IEEE 802 Standards

11:06 PM IEEE, network No Comments

 Brief background of IEEE802 standards for LAN and MAN

While connecting computers through networks we need to have set of rules/standards for the data to travel from one computer to other computer. The right example for this can be road traffic rules. It's self understood, why we need traffic rules while driving, in same sense for the data packets to travel from one computer terminal to other terminal they should also follow set of rules and regulations.
One such set of rules for the networking traffic to follow is IEEE802 standards. Its developed by IEEE (Institute of Electrical and Electronics Engineers, Inc.) The IEEE is the world's leading professional association for the advancement of technology. It's a non- profit organization offering its members immense benefits.
The standards such as IEEE 802 helps industry provide advantages such as, interoperability, low product cost, and easy to manage standards.

IEEE standards deal with only Local Area Networks (LAN) and Metropolitan Area Networks (MAN). See in the figure below, to know where exactly the IEEE802 standards are used in a OSI layer.

The IEEE 802 standards are further divided into many parts. They are,

IEEE 802.1 Bridging (networking) and Network Management
IEEE 802.2 Logical link control (upper part of data link layer)
IEEE 802.3 Ethernet (CSMA/CD)
IEEE 802.4 Token bus (disbanded)
IEEE 802.5 Defines the MAC layer for a Token Ring (inactive)
IEEE 802.6 Metropolitan Area Networks (disbanded)
IEEE 802.7 Broadband LAN using Coaxial Cable (disbanded)
IEEE 802.8 Fiber Optic TAG (disbanded)
IEEE 802.9 Integrated Services LAN (disbanded)
IEEE 802.10 Interoperable LAN Security (disbanded)
IEEE 802.11 Wireless LAN & Mesh (Wi-Fi certification)
IEEE 802.12 demand priority (disbanded)
IEEE 802.13 Not Used
IEEE 802.14 Cable modems (disbanded)
IEEE 802.15 Wireless PAN
IEEE 802.15.1 (Bluetooth certification)
IEEE 802.15.4 (ZigBee certification)
IEEE 802.16 Broadband Wireless Access (WiMAX certification)
IEEE 802.16e (Mobile) Broadband Wireless Access
IEEE 802.17 Resilient packet ring
IEEE 802.18 Radio Regulatory TAG
IEEE 802.19 Coexistence TAG
IEEE 802.20 Mobile Broadband Wireless Access
IEEE 802.21 Media Independent Handoff
IEEE 802.22 Wireless Regional Area Network

Here we discuss most popular and key parts of above list

IEEE 802.3 Ethernet (CSMA/CD)

A method called Carrier Sense Multiple Access with Collision Detection (CSMA/CD) was used to send data over shared single co-axial cable connected to all computers on a network. In this method, the computer terminals (also called as stations) transmits the data over cable whenever the cable is idle, If more than one station transmit at same time and if they collide, the transmission will be stopped by such stations. They will wait for some random time and restart transmission.

The concept of sharing single cable or wire between multiple stations was used for first time in Hawaiian Islands. It was called ALOHA systems; built to allow radio communication between machines located at different places in Hawaiian Islands. Later Xerox PARC built a 2.94 mbps CSMA/CD system to connect multiple personal computers on a single cable. It was named as Ethernet.
Ethernet or IEEE802.3 standards only define MAC (Data link) and Physical layer of standard OSI model.
Wiring and cabling standards of 802.3

There are four cabling standards as per 802.3, each one has evolved over the time for their special advantages.
The four types of cables are,
1. 10Base5
2. 10Base2
3. 10Base-T
4. 10Base-F

The table below compares all four types of cables

Technical Name	Cable/Wire type	Max. Segment/wire Length	Maximum number of Nodes/Segment	Advantages
10Base5	Thick coaxial	500 meters	100	Long cable length
10Base2	RG58 (thin) coaxial	185 meters	30	Low cost
10BaseT	Twisted pair (like telephone wire)	100 meters	1024	Easy to maintain
10BaseF	Fiber-optic	2,000 meters	1024	No noise interference

The 10 in the technical name refer to data speed of 10Mbits/sec.
"Link Integrity" and "Auto-partition" are part of the 10BaseT specification. This means that all network equipment claiming compliance with 10BaseT must support Link Integrity and Auto-partitioning.

10Base5
10 Base5 is also called as ThickNet or thick Ethernet. It uses RG-8 thick coaxial trunk cable, which looks like orange colored garden hose. The cable is tapered with taps called vampire taps in which a pin is carefully forced halfway into the cable's core. The connection can be made to the desired computer network interface card (NIC) from these vampire taps. ThickNet can travel 500 meters per segment, and it can have a maximum of 100 taps per segment. Each tap requires a minimum distance of 2.5 meters before the next tap and has a maximum drop distance of 50 meters. The cable must be terminated with a 50-ohm terminator resistor.

