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Tele Communications - IEEE 802.11

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The assignment covers the following topics:
IEEE 802.11 Architecture
IEEE LAN Standards
MAC Addressing
MAC Frame Format
MAC Modes

Tele Communications - IEEE 802.11

  1. 1. TELE COMMUNICATIONS Assignment Topic: IEEE 802.11 Architecture Assignment Submitted To: Miss Anila Majeed Assignment Submitted By: Shefa Idrees (101631049) Assignment Submission Date: 20-May-2019 Post Graduate College for Women, Samnabad Lahore
  2. 2. IEEE 802.11 Architecture What is IEEE 802.11? In 1990, IEEE 802 Committee formed a new working group, IEEE 802.11, specifically devoted to wireless LANs, with a charter to develop a MAC protocol and physical medium specification. WLANs Wireless LANs are those Local Area Networks which use high frequency radio waves instead of cables for connecting the devices in LAN. Users connected by WLANs can move around within the area of network coverage. Most WLANs are based upon the standard IEEE 802.11 or WIFI. The Architecture of IEEE 802.11 The IEEE 802.11 architecture consists of several components. These components interact to provide a wireless LAN that supports station mobility transparently to the upper layers. They include:  STA - Station  AP - Access Point  BSS - Basic Service Set  IBSS- Independent BSS  ESS - Extended Service Set  A set of Infrastructure BSSs.  Connection of APs  Tracking of mobility  DS - Distribution System  AP communicates with another 802.11Architecture
  3. 3. ESS  WLAN is based on cellular architecture.  Stations (STAs) comprise all the devices and equipment which are connected to the WLAN. A station can be of two types: o Wireless Access Points (WAP): WAPs or simply Access Points (AP) are generally wireless routers which form the Base Stations or Access. o Client: Clients are workstations, computers, laptops, printers, smartphones, etc.  Basic Service Set (BSS) is a group of stations communicating at Physical Layer level. BSS can be of two categories depending upon the mode of operation: o Infrastructure BSS: Here, the devices communicate with other devices through Access Points. o Independent BSS (IBSS): Mobile Station (MS) in BSS with no connection to other BSSs form IBSS. Here, the devices communicate in peer-to-peer basis in an ad-hoc manner.  Each cell/Basic Service Set (BSS) is controlled by a base station/Access Point (AP).  Access Points are connected with backbone called Distribution System (DS).  The whole interconnected WLAN through DS form Extended Service Set (ESS).  AP functions as a bridge and a relay point.  In BSS, MS communicate through the AP  IBSS is since an ad hoc network, where station communicate directly.  To integrate 802.11 with 802.2 (Wired LAN), a portal is used.  Portal is a device such as bridge or router attached to DS.
  4. 4. IEEE LAN Standards Layer 1 Physical Layer Limitations:  Cannot organize streams of bits.  Cannot name or identify computers.  Cannot communicate with the upper-level layers.  Cannot decide which computer will transmit binary data. Layer 2 Data Link Layer Uses:  Framing to organize or group the data bits.  An addressing process to identify computers called flat addressing convention.  Logical Link Control (LLC) to communicate with the upper-level layers.  Media Access Control (MAC) to decide which computer will transmit binary data, from a group in which all computers are trying to transmit at the same time. Purpose of Sub-layers  LLC or Logical Link Control serves to communicate upward to Network layer, independent of the specific LAN technology used and Upper layer.  MAC or Media Access Control serves to access and communicate downward to the technology-specific Physical layer.
  5. 5. MAC Addressing  Every computer has a unique way of identifying itself via MAC address or physical address.  The physical address is located on the Network Interface Card (NIC).  MAC addresses have no structure, and are considered flat address spaces.  MAC addresses are sometimes referred to as burned-in addresses (BIAs) because they are burned into read-only memory (ROM) and are copied into random-access memory (RAM) when the NIC initializes. MAC Frame Format The IEEE 802.11 MAC accepts MSDUs (MAC Service Data Unit) from higher layers in the protocol stack for the purpose of reliably sending those MSDUs to the equivalent layer of the protocol stack in another station.  MAC adds information to the MSDU in the form of headers & trailers to create an MPDU (MAC Protocol Data Unit).  MPDU is then passed on to the physical layer to be sent over the wireless medium to the other station.  MAC may fragment MSDUs into several frames.  The maximum size of a MAC frame is 2048 octets. Frame Fields  Frame Control: Indicates the type of frame provides control information. Control information includes whether the frame is to or from a DS and privacy information.  Duration/ID: If used as a duration field, indicates the time (in microseconds) the channel will be allocated for successful transmission of a MAC frame.  Address 1: MAC address of wireless host or AP to receive this frame.  Address 2: MAC address of wireless host or AP transmitting this frame.  Address 3: MAC address of router interface to which AP is attached.  Address 4: Used only in ad hoc mode.  Sequence Control: Sequence number used to number frames sent between a given transmitter and receiver.  Frame Body or Payload: Contains the message.  CRC: The last field contains error detection information.
  6. 6. MAC Modes The 802.11 MAC protocol designed with two modes of communication  Distributed Coordination Function (DCF) The basic 802.11 MAC layer uses the Distributed Coordination Function (DCF) to share the medium between multiple stations, based on Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) o All stations are equal o "Listen before talk” o Station waits for quiet period on network o Begins to transmit data o Detects possible collisions  Point Coordination Function (PCF) This is available only in "infrastructure" mode, where stations are connected to the network through an Access Point (AP). This mode is optional, and only very few APs or Wi-Fi adapters actually implement. PCF defines two periods: o The Contention Free Period (CFP) - In the CP, DCF is used. o The Contention Period (CP) - In the CFP, the AP sends Contention-Free-Poll packets to each station, one at a time, to give them the right to send a packet. The AP is the coordinator.
  7. 7. LLC Services The services of Logical Link Control (LLC) include:  Unacknowledged connectionless service o No flow- and error-control mechanisms o Data delivery not guaranteed  Connection-mode service o Logical connection set up between two users o Flow- and error-control provided  Acknowledged connectionless service o Cross between previous two o Datagrams acknowledged o No prior logical setup LLC Operations Type 1 Operation: Type 1 operation supports unacknowledged connectionless service. There is no acknowledgment, flow control, or error control. Type 2 Operation: Type 2 operation supports connection-mode service, using mechanisms similar to HDLC. Type 3 Operation: Type 3 operation supports acknowledged connectionless service. Each transmitted PDU is acknowledged using a stop-and-wait technique.
  • FaizaAslam18

    Apr. 11, 2021
  • DianaDenhere

    Mar. 22, 2021

The assignment covers the following topics: IEEE 802.11 Architecture IEEE LAN Standards MAC Addressing MAC Frame Format MAC Modes


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