What is Multistation access unit (MSAU)?

A multistation access unit (MSAU), also called a media access unit (MAU), is a central device that acts as Ethernet transceivers in local area networks. It is used to connect network stations or nodes in LANs and operates according to the principle of token ring. The multiple stations are connected in a star topology physically but are internally wired into a logical ring.

How MSAU Works

The logical configuration forms a ring topology where each message passes through every device one by one. Each device passes the message on to the next station in a continuous circle. However, an advantage of MSAU over conventional ring topology is that if one device in the ring fails, the MSAU can bypass it and forward the message to the next device in the ring, thus keeping the connection intact.

Connecting Multiple MSAUs

The ring-in (RI) and ring-out (RO) ports allow multiple MSAUs to be connected in a ring, thus extending the size of the LAN in multiples of 8. For example, if we have four MSAUs, the total number of computers that can be connected will be 4 × 8 = 32. The MSAUs are connected so that RI of one MSAU is connected to the RO of the next MSAU.

Advantages of MSAU

• Fault tolerance − Can bypass failed devices and maintain network connectivity

• Scalability − Multiple MSAUs can be chained to expand network capacity

• Centralized management − All connections go through the central hub for easier administration

• Physical star topology − Easier cable management compared to pure ring networks

Conclusion

A multistation access unit (MSAU) combines the benefits of star topology's physical layout with token ring's logical operation. It provides fault tolerance by bypassing failed devices and allows network expansion by connecting multiple MSAUs together through ring-in and ring-out ports.