Presentation on theme: "Bridging & Broadcast Scenarios Carlos Ribeiro CTBC Telecom."— Presentation transcript:
Bridging & Broadcast Scenarios Carlos Ribeiro CTBC Telecom
Bridging on the Access Network Access network topology –The Service Provider need to have full control over the access network topology –For the Spanning Tree Protocol, this means that the SP must always be the root of the spanning tree topology Nightmare scenarios –Multiple EFM-based SP connected together –Multihomed EFM accesses –Who is in charge of the resulting network?
Single Copy Broadcast Desired behavior –Allows for very efficient use of bandwidth –Well suited for multimedia applications Digital video distribution Digital audio distribution Conflicts with P2P emulation mode –Broadcast frames need to be copied for every user! Potential issues –Spanning Tree Topology, broadcast floods
Case studies Objectives –Show how do some proposed topologies behave with regards to single copy broadcast Assumptions –EPON works in P2P emulation mode –Single Copy Broadcast is enabled A single frame is sent to all stations downstream –No special routing behavior for SCB SCB is always on the downstream; upstream traffic is always subject to P2P emulation rules If a P2P emulation port is disabled by the STP protocol, then it will discard all broadcast frames received
Single Copy Broadcast (without spanning tree) OLT DS User managed link Access Network 1 2 ONU 1ONU 2 1 2 US1 US2 Time diagram: frame duplication due to a loop Configuration: All ports work on P2P emulation mode Downstream is seen by all ports, even with P2P emulation It wont work without spanning tree scb Single Copy Broadcast frame uf User Frame scb Both frames are accepted
Single Copy Broadcast (with spanning tree: case 1) OLT User managed link Access Network 1 2 ONU 1ONU 2 1 2 US1 US2 Time diagram: STP enabled, user link disabled Configuration: The user port is disabled by the STP Both P2P emulation ports are enabled The user loses the internal link Some user traffic may go through the SP network, instead of the direct route! uf1 2 scb Single Copy Broadcast frame uf User Frame DS scb Both frames are accepted Unicast frame is received by ONU2 uf1 2
Single Copy Broadcast (with spanning tree: case 2) OLT User managed link Access Network 1 2 ONU 1ONU 2 Time diagram: STP enabled, one P2PE link disabled Configuration: One P2P emulation port is disabled The user link is still alive Consequence: Upstream traffic from the user network goes to the other ONU to be forwarded upstream scb Single Copy Broadcast frame uf User Frame 1 2 US1 US2 DS scb uf2 O OLT receives the frame through ONU1 scb ONU 2 discards the frame (link is disabled)
Summary Routing behavior is not absolutely needed –P2P Emulation can work with SCB With STP enabled, loops are avoided, but... –User traffic may flood through the SP network –SP traffic may turn out to be carried through user links There are no guarantees that the root will always be the SP –There may be two SP providers connected through a single customer!
Additional ideas Force VLANs in the access network –All ports should apply SP-specific VLAN tags –All frames which enter the access network with VLAN tags applied should be tunneled with VLAN-inside-VLAN, or 802.1q inside 802.1q –This implementation resembles a administrative domain paradigm, as already implemented for routed networks –Comment: to require 802.1q implementation may be beyond 802.3ah scope; but so is the requirement to use a router for SE support. Special MAC addresses –Reserve MAC addresses for the applications that use single copy broadcast on the downstream –Apply filtering to avoid loops on the network
VLANs inside VLANs ONU S1 S2S3 S4 S1 S2 S1 S2 S3 OLT/Bridge (802.1d compliant) Service layer Bridges, Routers... STP Domain Inside the Access Network
VLANs inside VLANs SP Requirements A standard way to implement VLAN-inside-VLAN –Encapsulation levels: 1 level of encapsulation only n levels of encapsulation Arbitrary encapsulation –Maximum frame size (depends on the maximum encapsulation allowed) A standard way to provision and manage VLANs –Standard MIBs –Standard VLAN-to-VLAN mapping features
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