Since I don't have a switch which is capable of timestamping, I would simply
loop the packet back to the sender on a different interface:
eth0 -> ingress switch ... egress switch -> eth1
This is a common approach - you don't need NOX or OpenFlow to do this, and no
time synchronization is required since there is a single clock.
On Dec 19, 2011, at 1:59 PM, Walid van Boetzelaer wrote:
> Hello, and thank you for your answer.
>
> I got this working and using send_stats_request was the way to go. I now have
> something similar to an available bandwith (assuming speed is the
> max_bandwidth, i do speed-link_utilization)
>
> I would like now to get the latency between two switches. I would be curious
> to know what the best way to do this is.
> My idea, though i can't figure out which commands to use, is the following:
> have a switch send a packet to the neighbor switch, have it timestamp it,
> send it back to the first switch, have it timestamp it, return it to the
> controller, and from that, get the latency.
>
> If someone has thought of this already, could you point me to the functions i
> should be using to get this working?
>
> Thank you in advance,
>
> Walid van Boetzelaer
>
>
>
>
>
> 2011/12/18 Murphy McCauley <jam...@nau.edu>
> On Dec 18, 2011, at 11:52 AM, Walid van Boetzelaer wrote:
>
> > Openflow does maintain counters for each flow table, and these counters
> > have the number of received packets per port, etc... How can I retrieve
> > these?
>
> At the OpenFlow level, you do this by sending an ofp_port_stats_request
> asking for stats of type OFPST_PORT. You'll get back a response of
> ofp_port_stats which contains byte and packet counters for the port.
>
> The easiest way to do this from Python in NOX is using component's
> register_for_port_stats_in() to set a callback for port stats messages, and
> then using pycontext's send_port_stats_request() to send an actual request.
> (From inside your component, I think these are
> self.register_for_port_stats_in() and self.ctxt.send_port_stats_request().)
>
> Alternatively, the switchstats or monitoring components may do what you need.
>
> Hope that helps.
>
> -- Murphy
>
>
> Walid wrote:
> Hi all!
> I need to calculate the bandwidth and latency between two switches. To
> achieve this, I plan to:
> C
> ___|___
> / \
> / \
> h1------p1:s1:p2-----p1:s2:p2--------h2
> -bandwidth:
> stat0 = number of packets that went through s1_p1 and s2_port1 at time t1
> generate traffic from s1 to s2
> stat1 = number of packets that went through s1_p1 and s2_port1 at time t2
> bandwidth = (stat1-stat0)*size_of_packet/(t2-t1)
> -latency:
> latency = send a packet from s1 to s2, check the timestamp at s1, s2,
> subtract them
>
> However, I am having trouble as to generating traffic. I checked the stats
> variable passed to the datapath_join events, and i get the following:
> I've been looking into these stats (and switchstats as well) for a while,
> because I believe they can help me retrieve the information I need. However,
> I am unsure as to what 'speed' here means. Also, I can't see where the number
> of packets that traverse a port is.
> Openflow does maintain counters for each flow table, and these counters have
> the number of received packets per port, etc... How can I retrieve these?
> Thank you in advance!
> Best regards
> {'ports': [
> {'hw_addr': 'b\x9e\x04\xb9h,', 'curr': 192, 'name': 's1-eth2', 'speed':
> 10000, 'supported': 0, 'enabled': True, 'flood': True, 'state': 0, 'link':
> True, 'advertised': 0, 'peer': 0, 'config': 0, 'port_no': 2}, {'hw_addr':
> '\x00# \xba\xc0\x97', 'curr': 0, 'name': 'dp0', 'speed': 0, 'supported': 0,
> 'enabled': False, 'flood': True, 'state': 1, 'link': False, 'advertised': 0,
> 'peer': 0, 'config': 1, 'port_no': 65534}, {'hw_addr':
> '\x9e\xe7\xf1\xcb\xdd\x17', 'curr': 192, 'name': 's1-eth1', 'speed': 10000,
> 'supported': 0, 'enabled': True, 'flood': True, 'state': 0, 'link': True,
> 'advertised': 0, 'peer': 0, 'config': 0, 'port_no': 1}], 'n_tables': 2,
> 'n_bufs': 256L, 'actions': 4095L, 'caps': 135L}
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