Spirent SmartBits System, Reference Manual

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Glossary of Terms
Features and Terminology
254 SmartBits System Reference
Features and Terminology
Most of the following features are available in SmartWindow and have corresponding
commands in SmartLib; many features and terms are used throughout other SmartBits
applications as well.
Important: For variations on a given feature, please consult the online help or user guide
of each application.
Address Resolution Protocol (ARP)
In order for data streams to be sent through a router, the SmartBits cards have to know the
MAC address of the router port and the router has to know the MAC addresses of the
SmartCards. This is done using ARP (Address Resolution Protocol) packet exchanges.
ARP maps an IP address to a MAC address. This IP address is the address of the router
port connected to the SmartCard, not the IP destination of a packet. The router port
IPaddress is specified in the entry called
Default Gateway . When this entry is set–that is,
not zero–the ARPs generated by the SmartCard will go to this address instead of the
specified IP destination address.
The router will also issue ARP requests to the SmartCards. These will be replied to by
either the local stack or the protocol stream if the target IP address in the ARP request
packet matches the Source IP address in the stream or stack.
Setting the gateway to all 0’s will direct frames to the destination IP address. This will
perform ARP exchanges with the destination port for local traffic, or in Layer 2 tests will
serve the purpose of learning frames through a Layer 2 device.
authentication setup
Certain SmartCards that use PPP (ATM, WAN, POS) can act as an authentication client,
authentication server, or as a client and server simultaneously.
backoff truncation exponent
By default, all Ethernet SmartCards are configured for a Backoff Truncation Exponent
value of 10 that coincides with the 802.3 backoff requirement standards.
In SmartWindow, this default value can be changed on a per port basis by selecting
Backoff Truncation Exponent from the Options pull down menu. When selected, two
windows appear: one for selecting the ports to modify and the other for selecting the new
Backoff Exponent value. Integer values from 1 to 10 can be chosen. Smaller values result
in the test port being more
aggressive in a collision situation, since the truncation for
backoff times will start at a lower number of successive collisions.
Class of Service
Used to designate a forwarding device as capable of prioritizing data traffic.