IEEE LAN Standards

Why IEEE?

The IEEE is a professional society for engineers and the like, so pardon me for being irreverent if I say that it was never clear to me why standardization should be one of their functions. As a point of comparison, APS, the American Physical Society, is a professional organization for physicists and I don't see it part of their mission to write standards for, say, a radial-azimuthal polarization converter.

I suspect that the motivation for me sounding off like this is that I was always confused as to why so many standards groups - ISO (a real standards organization), ANSI (The American National Standards Institute), and IEEE all include the 802 LAN standards in their sets of standards. If IEEE set up a committee (the IEEE 802 LAN/MAN Standards Committee), what purpose does it serve for ISO and ANSI to reissue those standards? If they want to give their stamp of approval, they could do that without all the waste of reissuing the same standards.

In any event, the standards are certainly best known as the IEEE 802 standards, and these days they certainly deserve to have the greater fame. I can download the IEEE 802 standards for free (though they weren't always free, and even today, they are only free after a year has passed from the initial publication date). Why in the world would I want to pay 468 Swiss Francs to download a PDF of the ISO document for the same standard?

So with that admittedly weird introduction, let's take a look at the structure of the IEEE 802 family of LAN/MAN standards.

The 802 Standards

We'll start with a historic look at the 802 LAN Standards protocol set, when these standards were first defined, depicted in Figure 4.

Figure 4: 10Base5 Components

We see that initially, the IEEE defined three LAN standards: 802.3, which was the IEEE version of the original DIX (Digital Intel Xerox) Ethernet, 802.4, a LAN that uses an access method called "token bus", and 802.5, the IEEE version of the IBM Token Ring. It is now 30 years after the 802 committee started its work. The token bus is no longer on the scene (as far as I can tell - I've looked pretty hard), and its working group has been disbanded. In fact, the token bus was successful for a time, but only in very specific industrial environments. The token ring LAN had significant and widespread success, and as was pointed out in the previous chapter, the IBM Token Ring presented serious competition for Ethernet, for a time. But various factors led to the fading away of token ring (though it appears to still be possible to purchase network adapters), and its working group is in a status of "hibernation". I don't know how long something has to "hibernate" before it is "disbanded".

So the only true survivor - in fact, not just a survivor, but an amazing victor - from those early days is 802.3, known to the world as Ethernet, according to it original name. However, a whole slew of other LAN standards, and also MAN standards (not conceived of 30 years ago) have come on the scene during these decades. Some of them have also left the scene. The following is a list of the active working groups (but not the technical advisory groups, called TAGs):

The RAD University website contains tutorials on some of these standards, and I've provided links (in the list above) to those tutorials that are not included in this LAN portal. This LAN portal only includes tutorials on the LAN technologies, including token ring technologies (802.5 and FDDI) that are "hibernating", to use IEEE's euphemism. Though 802.5 is a hibernating IEEE standard, FDDI was not an IEEE standard. As I explained in the introduction to this portal, I included the token ring technologies because they represent some excellent concepts, which are still frequently taught in computer networking courses, too. You can conclude, then, that there are only two types of LANs that are commonly used these days - Ethernet and Wireless LAN, which are the types of LAN connectivity you would likely find on a home computer these days.

So far, you've seen a series of numbers (802.X) to identify standards, but I need to explain the layers that you see above in Figure 4, and the function of each layer, which is what I'll do in the next section.

802 Protocol Layers

We'll start with 802.1. As you can see from Figure 4, the 802.1 standards were intended to address those issues that are common to all 802 LANs, at all protocol levels, including interfacing to the layer above. The issues addressed include addressing, management, and bridges. The mission of the 802.1 Working Group as described on its website is as follows:

The IEEE 802.1 Working Group is chartered to concern itself with and develop standards and recommended practices in the following areas: 802 LAN/MAN architecture, internetworking among 802 LANs, MANs and other wide area networks, 802 Security, 802 overall network management, and protocol layers above the MAC & LLC layers.

The 802.1 working group has four active task groups: Interworking, Security, Audio/Video Bridging and Data Center Bridging.

The aspect of the 802.1 standards that is of most interest is bridging, including the Spanning Tree Protocol. This subject matter is covered, as you can see from the link that just I provided, in the bridge tutorial in this portal.

Though Figure 4 shows a layer called Logical Link Control (LLC), 802.2, from the list above you can see that this protocol does not have an active working group. In fact, this is another protocol that is in "hibernation". The 802.2 standard is from 1998, and in 2003, the standard was "reaffirmed" by the IEEE.

The LLC is actually a sub-layer of the data link layer (using the OSI terminology), which consists of the LLC and the MAC (Medium Access Control) layer in the IEEE model. The LLC is a sub-layer that is common to all 802 LAN protocols (as well as being adopted to some extent by some non-IEEE protocols), while the MAC sub-layer is specific to each LAN type. Among the functions of the LLC is definition of fields that allow multiple higher-layer protocols (such as IP, ARP, and other not-so-common-these-days protocols) to share the same data link. I will discuss this function further in the section on the Ethernet frame format.

The other function of the LLC turned out to be kind of useless. Ethernet, as is apparent from the way it operates, is a connectionless protocol. That means that there is no connection establishment before sending a frame. Ethernet is also an unreliable protocol, which means that there is no acknowledgment of frames sent by the Ethernet protocol. If any acknowledgment is sent, it is a higher layer protocol that is responsible. This type of connectionless, unreliable service is often called a datagram service, though this term is more commonly used to describe IP.

When the standards for 802 were first being defined, there were those people on the committee who thought that there should be greater functionality available, so that several types of LLC were defined, in addition to the datagram model (LLC Type 1). A reliable, connection-oriented option was defined (LLC Type 2), as was a connectionless reliable model (LLC Type 3).

When we look at the IEEE 802.3 frame format, I'll point out how one can tell what LLC type is implemented, but we will not see any application of this. As we shall see, most Ethernet users do not use the IEEE 802.3 frame format, so they don't have the LLC header, and even those protocols that do (or did) use 802.3, did not use anything other than LLC Type 1. Though token ring protocols have some kind of data link level reliablity, in a very basic manner, they do not make use of the LLC functionality for this purpose.

At the MAC layer, we have a different protocol for each of the LAN types, and since this portion of the portal is about Ethernet, what interests us is 802.3. For each LAN type, there is also a physical layer defined. The MAC layer is responsible for the definition of the medium access method (in the case of Ethernet, that's CSMA/CD) and for the definition of the frame format. The physical layer of 802.3 defines the connectors, the cabling, etc., and you read about some of the features of the physical layers for 802.3 10Base5 and 802.3 10Base2 in the previous chapter.

With this background on the IEEE 802 protocol family, we can now proceed to discuss the development of 802.3 to include hubs, a range of cabling options, and higher speeds. The IEEE 802.3 standard continues to evolve. We can only touch on the main concepts in this tutorial. The latest 802.3 standards can be found here on the IEEE Get 802 website.

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