Communication between different Scrum teams can be ensured by a virtual Scrum team or Scrum-of-Scrums. The Scrum-of-Scrums is formed by team members from different Scrums. The conversations to the Scrums are not timeboxed so that the issues can be handled in the teams. The Scrum-of-Scrums should take place 2-3 times right after the Daily Stand-up and last 30-60 minutes to live up to the idea of a problem-solving meeting.
For large projects, each Scrum team should handle tasks from a product back-log. The Chief Product Owner takes care of maintaining the product backlog and passes the tasks to the Scrum teams. Each team works synchronously, the sprint ends at the same time and the meetings take place synchronously. Each team has its own product owner. Each team can have its own Scrum Master. One Scrum Master can supervise all Scrum Teams. Each Scrum team must be cross-functional (tester, developer, software architect in each team). There is a Definition of Done which applies to all Scrum teams.
There are several ways to split teams. Team members of an existing team can be assigned to other Scrum teams. On the other hand, it is possible to start with a Scrum team, gain experience and assign experienced team members to a Scrum team. A product owner should manage one team and a maximum of two teams. If there are more than two teams, then a Product Owner should be hired for each team. A Chief Product Owner coordinates the individual Product Owners and the common Product Backlog with the Product Owners.
For distributed teams, a Scrum Master should ensure that video conferences are set up, for example, teams with people or rooms. Distributed teams should come together once for an informal or formal meeting. Overlapping working hours should be found once a day. Low productivity can be expected.