3G Direct Tunnel
3G Direct Tunnel
3G Direct Tunnel
OVERVIEW
Non-3GDT
Iu-C GTP-C
MS SGSN
RNC GGSN
Iu-U GTP-U
3GDT
Iu-C GTP-C
MS SGSN
RNC GGSN
Iu-U GTP-U
The main task of the SGSN is to provide the GGSN and the RNC with
the corresponding data.
The 3GDT feature enables a payload boost in the WCDMA packet Core Network
(CN) and is beneficial when the payload exceeds the SGSN limits. In other word,
3GDT bypasses the SGSN so that the RNC could connect directly to the GGSN
eliminating the bottleneck at the SGSN. Typically, this is expected to happen
when Turbo-3G High Speed Packet Access (HSPA) becomes a mass-market
service.
TRAFFIC CASE
The following conditions must be met in order to set up a direct tunnel between
the GGSN and RNC:
• The MS must be attached in the Universal Mobile Telecommunications
System (UMTS) Radio Access Technology (RAT) domain.
• The license-controlled 3GDT feature must be activated.
• The MS must be attached within a home Public Land Mobile Network
(PLMN), that is, the MS may not be a visiting subscriber.
• The subscriber profile may not contain a CAMEL Subscription Information
data.
• The MS must be attached through an RNC configured as 3GDT compliant.
• The 3GDT prefix in the subscribed APN received in the subscription data for
the MS, from the HLR, indicates if 3GDT is applicable for a particular APN and
MS. The 3GDT prefix in the APN entry, in the DNS, indicates if 3GDT is
applicable for a particular APN and GGSN.
• The GGSN must support GTP protocol version 1.
The APN must indicate that both the MS and the GGSN are candidates for 3GDT,
for that particular APN. In the PDP context activation procedure, the following
messages are effected by 3GDT
RNC UP TEID
RESTRICTIONS
1) In roaming case
3GDT Restrictions
3GDT has restrictions in implementation according to 3GPP 23.060 v.7.4.0
chapter 15.6. Direct Tunnel shall not be used in following traffic cases:
IMPLEMENTATION IN SGSN R8
Implementation in SGSN R8
The following parameters are related to 3GDT:
• 3gdt
• DirectTunnel
• SGSN_3gdt_prefix
Network Impact
The added signaling will decrease the SAU capacity in the SGSN
with at most 10%.
Signaling will increase with the use of 3GDT. For example, in PDP context
activation, GTP messages is modified to accommodate sending and updating
RNC TEID and GGSN TEID across the GPRS backbone. Additional GTP
procedures is also put to support 3GDT. Limitiation in SGSN regarding payload
is no longer applicable for the DT payload since it bypasses the SGSN.
Since 3GDT impacts both payload and signaling, on network as well as on node
level, it is strongly recommended to perform a network analysis of the specific
operator traffic case. This is done in order to determine optional configurations
and node sizes. The analysis may also involve SGSN Pool and HSPA. For
dimensioning of the SGSN, consider the payload and signaling described below.
The total payload through the SGSN is the sum of the following payloads:
• The roaming WCDMA traffic payload.
• The GSM payload, for Dual Access SGSN.
• The non-roaming WCDMA payload for WCDMA users
configured for 3GDT OFF.