现代通信新技术导论
第二章 下一代网络与MPLS
Chapter 2 Next Generation Network and MPLS
电控学院 电子工程学科部
司鹏搏 综合楼825室
sipengbo@bjut.edu.cn
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现代通信新技术导论 第二章 下一代网络与MPLS
Main Contents
• Next Generation Network
–
–
–
–
Background of Next Generation Network (NGN)
Definition of NGN
Characteristics of NGN
Architectures of NGN
• 3GPP
• ETSI
• With Softswitch
• MPLS
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现代通信新技术导论 第二章 下一代网络与MPLS
Main Contents
• Next Generation Network
• MPLS
– Need for MPLS
– MPLS Architecture
• Label Switching
• MPLS Basics
– MPLS Labels
•
•
•
•
•
Label Forwarding
Label Distribution and Management
MPLS Forwarding Table
LSP Loop Detection
LDP
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现代通信新技术导论 第二章 下一代网络与MPLS
Main Contents
• Next Generation Network
–
–
–
–
Background of Next Generation Network (NGN)
Definition of NGN
Characteristics of NGN
Architectures of NGN
• 3GPP
• ETSI
• With Softswitch
• MPLS
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现代通信新技术导论 第二章 下一代网络与MPLS
Background of NGN
• Limited Capacity of Traditional Internet
– Simple services are not sufficient
• Voice, text message, e-mail
– Non-open system
– Different networks are independent
– Old technologies are not ready for evolution
• Why Next Generation Network?
–
–
–
–
The fast growing of data service requirement
The slow growing/decreasing of voice service
The increasingly cut-throat competition
The rapid development of new technologies
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现代通信新技术导论 第二章 下一代网络与MPLS
Video Movies
Music
Ring tone
Photos
Person-to-Content
known usability patterns
Internet
Text/Pictures
Streaming
Download
Multimedia
Content
HTTP
Video
SMS/MMS
Active
phonebook
Person-to-Person
Image
dominates traffic growth
Social Networking
Text
P2P Calls
Voice
Presence
Push-To-Talk
MMS
SMS
Voice
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现代通信新技术导论 第二章 下一代网络与MPLS
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现代通信新技术导论 第二章 下一代网络与MPLS
Societal and Business trends
Convergence
• Internet is becoming a major enabler
of communications
• Converged devices (Mobile, WLAN,
Internet etc.)  Connectivity
• Consumers are embracing
computing, mobile and digital
technology in their everyday life
• Converged services  Ease of use
• Evolution of Business models require
increased levels of personal mobility
• Converged business models 
Increased margins, Avoidance of twin
pitfalls risk
• Converged networks  Reliability,
Security, Reduced OPEX/CAPEX
Access Technology Enhancements
• HSPA (High Speed Packet Access) – evolved
WCDMA
• OFDMA (Orthogonal Frequency Division
Multiple Access) – 3GPP LTE, WiMAX, MBWA,
ADSL/VDSL, DVB-T/H etc.
• Spatial Processing – multi-antennas Base
Stations supporting advanced spatial processing
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现代通信新技术导论 第二章 下一代网络与MPLS
Main Contents
• Next Generation Network
–
–
–
–
Background of Next Generation Network (NGN)
Definition of NGN
Characteristics of NGN
Architectures of NGN
• 3GPP
• ETSI
• With Softswitch
• MPLS
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现代通信新技术导论 第二章 下一代网络与MPLS
Definition of NGN
• By ITU-T
– In Feb. 3 - 12, 2004, ITU-T SG13
– A Next Generation Network is a packet-based network
able to provide telecommunication services, able to
make use of multiple broadband, QoS-enabled
transport technologies and in which service-related
functions are independent from underlying transportrelated technologies.
– It offers unrestricted access by users to different service
providers.
– It supports generalized mobility which will allow
consistent and ubiquitous provision of services to users.
