Maximum packet rate per second on 100BaseT

[Tony Williams]

Does anyone know what the maximum packets per second on a 10/100 TX lan card is?

We see through Measureware about 4500 packets per second both inbound and outbound, and we would like know if this is a high rate, and the card is set at 100Mbps and Full Duplex.

[Tom Danzig]

Defaul MTU is 1500. Therefore 1500 * 4500 packets = 6,750,000 bps. Theoretical max should be about 80-90% of 100Mb/s.

[Berlene Herren]

Tony, to get a realistic throughput figure on the 100BaseT card, you can download netperf and run that, then compare the throughput with the database, located at

http://www.netperf.org

A shameless plug for Rick Jones!

Berlene

[Brian Hackley]

The question you ask is most interesting. The first responder assumes you are transmitting maximum sized packets, such as would be seen during file transfer with NFS, ftp and rcp.

However, in some interactive environments, you'll see 64 byte packets as being the norm. Full duplex gives you 100Mbit/sec inboard and 100Mbit/sec outbound simultaneously, so you can assume a potential thruput at that rate. However, and there is a small IFG (Inter Frame gap) to take into account in all Ethernet environments. I believe this is 512 bit times end-to-end.

Cranking some numbers into your trusty HP Calculator here are two interesting measures:

Bit/sec rate of 4500 64-byte packets:
((64bytes/packet * 8bits/byte) + 512 IFG bits) * 4500 packet/sec = 4,608,000 bit/sec used of possbile 100BaseT LAN bandwidth.

Total # of possible 64-byte packets/sec theoretically possible on 100BaseT link:
100,000,000 bit/sec / ((64 bytes/packet * 8 bits/byte + 512 bit IFG) = 97,656 packet/sec

System overhead on a host is often limited by system load, interrupt service time, kernel thread switching time, and Bus speeds. This is most often why "your milage will vary". Host-based tools such as Berlene mentioned also will add overhead, but will give you an excellent baseline to measure your potentional performance. You might find testing with netperf or ttcp, and experimenting with a variety of packet sizes will help you determine exactly what network performance is possible in your environment!

Hope this helps,
Brian Hackley