Chapter 10 - X.25 and Network Management This is about the Wide Area Network using X.25 packet switching. Sunday, April 21, 2019Sunday, April 21, 2019 Y K Choi

Objectives The X.25 network The network management in various networks Modem diagnosis Network design Sunday, April 21, 2019Sunday, April 21, 2019 Y K Choi

X.25 Defines three layers only not the whole seven layers including: Physical layer Data link layer Network layer Does not define internal subnet protocols. Sunday, April 21, 2019Sunday, April 21, 2019 Y K Choi

Example of X.25 Network Sunday, April 21, 2019Sunday, April 21, 2019 Y K Choi

X.25 Level 1 Equivalent to ISO/OSI Physical layer X.21 bis Interface to analog network Equivalent to RS-232C - V.24. X.21 Interface to digital network (may also support X.21 bis/RS232C to those which does not support). Limited Support in Hong Kong Sunday, April 21, 2019Sunday, April 21, 2019 Y K Choi

X.25 Level 2 This is consistent with OSI layer 2. The function of this level is to ensure reliable communication between DTE and DCE. Sunday, April 21, 2019Sunday, April 21, 2019 Y K Choi

X.25 Level 2 protocols LAP (SARM) (Set Asynchronous Response Mode) LAP-B (SABM) (Set Asynchronous Balance Mode) Sunday, April 21, 2019Sunday, April 21, 2019 Y K Choi

comparison between the OSI and X.25 protocol structure. Sunday, April 21, 2019Sunday, April 21, 2019 Y K Choi

X.25 Level 3 This is similar to OSI layer 3 and is called the X.25 Packet Level Protocol (PLP). It provides: Virtual circuits. (With permanent virtual circuits and switched virtual circuits analog to leased and switched lines in PSTN.) Datagram (Sending individual connectionless oriented packets through different communication paths) PAD support Sunday, April 21, 2019Sunday, April 21, 2019 Y K Choi

Call Establishment Establish virtual circuit Call request by sending a Call Request packet Call accepted by responding a Call Accepted packet Data exchange once the connection has been established. To terminate the connection is To send a Clear Request packet Wait for the confirmed by receiving a Clear Confirmation packet Time-out is used to establish limits on how long it takes to get connections. Sunday, April 21, 2019Sunday, April 21, 2019 Y K Choi

Procedures of exchanging data packets Sunday, April 21, 2019Sunday, April 21, 2019 Y K Choi

Packet assembler-disassembler Terminal to X.25 Network X.28 - this defines the interface between the terminal and the PAD. X.29 - this defines the host (DTE)-PAD interface. Sunday, April 21, 2019Sunday, April 21, 2019 Y K Choi

X.25 packet header The relationship between a frame and a packet with appropriate labelling for virtual channels and paths. Sunday, April 21, 2019Sunday, April 21, 2019 Y K Choi

The services offered by X.25 include: Switched virtual circuits (SVC) (Analog to public switched telephone service) Permanent virtual circuits (PVC) (The connection is automatically established once the device connecting to X.25 network is booted up.) Datagrams(Equivalent to connectionless service. Not explicit virtual path is set up prior to sending packets.) Sunday, April 21, 2019Sunday, April 21, 2019 Y K Choi

Network Management Once a network has been established, it is a good idea if one can control it; monitor its performance; diagnose faults; reconfigure in the event of failure. Sunday, April 21, 2019Sunday, April 21, 2019 Y K Choi

THREE Factors for Network Management People, There are not many on the market and requires on-the-job training. Usually,, the problem for the systems designer (network engineer) is to estimate the likely incidence of faults for each component in the data communications systems. Equipment, This includes: testing equipment for diagnosing faults; reconfiguring equipment such as patching and switching facilities. Software, Among other things,, the software can provide performance statistics to help sort out the bottleneck. Sunday, April 21, 2019Sunday, April 21, 2019 Y K Choi

Measures of System Effectiveness Three factors, namely, availability, reliability and cost-effectiveness are used to measure how well the system is. Availability, It means that all necessary components are operable and accessible. For a connection to CityU through the CityU Link Plus, it includes your PC, Windows 95, Browser, modem, telephone exchange, remote server etc. Accessibility means the user can make use of the component when needed. Sunday, April 21, 2019Sunday, April 21, 2019 Y K Choi

Performance Factor Mean Time Between failures (MTBF), and Mean time to Repair (MTTR). A modem with MTBF of 1000 hours that operates an average of three days a week, 20 days a month, would be expected to fail once every 1000/(3 x 20 ) = 16 months. MTTR is the average amount of time required to restore the failure into normal service such as replacing faculty modem using 30 minutes. Sunday, April 21, 2019Sunday, April 21, 2019 Y K Choi

