Reading Read 3 MPLS links on the class website Read the following Wikipedia entries: Advanced Mobile Phone System, GSM, 1xEVDO, Cell site, Cellular network, 802.11ac
Beyond IP Routing Traffic engineering Classic Fish problem Tunneling Is this just virtual circuits again? ATM, Frame Relay These approaches require an entire network layer Scaling difficulties
MPLS Traffic Labeled Switch Paths (LSP) Take into account bandwidth, QoS, rerouting Distributed or central computation Static or Dynamic MPLS is a control plane reservation protocol! Call Admission Control
MPLS Terminology Disjoint pairs Node diverse and Link diverse Shared risk group Underlaying technology may not divulge IGP extensions for MPLS--hints of lower level Optical/SONET not as helpful--possible multi-carrier
MPLS Setup Required parameters Gather topology TE LSP computation (Labeled Switch Path) TE LSP Setup RSVP-TE path, resv, path error, path tear, resv error, resv confim, resv tear Packet forwarding--32 bit label on IP packet Label(20), QoS(3), stack(1), TTL (8)
MPLS Preemption Preemption process for higher priority req. local RSVP states cleared, no forwarding RSVP path error upstream RSVP resv error downstream Hard preemption is disruptive
MPLS Soft Preemption Preemptiong LSP signals to the respective head-end LSR the need to reroute Make-before-break Local states of soft preempted TE LSP are not cleared and traffic is still forwarded Encourages temporary over-booking
Why MPLS Better bandwidth utilization Strict QoS Better control of link utilization Routing via reservation Reduced probability of congestion Fast Recovery Can be a motivation by itself
Fault Recovery Time Fault detection time Hold-off time Fault notification time Recovery Operation Time Local protection Global protection or restore Traffic Recovery Time
Fault Signaling IP Route update RSVP Path Error Sent to head LSR Usually received first (10s of ms)
Global Default Restoration Head LSP Receives RSVP Path Error Checks for presence of alternative path Does it satisfy TE LSP constraints? Relax constraints? Bandwidth, Affinities, etc. Dynamically recompute new LSP A few ms for a, depending on P delay
Global Path Protection For each Primary LSP A secondary which is node or link diverse is preconfigured Configured and signaled just as primary Or configure with less, say 50% Up and ready to go Fast recovery time
Local Protection Recovery No communication with the head LSP required Facility Backup Backup LSP used to protect all fast-reroutable TE LSPs Swap label, send label switch packet, send via backup link Link vs node failure
MPLS recovery Default Global Restoration no preconfig Slow and may not converge Global Path Protection faster, more deterministic At least twice as many TE LSPs
MPLS Recovery Local Protection Fastest Facility backup One-to-one backup More preconfiguration
One-to-one backup Separate backup LSP for each TE LSP Full TE LSP by each node Detour LSP Merging allowed Merge shared link portions of path
Local Facility backup Just one backup tunnel per net hop required By Link or by node
Local Repair Notification New path may be suboptimal Non-disruptive RSVP Path Error No states cleared Head-end LSR recomputes path Implemented better path with make before break IP Router error will also be received Unless in a different routing area
Fast Recovery Deployment Full Mesh Unconstrained TE LSP Head will produce IP SPF path One-Hop unconstrained TE LSP Without bandwidth constraints, results in fewer LSPs But typically bandwidth matters Service Level Agreements (SLA)
Differentiated Services Aware Network Over Provisioning IP routing recovery, no QoS during, after Router queuing with limited high priority Limited priority traffic (30%) IP Routing, no QoS during failure Traffic Engineered network Maintain QoS during and after failure
Global vs Local Recovery Recovery time Global recovery requires waiting for head LSP to get failure message--propagation time Scalability 50 node full mesh network Global Path Protection: 4900 Local facility backup: 3200 Local Protection: 24,500
