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Ethernet in Carrier Networks

Ethernet in Carrier Networks. Ethernet Reminder. Shared access medium widespread in LAN environments CSMA/CD Frames. 2. 46 to 1500*. 4. 6. 6. Type. Payload. FCS. Dest. MAC. Source MAC. Ethernet. Flat Address Space. Ethernet. Ethernet parts are cheap Ethernet is fairly simple

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Ethernet in Carrier Networks

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  1. Ethernet in Carrier Networks

  2. Ethernet Reminder • Shared access medium widespread in LAN environments • CSMA/CD • Frames 2 46 to 1500* 4 6 6 Type Payload FCS Dest. MAC Source MAC

  3. Ethernet Flat Address Space

  4. Ethernet • Ethernet parts are cheap • Ethernet is fairly simple • but can be extended • Ethernet is ubiquitous • Ethernet can carry many different Layer-3 protocols

  5. Ethernet in Carrier Networks • PHY types • OAM • Link Aggregation • VLANs • Quality of Service

  6. Ethernet PHY • Ethernet Physical Layer (PHY) • Layer 1 in OSI model

  7. Ethernet PHY • Wide and varied PHY standards • Common Ethernet frame format • Coax / Category 5 Twisted Pair / Wireless / Fiber Optic • Fiber Optics == Lasers • CSMA/CD, CSMA/CA • Coding method: Manchester, 4B/5B, 8B/10B, 64B/66B • Full duplex vs. half duplex • etc

  8. Ethernet PHY • Relatively short distances • 100baseT – up to 100m • 100baseFX – up to 4km full duplex • GigE over Fiber – up to 100km • 10GigE over Fiber – up to 40km

  9. 10GigE PHY • 10GBASE-SW,EW,LW define Ethernet over SDH STS-192c networks • S = 850nm, L = 1310nm, E = 1550nm • W == WAN Interface Sublayer • useful for carriers which already have these links in place • reuse existing technology == cheaper.

  10. OAM • Operation, Administration, and Maintenance • Detect network defects • Anomaly • smallest detectable discrepancy between observed and expected behaviour • Defect • function is impaired by density of anomalies • Single Fault • many different correlated defects caused by fault • Failure • fault persists for long enough that network function terminates • Alarm • indication to human of failure Source: Ethernet OAM Whitepaper, RAD Data Communications

  11. Ethernet OAM • 802.3ah: “Ethernet in the First Mile” • Ethernet link-layer OAM • 802.1ag: “Connectivity Fault Management” • Ethernet Service OAM

  12. Ethernet OAM • Continuity Check (CC) • Special frame sent at regular intervals • Absence of CC message in 3.5x configured interval indicates failure earlier in the link CC alarm Detects fault

  13. Ethernet OAM • Link Trace (LT) message for identifying intermediate points • Loopback (LB) message for diagnosing faults • In-service (non-intrusive echo) • Out-of-service (intrusive loopback) • Send LB to first intermediate, then second, until LB is not returned

  14. 802.3ad link aggregation • aggregate multiple physical ports into single logical link • increase capacity • fault tolerance

  15. 802.3ad link aggregation • Does not reorder packets in a given conversation • Does not change Ethernet frame format • Does not necessarily provide N times more capacity unless Ethernet-layer traffic is diverse PC Switch Switch

  16. 802.3ad link aggregation • requires protocol support from switch • switch sees same MAC address arrive on multiple ports • otherwise would get quickly confused • Link Aggregation Control Protocol (LACP) • Uses EtherType 0x8809 • Aggregator advises switch which ports it is aggregating

  17. 802.1Q Virtual LANs (VLANs) • Allow multiple networks to share same physical Ethernet link VLAN Switch

  18. 802.1Q VLANs • Want to do this without introducing security concerns • Ethernet has a flat address space • Want to do this in a scalable way

  19. 802.1Q VLANs 4 46 to 1500* 4 6 6 • 4 byte tag • Tag Protocol ID • User Priority • Canonical Format Indicator • VLAN ID • FCS is recalculated on VLAN tag insertion Destination MAC VLAN Type Payload FCS Source MAC TPID UP VID 0x8100 16 bits 3 1 12 bits

  20. 802.1Q VLANs • Switch is configured to insert specific VLAN ID for a given port • Ethernet switches route VLAN frames based on VLAN ID • Ethernet switches may prioritise traffic based on the User Priority field • Defined in 802.1p

  21. 802.1p Traffic Class Expediting • 802.1p provides recommended actions for 3 User Priority bits in VLAN tag. • 1, BK, Background • 0, BE, Best Effort (default) • 2, EE, Excellent Effort • 3, CA, Critical Applications • 4, VI, Video < 100ms latency + jitter • 5, VO, Voice < 10ms latency + jitter • 6, IC, Internetwork Control • 7, NC, Network Control • Approximately maps to first DSCP precedence Source: 802.1Q-2005.pdf, page 282

  22. Summary • Ethernet is fairly simple, but has many useful standardised extensions

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