Triple-Play Service Deployment

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Chapter 2: Triple-Play Service Delivery over Ethernet Networks
CoS Prioritization Schemes
A variety of mechanism and tunneling technologies exist today
that allow providers to choose the network implementations that
will best meet their needs to reliably carry triple-play services
while maintaining CoS for those services. These can be grouped
into two emerging trends:
– Native Ethernet protocol extensions that are considerations of
the IEEE standards body–VLAN technique (often referred to as
802.1Q/p), Q-in-Q technique (often referred to as VLAN Stacking
or 802.1ad), and MAC-in-MAC technique
– Encapsulations by multi protocol label switch (MPLS) networks,
which also include the Layer 2 (VPLS) and Layer 3 versions
These schemes insert additional tags/fields in the customer
Ethernet frames at the ingress nodes (crossing the edge node into
the Metro domain) and strip them off at the egress nodes
(crossing the edge node out of the Metro domain) before the
frames are handed over to the appropriate customer traffic
segments. Issues such as backward compatibility, comparative
performance, and complexity are key elements that influence the
choice of one scheme over the others.
Some networks deploy a combination of these techniques. For
example, portions of the core network may utilize MPLS-based
CoS methodologies (where MPLS sub-50 ms recovery times are
leveraged to improve the recovery times if a link failure occurs in
this part of the network), which are then converted into a VPLS
mesh of elements (with the focus on improving routing and
handling MAC table explosions). Meanwhile in the access network,
VLANs are utilized for their simplicity and ability to prioritize traffic
in proper granularity. This type of network topology provides
channel-changing response times that are comparable to
traditional networks.