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Configuring ATM Pseudowires

ATM pseudowires are described in RFC 4717. Pseudowire encapsulation is selected by configuring for a cell-relay pseudowire:

[edit interfaces at-fpc/pic/port:unit n]
encapsulation atm-ccc-cell-relay;atm-l2circuit-mode cell;

Or for an AAL5 pseudowire:

encapsulation atm-ccc-vc-mux;atm-l2circuit-mode aal5;

Note: encapsulation atm-ccc-cell-relay can be set at either the physical interface or logical interface level. atm-ccc-vc-mux can only be set at the logical interface level.

The following sections describe:

Cell Relay Mode (atm-l2circuit-mode cell)

In cell relay mode, one or more cells are bundled together to form a packet that is sent across the PSN tunnel. N-to-one mode is used to encapsulate cell bundles. In this mode, 52 bytes of each cell are transported across the PSN (the HEC field of the ATM header is omitted). The optional one-to-one mode is not supported.

By default, each ATM cell is encapsulated into a pseudowire packet (per RFC 4717) and sent over the pseudowire (cell-bundle-size = 1). The pseudowire may be configured to aggregate a user-configured number of cells into a packet to increase network utilization efficiency.

[edit interfaces at-fpc/pic/port]atm-options {cell-bundle-size cells;}

where cells is the number of cells each pseudowire packet should contain.

Configuring VP or Port Promiscuous Mode

By default, all incoming cells are mapped from a single VC to an ATM pseudowire. For ATM physical interfaces configured with atm-l2circuit-mode cell, you can configure port or VP promiscuous mode.

In VP promiscuous mode, all cells with the same VPI are forwarded on a single pseudowire:

[edit interfaces at-fpc/pic/port]atm-options {pic-type atm-ce;promiscuous-mode {vpi number;}}unit 0 {vpi ;}

In port promiscuous mode, all cells received on a T1 or E1 ATM port are forwarded across a single pseudowire:

[edit interfaces at-fpc/pic/port]encapsulation atm-ccc-cell-relay;atm-options {pic-type atm-ce;promiscuous-mode}unit 0 {allow-any-vci;}

Use the show interface at-x/y/z:n command to view cell relay statistics.

Configuring AAL5 SDU Mode (atm-l2circuit-mode aal5)

In AAL5 SDU mode, the ATM logical interface (VC) expects all data to be either AAL5 encapsulated packets or OAM cells. AAL5 packets are deencapsulated (AAL5 trailer is stripped off), prepended with an ATM pseudowire control word (RFC 4717) and forwarded on the pseudowire.

OAM cells that are received while an AAL5 packet is being reassembled are forwarded on the pseudowire immediately (they are reordered ahead of the packet being reassembled).

Use the show interface at-x/y/z:n command to view AAL5 statistics.


Published: 2010-04-20

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