An Investigation into Transport Protocols and Data Transport ...

A.2. Network Interface Cards 275
determine how close to theoretical hardware limits data transport is
capable of getting [HJS00].
In general, the the transfer of data between networked computers must
involve the interaction of both hardware and software. In the case of the
hardware requirements, the data must be transferred from memory to the
network interface before the data can be placed onto the network. Therefore,
the interaction and co-operation between the memory subsystem, the
CPU, the bridge to the input-output bus, the input-output bus (in this case
PCI/PCI-X) and finally the NIC are important [HJS00].
In terms of software, the design and implementation of application layer
programs, the network stack, and network drivers is also of importance to be
able to both schedule and regulate data flows into and out of the hardware
subsystems. An overview of some of these major components is presented
below.
TCP/IP Kernel Implementation The translation of data flows from userspace
into transport layer datagrams (with relevant source-destination
and checksum information) are performed here. The encapsulation into
IP packets and then consequently Ethernet frames is also performed
here.
NIC driver The driver provides the translation between the kernel level
data and bit formats which the underlying layer 1 hardware can understand.
Scheduling both input and output data are also managed here
by managing interrupts [PJD04].
NIC hardware The chipset of the network interface card actually does the
work of forming/receiving the electrical, photonic or RF signals for