# Age of Information in Multicast Networks with Multiple Update Streams

## TL;DR

This paper analyzes the age of information in multicast networks with two types of updates, proposing a threshold-based scheme to keep the age constant regardless of network size and optimizing thresholds for minimal age.

## Contribution

It introduces a threshold-based multicast scheme for two update types, ensuring age independence from network size and deriving optimal thresholds for minimized age.

## Key findings

- Age can be kept constant regardless of number of receivers.
- Optimal thresholds depend on link delay distributions.
- Pareto optimal trade-off curve for both update streams' age.

## Abstract

We consider the age of information in a multicast network where there is a single source node that sends time-sensitive updates to $n$ receiver nodes. Each status update is one of two kinds: type I or type II. To study the age of information experienced by the receiver nodes for both types of updates, we consider two cases: update streams are generated by the source node at-will and update streams arrive exogenously to the source node. We show that using an earliest $k_1$ and $k_2$ transmission scheme for type I and type II updates, respectively, the age of information of both update streams at the receiver nodes can be made a constant independent of $n$. In particular, the source node transmits each type I update packet to the earliest $k_1$ and each type II update packet to the earliest $k_2$ of $n$ receiver nodes. We determine the optimum $k_1$ and $k_2$ stopping thresholds for arbitrary shifted exponential link delays to individually and jointly minimize the average age of both update streams and characterize the pareto optimal curve for the two ages.