Cisco ASR 5000 Series - Page 678

Serving GPRS Support Node (SGSN) Overview
▀ Features and Functionality - Basic
▄ Cisco ASR 5000 Series Product Overview
OL-22938-02
Figure 165. SGSN NPU FastPath
320 Gig switch
Iu Gn
(Iu)
PSC1
PSC2
1
2
CPU
CPU CPU
CPU
CPU
3
(Gn)
PSC3
NPUNPU
CPU
NPU
LC
17
LC
33
LC
19
LC
35
CPU Path
GTP-C/RANAP
GTP-U
FastPath is established when both ends of a tunnel are available. Two FastPath flows are established, one for the uplink
and one for the downlink direction for a given PDP context. FastPath will temporarily go down or be disengaged so that
packets temporarily do not move through FastPath when either an Intra-SGSN RAU or an Iu-Connection Release
occurs.
If FastPath cannot be established, the NPU forwards the GTP-U packets to a CPU for processing and they are processed
like all other packets.
FastPath can not be established for subscriber PDP sessions if:
Traffic Policing & Shaping is enabled.
Subscriber Monitoring is enabled.
Lawful Intercept (LI) is enabled,
IP Source Violation Checks are enabled.
GTP-v0 tunnel is established with an GGSN.
For NPU fast path configuration, refer to Enabling NPU Fast Path for GTP-U Processing section of ―Service
Configuration Procedures‖ chapter of SGSN Administration Guide.