Global attributes

Node attributes

The compile attribute indicates which C source files are to be compiled and executed by cnet. In the example topology file, above, an instance of the source code in the single file stopandwait.c will be executed by each of Perth and Melbourne. Each node will have its own copy of all variables declared in the file stopandwait.c (globals, static globals, locals and static locals).

When executing, each node's protocol code (in C) has access to its own CnetNodeinfo structure describing the node's attributes. This structure is best considered read-only as its contents are ``refreshed'' as each node is scheduled for execution.

typedef struct { char nodename[MAX_NODENAME_LEN]; CnetNodetype nodetype; /* Either a NT_HOST or a NT_ROUTER */ int nodenumber; /* Ranging from 0.._NNODES-1 */ CnetAddr address; /* Possibly different to the nodenumber */ int nlinks; /* Ranging from 0(=LOOPBACK) .. nlinks */ int minmessagesize; /* min size (in bytes) of msgs generated */ int maxmessagesize; /* max size (in bytes) of msgs generated */ int messagerate; /* rate of msg generation (in ms) */ long time_in_ms; /* a monotonically increasing clock */ struct { long sec; long msec; } time_of_day; /* a reflection of the wall-clock time */ } CnetNodeinfo; CnetNodeinfo nodeinfo;

Link attributes

When executing, each node's protocol code (in C) has access to its own CnetLinkinfo structure describing the link's attributes. This structure is best considered read-only as its contents are ``refreshed'' as each node is scheduled for execution. The global variable linkinfo is a vector of CnetLinkinfo structures. linkinfo[0] maintains attributes of the pseudo LOOPBACK link, linkinfo[1] maintains attributes of the first true physical link, and so on.

typedef struct { int linkup; /* TRUE if link not severed */ int bandwidth; /* in bits per second */ int propagationdelay; /* in ms */ int transmitbufsize; /* in bytes */ int costperbyte; /* in cents(?) */ int costperframe; /* in cents(?) */ } CnetLinkinfo; CnetLinkinfo *linkinfo; /* linkinfo[0]..linkinfo[nodeinfo.nlinks] */

To find the propagation delay of the first ``real'' link in a 2 node simulation, each node would simply access linkinfo[1].propagationdelay .

Units and their specification

All times are stored internally in milliseconds though in the topology file their integral values may be followed by suffixes such as ms and s.

All data sizes are stored internally in bytes though in the topology file their integral values may be followed by suffixes such as bytes, Kbytes, KB, and MB.

Link bandwidths are stored internally in bits-per-second though in the topology file their integral values may be followed by suffixes such as bps, Kbps, and Mbps.

Boolean attributes may take on the values true, false, and toggle.

Strings are enclosed within double quotes.

Probabilities specify a uniform distribution, with their value being the log-base-2 of the chance of failure (yes, this is ugly). In a typical topology file, the global probframecorrupt attribute may declare that a frame will be corrupted with probability of 1 in 8 (2 to the power 3) while the link from Melbourne to Perth will lose (on average) every fourth frame. A probability of 0 (the default) means that no errors will be introduced.

cnet was written and is maintained by Chris McDonald (chris@cs.uwa.edu.au)