# FANT: Flexible Attention-Shifting Network Telemetry
## 1 Introduction  
In recent years, the scale of data center networks has grown significantly due to the continuous expansion of cloud services and virtualization. To manage and control these large-scale networks effectively, various network applications such as congestion control [1], load balancing [2], and network verification [3] have been developed. These network applications require accurate network measurements that cover a broader range of metrics (the content supported for monitoring, such as port rate, queue occupancy, and timestamps, is named differently by various standardization organizations, such as metadata or data fields. For simplicity, in this paper, we will uniformly refer to each type of content supported for monitoring as a metric), offer finer granularity, and provide higher measurement frequency. Traditional network measurement solutions, such as SNMP [4] and SFlow [5], cannot meet these requirements. To address these needs, a contemporary measurement solution, inband network telemetry (INT), has been introduced. INT provides precise in-device network visibility, making it an increasingly preferred choice for network monitoring. INT is a network measurement mechanism that depends on network infrastructure, such as switches. It can be broadly categorized into two types based on the nature of thedata packets that carry the INT header: passive inband network telemetry (PINT) and active inband network telemetry (AINT). **PINT**: PINT embeds the INT header into data packets of users' traffic. Consequently, PINT can insert network status into all packets and achieve more accurate and timely measurements. This capability facilitates real-time control of traffic in data planes, supporting network applications that require rapid decision-making, such as congestion control [1] or load balancing [2]. The basic process of PINT is as follows:  
1. The INT source switches embed an INT header into the user's data packets. 2. As these packets traverse the network, switches insert their internal state (e.g., queue length, queuing time, port speed) into the INT header. 3. The INT sink switches extract the network status from the packets' INT header and report it to the INT controller. **AINT**: AINT embeds the INT header into specially made probe packets. Since these probe packets are generated by the AINT system, they can be sent to any location in the network at any time (PINT can only measure the network status when users' flows go through the switches or links). Thus, AINT primarily provides network status information for applications that require a comprehensive view of the network state at low frequency (around every 10 s), such as traffic engineering [6], network-wide monitoring [7], and network verification [3]. The basic process of AINT is as follows: (i.) INT generators/collectors dispatch probe packets into the network. (ii.) As these probe packets traverse the network, switches insert their internal state into the INT header. (iii.) The INT generators/collectors then extract the network status from the packets and report it to the INT controller. Although AINT's measurement frequency is relatively slower, it covers a broad range. In this paper, we primarily focus on active inband network telemetry (AINT). AINT offers comprehensive network visibility with low network overhead and can be seamlessly integrated into existing data centers. However, as network applications continue to evolve--such as the automation of network fault diagnosis, expansion of network monitoring, and refined traffic scheduling--there is a growing need for more dimensions of network status to enhance the capabilities of network applications. Consequently, the range of metrics that needs to be reported by the telemetry system is increasing (from 96 bit/probe to 128 bit/probe), as shown in Figure 1. The initially required reporting content of the measurement system for the application was a few coarse metrics such as port rate, queue length, and device packet loss rate.