question about serialiation delay

[Dr.X]

hi all ,

im asking about serialization delay

assume i have speed of 1 M  or 8 M  or 16 M ,

if i ping 8.8.8.8

i have

Reply from 8.8.8.8: bytes=32 time=79ms TTL=42

does the time 79 is the serialization delay ???

does this time mean that it is the time , the rouiter took to put data in wires ???

is this time for one  direction ? uplink ??

or it is for  dow directions , (up and down ) ???

regards

[daniel.dib · Accepted solution]

Hi,

Serialization dely is the time it takes to serialize the packets. One thing to consider though is that if you have a subrate speed, buying 20Mbit/s but the interface is FastEthernet. Then the packets are still serialized at the physical interface speed but the Service Provider will shape/police traffic to appropiate rate.

Assume that you want to send a full size packet at 1500 bytes. If it's a TCP packet then the payload is 1460 bytes, TCP header is 20 bytes, IP header is 20 bytes and Ethernet header is 18 bytes. So the packet is 1518 bytes. If you have 1Mbit/s connection then this is the time to serialize 1518 bytes:

1000000 bits/s /8 = 125000 bytes/s

1518 / 125000 = 0,012144 seconds

0,012144 * 1000 = 12,144 ms

It takes 12ms to serialize the packet at 1Mbit/s.

For 8 Mbit/s:

8000000 bits/s /8 = 1000000 bytes/s

1518 / 1000000 =  0,001518 seconds

0,001518 * 1000 = 1,518 ms

For 16 Mbit/s:

16000000 bits/s /8 = 2000000 bytes/s

1518 / 2000000 = 0,000759 seconds

0,000759 * 1000 = 0,759 ms

When you ping something the Round Rrip Time (RTT) you get is the time that it takes from your PC to reach the destination and back. If you have 79 ms to 8.8.8.8 that is a pretty long distance and unless you have a very slow connection the serialization delay should not be a major part of that delay.

Always keep in mind though that replying to ICMP may not be prioritized for whatever you are trying to ping, so using ICMP may not always be a good way of measuring latency.

Daniel Dib
CCIE #37149

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Posting

i have
Reply from 8.8.8.8: bytes=32 time=79ms TTL=42
does the time 79 is the serialization delay ???

No, but it would include that.

does this time mean that it is the time , the rouiter took to put data in wires ???

Partially.  It's the RTT (round trip time).  I.e. the time between sending the ping request and getting a ping reply.  Serialization delay is part of the overall time.

is this time for one  direction ? uplink ??

It's, as just noted, total round trip time.  I.e. both directions contribute.  (NB: BTW, times in different directions might differ, but you cannot tell from just one simple ping test.)

As Daniel noted, serialization delay is the time it take to physically transmit the frame/packet.  Such delay increases as the packet size increases (more bits to transmit) and increases as interface bandwidth decreases (less bandwidth takes longer to transmit).

BTW, if you want to see the impact of serialization delay, assuming everything else is equal, ping a small(est) packet vs. a large(st) packet, and you'll probably see an increase in RTT, which reflects the time it takes for the additional bits in the larger packet to be transmitted.

Also BTW, serialization delay happens every hop (switch or router) when the frame/packet is retransmitted.  So, more hops, more delay.

Lastly, RTT time has many other components than just serialization delay.

[Dr.X]

1st of all I would like to thank u both , very nice explanation and simple .

I had made a nice understanding for serialization delay

Thanks a lot
Regards


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