East-West Interfaces - Horizontal OSS Coordination
🎯 Learning Objective: Understand East-West interfaces in very simple terms. These interfaces are used when one OSS system talks directly to another OSS system at the same level so that different network domains can work together.
The Three OSS Communication Directions
Northbound (↑)
OSS → BSS / Portals / Analytics
Going upward
OSS / Orchestration Layer
Southbound (↓)
OSS → Network Devices
Going downward
Peer OSS Domains • Orchestrators • Controllers
What Are East-West Interfaces?
East-West interfaces are used when one OSS system needs to talk to another OSS system directly. Both systems are usually at the same level, and they exchange information so that one end-to-end telecom service can be delivered properly.
Key Characteristics
- Direction: Sideways or horizontal
- Purpose: Help different OSS systems coordinate
- Common style: Peer-to-peer communication
- Simple example: RAN system talks to Transport system
Why It Matters
- One telecom service usually touches many domains
- Different OSS systems must share updates
- Automation needs systems to work together
- Very important in 5G and cloud-native networks
Why East-West Interfaces Matter
Multi-Domain Service Delivery
A telecom service may need RAN, transport, and core systems to work together. East-West communication helps them coordinate.
Fault and Performance Sharing
If one system detects a problem, it can inform another system so both understand the service impact.
Inventory Alignment
If one system changes a resource or service record, another system may also need that update.
Automation
One OSS system can trigger another OSS system automatically when a condition is met.
Distributed Architectures
Modern telecom platforms are made of many specialized systems, so coordination between them becomes essential.
5G Services
5G services often span multiple domains, so sideways coordination between systems becomes very important.
Common East-West Integration Scenarios
1. Assurance and Orchestration
One system detects a problem. It informs another system. The second system takes action to fix or improve the service.
2. Inventory Synchronization
When one OSS system updates equipment or service data, another OSS system may need the same update.
3. O-RAN Coordination
In O-RAN, different functions exchange management, policy, and control information through standard interfaces.
Common O-RAN interfaces include: O1 for management, O2 for cloud and infrastructure management, A1 for policy guidance, and E2 for near-real-time RAN control.
4. 5G Slice Coordination
To build one 5G slice, different domain systems must coordinate resources across the network.
Common East-West Protocols and Technologies
| Technology | Use Case | Simple Example |
|---|---|---|
| REST APIs | One system asks another system for data or action | Orchestrator checks inventory status |
| Kafka / Event Bus | One event is shared with many systems | Fault event sent to multiple OSS tools |
| gRPC | Fast communication between cloud-native services | Microservices exchange data quickly |
| TMF Open APIs | Standardized OSS integration | Service and inventory systems exchange information |
| Message Queues | Reliable asynchronous communication | Workflow messages passed step by step |
| Service Mesh | Communication inside cloud-native platforms | Microservices communicate securely inside Kubernetes |
| O-RAN Interfaces | Management, orchestration, policy, and control inside O-RAN | O1, O2, A1, and E2 |
Why East-West Integration Is Challenging
Different Vendors
Not all vendors use the same APIs, models, or workflows.
Keeping Data Consistent
Different domains must see the same service, topology, and inventory information.
Timing Issues
Some actions must happen quickly and in the right order.
Troubleshooting
When many systems are involved, it becomes harder to find the exact root cause.
Standards Keep Changing
Telecom standards continue to evolve, so designs must stay flexible.
Security
Systems in different domains must trust each other and exchange data safely.
Real-World Example: 5G Network Slice Orchestration
Scenario: An operator wants to create a special 5G service with low latency.
1. Northbound
The business side sends the service request to OSS.
2. East-West
RAN, transport, and core OSS systems coordinate with each other.
3. Southbound
Configurations are sent to devices and network functions.
4. Northbound
The result is reported back to the business side.
• RAN system prepares radio resources
• Transport system prepares bandwidth and path
• Core system prepares the required network functions
• All these systems must coordinate so the service works end to end
This is a simple example of East-West coordination.
O-RAN and East-West Coordination
O-RAN (Open Radio Access Network) is a good example of distributed telecom architecture. Different functions in O-RAN exchange management, orchestration, policy, and control information through standard interfaces.
O-RAN uses standard interfaces such as O1, O2, A1, and E2 for internal coordination between management, control, and RAN functions.
Main O-RAN Interfaces
- O1 Interface: Management and monitoring between SMO and O-RAN nodes such as O-CU, O-DU, and O-RU.
- O2 Interface: Management between SMO and O-Cloud infrastructure.
- A1 Interface: Policy guidance between Non-RT RIC and Near-RT RIC.
- E2 Interface: Near-real-time control and telemetry between Near-RT RIC and RAN nodes such as O-CU and O-DU.
How OSS Integrates with O-RAN
- OSS → SMO: OSS often treats SMO as the main RAN domain management and orchestration point.
- SMO → OSS: SMO can provide alarms, performance data, and domain management functions upward to OSS workflows.
- Inside O-RAN: Detailed coordination between SMO, RIC functions, O-Cloud, and RAN nodes happens through O-RAN standard interfaces.
- Simple view: OSS usually integrates mainly with SMO rather than separately with every internal O-RAN component.
↓
SMO / Non-RT RIC uses the A1 interface to send policy guidance to the Near-RT RIC
↓
Near-RT RIC uses the E2 interface to interact with O-CU/O-DU for near-real-time control
↓
O-CU/O-DU apply changes to the RAN according to those policies and control loops
In many designs, OSS mainly talks to SMO. The detailed coordination happens inside the O-RAN domain over standard interfaces.
When working with O-RAN, OSS typically integrates with the SMO (Service Management and Orchestration) function. SMO acts as the main RAN domain management and orchestration point, while detailed internal coordination is handled through interfaces such as O1, O2, A1, and E2.
Common Questions
Q1. What is an East-West interface in OSS?
It is communication between two peer OSS systems at the same level.
Q2. How is East-West different from Northbound and Southbound?
Northbound goes upward, Southbound goes downward, and East-West goes sideways between peer systems.
Q3. Why is East-West important?
Because one telecom service usually needs more than one OSS system to work together.
Q4. How does O-RAN use internal coordination interfaces?
O-RAN uses interfaces such as O1, O2, A1, and E2 for management, orchestration, policy guidance, and control between internal O-RAN functions.
Q5. How does OSS integrate with O-RAN?
OSS typically integrates mainly with the SMO function, which acts as the main RAN domain management and orchestration point.
Q6. What are the main O-RAN interfaces?
O1 is used for management, O2 for cloud and infrastructure management, A1 for policy guidance, and E2 for near-real-time control and telemetry.
📌 Key Takeaways:
- East-West means sideways communication between peer OSS systems
- Northbound means communication upward to business or upper-layer systems
- Southbound means communication downward to devices or network functions
- Main idea is coordination between domains
- Used in 5G slicing, automation, inventory sync, and distributed OSS
- Not one protocol but a communication pattern
- O-RAN uses internal standard interfaces such as O1, O2, A1, and E2 for management, orchestration, policy guidance, and control.
- OSS integrates with O-RAN via SMO - treat SMO as the main RAN domain management and orchestration point.