AN EFFICIENT APPROACH FOR THINNING WIRELESS MOBILE MESSAGES. P P Abdul Haleem and M P Sebastian. Received October 2008; accepted December 2008

Transcription

1 ICIC Express Letters ICIC International c 2009 ISSN X Volume 3, Number 1, March 2009 pp AN EFFICIENT APPROACH FOR THINNING WIRELESS MOBILE MESSAGES P P Abdul Haleem and M P Sebastian Department of Computer Science and Engineering National Institute of Technology Calicut NIT Campus P O, Calicut, Kerala , India ppabdulhaleem@gmail.com; sebasmp@nitc.ac.in Received October 2008; accepted December 2008 Abstract. Increasing popularity and wide usage make wireless mobile devices as quintessential entities of today s network. Formulating a uniform platform for messaging across a wide range of wireless mobile devices with varying standards, is a potential challenge. The extensible Markup Language (XML), though a legacy technology still is in use as a universal solution for the representation of heterogeneous data formats. But the storage requirements and processing requirements make XML less acceptable to the designers. This paper presents a method (based on YAML Ain t Markup Language - YAML) for thinning the message size in heterogeneous wireless mobile devices. The proposed scheme yields better results than XML as a message format. Keywords: Wireless networks, Mobile messaging, Thinning of messages, Knowledge representation, Mobile computing, XML 1. Introduction. Being active members of every network, the presence of wireless mobile devices cause several issues for the existing network protocols and applications. This is mainly due to the inherent deficiencies of the wireless mobile environment. Poor quality of wireless networks, particularly the bandwidth and latency are the major limiting factors in their performance. The usage of heterogeneous wireless mobile devices poses new challenges to the research community. The search for an acceptable standard for a heterogeneous network naturally converges to XML. In Simple Object Access Protocol (SOAP), XML is already in use as a message syntax format [3]. But XML, in its present format, has many limitations, particularly in wireless mobile devices. Increased verbosity of XML results in the generation of more number of packets, which overloads the various layers of the network protocol. This consumes more battery power also. Several attempts are in progress to arrive at an energy efficient communication scheme for wireless mobile devices [16]. Transmission and reception of messages consume the biggest chunk of battery power. Thinning of messages is helpful for devices under heavy use. This paper introduces a new scheme for optimizing the message sizes in wireless mobile devices. The proposed message format must retain the strong points of XML, but improve upon its limitations, specific to the wireless mobile environment. Our messaging format intends to have the following features: (i) simple and flexible - both for user and application programmer (ii) legible and easily editable (iii) schema aware (iv) consumes less bandwidth by reducing the verbosity of content without using any compression techniques and(iv)secureandfast. Our scheme is based on YAML. The proposed message format simplifies the message preparation, with less storage requirements. The thinning measures used in our scheme yields significant improvements in terms of schema size, message size and transmission time in comparison with XML. 99

2 100 P P ABDUL HALEEM AND M P SEBASTIAN 1.1. extensible Markup Language. The traditional use of XML is for the representation of data-oriented facts. Users are free to develop their own structures and generating huge databases over the web. Currently, XML is widely perceived as a message syntax format. SOAP is an example where XML is used as a message syntax format. The most attractive feature of XML is that it is compatible with the latest Internet technologies. It is the defacto standard to represent data over heterogeneous systems. Studies on XML based packet routing and filtering establishes its viability and applicability. However, XML has limitations when used in the wireless mobile environments [2]. These limitations include (i) highly textual nature, requiring string parsing for further processing (ii) strict structuring and adherence of the document to the accompanying structure needs verification by parsers, which makes XML parsing a heavyweight activity (iii) XML buffers need to be flushedmoreoftenatthetimeofinputand output due to the verbosity, leading to lesser throughput (iv) larger messages are vulnerable to retransmissions, particularly in wireless environments and (v) an easy target for hackers. The rest of the paper is organized as follows: Section 2 outlines the related work. Section 3 describes the problem definition. Performance evaluation of the results obtained are discussed in Section 4. Section 5 concludes the paper with a brief discussion on the future work. 2. Related Work. Several solutions are proposed in the literature to address the verbosity of messages in wireless mobile devices. They can be broadly classified into the following categories: (i) Standard compression techniques (ii) Alternative formats for XML and (iii) Binary Encoding. However, these methods are not very effective in the wireless mobile environment. For instance, standard compression techniques such as Millau [12], Gzip [13], XMill [13] yield better performance with larger messages with a high redundancy rate. More over, a compression/decompression layer will be an additional burden for the resource intensive wireless mobile devices [4]. In order to achieve a messaging format that demands less bandwidth requirements, several alternative serialization formats have been proposed. Wireless Application Protocol(WAP)BinaryXML(WBXML),alsocalledBinaryXML[15],istheoldestknown format in this area. Prominent examples using WBXML are Fast Web Services [5] and Fast InfoSet [7] proposals of Sun. WBXML is a good attempt in killing the verbosity of XML, but suffers from inadequate support for the XML name-spaces [6]. The Xebu [8] format builds up its tokenization using a stream of messages, instead of considering each XML document in isolation as most other formats. The compression/decompression layer will be an additional burden for the resource intensive wireless mobile devices [4]. Alternative formats for XML, including binary formats are suffered from the lack of self descriptive nature and easy readability that exists in XML. 3. The Proposed Method for Thinning of Wireless Mobile Messages. We propose a messaging protocol that retains the features of XML such as self descriptive nature, readability, ease of preparation and schema awareness, but with less verbosity. YAML Ain t Markup Language (YAML) [9], a data serialization language which is both human readable and computationally powerful, is utilized to achieve this goal. Apart from introducing YAML as a viable alternative, we plan to make significant value additions to the standard in order to achieve maximum throughput YAML. YAML (rhymes with camel ) is a human-readable data serialization format that takes concepts from languages such as XML, C, Python, Perl, as well as the format for electronic mail as specified in RFC YAML is a straightforward machine parsable data serialization format designed for human readability and interaction. YAML

