6.4 Commands at a glance

Following is a list of common link commands used in simulation scripts:

$ns_ simplex-link node1 node2 bw delay qtype args
This command creates an unidirectional link between node1 and node2 with specified bandwidth (BW) and delay characteristics. The link uses a queue type of <qtype> and depending on the queue type different arguments are passed through <args>.

$ns_ duplex-link node1 node2 bw delay qtype args
This creates a bi-directional link between node1 and node2. This procedure essentially creates a duplex-link from two simplex links, one from node1 to node2 and the other from node2 to node1. The syntax for duplex-link is same as that of simplex-link described above.

$ns_ duplex-intserv-link n1 n2 bw dly sched signal adc args
This creates a duplex-link between n1 and n2 with queue type of intserv, with specified BW and delay. This type of queue implements a scheduler with two level services priority. The type of intserv queue is given by <sched>, with admission control unit type of <adc> and signal module of type <signal>.

$ns_ simplex-link-op n1 n2 op args
This is used to set attributes for a simplex link. The attributes may be the orientation, color, label, or queue-position.

$ns_ duplex-link-op n1 n2 op args
This command is used to set link attributes (like orientation of the links, color, label, or queue-position) for duplex links.

$ns_ link-lossmodel lossobj from to
This function generates losses (using the loss model <lossobj> inserted in the link between <from> node and <to> node) in the link that can be visualized by nam.

$ns_ lossmodel lossobj from to
This is used to insert a loss module in regular links.

Following is a list of internal link-related procedures:

$ns_ register-nam-linkconfig link
This is an internal procedure used by "$link orient" to register/update the order in which links should be created in nam.

$ns_ remove-nam-linkconfig id1 id2
This procedure is used to remove any duplicate links (duplicate links may be created by GT-ITM topology generator).

$link head
Returns the instance variable head_ for the link. The head_ is the entry pont to the link and it points to the first object in the link.

$link add-to-head connector
This allows the <connector> object to be now pointed by the head_ element in the link, i.e, <connector> now becomes the first object in the link.

$link link
Returns the instance variable link_. The link_ is the element in the link that actually models the link in terms of delay and bandwidth characteristics of the link.

$link queue
Returns the instance variable queue_. queue_ is queue element in the link. There may be one or more queue elements in a particular link.

$link cost c
This sets a link cost of <c>.

$link cost?
Returns the cost value for the link. Default cost of link is set to 1.

$link if-label?
Returns the network interfaces associated with the link (for multicast routing).

$link up
This sets the link status to "up". This command is a part of network dynamics support in ns.

$link down
Similar to up, this command marks the link status as "down".

$link up?
Returns the link status. The status is always "up" as default, if link dynamics is not enabled.

$link all-connectors op
This command applies the specified operation <op> to all connectors in the link. Like, $link all-connectors reset or $link all-connectors isDynamic.

$link install-error errmodel
This installs an error module after the link_ element.

In addition to the Link and link-related commands listed above, there are other procedures to support the specific requirements of different types of links derived from the base class "Link" like simple-link (SimpleLink), integrated service (IntServLink), class-based queue (CBQLink), fair queue (FQLink) and procedures to support multicast routing, sessionsim, nam etc. These and the above procedures may be found in ns/tcl/lib(ns-lib.tcl, ns-link.tcl, ns-intserv.tcl, ns-namsupp.tcl, ns-queue.tcl), ns/tcl/mcast/(McastMonitor.tcl, ns-mcast.tcl), ns/tcl/session/session.tcl.