Selection and connection scheme of access layer switch and aggregation layer switch

When selecting a switch, we need to consider the backplane bandwidth and packet forwarding rate (port throughput) of the switch. The calculation method of backplane bandwidth is port number * port speed * 2=backplane bandwidth, that is, a gigabit switch with 24 ports has a backplane bandwidth of 48Gbps.

The second thing to consider is the packet forwarding rate, also known as the port throughput. The higher the throughput, the stronger the switch's ability to forward data. This is proportional to the number of ports and the transmission rate of the switch. The packet forwarding rate of one gigabit port is 1.488 Mpps, and the packet forwarding rate of one gigabit port is 0.1488 Mpps.

To sum up the above two factors, when selecting switches, we need to select switches with corresponding parameters according to the end use. We can take the digital monitoring system as an example. At present, the network adopts the dynamic coding mode, and the peak value of the 720P network camera may exceed the 4M bandwidth. Therefore, a camera needs a bandwidth of 4M. In addition, the actual bandwidth of the switch is 50% - 70% of the theoretical value, so the actual bandwidth of a 100M port is 50M-70M. Therefore, a 100M access switch is recommended to access 12 cameras.

After talking about the access layer switch, let's look at the lower aggregation layer switch. Compared with the access layer switch, the aggregation layer switch has stronger performance, higher port rate, fewer ports, and higher packet forwarding rate. Convergence layer switch is the convergence point of multiple access layer switches, which is used to unify the access node's exit, and also for forwarding and routing. It must be able to handle all traffic from the access layer devices and provide uplink to the core layer.

Next, let's learn about the connection scheme between the lower convergence layer switch and the access layer switch. Taking the interconnection between the gigabit switch and the 100M switch as an example, we can connect the upstream port of the 100M switch to the downstream port of the gigabit switch. At this time, we need to consider what products are more appropriate for interconnection? Generally, the access layer switch is closer to the user end, so sometimes it is relatively far away from the convergence layer switch. At this time, we can use gigabit multimode optical modules or gigabit single-mode optical modules with optical fiber jumpers.

The transmission distance of the gigabit multimode optical module is 550 meters, which needs to be connected to the multimode OM2 optical fiber jumper for use. The transmission distance of the gigabit single-mode optical module starts at 2 kilometers, and can be transmitted to 160 kilometers at most. We can choose the corresponding products according to the actual needs.