My company is connected to the internet via a leased line which is
rated at 128k.  That connects to a router which is said to have a
throughput of '72 packets per second'.

How do I compare these figures?

---

Request for Question Clarification by tutuzdad-ga on 07 Jan 2003 07:56 PST

If you are just looking to determine your own bandwidth I can tell you
how to do that, if that will suffice as an answer?

Regards;
tutuzdad-ga

---

Clarification of Question by michael2-ga on 07 Jan 2003 08:50 PST

Yes, I'm looking to compare the bandwidth of the router with that of
the line. Which limits our overall bandwidth?  If you need more info,
please ask.

---

Request for Question Clarification by tutuzdad-ga on 07 Jan 2003 09:12 PST

The method I was going to offer was a reliable bandwidth test for your
own bandwidth.

tutuzdad-ga

---

Clarification of Question by michael2-ga on 07 Jan 2003 09:21 PST

Thanks, but I was looking for a quantative comparison of the two
figures - based on eg how many bits/bytes in a typical packet?

---

Request for Question Clarification by tisme-ga on 07 Jan 2003 11:26 PST

I understand that packets can have different sizes. I find it highly
unlikely that the router is what is slowing down your connection.

tisme-ga

Dear michael2-ga,

Packet size can vary quite widely, as can be seen from the following
paper:

"Packet size also varied over time and amounted to an average of about
170 bytes per packet during the night and 200 bytes during daytime.
Plotting packet size in a histogram, we can observe a predominance of
small packets. About 40% of all packets were 40 bytes and smaller,
indicating TCP ACK, SYN, FIN packets. Other peaks occurred at around
552 bytes and 1500 bytes. The mode observed at 552 bytes per packet is
probably due to missing PATH MTU discovery. 10% of all packets were
1500 bytes of size. This indicates Ethernet attached hosts."
 - Characterisation of Internet Traffic: Interesting Facts and Figures
   http://www.ccic.ethz.ch/Lectures/Seminar_IuK/SS00/files/karrer_sum.pdf

Taking this as equivalent proportions for a typical Internet
connection, we can calculate that by the raw nunbers, 72 of the
average 200-byte packets per second is equivalent to 115,200 bits per
second, or 112.5Kbps, which would make the router appear to be a small
bottleneck.

However, as an IP router only needs to inspect the packet header to
perform routing, and thus packet size does not greatly affect the
speed of routing, it is probably more appropriate to perform this
calculation using the 1500-byte packet - the largest Ethernet packet -
which gives quite different results: 72 1500-byte packets per second
is equivalent to 864,000 bits per second, 843.75Kbps.

In reality, the router throughput is likely to vary somewhere between
these extremes depending on the current mix of packets it has to
process and any special handling, such as filtration, fragmentation,
etc. it has to perform on them, but I would consider it extremely
unlikely that it is a bottleneck on your connection under anything but
the most unusual of circumstances.

Additional Links:

Routers
http://www.erg.abdn.ac.uk/users/gorry/course/inet-pages/router.html

Operation of a Router
http://www.erg.abdn.ac.uk/users/gorry/course/inet-pages/router-opn.html

Maximum Transfer Unit (MTU)
http://www.erg.abdn.ac.uk/users/gorry/course/inet-pages/mtu.html

If this answer isn't quite what you're looking for, please feel free 
to request a clarification. 
  
Hope this helps,  
  
cerebrate-ga

Search Strategy:

Personal knowledge as sysadmin.
"average packet size" -
://www.google.com/search?sourceid=navclient&ie=UTF-8&oe=UTF-8&q=average+packet+size
"IP routers packet size" -
://www.google.com/search?sourceid=navclient&ie=UTF-8&oe=UTF-8&q=IP+routers+packet+size

Thank you very much for that.