IEEE 802 Standards
Institute of Electrical and Electronics Engineer's (IEEE) Standards Committee develops and maintains the networking standards for local, metropolitan, personal area network, and for other area networks. IEEE 802 covers the data-link layer specification for technologies such as 802.3 (Ethernet), 802.11(Wi-Fi) and 802.15 (Bluetooth / ZigBee) etc. IEEE 802 specifications also split the data link layer into two different layers i.e., a logical link control (LLC) layer and a MAC layer.
Why IEEE 802 Standards are important?
Without these standards, companies could manufacture
network hardware that would only connect to certain computers. It is much more
difficult to connect to systems not using the same set of networking equipment.
The IEEE 802 working groups define the standards as
below:
|
Name |
Overview |
Status |
|
IEEE
802.1 |
Higher
Layer LAN Protocols Working group |
Active |
|
IEEE
802.2 |
Logical
link control (LLC) |
Disbanded |
|
IEEE 802.3 |
Ethernet |
Active |
|
IEEE 802.4 |
Token bus |
Disbanded |
|
IEEE 802.5 |
Token
Ring |
Disbanded |
|
IEEE
802.6 |
MANs (DQDB) |
Disbanded |
|
IEEE
802.7 |
Broadband
LAN using Coaxial Cable |
Disbanded |
|
IEEE
802.8 |
Fiber
Optic TAG |
Disbanded |
|
IEEE
802.9 |
Integrated
Services LAN (iso-Ethernet) |
Disbanded |
|
IEEE
802.10 |
Interoperable
LAN Security |
Disbanded |
|
IEEE 802.11 |
Wireless
LAN and Mesh (Wi-Fi certification) |
Active |
|
IEEE
802.12 |
100-BaseVG |
Disbanded |
|
IEEE
802.14 |
Cable Modems |
Disbanded |
|
IEEE
802.15 |
Wireless
PAN |
Active |
|
IEEE
802.15.1 |
Bluetooth
certification |
Disbanded |
|
IEEE
802.15.2 |
IEEE
802.15 and IEEE 802.11 coexistence |
Hibernating |
|
IEEE
802.15.3 |
High-Rate
WPAN |
-- |
|
IEEE
802.15.4 |
Low-Rate
WPAN (e.g. Zigbee, WirelessHART, etc) |
Active |
|
IEEE
802.15.5 |
Mesh
networking for WPAN |
-- |
|
IEEE
802.15.6 |
Body area
network |
Active |
|
IEEE
802.15.7 |
Visible
light communications |
-- |
|
IEEE
802.16 |
Broadband
Wireless Access (WiMAX certification) |
Hibernating |
Ethernet
IEEE 802.3 standards were first standardized in the 1980s for primarily used in LANs. IEEE 802.3 also known as ethernet defines the physical layer and the medium access control (MAC)sub-layer of the data link layer for wired Ethernet network.
Ethernet is usually referred to as 10BASE-X where 10 represent maximum throughput or speed i.e. 10Mbps, BASE denote the baseband transmission and X represent the type of medium used. Some of the examples are as follows:
10BASE-T means 10Mbps over twisted pair copper wire as a medium of transmission.
10BASE-F means 10Mbps over fiber optic cables as a medium of transmission.
Frame Format of Ethernet:
Figure 1: Shows the IEEE 802.3 Frame Format Standard.
PREAMBLE – Ethernet frame starts with 7-Bytes Preamble indicates starting of the frame and allow sender and receiver to establish bit synchronization. Initially, PRE (Preamble) was introduced to allow sender and receiver to establish bit synchronization. PRE (Preamble) indicates the receiver that frame is coming and allow the receiver to lock onto the data stream before the actual frame begins.
Start of frame delimiter (SFD) – This is a 1-Byte field that is always set to 10101011. SFD indicates that upcoming bits are starting of the frame, which is the destination address. The SFD warns the station that this is the last chance for synchronization.
Destination Address – Destination address is a 6-Byte field that contains the MAC address of the machine to which we have sent data.
Source Address – This is a 6-Byte field that contains the MAC address of the sender. Source Address is usually an individual address (Unicast), the least significant bit of the first byte is always 0.
Length – Length is a 2-Byte field, which indicates the length of the entire Ethernet frame. This 16-bit field can hold the length value between 0 to 65534, but length cannot be larger than 1500 because of some own limitations of Ethernet.
Data – Data is the actual message the sender has sent to the destination machine. It is also known as Payload.
Cyclic Redundancy Check (CRC) – CRC is 4 Byte field. CRC contains a 32-bits hash code of data to check whether there is any error or corrupted bits. If the checksum is computed by destination is not the same as the sent checksum value, the data received is corrupted.
IEEE 802.4 standard is popularly known as Token Bus. In Token bus, the physical media is a bus and a token is passed from one user to another in the network wither in a clockwise or anticlockwise direction. A computer can transmit data only when it has the token.
What is token? What is token passing mechanism?
A token is a small message that gives permission to transmit the message between the neighbor's computer only after acquiring the token. If any computer wants to transmit data first has to take a token, then only the computer can transmit the data. The token bus network can be explained using the simple diagram given below:
In this network, nodes are physically connected as a bus, but logically form a ring which requires a token to transmit data or information.
Frame Structure:
An IEEE 802.4 standard has the following fields:
Preamble: It is used to synchronize the receiver’s clock.
Start Delimiter: This 1-byte field marks the beginning of frame.
End Delimiter: This 1-byte field marks the end of frame.
Frame Control: This 1-byte field specifies the type of frame i.e. data frame or control frames.
Source Address and Destination Address: The source or destination address consist of 2 to 6-byte fields and contain the source address and destination address respectively.
Data: This field contains the data or payload. It is actual data we want to transmit to the receiver.
Checksum: This is a 4-byte field that is used to detect the errors in the transmitted data.
IEEE 802.5 Standard: Token Ring
Token Ring:
IEEE 802.5 standard is popularly known as Token Ring. In Token Ring, all the systems are connected in ring form, and token is passed between one system to another for channel acquisition. If a system or node has data to transmit, first nodes have to acquire the token, then only it can transmit its data. However, in token ring, the data flow is unidirectional and system or node is removed from the network once their transmission is complete. The below diagram shows the flow of token in ring network.
There is 3 mode of operation:
1. Listen Mode: In this mode, the node listens to the data and transmits the data to the next node. There will be one bit delay during the transmission.
2. Transmit Mode: In this mode, the node will discard the data and put that data onto the network.
3. By-pass Mode: In this mode, the node is not active and passes all the data. There is no one-bit delay during the transmission.
Difference between Token Ring and Token Bus:
Token Ring | Token Bus |
It is defined by IEEE 802.5 Standard. | It is defined by IEEE 802.4 standard. |
In token ring, token is passed over the physical ring formed by the nodes and the coaxial cable. | In token bus, token is passed along the virtual ring of nodes connected to LAN. |
Nodes are connected by ring or star topology. | Nodes are connected by bus or tree topology. |
The maximum time to reach the last station in the token ring can be calculated. | The maximum time to reach the last station in the token ring is not easy to calculate. |
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