hub-spoke topology and response time

Fellow experts,

I have a simple topology: R5 is hub and R1, R3 are spokes.
IP range is 155.1.0.x/24 where x=router number.
I am using static FR mapping

R5#sh fram map
Serial0/0 (up): ip 155.1.0.1 dlci 501(0x1F5,0x7C50), static,
              broadcast,
              CISCO, status defined, active
Serial0/0 (up): ip 155.1.0.3 dlci 503(0x1F7,0x7C70), static,
              broadcast,
              CISCO, status defined, active

I have a question: why unicast and broadcast response times are so different?

For unicast, I have about 57 ms:

R5#pi 155.1.0.1

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 155.1.0.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 56/57/60 ms
R5#pi 155.1.0.3

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 155.1.0.3, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 56/57/60 ms

For broadcast, I have almost double:

R5#pi 255.255.255.255

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 255.255.255.255, timeout is 2 seconds:

Reply to request 0 from 155.1.0.3, 88 ms
Reply to request 0 from 155.1.0.1, 100 ms
Reply to request 1 from 155.1.0.3, 88 ms
Reply to request 1 from 155.1.0.1, 100 ms
Reply to request 2 from 155.1.0.3, 113 ms
Reply to request 2 from 155.1.0.1, 125 ms
Reply to request 3 from 155.1.0.3, 116 ms
Reply to request 3 from 155.1.0.1, 128 ms
Reply to request 4 from 155.1.0.3, 116 ms
Reply to request 4 from 155.1.0.1, 128 ms

Not a big deal, but anyone tell me why this?

TIA, MIhai

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Received on Thu Jul 02 2009 - 08:11:43 ART