Network Systems for Emerging WAN Applications Hitachi Review Vol. 48 (1999), No. 4 169 Akihiko Takase, D.Sc. OVERVIEW: This paper describes wide-area-network architecture from the viewpoints of networking functions and its allocation to networking technologies like Internet Protocol (IP), Asynchronous Transfer Mode (ATM), and Synchronous Optical Network/Synchronous Digital Hierarchy (SONET/ SDH). We summarize requirements for the future wide-area network applications by considering Internet applications and mobile communication. Then, we discuss about each technology from the aspect of generic networking functions including protection, virtual networking, addressing, routing, and network applications. And we present an appropriate functional allocation and combination of the networking technologies. We also evaluate network-centric services such as an electronic-commerce platforms and digital contents distribution. Three functional elements, application programming interface (IP-API), quality of service (QoS) mapping between the API and networking functions, and interaction interface between the API and network intelligence, should be the key elements for advanced network services. INTRODUCTION TELECOMMUNICATIONS networks have been experiencing a number of trends over the last few years. One trend is the change from voice communication to data, and another is the change from fixed to mobile communication. Many technologies, such as SONET/ SDH, ATM, IN, and TCP/IP, have been developed to support these changes in networking requirements. These technologies have been developed with diverse background. SONET/SDH originally came from timedivision multiplexing with network-wide synchronization, but currently its distinctiveness is mainly its fast and self-healing restoration architecture. ATM was aimed at multimedia communications in almost all aspects of networking. ATM s appropriate application area, however, is still under discussion. TCP/IP or Internet has taken the main role in various networking applications and activities. It therefore provides secure, multimedia, and large-scale carrier networking. On the other hand, networking capabilities of voice telephony have been improved to support sophisticated network-centric services by using an intelligent network (IN) architecture. Mobile telephony can be considered an extension of the IN technologies in a sense of the database application inside carrier networks. These various networking technologies seem to cause confusion because of the function overlapping between the technologies. There may not be a simple technology solution that provides all the networking functions. Each technology has its own distinctiveness and suitable application area. The main issue, however, might be if we should use IP over X. The Internet or IP-based networking is considered the basis of the future network. So what is the role of the other networking technologies that are currently widely deployed in wide-area carrier networks? In this paper, we discuss the above mentioned technologies from the viewpoint of wide-area networking especially for voice/data integration and mobile communication support. First, we summarize the requirements for future wide-area networking applications, then we discuss each technology from the aspect of generic networking functions. After describing suitable technology for each networking function, we review on network-centric services of future wide-area networks. TRENDS IN CARRIER NETWORKING Data Communications The most significant trend in carrier networking is the shift in traffic volume from telephony to data communication and multimedia communication. In light of this trend, wide-area networks face the following three main issues.
Network Systems for Emerging WAN Applications 170 Quality of service (QoS) Multimedia communication or service integration requires QoS controllability in the network. The QoS controllability is composed of connection handling capability and end-to-end traffic manageability. The QoS aware network should have these two abilities even in the Internet architecture that has been recognized as typical connectionless network. Although the connection handling in heterogeneous networks is not easy, the future network will resolve this problem by using a simpler network architecture; that is, access and core architectures with an edge node that is a single point of connection handling. The toughest issue is managing end-to-end traffic with bursty traffic. And there are three possible approaches to resolve this issue. (1) connection admission control and shaping, (2) flow control, or (3) over engineering. The first approach has been intensively studied from the viewpoint of ATM, but the difficulty here is modeling the source traffic. That is, no one can predict the source traffic characteristics of non-conventional applications. This approach, however, can be improved if combined with an appropriate shaping function. The second approach is included in TCP/IP architecture. The TCP flow-control mechanism, however, is not sufficient for wide-area networks because the time constant of the TCP feedback loop is too large to achieve higher utilization of network capacity. An approach other than TCP flow control, such as available bit rate (ABR) control, in ATM architecture is not efficient for wide-area networks because of the intrinsic transmission delay of the flow control signal. The third approach is the basis of recent development of WDM transmission s and veryhigh-capacity router nodes. This approach is not a final solution, because once a better approach is found the old one will no longer be competitive. Anyway, currently there is no ultimate solution for managing end-to-end traffic, so a carrier network should utilize a combination of several concepts: connection management at the edge node, a shaping function both at the source and the edge node, and traffic management within the core network. Billing Billing is another feedback mechanism for balancing traffic explosion and infrastructure investment. Though current Internet architecture does not have this mechanism, it should be essential to achieve sound growth. Telephony has been utilizing this mechanism very sophisticatedly by means of the IN architecture based on a signaling standard. This means that future wide-area networks should have similar capabilities as those of current telephony services; for example, free-dial services and inter-carrier billing adjustment. Signaling System No. 7 (SS7) will probably be a basic tool to achieve this capability. Node architecture Many discussions are on going for node architecture, such as IP-over-X. We will discuss this architecture in the next section NETWORKING TECHNOLOGIES in more detail; here we only describe node architectures for future networks. The basic node functions are (1) line interface, (2) routing table look-up for output port binding, (3) traffic management, (4) switching with queue and buffer management, and (5) routing table maintenance. IP router and ATM switching, the two typical node technologies, are being utilized in a similar approach. For example, recent IP routers utilize a hardware tablelook-up mechanism and hardware switching that were originally developed for s. So the node architectures of networking technologies, IP and ATM are similar at least from the viewpoint of hardware implementation in a broader sense. Mobile Communications Mobility support is another crucial requirement for future wide-area networks. The Internet architecture does not have the same mobility management capability as that of the current mobile telephony. Even though the Internet can accommodate changes in dynamic network configuration in a distributed and autonomous manner, it cannot support mobility when the current IP routing protocol alone is enhanced. Mobility management Intrinsically, mobile communications require a network centric database for location registration and inquiry. Since this architectural requirement does not meet that of the distributed autonomous architecture of the Internet, mobile support of the Internet should have improved database capability.
