DIAMETER Protocol in IMS Network Architecture Notes

DIAMETER Protocol in IMS Network Architecture

Introduction

• DIAMETER is a next-generation protocol in IP Multimedia Subsystem (IMS) architecture and LTE networks.
• It provides higher data rates, increased throughput, and AAA (Authentication, Authorization, and Accounting) services.
• Developed by the Internet Engineering Task Force (IETF) and Third Generation Partnership Project (3GPP).
• DIAMETER evolved from the RADIUS protocol, offering flexibility for new access features.
• It operates on both SCTP and TCP using port 3868 for reliable communication between diameter nodes.
• Each message received by a DIAMETER node is acknowledged with a positive or negative answer message.
• Supports interfaces like s6a, Gx, Gy, Gz, Sd, Rf, and Ro, extending attributes support, security, network-access servers accounting, and resource management.

DIAMETER Protocol

Diameter Client and Server

• DIAMETER can act as both a client and a server in a peer-to-peer architecture.
• A DIAMETER node receiving a request acts as a client (e.g., a network access server).
• After obtaining user credentials, the client node sends an access request to a DIAMETER server node.
• The server responds with user privileges based on the request information.

Agent Support

• Relay agents: Forward DIAMETER request and answer messages based on Attribute Value Pairs (AVPs) related to routing. They aggregate messages from different realms, reducing server configuration burdens.
• Proxy agents: Make policy decisions and modify message contents to provision network resources. They can reject or originate messages if policies are violated, requiring understanding of message contents.
• Redirect agents: Act as centralized repositories for all DIAMETER nodes, aiding servers that cannot maintain routing lists locally. They handle different message types.
• Translation agents: Convert messages between different AAA protocols, useful for integrating user databases from different domains and providing backward compatibility during migration.

DIAMETER vs RADIUS

• DIAMETER provides additional features and flexibility in offering AAA services compared to RADIUS.

Handling of Errors

• DIAMETER nodes handle application errors and protocol errors.
• Application errors indicate issues within the protocol itself.
• Nodes check the result code AVP to proceed with message processing.
• Result codes provide status information:
  • 1XXX: More information needed to grant the service.
  • 2XXX: Request processed with no errors.
  • 3XXX: Protocol error detected; messages redirected to an alternate peer.
  • 4XXX: Service cannot be processed due to a transient failure.
  • 5XXX: Permanent failure; service request completely denied.

Implementation

• DIAMETER is implemented in LTE/4G networks above the SCTP/TCP layer.
• It provides communication between different entities in the LTE architecture.
• The DIAMETER protocol sits between the application interface and other DIAMETER peers to provide AAA services.
• Monitoring processes maintain messages in a queue for future processing as part of the DIAMETER protocol.
• Gx interface elements are mapped onto attribute value pairs (AVPs) in the call flow.

Results

• The implementation uses a Linux machine with RHEL 7.1.
• Results are verified using Wireshark traces, a packet analyzer for network troubleshooting, analysis, and protocol development.
• Wireshark captures all traffic visible on a particular interface.
• Real-time working of the Gx interface DIAMETER is observed with 12k TPS (Transactions per second) calls, each lasting 30 seconds.

Configuration Information

• Interface: Gx
• Timers:
  • Auth Time Out: $400$
  • Life Time out: $200$
  • Grace Time out: $100$
• AT Timers:
  • NOACTIVITYTIMER: $5$
  • ACTIVITYRETRYCOUNT: $2$
  • ACTIVITYRESPONSETIMEOUT: $2$
• Transport: SCTP on DIAMETER
• Load: $72k$ TPS for 12 Hours

Load Run Information

• Duration: 12 hours
• Simulator: Gx Simulator
• Call Rate: Burst size of 300 messages every 10 milliseconds from one client to four servers
• Interface: GX on Diameter
• Load: $72k$ TPS

Memory Utilization

• Resident and Virtual memory utilization is measured for a load of $72k$ TPS over 12 hours.

CPU Utilization

• System CPU utilization by IWF (SUT) is measured for a load of $500$ TPS over 2 hours, with maximum CPU utilization below $30$.

Active Sessions

• The number of active sessions is measured for a load of $72k$ TPS over 12 hours, with a maximum of $3900$ sessions handled.

Conclusion

• DIAMETER agents (e.g., relay, proxy) provide flexibility in message sending and receiving with proper result codes.
• DIAMETER nodes offer Authentication, Authorization, and Accounting services with error handling.
• The protocol provides high throughput and data rates in both service and control planes.
• Reference points between entities in IMS architecture exchange roaming details, accounting information, and user credentials.
• Interfaces like s6a, Gx, and Gy use DIAMETER for client notification and subscription purposes via defined attributes.
• Performance test results demonstrate DIAMETER's capability to handle messages under high load conditions, optimize memory utilization, and provide AAA services efficiently.