Extract from Wholesale NGN Ethernet Technical Handbook The below text is the proposed additions to the Wholesale NGN Ethernet Technical handbook. 2.3 Bitstream Ethernet Connectivity Service eircom NGN Operator Site IES 7750PE eircom NTU 7450ESS WEIL (EIL) NGN BECS Bitstream (NBB) NGN BECS Bitstream Managed Backhaul (NBM) Figure 1: NGN BECS The eircom Wholesale NGN BECS service consists of the following components: 1. Wholesale Ethernet Interconnect Link (EIL) provides (physical) connectivity from an Operator’s handover site to the 7450ESS. 2. Logical connection providing handover of ADSL Bitstream L2TP traffic from ADSL DSLAMs to an Operator’s IP network. Two options are available for the logical connection: a. NGN BECS Bitstream logical connection (NBB) b. NGN BECS Bitstream Managed Backhaul logical connection (NBM) For purposes of clarity, NGN BECS is a layer 3 service and will be available on all EIL types (e.g. ISH, IBH, CSH and ENH) and whether the EIL is configured as a port or a lag. 3.3 Bitstream Ethernet Connectivity Service The Bitstream Ethernet Connectivity Service (BECS) is used for handing over standard (NGB and Legacy) Wholesale Bitstream traffic to an Operator using L2TP. BECS is not used for hand-over of the Bitstream Ethernet Access (BEA) service which is described in this document. For simplicity, the description is based on an NTU being deployed on the EIL connection. However, as described in the previous sections it is possible to have an EIL connection with no NTU. 3 2 1 4 5 6 Bitstream Traffic Modem Modem ADSL ADSL ADSL Operator Handover Site DSLAM DSLAM BRAS eircom Aggregation Network Modem DSLAM Operator Network (LNS) L2TP Tunnels BRAS eircom NGN Node BRAS eircom IP Core eircom NTU E-NNI 1G/10G Optical/Electrical Port Figure 2: NGN BECS Traffic Flow The following describes how End User traffic is treated for the NGN BECS service: 1. The Operator’s customers connect to an eircom ADSL line with PPPoE credentials on the ADSL modem set according to the Operator’s requirements (e.g. username@OAO1.ie, password) 2. The Bitstream traffic is forwarded from the eircom DSL Access Multiplexer (DSLAM) to the eircom BRAS nodes. First stage End User authentication is performed on the eircom BRAS based on the realm associated with the Operator (e.g. @OAO1.ie). 3. An L2TP tunnel is established between the eircom BRAS (LAC) and the Operator BRAS (LNS) based on the RADIUS profile associated with the realm. The L2TP traffic is routed over the eircom IP core to the BECS handover site. 4. At the BECS handoff an S-VLAN is added to the traffic and the appropriate service policy (e.g. CoS profile/bandwidth) is applied. All of the L2TP traffic for a particular NBB or NBM connection is presented on this S-VLAN. 5. The BECS traffic is passed to the eircom managed NTU located at the Operator’s handover site. The S-VLAN on the network-facing port is mapped to the Operator facing port on the NTU (E-NNI port). The E-NNI port is configured as an 802.1ad port. The S-VLAN ID is assigned by eircom and is used to identify the end user traffic associated with an individual NBB or NBM connection. The Operator can optionally specify the S-VLAN ID presented at the E-NNI. 6. BECS traffic is handed off to the Operator’s IP network where it is routed to the Operator’s LNS to terminate the L2TP tunnels and perform second stage authentication for the end users PPP session. The BECS product supports the hand-off of ‘legacy’ Bitstream (NBB) and Bitstream Managed Backhaul (NBM) traffic types on the same physical BECS connection. The handoff of both types of traffic is on separate S-VLANs. eircom NGN SAP Individual WES Logical Connections SAP E-NNI SAP Bitstream NGN BECS Connections BMB SAP eircom NTU SAP SABs 7450ESS Figure 3: Support for BMB and Legacy Bitstream Traffic on EIL Individual NGN BECS connections are required to carry the ‘Legacy’ Bitstream (NBB) and Bitstream Managed Backhaul traffic (NBM) on the same EIL. Usage based measurements are required for the BMB traffic and therefore this traffic cannot be carried in the same service as the ‘Legacy’ Bitstream traffic. 3.3.1 Layer 3 Redundant Connectivity In order to offer increased levels of resilience to their End Users, Operators can add further physical connections to the eircom IP network. In the event of one link failing, the remaining link(s) will carry the IP traffic. Bitstream traffic is only permitted to flow to and from the Operator over these specific links. In summary, the redundant solution will permit the eircom BRAS’s to build multiple L2TP tunnels to multiple Operator BRAS’s (LNS’s). Individual PPP sessions will be carried in these L2TP tunnels. The BRAS actually selects the LNS randomly from the list, but where there is a high number of PPP sessions, the distribution becomes evenly spread across the LNSs. eircom IP Network L2TP Tunnels Operator IP Network BRAS NGN BECS eircom ADSL Network NGN BECS NGN BECS L2TP Tunnels Operator Edge Router 1 LNS 1 Operator Edge Router 2 Operator Edge Router 3 LNS 2 Figure 4: Load-balancing Network Map When an Operator’s End User enters their username and password, the PPP session causes the eircom BRAS to lookup one of the eircom DSL RADIUS servers. Based on the domain name entered by the End User, the eircom RADIUS server will send back the IP addresses of the Operator’s LNS devices. The first PPP session to each LNS will cause the eircom BRAS’s to build L2TP tunnels to each of these IP addresses. Subsequent PPP sessions to each LNS will travel within the existing L2TP tunnel. The BRAS’s will load-share PPP sessions into the L2TP tunnels. 