Hitachi Review Vol. 48 (1999), No. 4 171 Mobile data networking The network centric database has already been employed in the Internet; that is, the domain name (DNS). The DNS, however, is rather static compared to a mobile telephony. It would be better to utilize the current mobile-communication architecture to support mobile data networking. This is because the mobility management performance might not be strongly correlated to bandwidth and a mobile access can essentially have the statistical multiplexing capability. New Applications The future wide-area carrier network will not be just a network but also a multifunctional shared resource for various network-based applications. The shared resource can include the network, operation s, a billing, web-hosting servers, authentication s for electronic settlement, and so on. The shared-resource nature of wide-area networks will be an essential advantage for future network applications. NETWORKING TECHNOLOGIES As a result of the huge recent growth in Internet traffic, the IP-over-X protocol is currently receiving much attention. In this section, we describe the relationships between various networking technologies that is, IP, ATM, SONET/SDH, WDM, and telephony in order to clarify the application areas of each technology. Network Structure A generic view of a hierarchical network structure is depicted in Fig. 1. The bearer consists of STM and s over a SONET/SDH ring for core. The router or IP handling function on top of the bearer supports an IP-packet capability. In other words, the IP utilizes the bearer as one of the users of the infrastructure. Billing Billing Customer Ops Design Operation SCP Server Service control Signaling IP Dial-up router IP handler IP handler ADSL modem Cellular ATM-OLT OLT DSLAM (LS) Edge node (LS) ATM/ SONET /SDH Gateway Bearer W-CDMA (Mobile-LS) Fig. 1Network Structure. BTS Edge node (Mobile) BS Gateway ATM/ SONET/SDH ATM node
TABLE 1. Networking Technologies and Functions Technologies Functions Networkbased Service Hostbased Connectivity (address, routing) Virtual networking Protection IP DNS, etc. Socket IP address OSPF, etc. IP-tunneling ICMP & routing protocol 2.5 Gbit/s ATM IN (B-ISUP) ATM-API E.164, etc. MPLS, etc. VP VP-protection Network Systems for Emerging WAN Applications 172 SONET SDH Bit 10 Gbit/s 40 Gbit/s T bit/s B-ISUP: broadband-isdn user part OSPF: open shortest path first ICMP: Internet control message protocol Path APS WDM Wavelength PSTN IN (ISUP) E.164 Dynamic-routing Dynamic-routing The signaling is based on the SS7 signaling network. It provides the transfer capability of routing and addressing information between the nodes in the bearer or bearer carriers. Additionally, it can offer connection-related information exchange between a public switched telephone network (PSTN) and an IP network with a protocol conversion gateway. The operation and billing are both essential functions of public carrier networks for profitable operation even in the case of the IP packet transfer. Networking Technologies As described in the previous section, various networking technologies have been deployed in widearea networks. Each technology has its own scheme to support diverse networking functions. And these functions overlap as listed in Table 1. IP and ATM have almost all the capabilities over the spectrum of networking functions. IP has an advantage in host-based service area because the application programming interface (API) dominates the network interface of the PC and server. Probably there would be a very slight chance for ATM-API in future. Consequently, IP address should be the main addressing scheme in the connectivity area. However, there are many alternatives for routing protocols and solution for wide-area networks is not so clear as that for addressing. Different routing architectures will be deployed for the access and core portions of the network. Wide-area networks will utilize simplified and topology-based routing scheme like multi protocol label switching (MPLS) to ease the difficulties of maintaining large-volume routing operation. Virtual networking is the function of mapping between physical networks and logical ones. This function has a tight relationship with protection scheme introduced by the SONET/SDH APS (automatic protection switch) architecture. IP-based alternatives like IP tunneling might be possible and legacy IP routing protocol can also provide an alternative for protection; however these IP alternatives are not so powerful or effective as other technologies from the viewpoint of protection speed and virtual networking flexibility. Moreover, virtual networking is related to traffic management of the networks. This is another advantage of ATM, since ATM architecture has been developed to handle various traffic management capabilities. For WDM technology, though there will be a similar alternative, an efficient protection scheme has not been developed. We can summarize above discussion as follows; IP has superiority in API and addressing for access, and ATM has advantages for core network routing and flexible virtual networking with traffic management functions. Protection will be provided by VP (virtual path) or SONET/SDH path depending on the requirements for protection path granularity. NETWORK SERVICE ARCHITECTURE Table 1 also lists a network-based-service support functions of IP and ATM. Originally, Internet architecture was based on host-based applications and almost all the networking intelligence resides in the hosts. On the other hand, telecommunication architecture does not require any intelligence for terminals. The IP and ATM networking concepts are not sufficiently complementary to provide flexible and effective communications. The telecommunications infrastructure provides reliable service due to the node and path redundancy attributable to the self-healing capability of SONET/SDH. And it can serve as a common resource even for host-to-host applications, such as IP-based services, since it can be used for