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现代通信新技术导论 第二章 下一代网络与MPLS
Definition of NGN
Support Broad
Variety of
Services
Openess and
Flexibility
Regarding New
Services
Packet Oriented
Network
NGN
CONCEPT
Seperation into
Different Layers
Using Open
Interfaces
Integration of
Existing
Infrastructure
Application
Focused Access
Independent
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现代通信新技术导论 第二章 下一代网络与MPLS
Main Contents
• Next Generation Network
–
–
–
–
Background of Next Generation Network (NGN)
Definition of NGN
Characteristics of NGN
Architectures of NGN
• 3GPP
• ETSI
• With Softswitch
• MPLS
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现代通信新技术导论 第二章 下一代网络与MPLS
Characteristics of NGN
• Packet-based transfer
• Separation of control functions
• Decoupling of service provision
• Support for a wide range of services
• Broadband capabilities with end-to-end QoS
• Interworking via open interfaces
• Generalized mobility
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现代通信新技术导论 第二章 下一代网络与MPLS
Characteristics of NGN
• Unrestricted access
• A variety of identification schemes
• Unified service characteristics
• Converged services between Fixed/Mobile
• Independence of service-related functions
• Support of multiple RATs
• Compliant with all regulatory requirements
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现代通信新技术导论 第二章 下一代网络与MPLS
Main Contents
• Next Generation Network
–
–
–
–
Background of Next Generation Network (NGN)
Definition of NGN
Characteristics of NGN
Architectures of NGN
• 3GPP
• ETSI
• With Softswitch
• MPLS
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现代通信新技术导论 第二章 下一代网络与MPLS
Architecture Evolution
Traditional Architecture
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现代通信新技术导论 第二章 下一代网络与MPLS
Architecture Evolution
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现代通信新技术导论 第二章 下一代网络与MPLS
Architecture Evolution
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现代通信新技术导论 第二章 下一代网络与MPLS
Architecture Evolution
Pol. A
Reg. a
Pol. B
Reg. b
Service-based Pol./Reg.
Pol. C
Reg. c
Voice Internet Video
Phone
Internet
M-Ph
NGN
PSTN
IP-Net
MM
Pol.
Reg.
Mobile
IP (Future Packet ?) Platform
Pol. X
Reg. x
xDSL/Optic based Fixed-Mobile
Resource-based Pol./Reg.
Current PolicyRegulation
Environment (Vertical)
New PolicyRegulation
Environment (Horizontal)
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现代通信新技术导论 第二章 下一代网络与MPLS
Architecture Evolution
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现代通信新技术导论 第二章 下一代网络与MPLS
Architecture Evolution
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现代通信新技术导论 第二章 下一代网络与MPLS
The Players of NGN
ITU-T
NGN FG
ATIS
NGN FG
ETSI
TISPAN1
3GPP
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现代通信新技术导论 第二章 下一代网络与MPLS
Main Contents
• Next Generation Network
–
–
–
–
Background of Next Generation Network (NGN)
Definition of NGN
Characteristics of NGN
Architectures of NGN
• 3GPP
• ETSI
• With Softswitch
• MPLS
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现代通信新技术导论 第二章 下一代网络与MPLS
3GPP Architecture of NGN with IMS
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现代通信新技术导论 第二章 下一代网络与MPLS
3GPP Architecture of NGN with IMS
• IMS is an open IP-based architecture using the Client-Server
Network Computing model
– 3GPP originally specified IMS to enable real-time multimedia services over the IP
bearer, in GSM and WCDMA networks.
– 3GPP2 specified the MMD architecture for CDMA2000 networks based on IMS.
3GPP2 requirements are part of Common IMS in IMS release 8.
– The xDSL access, specified by TISPAN, is integrated into IMS.
– The cable access specified by CableLabs in PacketCable 2.0 is part of IMS release 8.
– Interworking with WLAN was specified in IMS release 6, while the mobility with
WiMAX has been addressed in EPC specifications.
• If IMS is not used:
– Multimedia communication at best effort
–
Service roaming can be difficult to implement
–
Provisioning and charging are service specific
–
Compliance with LI requirements can be an issue
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现代通信新技术导论 第二章 下一代网络与MPLS
Main Contents
• Next Generation Network
–
–
–
–
Background of Next Generation Network (NGN)
Definition of NGN
Characteristics of NGN
Architectures of NGN
• 3GPP
• ETSI
• With Softswitch
• MPLS
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现代通信新技术导论 第二章 下一代网络与MPLS
ETSI TISPAN
NGN Architecture
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现代通信新技术导论 第二章 下一代网络与MPLS
NGN Architecture Principles
• A Layered Approach Including
– A transport layer, including functional entities that do
transport routing
– A service layer, including functional entities that
provide services
• A Sub-System Oriented Approach Enabling
– The addition of new subsystems over the time to cover
new demands and service classes
– To import (and adapt) subsystems from other
standardization bodies
– Flexibility to adjust a subsystem architecture with no or
limited impact on other subsystems
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现代通信新技术导论 第二章 下一代网络与MPLS
NGN Architecture Principles
• IP Connectivity is Provided Using Two Sub-Systems:
– Network Attachment Subsystem (NASS)
– Resource and Admission Control Subsystem (RACS)
• First Service-Oriented Sub-Systems Include
– the 3GPP IMS, a PSTN/ISDN Simulation Sub-system
– a PSTN/ISDN Emulation Subsystem (PES)
• Future Service-Oriented Sub-Systems may Include
– A streaming subsystem
– A TV Broadcasting subsystem
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现代通信新技术导论 第二章 下一代网络与MPLS
Common Components
• Common components are functions that are used by more
than a subsystem
– USPF: User Profile Server Function
– Service-level user identification, numbering, and addressing
information
– Service-level user security information
– Service-level user location information
– Service-level user profile storage
– The IMS part of the USPF is similar to the 3GPP HSS without the
HLR/AUC
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现代通信新技术导论 第二章 下一代网络与MPLS
Common Components
• ASF: Application Server Function
– Offers services
– Two types of ASFs:
• Type 1: may interact with RACS for resource control purposes
• Type 2: relay on the control subsystem.
