5G Transport Network Technology.pptx

5G Transport Network Technology

Contents
MPLS VPN
FlexE
Segment Routing
5G transport network
IP Routing

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New requirement to 5G Transport Network
infrastructure
Requirement
Changes
5G transport network need to be re-architected
due to brand new requirement for bandwidth, delay, synchronization, infrastructure, architecture etc.
uRLLC
mMTC
eMBB
5G new scenarios
Networking
architecture
Changes
Service
Requirement
Changes
Infrastructure
Requirement
Changes
Bandwidth
320M -> 10Gbps
Single station
New challenges to transport network
5G RAN
CU/DU Decouple
5G Core
Cloud core network,
UPF sink, MEC
Delay
10ms -> 1ms
One-way
delay
Slicing
eMBB
uRLLC,
mMTC
Sync.
1.5µs ->
400ns
Time sync.
Optical Fiber
High 5G site density
demands numerous terminal
optical fibers
Equipment Room
More requirement requests more
rooms, power supply and heat
dissipation
5G_CP
mMTC CP/UP
5G_CP 5G_CP
5G_UP
5G_
UP
5G_UP 5G_UP
Connections among
NE devices
change to
Unified and flexible
interconnection
among clouds

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Key technologies of 5G transport network
IP Routing
• Centralized control plane.
• Distributed UPF.
• Full mesh communication
between 5G gNB.
MPLS VPN
• Connection-oriented unified
NMS
• Compatible with 3G/4G
transport network
FlexE
• Hard/soft slicing deploy on
demand
• Achieves many possibilities
in physical traffic separation,
traffic multiplexing, and traffic
cross-connection.
Segment Routing
• Ready for SDN
• Simplified protocol
• Supports Fast Reroute
• Large-scale Data Center
• Centralized Traffic Engineering
Controller
N*100/400GE
N*100GE
50GE/100GE
Fronthaul
Edge DC Regional DC Central DC
Access Aggregation Core
Unified SR/EVPN
Netconf/PCEP BGP-LS
10GE/25GE to Site CU
DU
UPF/MEC

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Business drivers for network evolution to IP
 Convergence
- One IP network supporting all services
(voice,video,data,etc)
- All services on IP protocol
 Significant cost and investment reduction.
 New opportunities for service providers
- Profitable service offerings
- E-commerce
- E-marketing
- etc.

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One IP Network Supporting All Services
 Convergence: Voice, Data, TV, VoD, Mobility, etc.

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OSI Model and TCP/IP Model

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 IPv4 is a header which is made up of a number of fields.
 Each field in the IPv4 header has a task.(e.g. Addresses, QoS,
Packet Fragmentation)
 Router examines IP header (reads the fields) and decides on the next hop by
looking at the ‘Destination’ IP field.
IPv4 Packet Structure

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Process of IP Routing
R1
（100.1.0.0）
（200.2.0.0）
R5
R2
R3
R4
100.1.1.1
Desti./MASK NEXTHOP
100.1.0.0/16 R1
…..
Desti./MASK NEXTHOP
100.1.0.0/16 R2
…..
Desti./MASK NEXTHOP
100.1.0.0/16 DIRECT
…..

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Components of Routes
Destination/Mask
Protocol
Administrative
Distance
Metric
nexthop
Out-interface
a route

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 Source of routes:
 Direct route：the links are direct connected, and routes are automatic discovered.
 Static route：the routes are manually configured.
 Dynamic route：the routes are discovered and calculated by routing protocols such as BGP,
ISIS, OSPF and RIP, etc.
How are the routes generated?
Static OSPF
Routing table
10.0.0.0 R0
10.0.0.0 R0
10.0.0.0 R1
Source
Administrative
Distance
connected 0
OSPF 110
STATIC 1
ISIS 115 or 116
BGP 200
UNKNOWN 255

