Difference between serial and Ethernet interface

[trane.m]

Hi,

I'm reading up for a CCNA certification.
In my reading up (and labs) i've seen serial interfaces between some of the network devices. I'm not sure i understand the difference between serial and Ethernet connections.

Why and when would you choose one over the other?
What can one do that the other can't?

I tried searching online for an explanation and even found a similar discussion on this community, but did not understand the answers. I think they were a bit deeper than my level. I hope someone can clarify

[Kasun Bandara]

these two connections using different connectors and standards.

Ethernet uses RJ45 connectors and serial uses V.35 or RS232.

each needs separate network cards to install in routers. for old PCs, serial is motherboard inbuilt. routers support smart serials

Ethernet using IEEE 802.3 standard and serial using frame relay, T1 , etc.

serial ports need bit more configurations such as clock speed sand DTE,  DCE ends.

https://www.ciscoforall.com/difference-between-ethernet-and-serial/

https://www.sluiceartfair.com/2020/other/what-is-the-difference-between-serial-interface-and-ethernet-interface/

https://www.ciscopress.com/articles/article.asp?p=2202412&seqNum=4

[anboom]

Good answer, Kasun plus adding the additional links. 

Additionally, speed and data connections are important to note. Serial will max out 115,000 bps (Serial HOWTO: Speed (Flow Rate) (tldp.org)) where Ethernet is still going up--check this out 400G - Cisco Blogs.

Please let us know if this helps you understand the difference. AB

[trane.m]

@Kasun Bandara  and @anboom, thank you for you descriptions on what the differencies are.

Although, i feel like i still need answers to the following two questions:
Why and when would you choose one over the other?
What can one do that the other can't?

Thank you in advance

[Kasun Bandara]

1. early networks most of ISPs used serial links to terminate connections from ISP end to client end. that is gave required bandwidth (earlier times :)) to WAN connections. with new technologies like MPLS and high bandwidth requirements, ISPs moved to ethernet terminations using fiber and copper

2. there is limitations on speeds for serial than ethernet

[trane.m]

"early networks most of ISPs used serial links to terminate connections from ISP end to client end. that is gave required bandwidth (earlier times :)) to WAN connections"
So, in earlier days, ISPs used serial links instead of ethernet links, because serial would provide the required bandwidth to the customer?

[MHM Cisco World]

friend the main different is dialer interface, 
dialer interface is virtual interface and need physical interface and serial is the best choose, many ISP use dialer interface. 
ehernet not support dialer interface but interface protocol called PPPoE.

[Joseph W. Doherty]

"In my reading up (and labs) i've seen serial interfaces between some of the network devices. I'm not sure i understand the difference between serial and Ethernet connections."

Not surprising, as there are both differences and similarities.  Unclear, though, how deep you want to go into that rabbit hole.

"Why and when would you choose one over the other?"

All the typical issues, such as, what can you actually use (i.e. from one extreme to the other - is there something I can connect to now and immediately use or do we need a whole new physical "plant" installation to use?).  Cost?  Usage requirements (e.g. "speed", latency, etc.)?

"What can one do that the other can't?"

There are some feature differences (simple example, half vs. full duplex) beyond moving digital data from A to B, which also vary between specific variants of each technology, but, again, there can be many reasons why you're "forced" to select one vs. the other, or why you might prefer to select one vs. other.

Many years ago, I was working at a large company that was "True Blue" (i.e. IBM for equipment).  They were still using token-ring for the LANs.  Then PCs started to come out with Ethernet NICs as standard equipment on those PCs.  Further, the price of the token-ring NICs, for those PCs was as much, or a little more, than the purchase price of the whole PC system.

We could get into a lengthy discussion of token-ring vs. Ethernet, but when it came to cost, Ethernet was the hands-down winner.  So, that company moved to Ethernet.

Laugh, though, I had my department stay on TR!  Why?  Well, their first Ethernet implementation was hub-based.  When they finally moved to switched-based Ethernet, then I okayed moving from TR to it.  (Again, lots of technical differences [often not well understood by many].)

