line-rate, latency, enterprise edge

[flokki123]

hi,

i have 3 questions.

1.

i read that the line rate is the speed of all ports sending traffic at the same time, full-duplex, at the maximum speed of the interface.

would that mean if i talk about the line-rate of a switch (e.g. 24 port switch gigabit) the line rate would be 48 Gbit?

or if i want to switch or route at line speed that the switch would at leat 48gbit of througput?

2.

can someone explain the term "latency" in regards to networking. had a look on the internet but couldnt find helpful stuff.

i have read that e.g. nexus switche have a lower latency than e.g. catalyst switches, but still both can switch non-blocking.

i know that e.g voice traffic is latency dependent, but what does that mean?

3.

i started studying for the ccnp and read the ccnp switch book from richard froom.

the book says that there are 5 - 6 parts of a enterprise network(campus, core, data center, internet edge, wan/branch and teleworker)

but then suddenly mentions the "client-enterprise edge appliations" . according to the book these applications use servers on the "enterprise edge".

is the "enterprise edge" interchangeable with "internet edge"?

thanks for any help!

florian

[Joseph W. Doherty]

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Posting

#1 No, aggregate throughput would be 24 Gbps for 24 gig duplex ports, this because one port's in is another port's out.  (NB: packets-per-second would be based on this.)  However, the fabric for such a switch would be rated at 48 Gbps.

#2 latency is just delay.  Switches (and routers) take some time to process a frame (packet) so they add latency.  Switches that store-and- forward, wait for the frame to be fully received before forwarding it, so even without any additional processing, this adds latency (that's not on hubs which regenerate at the bit level).  Nexus switches have revived another method besides store-and-forward, cut-through.  In this method, the switch doesn't wait for the whole frame to be received before starting to forward it, which reduces latency.  Store-and-forward latency is lower with "faster" links (takes less time to receive a frame), and as FastEtherent and GigEthernet came along, cut-through fell out of favor, but with resurgence of cluster type computing, cut-through has been found needed to reduce latency even for gig links.  There's at least two kinds of cut-through that I'm aware of, dealing with whether a frame fragment might be forwarded or not, but don't recall which or both the Nexus supports.

[flokki123]

1)

but i thought if it states that its full-duplex, then its sending and receiving per port, so for 1gbit port 2gbit.

or because one port is receiving and another one sending the packet out, each port is only calculated with 1gbit?

2)

thanks for the info, makes total sense!

[Joseph W. Doherty]

Disclaimer

The      Author of this posting offers the information contained within this      posting without consideration and with the reader's understanding   that    there's no implied or expressed suitability or fitness for any    purpose.   Information provided is for informational purposes only  and   should not   be construed as rendering professional advice of any  kind.   Usage of  this  posting's information is solely at reader's own  risk.

Liability Disclaimer

In      no event shall Author be liable for any damages whatsoever    (including,   without limitation, damages for loss of use, data or    profit) arising  out  of the use or inability to use the posting's    information even if  Author  has been advised of the possibility of   such  damage.

Posting

but i thought if it states that its full-duplex, then its sending and receiving per port, so for 1gbit port 2gbit.
or because one port is receiving and another one sending the packet out, each port is only calculated with 1gbit?

Envision a single gig wire, full-duplex.  We have gig in both directions, or 2 gig total.  Now drop a two port switch into the middle of the wire, what's changed?  Do we still have 2 gig (each port x 1 gig) or do we now have 4 gig (each port x 2 gig)?

[flokki123]

i would say we now have 2x 2gbit, so 4gbit, cause each port has 1gbit in each direction.

but still with the full line rate i thought as it states full-duplex i have to take the number times twice.

[Joseph W. Doherty]

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

Well you can say that, but there's only 2 gig passing through the switch.  Also, when you look at PPS (packets per seconds) switch specs, you'll see they too recognize that.

The fabric, though, does have to deal with each port's duplex traffic so it "sees" 4 gig, which is why fabrics specs are 2x nominal duplex port bandwidths.