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I finished my middle school IT & Networking education about 2 years ago. Now I recently got a job and started to refresh my knowledge.

I've been searching the internet first of course but I still can't really seem to understand/see any diferrence between CSMA/CD and TCP/IP.

Maybe someone here could give me a clear answer so I could understand it.

(If there is a difference after all) Thanks in advance!

3 Answers 3

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CSMA/CD is a set of rules for Ethernet technologies working on Layer 2 and really uses with half duplex links to drop and resent broken frames. TCP/IP is a big set of protocols for sending data. IP is a protocol for logic adressin, TCP is a protocol for data delivering.

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  • CSMA/CD is an access protocol for shared physical layer media, so it's layer 1.
    – Zac67
    Jan 15, 2018 at 22:06
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Are you familiar with the OSI protocol stack model? It does not apply exactly to the Ethernet and TCP/IP protocols, but it is a useful tool for describing network protocols and their relations to each other.

CSMA/CD and TCP/IP are on very different layers of the conceptual OSI protocol stack, and perform different functions.

CSMA/CD is the media access control method when using half-duplex Ethernet on various types of cabling:

  • 10base2, the "thin" coaxial Ethernet
  • 10base5, the "thick" coaxial Ethernet (the original version
  • 10base-T, the first twisted-pair Ethernet standard in half-duplex mode
  • 100base-TX and other faster twisted-pair Ethernet standards in half-duplex mode

The implementation of CSMA/CD is specific to Layer 1, the physical layer: on coaxial cables it defines a signal amplitude level that indicates a collision, on twisted-pair cabling it's a simple logic: if there is a signal on both this and that pair of wires at the same time, a collision exists.

The Layer-2 protocol of Ethernet has a built-in expectation for CSMA/CD. So it could be said that CSMA/CD is somewhere between Layer 1 and Layer 2, or perhaps part of the interface between the two layers.

When twisted-pair Ethernet cabling is used, CSMA/CD can be essentially turned off it the network is implemented using switches (= multi-port bridges) rather than hubs (= multi-port repeaters). The result is the full-duplex Ethernet we know and love.

On top of the physical layer, there is the data link protocol: Ethernet II/IEEE 802.3. This is Layer 2: the low-level protocols used between devices with effectively direct connections to each other. This layer defines things like MAC addresses and Ethernet-level unicast/multicast/broadcast.

The next higher layer in the usual Internet protocols is IP: it's a protocol that can be routed between multiple distinct networks. This is a significant dividing line: anything at Layer 2 and below is usually tied to a specific hardware technology like Ethernet, but Layer 3 and above are hardware-agnostic.

Beyond Layer 3, the OSI model becomes increasingly inapplicable to the usual Internet protocols, but TCP, UDP and ICMP are all built on top of IP.

IP is not tied to Ethernet at all: you can have one IP network segment using Ethernet and another using Token Ring, and both can talk to each other (and to the rest of the internet) over IP if there is a router between them that has interfaces for both Layer-2 technologies. Since the development of Internet, most Layer-2 network technologies have included provisions to run IP (and/or IPv6) over them. You can even run IP over FibreChannel, a protocol that's usually used in storage networking context, if you want to.

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  • Any half-duplex Ethernet uses CSMA/CD - so don't forget 10BASE-FL, 100BASE-FX, theoretically 1000BASE-T, ...
    – Zac67
    Jan 15, 2018 at 22:16
  • 10BASE-FL and 100BASE-FX are fiberoptic, and have one fiber for incoming and another for outgoing data, so the technology is fundamentally full-duplex but can emulate a half-duplex link if necessary. Basically you cannot generate a collision on a fiberoptic link itself, but many fibre Ethernet standards still include a way of signaling a "collision state" if there is a media converter to a true half-duplex link at the end of a fiberoptic link.
    – telcoM
    Feb 9, 2018 at 16:29
  • You're correct, but this isn't any different with 10BASE-T and 100BASE-TX. All major PHYs but coax are inherently full-duplex. Yet, 10 Mbit/s and for quite some time even 100 Mbit/s PHYs were most commonly used in half-duplex mode.
    – Zac67
    Feb 9, 2018 at 17:55
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Basically, CSMA/CD and TCP/IP have nothing in common except that both may be present in a network.

CSMA/CD is the access protocol for (early) Ethernet shared media, i.e. arbitrate access to a physical medium that only one node can talk over at a given time.

TCP/IP is a family of protocols based on IP, located at least two layers above the physical layer. Their purposes include routing packetized network traffic over vast networks (esp. the Internet), disassembling and reassembling data streams, and providing comfortable socket services for applications so they don't have to fuzz with the networking business.

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