Flexi ISN 4.0 Commissioning,
Integration, and O&M
Flexi ISN and Core Network Overview
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Contents
Contents
Summary of changes .............................................................................5
1
Objectives ...............................................................................................6
2
2.1
GPRS/3G elements and interfaces .......................................................7
Exercise: review of GPRS/3G network.....................................................7
3
3.1
3.2
Tunnelling ...............................................................................................9
Overview ..................................................................................................9
Exercise: review GTP tunnelling ..............................................................9
4
4.1
4.2
4.3
Role of Flexi ISN ...................................................................................12
Flexi ISN in GPRS/3G network ..............................................................12
Flexi ISN ecosystem...............................................................................13
Flexi ISN in multi-access system............................................................15
5
5.1
5.1.1
5.1.2
5.1.3
5.1.4
5.1.5
5.1.8
5.1.9
5.1.10
5.2
5.3
5.4
5.5
Functionality and features...................................................................16
Supported interfaces ..............................................................................16
Gn and Gp interfaces .............................................................................17
Gi interface .............................................................................................17
Gi interface with NAS .............................................................................17
Gx interface ............................................................................................17
Ga/Gz post-paid charging interface with NSN Charge@Once
Mediate (CMD) .......................................................................................18
Bp for CDR retrieval with FTP ................................................................18
Prepaid charging interface (Gy) with NSN Unified Charging
Suite and Online Service Controller (UCS/OSC) ...................................18
Interface with NSN Profile Server (NPS)................................................18
Network management system interface .................................................19
Lawful Interception Interface ..................................................................19
Scalability and performance ...................................................................19
Enhanced features .................................................................................20
Pre-3GPP Rel 7 Direct Tunnel and I-HSPA ...........................................20
I-HSPA Architecture and Interfaces .......................................................22
6
6.1
6.2
6.2.1
6.2.2
6.2.3
6.2.4
Flexi ISN high availability basics ........................................................24
Availability ..............................................................................................24
Redundancy models in Flexi ISN ...........................................................24
Active/standby ........................................................................................25
N+1 redundancy.....................................................................................25
Dual roles ...............................................................................................26
Other HA mechanisms ...........................................................................28
5.1.6
5.1.7
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© Nokia Siemens Networks
Summary of changes
Summary of changes

Update figure 1, 2, 6

Add new figure 5, 8

Remove Go interface matter

Remove Centralised Network Services Manager (CNSM) matter

Add Gx interface matter in sub-chapter Supported Interfaces

Add Pre-3GPP Rel.7 Direct Tunnel and I-HSPA
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1 Objectives
After this training module the participant can:

Describe the basic functionality of the GPRS / 3G network
elements and interfaces especially in the IP core network.

Review the concept of tunnelling.

Explain the role and use cases of Flexi ISN in NSN solutions.

Explain the basic functionality and features of NSN Flexi ISN.

