Chapter 4 outline

1
Chapter 4 outline

• Introduction to mobile and wireless networking
• Mobile and wireless protocols and standards
• Mobile IP
• Wireless application protocol and related
  standards
• Wireless technologies
• 802.11
• Bluetooth
• Cellular (PCS, GSM, GPRS, etc.)
• Satellite

2
Wireless Application Protocol (WAP)

• WAP is aimed at providing users of mobile and
  wireless devices like cell phones, pagers, and
  personal digital assistants (PDAs) access to
  information services, like the Internet.
• Standardized by the WAP Forum (founded in 1997
  by Ericsson, Motorola, Nokia, and others).
• The WAP specification includes the following
• A programming model based on the WWW model.
• A markup language, the Wireless Markup Language
  (WML), that adheres to XML.
• A specification of a small browser suitable for a
  mobile wireless device.
• A framework for wireless telephony applications.
• A lightweight communications protocol.

3
The WAP Protocol Stack
4
Why WAP?

• WAP is a useful protocol suite for mobile and
  wireless platforms for many reasons
• The devices have limited processors, memory, and
  battery life.
• The user interface is typically quite limited and
  the displays used are relatively small.
• The wireless networks are characterized by
  relatively low bandwidth, high latency, and
  unpredictable availability and reliability
  compared to wired connections.
• The features available vary widely from device to
  device and from network to network.
• Mobile and wireless users have different
  expectations and needs from other information
  systems users (e.g. ease of use).

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The WAP Programming Model

• The WAP programming model is based on three
  elements
• Clients These are the mobile and wireless
  devices in the wireless network.
• Gateways These act as proxy servers for the
  wireless network, providing services that offload
  processing activities to make up for the limited
  capabilities of the mobile and wireless devices.
  (This includes DNS services, caching, protocol
  conversion from WAP to TCP/IP, and encoding and
  decoding information to make it usable on the
  devices.)
• Origin servers These are the original content
  providers to the mobile and wireless devices, and
  need not understand WAP. (The gateways do
  protocol conversions for them.)

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The WAP Programming Model
7
WAP Infrastructure
Might be partof the WAP Proxy,or might be
separate
More compact form of WML
8
Wireless Markup Language (WML)

• WML was designed to describe content and format
  for presenting data on devices with limited
  bandwidth, screen size, and user input.
• The main features of WML
• Text and image support formatting and layout
  commands.
• Deck/card organizational metaphor WML documents
  subdivided into cards, which specify one or more
  units of interaction (a menu, screen of text, or
  a text-entry field).
• Support for navigation among cards and decks
  includes provisions for event handling used for
  navigation or executing scripts.

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Wireless Markup Language (WML)
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Wireless Markup Language (WML)

• The canonical Hello World example in WML
• ltwmlgt
• ltcard idcard1gt
• ltpgt
• Hello WAP World.
• lt/pgt
• lt/cardgt
• lt/wmlgt

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WMLScript

• WMLScript is a scripting language with
  similarities to JavaScript.
• WMLScript is designed to define script-type
  programs in a device with limited processing
  power and memory.
• Important WMLScript capabilities include
• Checking the validity of user input before it is
  sent.
• Accessing device facilities and peripherals.
• Interacting with the user without introducing
  round trips to origin server (for example, to
  display an error message of some kind).

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WMLScript

• Key WMLScript features include the following
• JavaScript-based scripting language WMLScript
  is a subset of JavaScript, with some extensions.
• Procedural logic WMLScript adds procedural
  logic to the Wireless Application Environment
  (WAE).
• Event-based WMLScript may be invoked in
  response to certain user or environmental events.
• Compiled implementation WMLScript can be
  compiled to a more efficient bytecode for client
  use.
• Integrated into WAE WMLScript is fully
  integrated with the WML browser, so services can
  be easily built with both WML and WMLScript.
• Efficient extensible library support WMLScript
  can be used to extend device functionality
  without changes to the device software.

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Wireless Application Environment (WAE)

• The WAE specifies an application framework
  (tools, formats) for wireless devices to ease the
  development of WAP applications and devices.
• Major WAE elements include
• WAE User agents Software that executes in the
  wireless device that provides specific
  functionality.
• Content generators Applications on origin
  servers that produce standard content formats in
  response to requests from user agents in the
  mobile terminal.
• Standard content encoding Defined to allow a
  WAE user agent (e.g. a browser) to navigate Web
  content.
• Wireless telephony applications (WTA) A
  collection of telephony-specific extensions for
  call and feature control mechanisms that provide
  authors with advanced mobile network services.

