The Input/Output Module (IOM) is the line card in the Nokia 7750 SR responsible for data plane processing. Each IOM contains a forwarding engine and maintains a local copy of the Forwarding Information Base (FIB). When a packet arrives on a physical interface of a Media Dependent Adapter (MDA), it is passed to the parent IOM. The IOM's forwarding engine then performs the longest prefix match lookup against its local FIB to determine the packet's next hop and egress interface. This distributed architecture allows for high-performance, line-rate forwarding.

A. The Control Processing Module (CMP) is the control plane. It builds the routing tables but delegates the actual per-packet forwarding lookups to the IOMs.

B. The Media Dependent Adapter (MDA) provides the physical interfaces (ports). It handles Layer 1 and Layer 2 functions, passing packets to the IOM for Layer 3 processing.

C. The Switch Fabric (SF) is a high-speed backplane that transfers packets between IOMs after the forwarding decision has already been made by the ingress IOM.

1. Nokia 7750 Service Router OS Basic System Configuration Guide

Release 21.10.R1. In the "System Overview" chapter

the section on "IOMs" describes their role: "The IOMs provide the packet processing and forwarding capabilities of the router. Each IOM has a local forwarding table that is a copy of the active forwarding table."

2. Nokia 7750 Service Router Datasheet. The document describes the hardware architecture

stating that the IOMs are responsible for packet processing and forwarding functions

which inherently includes IP lookups.

3. Nokia

"Building a Smarter

More Automated

and Scalable IP Network with the 7750 SR-s

" White Paper

2019. This paper discusses the distributed hardware architecture

explaining that forwarding decisions are made on the line cards (IOMs) to achieve high scalability and performance. See section "A purpose-built hardware architecture".