Network performance test

Throughput

throughput means as data transfer rate or digital bandwidth consumption and denotes the achieved average useful bit rate in a com-

puter network over a physical communication link. so it is measured below the network layer and above the physical layer, e.g, data link layter in OSI 7 layer concept.

In network terminology, one Kbit/s means 1,000 bit/s and not 1,024 bit/s

Round trip time

Round trip time (RTT) is the total amount of time that a packet takes to reach the target destination and get back to the source address.

round-trip delay is typically between 1msec and 100 msec, which can be measured using ping or traceroute.

Bandwidth delay product

Bandwidth Delay Product (BDP) is an approximation for the amount of data that can be in flow in the network during a time slice.

To compute the BDP, it is required to know the speed of the slowest link in the path and the Round Trip Time (RTT) for the same path, where the bandwidth of a link is expressed in Gbit/s and the RTT in msec.

The BDP is very important in TCP/IP to tune the buffers in the receive and sender side. Both side need to have an available buffer Bigger than the BDP in order to allow the maximum available throughput, otherwise a packet overflow can happen because of out of free space.

Jumbo Frames

Jumbo frames are Ethernet frames that can carry more than the standard 1500 bytes of payload It was defined that jumbo frames can carry up to 9000 bytes, but some devices can support up to 16128 bytes per frame (called as Super Jumbo Frames).

Almost all 10 Gbit/s switches support jumbo frames, and new switches supports super jumbo frame

The size of the frame is directly impact to

• increase the performance on the network, once the amount of overhead is smaller
• the interface Maximum Transfer Unit (MTU), and it is a specific adapter configuration that must be set for each node in a network, all interfaces in the same network should have the same MTU in work to communicate properly, a different MTU on a specific node could cause awful issues.

MTU size can be changed $ifconfig <interface> mtu <size>

Jumbo frames not only reduce I/O overhead on end-hosts, they also improve the responsiveness of TCP by accelerating the congestion window increase by a factor of six compared to the standard MTU.

Setting the MTU to a high number does not mean that all your traffic would use jumbo packets. For example, a normal ssh session is almost insensible to a MTU change, once almost all SSH packets are sent using small frames