1 / 25

Intro Wireless Application Protocol

Intro Wireless Application Protocol. WebTP Meeting H. Wilson So 14 Feb, 2000. Outline. What is Wireless Application Protocol? Architecture Overview (layers) Bottom up description of the stack Relation to WebTP and differences. What is WAP?.

page
Download Presentation

Intro Wireless Application Protocol

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Intro Wireless Application Protocol WebTP Meeting H. Wilson So14 Feb, 2000.

  2. Outline • What is Wireless Application Protocol? • Architecture Overview (layers) • Bottom up description of the stack • Relation to WebTP and differences

  3. What is WAP? • "WAP specifies an application framework and network protocols for wireless devices such as mobile telephones, pagers, and personal digital assistants (PDAs)." • WAP is the mobile phone industry’s answer to interactive web applications. • WAP defines its own set of protocols but models after existing web protocols.

  4. GSM, CDMA, etc. WDP WTLS WTP WML WML Script IP UDP TLS (from SSL) no counterpart HTML JavaScript WAP and the Web Rationale: reuse as much as possible from IP world, but optimize for the wireless world (i.e. compression, adapt to high-loss rate.)

  5. Accessing Web from Cell Phones

  6. WAP Protocol Architecture

  7. Protocol Features

  8. WAP Reference Model

  9. 1. Datagram Protocol (WDP) • Goal: To allow transport, security, and session protocols to operate independent of the underlying bearer (e.g. GSM, CDMA, etc.) • To provide a UDP-like interface

  10. WDP Basic Features • Port Numbers: Demux lower layer packets to different higher layers • Segmentation/Reassembly: only present if underlying bearer does not support it already • Details: More than you ever want to know about the differences between some 30 kinds of cellular data network.

  11. WDP Summary • If bearer (e.g. GSM USSD) speaks IP, WDP equals UDP. • Otherwise, WDP adapts to the underlying network and provides Demux & Segmentation normally provided by UDP/IP. • Reliable transport builds on top of WDP, not the underlying bearer even if bearer speaks IP

  12. 2. WTLS (Transport Layer Security) • Goal: provides the upper-level layer of WAP with a secure transport service interface that preserves the transport service interface (datagram) below it. • Security level of WTLS depends on the requirements of the given application

  13. WTLS Handshake

  14. Handshake Simplified Client says Hello Server says HelloServer sends Public KeyInitiates key exchange Client generates Session Key Server acks session key Encrypted Data Encrypted Data

  15. WTLS Summary • Very similar to SSL, but SSL is usually implemented on top of TCP; WTLS includes retransmission mechanism • Client/Server can authenticate each other (optional) • Client/Server can negotiate ciphers to be used • Client/Server can negotiate a “datagram mode” that has no sequence numbers

  16. 3. WTP (Transaction Protocol) • Goal: A light-weight transaction protocol necesaary for interactive "browsing" applications. • T stands for Transaction, not transport. • WTP is message-oriented protocol, not stream-based. • Each new transaction has a new Transaction ID (~ seq no.) • Provides 3 classes of service

  17. Class 0 (Unreliable 1-way) • Sender sends a message but does not wait for an ack • Receiver delives message to application w/o checking for duplicates • No acks are sent • Sample app: unreliable weather update (push)

  18. Class 1 (Reliable 1-way) • Sender sends a message and waits for an ack (retx if necessary) • Receiver checks for duplicates before delivering message to application • Acks are sent and retransmitted if client retransmits request erroneously

  19. Class 2 (Reliable 2-way) • Sender sends a message and waits for an ack (retx if necessary) • Receiver checks for duplicates before delivering message to application • Ack for request is piggy-backed on top of the reply from the server application • Client acks the receipt of the result

  20. WTP Duplicate Detection • Since there is no handshake, how does it detect duplicates? • For class 0, duplicate packets are delivered with checking. • Server initiates handshake to verify (and resynchronize TrasactionID if necessary)

  21. WTP Duplicate Detection Client Server Class 1, TID =1 Ack TID = 1 Timeout Class 1, TID =1 Verify TID = 1 Abort

  22. WTP Duplicate Detection Client Server Class 1, TID =1 Ack TID = 1 Class 0, TID =2 Class 0, TID =3 Class 0, TID =N Class 1, TID =1 Verify TID = 1 Ok

  23. WTP: Other interesting features • User-level acks (more precisely, application-level acks) • May do Segmentation and Reassembly • Allow multiple messages (PDUs) to be concatenated into one SDU (link-layer frames) • Re-transmit bit to distinguish fresh vs. retransmitted packets

  24. Relation to WebTP • WAP uses a transaction oriented protocol, WebTP advocates ADUs • WAP allows per PDU-level reliability over same connection • WAP does not require handshake, WebTP has a Fast WebTP option. • Unclear: congestion / flow control in WAP

  25. Areas need to be improved • A tradeoff between connection setup and duplicate detection is required, but analysis is missing. • WAP often talks about “keeps states for some time” but never really discuss why their system is correct.

More Related