figure1.pic

早期freebsd实现

.PS
B1: box "user"
B2: box "UA" with .n at (B1.s.x, B1.s.y-(lineht/2))
B3: box "MTA" with .n at (B2.s.x, B2.s.y-(lineht*4))
B4: box "PhoneNet" with .n at (B3.s.x, B3.s.y-lineht)
B5: box "{\it modem}" with .n at (B4.s.x, B4.s.y-lineht)
B6: box "{\it modem}" with .w at (B5.e.x+(linewid*2), B5.e.y)
B7: box "PhoneNet" with .s at (B6.n.x, B4.s.y)
B8: box "MTA" with .s at (B7.n.x, B3.s.y)
B9: box "MTA" with .w at (B8.e.x+linewid, B8.e.y)
B10: box "PhoneNet" with .n at (B9.n.x, B7.n.y)
B11: box "{\it modem}" with .s at (B10.s.x, B6.s.y)
B12: box "{\it modem}" with .w at (B11.e.x+(linewid*2), B11.e.y)
B13: box "PhoneNet" with .s at (B12.s.x, B10.s.y)
B14: box "MTA" with .s at (B13.n.x, B3.s.y)
B15: box "UA" with .s at (B14.n.x, B2.s.y)
B16: box "user" with .s at (B15.n.x, B1.s.y)
line from B1.s to B2.n
line from B2.s to B3.n
line from B3.s to B4.n
line from B4.s to B5.n
line from B5.e to B6.w
line from B6.n to B7.s
line from B7.n to B8.s
line from B8.e to B9.w
line from B9.s to B10.n
line from B10.s to B11.n
line from B11.e to B12.w
line from B12.n to B13.s
line from B13.n to B14.s
line from B14.n to B15.s
line from B15.n to B16.s
line dashed from (B8.e.x+(linewid/2), B8.e.y-(lineht/2)) to \
	(B8.e.x+(linewid/2), B6.s.y)
line dotted from (B2.sw.x+(linewid/8), B3.n.y+(lineht*1.5)) to \
	(B2.se.x-(linewid/8), B3.n.y+(lineht*1.5))
line dotted from (B15.sw.x+(linewid/8), B3.n.y+(lineht*1.5)) to \
	(B15.se.x-(linewid/8), B3.n.y+(lineht*1.5))
move to (B1.n.x, B1.n.y+lineht); "{\tt Any Host}"
move to (B16.n.x, B1.n.y+lineht); "{\tt Any Other Host}"
move to (B8.e.x+(linewid/2), B1.n.y+lineht); "{\tt Relay Host}"
move to (B2.s.x+(linewid/2), B3.n.y+(lineht*1.75)); "{\it slot}"
move to (B15.s.x-(linewid/2), B3.n.y+(lineht*1.75)); "{\it slot}"
.PE