pseudowires a short introduction - DSPCSP

1 Pseudowirespseudowirespseudowirespseudow iresa a shortshortintroductionintroductionYaakov (J) Stein July 2010 Chief ScientistRAD Data CommunicationsContentsContentsContentsCo ntents pseudowiresp PW encapsulations TDM PWs Ethernet PWs L2 VPNsL2 VPNs OAM for PWs PWE control protocol PWE control protocolY(J)S PWE short Slide 2 PseudowiresPseudowiresPseudowire (PW): Pseudowire (PW): A mechanism that emulates the A mechanism that emulates the essential attributes of a native service while transporting essential attributes of a native service while transporting over a packet switched network (PSN)over a packet switched network (PSN)()()Y(J)S PWE short Slide 3 PseudowiresPseudowiresPseudowiresPseudow iresPacket Switched Network (PSN) a network that forwards packets IPv4, IPv6, MPLS, Etherneta pseudowire (PW)is a mechanism to tunnel traffic through a PSNPWs are usually bidirectional (unlike MPLS LSPs)PW architectureis an extension of VPN architectureY(J)S PWE short Slide 4 Basic (LBasic (L22,L,L33)VPN model)VPN modelBasic (LBasic (L22,L,L33)VPN model)VPN modelcustomernetworkcustomernetworkphysi cal linknetworknetworkemulated linkProviderEdgeCustomerEdge(CE)

2 ProvidernetworkcustomernetworkProviderEd geCustomerEdge(CE)customernetwork(PE)(CE )network(PE)(CE)networkAC = Attachment CircuitAC = Attachment Circuittransported traffic may be L3( IP) or L2( Ethernet)Y(J)S PWE short Slide 5(L(L22,L,L33)VPN in more detail)VPN in more detail(L(L22,L,L33)VPN in more detail)VPN in more detailCCCCCECE customer2networkcustomer 1 networkCCPPPACAC customer 2 networkPPEPEPPACCCCE provider networkCCECACACC customer2networkcustomer 1 networkKeyCCustomer router/switchCECustomer Edge router/switchCcustomer 2 networkCE Customer Edge router/switchPProvider router/switchPEProvider Edge router/switchY(J)S PWE short Slide 6 PPseudowire seudowire EEmulationmulation(provider)(provider)EE dgedgetotoEEdgedge(provider) (provider) EEdge dge to to EEdgedgePWEPWE33 CustomerEdEdge(CE)provider sPSNC ustomerProviderCustomerEdgeEdge(CE)Provi derEdge(PE)C stomer(CE)()CustomerEdEdge(PE)CustomerEd ge(CE)nativeservicePseudowires (PW )Edge(CE)nativeserviceAC(CE)serviceAC(PW s)Y(J)S PWE short Slide 7 Native services defined in IETF PWEN ative services defined in IETF PWE33 Native services defined in IETF PWEN ative services defined in IETF PWE33 The PWE3 Working Group in the IETFThe PWE3 Working Group in the IETF has defined the following native services.

3 ATM ATM (port mode, cell mode, AAL5-specific modes) RFC 4717, 4816 Frame Relay RFC 4619 HDLC/PPP RFC 4618C/C68 TDM (E1, T1, E3, T3) RFC 4553, 5086, 5087 SONET/SDH (CEP) RFC 4842 Fiberchannel Fiber channel Multiprotocol packet service Ethernet (raw, VLAN-aware) RFC 4448 Note that most are legacyservicesbut the most interesting service today is EthernetY(J)S PWE short Slide 8 What else ?What else ?What else ?What else ?PWs emulate the native service PWs emulate the native service but may not completely reproduce it (applicability statement)PWk ttlfdibi(lik MPLSlik IPEtht)PW packets are not self-describing (like MPLS, unlike IP or Ethernet)An demultiplexing identifier is provided to uniquely identify PWsWe may also need : Native Service Processing (NSPs)Native Service Processing (NSPs) PW-layer OAM (at least Continuity Check) PW control protocol Load balancing Protection (redundancy) mechanism MultisegmentPWs (MSPWs) MultisegmentPWs (MS-PWs)Y(J)S PWE short Slide 9 SimplisticSimplisticMPLS solutionMPLS solutionSimplistic Simplistic MPLS solutionMPLS solutionCECEPPEPEPCECECECECEACsACseach customer network mapped to pair of (unidirectional) LSPsCECE each customer network mapped to pair of (unidirectional) LSPssupports various AC technologieshtik t/fl t d ith MPLS l b leach native packet/frame encapsulated with MPLS labelscaling problem.

