OSI MODEL

[turborob]

Could you please tell me, on what level of the osi model do these items operate?::

network interface cards
Concentrators/Hubs
thanks..rob

 

[benzito]

Concentrators/Hubs Are layer 1 <physical layer> devices.

Network Interface cards reside @ layer 2 <datalink layer> of the OSI model.

 

[Guest_imported]

Actually the way I understand it, both hubs and NICs are layer 1. Hardware is generally physical layer. The protocol that runs across the NIC and hubs (Ethernet) is layer 2 with TCP/IP covering layers 3 and 4.

 

[benzito]

a nic is a layer 2 device. when u think nic think mac address and ethernet. i don't understand what you mean by &quot;Hardware is generally physical layer&quot;. a router is a piece of hardware, but it operates @ layer 3 b/c of the protocols it incorportes. get away from thinking hardware = physical layer. instead look @ what protocols drive the h/w to determine what layer of the osi model it resides in.

 

[daronwilson]

Well...almost. Again most of the confustion appears to be terminology. Since this isn't a WaReZ group, I'll use full words and sentences.

&quot;The physical layer is really a set of rules regarding the hardware used to transmit data. Among the items covered at this level are the voltages used, timing and rules for establishing the initial handshaking communication connection. The physical layer also includes descriptions of the acceptable connectors and interfaces to the media. At this level, the OSI model is really concerned with the electrical considerations and bits. The bits do not really have any meaning here - that is the responsibility of the next OSI layer&quot;

&quot;The data link layer is concerned with packaging the data into data frames, it adds flags and error checking.&quot;

&quot;The data link layer is divided into two sublayers, the Logical Link Control (LLC) and the Medium Access Control (MAC) layer.&quot;

&quot;The MAC layer is responsible for defining the rules that govern how the devices on a LAN share a common network communications channel. Processes at the MAC sublayer include: Medium access management, framing, addressing, error detection.&quot;

&quot;The LLC layer defines a common set of services to be used by all LAN technologies for communications between the MAC sublayer and the Network layer. The role of this sublayer is to shield the upper layers from the low level signaling specifications associated with the MAC sublayer and the Physical layer of each LAN technology. The LLC includes processus such as initiating control signal interchanges, organizing data flows, interpreting commands, generating responses, carrying out error control and recovery.&quot;

Now....to paraphrase that, as I see it, if there is a physical connection on the device in question, it must operate at the physical layer. After that, it MAY operate at higher levels depending on its function. NIC's operate at the physical layer, the MAC sublayer, and the LLC sublayer. Hubs operate at the same layers. When you step above that to switches and routers, they operate at the lower levels as well as upper layers depending on the device and the software associated with it.

References quoted are Business Data Communications and Networks - Raymond Panko, Understanding Local Area Networks - Stan Schatt, Telecommunications Distributions Design Manual - BICSI.

Hopefully that answers your questions, the OSI model always makes me dig out the books because there are different explanations and ideas. If I misinterpreted the text, please help me understand.


Daron J. Wilson, RCDD
Telecom Manager
LH Morris Electric, Inc.
daron.wilson@lhmorris.com

 

[faieez]

The above mentioned question about the hubs and the Nic.
the picture is very clear about them.
If you would done the CCNA it would have been a lot easier to understand about them anyhow. the NIC is sured to be operable at the layer 2 and hub is many people say is a dumb device it has noting to do with the routing of information it just passes all the info at all the ports it also works at the same layer but comparing it to another device which works on the layer 2 is the switch which doesn't broadcast all the info at its prots. The Nic usually comes in the internal heraricy of the computer from where the data is enclosed into a box which has a mac address of that Nic from where it is been packed for the further transfer of the data from one computer to another.

 

[benzito]

Daron,

I can see how you would think that but stick by my original position. The fact that a layer 2 device is also a layer 1 device should be assumed when dealing w/ the osi model b/c the osi model is essentially a stack. You can't have a network w/o layer 1. You made the following incorrect assumption...

&quot; NIC's operate at the physical layer, the MAC sublayer, and the LLC sublayer. Hubs operate at the same layers. &quot;

A Hub is a Layer 1 device. The MAC and LLC sublayers are part of Layer 2.
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Here's a quote from a Networking Essentials book I keep around for reference..

&quot;The Data Link layer is responsible for the physical addresses of devices on the network. Every device on a network has a hard-coded address attached to it. An example of this address for an Ethernet card would be 00-AA-00-59-65-71. From here I refer to this as the MAC address&quot;

That quote clearly binds Ethernet cards to the Data Link layer.

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Also see Section 2 of the following link.

http://searchwin2000.techtarget.com/sDefinition/0,,sid1_gci212627,00.html