NS2
Chapter 26
Trace Support
報告者：黃亮維
Outline
 Trace Support
‧OTcl Helper Functions
 Library support and examples
 The C++ Trace Class
 Trace File Format
 Packet Types
Trace Support
 Traces
=> Record each individual packet as it arrives, departs, or
is dropped at a link or queue.
 Trace data is either displayed directly during execution
of the simulation, or (more commonly) stored in a file
to be post-processed and analyzed.
Trace Support
 The trace support in OTcl consists of a number of
specialized classes visible in OTcl but implemented in
C++
=> Combined with a set of Tcl helper procedures and
classes defined in the library.
Trace/Hop： trace a hop
Trace/Enque： packet arrival
Trace/Deque： packet departure
Trace/Drop： packet drop
Trace/Recvpacket： receive event at the destination
node of a link
OTcl Helper Functions
 The following helper functions may be used within
simulation scripts to help in attaching trace elements
(see tcl/lib/ns-lib.tcl).
$ns_ flush-trace
This command flushes the trace buffer.
$ns_ create-trace type file src dst
This command creates a trace object of type <type>
between the <src> and <dst> nodes. The traces are
written into the <file>.
OTcl Helper Functions
$ns_ trace-queue n1 n2 optional:file
This command creates a trace object for tracing events
on the link represented by the nodes <n1> and <n2>.
$ns_ drop-trace n1 n2 trace
This command makes the given <trace> object a droptarget for the queue associated with the link between
nodes <n1> and <n2>.
Library support and examples
 The Simulator procedures described above require the
trace and init-monitor methods associated with the
OTcl Link class.
 The trace function is defined as follows (in ns-link.tcl):
Library support and examples
 1
加入Trace對象
The C++ Trace Class
 The single C++ Trace class is used to implement the
OTcl classes Trace/Hop, Trace/Enque, Trace/Deque,
and Trace/Drop.
 The type _ field is used to differentiate among the
various types of traces any particular Trace object
might implement. Currently, this field may contain
one of the following symbolic characters:
=> + for enque, - for deque, h for hop, and d for drop.
The C++ Trace Class
 The overall class is defined as follows in trace.cc:
Trace File Format
 The []Trace::format method defines the trace file
format used in trace files produced by the Trace class.
 It formats the source, destination, and type fields
defined in the trace object (not in the packet headers),
the current time, along with various packet header
fields including, type of packet (as a name), size, flags
(symbolically), flow identifier, source and destination
packet header fields, sequence number (if present), and
unique identifier.
Trace File Format
Trace File Format
 An example of a trace file (without the tcp header
fields) might appear as follows:
Trace File Format
 flags are used for ECN:
=>TCP/IP 明確擁塞通知 (ECN) 讓路由器能夠通知「傳
輸控制通訊協定」(TCP) 對等體，由於網路擁塞，
緩衝區已滿。TCP 對等體會以減緩資料傳輸來回
應，協助防止封包損失。
Packet Types
 Each packet contains a packet type field used by
Trace::format to print out the type of packet
encountered.
 Initialization of the type field in packets is performed
by the Agent::allocpkt method.
 The type field is set to integer values associated with
the definition passed to the Agent constructor.
Trace Support (wireless)
 cmu-trace objects are of three types
 CMUTrace/Drop
 CMUTrace/Recv
 CMUTrace/Send
Trace Support (wireless)
 An example of a trace for a tcp packet is as follows:
 CMUTrace::format() defines and dictates the trace file
format. (cmu-trace.cc)
Revised format for wireless traces
 cmu-trace objects
 $ns use-newtrace
=>This command should be called before the universal
trace command $ns trace-all <trace-fd>
 Note: Currently this new trace support is available for
wireless.
new trace format
new trace format
 Event type
 In the traces above, the first field (as in the older trace
format) describes the type of event taking place at the
node and can be one of the four types:

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s send
r receive
d drop
f forward
new trace format
 General tag
 The second field starting with "-t" may stand for time
or global setting
 -t time
 -t * (global setting)
new trace format
 Node property tags
 denotes the node properties like node-id, the level at
which tracing is being done like agent,router or MAC.
The tags start with a leading "-N" and are listed as
below:

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-Ni: node id
-Nx: node’s x-coordinate
-Ny: node’s y-coordinate
-Nz: node’s z-coordinate
-Ne: node energy level
-Nl: trace level, such as AGT, RTR, MAC
-Nw: reason for the event. The different reasons for
dropping a packet are given below:
new trace format
 Packet information at IP level
 The tags for this field start with a leading "-I" and are
listed along with their explanations as following:

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-Is: source address.source port number
-Id: dest address.dest port number
-It: packet type
-Il: packet size
-If: flow id
-Ii: unique id
-Iv: ttl value
new trace format
 Next hop info
 This field provides next hop info and the tag starts with
a leading "-H".
 -Hs: id for this node
 -Hd: id for next hop towards the destination.
 Packet info at MAC level
 This field gives MAC layer information and starts with
a leading "-M" as shown below:

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-Ma: duration
-Md: dst’s ethernet address
-Ms: src’s ethernet address
-Mt: ethernet type
new trace format
 Packet info at "Application level“
 The packet information at application level consists of
the type of application
 like ARP,TCP, the type of adhoc routing protocol like
DSDV, DSR, AODV etc being traced.
 This field consists of a leading "-P“ and list of tags