514 Wrap-up

Summary of Course

• This was a course on modern Carrier Networks– i.e., how a telco might organise its IP network

from the customer to the core.– ATM, SDH, DSL, DSLAM, BRAS, Wifi, PPP,

DHCP, QoS, RADIUS, RED, GRE, L2TP, Ethernet, VLAN, BFD, VoIP, Multiplay, MPLS, LDP, RSVP, BGP

– Plus: L3VPN, VPLS, iBGP scaling

ATM

• Goal: converge on single transmission network– Phone– Data– Video

• Cells

• Circuit switched

• QoS

SDH

• STM frames sent at regular intervals– STM frames are byte-multiplexed to form higher rate

SDH links– ADM, DXC

• Self healing rings• OAM

– Performance monitoring– Fault detection– Fault notification– System protection– Point-of-fault identification

Access Networks

• PSTN

• ADSL– Line Splitter/Filter

• DSLAM, MDF, Central Office

Wireless

• 802.11– Unlicensed vs. licensed spectrum– CSMA/CA– Channels, overlapping– Interference, hidden node, multi-path

PPP, DHCP

• PPP– LCP, NCP, IPCP– Authentication– Used extensively in dial-up ISP environments– PPPoE

• DHCP– Assign host configuration parameters– No authentication– DHCP option 82: customer port

RADIUS

• Authentication, Authorisation, Accounting• RADIUS server stores user profiles

centrally• Return framed parameters to RADIUS

client to apply– QoS– Filters– Rate-limit profiles– IP addresses

QoS

• Some applications require better than best-effort service• IP ToS byte used for IP QoS• DiffServ vs IntServ

– DSCP reused IP ToS byte

• Classification: protocol/ports, addresses• Marking: signal priority• Policing vs Shaping• Rate-limiting techniques• Queuing strategies: tail-drop vs RED• Call admission and control

Tunnelling

• VPN services: network link routed over existing available networks

• GRE – Generic tunnelling protocol– tunnels over IP

• L2TP – Layer 2 tunnelling protocol– Tunnels PPP over IP (UDP)– LAC / LNS

Ethernet

• PHYs

• 802.1Q VLANs

• 802.3ad Link Aggregation

• 802.1p Traffic Class Expediting (QoS)

• OAM

Wholesale

• Radius proxy on BRAS, forward to appropriate ISP

• BRAS part 1: carrier aggregates sessions– LAC

• BRAS part 2: forward to appropriate ISP– LNS

VoIP

• Concerned about delay– Propagation, serialisation, switching, queuing

• Concerned about reliability

• BFD – Bidirectional Forwarding Detection

Triple Play

• COPS: Common Open Policy Service– PEP: policy enforcement point

• BNG

– PDP: policy decision point

• BNG aggregates VoIP, data, video

MPLS

• Multi-protocol Label Switching

• Labelled packets

• Label stacking

• LIB, LER, LSR, LSP

• CE / PE / P

• MPLS VPNs use two labels, why?

• VRF : VPN Routing and Forwarding

Signalling LSPs

• Need way to distribute LSPs through network

• LDP : Label Distribution Protocol

• RSVP-TE: Resource Reservation Protocol, Traffic Engineering– Create LSPs with particular characteristics

Traffic Engineering

• Traffic trunk: specified path through network– multiple LSPs provide redundancy; fast-

reroute, link protection, node protection.– Primary, secondary– RSVP reserves capacity for backup paths

BGP

• Decentralised Internet routing– Path/Vector

• Autonomous Systems

• Update message contains NLRI

• Attributes:– MED, Communities, LocalPref, etc.– Classes: non-transitive, mandatory, etc.

• MBGP – Multi-protocol BGP

MBGP – VPN-IPv4 Customer Routes

• Route target – tag routes for import/export

• Route distinguisher – distinguish routes of separate customers– A customer’s address space may overlap with

another’s, without interfering– E.g. private addresses

• PEs peer to exchange customer IPv4 routes

VPLS

• Layer-2 MPLS VPN

• Mostly same parts as IPv4 MPLS VPN

• Multi-point Ethernet

• u-PE

• VE

• PEs learn which PE has specific customer MAC address behind it.

Scaling BGP

• iBGP Requirement for full mesh

• Two approaches– Confederations– Route Reflection

Summary

• This course looked at how a carrier network might be assembled

• Important things learned:– How to read an RFC / exposure to RFCs– MBGP– MPLS– Customer, physical access technologies

Reminder

• Test, 50%

• Friday 19th Oct, 2pm-5pm, G.B.13