Mobile Packet Network for LTE

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10 Δεκ 2013 (πριν από 4 χρόνια και 7 μήνες)

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Mobile Packet Network for LTE
Suleman Saleem Chaudhry
Supervisor: Raimo Kantola
Instructor: Heikki Almay
Work is carried out in NSN
Methods: Literature, Work Experience, Trials, Test bed Support

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 doesn’t 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


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.


Requirements Model

Design Concerns/Challenges

Design Model
Long Term Evolution (LTE)

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)


Radio Network of LTE.

Flat i.e. No controllers, just eNodeB.


Packet Switched Optimized

Split Control Plane/User plane

SAE-GW (User plane, “ex-GGSN”)

MME (Control Plane, “ex SGSN”)




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.


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
Less Latency Low cost
Less Hops Less complexity
High capacity
Scalability Low cost
Converged QOS Less complexity
High capacity
High capacity interfaces (+10G)
Converged and Optimized Design
High Availability
Multiservice backbone
Converged QOS
Multiservice Support (NAT, VPN)
Mobile Backhaul
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

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


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

Multihoming vs. Multipoint (L3)


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

QCI (QOS Class Identifier) vs. DSCP

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
Mobile Backhaul of LTE
L2 vs. L3 Design
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

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.
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
LTE Core Network

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
Thank You