Transcript 21-05-0305-00

• IEEE 802.21 MEDIA INDEPENDENT HANDOVER
• DCN: 21-05-0305-00-0000
• Title: XML framework for component communication
• Date Submitted: July 19, 2005
• Presented at IEEE 802.21 session #9 in San Francisco
• Authors or Source(s):
Ania Halliop, Michael Montemurro
• Abstract:
Chantry Networks's message based middleware is XML-based
framework created to provide a publish/subscribe message
bus used for local and remote inter-process communication
21-04-0305-00-0000
IEEE 802.21 presentation release statements
• This
document has been prepared to assist the IEEE 802.21 Working Group. It
is offered as a basis for discussion and is not binding on the contributing
•
•
individual(s) or organization(s). The material in this document is subject to
change in form and content after further study. The contributor(s) reserve(s)
the right to add, amend or withdraw material contained herein.
The contributor grants a free, irrevocable license to the IEEE to incorporate
material contained in this contribution, and any modifications thereof, in the
creation of an IEEE Standards publication; to copyright in the IEEE’s name
any IEEE Standards publication even though it may include portions of this
contribution; and at the IEEE’s sole discretion to permit others to reproduce in
whole or in part the resulting IEEE Standards publication. The contributor also
acknowledges and accepts that this contribution may be made public by IEEE
802.21.
The contributor is familiar with IEEE patent policy, as outlined in Section 6.3
of
the
IEEE-SA
Standards
Board
Operations
Manual
<http://standards.ieee.org/guides/opman/sect6.html#6.3>
and
in
Understanding Patent Issues During IEEE Standards Development
http://standards.ieee.org/board/pat/guide.html>
21-04-0305-00-0000
Table of Contents
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
An XML-based communication engine
What is XML?
Why use XML?
Disadvantages of XML
Flexible software development
Example XML message
Services & transport mechanism
Communication topology
Registration process
Security
Error Handling
Communication Engine message flow
Message Flow Example 1
Message Flow Example 2
Application to IEEE 802.21
Appendix & References
21-04-0305-00-0000
An XML-based communication engine
Chantry’s publish/subscribe mechanism consists of:
• a message processing engine
• a set of messages that forms a protocol
• a transport layer (in our case, we use sockets over TCP/IP)
The communication framework is based on XML.
• Chantry uses only a small subset of XML capabilities
• It provides an flexible framework for defining or modifying
new messages
• It provides a simple mechanism for implementing protocol
changes
21-04-0305-00-0000
What is XML?
• XML (Extensible Markup Language) is a specification
developed by the W3C
• XML is a simpler version of SGML, originally designed for
Web documents but now extended for use in a variety of
applications
• XML allows developers to “create their own customized tags,
enabling the definition, transmission, validation, and
interpretation of data between applications[1]”
• XML allows users to define their own markup languages (in
this case, for communication protocols)
• XML libraries are widely available and portable for many
systems
21-04-0305-00-0000
Why use XML?
Advantages:
• extensibility
• easy to revise (can add new fields, messages anytime)
• easy to troubleshoot (not binary),
• easy to test and write test apps
• transport agnostic
• supported by many languages
• well-known standard
• supported on many systems
• free to use!
21-04-0305-00-0000
Disadvantages of XML
• Flexibility has a cost:
•
text-based – not efficient
•
encoding required to create message
•
parsing required to extract data
•
need to well define markups to use (need to agree on tags)
21-04-0305-00-0000
Flexible software development
XML provides flexibility in the software:
• can define new tags, attributes, and attribute values: new fields can be added
easily without needing to rewrite the message communication protocol
• client can read properties in any order
• client only needs to read properties it is interested in
• new messages can be added anytime
• developer can create optional or required tags
• XML can easily represent hierarchical data structures (for example, arrays or
arrays within array)
• can use DTD (Document Type Definitions) to define markups to use and
verify sent/received data is valid
• can use DOM (Document Object Model) to convert XML document to
collection of objects, accessible in any order for manipulation
21-04-0305-00-0000
Example XML message
An example XML message:
<?xml version="1.0"?>
<payload>
<header>
<msg_type>40</msg_type>
<options>0</options>
</header>
<ap_array type="array">
<item>
<id_no type=“int">880</id_no>
<ap_name type="string">Entrance</ap_name>
</item>
</ap_array>
</payload>
21-04-0305-00-0000
Services & transport mechanism
Services:
• Publish and Subscribe
• can be used as an event interface, API, or protocol
• provides a mechanism to distribute messages to multiple clients
Transport Mechanism:
• L2, L3, or L4 mechanisms
• take advantage of existing standards
• Chantry's messaging system uses TCP stream sockets
21-04-0305-00-0000
Communication topology
• Hub & Spoke topology:
•
central communication component to which multiple
components can connect
•
supports local and remote connections (on and off box)
•
sender does not need to know all interested receivers
•
can send messages privately or multicast/broadcast
•
client can connect multiple times to framework
•
framework can accommodate multiple Hubs that are
interconnected
21-04-0305-00-0000
Registration process
• using provided APIs, clients securely connect to XML
communication engine, set options, and subscribe for messages
• options include specifying whether client wants to have
received messages queued or processed right away
• communication engine can generate messages as well (i.e.,
inform subscribed clients that another client has registered)
• clients only need to register for the messages for which they are
interested
• clients can have multiple connections to communication engine
and subscribe for different messages on each connection (useful
in multi-threaded applications)
21-04-0305-00-0000
Security
• communication engine can use a variety of authentication
options such as certificates, or shared secrets
• encryption keys can be derived based on authentication material
• support for security can be built into the APIs used by clients
• depending on transport layer, can make use of standards such as
IPSec, SSL, etc.