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Example of Direct Route
10.1.1.0/30
RTA
10.1.2.0/30
.1
.1 .2
.2
RTB
RTC
Ethernet0/2
Ethernet0/1
[RTB]show ip route
Destination/Mask Protocol Administrative Distance Metric Nexthop Interface
10.1.1.0/30 connected 0 0 10.1.1.1 Ethernet0/2
10.1.1.1/32 connected 0 0 127.0.0.1 InLoopBack0

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Example of Static Route
[RTA] show ip route
2.2.2.2/32 Static 1 0 10.1.2.2 Ethernet0/1
Configure the route to reach 2.2.2.2/32
RTB
2.2.2.2/32
10.1.1.0/30
RTA
.1 .2
Ethernet0/1

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10.1.1.0/24
10.2.2.0/24 10.3.3.0/24
10.4.4.0/24
A B C
.1 .1
.2 .2
Command on PC:
router(config) # ip route 50.13.100.0/24 50.8.1.1
• Requirement: 10.1.1.0/2/24 visits 10.4.4.0/24
• How many static routes?
Configuration of Static Route
 Manually create a route that specifies Destination/mask, the nexthop or out interface
Command on devices:

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 Default route is a special kind of routing.
 Default route is used when no matching route is found.
 In the routing table, the default route is represented as destination 0.0.0.0 (with mask
0.0.0.0).
 Application: when there is only one exit (that is, gateway) to other segments.
Default Route
10.1.1.0/24
10.2.2.0/24 10.3.3.0/24
10.4.4.0/24
A B C
.1 .1
.2 .2
RouterA(config) # ip route 0.0.0.0 0.0.0.0 10.2.2.2

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[RTB]show ip route
……
172.16.1.1/32 OSPF 110 10 10.1.2.2 Ethernet0/1
192.168.1.0/24 ISIS 115 10 10.1.1.1 Ethernet0/2
10.1.1.0/30
RTB
10.1.2.0/24
.1
.1
OSPF
ISIS
RTA
RTC
172.16.1.1/32
192.168.2.1/24
.2
.2
Ethernet0/1
Ethernet0/2
Example of Dynamic Route

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Classification of Dynamic Routing Protocols
 According to the working range:
 Distance Vector: such as RIP, BGP
 Link State: such as OSPF, ISIS
 According to the working algorithm:
 Internal gateway protocol (IGP) : RIP, OSPF, ISIS.
 External gateway protocol (EGP) : such as BGP.
AS 100
BGP
ISIS
AS 200
ISIS
ISIS
ISIS
OSPF OSPF
OSPF
OSPF
An autonomous system (AS) is a collection of connected routers
under the control of one operators on behalf of a single
administrative entity or domain that presents a common, clearly
defined routing policy to the Internet.

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Working Range Of MAC and IP Address
 MAC addresses are used to communicate within the same subnet, and IP
addresses are used to communicate across segments.
 MAC addresses are physical addresses, and IP addresses are logical addresses.
E0
A B
E1 E1
E0
PC1
PC2
.2
.1 .2
.2
.1
.1
10.2.2.0/24
Working Range of MAC address
Working Range of IP address

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ARP Protocol
IP1
MAC1
PC1
 Address Resolution Protocol (ARP) is used to acquire the MAC address of a specific IP
address.
 ARP request message is to require Destination MAC address of a specific IP address .
 ARP reply message is to advertise the required Destination MAC address.
PC2
IP2
MAC2
SW
ARP reply message
ARP request message
Sender MAC：
MAC1
Sender IP：
IP1
Target MAC：
00-00-00-00-00-00
Target IP：
IP2
Sender MAC：
MAC2
Sender IP：
IP2
Target MAC：
MAC1
Target IP：
IP1

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I know, =MAC2
I know, =MACb.1
Example of an ARP (1/2)
 PC1 sends a message to PC2.Assuming there is no corresponding table item in the ARP
table.
E0
A B
E1 E1
E0
PC1 PC2
.2
.1 .2
.2
.1
.1
10.2.2.0/24
ARP request
ARP reply
PCI
Port E0 of
Router A
Port E1 of
Router A
Port E1 of
Router B
Port E0 of
Router B
PC2
IP address IP1 IPa.0 IPa.1 IPb.1 IPb.0 IP2
MAC address MAC1 MACa.0 MACa.1 MACb.1 MACb.0 MAC2
MAC address of nexthop?