3 ICIC EXPRESS LETTERS, VOL.3, NO.1, is optimized for data serialization, configuration settings, log files, Internet messaging and filtering [9]. The decision to make use of YAML for our work is motivated by the following (i) it is easily readable and editable by any standard word processor (ii) it interacts well with scripting languages (iii) it uses host languages native data structures. (iii) it has a consistent information model (iv) it enables stream-based processing (v) it is as expressive and extensible as XML (vi) its serialization reduces the verbosity of the message considerably, that too without affecting its readability System design. The design includes three main stages: (i) bifurcation of structure and content (ii) thinning - Phase I and (iii) thinning - Phase II Bifurcation of structure and content. YAML data serialization includes both data description and content. The aim of this stage is to achieve separation of structure and content. This reduces the message size, particularly, when there is a set of messages as per some common structure. This is a technical improvement over YAML in its original format. For this, the document is scanned one node at a time. There are three kinds of nodes in YAML - scalar, sequence, and mapping. Apart from this, there are mappings of sequences and sequences of mappings. The message structure is to be evaluated to decide the type of schema to be constructed. Thetypecanbeofanyofthethreekinds-scalar, sequence and mapping. Mappings of sequences and sequences of mappings are considered as special cases. Primitive details likenameofthe field, its data type and an ID value are added to the schema for every member in the node. Further details to the schema could be added in the validation and verification stages. Once this process is completed, we get a schema description of the message to be transmitted YASchema. Kuwata-lab developed a schema validator for YAML. This schema validator is known as Kwalify [10]. Our method, christened as YASchema, is designed with the objective of making YAML schema aware. The structure of the document and the primitive details regarding the elements of each node are defined in the schema. Additional information like expected pattern of inputs to the attribute values can also be added to the schema definition. YASchema has significant advantages over the other method which include (i) use of thinning techniques to define schema definitions in flow styles (ii) require only minimum bytes and is human readable (iii) facility to define ID codes for elements of YAML, and (iv) reuse of the same schema across multiple sessions are envisioned. Apart from constructing the schema entries, identification of squeezable elements are also being done in this stage. For e.g., if the file contains several occurrences of items with the same format like item details in an invoice, these records will be marked as squeezable. This information is utilized in the next stage for further thinning of the contents Thinning phase I. The attempts for thinning the message size is initiated in this stage. Different styles of serializations are possible in YAML [14]. YAML s natural approach of representing information is as per the guidelines of legacy XML, to a certain extent. This adherence to the XML style, provides high degree of readability, at the same time boosts the memory requirements needed for representing the information. The Flow style method specified in YAML helps one to squeeze the size considerably. When reorganizing the contents to this style, some cases may yield better performance. For e.g., a complex message consisting of customer invoice having many product details can be presented to this stage for better conservation of message size. The entire document is scanned and squeezable portions are squeezed into flow style.