Reliability It is about the probability that the system will continue to function over a given operating period. If a transaction requires 1 second for a response to be received, then the reliability of the system is the probability that the system will not fail during that second. Reliability includes the error characteristics of component such as modem, PC, Windows 2000 and the transmission telephone line. Sunday, April 21, 2019Sunday, April 21, 2019 Y K Choi

Performance Statistics Statistical information can be collected in the following IBM devices: IBM Host (IBM Product Code 3090) Front End Processor (3725) Intelligent Terminal Control Unit (3174) External Equipment (3278/3279) Sunday, April 21, 2019Sunday, April 21, 2019 Y K Choi

Performance Statistics Factor Character in/out, This indicates the loading on the system and the traffic fluctuation during the day. It is helpful in keeping track of traffic growth. Polls sent, Is particular useful on networks using statistical multiplexers Retries, This indicates the number of messages that are re-transmitted. This statistic can be a useful diagnostic tool and can foreshadow a potential network component failure. Time-outs, Indicates how many polls or messages sent to terminals did not get a response. Response Times, This is both a planning tool and a diagnostic aid. Line utilization, This gives an indication of the loading on a line. Sunday, April 21, 2019Sunday, April 21, 2019 Y K Choi

Goals of Datacomm Testing The goals of datacommunication testing are to: Increase system availability by Minimizing the network down time Expediting repairs by identifying precisely the faulty network components Eliminating finger pointing by randomly repairing functioning network components Debug network applications Develop good relationships with data communications vendors Isolate the failing component within the network Sunday, April 21, 2019Sunday, April 21, 2019 Y K Choi

Testing domain Analog testing Transmission impairment and continuity Measuring sets include voltmeter Digital Bit Error Rate Tester. It is used to measure the ratio between the error bits against the totally received bits including the error bit. Protocol Serial Data Analyzer (It captures the status of every V24 interface lead for every bit time on the interface. Data can be stored on tape or diskette for later analysis.) LAN Protocol Analyzer (To measure the network loading, performance and traffic pattern.) Sunday, April 21, 2019Sunday, April 21, 2019 Y K Choi

Breakout box The use of break-put box to diagnose the network connection between a modem and terminal. Sunday, April 21, 2019Sunday, April 21, 2019 Y K Choi

Protocol Analyzer The use of protocol analyzer to monitor the contents of data movement between a computer and a modem. Sunday, April 21, 2019Sunday, April 21, 2019 Y K Choi

Characteristics of protocol analyzer Simulate and Monitor Modes Simulate mode is to configure the protocol analyzer to act as a DTE or DCE in the network usually used to perform software verification. Monitor mode is to configure the protocol analyzer to act as a monitor to keep check the data movement between a DTE and DCE. Softkey menu operation instead of using hard-code keys in the small console to configure the protocol analyzer Use BASIC language to program the analyzer to emulate DTE/DCE and capture special data stream. Sunday, April 21, 2019Sunday, April 21, 2019 Y K Choi

Modem diagnostics By looping the analog side, the messages sent by DTE will be returned and processed by DTE to ensure that the analog and digital side of modem, and data link between two modems are working properly. Sunday, April 21, 2019Sunday, April 21, 2019 Y K Choi

End-to-end Test The text messages will be sent by one of the computers and be captured by another to verify the communication is in proper condition. Sunday, April 21, 2019Sunday, April 21, 2019 Y K Choi

Remote Digital Loopback test It uses a machine to perform loop-back text by looping the remote digital side. This can detect the send/return path. Sunday, April 21, 2019Sunday, April 21, 2019 Y K Choi

To design a network Must be within the capabilities of the protocols supported by terminal and host computer Must be fast enough to carry all the traffic at the required times Must be sufficiently reliable to meet the needs of users of the service. Sunday, April 21, 2019Sunday, April 21, 2019 Y K Choi

Redundancy Standby modem Standby line Standby Equipment Sunday, April 21, 2019Sunday, April 21, 2019 Y K Choi

Standby modem A single standby modem is installed to replace the defective modem once a hardware problem is found Sunday, April 21, 2019Sunday, April 21, 2019 Y K Choi

Standby telecommunication lines A duplicated telecommunication line is leased from Hong Kong Telecom using different route to replace the defective line once it is identified. Sunday, April 21, 2019Sunday, April 21, 2019 Y K Choi

Standby Front end processor A Front-end Processor is standby to replace the defective machine in case it is not working properly. Sunday, April 21, 2019Sunday, April 21, 2019 Y K Choi