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Silver

serial interface speed

hello

TFGen is a traffic generator

i am trying to test it in GNS3 with a LL connections between 2 routers.

the traffic is continuous and constant. the destination address is the remote router LAN interface.

my problem is: when generating a traffic with 64Kbps for example:

-in show interface f0/0 on local router it shows

R1#sho int f0/0 | inc rate

  Queueing strategy: fifo

  30 second input rate 63000 bits/sec, 65 packets/sec

  30 second output rate 2000 bits/sec, 3 packets/sec

that's ok. but

- in show interface s1/0 on local router it shows

R1#sho int s1/0 | inc rate

  Queueing strategy: weighted fair

  30 second input rate 1000 bits/sec, 2 packets/sec

  30 second output rate 58000 bits/sec, 64 packets/sec

why  serial interface speed is < Lan interface speed ? shouldn't be the same?

thanks for your help

1 ACCEPTED SOLUTION

Accepted Solutions
Hall of Fame Super Silver

Re: serial interface speed

Hello Ohassairi,

serial interface has a different encapsulation like HDLC or PPP. LAN interface uses Ethernet II framing.

.Router interface speed is an OSI Layer2 information not OSI Layer3.

For LAN interfaces with no vlan tagging the overhead is 14 bytes because the 4 byte FCS is not counted

For serial interface the overhead is less 4-5 bytes with 2 bytes CRC not taken in account.

To be correct we should say that in LAN interfaces also the inter frame gap ( silence between two frames) plays a role..

However, for router interface counters the different encapsulation overhead is enough to explain the differences.

As a result of this the traffic speed in bit per second is less on the serial interface even if the packet rate pps is the same

What you see is normal

Hope to help

Giuseppe

2 REPLIES
Hall of Fame Super Silver

Re: serial interface speed

Hello Ohassairi,

serial interface has a different encapsulation like HDLC or PPP. LAN interface uses Ethernet II framing.

.Router interface speed is an OSI Layer2 information not OSI Layer3.

For LAN interfaces with no vlan tagging the overhead is 14 bytes because the 4 byte FCS is not counted

For serial interface the overhead is less 4-5 bytes with 2 bytes CRC not taken in account.

To be correct we should say that in LAN interfaces also the inter frame gap ( silence between two frames) plays a role..

However, for router interface counters the different encapsulation overhead is enough to explain the differences.

As a result of this the traffic speed in bit per second is less on the serial interface even if the packet rate pps is the same

What you see is normal

Hope to help

Giuseppe

Silver

serial interface speed

thanks for your reply

i understand that L2 header is different from LAN to WAN but at least we should have the same packet rate.

however in LAN we send :  65 packets/sec and in WAN only 64 packets/sec

i think there is one missing packet. but there is no drops in sho interface !

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