Explain the basic high availability functionality of NSN Flexi ISN
This training module is a high level theory overview of the topics and
does not require access to any laboratory equipment.
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GPRS/3G elements and interfaces
2
GPRS/3G elements and interfaces
2.1
Exercise: review of GPRS/3G network
Figure 1 shows the generic structure of GPRS and 3G networks from
core network point of view. With your trainer, review the relevant
elements and the various tasks they are performing.
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Figure 1.
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© Nokia Siemens Networks
GPRS/3G elements and interfaces
Tunnelling
3
Tunnelling
3.1
Overview
IP tunnelling in general means encapsulating IP packets in other IP
packets. Examples of protocols used for the purpose are Generic
Routing Encapsulation (GRE) and IP in IP.
Usually encapsulation is used as a mechanism to alter the IP routing for
a datagram by delivering it to an intermediate destination that would
otherwise not be selected based on the IP destination address field in
the original IP header.
3.2
Exercise: review GTP tunnelling
Tunnelling is a technique which is used for different purposes in packet
switched networks. There are several tunnelling protocols to choose
from. GPRS Tunnelling Protocol (GTP) is used in GPRS and 3G. The
basic concept of GTP is shown in Figure 2. Discuss with you trainer the
following questions:
1.
Why is tunnelling required in GPRS/3G core?
_____________________________________________________
_____________________________________________________
2.
Why is GTP used instead of other tunnelling protocols?
_____________________________________________________
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_____________________________________________________
Figure 2.
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© Nokia Siemens Networks
Tunnelling in GPRS/3G network with GTP
Tunnelling
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4
Role of Flexi ISN
4.1
Flexi ISN in GPRS/3G network
In GPRS/3G network the GPRS Gateway Support Node (GGSN)
provides access termination to the Access Point for the mobile users.
By doing this, it serves the PDP Contexts of the users. NSN Flexi ISN is
capable of doing this, as well as the other tasks a GGSN should perform
(Figure 3).
Figure 3.
Flexi ISN in GPRS/3G network
The user session is established to Flexi ISN by one of the SGSN
elements via the Gn interface. Flexi ISN handles each session with its
relevant identifiers, and makes sure the user packets are routed out from
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Role of Flexi ISN
the core network via one of its Gi interfaces. In similar way, the downlink
data arriving from Gi is identified belonging to the respective mobile
user, and handled properly back towards the mobile. Thus, Flexi ISN is
routing user traffic between the core (Gn) and external networks (Gi).
While switching packets, the Flexi ISN investigates them against certain
security rules to identify potential attacks or otherwise unwanted actions
and treats these accordingly.
To provide proper service for timing- or bandwidth-sensitive applications,
the Flexi ISN can classify them and give priority to some of them. This
is especially important for multimedia applications, and therefore Flexi
ISN has capability to apply policy management for IP Multimedia
sessions, as specified by 3GPP.
More precise description of the role of Flexi ISN will be given later on in
the chapter 5: Functionality and features, together with the list with its
supported integration interfaces.
4.2
Flexi ISN ecosystem
NSN Flexi ISN can extend the 3GPP model of routing, subscription, and
charging functions of the mobile network (Figure 4). Many of the
extensions are involved with the GGSN function. NSN Flexi ISN
(Intelligent Service Node) has native support for these extensions, also
called Service Awareness. Simultaneously, the ISN supports 3GPP
defined GGSN functionality.
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Figure 4.
Flexi ISN ecosystem
The Service Aware analysis functionality deals with user traffic arriving
from 2G or 3G networks. The ISN provides Service Aware Connectivity,
which includes both Service Connectivity and Traffic Analysis. The ISN
interfaces with other elements that support charging functionality, and
service and subscription management functionality. Flexi ISN can be
used as stand-alone element providing both GGSN and traffic analysis
functionality, or used together connected to another GGSN or ISN
providing just one of these functions.
The service connectivity extends the 3GPP model with internal service
differentiation which makes it possible to create very user-friendly
service environments. From user viewpoint this enables single-click
access to all services.
Charging functionality of the Flexi ISN ecosystem supports both offline
and online charging and rating. It interfaces with the billing system, and
optionally with external balance handling systems.
