17-11-2012, 01:54 PM
IEEE 802 Protocol Architechture
IEEE 802 Protocol Architechture.pptx (Size: 172.04 KB / Downloads: 24)
Physical Layer
Physical layer, includes such functions as:
Encoding and decoding of signals
Preamble generation and removal
Bit transmission and reception
For some IEEE standards this layer is further subdivided:
- Physical Layer Convergence Procedure (PLCP)
- Physical Medium Dependent sub layer (PMD)
Logical Link Control
LLC is concerned with transmission of link-level PDUs between two stations
LLC has two special characteristics:
Must support multiaccess, shared medium (no primary node as in multidrop line)
Relieved of some link access details by MAC layer
Addressing involves specifying source and destination LLC users
Referred to as service access points (SAP)
Service users are typically higher level protocols
LLC Services
The operation and format of this standard is based on HDLC.
Provide three different services for attached devices:
Unacknowledged connectionless service:
Datagram-style service.
No flow-control and no error-control mechanisms.
Reliability depend to some higher layer of software.
Connection mode service:
Similar to that of HDLC.
Provides flow- and error-control.
Acknowledged connectionless service
Datagrams are to be acknowledged.
No prior logical connection is set up.
Media Access Control
Key parameters of MAC technique is where and how:
Where
Central
Adv.: Greater control and simple access logic at station (no coordination complexities)
Disadv.: Single point of failure and potential bottleneck
Distributed: opposite of central.
How
Synchronous: specific capacity dedicated to connection
Asynchronous: in response to demand; can be subdivided into three categories (round robin, reservation, contention)