• can accept only local connections (127.0.0.1) and have
communication engine act as proxy for connections to remote
communicate engines. Then, only need to add security to
remote connection.
21-04-0305-00-0000
Error handling
• can build-in error handling into APIs or take advantage of
existing error handling, such as in the case of TCP sockets
• clients can close and re-open connection to XML
communication framework anytime, and vice-versa, if concern
regarding state of connection
• higher layer protocol enhancement could accommodate more
robust error handling
21-04-0305-00-0000
Communication Engine message flow
The following message flow examples depicts components connecting to the
communication engine and sending and receiving messages, using a series of
TCP-based APIs.
At the beginning of start-up or after a breakdown in communication, a
component:
•
connects (comm_connect) to the communication engine and receives a
socket
• and subscribes (comm_subscribe) for specific messages
The component can then:
• send (comm_send) and receive (comm_recv) messages
To disconnect from the communication engine, the component uses the
comm_close API to clean up its session and close its socket.
21-04-0305-00-0000
Message Flow Example 1
ComponentA
CommEngine
ComponentB
ComponentC
comm_connect(ComponentA_ID)
Assume already connected to CommEngine
comm_connect_resp(socket_A)
comm_subscribe(CLIENT_CONNECT_NOTIFY)
comm_connect(ComponentB_ID)
comm_connect_resp(socket_B)
comm_subscribe(CLIENT_CONNECT_NOTIFY)
Client A connects to Component C
comm_send(CLIENT_CONNECT_NOTIFY[ClientA])
CommEngine determines subscribers for message
CLIENT_CONNECT_NOTIFY
CLIENT_CONNECT_NOTIFY
comm_recv(socket_A)
comm_recv(socket_B)
...
Multiple messages received by CommEngine and sent to subscribers
...
21-04-0305-00-0000
Message Flow Example 2
ComponentA
CommEngine
ComponentB
ComponentC
ComponentA is shutting down
comm_close
comm_close_ack
CommEngine closes session
Client B connects to Component C
comm_send(CLIENT_CONNECT_NOTIFY[ClientB])
CommEngine determines subscribers for message
CLIENT_CONNECT_NOTIFY
comm_recv(socket_B)
...
Multiple messages received by CommEngine and sent to subscribers
...
21-04-0305-00-0000
Application to 802.21
• XML-based publish/subscribe mechanisms could be used for:
• MIH Event Service
• MIH Information Service
• MIH Event Service
• Distribution of link events to all subscribed components
• MIH Information Service
• Query/Distribution information on handover candidates.
21-04-0305-00-0000
802.21 Topology and Communications
• There are two topology options which are independent of the
messaging:
• A centralized mobility server that all participating MIH
MAC’s connect
• Each participating MAC acts as a publish/subscribe service
• The protocol could run on top of:
• L2 with an appropriate SAP definition
• L3? Don’t know why you would do this.
• L4 likely on top of either TCP/IP or UDP/IP
• During the connection process, each MAC subscribes to the
events that it needs
21-04-0305-00-0000
Discovery and Registration
• MIH MAC discovery procedure would be out of scope of
802.21, however:
• Could be provisioned on Access Points
• Could use Service Location Protocol (SLP)
• Could use a multicast mechanism.
• Secure authentication procedure based on certificates, or shared
keys
• Connected MIH MAC’s would subscribe to messages
• MIH MAC would send messages to the appropriate HUB to
send a message or indicate a state change.
21-04-0305-00-0000
Message Definitions
• MIH Event Service Definitions:
• Treat as publish/subscribe service
• Could use MIH Event Service Definitions to build the
neighbour graph.
• MIH Information Service:
• Create request/response messages
• Use XML schema as defined.
21-04-0305-00-0000
Comments/Questions?
21-04-0305-00-0000
Appendix
W3C – World Wide Web Consortium
SGML – Standard Generalized Markup Language
References
[1] http://www.webopedia.com/TERM/X/XML.html
21-04-0305-00-0000