UNIT 4

MOBILE TCP/IP & WAP

TCP/IP Protocol Suite

Key Features of a Protocol

• Syntax– Concerns the format of the data blocks

• Semantics– Includes control information for coordination and

error handling

• Timing– Includes speed matching and sequencing

Agents Involved in Communication

• Applications– Exchange data between computers (e.g., electronic

mail)

• Computers– Connected to networks

• Networks– Transfers data from one computer to another

TCP/IP Layers

• Physical layer• Network access layer• Internet layer• Host-to-host, or transport layer• Application layer

TCP/IP Physical Layer

• Covers the physical interface between a data transmission device and atransmission medium or network

• Physical layer specifies:– Characteristics of the transmission medium– The nature of the signals– The data rate– Other related matters

TCP/IP Network Access Layer

• Concerned with the exchange of data between an end system and the network to which it's attached

• Software used depends on type of network– Circuit switching– Packet switching (e.g., X.25)– LANs (e.g., Ethernet)– Others

T:TCP/IP Internet Layer

• Uses internet protocol (IP)• Provides routing functions to allow data to

traverse multiple interconnected networks• Implemented in end systems and routers

TCP/IP Host-to-Host, or Transport Layer

• Commonly uses transmission control protocol (tcp)

• Provides reliability during data exchange– Completeness– Order

TCP/IP Application Layer

• Logic supports user applications• Uses separate modules that are peculiar to

each different type of application

Protocol Data Units (PDUs)

Common TCP/IP Applications

• Simple mail transfer protocol (SMTP)– Provides a basic electronic mail facility

• File Transfer Protocol (FTP)– Allows files to be sent from one system to another

• TELNET– Provides a remote logon capability

Layers of the OSI Model

• Application• Presentation• Session• Transport• Network• Data link• Physical

OSI Application Layer

• Provides access to the OSI environment for users

• Provides distributed information services

OSI Presentation Layer

• Provides independence to the application processes from differences in data representation (syntax)

OSI Session Layer

• Provides the control structure for communication between applications

• Establishes, manages, and terminates connections (sessions) between cooperating applications

OSI Transport Layer

• Provides reliable, transparent transfer of data between end points

• Provides end-to-end error recovery and flow control

OSI Network Layer

• Provides upper layers with independence from the data transmission and switching technologies used to connect systems

• Responsible for establishing, maintaining, and terminating connections

OSI Data link Layer

• Provides for the reliable transfer of information across the physical link

• Sends blocks (frames) with the necessary synchronization, error control, and flow control

OSI Physical Layer

• Concerned with transmission of unstructured bit stream over physical medium

• Deals with accessing the physical medium–Mechanical characteristics– Electrical characteristics– Functional characteristics– Procedural characteristics

Comparison of OSI and TCP/IP

TCP/IP Architecture Dominance

• TCP/IP protocols matured quicker than similar OSI protocols–When the need for interoperability across networks

was recognized, only TCP/IP was available and ready to go

• OSI model is unnecessarily complex– Accomplishes in seven layers what TCP/IP does

with fewer layers

Elements of Standardization within OSI Framework

• Protocol Specification– Format of protocol data units (PDUs) exchanged– Semantics of all fields– Allowable sequence of PDUs

• Service Definition– Functional description that defines what services are

provided, but not how the services are to be provided

• Addressing– Entities are referenced by means of a service access point

(SAP)

Internetworking Terms

• Communication network – facility that provides a data transfer service among devices attached to the network

• Internet – collection of communication networks, interconnected by bridges/routers

• Intranet – internet used by an organization for internal purposes– Provides key Internet applications– Can exist as an isolated, self-contained internet

Internetworking Terms

• End System (ES) – device used to support end-user applications or services

• Intermediate System (IS) – device used to connect two networks

• Bridge – an IS used to connect two LANs that use similar LAN protocols

• Router - an IS used to connect two networks that may or may not be similar

Functions of a Router

• Provide a link between networks• Provide for the routing and delivery of data

between processes on end systems attached to different networks

• Provide these functions in such a way as not to require modifications of the networking architecture of any of the attached subnetworks

