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Configuring Compressed Real-Time Transport Protocol

Real-Time Transport Protocol (RTP) can help achieve interoperability among different implementations of network audio and video applications. However, in some cases, the header, which includes the IP, UDP, and RTP headers, can be too large (around 40 bytes) on networks using low-speed lines such as dial-up modems. Compressed Real-Time Transport Protocol (CRTP) can be configured to reduce network overhead on low-speed links. CRTP replaces the IP, UDP, and RTP headers with a 2-byte context ID (CID), reducing the header overhead considerably.

Figure 41 shows how CRTP compresses the RTP headers in a voice packet and reduces a 40-byte header to a 2-byte header.

Figure 41: CRTP

Image g017259.gif

On J-series Services Routers, you can configure CRTP with MLPPP or PPP logical interface encapsulation on link services interfaces. For more information about configuring MLPPP, see Configuring an MLPPP Bundle.

When you configure CRTP, link fragmentation and interleaving (LFI) is automatically enabled. LFI reduces excessive delays by fragmenting large packets into smaller packets and interleaving them with real-time frames. This allows real-time and non-real-time data frames to be carried together on lower-speed links without causing excessive delays to the real-time traffic. For more information about LFI, see Link Fragmentation and Interleaving Overview.

On the Services Router, CRTP can be configured as a compression device on a T1 or E1 interface with PPP encapsulation, using the link services interface.

For more information about configuring CRTP on a single link, see the JUNOS Network Interfaces Configuration Guide and the JUNOS Services Interfaces Configuration Guide.

To configure CRTP on the Services Router:

  1. Navigate to the top of the interfaces configuration hierarchy in either the J-Web or CLI configuration editor.
  2. Perform the configuration tasks described in Table 75.
  3. If you are finished configuring the router, commit the configuration.

Table 75: Adding CRTP to an T1 or E1 Interface

Task

J-Web Configuration Editor

CLI Configuration Editor

Navigate to the Interfaces level in the configuration hierarchy.
  1. In the J-Web interface, select Configuration>Edit Configuration>View and Edit.
  2. Next to Interfaces, click Edit.

From the [edit] hierarchy level, enter

edit interfaces interface-name

Select an E1 or T1 interface—for example, t1–1/0/0.

Set PPP as the type of encapsulation for the physical interface.

  1. Next to a T1 or E1 interface, click Edit.
  2. From the Encapsulation list, select ppp as the encapsulation type.
  3. Next to Unit, click Add new entry.
  4. In the Interface unit number box, type 0.
  1. Enter

    set encapsulation ppp

  2. Enter

    edit unit 0

Add the link services interface, ls-0/0/0.0, to the physical interface.

  1. In the Compression device box, enter ls-0/0/0.0.
  2. Click OK until you return to the Interfaces page.

Enter

set compression-device ls-0/0/0.0

Add the link services interface, ls-0/0/0, to the Services Router.
  1. Next to Interface, click Add new entry.
  2. In the Interface name box, type ls-0/0/0.
  3. Click OK to return to the Interfaces page.
  4. On the main Interface page, next to ls-0/0/0, click Edit.
  5. Next to Unit, click Add new entry.
  6. In the Interface unit number box, type 0.

From the [edit interfaces] hierarchy level, enter

edit interfaces ls-0/0/0 unit 0

Configure the link services interface, ls-0/0/0, properties.

F-max period—Maximum number of compressed packets allowed between transmission of full headers. It has a range from 1 to 65535.

Maximum and Minimum—UDP port values from 1 to 65536 reserve these ports for RTP compression. CRTP is applied to network traffic on ports within this range. This feature is applicable only to voice services interfaces.

  1. Next to Compression, select yes, and then click Configure.
  2. Select RTP, and then click Configure.
  3. In the F-Max period box, type 2500.
  4. Select Port, then click Configure.
  5. In the Minimum value box, type 2000.
  6. In the Maximum value box, type 64009.
  7. Click OK.

Enter

set compression rtp f-max-period 2500 port minimum 2000 maximum 64009

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