Due to its complex and slow nature 10Base5 is no more preferred. The severe drawback is entire line will fail for any single failure on the trunk. This cable can be termed as obsolete/outdated technology.

The one plus point of ThickNet is that, once it's up and running, it will continue to do so until you tell it otherwise. Although it is slow and unwieldy, 10Base5 technology is very reliable.

Here is the figure showing how the cables are connected to Network Interface Cards inside the computer using 10base5.

10Base2
10Base2 is not very different from 10 Base5. The most notable physical difference between 10Base2 and 10Base5 is the size of the co-axial cable. 10Base2 is thinner than the 10Base5 and so is called as ThinNet or thin Ethernet. Another difference is that 10Base2 is set up in a daisy chain. Daisy chain is a wiring scheme in which, for example, device A is wired to device B, device B is wired to device C, device C is wired to device D, et cetera.

10Base2 uses BNC connectors attached to a thin coaxial cable. The maximum segment length of 10Base2 is 185 meters, and the maximum number of devices per segment is 30.

10Base is also outdated/obsolete technology. In rare cases it could be deployed as a backbone for a network.

10Base-T
10Base-T is the most popular cabling method. Its also called Standard Ethernet, or twisted pair, 10Base-T works on a star topology connecting all computers to a hub. It is best used with Category 5 cable (so it can be upgraded to Fast Ethernet) and can have a maximum of three hubs daisy-chained together.

Since it is simple and cheap to implement it is most opted one. The specifications of Standard Ethernet include the following:
It uses RJ45 connectors on unshielded twisted-pair (UTP) cable.
The maximum cable length is 100 meters (before a repeater is needed).
The maximum number of devices per segment is 1,024 (although performance will become quite poor before that number is ever reached).

The 10Base-T standard is best employed within a LAN where cost is a factor-and speed and distance are not.

Link Integrity is concerned with the condition of the cable between the network adapter and the hub. If the cable is broken, the hub will automatically disconnect that port.
Auto partitioning occurs when an Ethernet hub port experiences more than 31 collisions in a row. When this happens, the hub will turn off that port, essentially isolating the problem.

10Base-F
In 10BaseF the twisted copper wires are replaced by a optical fiber. 10Base-F uses a higher quality cabling technology, multimode (or single-mode) fiber-optic cable, to transport data. The particular technology has two subdivisions that must be addressed: the newer 10Base-FL and 10BaseFOIRL.

Because it is older, the 10BaseFOIRL (Fiber-optic Inter-repeater Link) technology doesn't have quite the capabilities of the newer 10Base-FL. With 10BaseFOIRL, you have the following specs:
It's based on IEEE 802.3.
The segment length is 1,000 meters.
There are three sizes of duplex multimode fiber: 50-, 62.5-, or 100-micron. Of these three, 62.5-micron is the most common.
ST or SMA 905 connectors are used by 10BaseFOIRL.
It must be used in a star configuration.
AUI connectors have to be connected to fiber transceivers.

The much-improved 10Base-FL technology offers a different set of specs:
It's based on the 10Base-F IEEE 802.3 spec.
It's able to interoperate with FOIRL and is designed to replace the FOIRL specification.
The segment length is 2,000 meters (if exclusively using 10Base-FL).
The maximum number of devices per segment is two; one is the station and the other is the hub.
The maximum number of repeaters that may be used between devices is two.
NICs with standard AUI ports must use a fiber-optic transceiver.

The benefits of optical fiber are,
No radio or magnetic interference.
Transmissions are safe from electronic bugging,
Cable is extremely lightweight,

10Base-FL fiber-optic technologies are best implemented in long runs where reliability and security are critical.

IEEE802.4: Token bus
In this system, the nodes are physically connected as a bus, but logically form a ring with tokens passed around to determine the turns for sending. It has the robustness of the 802.3 broadcast cable and the known worst case behavior of a ring. The structure of a token bus network is as follows:

Token bus or 802.4 is more robust and reliable than 802.3 frames. The standard 802.4 is a linear or tree shaped cable onto which the stations are attached.

Network is a physical bus but a logical ring. The stations are numbered and are allowed to access the medium sequentially. If there are n stations, and packet transmission time is bounded to T, then the maximum waiting time is nT. Token bus MAC is simple and robust. Token bus is mostly used in automation systems.
Data is subdivided into four priority classes. Each station has four packet queues, one for each priority. When a station receives token, it is allowed to transmit certain fixed time. During that time it transmits packets in the decreasing order of priorities.

