Traffic Engineering
Traffic Engineering For a network operator it is important to analyse and tune the performance
of the network in order to make the best use of it. The process of performance evaluation and
optimization of operational IP-networks is often referred to as traffic engineering. One of the
major objectives is to avoid congestion by controlling and optimizing the routing function. The
traffic engineering process can be divided in three parts as illustrated in Figure 2. The first step is
the collection of necessary information about network state. To be specific, the current traffic
situation and network topology. The second step is the optimisation calculations. And finally, the
third step is the mapping from optimization to routing parameters. Current routing protocols are
designed to be simple and robust rather than to optimize the resource usage. The two most
common intra-domain routing protocols today are OSPF (Open Shortest Path First) and IS-IS
(Intermediate System to Intermediate System). They are both link-state protocols and the routing
decisions are typically based on link costs and a shortest (least-cost) path calculation. While this
approach is simple, highly distributed and scalable these protocols do not consider network
utilization and do not always make good use of network resources. The traffic is routed on the
shortest path through the network even if the shortest path is overloaded and there exist
alternative paths. With an extension to the routing protocols like equal-cost multi-path (ECMP)
the traffic can be distributed over several paths but the basic problems remain. An underutilized
longer path cannot be used and every equal cost path will have an equal share of load.
This section introduces and analyses different approaches to traffic engineering in IP networks.
In the next subsection we present a framework to categorize different methods of traffic
engineering. This framework is used in the following section to analyse a selection of suggested
methods for traffic engineering.
Classification of Traffic Engineering Methods
A classification of traffic engineering schemes is possible along numerous axis. Our framework
is intended to facil- itate the analysis and help us identify the requirements for traffic engineering
in Ambient Networks.
• Optimize legacy routing vs novel routing mechanisms. One approach is to optimize legacy
routing protocols. The advantage is easy deployment of the traffic engineering mechanism.
However, the disadvantage is the constraints imposed by legacy routing.
• Centralized vs distributed solutions. A centralized solution is often simpler and less complex
than a distributed, but is more vulnerable than a distributed solution.
• Local vs global information. Global information of the current traffic situation enables the
traffic engineering mechanism to find a global optimum for the load balancing. The downside is
the signaling required to collect the information. In addition, in a dynamic environment, the
information quickly becomes obsolete.
• Off-line vs on-line traffic engineering. Off-line traffic engineering is intended to support the
operator in the management and planning of the network. On-line traffic engineering on the other
hand, reacts to a signal from the network and perform some action to remedy the problem.
The taxonomy above is intended to assist us in the analysis of traffic engineering methods in
Ambient Networks and should not be regarded as complete.
Wireless Application Protocol (WAP)
WAP stands for Wireless Application Protocol. It is a protocol designed for micro-browsers
and it enables the access of internet in the mobile devices. It uses the mark-up language WML
(Wireless Markup Language and not HTML), WML is defined as XML 1.0 application. It
enables creating web applications for mobile devices. In 1998, WAP Forum was founded by
Ericson, Motorola, Nokia and Unwired Planet whose aim was to standardize the various
wireless technologies via protocols.
WAP protocol was resulted by the joint efforts of the various members of WAP Forum. In
2002, WAP forum was merged with various other forums of the industry resulting in the
formation of Open Mobile Alliance (OMA).
WAP Model:
The user opens the mini-browser in a mobile device. He selects a website that he wants to
view. The mobile device sends the URL encoded request via network to a WAP gateway using
WAP protocol.
The WAP gateway translates this WAP request into a conventional HTTP URL request and
sends it over the internet. The request reaches to a specified Web server and it processes the
request just as it would have processed any other request and sends the response back to the
mobile device through WAP gateway in WML file which can be seen in the micro-browser.
WAP Protocol stack:
1. Application Layer:
This layer contains the Wireless Application Environment (WAE). It contains mobile device
specifications and content development programming languages like WML.
2. Session Layer:
This layer contains Wireless Session Protocol (WSP). It provides fast connection suspension
and reconnection.
3. Transaction Layer:
This layer contains Wireless Transaction Protocol (WTP). It runs on top of UDP (User
Datagram Protocol) and is a part of TCP/IP and offers transaction support.
4. Security Layer:
This layer contains Wireless Transaction Layer Security (WTLS). It offers data integrity,
privacy and authentication.