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WAE Client Components
15
Wireless Session Protocol (WSP)

• WSP provides applications with interfaces for two
  session services
• Connection-oriented session service Operates
  above the reliable transport protocol WTP.
• Connectionless session service Operates above
  the unreliable transport protocol WDP.
• WSP is similar to HTTP with some additions and
  modifications to optimize it for wireless use.
• It is a transaction-oriented protocol based on
  the concept of a request and a reply.
• Each WSP message consists of a body (which may
  contain WML, WMLScript, images) and a header
  (which contains information about the data in the
  body and about the transaction).

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Wireless Session Protocol (WSP)

• WSP provides the following basic services
• Establish a reliable session from client to
  server and release (if in connection-oriented
  mode).
• Agree on a common level of protocol functionality
  using capability negotiation.
• Exchange of content between client and server
  using compact encodings.
• Suspend and resume a session.
• Push content from server to client in an
  unsynchronized manner. This is useful for
  broadcast messages or for services such as news
  headlines, stock quotes, and so on.

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Wireless Session Protocol (WSP)
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Wireless Transaction Protocol (WTP)

• WTP manages transactions by conveying requests
  and responses between a user agent and an
  application server.
• It is a lightweight protocol (without much of the
  overhead from a protocol like TCP) suitable for
  "thin" clients over low-bandwidth wireless links.
• WTP features include
• Three classes of transaction service.
• Optional user-to-user reliability WTP user
  triggers confirmation of each received message.
• Optional out-of-band data on acknowledgments.
• PDU concatenation and delayed acknowledgment to
  reduce the number of messages sent.
• Asynchronous transactions.

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Wireless Transaction Protocol (WTP)

• WTP is transaction-oriented rather than
  connection-oriented.
• With WTP, there is no explicit connection setup
  or teardown, but rather a reliable connectionless
  service.
• WTP provides three transaction classes to be
  invoked by WSP or some other higher protocol
• Class 0 Unreliable invoke message with no result
  message.
• Class 1 Reliable invoke message with no result
  message
• Class 2 Reliable invoke message with one
  reliable result message

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Wireless Transaction Protocol (WTP)
21
Wireless Transport Layer Security (WTLS)

• WTLS provides security services between a mobile
  device and the WAP gateway.
• WTLS is based on the Transport Layer Security
  (TLS) Protocol, which is a refinement of SSL.
• WTLS is more efficient than TLS, requiring fewer
  message exchanges.
• To provide end-to-end security, WTLS is used
  between client devices and the gateway, and TLS
  is used between the gateway and the target
  server.
• WAP systems translate between WTLS and TLS within
  the WAP gateway.
• Thus, the gateway is a point of vulnerability and
  must be given a high level of security!

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Wireless Transport Layer Security (WTLS)

• WTLS provides the following features
• Data integrity Ensures that data sent between
  a client and its gateway are not modified, using
  message authentication codes (encrypted
  messagedigests).
• Privacy Ensures that the data cannot be read by
  a third party, using encryption.
• Authentication Establishes authentication of
  the two parties, using digital certificates.
• Denial-of-service protection Detects and
  rejects messages that are replayed or not
  successfully verified.

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Wireless Transport Layer Security (WTLS)

• WTLS consists of two layers of protocols
• WTLS Record Protocol Provides basic security
  services to the higher-layer protocols.
• Higher-layer protocols, including
• Handshake Protocol Allows the server and client
  to authenticate each other, and negotiate
  encryption and message authentication algorithms,
  cryptographic keys, and so on.
• Change Cipher Spec Protocol After successful
  handshaking of security parameters, this simple
  protocol enables the security mechanisms.
• Alert Protocol Conveys WTLS-related alerts to
  the client or to the server (warnings, critical
  errors, or fatal errors).
• WTP

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Wireless Transport Layer Security (WTLS)
25
Wireless Datagram Protocol (WDP)

• WDP is used to adapt a higher-layer WAP protocol
  to the communication mechanism (called the
  bearer) used between a mobile node and its WAP
  gateway.
• WDP hides the details of the various bearer
  networks from the other layers of WAP.
• In some instances, WAP is implemented on top of
  IP!
• The adaptation required may include
• Partitioning data into segments of appropriate
  size for the bearer.
• Interfacing with the bearer network.

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Wireless Control Message Protocol (WCMP)

• Essentially, WCMP performs the same support
  functions for WDP as ICMP does for IP.
• WCMP is used in environments that do not provide
  an IP bearer and do not lend themselves to the
  use of ICMP.
• It is used by wireless nodes and WAP gateways to
  report errors encountered in processing WDP
  datagrams.
• It can also be used for informational and
  diagnostic purposes.