Though Defence Networks are NOT commercial networks driven by revenue, still least cost per bit approach is necessary as it is funded by the taxpayer. Defence has generations of legacy networks but is now looking ahead towards a pure IP future. Is this vision justified? Operators today are re-introducing a new TDM standard for reducing the cost per bit. Should Defence networks use a pure IP or a IP-TDM combination approach? May we have an informed debate as to what is best for the country. The article below is your start point.
The fiber optic networks of many telecommunications companies in metropolitan areas are experiencing a shift from carrying primarily voice traffic to carrying a growing mix of data, video and voice traffic. Data transmissions are based on internet protocol, or IP, and carry services such as voice over IP, or VoIP, Internet access, and various video services. Video services include broadcasting streaming video and multicasting streaming video that is either identical or can be differentiated by subscriber choice, either at standard definition capacity or at HDTV capacity. In addition, these services include transmission of all of these services over a cellular network to advanced handheld devices over third generation, or 3G and 3.5G, cellular networks.
Data traffic volumes carried over these metropolitan area networks are surpassing voice traffic volumes. Data traffic is forecast for further growth over the coming years. This increase in data relative to voice traffic is mainly a result of the rapid growth of the Internet, video services and local area networks. Offerings of high speed data services at rates of up to 100 mega bits per second, or Mbps, have reached millions of subscribers in a number of Asian markets, including Japan and Korea. These services are offered either over fiber connections or a combination of fiber and fast access technologies, such as ADSL release 2, very high speed digital subscriber line, or VDSL, and VDSL release 2, wireless or cable networks. Similar expansion of fiber to the premise and fiber to the curb has reached millions of subscribers in the United States as well. Connecting subscribers with fiber is expected to allow for significantly higher speed services, mainly data and video services and, as a result, will require an upgrade of metro telecom equipment with technologies that enable very high speed transmissions of data services over fiber networks.
Telecommunication companies have typically managed their data transfer capacity needs through their existing metro transport technologies. These technologies were originally designed for transporting voice services. These traditional solutions, however, are not designed to support high levels of data services traffic. Traditional networks are also inefficient when transporting data as they fail to utilize inherent differences in the type of network support that is required for the transmission of data traffic.
Data traffic is generally less susceptible to corruption resulting from minor time delays and less time-sensitive than voice traffic. In addition, data traffic often exhibits a bursty nature, with dynamically varying levels of utilization of communication channels, as opposed to voice traffic which normally requires constant levels of channel utilization. Substantially all of the metropolitan area networks are based on transmission equipment that is limited to transmission capacities of 2.5 Gbps and below. Telecommunications carriers are expected to upgrade their metro networks over the next few years to be able to support transmission capacities of up to 10Gbps in order to better support high bandwidth data services. A range of new solutions is being developed to address the need of carriers and service providers to be able to support higher levels of data traffic within and between metropolitan areas, commonly referred to as metro transport.
One type of solution, consisting of a router or switch that transports packets of data, focuses on the characteristics of data traffic without supporting legacy voice and other circuit-based data services. In this type of solution, data services and legacy services are transmitted and maintained in different metro networks. Another type of solution attempts to take advantage of the characteristics of data traffic while continuing to support traditional voice traffic over a converged metro network. This second type of solution offers transmission capacities of 10 Gbps and, to a lesser extent, 2.5 Gbps, and supports transmission of both packets of data and traditional circuit-based voice and data services over the same network. Data services supported include the transmission of a range of video services, whether in standard or high definition mode, as well as over cellular networks. We may expect that the metro transport solution for the transmission of traditional voice and increased data traffic will combine the efficient transport of data services based on Ethernet protocol with high reliability voice services based on SONET/SDH protocol.
Major metro transport technologies include the following voice and/or data protocols:
SONET / SDH . SONET is the American National Standards Institute, or ANSI, standard for synchronous voice transmission on optical media. The international equivalent of SONET is synchronous digital hierarchy, or SDH. Together, these two voice protocols ensure standards to enable digital networks to interconnect internationally and existing conventional transmission systems to utilize fiber with the help of interfaces that connect network end-users, called tributary attachments.
Ethernet. Ethernet is the most widely-installed local area network, or LAN, technology. It is often used in college dormitories and office buildings. The most commonly installed Ethernet systems are called 10BASE-T and provide transmission speeds up to 10 Mbps.
RPR . Resilient packet ring, or RPR, is an emerging technology that is being designed to integrate Ethernet data protocols for the efficient transmission of data with traditional SONET voice protocols. An industry standard for RPR, IEEE 802.17, was approved in 2004. RPR is being developed as an alternative to SONET transport for networks that support high levels of data traffic, while allowing carriers to maintain traditional SONET attributes, such as resiliency. Resiliency refers to the ability to employ a back-up or alternate route in the event of a system or optical fiber failure, as well as the fast restoration of service in the event of any other failure. RPR is expected to allow carriers to conduct performance monitoring of transmission rates, traffic volume, and failures and alarms, comparable to the monitoring available with traditional SONET-based networks.
Multiprotocol Label Switching. Multiprotocol label switching, or MPLS, is a standards-approved technology for speeding up network traffic flow and making it easier to manage. MPLS involves setting up a specific path for a given sequence of packets, identified by a label put in each packet, thus saving the time needed for a router to look up the address to the next node to forward the packet to. MPLS is called multiprotocol because it works with the Internet Protocol, or IP, Asynchronous Transport Mode, or ATM, and frame relay network protocols.
In addition to moving traffic faster overall, MPLS makes it easy to manage a network for quality of service, or QoS. For these reasons, MPLS is gradually being adopted as networks begin to carry more and different mixtures of traffic.
Pseudo Wire Emulation. Pseudo wire emulation, or PWE, is a standards-approved technology for mapping different services over packet switched networks, such as MPLS. A pseudowire emulates a point-to-point link, and provides a single service which is perceived by its user as an unshared link or circuit of the chosen service, and can be used as a convergence layer for multiservice systems.
RPR’s Advantages over Existing Data and Voice Transport Protocols
RPR is a more efficient voice and data transport protocol than traditional SONET rings that have been retrofitted to handle data traffic for the following reasons:
Usage of a single fiber ring and spatial reuse capabilities. SONET utilizes only one ring of optical fibers. A second ring is available in case of a failure in the first ring, but is otherwise not used. This creates unutilized capacity in SONET, as half of the network capacity is idle during normal operations. RPR enables the use of this redundant bandwidth under normal operating conditions, while maintaining the redundancy capabilities. In addition, RPR supports spatial reuse, which allows the re-use of the same ring bandwidth over different spans of the ring.
Statistical multiplexing qualities. With SONET, data transmitted from one specific network element, or node, to another may be sent only using bandwidth that has been dedicated for that transmission. RPR increases bandwidth efficiency by allowing data transmissions to be broken up into packets and inserted in bandwidth that might have otherwise been dedicated (but not used) for a separate transmission. This process is called statistical multiplexing. When less than all network users are actively transmitting or receiving data at the same time, it results in a more efficient utilization of the total available bandwidth on a network.
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