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IEEE 802 StandardsIEEE 802 Standards

IEEE 802 is a family of IEEE 802 is a family of standardsstandards

for LANs, which defines anfor LANs, which defines an

LLC and several MAC sub LLC and several MAC sub layerslayers

IEEE 802.3 Ethernet LANsIEEE 802.3 Ethernet LANs– The MAC layer uses CSMA/CD (Carrier Sense The MAC layer uses CSMA/CD (Carrier Sense

Multiple Access with Collision Detection) Multiple Access with Collision Detection) technology.technology.

When a computer wants to transmit a When a computer wants to transmit a frame it:frame it:– Listens for a frame on the cable, if busy, the computer Listens for a frame on the cable, if busy, the computer

waits for a random time and attempts transmission waits for a random time and attempts transmission again. This is known as again. This is known as Carrier SenseCarrier Sense..

– If the cable is quiet, the computer begins to transmit.If the cable is quiet, the computer begins to transmit.– Two computers could transmit at the same time. To Two computers could transmit at the same time. To

prevent this happening, the transmitting computer prevent this happening, the transmitting computer listens to what it is sending.listens to what it is sending.

– If what it hears is different to what it is sending, then If what it hears is different to what it is sending, then a collision has occurred. This is known as a collision has occurred. This is known as Collision Collision DetectionDetection..

802.5 Token Ring LANs802.5 Token Ring LANs– A Token Ring LAN consists of a collection of A Token Ring LAN consists of a collection of

ring interfaces connected by point-to-point ring interfaces connected by point-to-point lines.lines.

Unidirectional Ring – One Way

Ring interface

Computers

IEEE 802.5 Token Ring LANsIEEE 802.5 Token Ring LANs– The MAC sub layer uses Token Ring The MAC sub layer uses Token Ring

Technology.Technology.

– In a Token Ring LAN, a special bit pattern In a Token Ring LAN, a special bit pattern called the token circulates around the ring called the token circulates around the ring whenever all computers are idle.whenever all computers are idle.

– When a computer wants to transmitWhen a computer wants to transmit:: It waits for the token to arrive.It waits for the token to arrive.

When it arrives, it removes the token from the When it arrives, it removes the token from the ring. There is only one token so only one ring. There is only one token so only one computer can transmit at any one time.computer can transmit at any one time.

The computer can now transmit its frame on its The computer can now transmit its frame on its output link.output link.

This frame will now propagate around the ring This frame will now propagate around the ring until it arrives back at the sender who removes until it arrives back at the sender who removes the frame from the ring.the frame from the ring.

The sender then regenerates the token and The sender then regenerates the token and passes it to the next computer (restarting the passes it to the next computer (restarting the above steps).above steps).

IEEE 802.5 Frame FormatIEEE 802.5 Frame Format

– Start of Frame and End Delimiters mark the Start of Frame and End Delimiters mark the beginning and ending of a frame.beginning and ending of a frame.

– Destination Address, Source Address and Destination Address, Source Address and Checksum are used in a similar fashion to Checksum are used in a similar fashion to IEEE 802.3 Ethernet.IEEE 802.3 Ethernet.

DestinationAddress

Data – No LimitEnd

Delimiter

ChecksumSame as

802.3

SourceAddress

Start ofFrame

Delimiter

Bytes 3 2 or 6 2 or 6 4 1 1

Difference between Start of Frame and Token is only 1 bit in 3rd byte.

FrameStatus

Token3 Bytes

What is 802.11 ??What is 802.11 ??

802.11 refers to a family of specifications 802.11 refers to a family of specifications developed by the IEEE for wireless LAN developed by the IEEE for wireless LAN technology. 802.11 specifies an over-the-air technology. 802.11 specifies an over-the-air interface between a wireless client and a interface between a wireless client and a base station or between two wireless clients. base station or between two wireless clients.

The IEEE accepted the specification in 1997. The IEEE accepted the specification in 1997.

IEEE 802.11…….IEEE 802.11…….

Defines two services:Defines two services:

1- the basic services set (BSS)1- the basic services set (BSS)

2- the extended service set (ESS)2- the extended service set (ESS)

BSS……BSS……

Made of mobile wireless stations Made of mobile wireless stations and an optional central base and an optional central base station, known as station, known as Access point Access point (AP).(AP).

Without AP BSS can’t send data Without AP BSS can’t send data to other BSS s.to other BSS s.

With AP is called an With AP is called an “infrastructure network”.“infrastructure network”.

ESS…….ESS…….

-Made up of two or more BSSs with APs.-Made up of two or more BSSs with APs.

-BSS s are connected through distribution -BSS s are connected through distribution system, which is usually a wired LAN.system, which is usually a wired LAN.

-uses two types of stations: mobile and -uses two types of stations: mobile and stationary.stationary.

802.11 Family Members802.11 Family Members There are several specifications in the 802.11 family: There are several specifications in the 802.11 family:

802.11802.11

– Applies to wireless LANs and provides 1 or 2 Mbps Applies to wireless LANs and provides 1 or 2 Mbps transmission in the 2.4 GHz band using either frequency transmission in the 2.4 GHz band using either frequency hopping spread spectrum (FHSS) or direct sequence hopping spread spectrum (FHSS) or direct sequence spread spectrum (DSSS).spread spectrum (DSSS).

802.11a802.11a

– An extension to 802.11 that applies to wireless LANs and An extension to 802.11 that applies to wireless LANs and provides up to 54 Mbps in the 5GHz band. 802.11a uses provides up to 54 Mbps in the 5GHz band. 802.11a uses an orthogonal frequency division multiplexing encoding an orthogonal frequency division multiplexing encoding scheme rather than FHSS or DSSS. scheme rather than FHSS or DSSS.

802.11b802.11b

– ((also referred to as 802.11 High Rate or Wi-Fi) also referred to as 802.11 High Rate or Wi-Fi) is an extension to 802.11 that applies to is an extension to 802.11 that applies to wireless LANs and provides 11 Mbps wireless LANs and provides 11 Mbps transmission (with a fallback to 5.5, 2 and 1 transmission (with a fallback to 5.5, 2 and 1 Mbps) in the 2.4 GHz band. 802.11b uses only Mbps) in the 2.4 GHz band. 802.11b uses only DSSS. 802.11b was a 1999 ratification to the DSSS. 802.11b was a 1999 ratification to the original 802.11 standard, allowing wireless original 802.11 standard, allowing wireless functionality comparable to Ethernefunctionality comparable to Ethernet.t.

802.11g802.11g

– Applies to wireless LANs and provides 20+ Applies to wireless LANs and provides 20+ Mbps in the 2.4 GHz band.Mbps in the 2.4 GHz band.