网络通信-Chapter9.pptVIP

Network Management 9-* Presentation problem: potential solutions 1. Sender learns receiver’s format. Sender translates into receiver’s format. Sender sends. real-world analogy? pros and cons? 2. Sender sends. Receiver learns sender’s format. Receiver translate into receiver-local format real-world-analogy pros and cons? 3. Sender translates host-independent format. Sends. Receiver translates to receiver-local format. real-world analogy? pros and cons? Network Management 9-* Solving the presentation problem 1. Translate local-host format to host-independent format 2. Transmit data in host-independent format 3. Translate host-independent format to remote-host format aging 60’s hippie 2007 teenager grandma Network Management 9-* ASN.1: Abstract Syntax Notation 1 ISO standard X.680 used extensively in Internet like eating vegetables, knowing this “good for you”! defined data types, object constructors like SMI BER: Basic Encoding Rules specify how ASN.1-defined data objects to be transmitted each transmitted object has Type, Length, Value (TLV) encoding Network Management 9-* TLV Encoding Idea: transmitted data is self-identifying T: data type, one of ASN.1-defined types L: length of data in bytes V: value of data, encoded according to ASN.1 standard 1 2 3 4 5 6 9 Boolean Integer Bitstring Octet string Null Object Identifier Real Tag Value Type Network Management 9-* TLV encoding: example Value, 5 octets (chars) Length, 5 bytes Type=4, octet string Value, 259 Length, 2 bytes Type=2, integer Network Management 9-* Network Management: summary network management extremely important: 80% of network “cost” ASN.1 for data description SNMP protocol as a tool for conveying information Network management: more art than science what to measure/monitor how to respond to failures? alarm correlation/filtering? * * * * * * * * * * * * * * * * * * * * * * * * * * Network Management 9-* Chapter 9: Network Management Chapter goals: introduction to network management moti