PDN Gateway Overview
Features and Functionality - Inline Service Support ▀
Cisco ASR 5x00 Packet Data Network Gateway Administration Guide ▄
75
maintained in a state table. Filtering decisions are based not only on rules but also on the connection state established by
prior packets on that connection. This enables to prevent a variety of DoS, DDoS, and other security violations. Once a
connection is torn down, or is timed out, its entry in the state table is discarded.
The Enhanced Charging Service (ECS) / Active Charging Service (ACS) in-line service is the primary vehicle that
performs packet inspection and charging. For more information on ECS, see the
Enhanced Charging Service
Administration Guide
.
Important:
For more information on Personal Stateful Firewall, refer to the
Personal Stateful Firewall
Administration Guide
.
Traffic Performance Optimization (TPO)
Though TCP is a widely accepted protocol in use today, it is optimized only for wired networks. Due to inherent
reliability of wired networks, TCP implicitly assumes that any packet loss is due to network congestion and
consequently invokes congestion control measures. However, wireless links are known to experience sporadic and
usually temporary losses due to several reasons, including the following, which also trigger TCP congestion control
measures resulting in poor TCP performance.
Reasons for delay variability over wireless links include:
Channel fading effect, subscriber mobility, and other transient conditions
Link-layer retransmissions
Handoffs between neighboring cells
Intermediate nodes, such as SGSN and e-NodeB, implementing scheduling polices tuned to deliver better QoS
for select services; resulting is variable delay in packet delivery for other services
The TPO inline service uses a combination of TCP and HTTP optimization techniques to improve TCP performance
over wireless links.
Important:
For more information on TPO, refer to the
Traffic Performance Optimization Administration Guide.