Bandwidth Sharing Bandwidth sharing vs global and local protection Global protection and sharing requires offline computation Local protection allows bandwidth sharing Cannot allow simultaneous use of backup path. (MTF failure calculation)
Wireless Specific Issues Exposed and Hidden station problems Hidden station problem causes interference at receiving station by station which is out of range from transmitting station Exposed station problem creates and appearance of a problem when transmitting stations hears station which would be out of range of receiving station
MACA Listening stations hear RTS and remain silent long enough for CTS. Listening stations hear CTS and must remain silent during next data frame transmission Collisions of RTS can still occur, if no CTS, use Ethernet style Exponential backoff RTS has size of transmission, so silence time can be calculated by all listeners
MACAW MACA for Wireless Lost frames not noticed for a relatively long time (transport layer) Add an ack for each data frame Use CSMA for RTS sending One backup calculation for each data stream
Wireless noise Wireless networks have much more noise than wired networks For bit error p, probability of entire frame of length n being received is (1-p)**n Frames are fragmented into small pieces, each with checksum, sent via stop-and-wait. Fragment bursts send with one RTS
Wireless Lans 802.11 Stack Logical Link Control MAC Sublayer Physical: Infrared, FHSS, DSSS, OFDM
802.11 Physical Layer Infrared Gray code of 1 or 2 Mbps 4 bits in 16 bit code word for 1 Mbps 2 bits in 4 bit code word for 2 Mbps Hamming code?
FHSS Frequency Hopping Spread Spectrum 79 channels of 1 KHz in 2.4 GHz ISM Adjustable dwell time Use of same pseudorandom seed keeps stations synchronized Provides some security
CDMA cont. Chip sequences are chosen to be orthogonal S * T = 0 and S * ~T = 0 (*= Normalized inner product) Decode sum signal S=A+~B+C Decode Cs signal by computing S*C=(A+~B+C)*C A*C + ~B*C + C*C 0 + 0 + 1 = 1
CDMA Example
CDMA cont. Implementation Issues Can t synchronize all chips in time Unsynchronized chips look like noise Longer chip sequences are easier to detect in noisy environments
DSSS Direct Sequence Spread Spectrum Like CDMA CDMA vs TDM vs FDM 1 bit transmitted as a chip consisting of station ID or complement of id Simultaneous transmissions add Adjust mobile power level so this works (inverse of receive)
802.11a High Speed WLAN Orthogonal Frequency Division Multiplexing 54 Mbps on 5 GHz ISM band 52 frequencies (48 data, 4 control) Spread spectrum Complex coding: phase shift up to 18 Mbps, QAM above 18. At 54 Mbps, 216 data bits in 288 bit symbols
802.11b HS WLAN Hight Rate Direct Sequence Spread Spectrum (HR-DSSS) Data rates of 1,2, 5.5 and 11 Mbps 1 & 2 Mbps rates use DSSS Faster rates use 4 or 8 bits per baud at 1.375 Mbaud using Walsh/Hadamard codes. Speed adjusted dynamicall.
802.11g 54 Mbits in 2.4 GHz band of 802.11b Uses OFDM modulation of 802.11a Chipsets handle both with one antenna Market winner
802.11n increase to 600 Mbit/sec raw throughput 4 40 MHz spatial streams Miltiple-input, multiple output (MIMO) antennas 40 MHz vs 20 MHz channels Can operate in 2.4 or 5 GHz band Frame Aggregation
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802.11n Compatibility Shares spectrum with 801.11[a,b,g] Mixed mode format protection 802.11n frames inside 802.11[a-g] trans. Use CTS before sending 40 MHz frames when b-g frames around Use RTS/CTS for subsequent frames
802.11n Compatibility Best throughput with pure 802.11n network 5 GHz channel is more open with less overlap 2.4 GHz has some channels not usable everywhere
802.11ac Approved January 2014 Devices expected in 2015 Expected to be 1 billion devices 1 Gigabit net throuput, 500 Mbits/node 5 GHz, compatible with 2.4 GH 802.11n 8 way MIMO (4 day in 801.11n) 256 QAM
808.11ac
Wireless Broadband Difficulties Pathloss Received power falls of as quad of carrier frequency Free-space approximation Multipath Shadowing