Transcript Differentiated Services/MPLS (Lecture 10)

• End-to-end resource management in DiffServ
Networks
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DiffServ focuses on singal domain
Users want end-to-end services
No consensus at this time
Two proposals:
• Integrated Services over Differentiated Services
• Bandwidth Broker
• Integrated Services over Differentiated
Services
– Apply integrated services model end to end across a
network with one or more DiffServ domains.
– DiffServ networks are treated as a link layer medium
– Integrated Service requests are mapped to diffserv
capability
• Services to PHB
– Two tier resource allocation
• DiffServ distributes aggregated resources at core
• IntServ allocates the resources to indivudual users
– Example: Figure 3.8
– Do we have end-to-end QoS guarantees in this model?
• Bandwidth Broker (BB)
– Resource allocation between different backbone service
providers, as well as support QoS on local LAN.
– Each network is associated with one or model BB,
which keep track on local network usage
• Admission control, policy control, reservation aggregation
– BB needs the knowledge of routing
– Example, Figure 3.9
– Per flow end-to-end QoS guarantee?
Multiprotocol Label Switching
• Virtual circuit at IP level
– A short, fixed length label is used for forwarding.
– Similar too other circuit switched technology: ATM,
Frame Relay, WDM
• Convergence of datagram and virtual circuit.
– How virtual circuit/datagram works?
– Fundamental trade-off: complexity at routing and
signaling.
• Motivation: IP over ATM integration.
– Without MPLS:
• Overlay model (classical IP over ATM)
– ATM is treated like another subnet technology.
– When ATM is treated as a subnet, it is different from both
point-to-point or shared media network:
» multiple neighbors, but no broadcast capability (ARP)
» ATM may contain multiple logical IP subnets (LIS)
– ATM ARP: need to emulate ARP.
– NextHop Resolution Protocol (NHRP)
• Problems:
– Have scaling problems. Need VC to connect hosts in a
logical subnet. O(N^2) connections and O(N) neighbors.
– Going through IP layer in an ATM cloud is not efficient.
– Lose QoS capability
• Motivation: IP over ATM integration.
– With MPLS:
• IP routing and signaling protocols take over the
control path.
• ATM switches are used only to data transmission.
• ATM switches are now in the IP routing domain.
• NHRP and on demand SVCs are no longer needed
• MPLS matches ATM’s capability
– Labels are SVC circuit IDs
– Switching is done by ATM switches
– QoS can be preserved in a LSP.
• Some advantages for MPLS:
– Simpler packet classification and table lookup
• Trade off between simple forwarding and
complexity in signaling.
– Protocol independent forwarding
• Even IP has many protocols. (CIDR, v4, v6, etc)
– Finer forwarding granularity
• Can treat different customers differently.
– Traffic Engineering
• MPLS can setup explicit route between two nodes.
• key application
• IP packet forwarding (Figure 4.2):
– Control path: making routing decisions.
• unicast routing protocols and multicast routing
protocols
– Data path: move packet from input ports to
output ports.
• unicast forwarding table, unicast forwarding engine,
multicast forwarding table, multicast forwarding
engine
• Forwarding is done by longest match between dst
address and entries in the forwarding table.
• MPLS packet forwarding (Figure 4.4):
– Control path: making routing decisions.
• unicast routing protocols and multicast routing
protocols
• Other control protocols (ATM, FR)
– Data path: move packet from input ports to
output ports.
• Label-switching table
• Label-based forwarding engine
– IP centric control:
• IP is here to stay.
• IP control protocols are more mature and scalable
than other alternative protocols.
• IP control protocols for everything (ATM, FR,
optical WDM)
– A unified control plane integrated IP with different link
layer technologies and simplify the management.