Network Differences Routers Must Accommodate

• Addressing schemes– Different schemes for assigning addresses

• Maximum packet sizes– Different maximum packet sizes requires segmentation

• Interfaces– Differing hardware and software interfaces

• Reliability– Network may provide unreliable service

Mobile IP and Wireless Application Protocol

Mobile IP Uses

• Enable computers to maintain Internet connectivity while moving from one Internet attachment point to another

• Mobile – user's point of attachment changes dynamically and all connections are automatically maintained despite the change

• Nomadic - user's Internet connection is terminated each time the user moves and a new connection is initiated when the user dials back in– New, temporary IP address is assigned

Operation of Mobile IP

• Mobil node is assigned to a particular network – home network

• IP address on home network is static – home address• Mobile node can move to another network – foreign

network• Mobile node registers with network node on foreign

network – foreign agent• Mobile node gives care-of address to agent on home

network – home agent

Capabilities of Mobile IP

• Discovery – mobile node uses discovery procedure to identify prospective home and foreign agents

• Registration – mobile node uses an authenticated registration procedure to inform home agent of its care-of address

• Tunneling – used to forward IP datagrams from a home address to a care-of address

Discovery

• Mobile node is responsible for ongoing discovery process– Must determine if it is attached to its home network or a

foreign network

• Transition from home network to foreign network can occur at any time without notification to the network layer

• Mobile node listens for agent advertisement messages– Compares network portion of the router's IP address with

the network portion of home address

Agent Solicitation

• Foreign agents are expected to issue agent advertisement messages periodically

• If a mobile node needs agent information immediately, it can issue ICMP router solicitation message– Any agent receiving this message will then issue

an agent advertisement

Move Detection

• Mobile node may move from one network to another due to some handoff mechanism without IP level being aware– Agent discovery process is intended to enable the agent to

detect such a move

• Algorithms to detect move:– Use of lifetime field – mobile node uses lifetime field as a

timer for agent advertisements– Use of network prefix – mobile node checks if any newly

received agent advertisement messages are on the same network as the node's current care-of address

Co-Located Addresses

• If mobile node moves to a network that has no foreign agents, or all foreign agents are busy, it can act as its own foreign agent

• Mobile agent uses co-located care-of address– IP address obtained by mobile node associated with mobile

node's current network interface

• Means to acquire co-located address:– Temporary IP address through an Internet service, such as

DHCP– May be owned by the mobile node as a long-term address

for use while visiting a given foreign network

Registration Process

• Mobile node sends registration request to foreign agent requesting forwarding service

• Foreign agent relays request to home agent• Home agent accepts or denies request and

sends registration reply to foreign agent• Foreign agent relays reply to mobile node

Registration Operation Messages

• Registration request message– Fields = type, S, B, D, M, V, G, lifetime, home

address, home agent, care-of-address, identification, extensions

• Registration reply message– Fields = type, code, lifetime, home address, home

agent, identification, extensions

Registration Procedure Security

• Mobile IP designed to resist attacks– Node pretending to be a foreign agent sends registration

request to a home agent to divert mobile node traffic to itself

– Agent replays old registration messages to cut mobile node from network

• For message authentication, registration request and reply contain authentication extension– Fields = type, length, security parameter index (SPI),

authenticator

Types of Authentication Extensions

• Mobile-home – provides for authentication of registration messages between mobile node and home agent; must be present

• Mobile-foreign – may be present when a security association exists between mobile node and foreign agent

• Foreign-home – may be present when a security association exists between foreign agent and home agent

Tunneling

• Home agent intercepts IP datagrams sent to mobile node's home address– Home agent informs other nodes on home network

that datagrams to mobile node should be delivered to home agent

• Datagrams forwarded to care-of address via tunneling– Datagram encapsulated in outer IP datagram

Mobile IP Encapsulation Options

• IP-within-IP – entire IP datagram becomes payload in new IP datagram– Original, inner IP header unchanged except TTL

decremented by 1– Outer header is a full IP header

• Minimal encapsulation – new header is inserted between original IP header and original IP payload– Original IP header modified to form new outer IP

header

• Generic routing encapsulation (GRE) – developed prior to development of Mobile IP

Wireless Application Protocol (WAP)

