information corresponding to a first portion of a first old identifier(ID);
• the second MAC PDU group comprises a first PDCP PDU, and a header of the first PDCP PDU comprises a first key ID;
• the first key ID is used to identify a first key, and the first key is used for generating a key used for a security algorithm applied to the first PDCP PDU;
• and
• a receiver of the second MAC PDU group, which transmits a first MAC PDU group, the first MAC PDU group comprising a second PDCP PDU, the second PDCP PDU comprising information corresponding to a first portion of the first PDCP PDU;
• when the first old ID is not updated as a first new ID, a header of any MAC PDU in the first MAC PDU group comprises information corresponding to a first portion of a third old ID and a header of the second PDCP PDU comprises the first key ID;
• when the first old ID is updated as the first new ID, the header of any MAC PDU comprised in the first MAC PDU group comprises information corresponding to a first portion of a third new ID and the header of the second PDCP PDU comprises a second key ID;
• wherein the first MAC PDU group comprises at least one MAC PDU, and the second MAC PDU group comprises at least one MAC PDU;
• the second key ID is used to identify the first key;
• the second key ID is different from the first key ID;
• a transmitter of the first PDCP PDU is different from a receiver of the second PDCP PDU, the first old ID, the first new ID, the third old ID and the third new ID are link layer IDs respectively, and the third new ID is different from the first new ID.

A method in a first node for wireless communications, comprising:

• receiving a second MAC PDU group, with a MAC Header of any MAC PDU in the second MAC PDU group comprising information corresponding to a first portion of a first old identifier(ID);
• the second MAC PDU group comprises a first PDCP PDU, and a header of the first PDCP PDU comprises a first key ID;
• the first key ID is used to identify a first key, and the first key is used for generating a key used for a security algorithm applied to the first PDCP PDU;
• and
• transmitting a first MAC PDU group, the first MAC PDU group comprising a second PDCP PDU, the second PDCP PDU comprising information corresponding to a first portion of the first PDCP PDU;
• when the first old ID is not updated as a first new ID, a header of any MAC PDU in the first MAC PDU group comprises information corresponding to a first portion of a third old ID and a header of the second PDCP PDU comprises the first key ID;
• when the first old ID is updated as the first new ID, the header of any MAC PDU comprised in the first MAC PDU group comprises information corresponding to a first portion of a third new ID and the header of the second PDCP PDU comprises a second key ID;
• wherein the first MAC PDU group comprises at least one MAC PDU, and the second MAC PDU group comprises at least one MAC PDU;
• the second key ID is used to identify the first key;
• the second key ID is different from the first key ID;
• a transmitter of the first PDCP PDU is different from a receiver of the second PDCP PDU, the first old ID, the first new ID, the third old ID and the third new ID are link layer IDs respectively, and the third new ID is different from the first new ID.

A method in a second node for wireless communications, comprising:

• transmitting a second MAC PDU group, with a MAC Header of any MAC PDU in the second MAC PDU group comprising information corresponding to a first portion of a first old identifier(ID);
• the second MAC PDU group comprises a first PDCP PDU, and a header of the first PDCP PDU comprises a first key ID;
• the first key ID is used to identify a first key, and the first key is used for generating a key used for a security algorithm applied to the first PDCP PDU;
• and
• a receiver of the second MAC PDU group transmitting a first MAC PDU group, the first MAC PDU group comprising a second PDCP PDU, the second PDCP PDU comprising information corresponding to a first portion of the first PDCP PDU;
• when the first old ID is not updated as a first new ID, a header of any MAC PDU in the first MAC PDU group comprises information corresponding to a first portion of bits in a third old ID and a header of the second PDCP PDU comprises the first key ID;
• when the first old ID is updated as the first new ID, the header of any MAC PDU comprised in the first MAC PDU group comprises information corresponding to a first portion of bits in a third new ID and the header of the second PDCP PDU comprises a second key ID;
• wherein the first MAC PDU group comprises at least one MAC PDU, and the second MAC PDU group comprises at least one MAC PDU;
• the second key ID is used to identify the first key;
• the second key ID is different from the first key ID;
• a transmitter of the first PDCP PDU is different from a receiver of the second PDCP PDU, the first old ID, the first new ID, the third old ID and the third new ID are link layer IDs respectively, and the third new ID is different from the first new ID.