14-11-2012, 04:22 PM
Wireless ATM
C08-Wireless_ATM[1].ppt (Size: 307.5 KB / Downloads: 226)
Why wireless ATM?
seamless connection to wired ATM, a integrated services high-performance network supporting different types a traffic streams
ATM networks scale well: private and corporate LANs, WAN
B-ISDN uses ATM as backbone infrastructure and integrates several different services in one universal system
mobile phones and mobile communications have an ever increasing importance in everyday life
current wireless LANs do not offer adequate support for multimedia data streams
merging mobile communication and ATM leads to wireless ATM from a telecommunication provider point of view
goal: seamless integration of mobility into B-ISDN
ATM - basic principle
favored by the telecommunication industry for advanced high-performance networks, e.g., B-ISDN, as transport mechanism
statistical (asynchronous, on demand) TDM (ATDM, STDM)
cell header determines the connection the user data belongs to
mixing of different cell-rates is possible
different bit-rates, constant or variable, feasible
interesting for data sources with varying bit-rate:
e.g., guaranteed minimum bit-rate
additionally bursty traffic if allowed by the network
Cell-based transmission
asynchronous, cell-based transmission as basis for ATM
continuous cell-stream
additional cells necessary for operation and maintenance of the network (OAM cells; Operation and Maintenance)
OAM cells can be inserted after fixed intervals to create a logical frame structure
if a station has no data to send it automatically inserts idle cells that can be discarded at every intermediate system without further notice
if no synchronous frame is available for the transport of cells (e.g., SDH or Sonet) cell boundaries have to be detected separately (e.g., via the checksum in the cell header)
ATM layers
Physical layer, consisting of two sub-layers
physical medium dependent sub-layer
coding
bit timing
transmission
transmission convergence sub-layer
HEC (Header Error Correction) sequence generation and verification
transmission frame adaptation, generation, and recovery
cell delineation, cell rate decoupling
ATM layer
cell multiplexing/demultiplexing
VPI/VCI translation
cell header generation and verification
GFC (Generic Flow Control)