Ethernet QoS Modeling in Emerging Scenarios M. Carmo, J. Sá Silva, E. Monteiro, P. Simões and F. Boavida University of Coimbra, Laboratory of Communications and Telematics DEI / CISUC Polo II, 3030 Coimbra, PORTUGAL Tel.: +351 239 790000 Fax: +351 239 701266 {maxweel, sasilva, edmundo, psimoes, boavida}@dei.uc.pt Abstract The lack of Quality-of-Service (QoS) in MAC layer of Ethernet networks was overcome with the advent of the IEEE 802.1Q and IEEE 802.1p standards. This paper describes the development of new modules to the NS-2 simulator that makes possible the simulation of QoS over Ethernet networks. The modules are related to the IEEE 802.1Q and IEEE 802.1p standards and implement the recommendations concerned to traffic prioritization. The modules are intended to run in a full-duplex switched LAN network and are part of the contribution of the Laboratory of Communications of the University of Coimbra (UoC) to EuQoS project [1]. 1. Introduction The Network Simulator NS-2 [2] is a discrete event simulation tool widely used in network research. It is an open source tool that allows the simulation of a huge variety of network protocols, ranging from application protocols, like FTP and HTTP, to network access technologies such as Ethernet. Written in C++ and Object-Oriented Tcl (OTcl), NS-2 is quite flexible and allows new modules to be added. Its extensibility is explored by several researchers and new modules are constantly being developed. NS-2 also offers several ways to process data output. Results of a simulation can be analyzed with tools like NAM (Network Animator), Xgraph[3] and gnuplot[4]. The development of 1 Gbps and 10 Gbps Ethernet has allowed the use of Ethernet technologies in a variety of scenarios, ranging from Small Office Home Office (SOHO) environments to Wide Area Networks (WANs). In this context, there is an increasing demand for QoS support on Ethernet networks. The IEEE 802.1p and 802.1Q [5] specifications deal with these requirements, bringing traffic prioritization capabilities to the MAC layer. The IEEE 802.1Q standard supports the operation of virtual LAN (VLAN) bridges that permit the definition, operation and administration of different topologies. The standard adds an extra 4 bytes tag in the MAC header (Figure 1). This tag is used for both VLAN operation and QoS priority identification. The first 2 bytes (TPI) of the tag is used to identify an 802.1Q frame (all 802.1Q frames have this field set to 0x8100). The next two bytes consist of 3 fields: a canonical format indicator (CFI), a VLAN field, and a 3 bits length field used to differentiate the priority of packets. . Figure 1. IEEE 802.1Q frame Although IEEE 802.1Q defines a priority field, it does not describe their possible values and functional details. This is performed by the IEEE 802.1p standard, which is part of the IEEE 802.1D [6]. The IEEE 802.1p standard supports the provisioning of expedited traffic in a LAN network. It defines up to eight classes of traffic (see Section 3.1) to allow differentiated treatment to frames. To accomplish this, the 3-bit priority field defined by 802.1Q is used. In this way, Ethernet can, for instance, prioritize video or audio frames. The IEEE 802.1p can also be defined as best-effort QoS at Layer 2, since the traffic is simply classified and sent to the destination; no resources reservations are established. The IEEE 802.1p standard is also concerned with provisioning of dynamic multicast filtering, but this subject is not taken into account in this paper. The rest of the paper is organized as follows. The next section discusses the main characteristics of Ethernet technology and briefly presents the EuQoS Project. Section 3 describes the implementation details of the modules related to 802.1p and 802.1Q. Related OTcl