Posted: Thu Jan 15, 2004 4:50 pm Post subject: [Asterisk-doc] (Fwd) Re: [Asterisk-Users] re hardware requir
Ok, here comes the first forwarding "food"!
See Rich's reply at the end, that's the valuable part.
I guess this best fits somewhere into the admin section?
Philipp
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Date sent: Thu, 15 Jan 2004 07:04:14 -0600
From: Rich Adamson <radamson@routers.com>
Subject: Re: [Asterisk-Users] re hardware requirement - asterisk
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For fxp0, the internal interface although the nic can do full-duplex it
seems to me that it is only running simplex!!
Same for xl0, the external interface. It is running 10BaseT but again it
is simplex.
Does that affect my voip performance? Is it true that every step of the
way the network has to be full-duplex?
There are no RFC standards on "how" duplex settings are negotiated across
a cat 5 cable, etc. Most vendors support auto-negotiate, but somewhere
near 50% of the time, its negotiated incorrectly. Part of the problem is
that both ends of the cable attempt to negotiate at roughly the same time,
one end locks into full while the other locks into half.
When that happens, the end that "thinks" full duplex is fine steps all over
the packets being sent from the half-duplex end, causing damaged packets,
etc. Since we're talking about UDP traffic, that's Not A Good Thing.
The system will run fine if both ends are operating at half duplex, however
bandwidth (and performance) will be limited to something below about 30%
utilization. In many systems, that is more then adequate. However, on a
heavily loaded system, statically locking the interfaces (at both ends)
to full duplex will allow utilizations up towards 90% without degradation.
Posted: Thu Jan 15, 2004 5:01 pm Post subject: [Asterisk-doc] (Fwd) Re: [Asterisk-Users] Re Hardware requir
Add this
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Date sent: Thu, 15 Jan 2004 09:37:14 -0500
From: Glen Ford <gford@idiom.com>
Subject: Re: [Asterisk-Users] Re Hardware requirement -Asterisk
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On my Linux box mii-tool yeilds the following which shows 100mbs full
duplex.
[root@glen gford]# mii-tool
eth0: negotiated 100baseTx-FD, link ok
Posted: Fri Jan 16, 2004 9:03 am Post subject: [Asterisk-doc] (Fwd) Re: [Asterisk-Users] re hardware requir
Here comes part three to the "duplex story" and why it matters.
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Date sent: Thu, 15 Jan 2004 13:54:00 -0600
From: Rich Adamson <radamson@routers.com>
Subject: Re: [Asterisk-Users] re hardware requirement - asterisk
To: asterisk-users@lists.digium.com
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[...]
Just for fun, I moved our * box to a 10meg al-cheapo hub to force 10-half,
placed a sip-to-sip call (via two C7960's) and noticed audio was very
much half duplex. Very irritating to say the least (worse then most digital
cell-to-cell calls).
Then without changing anything other then moving the * interface to an
upstream switch running 100 full (and verifying settings), the
half-duplex-sounding audio effects completely disappeared (as expected).
While both tests were being conducted, I ran a Sniffer analyzer to monitor
packets and validate results.
10-half vs 10-full does have a substantial impact on quality. Moving from
10-full to 100-full would have no impact unless I could have loaded it
with more rtp sessions then what I currently have the ability to do.
And, FWIW, an interface set to half-duplex on one end with full-duplex
on the other end was by far worse then when both ends of the cat 5 matched.
All tests were conducted by forcing rtp traffic "thru" * (didn't allow
the rtp to flow between the two sip phones).
BTW, 10-Full setting is truly available on a large number of NICs, but
not all. Obviously, the older stuff didn't support it, nor do the older
Cisco 10 meg interfaces, etc.
Posted: Sat Jan 17, 2004 10:42 pm Post subject: [Asterisk-doc] (Fwd) Re: [Asterisk-Users] re hardware requir
In the sake of making sure we don't falsely document everything, I have
some comments about this post:
Quote:
There are no RFC standards on "how" duplex settings are negotiated
Hold the phone! (bad pun, *har har*). It is true that there are no RFCs
about Ethernet auto-negotiation, but there are no RFCs about Ethernet,
either. Ethernet is defined in IEEE 802.3 (the CSMA/CD standard) which,
since 1995 (when the 802.3u supplement came out, my books tell me),
Auto-Negotiation has been part of the standard. Auto negotiation is
supported for the most common copper media.
Quote:
across a cat 5 cable, etc. Most vendors support auto-negotiate, but
somewhere near 50% of the time, its negotiated incorrectly. Part of the
If auto-negotiation fails, the link probably won't come up... the
negotiation is part of the FLP messages that also set up timing and such.
The only situation where this could happen is on devices that don't
support auto negotiation and are manually configured for a certain speed.
Quote:
problem is that both ends of the cable attempt to negotiate at roughly
the same time, one end locks into full while the other locks into half.
No, if they can't match, the link won't come up. If they do, you have
some broken devices. The only time this could ever happen is if one end
of the link was manually set at a speed.
Quote:
When that happens, the end that "thinks" full duplex is fine steps all
over the packets being sent from the half-duplex end, causing damaged
packets, etc. Since we're talking about UDP traffic, that's Not A Good
Thing.
Like I said, if speeds were manually set, and the device on the other end
of the link wasn't intelligent (i.e. a cheap repeater), there would be
late collisions and lost frames. This is why messing with
auto-negotiation on a repeater is an especially dangerous idea.
Quote:
The system will run fine if both ends are operating at half duplex,
however bandwidth (and performance) will be limited to something below
about 30% utilization. In many systems, that is more then adequate.
However, on a heavily loaded system, statically locking the interfaces
(at both ends) to full duplex will allow utilizations up towards 90%
without degradation.
I do agree that full-duplex will speed things up tremendously in VoIP
applications.
In most applications the difference is small. Consider this
over-simplification of how most protocols work:Alice Bob
------------------------------------------------
Opens connection.
Gives Go-Ahead
Asks for data
(Maybe) Acknowledges asking
Sends Some Data
Acks data
Sends some more
Acks that.
Tells Alice that he's done
Thanks Bob
Closes connection
In this example, the protocol is half-duplex by nature, thus making a
full-duplex connection is really just benefiting the other protocols that
are sending the occasional message in the background (DHCP or NTP, for
example) rather than the connection that the user is engaging in. But for
VoIP applications, both sides of the primary application are
connection-less and transmitting at the same time -- full duplex by
nature.
Not trying to be mean or arrogant, I just want to set the facts straight.
Posted: Sun Jan 18, 2004 3:00 pm Post subject: [Asterisk-doc] (Fwd) Re: [Asterisk-Users] re hardware requir
On Sat, 2004-01-17 at 17:42, Nick Bachmann wrote:
Quote:
Not trying to be mean or arrogant, I just want to set the facts straight.
And we appreciate that.
Any more comments on this posting ? Is this something we want to add to
the book? It's not very Asterisk specific. Maybe this is something
that should be learn from a Radia Perlman book.
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