LLC Services

Unacknowledged connectionless service

No flow- and error-control mechanisms

Data delivery not guaranteed

Connection-mode service

Logical connection set up between two users

Flow- and error-control provided

Acknowledged connectionless service

Cross between previous two

Datagrams acknowledged

No prior logical setup

MAC Frame Format

MAC control

Contains Mac protocol information

Destination MAC address

Destination physical attachment point

Source MAC address

Source physical attachment point

CRC

Cyclic redundancy check

Separation of LLC and MAC

The logic required to manage access to a shared-access medium not found in traditional layer 2 data link control

For the same LLC, several MAC options may be provided

Internetworking Terms

Communication network – facility that provides a data transfer service among devices attached to the network

Internet – collection of communication networks, interconnected by bridges/routers

Intranet – internet used by an organization for internal purposes

-Provides key Internet applications

-Can exist as an isolated, self-contained internet


End System (ES) – device used to support end-user applications or services

Intermediate System (IS) – device used to connect two networks

Bridge – an IS used to connect two LANs that use similar LAN protocols

Router - an IS used to connect two networks that may or may not be similar

Layers of the OSI Model

Application

Presentation

Session

Transport

Network

Data link

Physical


OSI Application Layer

Provides access to the OSI environment for users

Provides distributed information services


OSI Presentation Layer

Provides independence to the application processes from differences in data representation (syntax)


OSI Session Layer

Provides the control structure for communication between applications

Establishes, manages, and terminates connections (sessions) between cooperating applications


OSI Transport Layer

Provides reliable, transparent transfer of data between end points

Provides end-to-end error recovery and flow control


OSI Network Layer

Provides upper layers with independence from the data transmission and switching technologies used to connect systems

Responsible for establishing, maintaining, and terminating connections


OSI Data link Layer

Provides for the reliable transfer of information across the physical link

Sends blocks (frames) with the necessary synchronization, error control, and flow control


OSI Physical Layer

Concerned with transmission of unstructured bit stream over physical medium

Deals with accessing the physical medium

Mechanical characteristics

Electrical characteristics

Functional characteristics

Procedural characteristics

TCP/IP Layers

Physical layer

Network access layer

Internet layer

Host-to-host, or transport layer

Application layer

TCP/IP Physical Layer

Covers the physical interface between a data transmission device and a transmission medium or network

Physical layer specifies:

Characteristics of the transmission medium

The nature of the signals

The data rate

Other related matters


TCP/IP Network Access Layer

Concerned with the exchange of data between an end system and the network to which it's attached

Software used depends on type of network

Circuit switching

Packet switching (e.g., X.25)

LANs (e.g., Ethernet)

Others


TCP/IP Internet Layer

Uses internet protocol (IP)

Provides routing functions to allow data to traverse multiple interconnected networks

Implemented in end systems and routers


Transport Layer

Commonly uses transmission control protocol (tcp)

Provides reliability during data exchange

Completeness

Order


TCP/IP Application Layer

Logic supports user applications

Uses separate modules that are peculiar to each different type of application

Categories of Noise

Thermal Noise

Intermodulation noise

Crosstalk

Impulse Noise

Thermal Noise

Thermal noise due to agitation of electrons

Present in all electronic devices and transmission media

Cannot be eliminated

Function of temperature

Particularly significant for satellite communication