Mobile Packet Network for LTE

Suleman Saleem ChaudhrySupervisor: Raimo KantolaInstructor: Heikki Almay

Work is carried out in NSNMethods: Literature, Work Experience, Trials, Test bed Support

Agenda

Thesis Objective

Introduction to LTE

Mobile Packet Network of LTE

High Level Design

Low Level Design

Mobile Backhaul of LTE-Results

Core Network of LTE-Results

Future Work

Thesis Objective

Mobile Packet Network refers to the transport network (packet) designed to carry the traffic from access to the core and services network (IMS, Internet) in LTE.

LTE is the evolution of the mobile networks towards a packet switched optimized and flat IP architecture, aka 4G.

The LTE standardization doesnt cover the transport network design.

The objective of this thesis is to design a mobile packet network for LTE networks keeping in view the requirements of the technology. The two aspects of the thesis are

To design the mobile backhaul of LTE network by considering various attributes e.g. performance, cost, complexity and scalability as the criteria for selecting transport infrastructure.

To plan the core network of LTE by considering various traffic types, virtualization, forwarding (routing/switching) and additional services e.g. NAT and VPN as the challenging requirements.

Scope and Layout

Pre-requisite for the thesis:

Study of LTE network

Study of all legacy networks

Study of practical challenges in mobile networks

Comparison of mobile (data) vs. enterprise networks

Scope

The scope of this thesis is E2E mobile network. More emphasis has been put on access whereas the transport design for core network has been re-planned, keeping in view the legacy networks.

Layout

Requirements Model

Design Concerns/Challenges

Design Model

Long Term Evolution (LTE) Introduction

LTE, according to specification, is the evolution of the mobile radio networks, also known as E-UTRAN (Evolved-UMTS Terrestrial Radio Access Network)

System Architecture Evolution (SAE) is the name of the Third Generation Partnership Project (3GPP) standardization work which defines the evolution of the packet core network, more commonly referred to as Evolved Packet Core (EPC).

Evolved Packet System (EPS) is used to refer the evolved radio access, the evolved core network and the terminals that comprise the overall mobile system.

Generally LTE is used quite commonly to refer to LTE or 3GPP next generation mobile network- 4G.

The major objectives of LTE are:

Packet switched optimized architecture.

Higher data rates, lower latency, lower round trip times

Higher spectral efficiency and spectral flexibility

Mobility (3GPP and non-3GPP)

LTE Network

E2E IP Connectivity (Flat IP network)

E-UTRAN

Radio Network of LTE.

Flat i.e. No controllers, just eNodeB.

EPC

Packet Switched Optimized

Split Control Plane/User plane

SAE-GW (User plane, ex-GGSN)

MME (Control Plane, ex SGSN)

Services

Internet

IMS

What is not visible is the transport network

Long Term Evolution Historical Evolution

GSM (2G) designed to carry voice traffic, using circuit switched domain.

Support for data traffic added later, hence introducing packet switched domain.

Exponential data traffic growth always remained a driver for evolution.

The co-existence of circuit and packet switched domain along with the complex radio access networks were the major bottlenecks for the evolution.

EPS/LTE architecture introduces a flat and packet switched optimized network.

In mobile access, many interfaces have gradually evolved from TDM/ATM towards IP e.g. A over IP, IuCS over IP, Packet Ater etc but still not deployed to much extent so packetization in mobile backhaul is still in initial phases.

IP in mobile core has already been introduced since Release-4. So IP in core networks is not a major change but IP in mobile backhaul is.

Historical Evolution (Contd.)

Mobile Packet Network for LTE

High Level Design

Mobile Packet Network for LTE Physical Domains

Mobile packet network of LTE has be divided into four domains.

Access

Aggregation (Includes legacy connectivity)

Multiservice backbone (IP/MPLS)

Evolved Packet Core Domain

Access: Access domain is the network next to the eNodeB (Cell site).

Aggregation: The domain merging traffic from multiple cell sites as well as from legacy radio networks (BSC, RNC).

Multiservice backbone: The MPLS backbone connecting the radio network with core network and services domain (IMS, Internet)

Evolved Packet Core Domain: The network connecting all the core elements (EPC) on site.

Access and Aggregation are part of Mobile Backhaul whereas Multiservice backbone and EPC domain resides in the core network.

Mobile Backhaul of LTE

Mobile Packet Network for LTE

Low Level Design

Mobile Packet Network for LTE Requirements Model

Access

Less Latency Low costLess Hops Less complexityHigh capacity

Scalability

Aggregation

Scalability Low costConverged QOS Less complexityHigh capacity

Flexibility

CoreHigh capacity interfaces (+10G)ScalabilityConverged and Optimized DesignHigh Availability

Multiservice backboneConverged QOSMultiservice Support (NAT, VPN)Scalability

Mobile BackhaulCore

Mobile Packet Network for LTE Design Methodology

Mobile Backhaul of LTE

The architecture of mobile backhaul is studied through various angles i.e. transport medium, transport infrastructure, transport capabilities etc.

