There are a lot of complaints about lag (since the lighting update a few years ago). If you’ve played PvP during prime time, you’re certainly seen your ping spike into the hundreds if not thousands. Ping is a technical term (or tool) to describe an ICMP Echo request and reply. This is a type of packet that is sent over a network (or internet) from a source (in this case your computer) to a destination (in this case the ESO servers) and a measurement of how much time it takes for the response to be received. It is important to note that a ping is not a true measurement of the speed that your communications are processed, it is simply a measurement of the capability of the connection between you and the ESO server based on a lot of factors (most notably network congestion by your internet provider, or the ESO servers’ ability to process your requests in a timely manner).

Some of the causes of lag are known, and quite obvious. The more players who are in a particular area, the more processing the server will have to do, and the slower its relative performance. Here are examples:

• Healing springs is one of the most commonly used healing spells. It is an area spell, and thus affects a certain number of players who are within the area of it being cast. When someone casts it, there is a process to determine who is in the area, how much health they have missing, how much health each tick of the spell will add to their health pool, and communications between the server and all the clients of the players in the area to add each tick of health to their health pools. Each player has different gear and champion points which may affect increases in healing received, or debuffs that may affect decreases in healing received. All of this needs to be calculated for every tick of a healing springs. If the caster of healing springs is using a Master’s restoration staff, then there is an additional calculation on the return of stamina. If the caster is using the healing mage set, then there is an additional check on any opponents in the area of the heal that will reduce their weapon damage. Every effect that needs to have status determined or calculated increases the required processing on the server side and for each calculation to be sent to the clients for every player who is affected, and every player in range who may mouse-over players in their area.
• Steel tornado is an area damage skill in the dual wield line. It hits everyone within a certain area, though only a certain number of players receive full damage. Other opposing players receive reduced damage up to a point. Steel tornado is also an execute, so when any player is hit there is a check to determine if execution damage should apply. Every hit of damage has to be processed for every player in the area, and all that data sent to every other player in the area who, like with healing, may mouse-over other players in their area.
• Back in the good old days, ultimates such as Meteor (Mage’s guild) that hit an area also included a calculation to determine if your ultimate has already hit and done damage (so one person’s ultimate should not hit multiple times). The use of an ultimate brings your ultimate pool down to zero, though once lag starts this was not instantaneous – so multiple ultimates could go off from one person. Only one of them would do damage, though for each one the calculations and checks to determine if it will damage, to whom, and what debuffs will be applied need to be performed. This would significantly exacerbate the lag if someone (or multiple people) spamed Meteor during lag.

Every time that an area of effect (AoE) skill is used, calculations need to be performed and information updated in the game clients (computers) of every player who is within a certain range. The more players from each side, the more calculations need to be performed and the more updates need to be sent. There is a reasonably feasible number of such that can be performed without impacting timing of game play (lag) for the players involved, and this is largely dependent upon the way that both the game client and servers were programmed.

When you see / hear some players complaining about zerging, this is the main reason that they do so. If a guild runs tightly stacked in the same place all casting area of effect spells, then they are directly contributing to the increase in lag. It is debatable if it’s their fault knowing that what they do causes lag, ZOS’ fault for not delivering the large scale battle capabilities that the promised (many years later), or a combination of the two. I believe that the groups who zerg are responsible, and ZOS is accountable. If you know that running in large numbers exacerbates lag, then there’s no excuse to keep doing so unless you don’t care about other players – unless of course it’s a case of “the largest zerg wins the fight” .

There is no “lag switch”, and lag is not something that the developers “turn on” just to upset you. The people who believe that obviously don’t understand how technology works.