4 102 P P ABDUL HALEEM AND M P SEBASTIAN Thinning phase II. Phase I capitalizes on the inherent properties of YAML in thinning the message size. In Phase II, the enhancements over YAML are employed to maximize the results. In this stage, the possibilities of making use of YASchema for thinning the messages are explored. All primitive details regarding each element in the message are defined in the schema, in the schema creation stage itself. In addition to this, special ID codes are provided for each element. Together with these facilities, a scan over the message is done and the elements are encoded with the ID codes. ID codes can be referred from the accompanying schema, or if the sender likes to reuse a schema that has been sent earlier, the schema to be referred can be specified in the message itself. 4. Performance Evaluation. There are different types of messages exchanged between users with varying features such as size, complexity, structure etc. To establish consistency across all these diverse kinds of messages, messages are categorized into five types. Short type represents the simple messaging format with only text. Small category consists of a single record consisting of String, Float and DateTime types of data. Medium category contained the details of about 25 customer records. Large and Composite categories are constituted as invoice records with varying degrees of complexity. These categories are designed to apply test data to all the stages of the proposed scheme, thus ensuring consistency in the results. For each category of messages listed in Table 1, YAML (original, Phase I and Phase II) and XML versions are serialized. Since our objective is to propose a simple standard, with less verbosity, XML is selected as the benchmark. YAML serializations have been done in three stages - original, after applying Phase I of thinning and after applying Phase II of thinning. The parameters used for performance evaluation are (i) schema size (ii) message size and (iii) transmission speed Schema size. The gain in terms of number of bytes as per the YASchema definition is compared with the Kwalify definitionsinfigure1. ItisobservedthatYASchema performs much better than Kwalify for all types of messages. For e.g., the gain in schema size in Short, Small, Medium, Large and Composite categories over Kwalify are estimated to be 245, 539, 601, 1023 and 1089 bytes, respectively. The Short category reported the maximum advantage (66.94%). In the cases of repeated occurrences of records in Large and Composite categories, the performance gain (53.23% and 54.78%, respectively) is better. In the Medium category, the gain is above 50%. From the results, it is observed that YASchema outperforms its counterpart in all the 5 message types. The average overall performance is above 50%. This gain is significant, particularly when transmitting a set of messages with a common schema Message size. Each category of messages are coded in YAML and XML. The performance is evaluated under the following scenarios: (i) YAML Vs XML (ii) YAML (Phase II) Vs XML and (iii) YAML (Phase II) Vs YAML. The gain in message size (in bytes) using original YAML over XML is given in Table 1. The gain in size of messages (in YAML original format) in Short, Small, Medium, Large and Composite categories over XML are 46, 153, 2816, 5024 and bytes, respectively. The results after the Phase II thinning are very critical as far as the viability of the proposed method is concerned. After Phase II, schema size is also a part of the message. Hence the message size excluding and including schema size are compared. The message size comparison excluding the schema size is shown in Figure 2. It is seen that the gain is maintained at 62% against XML, for message categories of larger sizes. The comparison including the schema size is shown in Figure 3. It is to be noted that additional overhead needed for the schema results in a loss of about 40% in the Short

5 ICIC EXPRESS LETTERS, VOL.3, NO.1, and no gain in the Small category, respectively, over XML. But there is a gain in all the remaining categories. The reduced gains in Short and Small categories, need not be taken negatively; this trade off is advantageous when there is a need to send multiple messages with the same structure - as transmission of schema will only be a one-time payload. For other categories of messages (in particular, for larger types, the gain is of the order of 60%), this scheme works well due to the thinning measures adopted in two phases. It can be seen that the additional payload is a necessity, in order to maintain the correctness of the message after transmission. The performance gain in thinning the size of messages after the two phases of thinning compared to original YAML is shown in Figure 4. There is advantage in size after Thinning Phase I and Phase II over original YAML for categories Medium, Large and Composite. As expected, the additional payload of schema reports gains of (-56%) and (-35%) in Short and Small categories, respectively. These gains will become positive, when messages with same structure are streamed multiple times Transmission time. Transmission time is a very important factor in real time applications. Our measurements use three classes of record sets with varying levels of complexity - Simple, Medium and Complex. The bytes required for the representation of record sets are considered for the measurement of transmission speed. The number of bytes needed to represent each of these record sets are tabulated in Table 2. Assuming that there is no packet loss, transmission times of theoretical constant link speeds of 64kbps and 256kbps, are assumed for this analysis. It is to be noted that the actual performance would be inferior to the theoretical performance due to the overheads like packet loss, retransmission, noise etc. It is seen from Table 2 that each of the YAML data sizes, particularly the Complex type, just fits well into the limits of a single TCP/IP MSS, after two phases of thinning. The record sizes of XML in Complex category are greater than the MSS, which forces the data to be segmented into multiple packets. The transmission speed (64kbps link) comparison between the record sets of YAML and XML formats are shown in Table 3. It is observed from the Table 3 that the YAML record sets outperform the XML record sets by a factor of 1.3 for Small type, 1.4 for Medium type and 2.71 for Complex type. After applying phase II of thinning, we have the maximum advantage (refer Table 4) - by a factor of 2.18 for Small type, 1.71 for Medium type and 5.14 for Complex type. The advantages in the performance of YAML (after two phases of thinning) over XML, are clear for all categories. One interesting factor is the improvement of the transmission speeds of the thinned YAML (after applying the two phases of thinning) record sets over the original YAML (refer Table 5) - by a factor of 1.65 (Small), 1.23 (Medium) and 1.9 (Complex). These gains are significant as they are achieved without applying any binary encoding to the original message (i.e., without hampering the readability and user friendliness). One observes that the thinned YAML has significant advantages over the original YAML. 5. Conclusions. This paper presents an alternative messaging system to XML for the mobile wireless environment. The proposed system is based on YAML, a user friendly and light weight messaging format. YAML simply makes the process of preparing the message quite easier, with much less bytes of storage size. Thinning measures are applied to the original YAML format, including the introduction of a schema definition for the files. Introduction of a light weight platform for wireless mobile messaging, separation of data and content, formulation of a schema construction mechanism and further thinning measures helped in thinning the overall message size, sizes of various types of record sets and schema constructs. Interestingly, the experiments revealed that the proposed thinning