Service and subscription management functionality is necessary for the
successful delivery of services. The system implements a dedicated
repository for subscriber data and subscription attributes. It provides an
open interface to the operators’ existing provisioning systems and a
single interface to all subscription-related data.
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Role of Flexi ISN
4.3
Flexi ISN in multi-access system
Flexi ISN supports a generic access method, using connection to a
Network Access Server (NAS). The access network can be a WLAN
network, for example. Flexi ISN itself does not make difference on what
is the access method, since the NAS always provides the necessary
session parameters for each subscriber (Figure 5).
Figure 5.
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Flexi ISN in multi-access system
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5
Functionality and features
5.1
Supported interfaces
The supported integration interfaces to other network elements are
shown in Figure 6. A short description of each of them is given next.
Figure 6.
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© Nokia Siemens Networks
Supported external interfaces in Flexi ISN 4.0
Functionality and features
5.1.1
Gn and Gp interfaces
The Flexi ISN communicates with the SGSN through the Gn interface.
The communication is based on the GPRS Tunnelling Protocol (GTP).
To have a secure connection through the access network, each
subscriber is granted one GTP tunnel during the PDP context activation.
The GTP tunnel is terminated at the Flexi ISN. Very similar to the Gn
interface is the Gp interface. All the traffic through it goes through a
Border Gateway (BG), which has the necessary firewalls between the
different operators IP backbone networks. Like the Gn interface, the Gp
interface is based on GTP.
5.1.2
Gi interface
The Gi interface is a 3GPP-specified interface between the 3G/GPRS
and the external data network, for example, the Internet. For the external
network, the Flexi ISN appears as a normal IP router. For
interconnection with the external data network, Flexi ISN supports
several tunnelling, routing, and addressing options. In addition, the Flexi
ISN sends subscriber-related information with RADIUS messaging
during the PDP context creation process.
Gi interface uses multiple protocols. For example, traffic from UE can be
plain IPv4 or IPv6, or it can be encapsulated in GRE, IPIP, or L2TP
tunnels. Gi interface can also carry several types of signalling traffic,
such as DHCP, RADIUS accounting, and RADIUS authentication.
5.1.3
Gi interface with NAS
With the Network Access Service (NAS) interface, virtual PDP contexts
are created in the Flexi ISN for access methods not based on GTP. The
RADIUS protocol is used for authentication and signalling. User plane
traffic is carried in plain IP, or GRE and IP-in-IP tunnels. This interface
makes the Flexi ISN ready for multiple deployment options and also part
of the NSN multi-access solution.
5.1.4
Gx interface
The Gx interface effectively replaces Go interface for policy control. It is
used for controlling e.g. the quality of service of end-user sessions and
for implementing “fair usage” policy control. The Gx interface is based on
DCCA protocol. The Policy Control Rule Function network element can
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be implemented as part of IP Multimedia Subsystem (PCS 5000). It
could also be implemented by an OCS.
5.1.5
Ga/Gz post-paid charging interface with NSN Charge@Once
Mediate (CMD)
Post-paid charging is implemented by generating Charging Data
Records (CDRs). The CDR is transferred for further processing and
aggregation to the CG through the standard GTP’ interface. The content
of the CDR is based on the 3GPP standard. The G-CDR and SA-CDR
format is NSN proprietary.
Local CDR Adapter (LCA) is a network element used for converting the
CDRs sent by FlexiISN to a format supported by IPS (Intelligent Packet
Solution). LCA converts the Flexi ISN TLV CDR format into the ASN.1
variants supported by IPS. The IPS (Intelligent Packed Solution) CDR
Compatibility feature is meant only for customers migrating from IPS.
5.1.6
Bp for CDR retrieval with FTP
Charging information can be retrieved from Flexi ISN with FPT protocol,
using Bp interface.
5.1.7
Prepaid charging interface (Gy) with NSN Unified Charging Suite
and Online Service Controller (UCS/OSC)
For exchanging information related to prepaid charging, Flexi ISN
supports both RADIUS and Diameter. RADIUS accounting is supported
for backward compatibility reasons. NSN-specific extensions are used.
The Diameter implementation is based on IETF RFC 4006. Multiple
interface options and optimization possibilities exist. This interface
allows integration with third party Online Charging Server (OCS)
systems.
5.1.8
Interface with NSN Profile Server (NPS)
The Flexi ISN offers flexible and dynamic provisioning of services. The
Flexi ISN can optionally retrieve user profile information from the NPS
using Lightweight Directory Access Protocol (LDAP). Alternatively, the