4 Requires large number of LSPs P-routers need to be aware of customer networksY(J)S PWE short Slide 10(Martini) pseudowires (Martini) pseudowires (Martini) pseudowires (Martini) PseudowiresCEtransport tunnelPECECEPECECEACsACsCECEPWs are bidirectionaltransport MPLS tunnel set up between PEsmultiple PWs may be set up inside tunnelPW (inner) labelMPLS (outer) labelpypnative packet/frame encapsulated with 2 labelspayloadPEs contain the PW interworking functionP-routers are unaware of individual customer networksY(J)S PWE short Slide 11 PseudowirePseudowireencapsulationsencaps ulationsencapsulationsencapsulationsEnca psulation:Encapsulation:IIn order to enable transport over the PSNn order to enable transport over the PSNE ncapsulation: Encapsulation: IIn order to enable transport over the PSN, n order to enable transport over the PSN, native service Protocol Data Units (PDUs) must be inserted native service Protocol Data Units (PDUs) must be inserted into packets of the appropriate packets of the appropriate is usually accomplished by adding headersThis is usually accomplished by adding headersThis is usually accomplished by adding is usually accomplished by adding (J)S PWE short Slide 12 Generic PWEG eneric PWE33packet formatpacket formatGeneric PWEG eneric PWE3 3 packet formatpacket formatPSN / multiplexingPSN / multiplexingoptional RTP headeroptional RTP headeroptional control word (CW) hhigher lnative service payloadlayersnative service payloadWe will ignore the RTP header in the followingWe will ignore the RTP header in the followingY(J)

5 S PWE short Slide 13 MPLS PSNMPLS PSNtunnel PW CWPldMPLS PSNlabel(s)PW labelCWPayloadMPLS over EthernetEthernet MAC header (DA SA, ..)(,)MPLS label stackPW label(bottom of label stack S=1)Control Word PW label (bottom of label stack S=1)native service payloadEthernet FCSY(J)S PWE short Slide 14IP PSN using LIP PSN using L22 TPvTPv33IP PSN using LIP PSN using L22 TPvTPv33L2 TPv3 RFC 3931 (without UDP)IP header (5*4 B) ()IP protocol 115session ID (4 B)il ki(48B)poptional cookie (4 or 8 B)control word (4 B)native service payloadY(J)S PWE short Slide 15IP PSN using UDPIP PSN using UDPith PW l b l i dtititith PW l b l i dtititwith PW label in destination portwith PW label in destination portUDP/IP for TDM PWsIP header(5*4B)IP header (54 B) return PW label (2 B)(8B)PW label (2 B)P header (control word(4B)UDP length and checksum (4 B)UDPcontrol word (4 B)native service payloadpyPW labels between C000 and FFFFY(J))

6 S PWE short Slide 16IP PSN using UDPIP PSN using UDPith PW l b l itith PW l b l itwith PW label in source portwith PW label in source portUDP/IP - 5087IP header(5*4B)IP header (54 B) PW label (2 B)(8B)well known port (085E) (2 B)P header (control word(4B)UDP length and checksum (4 B)UDPcontrol word (4 B)native service payloadpyPW labels between C000 and FFFFY(J)S PWE short Slide 17IP PSN using RFCIP PSN using RFC40234023IP PSN using RFC IP PSN using RFC 40234023 MPLS over IP using RFC 4023IP h d(5*4B)IP header (5*4 B) IP protocol 47(GRE) or 137(MPLS)optional GRE header (8 B) GRE protocol 08847(MPLS Ethertype)PW label (4 B)control word (4 B)native service payloadY(J)S PWE short Slide 18 PWE ControlPWE ControlWordWord(RFC(RFC43854385))PWE Control PWE Control Word Word (RFC (RFC 43854385))0 0 0 0 flags FRGL engthSequence Number0 0 0 0 identifies packet as PW (not IP which has 0100 or 0110) gives clue to ECMP mechanismsg 0001 for PWE associated channel (ACh) used for OAMF lags (4 b) notall encapsulation definenot all encapsulation define used to transport native service fault indicationsFRGmay be used to indicate payload fragmentation may be used to indicate payload fragmentationz00 = unfragmented 01 = 1stfragment z10 = last fragment 11 = intermediate fragmentLth(6b)Length (6 b) used when packet may be padded by L2 Sequence Number (16 b) q() used to detect packet loss / misordering processing slightly different in TDM PWsY(J)S PWE short Slide 19 TDM PWsTDM PWsY(J))

