Agenda• Review of backhaul evolution• Evolved Packet System architecture and backhaul requirements No network controller• Example LTE backhaul network with centralised Evolved Packet Core (EPC)• Backhaul dimensioning• Backhaul performance requirements• Summary
Introduction• Mobile backhaul is defined as the connectivity between a cell site and its associated network controller In GSM this is between a BTS and BSC In UMTS this is between a NodeB and RNC• This definition of mobile backhaul tends to flex somewhat dependant upon the physical location of the BSC nodes If geographically deployed, A and Gb interface tend to fall within the overall mobile backhaul scope• Mobile backhaul networks were initially rolled-out as TDM E1s with PDH multiplexing followed by the integration of SDH• GPRS introduced Frame Relay as the transport technology for the Gb interface, now evolving to IP• UMTS introduced ATM however initially carried over E1 IMA groups• The future direction of mobile backhaul is packet over frame - IP over Ethernet• LTE (Strictly EPS) has no network controller…
Backhaul technologiesTransport Network Layer Physical Transmission• TDM • Copper• FR Cable and coax• ATM • Microwave radio• IP Point to point Point to multipointNetwork enablers • Optical fibre Dedicated point to point Shared infrastructure• PDH/SDH GPON• Carrier Ethernet WDM PON• MPLS …• PWE3
Evolved Packet SystemLong Term Evolution/Evolved Packet Core S1- C HSS eNB S6a Rx+ X2 MME Gx+ PCRF (S7) eNB S11 IP Services Internet IMS etc. X2 SAE PDN GW GW S5 SGi Control Plane eNB User Plane S1- U Note: Serving-GW and Packet Data Network-GW are likely to be implemented on a single network element (router based) Significant integration will be required with 2G/3G CS & PS networks to support wide area service mobility
LTE S1 interface• A direct logical interface between the eNB and evolved packet core S1-MME (S1-C) S1-AP• Separation of control and user plane MME S1-C (also known as S1-MME) S1-U SCTP IP -C Data Link S1 Physical IP Network S1-U eNB S1 UP PDUs -U• CP & UP protocol stacks employ IP as the transport network layer technology• As with all 3GPP specifications, the SAE GTP-U UDP GW underlying transport/transmission IP network is not specified Data Link• It is anticipated that S1 flex will be Physical implemented from day 1 in EPS
LTE X2 interface X2-C• A direct logical interface between adjacent X2-AP eNBs• Separation of control and user plane• X2-C SCTP IP• X2-U Data Link Physical eNB• CP & UP protocol stacks employ IP as the -C X2 U transport network layer technology X2 - X2-U• As with all 3GPP specifications, the UP PDUs underlying transport/transmission network is eNB not specified• Whilst X2 is employed to support mobility it GTP-U should be noted that S1 mobility is also UDP IP supported within EPS Data Link Physical
LTE backhaul networkCentralised EPC model Cell site #1 Connectivity site Super site X2 eNB S1 Cell site #2 X2 Mobile Core S1 Backhaul IP Switch/ S1 IP/MPLS MME/ eNB X2 Network Sec Router Network S-GW Cell site #3 X2 eNB S1 Latency, jitter and packet loss ratio• LTE backhaul can be built on today’s IP TNL backhaul architecture, an evolution…• All radio protocols terminate at the eNB therefore backhaul network performance is more visible - latency, jitter, packet error loss rate• 3GPP proposes optional security based on IPSec Tunnel mode connections established using IKE v2• Consider the location of services, SGi interface, on-net/off-net servers/hosting, CDN, peering/transit model etc…
EPS protocol architecture Roaming subs home PDN GW S8 interface In roaming Service LAN scenario Application External UDP/TCP Network(s) IP PDCP PDCP relay GTP-u GTP-u relay GTP-u GTP-u RLC RLC UDP/IP UDP/IP UDP/IP UDP/IP IPSec MAC MAC L2 L2 L2 L2 L1 L1 L1 L1 L1 L1 UE Uu interface eNodeB S1 interface Serving GW S5 interface PDN GW SGi interface Combined S/P GWConverging 2G/3G services and LTE on common backhaul infrastructure:• GSM will evolve from TDM based Abis to IP over Ethernet (or be PWE3)• UMTS is evolving from ATM over E1 IMA/PWE3 to IP over Ethernet• LTE introduces an IP TNL from day 1, 3GPP release 8 (as illustrated above)• However, LTE must co-exist with legacy RAN protocols, QoS considerations…
Backhaul dimensioningA topic of great debate…• Backhaul dimensioning can be considered from many perspectives however the model used will, in the main, be 1 of 3: All average Will result in an amount of blocking in some circumstances All average/single peak Seems a pragmatic middle ground, balance between marketing requirements and actual backhaul requirements All peak Will result in an over dimensioned backhaul network• There is no right or wrong answer as such, depends on network and business strategy• Any GSM/EDGE and UMTS/HSPA requirements for backhaul must be considered along with LTE• Engineering rules must be applied to ensure optimal network performance on the Ethernet based backhaul
Key backhaul parameters• S1-C (S1-MME) latency• S1-U latency• X2-C latency• X2-U latency• S1-C (S1-MME) jitter• S1-U jitter• X2-C jitter• X2-U jitter• S1-C (S1-MME) packet loss rate• S1-U packet loss rate• X2-C packet loss rate• X2-U packet loss rate• OAM/Management requirements, generally less stringent than those stated above• Synchronisation requirements, assuming FDD therefore fractional frequency offset only at this stage, no phase or time of day.• Backhaul sharing, if implemented, how do we manage QoS, fair access between operators etc.