user profile can be fetched from a RADIUS server as well by using
vendor-specific attributes. The interface can be integrated to non-NSN
equivalent functions.
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Functionality and features
5.1.9
Network management system interface
The Simple Network Management Protocol (SNMP) is the standard
interface for the Network Management System (NMS). NSN NetAct also
uses an enhanced SNMP (NE3S) as the NMS interface. The SNMP is
used for alarms and statistics. Configuration can be done through the
Web-based Voyager or CLI.
5.1.10
Lawful Interception Interface
Lawful Interception (LI) is required for providing the authorities the
possibility to monitor packet data traffic. The Flexi ISN duplicates the
data traffic of the end-user that is under monitoring and forwards the
data traffic to the Lawful Interception Gateway (LIG). The LI interface is
based on the NSN proprietary LIPv1 (Lawful Interception Protocol).
5.2
Scalability and performance
Flexi ISN uses modular, multi CPU Flexi Server hardware (Figure 7) for
excellent performance and scalability.
Figure 7.
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Flexi Server hardware used in Flexi ISN
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In the largest configuration the Flexi ISN supports up to 1000 Access
Points, with 1 million PDP Contexts and 1 Gbit/s throughput. In dual
chassis configuration, the throughput is increased to 5 Gbit/s and the
number of PDP contexts to 2 million.
It uses internal load sharing for performance-intensive tasks, and IPSO
operating system for the best possible IP routing performance.
5.3
Enhanced features
Flexi ISN has good selection of tunnelling options for Gi routing. For
those environments where tunnelling is not feasible, Flexi ISN supports
multiple routing instances to create dedicated Gi service domains. VLAN
trunks are supported for effective use of hardware network interfaces.
For future expansion with generic access technologies, Flexi ISN
provides a gateway via its NAS interface. For creating sustainable
service environments, Flexi ISN includes NSN Service Awareness
feature with versatile traffic analysis, user profiling, and charging options.
High Speed Downlink Packet Access (HSDPA) for increasing packet
data throughput. HDSPA allows the use of bit rates up to 16 Mbit/s for
downlink (otherwise up to 8 Mbit/s). Moreover, FlexiISN 3.2 also has
support for Internet High Speed Packet Access (I-HSPA) for even higher
data rates. This also means support for direct tunnel from Node-B to
FlexiISN for user plane traffic, thus by-passing SGSN.
Flexi ISN has all essential security features built-in, and offers a wide
selection of configurable security options.
5.4
Pre-3GPP Rel 7 Direct Tunnel and I-HSPA
Before 3GPP Release 7 the gateway is not aware of the Direct Tunnel /
I-HSPA access.
The Direct Tunnel approach often referred to as “One Tunnel”, offers a
3GPP Rel-7 solution which can be deployed to enhance the scalability of
the Universal Mobile Telecommunications System (UMTS) system
architecture without impacting the User Equipments (UEs).
In the traditional PS Core architecture the user plane goes through all
network elements, including SGSN (Figure 8).
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Functionality and features
In Direct Tunnel architecture, the Serving GPRS Support Node (SGSN)
controls the mobility, authentication and control plane accounting and
decides whether one or two tunnels are needed on a context-per-context
basis. Contrary to the normal “Two Tunnel” approach, Direct Tunnel
uses direct tunneling of user plane traffic data between Radio Network
Controller (RNC) and Flexi ISN bypassing the SGSN, while signaling
data are still routed through SGSN (Figure 8). In the I-HSPA architecture
the RNC HSPA functionality is integrated into BTS/Node-B (Figure 8).
For more information regarding the introduction to Direct Tunnel
approach and its functionality see:
• 3GPP One Tunnel Functional description; (Release 7).
• 3GPP Feasibility Study for Transport and Control Separation in the PS CN
Domain (Release 4).
• 3GPP Service description.
Figure 8.Pre-3GPP Rel 7 Direct Tunnel and I-HSPA
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5.5
I-HSPA Architecture and Interfaces
I-HSPA is a standard 3GPP packet core with a simplified flat architecture
network.
The RNC HSPA functionality is integrated into BTS/Node-B, and the
user plane can bypass SGSN (Direct tunnel).
Figure 9. I-HSPA Architecture
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Functionality and features
I-HSPA supports 3GPP standard Uu Air interface Rel.5/6, no changes to
Rel5/6 Terminals.
3GPP Rel-7 standardizes the flat architecture for both RAN and PaCo:
•
•
•
Flat PaCo: Direct Tunnel defined in SA WG2, for removing SGSN
from the U-plane.
Flat RAN: HSPA Evolution TR25.999 defines BTS collapsed RNC
(Without specification changes).
Agreement on allowing security in NodeB (S3-060654).
Support for CS calls and Multi RAB calls are handled with “CS enabling
