TCP/IP & Ethernet: How Does Ethernet Fit In?

[fog37]

TL;DR Summary

Understand the role of Ethernet protocol in data communication

Hello Forum,

I understand that the TCP/IP suite of protocols manages how data is transmitted/received over the internet. the data is broken into into packets/frames with max size of 1500 bytes. Each different layer applies all sorts of extra data, called headers, to the packets, etc.

Data packets go down the OSI layers and get bigger as more information is applied by each different layer (transfer layer, network, layer, etc.). Eventually the packets embark on their journey to their destination routed by all the routers on the Internet.

Assuming that is correct, I am trying to understand where the Ethernet protocol, which pertains to layer 2 of the OSI system right before the physical layer, fits. Is the ethernet protocol involved as data travels through the internet? I hear about the Ethernet protocol mainly in the context of LANs. For example, let's say we write a word document in Word and send it to a friend over the Internet. What exactly is the role of the Ethernet protocol in that scenario? Ethernet seems to be the important protocol used within a LAN. I have been thinking only the TCP and IP protocols were being used. Or is the ethernet protocol always applied to the data, in LAN, intranets, as well as in the Internet?

Thank you!

 

[anorlunda]

Have you checked Wikipedia before asking? It should be trivial to find tutorial information about Ethernet.

Ethernet is one of several methods that allow multiple nodes on a LAN to share the same pair of wires without interfering with each other. Ethernet's strategy is called CSMA (collision sense, multiple access). Token ring was another scheme. For the most part, all the others fell aside and Ethernet is king.

 

[fog37]

Thanks. I did, probably note well enough. Your comment is helpful explaining that ethernet is used in the LAN context. So if two LANs are communicating over the internet, the data leaving one LAN must already carry ethernet protocol information encapsulated in the packet. I guess I was wondering if that is true in general or if ethernet does not apply sometimes...

Thanks

 

[anorlunda]

Thanks. I did, probably note well enough. Your comment is helpful explaining that ethernet is used in the LAN context. So if two LANs are communicating over the internet, the data leaving one LAN must already carry ethernet protocol information encapsulated in the packet. I guess I was wondering if that is true in general or if ethernet does not apply sometimes...

Thanks

No. Ethernet is not used between LANS. It is not encoded inside the packets. Please read up on what Ethernet is and how it works.

 

[Svein]

1. TCP/IP does not follow the OSI model
2. IP is not concerned about the physical transmission of data packets. Whatever method is used to transfer bits (or symbols as they are known in physical transmission slang)
3. Ethernet is able to carry several protocol types, IP is just one of them (see rfc1700 for a list)

 

[MikeeMiracle]

1. TCP/IP does not follow the OSI model

I believe that all protocols follow the OSI model, it was created before most of today's protocols were to invented to demonstrate how data could be transmitted via a network. More of a theoretical "this is what you would have to do" type concept.

TCP just doesn't map 1-2-1 with the OSI model. TCP has 4 layers instead of 7, the 1st 3 layers match up with the OSI layers and the 4th encompases the last 4 OSI layers (4-7.)

 

[fog37]

Thanks MikeeMiracle. Good point.

As far as ethernet goes, it only extends to the LAN area, so not over the Internet. Ethernet is one form of LAN protocol. There are exceptions like wide area Ethernet.

 

[MikeeMiracle]

Indeed, I believe Ethernet was created as a local network protocol for transmission over copper cables to create a "spoke system" like the spokes on a bicycle wheel. With everything connecting to one central "hub/switch" which can then have other switches daily chained onto it. Older technologies include "Token Ring" where it was just 1 cable which ran between the network cards of each computer. Naturally the ring topology does not scale well, you can only get so much data onto 1 cable before physical limits are reached as you can only have 1 network device "talk" over the cable at a time.

There is also a limit to the speeds you can reach on a copper cable, connections from the ISP onwards to the internet are all carried out over fibre connections of various descriptions.

 

[pbuk]

You asked almost exactly the same question in 2016: that was a while ago so perhaps you have forgotten about it. But you also asked a similar question only five months ago, what's going on? Do you really retain so little information, or do you have some other reason for using the forum this way?

 

[fog37]

You asked almost exactly the same question in 2016: that was a while ago so perhaps you have forgotten about it. But you also asked a similar question only five months ago, what's going on? Do you really retain so little information, or do you have some other reason for using the forum this way?

Apologies. I need to be more careful when asking. I completely forgot about those threads. The topic resurfaced as I was resetting my home network and wondered about those same concepts...thanks for point that out.

