COMMUNICATION CONTROL CHAPTER 12 COMMUNICATION CONTROL

COMMUNICATION SUBSYSTEM EXPOSURE Transmission impairments Component Failure Subversive Threats

Subversive threats to the Communication Subsystem Release of message contents Passive Attacks Traffic analysis Message insertion Message deletion Message modification Changed message order Message duplication Denial of message services Spurious associations Subversive Threats Active attacks

PHYSICAL COMPONENT CONTROLS Tramsmision Media Twisted paier Coaxial cable Optical fiber Bounded Transimission media Terrestrial microware Satellite microwave Radio frequency Infrared Unbounded

Communication Lines Modems Port-Protection Devices Multiplexors and Concentrators

LINE ERROR CONTROLS Error Detection Sends message Receiver Sender Returns copy of message

Error Correction Forward error correcting codes Retransmission of data in error(backward error correction)

FLOW CONTROLS The simplest form of flow control is stop-and-wait flow control The stop-and-wait flow control protocol is inefficient because the communication channel remains unused for periods of time while the receiver isprocessing the frames received.

TOPOLOGICAL CONTROLS Local Area Network Topologies Bus Topology Tree Topology Ring Topology Star topology Hybrid Topologies Wide Area Network Topologies

CHANNEL ACCESS CONTROLS Polling Methods Contention Methods

CONTROLS OVER SUBVERSIVE THREATS Link Encryption End-to-End- Encryption Stream Ciphers Error Propagation Codes Message authentication Codes Message Sequence Numbers Request-Response Mechanisms

INTERNETWORKING CONTROLS Three types of devices are used to connect subnetworks in an internet : Bridge Router Gateway

COMMUNICATION ARCHITECTURES AND CONTROLS The architecture has seven layers of function.each of which has as sociated controls : Physical - Session Data link - Presentration Network - App;ication Transport

AUDIT TRAIL CONTROLS Accounting Audit Trail Operations Audit Trail

EXISTENCE CONTROLS Some additional backup and recovery controls follow : Where possible, place redundant components and spare parts throughout the network. Use equipment with in-built fault diagnosis capabilities. Acquire high-quality test equipment. Ensure adequate maintenance of hardware and software, especially at remote site Ensure that adequate logging facilities exist for recovery purposes, especially where store-and-forward operations must be carried out in the network.