图2.7跳到跳的传递 End Intermediate system system End Link × Link system Intermediate C D system Link End Intermediate system B system Link Link E Hop-to-hop delivery Hop-to-hop delivery Hop-to-hop delivery Data link Data link Hop-to-hop delivery Hop-to-hop delivery Hop-to-hop delivery 2.19 2.19 图 2.7 跳到跳的传递