Above Transport Layer,
The IP & Routing Networks Layer acts as The global navigation system of the Internet, deciding how every packet finds its way across millions of interconnected network. The primary roles within this category are as follows:

Network Operators:

Tier 1 Internet Network Operator

Operates a globally interconnected network that reaches other Tier 1 networks without purchasing IP transit.
Example: Lumen Technologies, Arelion, NTT Global IP Network

Tier 2 Internet Network Operator

Operates a regional or national network that exchanges traffic through peering and purchases transit from upstream providers.
Example: GTT Communications, RETN, KDDI

Tier 3 Internet Network(Access) Operator

Operates networks primarily providing Internet access to end users while purchasing upstream connectivity from higher-tier operators. 
Example: Comcast, Deutsche Telekom, NTT East

Content Network Operator

Operates an IP-based network infrastructure that interconnects content platforms, origin servers, caching systems, edge nodes, and end users for efficient content delivery.
Example: Cloudflare, Akamai, Alibaba

Cloud Network Operator

Operates large-scale networks connecting cloud computing infrastructure, regions, data centers, and customers across distributed environments.
Example: AWS, OVHcloud, Alibaba Cloud

Data Center Network Operator

Operates internal and interconnected networks within data centers, enabling connectivity among servers, systems, facilities, and external networks.
Example: Equinix, Digital Realty, NTT Global Data Centers

Mobile Network Operator

Operates cellular networks providing wireless connectivity and Internet access to mobile subscribers through nationwide or regional infrastructure.
Example: AT&T, Orange, NTT DOCOMO

Enterprise / Community / Research & Education / Government Network Operator

Operates dedicated networks supporting organizational, community, academic, research, or governmental communications and Internet connectivity requirements.
Example: Internet2, GÉANT, SINET / NII

Interconnection & Routing Service Operators

IP Transit Provider

Provides Internet Protocol transit services, enabling customer networks to reach external destinations through its globally or regionally interconnected IP network.
Example: Lumen, Arelion, NTT Global IP Network

IXP Operator

Operates Internet Exchange Point infrastructure that enables participating networks to exchange Internet traffic directly through shared switching platforms.
Example: Equinix Internet Exchange, DE-CIX, JPNAP

Route Server Operator

Operates route servers at Internet Exchange Points, facilitating multilateral BGP route exchange among participating networks without requiring bilateral sessions.
Example: Equinix Internet Exchange, DE-CIX, JPNAP

GP Route Collector / Route Monitoring Operator

Collects BGP routing information from participating networks to provide visibility into Internet routing, topology, reachability, and routing changes.
Example: RouteViews, RIPE NCC RIS, WIDE Project