Somewhat likewise, Ethernet (comparatively) has become so cheap compared to many "serial" technologies, just like it replacing token-ring for LANs, it's been replacing "serial" technologies (possibly first) in MANs and then WANs.

We could get into a lengthy discussion of "serial" technologies vs. Ethernet, and some of the former still have a couple of technologies edges over the latter, but COST is often a very, very large factor in making a choice between the two.

[trane.m]

"Not surprising, as there are both differences and similarities.  Unclear, though, how deep you want to go into that rabbit hole."

I'm having trouble understanding the very very basics of it, without even going into technical details. All i've ever worked with, when talking networking, is Ethernet.
I want to understand why the serial connections has been chosen for that specific link between those two specific network devices in my lab. Is it just to show me that there are other options than Ethernet or is there another reason, like serial has very low latency or fast speed?

"All the typical issues, such as, what can you actually use (i.e. from one extreme to the other - is there something I can connect to now and immediately use or do we need a whole new physical "plant" installation to use?).  Cost?  Usage requirements (e.g. "speed", latency, etc.)?"

I want to understand why there is/was a need for serial connections. Serial must be (or have been) better than Ethernet in some way, be it cost, speed, latency or whatever. Which?

"There are some feature differences (simple example, half vs. full duplex) beyond moving digital data from A to B, which also vary between specific variants of each technology, but, again, there can be many reasons why you're "forced" to select one vs. the other, or why you might prefer to select one vs. other."

Can you provide me with (very simple) examples of when you would consider a serial link instead of an Ethernet one?

Also, can we agree that the differences of the two is entirely on Layer 1? By that i mean, the only difference is physical? All the configurations commands are the same, whether it is Ethernet or serial? Or does serial have a whole other "library" (i dont know what else to call it) of commands?

[Richard Burts]

Let me try to address several points about these technologies. Going back some (perhaps many) years the distinctions between serial and Ethernet were more clear. Serial connections were able to connect over distances while Ethernet was for local networks. So if you had 2 offices that needed to communicate serial was effective and Ethernet was not. For communication within the office Ethernet was effective and serial was not. In modern times the distinctions are less clear, especially because Ethernet is now a viable option for communication over distances.

I will suggest that probably the most important difference in the technologies is that serial is for point to point (one device to one other device) communication and Ethernet supports device to multiple devices. We could get into technical details, such as that Ethernet needs ARP to be able to communicate with other devices and serial does not. But I do not believe that those details are significant to you.

[Joseph W. Doherty]

In a lab, learning about "serial" is, today, mostly learning about a technology you might still run into.  However, years ago, "serial" was the very common hand-off interface for WANs.  (Somewhat a similar situation when learning about classful addressing.)

"Serial must be (or have been) better than Ethernet in some way, be it cost, speed, latency or whatever. Which?"

Again, it's what interfaced with (analog) Telco equipment, going back decades.

"Can you provide me with (very simple) examples of when you would consider a serial link instead of an Ethernet one?"

What does your WAN providers support?  Years ago, it, generally, was just serial; today, it's often also, or even just, Ethernet.

"Also, can we agree that the differences of the two is entirely on Layer 1?"

No, there are differences at L2 too.  (BTW, there are different "flavors" of Ethernet, too, although, generally, today, only one "flavor" is used.  See dix vs. 802.3)  L3, though, is almost the same for both except for impact of L2's MTU.

"All the configurations commands are the same, whether it is Ethernet or serial? Or does serial have a whole other "library" (i dont know what else to call it) of commands?"

Interface commands vary based on the vintage of the device, when providing L1 and/or L2 configuration options.  Some devices configure a separate section, often "controller" for this information.  Some, though, incorporate the information within the interface config.

Simple example, if setting up a back-to-back serial connection in a lab, you'll need to configure the clock rate (determines the actual bandwidth) and, if I remember correctly, set one device to generate the clock signal which the other device will be configured to sync to.