Handover” as being described in TR 25.999. (Without specification changes).
Figure 10. I-HSPA Interfaces
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6
Flexi ISN high availability basics
6.1
Availability
One of the main design goals for Flexi ISN was High availability.
Availability can be understood as uninterrupted functioning of the
system. In other words, a system is available if there are no observed
failures.
Availability can be improved with redundancy. That is, multiple units of
hardware and software. To make use of them, one or more of the
following are required:
6.2
-
Monitoring of state information
-
Exchange of state data
-
Switchover when there is a failure
-
Selection of redundancy models
Redundancy models in Flexi ISN
In this and the following chapters we will take a high-level look into the
redundancy models implemented in the Flexi ISN. The basic categories
of the models are:
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1.
Active/standby
2.
N+1 redundancy
3.
Dual roles
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Flexi ISN high availability basics
6.2.1
Active/standby
In the active/standby redundancy model (Figure 11) there is one active
unit performing a specific task. There is also one standby unit which is
passive. This standby unit only stores the required state information,
which it gets from the active one at specific intervals.
If the active unit fails, the standby unit replaces the active one, and starts
to perform its functions. This is called switchover. Flexi ISN uses this
model for management and disk storage
Figure 11.
6.2.2
Active/standby redundancy model
N+1 redundancy
In N+1 redundancy model (Figure 12) there are several (N) active units.
These active units are like those we had in the active/standby model.
Again, there is exactly one standby unit.
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Figure 12.
N+1 redundancy model
The difference to the active/standby model is that there are no dedicated
pairs of any units. Instead, the single standby unit can replace any of the
active ones. This redundancy model is used in Flexi ISN for the power
entry modules, for example.
6.2.3
Dual roles
The dual roles redundancy model is the most versatile one, and provides
other beneficial options, like unit load balancing. In this redundancy
model there are several active units for the same functionality (Figure
13).
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Flexi ISN high availability basics
Figure 13.
Dual roles redundancy model
The service or application related data is kept inside the units in atomic
blocks. These blocks are formed in active/standby block pairs, and they
are distributed among all the active units. The active and standby blocks
of the same pair are never kept inside the same unit.
When all units are working normally, the standby blocks get the relevant
state information from the active block of the pair. Thus a single unit
might retrieve state information from several other units if the standby
blocks in its memory have their active counterparts in those other units.
If any active unit fails, the lost active blocks will always be recovered by
switching over to their standby counterparts in the other available units.
This redundancy model is used for PDP contexts in Flexi ISN. For each
PDP context, the data for its subscription, traffic and charging counters,
and routing information are kept in the atomic blocks as described here.
At the same time the system can vary the number of active blocks
created in each unit, to achieve even distribution of CPU load and
memory consumption.
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6.2.4
Other HA mechanisms
As an IP router, Flexi ISN supports dynamic routing protocols for
recovering failed paths in the network, and to advertise its own state to
the neighbouring IP routers.
For static routing environments, there is support for L2 interface
redundancy using active/standby pairs. The two interfaces can share an
IP address, and if the active interface fails, the standby interface will
appear in the network as soon as the neighbouring L2 switch recognises
the state change.
To guarantee reliable cooling of the Flexi ISN system, there are multiple
cooling fans. Any one of the fans can fail without causing a system
failure.
Flexi ISN system consists of multiple computing units, which need to
exchange a lot of information when the system is running. This internal
communication buses consist of redundant connection paths, in
active/standby fashion.
Most of the external interfaces support redundancy. For example the
NAS interface, DNS queries, DHCP queries, RADIUS authentication and
accounting, OCS, NSM/NPS, GRE/IPIP Gi tunnels, and the Charging
Gateways can all be configured to use at least one backup connection.
Finally, in case of a complete Flexi ISN failure – which is very unlikely –
the SGSN can still use the DNS round robin to activate PDP contexts in
another Flexi ISN – in similar way as has been possible for single CPU
GGSN elements.
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