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E0
A B
E1 E1
E0
 According to the instructions of ARP table, PC1 completes the packaging and sends a
message to PC2.
PC1
PC2
.2
.1 .2
.2
.1
.1
10.2.2.0/24 IP Packet
IP1
IP2
MAC1
MACa.0
DMAC SMAC DIP SIP
IP1
IP2
MACa.1
MACb.1
DMAC SMAC DIP SIP
IP1
IP2
MACb.0
MAC2
DMAC SMAC DIP SIP
Example of an ARP (2/2)
Network layer
Data link layer
Physical layer
Application layer
Transport layer
Network layer
Data link layer
Physical layer
5
4
3
2
1
Application layer
Transport layer
Network layer
Data link layer
Physical layer
5
4
3
2
1
Network layer
Data link layer
Physical layer

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 Please indicate the source destination IP and MAC addresses of the packet at points A, B, C
and D?
Internet
PC1 SW1 Router1
Server1
IP1/MAC1 IP2/MAC2 IP3/MAC3
IP4/MAC4
A B C
D
Question 5

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What Is A VPN Service?
Virtual Private Network
 A VPN is private,
because it has the same
properties as locally run
internal networks.
Customer sites are
separated.
 It is also virtual, all the
VPN’s will use the same
physical network under
their virtual ones. As the
VPN’s are private they
will not see each others
traffic.

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FR/ETH
ATM
FRAME
LABLE
FRAME
LABLE
FRAME
LABLE
FR/ETH
ATM
What are MPLS VPNs?
MPLS Network

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 Advantages of IP: Control plane: automatically calculates routes and dynamically updates
routes by using dynamic routing protocols.
 Advantages of ATM: Forwarding plane: forwards packets through label switching and is
connection-oriented, which guarantee quality of service (QOS).
Origin of MPLS

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MPLS Overview
 MPLS: Multi-Protocol Label Switching
 Multi-Protocol: Multiple layer 3 protocols, such as IP, IPv6, and IPX, are supported.
 Label Switching: MPLS operates at a layer that is generally considered to lie between
traditional definitions of OSI Layer 2 (data link layer) and Layer 3 (network layer), and thus is
often referred to as a layer 2.5 protocol. It was designed to provide a unified data-carrying
service for both circuit-based clients and packet-switching clients which provide
a datagram service model. It can be used to carry many different kinds of traffic, including
IP packets, as well as native ATM, SONET, and Ethernet frames.

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Label Forwarding (1)
Egress LER
IP header analysis
Binding between FECs and LSPs
Mapping from labels to FECs
Ingress LER LSR LSR
Label operation: Push
A B C D
A:
E1

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Ingress LER LSR LSR
Label operation: Swap
A B C D
…
Replace the original label with an L2
label
E0
C
L1
Others
Operation
Outgoing
interface
Next hop
Incoming label
B:
E0

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Ingress LER LSR LSR
Label operation: Swap
A B C D
…
Replace the original label with an
L3 label
E0
D
L2
Others
Operation
Outgoing
interface
Next hop
Incoming label
C:
E0

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Mapping from labels to FECs,
IP header analysis,
Mapping to next hop
Ingress LER LSR LSR
Label operation: Pop
A B C D
…
Remove the label
D
L3
Others
Operation
Outgoing
interface
Next hop
Incoming
label
D:

