Flexible A-bis

In the traditional BSC, the Abis interface transmission resources are allocated in fixed allocation

mode. That is, the transmission resources on the Abis interface and the TCH resources on the

Um interface are fixedly allocated according to the configuration in a one-to-one

correspondence. They cannot be shared with each other. In practice, the PS services and CS services in different cells and different BTSs are not always busy.

>> Generally, when the load of a BTS is heavy, the load of other BTSs is light.

>> When the traffic volume of PS services is heavy, that of CS services is light.

In such a case, if the Abis interface transmission resources can be shared among different BTSs,

cells, and services, the resource utilization can be greatly improved.  That is, the Abis interface transmission resources form a resource pool to share resources among CS services and PS services and also among different cells and BTSs.

Impact on System Performance:

The impact of Flex Abis on system performance is as follows:

>>Flex Abis uses dynamic allocation of Abis interface transmission resources. When the BSC allocates related resources, it notifies the BTS through signaling messages. Therefore, the signaling load on the  Abis interface increases.

>>The reliability of dynamic allocation is low relative to fixed allocation.

Impact on Other Features:

The impact of Flex Abis on other features is as follows:

>>Flex Abis serves as the basis of the BTS local switching feature. After the BTS local switching, the occupied Abis interface transmission resources are released. This can save the transmission resources on the Abis interface.

>>The ring topology of BTS I with Flex Abis enabled has the following impact on other features:

         – Flex Abis must be enabled in all the BTSs, and only the forward and reverse single E1 link is supported.

         – The Abis bypass function is not supported.

         – The 16 kbit/s LAPD link is not supported.

>>The Flex Abis and Abis bypass functions can be enabled simultaneously.

Flex Abis Timeslot Allocation:

In traditional mode, there is a one-to-one correspondence between the Um interface resources and the Abis interface transmission resources. Even if the Um interface resources are idle, the fixed Abis interface transmission resources are also occupied. After Flex Abis is enabled in the BSC, the Abis interface transmission resources use the resource pool mode. The associated Abis interface transmission resources are allocated on demand only when the Um interface resources

are occupied. This substitutes the traditional fixed resource allocation mode and improves the utilization of the Abis interface transmission resources. Except that the monitoring timeslot

(TS0), RSL, and OML still use the fixed allocation mode of the Abis interface transmission resources, other Abis interface transmission resources fall into the resource pool, as shown in

Figure.

The transmission resources on each Abis interface transmission link form a resource pool to share resources between CS services and PS services.

>>The transmission resources on Link1 form Pool0.  The resources in Pool0 can be shared by CS services and PS services on BTS0, BTS1, and BTS2.

>>The transmission resources on Link2 form Pool1. The resources in Pool1 can be shared by CS services and PS services on BTS1 and BTS2.

>>The transmission resources on Link3 form Pool2. The resources in Pool2 can be shared by CS services and PS services on BTS2.

If Flex Abis is enabled in the BSC, the BSC must allocate the Abis interface transmission resources and establishes the transmission link between the BSC and the BTS, as shown in Figure. When a channel on BTS2 is allocated, the BSC must dynamically allocate the Abis interface transmission resources on Link1, Link2, and Link3 for the channel and inform BTS0, BTS1, and BTS2 that the transmission links for the channel are established. To ensure the reliable transmission of connection messages between the BSC and the BTS, a new ESL is added for transmitting connection messages. In 64 kbit/s reuse mode, the ESL and OML must use the same 64 kbit/s timeslot on an E1. The maximum number of RSL links reused by the OML must be adjusted. A maximum of two RSL links can be reused.

During the second dynamic timeslot allocation, if FlexAbis Bypass-connect Status is set to YES, the BSC uses the timeslot occupied last time and does not sends the same connection message to the BTS again.

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