7 S PWE short Slide 20 TDM PWTDM PWProtocol ProcessingProtocol ProcessingTDM PW TDM PW Protocol ProcessingProtocol ProcessingTDMTDMPSN PacketsPSN PacketsTDMPSNS teps in TDM PW processing The synchronous bit stream is segmented The synchronous bit stream is segmented The TDM segments may be adapted TDMoIPcontrol word isprepended TDMoIPcontrol word is prepended PSN headers are prepended (encapsulation) Packets are transported over PSN to destinationPackets are transported over PSN to destination PSN headers are utilized and stripped Control word is checked, utilized and strippedpp TDM stream is reconstituted (using adaptation)and played outY(J)S PWE short Slide 21 FlagsFlagsFlagsFlags0 0 0 0 flagsFRGL engthSequence NumberL R M(2b)The PWE control word has 2 flags: L and R ()and a 2-bit field: MThey are used in the following way :ygy Lis set to indicate a forward defect (AIS) Rmay be set to indicate a reverse defect (RDI)Mdif thif th FDI Mcan modify the meaning of the FDIY(J)S PWE short Slide 22 TDM StructureTDM StructureTDM StructureTDM Structurehandling of TDM depends on its structureunstructured TDM(TDM = arbitrary stream of bits)unstructured TDM (TDM = arbitrary stream of bits).

8 Structured TDMS framed (8000 frames per second) (single byte timeslots)bits(1 byte) (J)S PWE short Slide 23 TDM transport typesTDM transport typesTDM transport typesTDM transport typesStructure-agnostic transport (SAToP RFC4553)gp for unstructured TDM even if there is structure, we ignore itiltf kild simplest way of making payload OK if network is well-engineeredStructure-aware transport (CESoPSN RFC 5086, TDMoIP RFC 5087) take TDM structure into account must decide which level of structure(framemultiframe) must decide which level of structure (frame, multiframe, ..) can overcome PSN impairments (PDV, packet loss, etc)The Frame Alignment Signal (FAS) is maintained at PSN egressOverhead bitsmaybe transportedOverhead bits maybe transportedY(J)S PWE short Slide 24 Structure Agnostic TransportStructure Agnostic TransportStructure Agnostic TransportStructure Agnostic TransportSAToP encapsulates N bytes of TDM in each packetThere is no TDM frame alignment !

9 There is no TDM frame alignment !N must be constant and preconfiguredIf packets are lost, the egress knows how many TDM bytes to fill inDefault values for N : E1 256 BT1192B T1 192 B E3 and T3 1024 BFor T1there is an optional special mode calledoctetaligned modeFor T1 there is an optional special mode called octet aligned modethat adds 7 bits of padding to every 193 consecutive bits (to make 25 B)Y(J)S PWE short Slide 25 Structure aware encapsulationsStructure aware encapsulationsStructure aware encapsulationsStructure aware encapsulationsStructure-locked encapsulation (CESoPSN)headersTDM structureTDM structureTDM structureTDM structureStructure-indicated encapsulation (TDMoIP AAL1 mode)headersAAL1 subframeAAL1 subframe AAL1 subframe AAL1 subframeStructure-reassembled encapsulation (TDMoIP AAL2 mode)headersAAL2ii llAAL2ii llAAL2ii llAAL2ii llheadersAAL2 minicellAAL2 minicellAAL2 minicellAAL2 minicellY(J)

10 S PWE short Slide 26 Structure indicationStructure indication--AALAAL11 Structure indication Structure indication AALAAL11 For robust emulation: adding a packet sequence number adding a pointer to the next superframe boundary only sending timeslots in use only sending timeslots in use allowing multiple frames per packetUDP/IPT1/E1 frames (only timeslots in use)seqnumptrfor example(with CRC)TS1 TS2 TS5 TS7 TS1 TS2 TS5 TS77@Y(J)S PWE short Slide 27 Structure reassemblyStructure reassembly--AALAAL22 Structure reassembly Structure reassembly AALAAL22 TDM frameTDM frameTDM frameTDM frameTDM frame12453112233445512345hdr12345hdr1234 5hdrPSN hdrsCWTS1TS2TS3 AAL1 is inefficient when timeslots are dynamically allocated each minicell consists of a header and buffered data minicell header contains: CID (Channel IDentifier) LI (Length Indicator) = length-1 UUI (UserUser Indication) counter + payload type ID UUI (User-User Indication) counter + payload type IDY(J)S PWE short Slide 28 CAS and CCS signalingCAS and CCS signalingCAS and CCS signalingCAS and CCS signalingChannel Associated Signaling is carried in the T1/E1 (T1uses robbed bitsE1uses a dedicated time slotTS16)(T1 uses robbed bits , E1 uses a dedicated time slot -TS16)Unlike VoIP, TDM PWs transparently transport CASand may add a separatesignaling substructure(ATM-like)and may add a separate signaling substructure (ATMlike)that carries the CAS signaling bitsCESoPSN must respect CAS multiframe boundaries Thus it may fragment the mutiframe (using the CW FRG bits)and a