Frame Structure:

A 802.4 frame has the following fields:
Preamble: The Preamble is for synchronizing the receiver's clock.
Starting Delimiter (SD) and End Delimiter (ED): The SD and ED fields are used to mark frame boundaries. Both contain analog encoding of symbols other than 1 or 0 so that they cannot occur accidentally in the user data. Lengthy field is no more needed.
Frame Control (FC): FC is used to distinguish data frames from control frames. Data frames carries the frame's priority as well as a bit which the destination can set as an acknowledgement. For control frames, the Frame Control field is used to specify the frame type. Token passing and various ring maintenance frames are the allowed frame types.
Destination and Source Address: The Destination and Source address fields may be of 2 bytes (for a local address) or 6 bytes (for a global address).
Data: This is the actual data and it is of 8182 bytes when 2 byte addresses are used and 8174 bytes for 6 byte addresses.
Checksum: A 4-byte checksum of the data for error detection.

IEEE 802.5: Token Ring Network

Token Ring is formed by the nodes connected in ring format as shown in the diagram below.

The principle used in the token ring network is that a token is circulating in the ring and whichever node grabs that token will have right to transmit the data. Whenever a station wants to transmit a frame it inverts a single bit of the 3-byte token which instantaneously changes it into a normal data packet. Because there is only one token, there can atmost be one transmission at a time.
Since the token rotates in the ring it is guarenteed that every node gets the token with in some specified time. So there is an upper bound on the time of waiting to grab the token so that starvation is avoided.
There is also an upper limit of 250 on the number of nodes in the network. To distinguish the normal data packets from token (control packet) a special sequence is assigned to the token packet. When any node gets the token it first sends the data it wants to send, then recirculates the token.

If a node transmits the token and nobody wants to send the data the token comes back to the sender. If the first bit of the token reaches the sender before the transmission of the last bit, then error situation araises. So to avoid this we should have:

propogation delay + transmission of n-bits (1-bit delay in each node ) > transmission of the token time

A station may hold the token for the token-holding time. which is 10 ms unless the installation sets a different value. If there is enough time left after the first frame has been transmitted to send more frames, then these frames may be sent as well. After all pending frames have been transmitted or the transmission frame would exceed the token-holding time, the station regenerates the 3-byte token frame and puts it back on the ring.

If a node transmits the token and nobody wants to send the data the token comes back to the sender. If the first bit of the token reaches the sender before the transmission of the last bit, then error situation araises. So to avoid this we should have:

propogation delay + transmission of n-bits (1-bit delay in each node ) > transmission of the token time

A station may hold the token for the token-holding time. which is 10 ms unless the installation sets a different value. If there is enough time left after the first frame has been transmitted to send more frames, then these frames may be sent as well. After all pending frames have been transmitted or the transmission frame would exceed the token-holding time, the station regenerates the 3-byte token frame and puts it back on the ring.

802.11 Wireless LAN Standards

Provides network connectivity over wireless media

An Access Point (AP) is installed to act as Bridge between Wireless and Wired Network

The AP is connected to wired network and is equipped with antennae to provide wireless connectivity

Range ( Distance between Access Point and WLAN client) depends on structural hindrances and RF gain of the antenna at the Access Point

To service larger areas, multiple APs may be installed with a 20-30% overlap

A client is always associated with one AP and when the client moves closer to another AP, it associates with the new AP (Hand-Off)

Three flavors:

Standard	Data Transfer Rate(Max)	Typical Indoor Range	Frequency
802.11b	11Mb/s	100-150feet	2.4Ghz
802.11g	54Mb/s	100-150feet	2.4Ghz
802.11a	54Mb/s	25-70feet	5Ghz

Fibre Distributed Data Interface (FDDI)

Fiber Distributed Data Interface (FDDI) is an expensive LAN technology that employs a pair of fibre-optic rings. One is primary ring and the second ring is used to replace the primary ring in the case of a network failure. Fiber Distributed Data Interface (FDDI) uses fiber-optic cable and is wired in a ring topology and Fiber Distributed Data Interface (FDDI) uses token passing as its media-access method and can operate at high speeds.

The Fiber Distributed Data Interface (FDDI) provides high-speed network backbones that can be used to connect and extend LANs.

Like token ring, FDDI also has error-detection and correction capabilities. In a normally operating Fiber Distributed Data Interface (FDDI) ring, the token passes by each network device fast. If the token is not seen within the maximum amount of time that it takes to circulate the largest ring, it indicates a network problem.

Fiber-optic cable such as the cable used with Fiber Distributed Data Interface (FDDI) can support very large volumes of data over large distances.

Fiber Distributed Data Interface (FDDI) is an expensive technology to set up because the network devices require a special network card and also fiber-optic cabling is required, which is expensive than twisted-pair cable. Because most Fiber Distributed Data Interface (FDDI) installations use a redundant second ring, more cabling is required.