5. Transport Layer:
This layer contains Wireless Datagram Protocol. It presents consistent data format to higher
layers of WAP protocol stack.
Wireless Application Environment
WAE follows an architecture that is more complicated than the WWW model because it needs to
address the specific limitations of wireless devices. The cellular phone community is made up of
a series of private networks. Because cellular phone providers maintain a partnership with a
discrete network, each phone complies with the standards of only one network and there is
limited synergy among the networks. WAE defines WAP as a public, standard protocol. Wireless
devices communicate via WAP in addition to the pre-existing protocols supplied by private
networks.
Why not use HTTP as the WWW model does? Because WAP is designed to handle slower
processors and the specific constraints of the wireless network, such as limited bandwidth and
high error rates, the markup languages available to wireless devices, such as WML and WML
script, are scaled-down and conform to a format that requires less memory and processing power
than HTML.
In short, WAE consists of two parts: protocols (WAP, which includes WSP, WTP, WDP) and
content (WML). Because a Web server only speaks HTTP, WAE uses a gateway to translate
between WAP and HTTP. Each wireless device communicates with a designated gateway that
makes calls to any number of Web servers.
WAE Model
WTA Architecture
Browsing the web using the WML browser is only one application for a handheld
device user. Say a user still wants to make phone calls and access all the features of the mobile
phone network as with a traditional mobile phone. This is where the wireless telephony
application (WTA), the WTA user agent (as shown in Figure), and the wireless telephony
application interface WTAI come in. WTA is a collection of telephony specific extensions for
call and feature control mechanisms, merging data networks and voice networks.
The WTA framework integrates advanced telephony services using a consistent user
interface (e.g., the WML browser) and allows network operators to increase accessibility for
various special services in their network. A network operator can reach more end-devices using
WTA because this is integrated in the wireless application environment (WAE) which handles
device-specific characteristics and environments. WTA should enable third-party developers as
well as network operators to create network-independent content that accesses the basic features
of the bearer network. However, most of the WTA functionality is reserved for the network
operators for security and stability reasons.
WTA extends the basic WAE application model in several ways:
● Content push: A WTA origin server can push content, i.e., WML decks or WMLScript, to
the client. A push can take place without prior client request. The content can enable, e.g., the
client to handle new network events that were unknown before.
● Access to telephony functions: The wireless telephony application interface (WTAI,
WAP Forum, 2000m) provides many functions to handle telephony events (call accept, call
setup, change of phone book entries etc.).
● Repository for event handlers: The repository represents a persistent storage on the client
for content required to offer WTA services. Content are either channels or resources. Examples
for resources are WML decks, WMLScript objects, or WBMP pictures. Resources are loaded
using WSP or are pre-installed. A channel comprises references to resources and is associated
with a lifetime. Within this lifetime, it is guaranteed that all resources the channel points to are
locally available in the repository. The motivation behind the repository is the necessity to react
very quickly for time-critical events (e.g., call accept). It would take too long to load content
from a server for this purpose.
● Security model: Mandatory for WTA is a security model as many frauds happen with
wrong phone numbers or faked services. WTA allows the client to only connect to trustworthy
gateways, which then have to check if the servers providing content are authorized to send this
content to the client. Obviously, it is not easy to define trustworthy in this context. In the
beginning, the network operator‟s gateway may be the only trusted gateway and the network
operator may decide which servers are allowed to provide content. Figure 10.30 gives an
overview of the WTA logical architecture.
The components shown are not all mandatory in this architecture; however, firewalls or other
origin servers may be useful. A minimal configuration could be a single server from the network
operator serving all clients. The client is connected via a mobile network with a WTA server,
other telephone networks (e.g., fixed PSTN), and a WAP gateway. A WML user agent running
on the client or on other user agents is not shown here.
WAP Push
WAP Push is a mechanism for directing an SMS recipient to a website or landing page without
them having to enter a URL in the phone’s browser.
WAP push works by including a link to the WAP address in the header of the SMS. When a user
receives the message containing the link (assuming they are on a device that supports WAP –
which almost all modern phones do) the phone will prompt them to open the content, at which
time they will be directed to the link address and the content will display.
What is WAP Push used for?
Typically, WAP Push is used to direct users to marketing content, usually to a landing page
displaying a specific offer or promotion, but can also be used for service messages for example
displaying Terms and Conditions.
