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Chapter 19 MPLS Configuration
Confidential and Proprietary Information of ZTE CORPORATION
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A backbone LSR receives the labeled packet, searches the
label-forwarding table and uses a new outgoing label to
replace the label in the input packet.
An egress border LSR receives the labeled packet, deletes
the label and performs the traditional L3 search for the IP
packet.
Operational Principles of MPLS
MPLS is a label-based IP routing method. These labels can be
used to stand for hop-by-hop mode or explicit routes and also to
indicate QoS, VPN and the transmission of special types of traffic
(or special user’s traffic) on a network.
MPLS uses a simplified technology to complete conversion
between L2 and L3. MPLS can provide a label for each IP packet
that can be encapsulated into a new MPLS packet in conjunction
with the IP packet, to determine the transmission path and
priority sequence of the IP packet.
Before forwarding the IP packet according to the corresponding
path, an MPLS router will read the header label of the MPLS
packet, but will not read the information such as the IP address
in each IP packet. Therefore, the switching and routing speed of
packets is greatly improved.
MPLS can use different types of L2 protocols. Up to now, the
MPLS Task Force has standardized labels used in frame relay,
ATM, PPP links and IEEE802.3 LANs. The advantage of the
running of MPLS in frame relay and ATM is that it brings the
random connectivity of the IP to these connection-oriented
technologies.
At present, the major development trend of MPLS is ATM,
because ATM supports powerful traffic management and
provides QoS. In addition, ATM, with the combination of the
MPLS technology can put its functions in traffic management and
QoS into full play.
Labels are used to forward headers of packets, and format of
packet headers depends upon network features. In a router
network, a label is an independent 32-bit header. In ATM, a label
is placed in the cell header of a Virtual Circuit Identifier/Virtual
Channel Identifier (VCI/VPI). For the scalability of MPLS, a very
key point is that a label is meaningful only between two pieces
of equipment in mutual communications.
When an IP packet enters the network core, a border router will
assign a label to it. Since then, the MPLS equipment will check
the label information all the time and switch the labeled packet
to the destination. Since route processing is reduced, the waiting
time of the network is shortened and the scalability is improved.
MPLS
Operational
Principles
MPLS in frame
relay
Labels
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