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Roles of VPN
 Custom Edge (CE): user equipment in direct connection with the service provider.
 Provider Edge Router (PE): edge router on the backbone network, which is connected to a
CE device and handles VPN service access.
 Provider Router (P): core router on the backbone network, which implements the routing and
fast forwarding functions.
VPN_A
VPN_A
VPN_B
CE
CE
CE
CE
PE
PE
CE
CE
CE
VPN_A
VPN_A
P
P
P
P
PE
PE
VPN_B
VPN_B

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LSP Establishment
Static LSP is established by manually allocating labels for FECs. A principle that must be followed
in manually allocating labels is that: the value of the outgoing label of current node is the same as
that of the incoming label of the next node.
Dynamic LSP is established dynamically using routing protocols and label advertisement
protocols. MPLS supports several label advertisement protocols:
Label Distribution Protocol (LDP): LDP specifies the messages to be exchanged during label
advertisement and relevant processing. Through LDP, two LSRs negotiate label advertisement
and establish an LSP. LSRs query their local forwarding tables for incoming labels, next-hop
node, and outgoing labels that correspond to specific FECs and combine these information to
build LSPs across the entire MPLS domain.

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Resource Reservation Protocol Traffic Engineering (RSVP-TE): RSVP is designed for the
Integrated Service model to reserve resource at nodes on a path. Despite working at the transport
layer, RSVP does not participate in application data transmission but functions as a control protocol,
like ICMP. As an extension of RSVP, RSVP-TE is used to establish Constraint-based Routed Label
Switched Paths (CR-LSPs), namely TE tunnels. RSVP-TE provides functions such as advertising
bandwidth reserve requests, bandwidth constraint, link coloring, and explicit path, which are
unavailable for common LDP LSP.
Multiprotocol Border Gateway Protocol (MP-BGP): MP-BGP is an extension of BGP. It
introduces the Community attribute and can be used to allocate labels for VPN routes and multi-
domain VPN labeled routes in MPLS VPN services.
LSP Establishment

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47.1
47.2
47.3
IP 47.1.1.1
Dest Out
47.1 1
47.2 2
47.3 3
1
2
3
Dest Out
47.1 1
47.2 2
47.3 3
1
2
1
2
3 IP 47.1.1.1
IP 47.1.1.1
IP 47.1.1.1
Difference between IP Routing and MPLS
DEST OUT
47.1.0.0 1
47.0.0.0 1
47.1.1.0 1
IP Networking

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MPLS Forwarding
During MPLS label forwarding, LSPs are established for packets beforehand by using allocated
labels. When a packet arrives at a device on such an LSP, only labels in the packet are switched
quickly.
Intf
In
Label
In
Dest Intf
Out
3 40 47.1 1
Intf
In
Label
In
Dest Intf
Out
Label
Out
3 50 47.1 1 40
47.1
47.2
47.3
1
2
3
1
2
1
2
3
3
IP 47.1.1.1
IP 47.1.1.1
Intf
In
Dest Intf
Out
Label
Out
3 47.1 1 50

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L2VPN Introduction
MPLS L2VPN means to transparently transmits L2 data of users on an MPLS network. From the
point of view of users, an MPLS L2 VPN is a two-layer switching network, on which an L2
connection can be established between different sites. MPLS L2VPN needs the following parts:
 Attachment Circuit (AC): An AC is an independent link or circuit attaching a CE to a PE. The AC
interface is a physical or logical interface. AC attributes include encapsulation mode, maximum
transmission unit (MTU), and interface parameters of specific link types.
 Virtual Circuit (VC): A VC is a logical connection between two PEs.
 Network Tunnel (Tunnel): transparently transmit user data.
CE
CE PE PE
tunnel
AC AC
VC
MPLS network

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MPLS L2VPN Principle
P
CE 1 CE 2
PE 1 PE 2
L2PDU L2PDU
L2PDU
T' V
L2PDU
T V
MPLS L2VPN also uses a label stack to transparently transmit user packets through an MPLS
network.
 Outer label (Tunnel label): used to transmit packets between PEs.
 Inner label (VC label in MPLS L2 VPN): used to identify connections of different VPNs. The PE
receiving a packet identifies the destination CE of the packet according to the VC label.

