A subscriber host session can signal one of many encapsulation types each with a different fixed offset in the last mile. These encapsulation types are described in RFC 4679 and are illustrated in Figure: Subscriber host session encapsulation types and Figure: Access-loop-encapsulation sub-TLV. The BNG node learns the encapsulation type of each subscriber host session by inspecting the Access-loop-encapsulation sub-TLV in the Vendor-Specific PPPoE Tags as specified in RFC 4679.When Ethernet is the last mile, the encapsulation type results in a fixed offset for all packet sizes. When ATM/DSL is the last mile, there is an additional expansion because of AAL5 padding to next multiple of 48 bytes and which varies depending on the packet size.
The software and hardware based implementations support both ATM and Ethernet access using PPP encapsulation options. Thus, both provide support for the Access-loop-encapsulation sub-TLV in the Vendor-Specific PPPoEv4/PPPoEv6 Tags with the ATM encapsulation values and Ethernet encapsulation values. ATM and Ethernet access using IP encapsulation are only supported using default encapsulation offset configuration in the subscriber profile in the software based implementation. Support for signaling the Access-loop-encapsulation sub-TLV in the DHCPv4/DHCPv6 Relay Options is included in the hardware based implementation. There is no support for DHCPv6 relay options.
The operational last-mile values for hosts on the same SAP, having the same SLA profile are displayed in following the show command:
CLI syntax:
show>service active-subscribers>ale-adjust
The data-link can have values: atm, other and, unknown. If no offset is supplied it is set to unknown. other is used when the data-link is non-atm, otherwise it states atm.
Operational per-queue values can also be found in the show command:
CLI syntax:
show>qos>scheduler-hierarchy
The following is an example of displaying whether the queue is operating in last-mile mode.
Last mile ATM:
*A:Dut-C# /show service active-subscribers ale-adjust
===============================================================================
Active Subscriber Access Loop Encapsulation adjustment
===============================================================================
Subscriber
SAP SLA profile
Data-link Offset(bytes)
-------------------------------------------------------------------------------
hpolSub81
1/1/11:2000.1 hpolSlaProf1
atm -10
-------------------------------------------------------------------------------
No. of Access Loop Encapsulation adjustments: 1
===============================================================================
*A:Dut-C# show qos scheduler-hierarchy subscriber "hpolSub81"
===============================================================================
Scheduler Hierarchy - Subscriber hpolSub81
===============================================================================
Ingress Scheduler Policy:
Egress Scheduler Policy :
-------------------------------------------------------------------------------
Root (Ing)
|
No Active Members Found on slot 1
Root (Egr)
| slot(1)
|--(Q) : Sub=hpolSub81:hpolSlaProf1 2000->1/1/11:2000.1->8->ATM (Port 1/1/11)
|
|--(Q) : Sub=hpolSub81:hpolSlaProf1 2000->1/1/11:2000.1->7->ATM (Port 1/1/11)
|
|--(Q) : Sub=hpolSub81:hpolSlaProf1 2000->1/1/11:2000.1->6->ATM (Port 1/1/11)
|
|--(Q) : Sub=hpolSub81:hpolSlaProf1 2000->1/1/11:2000.1->5->ATM (Port 1/1/11)
|
|--(Q) : Sub=hpolSub81:hpolSlaProf1 2000->1/1/11:2000.1->4->ATM (Port 1/1/11)
|
|--(Q) : Sub=hpolSub81:hpolSlaProf1 2000->1/1/11:2000.1->3->ATM (Port 1/1/11)
|
|--(Q) : Sub=hpolSub81:hpolSlaProf1 2000->1/1/11:2000.1->2->ATM (Port 1/1/11)
|
|--(Q) : Sub=hpolSub81:hpolSlaProf1 2000->1/1/11:2000.1->1->ATM (Port 1/1/11)
|
Last mile Ethernet:
*A:Dut-C# show service active-subscribers ale-adjust
===============================================================================
Active Subscriber Access Loop Encapsulation adjustment
===============================================================================
Subscriber
SAP SLA profile
Data-link Offset(bytes)
-------------------------------------------------------------------------------
hpolSub81
1/1/11:2000.1 hpolSlaProf1
other +12
-------------------------------------------------------------------------------
No. of Access Loop Encapsulation adjustments: 1
===============================================================================
*A:Dut-C# show qos scheduler-hierarchy subscriber "hpolSub81"
===============================================================================
Scheduler Hierarchy - Subscriber hpolSub81
===============================================================================
Ingress Scheduler Policy:
Egress Scheduler Policy :
-------------------------------------------------------------------------------
Root (Ing)
|
No Active Members Found on slot 1
Root (Egr)
| slot(1)
|--(Q) : Sub=hpolSub81:hpolSlaProf1 2000->1/1/11:2000.1->8->Eth (Port 1/1/11)
|
|--(Q) : Sub=hpolSub81:hpolSlaProf1 2000->1/1/11:2000.1->7->Eth (Port 1/1/11)
|
|--(Q) : Sub=hpolSub81:hpolSlaProf1 2000->1/1/11:2000.1->6->Eth (Port 1/1/11)
|
|--(Q) : Sub=hpolSub81:hpolSlaProf1 2000->1/1/11:2000.1->5->Eth (Port 1/1/11)
|
|--(Q) : Sub=hpolSub81:hpolSlaProf1 2000->1/1/11:2000.1->4->Eth (Port 1/1/11)
|
|--(Q) : Sub=hpolSub81:hpolSlaProf1 2000->1/1/11:2000.1->3->Eth (Port 1/1/11)
|
|--(Q) : Sub=hpolSub81:hpolSlaProf1 2000->1/1/11:2000.1->2->Eth (Port 1/1/11)
|
|--(Q) : Sub=hpolSub81:hpolSlaProf1 2000->1/1/11:2000.1->1->Eth (Port 1/1/11)
|