Hitachi Review Vol. 48 (1999), No. 4 173 sophisticated applications in addition to as a reliable bit-transfer medium. Most of the communication services over IP networks are implemented as host-to-host applications on top of the API of the host middleware as described in the previous section. Future communication services should continue using the API as a user-to-network access interface; however, it is not necessarily the ideal solution for some newly emerging network services such as electronic commerce (EC) and digital content distribution. For these services, network-centric communication services are essential for interacting with the host API and the telecommunications network intelligence. There should be two types of network intelligence. One type of intelligence resides inside of the telecommunications network, uses the same API as a host, and be shared by multiple users. Network server functions, such as web hosting and database mirroring function as hosts attached to the network. The other type, a network-specific service platform, is used for managing sophisticated network services related to routing and billing functions. Although the network-specific service platform resembles a service control point (SCP) in the IN architecture of the legacy telephone network, there is a basic difference between them in quality-of-service (QoS)-related capabilities. The term QoS used here refers to both traffic and reliability/security management in contrast with previous section where User access Internet QoS Mapping Authentication network Financial network Electronic settlement Internet Marketing Internet So-called Internet Fig. 2QoS Mapping Between Access Internet and Core Network. QoS is described just from traffic management aspect. In future multi-service networks, multiple virtual networks will be configured by using the virtual networking function of the ATM infrastructure (Fig. 2). Each type of virtual network has a unique QoS requirement in accordance with its function. For example, the network for the settlement process in electronic commerce must be secure and reliable, while the marketing virtual network will require high-speed, unidirectional multicast characteristics with less demand for security and reliability. Even in such a multi-service environment, host user APIs do not change drastically. User access signaling is based on the current IP/Internet architecture, while the network provides virtual networking that can recognize IP applications. At the edge of the network, the network intelligence routes each user to the appropriate virtual network by interpreting the QoS requirements from the destination address and/or the TCP port number. Service location functions will most likely be necessary to route the user to the optimal network server functions that we are also developing as another type of network intelligence. This routing architecture should use alternative billing schemes since the enhanced QoS manageability is a chargeable feature. CONCLUSIONS We discussed the networking technologies, IP, ATM, and SONET/SDH, from the viewpoint of wide-area networking especially for data communication applications and mobile communication. We summarized requirements for the future wide-area networking applications, then we discussed each technology from the aspect of generic networking functions including protection, virtual networking, addressing, routing, and network application. We presented an appropriate functional allocation and combination of the networking technologies. And we also evaluated network-centric services such as electronic-commerce platforms and digital contents distribution. Three functional elements, IP-API, QoS mapping between the API and networking functions, and interaction interface between the API and network intelligence, will be the key elements. In light of these findings, Hitachi has been developing SONET/SDH transmission s, ATM switching s, and IP node s. A dedicated article on each of these network s and relevant equipment is presented in this special issue. ABOUT THE AUTHOR Akihiko Takase Joined Hitachi, Ltd. in 1981, and now works at the Strategic Business Development Department of the Telecommunications System Group. He is currently engaged in the development of the business strategies of the group. Dr. Takase is a member of the IEEE and the Institute of Electronics, Information and Communication Engineers of Japan, and can be reached by e-mail at a-takase@comp.hitachi.co.jp