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L2VPN Forwarding
Vlan: 10 Vlan: 50
Vlan Payload
VC Vlan Payload
LSP VC Vlan Payload
Vlan: 10 Vlan: 50
 PE needs to allocate two layers of labels for each VC.
 LSP is outer layer label, used to transmit the packets on the public network.
 VC is inner layer label, used to decide which VC the packets are belong to.
Vlan Payload
MPLS network
CE
CE
PE
PE

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CE
PE
PE
CE
MPLS network
L2VPN E-Line Services
PE
CE

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S
S
CE
PE
PE
CE
MPLS network
L2VPN E-Tree Services
PE
S
S
CE
S
S
Root
Leaf
Leaf

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R
R
S
S
CE
PE
PE
R
R
CE
MPLS network
L2VPN E-LAN Services
PE
S
S
CE
S
S
R
R

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VSI1
VSI2
VSI1
VSI2
VSI1 VSI2
CE
VLAN1
CE
VLAN2
CE
VLAN1
CE
VLAN2
CE
VLAN2
CE
VLAN1
PE PE
PE
L2VPN E-LAN Services

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MPLS L3VPN
 MPLS L3VPN service is a VPN service based on an IP/MPLS backbone. It supports IP VPNs.
IP is a layer 3 (L3) protocol used to route packets through a network.
 MPLS is a label-switching protocol that is used to encapsulate IP packets with labels and
forwards them across the service providers backbone.
Internet
Employee on a trip
Private line
Office
HQ
Branch
Partner
Remote office

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MPLS L3VPN Implementation
CE
CE
CE
CE
IP
Packet
IP
PE
PE
P
IP
IP
IP
IP
Packet
IP
Packet
888
300 IP
Packet
888
400
IP
Packet
888
BGP
P
PE

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FlexE Overview
 FlexE adds a layer between Layer 2 (MAC layer) and Layer 1 physical interface rates (PHY layer). The main difference
between standard Ethernet and FlexE is how the MAC layer is mapped onto the PHY layer, using a ‘FlexE Shim’.
Essentially, FlexE uses this shim to dissociate the Ethernet rate on the client side from the actual physical interface rate.
This makes it possible to map Ethernet MAC rates, which can be greater than or less than the Ethernet PHY rates. The
terminologies on the next page, as defined in OIF FlexE 2.0, best describe how this is achieved.

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FlexE Applications in Transport Networks
 FlexE client is an Ethernet flow, based on a MAC data rate that may or may not correspond to any Ethernet
PHY rate. This can be 10, 40, or m*25Gbps.
 The Flex Shim schedules and distributes the data of multipleclient interfaces to different sub-
channels (groups) in timeslot mode.
 FlexE group refers to a group of one or many 100 Gbps FlexE instances, which may consist of 100, 200, or
400Gbps PHY/s. A 50Gbps PHY will be added within the OIF FlexE 2.1 Project.

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FlexE Mechanisms
The flexibility in mapping the MAC to PHY, together with the TDM-frame structure, achieves many
possibilities in physical traffic separation, traffic multiplexing, and traffic cross-connection.
FlexE has three main mechanisms include:
 Bonding of Ethernet PHYs
 Sub-rating of the Ethernet PHY.
 Channelization within a PHY or a group of bonded PHYs

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Bonding of Ethernet PHYs
Bonding allows aggregating lower rates to form a higher rate. It is an alternative to LAG (link
aggregation), in applications requiring deterministic performance and higher efficiency. Below is an
example of bonding 4x100GEs to achieve a 400GE MAC rate between two routers. If a 100GE PHY
fails, the link will continue to operate via the remaining 3x100GEs.

