Standardization of Wireless Networks-Wireless Networks-Lecture Slides, Slides of Wireless Networking

Download Standardization of Wireless Networks-Wireless Networks-Lecture Slides and more Slides Wireless Networking in PDF only on Docsity! 2 Outlines  Overview of IEEE 802.11  IEEE 802.11 Protocols  Architecture  Services  MAC Protocols ► DCF ► PCF docsity.com 3 Standardization of Wireless Networks  Wireless networks are standardized by IEEE.  Under 802 LAN MAN standards committee. Application Presentation Session Transport Network Data Link Physical ISO OSI 7-layer model Logical Link Control Medium Access (MAC) Physical (PHY) IEEE 802 standards docsity.com 6 WLAN Requirements  Throughput  Number of Nodes/Scalability  Connection to Backbone LAN  Service Area: 100 to 300 m  Power Consumption  Transmission Robustness and Security  Collocated network Operation  License-free operation  Handoff/Roaming  Dynamic Configuration docsity.com IEEE 802.11 Protocols ► IEEE 802.11a: PHY Standard : 8 channels : 54 Mbps : 5 GHz band: OFDM. ► IEEE 802.11b: PHY Standard : 3 channels : 11 Mbps : 2.4 GHz band: FHSS, DSSS. ► IEEE 802.11d: MAC Standard : operate in variable power levels : ► IEEE 802.11e: MAC Standard : QoS support : EDCF. ► IEEE 802.11f: Inter-Access Point Protocol : 2nd half 2002 ► IEEE 802.11h: Supplementary MAC Standard: Enhanced version of 802.11a to support European Regulatory provides TPC and DFS. ► IEEE 802.11i: Supplementary MAC Standard: Alternative WEP ► IEEE 802.11n: 100 + Mbps : Enhancement to 802.11g using MIMO ► IEEE 802.11s: mesh networking extension docsity.com 8 IEEE 802.11 Architecture  WLAN is based on cellular architecture  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) as a single layer in OSI model.  Mobile Station (MS) in BSS with no connection to other BSSs form Independent BSS (IBSS). docsity.com 11  Access Point functions as a bridge and a relay point.  In BSS, MS communicate through Access Point  IBSS is typically 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. docsity.com 12 802.11 Services  IEEE 802.11 defines nice services.  Three services for WLAN access and confidentiality.  Six services used to support delivery of MAC Service Data Unit (MSDU) between stations. docsity.com 13 Messages Distribution in ESS  Two services involved in distribution of messages within DS. ► Distribution • Primary service used to exchange MAC frames between stations of two BSSs. • Source sends to AP of one BSS, which sends to DS. DS then sends to AP of the destination. • Message transport in DS is beyond the scope of IEEE 802.11 standard. docsity.com 16 Access and Privacy Services ► Authentication • Establishes the identity of stations. • However, IEEE 802.11 requires mutually acceptable, successful authentication before association. ► De-authentication • Invoked to terminate existing authentication ► Privacy • Standard provides optional use of encryption to assure privacy docsity.com Station or RERviCe distribution service? Deseiysion ee ee Service used in frame delivery to determine Distribution Distribution destination address in infrastructure networks niiopeation Distribution Frame delivery to an IEEE 802 LAN outside the wireless network Association Distribution Used to establish the AP which serves as the gateway to a particular mobile station Reassociation [Distribution Used to change the AP which serves as the gateway to a particular mobile station Disassociation —_ [Distribution Removes the wireless station from the network Authentication _|Station Establishes identity prior to establishing association Deauthentication [Station Used to terminate authentication, and by extension, association Privacy Station Provides protection against eavesdropping MSDU delivery [Station Delivers data to the recipient 17 docsity.com 18 IEEE 802.11 Medium Access Control (MAC)  MAC Layer provides three functions ► Reliable data delivery ► Medium access control ► security docsity.com 21 MAC Protocol  Two types of algorithms: ► Distributed access protocol • Distribute the decision to transmit ► Centralized control • Better in ESS, when AP connected to DS docsity.com 22 Distributed Coordination Function (DCF)  DCF sub layer uses CSMA algorithm  Collision detection as in Ethernet is not possible in wireless comm.  It implements collision avoidance (CA) algorithm.  It uses a set of delays of different periods called inter-frame space (IFS) docsity.com 23 CSMA/CA  A Station willing to transmit senses the medium.  If the medium is busy, defers  If idle, wait for Distributed Inter-Frame Space (DIFS) or Exponential back off. docsity.com