一个IP报文是怎样在LTE网络中传送和封装的？

爱卫生

一个IP报文是怎样在LTE网络中传送和封装的？下图给出了流程，按照协议栈从上往下进行封装。

1 TCP/IP layer

A TCP/IP MTU can have up to 1500 byte including 40 byte header.

一个TCP/IP层的MTU最多允许包含1500字节的净荷（含40字节包头，TCP/UDP+IP包头）

2 PDCP layer

In the PDCP first RoHC can be applied this would reduce 40 byte TCP/IP header to typically 3 byte header. In the user plane PDCP needs 2 byte own header.

PDCP层，由RoHC执行头压缩，把40字节的TCP/IP包头压缩成3个字节的包头，用户面的PDCP额外需要2个字节自己的报文头。

3 RLC layer

According to the transport block size the RLC can assume variable RLC PDU size. Either the TB is so small that the PDCP PDU needs to be segmented or it is that big that multiple PDCP PDU’s fir in. For the RLC header it can be configured to have 1 or 2 byte in UM. For AM and 1 RLC SDU the header size is 2 byte in case of no segmentation and 4 byte in case of segmentation. For RLC AM each additional RLC SDU will add 1.5 byte header. In case a byte header is not filled completely 4 bit header padding has to be added. Flexible RLC PDU’s and multiple RLC SDU’s are new to LTE and are not used in UMTS RLC until. R7

RLC可以根据不同的传输模式来适配不同的TB的大小。UM模式下的RLC包头可以加1或2个字节。AM模式下如果没有分段则RLC SDU的包头大小是2个字节、如果有分段则是4个字节。如果不够则添加填充。这种灵活的RLC PDU和多个RLC SDU是LTE出现的，UMTS RLC直到R7才出现。

4 MAC layer

In case the MAC is transporting only 1 MAC SDU the header length will be 1 byte only in case more MAC SDU’s are transmitted the header will increase by 2-3 byte. Please also take into account that padding and MAC Control Elements will be unavoidable. The use of MAC control elements is new in LTE.

如果MAC只传输1个MAC SDU（1个TB）则只需要添加1个字节的MAC包头，如果有多个MAC SDU需要传送将增加到2-3个字节。对于MAC的控制元素也是LTE中新增的。

5 PHY layer

The physical layer has to deal with very huge TB’s. TB’s of 150000 bit cannot be protected with a single CRC check any more. This is why there is a own 3 byte CRC foreseen for every of the up to 6144 bit long Code Block Segments.

物理层可以处理大量的TB。将MAC PDU(TB)映射到PDSCH进行发送。

olleh

清晰明了；有助于加深理解

frameworks

这个资料好啊。。。。跟SDH帧复用一样，清楚明了。