Enterprise VoIP Services over Mobile Ad-Hoc Technologies

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Edgar Gardner
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1 Enterprise VoIP Services over Mobile Ad-Hoc Technologies 1 System Architecture Figure 1 illustrates the system architecture. We can divide it into 2 parts. One is the Mobile VoIP Box (MVB) node and the Ad-Hoc network comprised by the MVB users using different kind of devices (Figure 1 (1)), the other is the SIP platform (Figure 1 (2)). The MVB node provides MVB users using Voice over IP (VoIP) service based on Session Initiation Protocol (SIP). The MVB node is equipped with multiple external modules which can access cellular/infrastructure networks. The external modules are heterogeneous. They could be GSM handsets, GPRS handsets, 3G CDMA handsets, PHS handsets, or IEEE WLAN interfaces...etc. characterized by different bandwidths and latencies. It is clear nowadays that cellular networks have much wider coverage and longer transmission distances, but much lower communication bandwidths, compared to IEEE based networks. The MVB node does not always keep all external modules connect to the cellular/infrastructure networks at the same time, but establishes connections to the cellular/infrastructure networks on an as-needed basis. The MVB node would always keep at least one external connection to cellular/infrastructure network. This connection is a dedicated channel for SIP signaling messages between the MVB users and the SIP servers in Internet in peacetime. The MVB node could increase the maximum external bandwidth by adding the number of external modules. 1

The MVB node provides MVB users using Voice over IP (VoIP) service based on Session Initiation Protocol (SIP).

2 Inside the MVB node, it is a group of mobile nodes (MNs) all equipped with a wireless wireless LAN card. the MVB node s internal interface is also a wireless wireless LAN card. All MNs and the MVB node comprise an Ad-Hoc network. Therefore, each pair of nodes inside the MVB node, including the MVB node itself, could communicate with each other either directly or through multi-hops frame relay by some intermediate MNs. Hence, each device including the MVB node would run an Ad-Hoc routing protocol. Numerous protocols have been developed for Ad-Hoc mobile networks. The existing protocols may generally be categorized as 2 types. They are table-driven and on-demand Ad-Hoc routing protocols, respectively. Table-driven Ad-Hoc routing protocols attempt to maintain consistent, up-to-date routing information from each node to every other node in the network. These protocols require each node to maintain one or more tables to store routing information, and they respond to changes in network topology by propagating updates throughout the network in order to maintain a consistent network view. Some of the existing table-driven Ad-Hoc routing protocols are protocols such as Destination-Sequenced Distance-Vector (DSDV) routing protocol, Clusterhead Gateway Switching Routing (CGSR) protocol...etc.. On-demand Ad-Hoc routing protocols create route only when desired by the source node. When a node requires a route to a destination, it initiates a route discovery process within a network. This process is completed once a route is found or all possible route permutations have been examined. Once a route has been established, it is maintained by a route maintenance procedure until either the destination becomes inaccessible along every path from the source or until the route is no longer desired. On-demand Ad-Hoc routing protocols are protocols like Ad-Hoc On-Demand 2

Hence, each device including the MVB node would run an Ad-Hoc routing protocol. Numerous protocols have been developed for Ad-Hoc mobile networks.

3 Distance Vector (AODV) routing protocol, Dynamic Source Routing (DSR) protocol...etc.. Which Ad-Hoc routing protocol is the most suitable one for real-time VoIP application or whether there should be a new routing protocol being developed for VoIP is still an open question. The MVB node acts as a gateway between Internet and the MNs, which routes the VoIP signaling and voice packets between each MN and external Internet. By using Ad-Hoc routing technology, the MVB node could share its outbound bandwidth with more MNs. Taking IEEE b interface for example, the transmission range is 50m indoor and 100m outdoor. Hence, the MVB node communication radius is at least 50m 100m. Moreover, under the situation that there exists 2 3 nodes working as intermediate relay stations, the MVB node would extend its communication radius to 150m or far more through Ad-Hoc routing. SIP platform contains 3 components. They are SIP registrar, SIP proxy and Public Switched Telephone Network (PSTN) Gateway, respectively. SIP registrar is a database containing SIP users subscription and status information (e.g., on-line, off-line, the IP addresses now it is using... etc.). Users, who are using SIP VoIP services, periodically send SIP REGISTER message, containing their status and IP address information, to SIP registrar. Therefore, a caller could find each SIP user through SIP registrar. SIP proxy is responsible to the routes of SIP messages. PSTN Gateway inter-connects Internet and PSTN. Internet and PSTN run different telephony and network protocols. In Internet side, it is VoIP signaling protocol and Internet transmission protocol. In PSTN side, it is Signaling System 7 (SS7) signaling protocol. Therefore, there needs PSTN Gateway to act as a communication 3

The MVB node acts as a gateway between Internet and the MNs, which routes the VoIP signaling and voice packets between each MN and external Internet.