– Type 2 is equivalent to the Application Server defined by 3GPP IMS
• SLF: Subscription Locator Function
– Helps locating the USPF of a given user
– Like the SLF defined by 3GPP IMS
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现代通信新技术导论 第二章 下一代网络与MPLS
Common Components
• Charging Functions
– Data collection functions and mediation functions to the billing
systems
– Both on-line and off-line charging
• IWF: Interworking Function
– Between different SIP profiles
– Between SIP and H.323
• IBCF: Interconnection Border Control Function
–
–
–
–
Controls an operator’s boundary
Interacts with RACS
Inserts IWF when appropriate
Screening of signaling based on source/destination addresses
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现代通信新技术导论 第二章 下一代网络与MPLS
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现代通信新技术导论 第二章 下一代网络与MPLS
Transfer Functions
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现代通信新技术导论 第二章 下一代网络与MPLS
Transfer Functions
• BGF: Border Gateway Function
– Interface between two IP transport domains
– Open/close gates, packet marking, resource allocation, bandwidth
reservation, NAPT, NAT traversal, incoming traffic policing, usage
metering, IPv4/IPv6 interworking, topology hiding
– Three types of BGF:
• A-BGF (Access-BGF): located in between access and core network, at the
access network side
• C-BGF (Core-BGF): located in between access and core network, at the
core network side
• I-BGF (Interconnection-BGF): located in between two core networks
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现代通信新技术导论 第二章 下一代网络与MPLS
Transfer Functions
• L2TF: Layer 2 Termination Function
– Terminates Layer 2, e.g., PPP or DSLAM
• ARF: Access Relay Function
– Relay between the CPE and the NASS
– Located in the access network
– Resource reservation and admission control
• SGF: Signaling Gateway Function
– Conversion of SS7 protocols to IP control protocols
(e.g., SIP)
– SS7 screening of MTP and SCCP parameters
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现代通信新技术导论 第二章 下一代网络与MPLS
Transfer Functions
• MGF: Media Gateway Function
– Media mapping and transcoding between IP and CS
networks
– Three types of MGF:
• R-MGF Residential MGF: located in the customer premises
• A-MGF Access MGF: located in the access or core network
• T-MGF Trunking: MGF located in the boundary of the core
network and PSTN/ISDN network
• MRFP: Media Resource Function Processor
– Multimedia conferences, media sourcing, IVR
capabilities, media content analysis
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现代通信新技术导论 第二章 下一代网络与MPLS
RACS Functionality
• Support for Two Types of QoS:
– Guaranteed QoS: resources are reserved
– Support for Relative QoS: diffserv marking
• Service Based Local Policy Control: authorization of QoS
requests and definition of the polices to be enforced by the
bearer service network elements.
– Resource reservation
– Support for two mechanisms
• Application Function (AF)-initiated
• CPE-initiated (Authorization token a la 3GPP).
– QoS support over multiple access networks (e.g. ADSL and GPRS)
and CPE types.