6 104 P P ABDUL HALEEM AND M P SEBASTIAN measures contribute considerable gains over the original YAML without hampering the readability of the original message format. Several modifications may be necessary to make this a real time messaging protocol. This requires improvements including facility for a better encoding to Abstract Syntax Notation One (ASN.1), in the circumstances where ultimate squeezing of message is most needed (we would like to include the binary encoded serialization as a benchmark), security standards to be embedded to the message format at par with the specifications of XML Encryption and other related specifications,andintroductionofapolicybasedsecurity mechanism by utilizing the schema constructs. REFERENCES [1] T. Phan, L. Huang and C. Dulan, Requirements and design for XML messaging in the mobile environment, Workshop on Next Generation Networking Middleware, Helsinki Institute for Information Technology, Finland, [2] J. Kangasharju, Mobile XML messaging, Technical Report, Department of Computer Science, University of Helsinki, Available at [3] C. C. Albrecht, How clean is the future of SOAP?, Communications of ACM, vol.47, no.2, pp.66-68, [4] R. Schmelzer, Will Binary XML Solve XML Performance Woes?, November, 2004, Available at gci ,00.html. [5] P. Sandoz, S. Pericas-Geertsen, K. Kawaguchi, M. Hadley and E. Pelegri-Llopart, Fast Web Services, August, 2003, Available at [6] P. Sandoz and S. Pericas-Geertsen, Fast Java.net, XTech 2005: XML, the Web and Beyond, Available at [7] P. Sandoz, A. Triglia and S. Pericas-Geertsen, Fast Infoset, June, 2004, Available at [8] Xebu Serialization Format, Available at [9] Yaml, Available at [10] Kwalify, Available at [11] Adjusting IP MTU, TCP MSS, and PMTUD on Windows and Sun Systems, February, 2006, Available at [12] Girardot and Sundaresan, Millau: An encoding format for efficient representation and exchange of XML over the web, Pro. of the 9th International World Wide Web Conference on Computer Networks, The International Journal of Computer and Telecommunications Networking, pp , [13] Cai, Ghandeharizadeh, Girardot, Schmidt, SongGirardot and Sundaresan, A comparison of alternative encoding mechanisms for web services, Proc. of the 13th International Conference on Database and Expert Systems Applications, Aix en Provence, France, [14] YAML Ain t Markup Language (YAML) Version 1.1, Available at [15] WAP Binary XML Content Format, Available at [16] Y. Jin, J. Jo, and Y. Kim, Energy-efficient multi-hop communication scheme in clustered sensor networks, International Journal of Innovative Computing, Information and Control, vol.4, no.7, pp , Table 1. Comparison - Gain achieved in message size (in bytes) with YAML Message YAML XML Gain Over Category XML (a) (b) (b - a) Short Small Medium Large Composite

7 ICIC EXPRESS LETTERS, VOL.3, NO.1, Table 2. Record sets - Categories (size in bytes) Type YAML XML Original Thinning I Thinning II Small Medium Complex Table 3. Comparison (YAML vs XML) - Transmission speed (in msecs) using 64kbps link Record Set YAML XML Gain Over (a) (b) XML (b/a) Small Medium Complex Table 4. Comparison (YAML Phase II vs XML) - Transmission speed (in msecs) using 64kbps link Record Set YAML Phase II XML Gain Over (a) (b) XML (b/a) Small Medium Complex Table 5. Comparison (YAML vs YAML Phase II) - Transmission speed (in msecs) using 64kbps link Record Set YAML YAML Phase II Gain (a) (b) (a/b) Small Medium Complex

8 106 P P ABDUL HALEEM AND M P SEBASTIAN Figure 1. Schema size - YASchema vs Kwalify Figure 3. Message size - XML vs YAML Phase II (including schema) Figure 4. Message size - YAML vs YAML Phase II (including schema) Figure 2. Message size - XML vs YAML Phase II (excluding schema)