Design of Network Architecture Using Mobile Gateways for DLNA Devices in Wide Area Networks ()
1. Introduction
Recently, information appliances conforming to the DLNA (Digital Living Network Alliance) Guidelines [1,2] such as televisions, recorders and mobile phones are gaining popularity. The DLNA guidelines define a protocol and a set of features to let information appliances of various vendors communicate with each other without troubling the user with complex configurations. This lets the user, for instance, browse videos, pictures and music stored in a recorder and play them back on her television via a local network [3].
Also, with the prevalence of mobile PCs, mobile phones and smartphones, there is an increasing demand to use information appliances away from home. For instance, one could be at a friend’s house and want to watch a movie stored on a recorder at home. One could be outside and want to listen to music stored on a PC at home using a mobile device. Interconnectivity not only among devices on a local network but also on remote networks is expected to gain popular use [4].
However, because the DLNA Guidelines only assume usage contained in local networks, DLNA-conformant appliances residing in different networks cannot communicate with each other (we call this feature Wide Area DLNA Connectivity ).
To achieve Wide Area DLNA Connectivity, we have proposed a method (the SOAP method) [5,6] in which a home gateway is equipped with a SOAP (Simple Object Access Protocol [7-9]) Web service. Others have proposed methods employing similar gateway facilities to achieve Wide Area DLNA Connectivity. However, existing methods only enable Wide Area DLNA Connectivity among networks that have home gateways installed.
The aim of this paper is to expand on our SOAP method to achieve Wide Area DLNA Connectivity with networks where home gateways are not (or cannot be) installed. This is done by using mobile devices as gateways to communicate with gateways at home.
2. Wide Area DLNA Connectivity
2.1. Overview
As networked information appliances gain popularity, demands to use home information appliances away from home via the Internet are growing. For instance, one could be at a friend’s house and want to play a movie stored on a recorder at home. One could be outside and want to listen to music stored on a PC at home using a mobile device. Interconnectivity not only among devices on a local network but also on remote networks is expected to gain popular use. In this paper, we discuss how to share digital contents among DLNA-conformant appliances residing on different remote networks (we call this feature Wide Area DLNA Connectivity).
2.2. Challenges
Because the DLNA Guidelines only assume usage contained in local networks, it does not support Wide Area DLNA Connectivity natively. The following challenges must be addressed:
1) M-Search, used to discover DLNA-conformant devices, sends a multicast to 239.255.255.250:1900. Because this message cannot reach over the Internet, it cannot discover devices on remote networks.
2) When manipulating devices on the local network, DLNA-conformant devices send UPnP messages based on their local IP addresses. These messages cannot reach devices on remote networks.
3) Many household broadband routers use NAT (Network Address Translation). These routers cannot route messages sent from outside the local network to the desired device on the local network.
3. Existing Researches and Their Issues
3.1. Existing Researches
Let us discuss existing researches that aim to resolve the challenges described in Section 2.2 and achieve Wide Area DLNA Connectivity.
3.1.1. SOAP Method
The SOAP method requires that home gateways be placed at the borders of every network that is to participate in DLNA Wide Area Connectivity. These home gateways implement SOAP, the protocol to call remote data and services with HTTP and XML-based messages. The home gateways take the UPnP messages sent and received by DLNA-conformant devices, encapsulate them in SOAP messages, and transfer them over the Internet, thus enabling Wide Area DLNA Connectivity.
3.1.2. Wormhole Devices
Wormhole Devices [10,11] are placed and connected to broadband routers on different networks. These Wormhole Devices encapsulate UPnP messages in SIP messages and transfer them via an SIP server to achieve Wide Area DLNA Connectivity. Moreover, the DMSs and the DMPs involved can communicate as if they were on the same local network, so they do not need to be changed in design or implementation.
3.1.3. VPN Method
The VPN method [12,13] requires that home gateways and home servers be installed in each of the networks. The home gateways are to be placed at the borders of the networks, and the home servers are connected to their local home gateways. The home gateways perform secure communications with each other with IPSec while the home servers generate virtual DLNA-conformant devices that act as delegates of the remote DLNA devices. The gateways and servers provide secure Wide Area DLNA Connectivity.
3.2. Issues with Existing Researches
The researches described above have enabled us to link DLNA-conformant devices on different remote networks. DLNA-conformant devices are expected to gain more popularity as mobile phones, smartphones, STBs (set-top boxes) and printers adopt the DLNA Guidelines. Hence, it is imperative that Wide Area DLNA Connectivity among a variation of networks and devices is achieved. However, the existing researches have limited capabilities due to these issues:
1) They require that home gateways be placed at each and every one of the networks that are to participate in Wide Area DLNA Connectivity. High installation costs are introduced when setting up new networks to participate.
2) Many public settings such as hotels or restaurants make it impossible to set up home gateways. Wide Area DLNA Connectivity cannot be achieved in these settings.
3) They only support DLNA Guidelines version 1.0, which only supports 2-Box Pull. Hence, the devices that support DLNA Guidelines version 1.5 cannot fully utilize their 3-Box capabilities.
4. Proposed Method
4.1. Overview
In this paper, we expand on our SOAP method to resolve the issues discussed in Section 3.2 and achieve Wide Area DLNA Connectivity. We propose a network architecture that uses a mobile gateway in addition to a home gateway. The mobile gateways run on mobile devices with wireless LAN capabilities, such as notebook PCs, mobile phones and smartphones.
This setup has the following advantages. First, users do not have to set up home gateways at networks away from home, and installation costs are eliminated. Second, it enables Wide Area DLNA Connectivity anywhere wireless LAN is available. Third, because the proposed method uses the mobile gateway as a controller, devices conforming to the DLNA Guidelines version 1.5 can be used in 3-box setups. These advantages resolve all three issues discussed in Section 3.2.
Figure 1 is a schematic diagram of the proposed network architecture. The home gateway is placed either at the border of the home network or behind its broadband router. The mobile gateway uses wireless LAN to connect to whatever network is available.