Reassembly Segmented data must be reassembled into messages More complex if pdUs out of order 6/76
6/76 Reassembly • Segmented data must be reassembled into messages • More complex if PDUs out of order
PDUS and Fragmentation (Copied from chapter 2 fig 2. 4) Application Data Transport I Header Transport rotocol data units Transport Header protocol data units (packets Network Network Header Header
7/76 PDUS and Fragmentation (Copied from chapter 2 fig 2.4)
Connection Control Connectionless data transfer(无连接的传输) Each PDU treated independently -Eg. datagram(数据报) Connection- oriented data transfer(面向连接的传输) Eg. virtual circuit(虚电路) Connection-oriented preferred (even required) for lengthy exchange of data Logical association, or connection, established between entities Three phases occur Connection establishment Data transfer Connection termination May be interrupt and recovery phases to handle errors
8/76 Connection Control • Connectionless data transfer(无连接的传输) - Each PDU treated independently - E.g. datagram(数据报) • Connection-oriented data transfer(面向连接的传输) - E.g. virtual circuit(虚电路) • Connection-oriented preferred (even required) for lengthy exchange of data • Logical association, or connection, established between entities • Three phases occur - Connection establishment - Data transfer - Connection termination • May be interrupt and recovery phases to handle errors
Phases of Connection Oriented Transfer Protocol Protocol Entity Entity C connection red quest Connection acc Data Multiple Acknowledgement exchanges Te erminate-connect ion request Termin te-connection accep
9/76 Phases of Connection Oriented Transfer
Connection establishment Entities agree to exchange data Typically, one station issues connection request Receiving entity accepts or rejects(simple) May include negotiation Syntax, semantics, and timing(语法、语义、定时) Both entities must use same protocol May allow optional features Must be agreed E.g. protocol may specify max PdU size 8000 octets one station may wish to restrict to 1000 octets
10/76 Connection Establishment • Entities agree to exchange data • Typically, one station issues connection request • Receiving entity accepts or rejects (simple) • May include negotiation • Syntax, semantics, and timing(语法、语义、定时) • Both entities must use same protocol • May allow optional features • Must be agreed • E.g. protocol may specify max PDU size 8000 octets; one station may wish to restrict to 1000 octets