1. LAN Protocol Architecture

2. LAN Protocol Architecture
Lower layers of OSI model
IEEE 802 reference model, is a standardized protocol architecture for LANs, which describes:
Physical layer.
Logical link control (LLC) sub-layer,
Media access control (MAC) sub-layer.

3. IEEE 802 v OSI

4. IEEE 802 Protocol Layers Physical layer, includes such functions as:
Encoding and decoding of signals
Preamble generation and removal (for synchronization)
Bit transmission and reception
Logical Link Control, functions:
Assemble data into a frame with address and error-detection fields
Disassemble frame and perform address recognition and error detection
Govern access to the LAN transmission medium
Interface to higher levels and performs flow and error control

5. 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

6. 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.

7. LLC Protocol
Is modeled after HDLC, and has similar functions and formats.
LLC protocol operation:
LLC use asynchronous balanced mode of operation of HDLC to support connection mode LLC service (type 2 operation)
LLC supports an unacknowledged connectionless service using unnumbered information PDUs (type 1 operation)
LLC supports acknowledged connectionless service using unnumbered information PDUs (type 3 operation)
LLC permits multiplexing using LLC service access points (LSAPs)

8. Media Access Control Key parameters of MAC technique is where and how:
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)

9. Asynchronous MAC Techniques
Round robin:
Each station is given the opportunity to transmit. The right to transmit passes in a logical sequence.
Reservation: a node will reserves future slots from the medium time to transmit, this is good for stream traffic.
Contention
Good for bursty traffic
All stations contend for time
Distributed control
Simple to implement
Efficient under moderate load
Tend to collapse under heavy load

10. MAC Frame Format MAC layer receives data from LLC layer
The fields of MAC frame:
MAC control: protocol control like priority.
Destination MAC address
Source MAC address
LLC: data from next higher layer.
CRC: FCS for error detection.
MAC layer detects errors and discards frames
LLC optionally retransmits unsuccessful frames

11. Generic MAC Frame Format