Token, token ring

Token is one of those words that comes from English and is frequently used in networks, computers and even in banking operations. Surely where you have listened the most is in the " Token Ring " networks. In essence the meaning is going to be the same, somewhat ambiguous but which we hope to explain with the greatest possible precision and simplicity.

Index of contents

What is a Computer Token

Let's start by defining the general meaning of token, which represents an object or symbol (that would be its translation into Spanish), which can be both software and hardware that represents the ability or right to perform an operation.

One-time key generator token

This term is mainly used in the security field, since the token is an identifier that converts sensitive data into one that is secure. This process is called tokenization, in which you take a piece of information or an element or piece of information that could be, for example, plain text and add a layer of protection to convert it into encrypted or confidential data. There are also tokens in the form of single-use password generating devices.

Currently sensitive data that travels over the network and that is stored, for example, bank accounts, medical records and especially Internet stock transactions, must be tokenized, and a detokenizer will detokenize them for the systems to use it safely.. And, if we could have done a tongue twister with this topic.

We can distinguish all these types of token:

• Token Ring: This is a network topology in which a token circulates in a logical ring. We will see this in more detail below Access Token: it will be an object that represents an access control operation Security Token: in this case it will be an object whose purpose is to authenticate a user on a computer. It can be a hardware or software element. Session token: is a unique identifier that defines a session, for example the username

The token is a term quite related to the economy, and we talk about it as cryptocurrencies, casino tokens, physical currencies, etc.

Programming token example

If the tokens are logical or physical objects, each element that constitutes a program code is one of these elements, for example:

"IF string =! key THEN ”

Each of these elements is a token, some of them are class identifiers and other values.

• IF and THEN are reserved words, which are used as class tokens to create a condition. =! It is an operator token, it creates the logical condition that the string must be met and the identifiers are key, which can be encrypted so that its internal value is not decrypted by anyone except the program that uses it.

Token Ring network architecture

Although today it is an architecture that is no longer used and that has been replaced in all areas by Ethernet standards, it is worth making a reference to it merely to provide learning.

MAU IBM 8 port

This architecture appeared after the creation of the first data transfer networks such as ARPANET. Companies like Procom, Proteon and later IBM created the first networks of this type. It was precisely IBM that bet the most on them, although it offered extremely high prices for its license. But already in the 70s, the Ethernet standard began to be implemented through IEEE, using coaxial cables and star or mesh topology much cheaper, versatile.

Token Ring is not a ring topology network

It is important to make clear that Token Ring is not a ring network per se. In these networks each node is connected both to the right and to the left until it forms a closed ring. And a computer goes down, the network breaks and stops working, at least those in which information can only travel one way.

IBM multiport adapter

But a network of this type is not that, the implementation that IBM made was a network with a logical ring-shaped topology, but that physically looks like a mesh topology, as you see in the previous graphic. In it there is a multiple station access unit (MAU or MSAU), which through the token pass with a 3-byte frame that runs through the ring, connecting with the different nodes of the network placed in a star. As we see, it is very different from the basic ring network, since here the nodes are not directly connected to each other, but rather to a ring bus that closes on itself.

IBM dual RS-232 Ethernet port network card

That topology is standardized to IEEE 802.4, and is currently deprecated for the benefit of Ethernet. The characteristics of a Token Ring network would be:

• Ring logical and star physical topology Can use twisted pair cable and supports a maximum length of 366 m The distance between the MAU and a node cannot be more than 100 m The maximum capacity of a MAU is 8 nodes (8 mouths) Its maximum speed is 16 Mbps, although with HSTR it was raised to 100 Mbps

Token Passing protocol and operation

Actually the ring is inside the MAU, so all the information must go through that device so that it is sent not to the destination node directly, but to the next node in the order that has been established. This is the fundamental difference with a star network, in which the frame does not circulate through the ring until it finds its destination, but is sent directly to the destination node or to all at once if we use a hub.

Token passing is the protocol responsible for ensuring that everything runs in an orderly manner, so a team cannot transmit to the network until the token reaches that team. Although a team will not receive or transmit anything, the token will go through each of them continuously, being a witness that will only be used by the interested party at all times.

Token Ring Plot

The token is a 3 byte frame that contains:

• SD (Star Delimiter): 8 bits to indicate where the AC (Access Control) token begins : another byte to indicate if the token is free (0) or busy (1) ED (End Delimiter): same as the first to delimit the end of token

In addition, the entire frame will have 12 bytes to store the destination and source address, 4 bytes for CRC error control and another two bytes for frame control and status.

The token will stay in each node for a maximum of 10 ms, which is called holding time. As you enter the information, the frame will continue to travel until the interested node takes it and copies it. At this moment a bit will indicate that it has already been copied, so that when it reaches the MAU the token is restarted and goes through the ring again.

Possible errors in the Token Ring network

As in all networks, there can be errors both in the loss of the token and in the loss or breakage of a node in the network, so as it is completely defined it is convenient to know what would be done in these cases.

IBM 8 bit ISA network card

First of all, we must know that all the nodes connected to this network can adopt the condition of active monitor (AM) or stand-by (SM). There can only be one AM, which is responsible for monitoring the operation of the network, and is decided by the claiming token. When the AM fails, the closest SM will send a claim token frame, to the next node which will change the MAC address for the sender if it has a higher value. In this way it will go through all the nodes of the ring 3 times, and the MAC that remains in the claim token frame will be that of the new AM of the network.

The AM has other important functions, such as creating a new token if the current one disappears. And it is that when the token passes through the AM, it places a timer at 10 ms, if the token takes longer to pass, then it will be lost and a new one will be created.

It can also happen that the receiver of the packet is not present, so the AM must ensure that it reaches the destination by setting a bit to a certain value. If you go through AM again with that same value, the frame will be destroyed.

Conclusions about the token and why this network topology was discontinued

We have already seen the meaning of a token and its multitude of uses in computing, but it is undoubtedly best known for the topology that bears its name Token Ring, which is surely why you have entered this article.

At present this network has fallen into disuse for the benefit of Ethernet, since it offers a series of obvious advantages compared to this topology, such as allowing direct connection of equipment through crossover cables or automatic detection.

And while this topology prevents packet collisions, Ethernet is much faster and cheaper to deploy due to Token Ring's use of more expensive network cards and the requirement to use 8-port routers.

Did you know this network topology, did you weigh that Token Ring was simply a ring topology? If you want to clarify something, have a question, or liked it, leave it in a comment below.