point-to-point single path  
           +------+      +------+      +------+
       ---<>  R1  <>----<>  R2  <>----<>  R3  <>---
           +------+      +------+      +------+


       point-to-point multipath
                        +------+
                       <>  R2  <>
                      / +------+ \
                     /            \
           +------+ /              \ +------+
       ---<>  R1  <>                <>  R4  <>---
           +------+ \              / +------+
                     \            /
                      \ +------+ /
                       <>  R3  <>
                        +------+


       point-to-multipoint
                                   +------+
                                  <>  R4  <>---
                                 / +------+
                       +------+ /
                      <>  R2  <>
                     / +------+ \
           +------+ /            \ +------+
       ---<>  R1  <>              <>  R5  <>---
           +------+ \              +------+
                     \ +------+
                      <>  R3  <>
                       +------+ \
                                 \ +------+
                                  <>  R6  <>---
                                   +------+


       multipoint-to-point
           +------+
       ---<>  R1  <>
           +------+ \
                     \ +------+
                     <>  R4  <>
                     / +------+ \
           +------+ /            \ +------+
       ---<>  R2  <>              <>  R6  <>---
           +------+              / +------+
                       +------+ /
                      <>  R5  <>
                     / +------+
           +------+ /
       ---<>  R3  <>
           +------+


       multipoint-to-multipoint
           +------+                +------+
       ---<>  R1  <>              <>  R6  <>---
           +------+ \            / +------+
                     \ +------+ /
                      <>  R4  <>
                       +------+ \
           +------+              \ +------+
       ---<>  R2  <>             <>  R7  <>---
           +------+ \            / +------+
                     \ +------+ /
                      <>  R5  <>
                     / +------+ \
           +------+ /            \ +------+
       ---<>  R3  <>              <>  R8  <>---
           +------+                +------+