Understanding Bandwidth on Demand

Bandwidth on demand is an ISDN cost-control feature defining the bandwidth threshold that must be reached on all links before a device initiates additional ISDN data connections to provide more bandwidth.

You can define a threshold for network traffic on the device using the dialer interface and ISDN interfaces. A number of ISDN interfaces are aggregated together into a bundle and assigned a single dialer profile. A dialer profile is a set of characteristics configured for the ISDN dialer interface. Dialer profiles allow the configuration of physical interfaces to be separated from the logical configuration of dialer interfaces required for ISDN connectivity. This feature also allows physical and logical interfaces to be bound together dynamically on a per-connection basis.

Initially, only one ISDN link is active and all packets are sent through this interface. When a configured threshold is exceeded, the dialer interface activates another ISDN link and initiates a data connection. The threshold is specified as a percentage of the cumulative load of all UP links that are part of the bundle. When the cumulative load of all UP links, not counting the most recently activated link, is at or below the threshold, the most recently activated link is deactivated.

To enable bandwidth on demand, you must configure its properties:

• Dialer interface—You can configure multiple dialer interfaces for bandwidth-on-demand by incrementing the unit number—for example, dl0.1, dl0.2, and so on. For ISDN BRI, you can group up to four ISDN interfaces together when configuring bandwidth on demand, for a total of eight B-channels (two channels per interface) providing connectivity. For ISDN PRI, the pool limit is eight B-channels per channelized T1/E1/ISDN PRI port. Each ISDN interface must have the same pool identifier to participate in bandwidth on demand.

• Dialer options—Dialer options for bandwidth on demand include:

  • Dial string—Telephone number for the interface to dial that establishes ISDN connectivity. You can configure a maximum of 15 dial strings per dialer interface.
  • Load interval—Interval of time used to calculate the average load on the dialer interface. Default value is 60 seconds with a range of 20–180 seconds. The value must be a multiple of 10.
  • Load threshold—Threshold above which an additional ISDN interface is activated, specified as a percentage of the cumulative load of all UP links. Default value is 100 with a range of 0–100.
  • Pool—Name of a group of ISDN interfaces configured to use the dialer interface.
• Unit properties—Unit properties include the F max period, which is the maximum number of compressed packets allowed between the transmission of full packets. The value can be between 1 and 65,535.

• Logical properties—Logical properties for bandwidth on demand include:

  • Fragment threshold—Maximum size, in bytes, for multilink packet fragments. The value can be between 128 and 16,320 bytes. The default is 0 bytes (no fragmentation). Any nonzero value must be a multiple of 64 bytes.
  • Maximum received reconstructed unit (MRRU)—This value is expressed as a number between 1500 and 4500 bytes.

• Packet compression—You can configure the following compression types:

  • ACFC (address and control field compression)—Conserves bandwidth by compressing the address and control fields of PPP-encapsulated packets.
  • PFC (protocol field compression)—Conserves bandwidth by compressing the protocol field of a PPP-encapsulated packet.

Related Topics

• Junos OS Feature Support Reference for SRX Series and J Series Devices