• Open standard providing mobile users of wireless terminals access to telephony and information services– Wireless terminals include wireless phones, pagers and

personal digital assistants (PDAs)– Designed to work with all wireless network technologies

such as GSM, CDMA, and TDMA– Based on existing Internet standards such as IP, XML,

HTML, and HTTP– Includes security facilities

WAP Protocol Stack

WAP Programming Model

Wireless Markup Language (WML) Features

• 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

• Support for navigation among cards and decks – includes provisions for event handling; used for navigation or executing scripts

WMLScript

• Scripting language for defining script-type programs in a user device with limited processing power and memory

• WMLScript capabilities:– Check validity of user input before it’s sent– Access device facilities and peripherals– Interact with user without introducing round trips

to origin server

WMLScript

• WMLScript features:– JavaScript-based scripting language– Procedural logic– Event-based– Compiled implementation– Integrated into WAE

Wireless Application Environment (WAE)

• WAE specifies an application framework for wireless devices

• WAE elements:– WAE User agents – software that executes in the

wireless device– Content generators – applications 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 to navigate Web content

– Wireless telephony applications (WTA) – collection of telephony-specific extensions for call and feature control mechanisms

WAE Client Components

Wireless Session Protocol (WSP)

• Transaction-oriented protocol based on the concept of a request and a reply

• Provides applications with interface for two session services:– Connection-oriented session service – operates

above reliable transport protocol WTP– Connectionless session service – operates above

unreliable transport protocol WDP

Connection-mode WSP Services

• Establish reliable session from client to server and release

• Agree on common level of protocol functionality using capability negotiation

• Exchange content between client and server using compact encoding

• Suspend and resume a session• Push content from server to client in an

unsynchronized manner

WSP Transaction Types• Session establishment – client WSP user requests

session with server WSP user• Session termination – client WSP user initiates

termination• Session suspend and resume – initiated with

suspend and resume requests• Transaction – exchange of data between a client

and server• Nonconfirmed data push – used to send

unsolicited information from server to client• Confirmed data push – server receives delivery

confirmation from client

Wireless Transaction Protocol (WTP)

• Lightweight protocol suitable for "thin" clients and over low-bandwidth wireless links

• WTP features– 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

WTP Transaction Classes

• Class 0: Unreliable invoke message with no result message

• Class 1: Reliable invoke message with no result message

• Class 2: Unreliable invoke message with one reliable result message

WTP PDU Types• Invoke PDU – used to convey a request from an

initiator to a responder• ACK PDU – used to acknowledge an Invoke or

Result PDU• Result PDU – used to convey response of the

server to the client• Abort PDU – used to abort a transaction• Segmented invoke PDU and segmented result

PDU – used for segmentation and reassembly• Negative acknowledgment PDU – used to indicate

that some packets did not arrive

Examples of WTP Operation

Wireless Transport Layer Security (WTLS) Features

• Data integrity – ensures that data sent between client and gateway are not modified, using message authentication

• 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

WTLS Protocol Stack

• WTLS consists of two layers of protocols–WTLS Record Protocol – provides basic security

services to various higher-layer protocols– Higher-layer protocols:• The Handshake Protocol• The Change Cipher Spec Protocol• The Alert Protocol

WTLS Protocol Stack

WTLS Record Protocol Operation

Phases of the Handshake Protocol Exchange

• First phase – used to initiate a logical connection and establish security capabilities

• Second phase – used for server authentication and key exchange

• Third phase – used for client authentication and key exchange

• Forth phase – completes the setting up of a secure connection

Wireless Datagram Protocol (WDP)

• Used to adapt higher-layer WAP protocol to the communication mechanism used between mobile node and WAP gateway

• WDP hides details of the various bearer networks from the other layers of WAP

• Adaptation may include:– Partitioning data into segments of appropriate size for the

bearer– Interfacing with the bearer network

Wireless Control Message Protocol (WCMP)

• Performs the same support function for WDP as ICMP does for IP

• Used in environments that don’t provide IP bearer and don’t lend themselves to the use of ICMP

• Used by wireless nodes and WAP gateways to report errors encountered in processing WDP datagrams

• Can also be used for informational and diagnostic purposes