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Sub-rating of the Ethernet PHY
Sub-rating allows a link to use a portion of a PHY or a group of bonded PHYs. In the example below, two
routers are connected by 150G MAC rate over 2x100GEs. Each of the 100GEs are carrying only 75G of traffic.
The unused extra capacity may be reserved for a planned capacity upgrade or it can be further used by other
links, as shown in the case of the channelization example on the next page.

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Channelization within a PHY or a group of bonded PHYs
Channelization allows one link to carry several sub-rates. There is total separation of traffic between the sub-
rates, which is ideal for wholesale applications and network slicing. In this example, two routers are connected
via 6x10GEs, 2x25GEs, 1x40GE, and 1x50GE over two bonded 100GEs.

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FlexE in Building 5G Transport
Since the initial FlexE standard in 2016, FlexE has already been deployed in networks delivering flexible
Ethernet rates. It is continually being tested by both telecom equipment vendors and telecom operators for new
applications, especially in 5G. Industry acceptance of FlexE is also progressing with some key events in 2018
and 2019 as the industry prepares for the upcoming 3GPP Release 16, due in 2020. In late 2018, OIF
announced the launch of the FlexE 2.1 project, which enhances the FlexE 2.0 capabilities to include 5G use
cases, adapting 50GBASE-R PHY in FlexE Groups.

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Transport Network Slicing with FlexE
Network slicing is the partitioning of network resources into logical networks, called network slices. These are
assigned to specific services or customers, each having different network requirements and topologies. While this
network principle is driven mainly by 3GPP for 5G mobile networks, it is also becoming a practical approach for
transport networks that carry diverse types of services for different purposes.

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What is Segment Routing?
 Segment Routing (SR) is a protocol designed to forward data packets on a network based on source
routes.
 Segment Routing divides a network path into several segments and assigns a segment ID (SID) to
each segment and forwarding node. The segments and nodes are sequentially arranged into a
segment list to form a forwarding path.
 Segment Routing is divided into two types based on the forwarding plane. Segment Routing MPLS (SR
MPLS for short) is based on the MPLS forwarding plane, whereas Segment Routing IPv6 (SRv6 for
short) is based on the IPv6 forwarding plane.

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Background of Segment Routing
 Currently, networks that need to adapt to services are
evolving towards service-driven networks. Network
adaptation to services refers to reactive adjustments
of the network architecture and configurations based
on service requirements. This model does not match
the rapid development of services. Moreover, it makes
network deployment more complex and network
maintenance more difficult.
 Figure 1-1 shows a service-driven network where
explicit paths are calculated based on the
requirements of applications. The network is
dynamically adjusted in real time to rapidly meet
service change requirements. Figure 1-1

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Segment Routing Fundamentals
Segment Routing involves the following concepts:
 Segment Routing domain: a set of Segment Routing nodes.
 SID: unique identifier of a segment. A SID is mapped to an MPLS label on the forwarding plane.
 Segment Routing global block (SRGB): a set of local labels reserved for Segment Routing.

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Segment classification

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Prefix, adjacency, and node SID
Figure 1-2

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Prefix segment-based forwarding path
 Prefix segment-based mode: An IGP uses the shortest path first (SPF) algorithm to compute the shortest path.
This mode is also called Segment Routing-Best Effort (SR-BE).
 As shown in Figure 1-3, node Z is connected to the destination network with a prefix SID of 68. After an IGP
propagates the prefix SID, each node in the IGP area learns the prefix SID of the network from node Z and
then runs SPF to compute the shortest path to the network.
Figure 1-3

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Adjacency segment-based forwarding path
 Adjacency segment-based mode: As shown
in Figure 1-4, an adjacency segment is
allocated to each adjacency on the network,
and a segment list with multiple adjacency
segments is defined on the ingress, so that any
strict explicit path can be specified. In this mode,
path adjustment and traffic optimization can be
implemented in a centralized manner,
facilitating software-defined networking (SDN)
implementation. This mode is mainly used for
Segment Routing-Traffic Engineering (SR-TE).
Figure 1-4

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