Nigel Burgess Agilent Technologies
Introduction The object of this paper is to discuss the use and testing of Ethernet services in telecommunications transmission networks, with the emphasis on the commissioning through to maintenance phases of network deployment and use. These phases are generally taken to be: • • • •Commissioning Acceptance testing Service turn-up/hand-over Network maintenance/troubleshooting
There are several options for dealing with this increase in data traffic and the various approaches all have advantages and disadvantages. For example, one option is to build an entirely new data-only network. The biggest disadvantage of this approach, and most of the other options, is the largeamount of capital investment required. For this reason most network operators are integrating data services into their existing networks and they are doing this by utilizing the “next generation” of SONET/SDH network elements. These new network elements carry all of the traditional T-carrier/PDH and SONET/SDH services but also allow the transport of data services in their native format, Ethernet. Thisreduces the complexity of the network for both the customer and the operator leading to a lower overall cost and more efficient use of bandwidth. It is the use of these “next generation” elements that this paper addresses. Introduction to Ethernet Ethernet is an asynchronous, frame-based protocol originally intended to provide a means of communication between more than two data devices, usingshared media. Ethernet, fully defined by the IEEE 802.3 (2000) standard, has changed and evolved over time, increasing in speed and allowing the use of full-duplex transmission, rather than shared media. The current version of the standard allows for many variations of speed and media type and these are described by the following notation: For example, the standard contains a specification for a 10Mbit/s, baseband system with a maximum segment length of 500 m. The notation for this would be 10BASE5. A media type identifier often replaces the segment length, for example the ‘T’ identifier is used for systems running on unshielded twisted pair cabling. All of the variations of Ethernet share the same basic frame structure, access/control method (MAC - Media Access Control) and, for systemsusing shared media, the same collision detection scheme (CSMA/CD - Carrier Sense Multiple Access / Collision Detect).
This paper will introduce Ethernet in its various forms and discuss its increasing use as a transport protocol in telecommunications networks. It will then discuss what testing should be done, and how that testing can be carried out, in order to ensure quality of service for theend user of an Ethernet service. This paper is intended for telecommunications engineers and technicians involved in the deployment and use of Ethernet services. It will be of particular interest to those who are familiar with SONET/SDH services and who now find themselves deploying the “new” Ethernet services. The Need to Use Ethernet in Transmission The need to transmit data ontelecommunications networks is not new. In fact the very first telecommunications systems could only transmit “data”, in the form of Morse code. The networks that have since been built around the world however were designed to carry only one type of traffic - voice. The telephony network is the biggest machine in the world, with many millions of interconnections. Until recently this network served its purpose welland it is only with the huge increase in the need for data transport, driven mostly by the Internet, that there has been any real need for change. Until recently data traffic was carried on the telecommunication network by making it “look” like voice traffic, either by using a modem or, for higher bandwidth connections, packaging the data in such a way that it would fit into the standard 56/64...