Cisco Cisco ASR 5000
Serving GPRS Support Node (SGSN) Overview
SGSN Core Functionality ▀
SGSN Administration Guide, StarOS Release 18 ▄
The SGSN provides the following mechanisms to control MN attaches:
Attached Idle Timeout - When enabled, if an MN has not attempted to setup a PDP context since attaching, this
timer forces the MN to detach with a cause indicating that the MN need not re-attach. This timer is particularly
useful for reducing the number of attached subscribers, especially those that automatically attach at power-on.
useful for reducing the number of attached subscribers, especially those that automatically attach at power-on.
Detach Prohibit - When enabled, this mechanism disables the Attached Idle Timeout functionality for selected
MNs which aggressively re-attach when detached by the network.
Prohibit Reattach Timer - When enabled, this timer mechanism prevents MNs, that were detached due to
inactivity, from re-attaching for a configured period of time. Such MNs are remembered by the in-memory
data-VLR until the record needs to be purged.
data-VLR until the record needs to be purged.
Attach Rate Throttle - It is unlikely that the SGSN would become a bottleneck because of the SGSN’s high
signaling rates. However, other nodes in the network may not scale commensurately. To provide network
overload protection, the SGSN provides a mechanism to control the number of attaches occurring through it on
a per second basis.
overload protection, the SGSN provides a mechanism to control the number of attaches occurring through it on
a per second basis.
Beside configuring the rate, it is possible to configure the action to be taken when the overload limit is reached. Note,
this is a soft control and the actual attach rate may not match exactly the configured value depending on the load
conditions.
this is a soft control and the actual attach rate may not match exactly the configured value depending on the load
conditions.
GPRS Detach
The SGSN is designed to accommodate a very high rate of simultaneous detaches. However, the actual detach rate is
dependent on the latencies introduced by the network and scaling of peers. A GPRS detach results in the deactivation of
all established PDP contexts.
dependent on the latencies introduced by the network and scaling of peers. A GPRS detach results in the deactivation of
all established PDP contexts.
There are a variety of detaches defined in the standards and the SGSN supports the following detaches:
MN Initiated Detach - The MN requests to be detached.
SGSN Initiated Detach - The SGSN requests the MN to detach due to expiry of a timer or due to administrative
action.
HLR Initiated Detach - The detach initiated by the receipt of a cancel location from the HLR.
Mass detaches triggered by administrative commands are paced in order to avoid flooding the network and peer nodes
with control traffic.
with control traffic.
Paging
CS-Paging is initiated by a peer node - such as the MSC - when there is data to be sent to an idle or unavailable UE. CS-
paging requires the Gs interface. This type of paging is intended to trigger a service request from the UE. If necessary,
the SGSN can use PS-Paging to notify the UE to switch channels. Once the UE reaches the connected state, the data is
forwarded to it.
paging requires the Gs interface. This type of paging is intended to trigger a service request from the UE. If necessary,
the SGSN can use PS-Paging to notify the UE to switch channels. Once the UE reaches the connected state, the data is
forwarded to it.
Paging frequency can be controlled by configuring a paging-timer.
Service Request
The Service Request procedure is used by the MN in the PMM Idle state to establish a secure connection to the SGSN
as well as request resource reservation for active contexts.
as well as request resource reservation for active contexts.
The SGSN allows configuration of the following restrictions:
Prohibition of services