Oliver Hookins wrote:
O Plameras wrote:
Voytek Eymont wrote:
On Mon, December 11, 2006 11:21 am, Scott Waller (Lots of Watts) wrote:
Finally changed over to Layer2 1.5 meg
blah blah blah. And am having problems with my setup.
Scott, dumb question:
I thought about this.
what's the advantage of having a 'Layer2' connection over the usual
'userid/password/login' connection ?
Better throughput than Layer3, in general. Devices on Layer2 work
less as hard than
devices on Layer3. Layer3 assembles data before send and
dis-assembles at receive.
Layer2 does not. So, less latency.
Not quite right, you still have layer 2 frames which are disassembled
and reassembled. However your device is operating as a simple ethernet
(or ATM if your ISP supports it) bridge rather than also encapsulating
the traffic in PPP which is the norm, hence less overheads.
A somewhat detailed description.
1. Layer 2 networks are connected together using hubs, bridges and
switches. Common denominator
is that these devices only forward frames. None of these devices have to
disassemble or reassemble data.
Specifically,
1.1 Hubs take each frame that is received and send duplicate frames
simultaneously out to all other ports.
1.2 Bridges forward broadcasts between two connected networks until they
have located all hosts.
1.3 Switches forward broadcast traffic only when it doesn't know where a
host is.
1.4 Because nothing is done to the data along the way, layer 2 networks
are often
considered to be 'faster' than a layer 3 network.
2. Layer 3 networks are built to run on top of layer 2 networks.
2.1 In an IP layer 3 network, the IP portion of the datagram has to be
read.
2.2 This requires stripping off the datalink layer frame information.
2.3 Once the protocol frame information is stripped, the IP datagram
has to be reassembled.
2.4 Once the IP datagram is reassembled, the hop count has to be
decremented,
the header checksum has to be recalculated, a lookup for routing must be
made,
and only then can the IP datagram be chopped back up and inserted into
frames
and transmitted to the next hop. All of this takes extra time.
O Plameras
--
SLUG - Sydney Linux User's Group Mailing List - http://slug.org.au/
Subscription info and FAQs: http://slug.org.au/faq/mailinglists.html
