上层路 meaning in English

overlying roadway

The dissertation has proposed a solution of pos line card which has the aggregate rate of 10gbps . the function of the pos line card is to extract the ppp frame from the sdh payload area and then do conversion for the ppp data , supplying a high speed i / o for np ( network proecssor )
该pos线卡的设计目标是:恢复出封装在sdh帧中的ppp帧,并对其进行格式的转换,为上层路由设备提供一个高速的i / o接口。