Nortel 8630gbr 规格指南

With Provider Backbone Transport
(PBT) technology, efficient trunks can
be engineered thru the network to
deliver end-to-end traffic with deter-
ministic routing and QoS in support of
individual multiple-priority services or
aggregrated services being backhauled
across the MAN. PBT avoids the ineffi-
ciencies and lack of carrier-class resilience
that otherwise arise from use of the
traditional spanning tree algorithm.
Rolled out as a software release on the
Metro Ethernet Routing Switch 8600,
PBT functionality can be deployed as
needed, and need not be deployed
uniformly across the entire network.

Figure 1 shows the Metro Ethernet
Routing Switch 8600 deployed in
support of triple play services including
video (broadcast TV, video on demand),
voice over IP (VoIP) and high-speed
Internet access over a common network.
Residential subscribers are connected to
the network via various access technolo-
gies (xDSL, cable, direct fiber, Ethernet
access ring, etc.) while enterprise
subscribers are connected via direct
Ethernet VPNs using the same access
infrastructure. A mix of residential and
enterprise services are supported on
every port, creating a truly shared
Ethernet-based infrastructure without
compromising on performance.

Triple play services can be further
distributed via an Ethernet access ring
topology using Nortel Metro Ethernet
Services Units. The Metro Ethernet
Routing Switch 8600 supports services
through other access topologies, such as
point-to-point fiber, IEEE 802.1ad
access networks and broadband aggrega-
tion devices.

Determinism and Ethernet

In a carrier environment, the connectionless behavior of tradi-

tional Ethernet implies a level of unpredictability that is trouble-

some in a high availability environment. A recent development in

the Ethernet world has been the work on a connection-oriented

technique known as Provider Backbone Transport (PBT). PBT

builds on the hierarchical nature of PBB (or MAC-in-MAC) by

using the backbone address and VLAN tag as identifiers for a

deterministic “tunnel” through the network. PBT is being actively

worked in the IEEE 802.1Qay committee where it is known as

Provider Backbone Bridges — Traffic Engineering.

PBT provides Ethernet with a connection-oriented forwarding

mode, which enables dedicated Ethernet links with guaranteed,

deterministic performance levels. In this way, PBT delivers QoS

over an Ethernet network without the added cost of connection-

oriented alternatives. PBT also delivers the following benefits to

the service provider:

• Scalability — PBT does not rely on the traditional Ethernet

MAC address learning methods. This explicit learning approach

removes the undesirable MAC flooding behavior that otherwise

limits the size of the network.

• Resiliency — Since PBT allows creation of point-to-point

connections across the network, working and protection routes

can be provisioned to provide end-to-end resiliency across arbi-

trary mesh topologies.

• Network utilization — The ability to fully manage traffic paths

and know exactly which customer traffic is being carried over

which path allows customer SLAs to be met without over-

provisioning and under-utilizing network capacity.

• Manageability — Since the operations support system (OSS)

is aware of the route taken by each service, functions such as

alarm correlation, service-fault correlation and service-

performance correlation are simplified.

• Security — Using point-to-point Ethernet tunnels across the

network protects traffic from misconfiguration errors or inter-

ception by those with malicious intent. Furthermore, by avoiding

the flooding behavior of conventional Ethernet, unintentional

leakage of packets to endpoints for which they were not

intended can be avoided.