3.3.2 IP Routing for the Redundant Solution An eBGP peering is established across each link between eircom and the Operator. The eBGP peering uses an MD5 password. Each Operator router advertises the IP addresses of every L2TP tunnel termination point to eircom. Each eircom edge router only advertises the IP addresses of each required eircom BRAS tunnel initiation point to the Operator. Routing of traffic from the Operator to eircom is under the control of the Operator. eircom sets the MED to 100 for all eircom BRAS prefixes. By setting the MED to the same value for all prefixes, no link appears ‘closer’ than another. The use of the BGP MED (Multi-Exit Discriminator) parameter allows individual paths to be preferred for individual prefixes. For example, on the first link the Operator could advertise the IP addresses as follows: A.B.C.D/32 with MED of 10 A.B.C.E/32 with MED of 20 On the second link, the Operator would advertise the IP addresses as follows: A.B.C.D/32 with MED of 20 A.B.C.E/32 with MED of 10 In normal operation the eircom network will see two possible paths to each individual prefix, and the path advertising the lower MED will be preferred. In the event of the preferred link failing, the path with the less preferred higher MED will automatically be selected. Hence, in normal operation the outbound L2TP tunnel to A.B.C.D will prefer the first link; the outbound L2TP tunnel to A.B.C.E will prefer the second link. 3.3.3 Operator configuration for BGP The Operator must use their own public AS number. Private AS numbers are not used. The Operator (Peer) announces the /32s only for their L2TP LNS (home gateways) eircom announce /32s only for the BRAS loopbacks. Peer should not also announce their /32s at INEX as this could cause traffic to go the wrong way and be blackholed. eircom will honor the MED values the Operator sends to eircom unless there is an internal traffic engineering (capacity) requirement for eircom to sent the traffic back a different way. eircom will announce all of the eircom BRAS /32s with MED 100 so that they appear equidistant. Peer has control of which peering they send traffic to eircom on. If there are any capacity management issues this may have to be tweaked in co-operation with eircom to ensure optimum performance. 4.3 Bitstream Ethernet Connectivity Service This section summarises the service parameters associated with the eircom Wholesale NGN BECS service: Parameter Value CoS Offering All NGN BECS traffic will be mapped to the Best Effort queue. Bandwidth Sharing SAB Bandwidth may be shared across S-VLANs or dedicated to each service. Service Bandwidth Dedicated bandwidth per S-VLAN or shared across both (i.e. bandwidth sharing). Routing Options BGP AS Number Operator provides their own AS number BGP password Default: Operator provides BGP password LNS/HGW Addresses Operator provides their LNS/HGW IP addresses (/32s) Routing Table Options No Routing table options supported. eircom advertises all BRAS loopbacks (loopback0 for Bitstream, loopback2 for BMB) 1620 bytes MTU size 1 Layer 2 S-VLAN Tagging Tagged Layer 2 Access Model Tagged EPL type access Service Type Required A single SAB may support either Bitstream or BMB services or both (2 S-VLANs) S-VLAN allocation Default: Assigned by Eircom Option: Provided by Operator Table 1: NGN BECS Service Parameters 5.4 Bitstream Ethernet Connectivity Service The NGN BECS bandwidth options are shown in the following table: 1 Gbit/s EIL 10 Gbit/s EIL 100 100 250 250 500 500 750 750 1000 1000 2000 3000 1 The 1620 byte setting permits a standard customer MTU of 1500 bytes and the associated L2TP header. 4000 5000 6000 7000 8000 9000 10000 Table 1: NGN BECS Bandwidth Options (Mbit/s) As part of the BECS order, the Wholesale Operator will have to specify both the EIL and SAB reference IDs (and SAB bandwidth) to which the NGN BECS services are associated. NBM and NBB S-VLANs can be ordered against the same SAB or individual SABs. Refer to section Error! Reference source not found. for a description of SABs EIL Service Access Bandwidth 1 eircom NGN SAP Individual WSEA Logical Connections SAP E-NNI SAP Bitstream NGN BECS Connections BMB SAP eircom NTU SAP EIL Service Access Bandwidth 2 7450ESS EIL Service Access Bandwidth 3 Figure 5: Non-Bandwidth Sharing Model – NGN BECS In non-bandwidth sharing mode the ‘Legacy’ Bitstream and BMB NGN BECS services are each associated with their own dedicated SAB. EIL Service Access Bandwidth 1 eircom NGN SAP Individual WSEA Logical Connections SAP E-NNI SAP Bitstream NGN BECS Connections BMB SAP eircom NTU SAP EIL Service Access Bandwidth 2 7450ESS Figure 6: Bandwidth Sharing Model – NGN BECS In bandwidth sharing mode the ‘Legacy’ Bitstream and BMB NGN BECS services are both associated with the same SAB.
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