Traffic Parameters
Traffic parameters refer to the parameters used by each PVC for flow control. The traffic parameters include traffic rate and delay variation.
Parameter Name | Parameter ID | Description |
|---|---|---|
Traffic record index | TRFX | Identifies a traffic record. |
Service Type | ST | Indicates the type of service carried over ATM. CBR and RT-VBR indicate real-time services, which are usually carried on the user planes of the Iur, Iub, and Iu-CS interfaces. NRT-VBR and UBR indicate non-real-time services, which are usually carried on the user plane of the Iu-PS interface. |
Rate unit | UT | Indicates the unit of PCR, SCR, and MCR. |
Peak cell rate | PCR | Indicates the maximum rate of transmitting ATM cells. |
Sustainable cell rate | SCR | Indicates the average rate of transmitting ATM cells over a long time. |
Minimum cell rate | MCR | Indicates the minimum rate of transmitting ATM cells. |
Max burst size | MBS | Indicates the maximum number of continuous ATM cells. |
Cell delay variation tolerance | CDVT | Indicates the maximum tolerable variation in the unit of 0.1 μs. |
Traffic use description | REMARK | Describes the usage of the ATM traffic record. |
The traffic rate is indicated in the following ways:
- PCR: applicable when Service type is set to CBR and the traffic rate is a constant value.
- Combination of PCR and SCR: applicable when Service type is set to RTVBR or NRTVBR.
- MCR: applicable when Service Type is set to UBR_PLUS.
Parent topic: PVC Parameters of the ATM Layer
VPI and VCI
The main characteristics of the ATM technology are multiplexing, switching, and transmitting of ATM cells. All these operations are performed over Virtual Channels (VCs). A VC and a Virtual Path (VP) are identified by Virtual Channel Identifier (VCI) and Virtual Path Identifier (VPI) respectively.
Figure 1 shows the relation between VC and VP.
- A VC is identified by a VCI. It is a logical connection between ATM nodes and is the channel for transmitting ATM cells between two or more nodes. The VC is used for the data transmission between mobile terminals, between networks, or between mobile terminal and network.
- A VP is a group of VCs at a given reference point. The VCs in the group have the same VPI.
Parent topic: PVC Parameters of the ATM Layer
Service Type
The ATM services are of four types: Constant Bit Rate (CBR), Real-Time Variable Bit Rate (RT-VBR), Non-Real-Time Variable Bit Rate (NRT-VBR), and Unspecified Bit Rate (UBR).
Table 1 describes the types of service.
Type of Service | Abbreviation | Description |
|---|---|---|
Constant Bit Rate | CBR | No error check, flow control, or other processing |
Real-Time Variable Bit Rate | RT-VBR | Rate of a service with variable-rate data streams and strict real-time requirements, for example, interactive compressed video (video telephony). |
Non-Real-Time Variable Bit Rate | NRT-VBR | Rate of a service that is applicable to timing transmission. A service of this type, for example, e-mail, is relatively insensitive to delivery time or delay. |
Unspecified Bit Rate | UBR | Rate of a service with no commitment to transmission and no feedback on congestion. This type of service is ideal for the transmission of IP datagrams. In congestion, UBR cells are discarded, and no feedback or request for slowing down the data rate is delivered to the transmission end. |
Table 2 describes the characteristics of different ATM services.
Parent topic: PVC Parameters of the ATM Layer
