cisco培训16-Metro Ethernet architecture case study.pptVIP

Chapter 16 - Metro Ethernet Architectures Expanding the SP Backbone for Metro Ethernet Services Service providers want to know how to make their existing core make more money Intelligent, scalable Ethernet services seamlessly use existing IP/MPLS cores Ethernet Access: Logical Picture Metro Ethernet Architecture : The Big Picture Topology Considerations – Ring or Hub and Spoke? Significant performance and failover characteristics/differences Tune 802.1d wherever possible ; use 802.1w wherever possible ; use 802.1s wherever needed GE Rings – Cheapest solution for Ring based Topology Convergence – 802.1w No timer adjustment required! Standards based ~2-3 s convergence in a 10-switch ring Troublesome 802.1s implementation issues GE L2 Ring Characteristics Coupled with 802.1w convergence is in the order of 2-3 seconds Obviously the lowest cost ring based solution ? Residential Service focus BUT BUSINESS SERVICES AS WELL!! Fairness of access to the ring, relative bandwidth utilisation, delay/jitter behaviour, convergence time, etc… depends on where you are in the ring ! Difficult QoS configuration (limited to policing at the access-ports and prioritisation of voice/video) Number of nodes limited to 10-12 (with 802.1d) Access devices have no advanced features (Shaping, MPLS, BGP,…) No OAM capabilities on Ethernet currently, less ‘transport friendly’ Inferior MAC-layer QoS support in comparison to DPT/RPR 802.1s MST is not ‘ring’-friendly Point-to-point GE / Star Point to Point GE/Star Resiliency Enable Spanning Tree (802.1w) With 802.1w, convergence is as fast as 0.5 second! Good QoS and bandwith sharing/fairness characteristics Uplink load-balancing through per-vlan-spanning-tree or 802.1s Can be built on a fiber ring infrastructure with CWDM GE L2 Star Characteristics Sub-second convergence with 802.1w Better fairness of access to the core network 2 GE or more (GEC) from every PE-CLE to the PE-POPs More consistent delay/jitter characteristics Number of PE-CLEs can be