The most relevant and main concern is to design the mobile backhaul with only L2 capabilities (switches) or to design it with L3 based routers. The commercial arguments stretch as far as moving the IP/MPLS backbones from the core networks towards mobile backhaul. In principle, the underlying issue is L2 vs. L3 in mobile backhaul.

The L2 design and L3 designs are evaluated based on efficiency, resilience and quality of service.

In aggregation domain the packetized interfaces of the legacy networks are elaborated and a converged QOS model is presented for the transport of shared access network.

Mobile Backhaul of LTE L2 vs. L3 Design

Transport Medium:

Copper vs. Fiber vs. Microwave

Transport Infrastructure:

Ethernet vs. SDH (NG-SDH) vs. VDSL

Transport Capabilities:

L2 vs. L3

Resilience:

Resilient Ethernet Protocol (REP) vs. Multichasis Link Aggregation Protocol (L2)

Multihoming vs. Multipoint (L3)

QOS:

R97/98 PDP attributes vs. R99 PDP attributes vs. EPS bearer attributes

QCI (QOS Class Identifier) vs. DSCP

Results

The maximum bandwidth requirement in access network is 1Gbps/eNodeB (prospective). The capacity depends on the numbers of cells, frequency, antenna types.

In access, fibre must be always selected, microwave for remote and less bandwidth hungry regions. Copper is not scalable for LTE traffic, only possible to reuse for some more years to come.

Ethernet is cost efficient, scalable for the growing data traffic, easy to upgrade and should be preferred otherwise NG-SDH (reusable).

The design capability is evaluated using various attributes. The analysis concludes the selection based on only cost and complexity. L2 based design are simple and quite cost efficient whereas L3 based design can prove expensive and complexity can grow depending on the use of the transport.

LTE serving nodes are QOS aware, complete QOS is handled by each participating node whereas in legacy networks, QOS is handled by the transport network.

Mobile Backhaul of LTE L2 vs. L3 Design

Results QOS in LTE

Results QOS in Shared Radio

LTE Core Network

IP in mobile core networks has already been introduced since Release-4. Since the core sites from legacy sites are co-located so the design for the existing IP-transport has been modified to include the evolved packet core (EPC).

The complete core network design constitutes of EPC site connectivity as well the Multiservice backbone (IP/MPLS).

Evolved Packet Core in LTE is dominated with high capacity interfaces. Also EPC is a packet switched architecture i.e. voice is packetized as well so the QOS requirements are quite stringent.

EPC has interfaces toward legacy networks (3GPP and non 3GPP), hence there are quite many interfaces overall.

Finally the QOS model for the multiservice backbone domain is also updated according to the requirement put forward by EPC.

Results LTE Core Network

EPC has its interfaces for multiple traffic types (user, control, synchronization, management). The traffic is virtualized using VLANs and VRFs in order to increase efficiency and reduce the routing table lookup times.

Routing protocol (OSPF) needs to be optimized using timers or fast hellos in order to reduce convergence times.

Bidirectional Forwarding Detection has to be used with routing protocol in order to achieve convergence times in milliseconds.

Redundancy to be provided using either dual chassis solution or single chassis solution with high availability features i.e. Non stop forwarding (NSF), Graceful restart, In Service Software Upgrade (ISSU) etc.

Multiple resilience mechanisms have to be utilized etc. OSPF with ECMP, load balancing, multihoming, multipoint in order to achieve high availability.

QOS has to be provided in transport by mapping the traffic classes in EPC over to DSCP values.

EPC Site Solution

Results LTE Core Network

Conclusions

LTE introduces a complete all IP-flat architecture in mobile backhaul.

Mobile backhaul will likely go through significant changes. Existing infrastructure (SDH/PDH) cant cope with the high capacity requirements. Also the transport media used in backhauls cant fulfill the capacity of growing data traffic, so existing media should be replaced with better alternatives (fiber, packet microwaves).

Cost and complexity is likely to influence the decision to use Carrier Ethernet in mobile backhaul.

The transport design for legacy core networks has to be modified in order to support the packetized voice traffic in EPC.

Multiservice backbones have to support more stringent QOS requirements in order to support the packetized voice.

Mapping various QOS models (R97/98, R99, EPS) in shared radio networks is still an issue.

Future Work

Carrier Ethernet in Multiservice backbone and Core networks

Performance Evaluation of the design

Impact Analysis on design by IPv6 migration

Comparison with MPLS-TP based design

Questions

Thank You

Mobile Packet Network for LTEAgendaThesis ObjectiveScope and LayoutLong Term Evolution (LTE)IntroductionLTE NetworkLong Term EvolutionHistorical EvolutionHistorical Evolution (Contd.)Mobile Packet Network for LTEMobile Packet Network for LTEPhysical DomainsMobile Backhaul of LTEMobile Packet Network for LTEMobile Packet Network for LTE Requirements ModelMobile Packet Network for LTE Design MethodologyMobile Backhaul of LTEMobile Backhaul of LTE L2 vs. L3 DesignResultsMobile Backhaul of LTE L2 vs. L3 DesignResultsQOS in LTEResultsQOS in Shared RadioLTE Core NetworkResultsLTE Core NetworkEPC Site SolutionResultsLTE Core Network ConclusionsFuture Work Questions