 

[jbriggs444]

Indeed, I believe Ethernet was created as a local network protocol for transmission over copper cables to create a "spoke system" like the spokes on a bicycle wheel. With everything connecting to one central "hub/switch" which can then have other switches daily chained onto it. Older technologies include "Token Ring" where it was just 1 cable which ran between the network cards of each computer. Naturally the ring topology does not scale well, you can only get so much data onto 1 cable before physical limits are reached as you can only have 1 network device "talk" over the cable at a time.

There is also a limit to the speeds you can reach on a copper cable, connections from the ISP onwards to the internet are all carried out over fibre connections of various descriptions.

The original Ethernet (10Base5) was based on a single cable up to 500 meters long with stations on taps in the cable spaced at least 2.5 meters apart. That physical topology was linear. At least until one factors in repeaters.

[We didn't do many repeaters on our thick-wire networks. Just a DELNI here or there. Deployed a few DEMPRs on our thin-wire -- we were a DEC shop]

It was a shared medium (CSMA-CD) based around a broadcast model. Modern switched Ethernet shrinks the broadcast domains down to individual point to point links which can be run full duplex. No more CSMA-CD. No more restrictive distance limitations.

The use of store-and-forward switching on what is still conceptually a broadcast model leads directly to the need to enforce a spanning-tree topology which looks similar to hub and spoke. [Some fancier switch fabrics get away from IEEE spanning-tree and go with something like IS-IS]

In the good old days, Ethernet (and Token ring) were LAN while serial lines (T1's, DS3's, ISDN, DSL or even dial-up) running HDLC, DDCMP, PPP, or frame relay ruled the WAN. These days, carriers tend to use gig-E handoffs with dot1q tagged VLANs regardless of the actual transport protocol.

 

[Svein]

I believe that all protocols follow the OSI model, it was created before most of today's protocols were to invented to demonstrate how data could be transmitted via a network. More of a theoretical "this is what you would have to do" type concept.

TCP just doesn't map 1-2-1 with the OSI model. TCP has 4 layers instead of 7, the 1st 3 layers match up with the OSI layers and the 4th encompases the last 4 OSI layers (4-7.)

Sorry, TCP/IP does not follow the OSI model (it was up and running before the OSI model was created).

To quote Tanenbaum: "The OSI model is fine in theory, but almost impossible to implement. TCP/IP is easy to implement, but it does not fit any model except TCP/IP).

Again: IP does not care about the physical layer, it has only two main primitives: ReceivePacket and SendPacket. The implementation is responsible for attaching the physical layer to these primitives.

One more comment about the OSI model. Layer 2 - the Data Link Layer - had to be split into two sublayers very soon, the MAC layer (Media Access Control) and the upper Data Link Layer. The upper Data Link Layer can be used to implement a basic data integrity control, but this is usually not used in data transmission where the data integrity checks are performed in the transport layer.

 

[sysprog]

Alebra Technogies Parallel Data Mover (https://alebra.com/parallel-data-mover-pdm/) doesn't follow the OSI 7-layer model, but you could interpret some of it via that model . . .

 

[MikeeMiracle]

Sorry, TCP/IP does not follow the OSI model (it was up and running before the OSI model was created).

Yes they don't always exactly match but generally they all follow the pattern, I got the layers which matched muddle up in my earlier post but I did recall correctly that TCP/IP only had 4 layers instead of 7.

We may be talking semantics here...

 

[Svein]

The figure you have copied is at least misleading and in several cases wrong.

• Physical layer: RS232C is correct, UTP cables are just silly (they are cables - you can use them for whatever you want). DSL is a protocol and should be at the link layer, Optic fiber is a medium, not a physical layer protocol.
• Data link layer: Ethernet is present on the physical layer in several versions and in the lower half of the data link layer (the MAC layer).
• Network layer: All protocols cited here belong in the TCP/IP family. ARP is not a network protocol.
• Transport layer; The protocols cited here belong in the TCP/IP family. The OSI counterparts are not mentioned
• Session layer: NFS lives on top of UDP and is more or less extinct. What is SQL doing here?
• Application layer: Why is Modbus placed here?

https://en.wikipedia.org/wiki/List_of_network_protocols_(OSI_model) has a better list of the protocols at each layer.

I have a large poster where all the (original) OSI protocols are listed. Several of those seem to have disappeared;

• Network layer: ISO/DIS 8348, X.25, X.21
• Transport layer: ISO/DIS 8073 (X.224) class 0 and class 4
• Session layer: X.215, X.225

And so on. The poster is huge!