для Cisco Cisco 1900 2900 3900 Series 4-Port Gigabit Ethernet HS-WIC with PoE

The following restrictions apply to configuring the Cisco 3G EHWIC cards and C880G ISRs:

Data connection—Data connection can be originated only by the 3G EHWIC card or the 3G modem 
in the C880G ISR.

Throughput—Due to the shared nature of wireless communications, the experienced throughput 
varies depending on the number of active users or congestion in a given network. 

Latency—Cellular networks have higher latency compared to wired networks. Latency rates depend 
on the technology and carrier. Latency may be higher because of network congestion.

Carrier restrictions—Any restrictions that are a part of the terms of service from your carrier.

Performance—Multiple PDP contexts are supported only in the EHWIC card. This requires an 
additional 2 Mb memory.

The Global System for Mobile Communications (GSM) is the most widely deployed cellular network in 
the world. It is based on the specification from European Telecommunications Standards Institute 
(ETSI). 

GSM was primarily designed for voice and was circuit switched but due to the popularity of cellular 
networks and the great demand for data services, GPRS was introduced as a packet switched data overlay 
over the GSM radio network. 

The radio and network resources of GPRS are accessed only when data actually needs to be transmitted 
between the GPRS mobile user and the GPRS network. 

GPRS introduced several new network nodes into the GSM architecture for packet switching, they form 
the Mobile Packet Core. The Mobile Packet Core includes the Serving GPRS Support Node (SGSN) and 
the GPRS Gateway Support Node (GGSN). 

The SGSN is the node that in some ways carries out the same function as the Foreign Agent in Mobile 
IP. It tunnels IP packets towards the GGSN and detunnels packets back from the GGSN. It also carries 
out mobility managed and billing. 

The GGSN is the node which carries out the role in GPRS equivalent to the Home Agent in Mobile IP. 
The GGSN provides the connectivity to the IP network and the SGSN. It is responsible for IP address 
assignment and is the default router for the connected User Equipment (UE).