4 bridge in order to transform these different protocols. After describing the architecture of the system, following descriptions are the features of the MVB node. MVB provides VoIP service based on SIP.:(I should fill in sth) MVB automatically adjusts the outbound bandwidths to both guarantee the MNs voice quality and spend least internet access cost.:(i should fill in sth) MVB supports access control for users to access VoIP service.:(i should fill in sth) MVB acts as a router, which can monitor and control all traffic for the MSs.:()(I should fill in sth) 2 Software Architecture of the MVB node The software architecture (Figure 2) of the MVB node includes four major components. They are Network Controller, Authentication Center, OA&M and Push Center, respectively. Below describes these components in sequence.: Network Controller (Figure 2 (1)) provides the following functions for Internet access: 4

:(i should fill in sth) MVB supports access control for users to access VoIP service.:(i should fill in sth) MVB acts as a router, which can monitor and control all traffic for the MSs.

5 Access control: The MVB node only allows the authenticated users to access Internet and then establish their SIP calls. Unauthorized packets will be filtered out by the firewall. Only the authorized packets will be able to pass through the firewall. IP address translation: It is a private network inside the MVB node, whether MNs use public IP addresses or private IP addresses. An Network Address Translator (NAT) server is placed on the MVB node to perform address translation when the IP packets are delivered. NAT server has a table consisting of pairs of local IP addresses and external IP addresses. Ad-Hoc routing support: In order to support Ad-Hoc routing, the MVB node implements Ad-Hoc routing protocol as a module. Each node exchanges routing information and maintains a routing table so that hosts may communicate with each other or access Internet in a multi-hop manner. SIP application support: Congenitally, SIP-based VoIP application has NAT traversal problem under the NAT environment. NAT Traversal module modifies the formats of SIP packets so that these packets can be transformed between MNs and outside corresponding nodes through the MVB node. Therefore, SIP sessions will be successfully established. Session management: The MVB node could increase or decrease the external bandwidth according to the number of SIP sessions. As the bandwidth is not enough, the MVB node would increase external bandwidth by dialing a new connection. New SIP sessions would be allocated on the newly con- 5

An Network Address Translator (NAT) server is placed on the MVB node to perform address translation when the IP packets are delivered.

6 nected external module. As some bandwidth is not being used, the MVB node would combine SIP sessions into as minimum external modules as possible and guarantee the quality of service. For example, as a new call arrive but the external bandwidth is not enough, the MVB node would open an external module and establish the connection between it and the cellular/infrastructure network to increase bandwidth. Therefore, the new session would run on the newly opend external module. Authentication Center (Figure 2 (2)) leads unauthorized MNs to the Authentication, Authorization, Accounting (AAA) server which is in the core network. MNs packets will be filtered out by the MVB node before they are successfully authenticated by the AAA server. After authentication, the MVB node would permit packets transmission between MSs and corresponding nodes in Internet through it. Operation, Administration and Maintenance (OA&M) (Figure 2 (3)) controls and monitors individual MVB user traffics. MVB utilizes Simple Network Monitoring Protocol (SNMP) as the network management protocol. With Management Information Base (MIB), every managed network element is represented by an object with an identity and several attributes. An SNMP agent is implemented in the MVB node, which interacts with the managed network element through SNMP. For example, the traffic statistics of an AP can be accessed by the OA&M (through the corresponding MIB object) and displayed in a web page using Multi Router Traffic Grapher (MRTG). A log handler is implemented in the OA&M to record all events occurring in the MVB node. A billing handler generates billing records for charging purpose. Push Center (Figure 2 (4))(I should fill in sth) 6

to increase bandwidth. Therefore, the new session would run on the newly opend external module.

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CHAPTER 6. VOICE COMMUNICATION OVER HYBRID MANETs

CHAPTER 6. VOICE COMMUNICATION OVER HYBRID MANETs CHAPTER 6 VOICE COMMUNICATION OVER HYBRID MANETs Multimedia real-time session services such as voice and videoconferencing with Quality of Service support is challenging task on Mobile Ad hoc Network (MANETs).