Thursday, November 26, 2009

UMTS Layers, Interfaces, Protocols - Iub interface.

Just to remind - Iub interface connects Node B (RBS) and RNC.
As for general view (general info) in this interface one can describe layers (i.e. Radio and Transport Network Layer), planes (i.e. user and control plane) and some protocols within those planes.

Figure 1. Iub Control Plane - ATM transport.

NBAP - Node Application Part
SSCF-UNI - Service Specific Coordination Function for support of signaling at the User Network Interface [ITU-T 2130]
SSCOP - Service Specific Connection Oriented Protocol
AAL5 - ATM Adaptation Layer 5

Monday, November 23, 2009

Simplified UMTS network architecture

Figure 1 shows simplified UMTS network architecture.
Simplified UMTS network architecture
Figure 1. Simplified UMTS network architecture.

Note: Not all nodes and interfaces are included in this picture.

Abbreviations used in the picture:
RNC - Radio Network Controller
MSC - Mobile Switching Center
Ue - User Equipment
SGSN - Serving Gprs Support Node
PDN - Packet Data Network
PSTN - Public Switched Telephony Network

UMTS Layers, Interfaces, Protocols - General

Previous post was a short introduction for general information regarding layers, protocols, interfaces and planes.
In UMTS one can find all mentioned objects and divisions.

As for the layers the Figure 1 shows what layers are defined for UMTS.

UMTS network protocols layers
Figure 1. UMTS network protocols layers [1]

As mentioned in each layer may have its User and Control Plane. Each layer has dedicated protocol to work in proper plane. Detailed description of theses protocols will be placed in next posts.

General Layer, Plane and Protocol Model for interfaces in UTRAN
Figure 2. General Layer, Plane and Protocol Model for interfaces in UTRAN [2]

Signaling bearers for Transport Network User Plane and for Transport Network Control Plane may be different but may be the same. It is up to configuration if the same Signaling Bearers would be used [2]

Based on:
[1] UMTS System Telefonii Komórowej Trzeciej Generacji - J. Kołakowski, J. Cichocki. WKŁ 2006
[2]  3GPP TS 25.401

Saturday, November 21, 2009

Protocols, interfaces, User Plane and Control Plane

When two devices would like to communicate with each other they would use a defined protocol. Protocol is set of rules describing how those two devices can communicate in way that receiver would understand what sender “had in mind” while sending message. Protocol description is usually description of messages (signals) that can be sent and received, it is also description for particular procedures and functions.
Now, our two devices know “how to talk” to each other, but they need to be connected somehow. For this purpose an Interface would be defined. Interface would be generally another device, with or without dedicated software, that would allow connecting, inter-working and changing messages(signals) between our devices – connected using this interface.
Sometimes when connecting two devices using interface there is a need for two protocols. First protocol would allow first device to control how works the second one. This kind of protocol is part of control plane. Second protocol would send just raw data from one device to another. This would be a part of user plane.

User and Control Plane
Figure 1. User and Control Plane.
Often when two devices connected over the interface not one protocol would be used but set of protocol divided into layers. Each layer with its specific dedicated tasks.
Sample Layer Stack
Figure 2. Sample Layer Stack.
Important to mention that each layer may has its own user and control plane. What is control plane for one protocol can be (would be) user plane for protocol located below in stack.

 User and Control Plane used with Layers
Figure 3. User and Control Plane used with Layers