3GPP TS 23.203 V8.11.0 (2010-09) Packet Resource Scheduling Packet Delay QCI Error Loss Example Services Type Priority Budget (Target) Rate 1 2 100ms 10-2 Conversational voice 2 4 150ms 10-3 Conversational video (live streaming) GBR 3 3 50ms 10-3 Real-time gaming 4 5 300ms 10-6 Non-conversational video (buffered streaming) 5 1 100ms 10-6 IMS signalling Best-effort video (buffered streaming), TCP based (eg. www, email, 6 6 300ms 10-6 chat, ftp, P2P file sharing, progressive video etc.) Non-GBR 7 7 100ms 10-3 Best-effort voice, video (live streaming), and interactive gaming 8 8 300ms 10-6 Best-effort video (buffered streaming), TCP based (eg. www, email, 9 9 300ms 10-6 chat, ftp, P2P file sharing, progressive video etc.)A delay of 20 ms for the delay between a PCEF and a radio base station should be subtracted from agiven PDB to derive the packet delay budget that applies to the radio interface. This delay is theaverage between the case where the PCEF is located "close" to the radio base station (roughly 10 ms)and the case where the PCEF is located "far" from the radio base station, e.g. in case of roaming withhome routed traffic (the one-way packet delay between Europe and the US west coast is roughly 50ms). The average takes into account that roaming is a less typical scenario. It is expected thatsubtracting this average delay of 20 ms from a given PDB will lead to desired end-to-end performancein most typical cases. Also, note that the PDB defines an upper bound. Actual packet delays - inparticular for GBR traffic - should typically be lower than the PDB specified for a QCI as long as the UEhas sufficient radio channel quality.
3GPP TS 23.203 V8.11.0 (2010-09) Packet Resource Scheduling Packet Delay QCI Error Loss Example Services Type Priority Budget (Target) Rate 1 2 100ms 10-2 Conversational voice 2 4 150ms 10-3 Conversational video (live streaming) GBR 3 3 50ms 10-3 Real-time gaming 4 5 300ms 10-6 Non-conversational video (buffered streaming) 5 1 100ms 10-6 IMS signalling Best-effort video (buffered streaming), TCP based (eg. www, email, 6 6 300ms 10-6 chat, ftp, P2P file sharing, progressive video etc.) Non-GBR 7 7 100ms 10-3 Best-effort voice, video (live streaming), and interactive gaming 8 8 300ms 10-6 Best-effort video (buffered streaming), TCP based (eg. www, email, 9 9 300ms 10-6 chat, ftp, P2P file sharing, progressive video etc.)The rate of non congestion related packet losses that may occur between a radio base station and aPCEF should be regarded to be negligible. A PELR value specified for a standardized QCI thereforeapplies completely to the radio interface between a UE and radio base station. Open question: What’s really required from a mobile backhaul network in terms of latency, jitter and packet error loss rate..? - One to discuss!
Summary• The introduction of LTE will drive backhaul evolution• LTE backhaul will integrate into an evolved 2G/3G backhaul infrastructure• L2 and L3 capability will be required to ensure an optimised backhaul solution between the cell site and core connectivity site• However, don’t forget the underlying L1 requirements!• Separation of control and user plane is an architectural consideration• Capacity is one consideration, latency, jitter and packet error loss rate are also important considerations…• Key industry initiatives are on-going within the BBF, MEF and NGMN Alliance, check out their websites for details
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