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现代通信新技术导论 第二章 下一代网络与MPLS
RACS Functionality
• Admission Control: Apply admission control to resource
reservation requests
– Based on knowledge of transport resource availability over the
“last-mile access” and aggregation segments of the access network
• NAPT/ Gate Control: controls near-end and far-end NAPT
and FW functions, when required, between:
– two core TISPAN NGN networks or,
– at the border between core and access TISPAN NGN networks
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现代通信新技术导论 第二章 下一代网络与MPLS
RACS Architecture
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现代通信新技术导论 第二章 下一代网络与MPLS
RACS Architecture
• SPDF: Service-based Policy Decision Function
– Provides to AF a single point of contact
– Authorization decision for QoS resource
• A-RACF: Access Resource and Admission Control
Function
– Located in the access network
– Resource reservation and admission control
– In Guaranteed QoS mode, it sets L2/L3 QoS policies in RCEF
– In Relative QoS mode, it sets dynamically the diffserv QoS
parameters in RCEF
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现代通信新技术导论 第二章 下一代网络与MPLS
RACS Architecture
• C-BGF: Core Border Gateway Function
– Essentially, an edge router
– Located at the border of networks (access/core – core/core)
– NAPT, Gate Control, packet marking, usage metering, policing
enforcement function
– SPDF controls the gates of the C-BGF based on a 5-tuple (source and
destination IP addr., source and destination port numbers, protocol)
• RCEF: Resource Control Enforcement Function
– Performs policy enforcement under the control of the A-RACF
– Located in the access network
– Gate control, packet marking, policing
– A-RACF controls the gates of the RCEF based on a 5-tuple (source and
destination IP addr., source and destination port numbers, protocol)
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现代通信新技术导论 第二章 下一代网络与MPLS
RACS Architecture
• L2TF: Layer 2 Termination Functions
– Layer 2 (e.g., PPP, ATM) is terminated here
– Authorization decision for QoS resource
• AF: Application Function
– Officially, not part of RACS. Just a RACS user
– Requests bearers resources, gest informed when resources are
reserved and released
– It is specific of the application. E.g., P-CSCF in IMS
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现代通信新技术导论 第二章 下一代网络与MPLS
NASS Functionality
• Dynamic provision of IP address and other
user equipment configuration parameters
(e.g., using DHCP)
• User authentication, prior or during the IP
address allocation procedure
• User authentication based on user network
profile
– Based on PPP, IEEE 802.11X or IETF PANA
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现代通信新技术导论 第二章 下一代网络与MPLS
NASS Functionality
• Line authentication based on Layer 2 line
identification
• Location management (e.g. for emergency
call, …)
• Customer Premises Equipment configuration
• The NASS can be distributed between a visited
and a home network
– Allows nomadicity and roaming
• P-CSCF announcement
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现代通信新技术导论 第二章 下一代网络与MPLS
NASS Architecture
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现代通信新技术导论 第二章 下一代网络与MPLS
NASS Architecture
• Network Address Configuration Function (NACF):
– IP address allocation to the CPE
– Distribution of other network configuration parameters such as address of
DNS server(s), address of signaling proxies for specific protocols (e.g., PCSCF)
– Typically implemented as RADIUS servers or DHCP servers
• Access Management Function (AMF):
– Translates network access signaling between CPE and NACF/UAAF
– Forwards requests to he UAAF to authenticate the user, authorize/deny
network access, and retrieve user-specific access configuration parameters
– Typically implemented as RADIUS client if the NACF is a RADIUS
server.
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现代通信新技术导论 第二章 下一代网络与MPLS
NASS Architecture
• Connectivity Session Location Repository Function (CLF):
– Registers association between the IP configuration of the
CPE and
– access transport characteristics, line identifier, IP edge
identity, geographical location, etc.
– Provides user network profile information to the RACS.
– Provides location information to TISPAN NGN core
subsystems
• User Access Authorization Function (UAAF):
– Performs user authentication and authorization based on
user profiles
– Collects accounting data
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现代通信新技术导论 第二章 下一代网络与MPLS
NASS Architecture
• Profile Database Function (PDBF):
– Stores the user network profile, containing
• User identity
• Supported authentication methods
• Keys
– Can be co-located with the UPSF
• Customer Premises Equipment Configuration Function (CPECF):
– Provides the CPE with additional initial configuration information
(firewall, diffserv packet marking, etc.)
• Customer Network Gateway (CNG):
– Single point of entrance in the customer’s network (e.g., ADSL router)
– Participates in line and access authentication
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现代通信新技术导论 第二章 下一代网络与MPLS
Service Layer
• Modular Subsystem design
• Two subsystem targeted in NGN Release 1:
– PSTN/ISDN Emulation Subsystem (PES)
• Emulates the PSTN/ISDN, users don’t notice the change
• Support for legacy equipment including black phones
– PSTN/ISDN Simulation Subsystem (a.k.a. IMS)
• Multimedia terminals, new services based on the IMS model.
• Includes PSTN/ISDN simulation services (similar to the PSTN/ISDN Supplementary
Services)
• Other subsystem may come in future NGN releases
– Streaming Subsystem
– Content Broadcasting Subsystem
– Others as needed
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现代通信新技术导论 第二章 下一代网络与MPLS
IMS Architecture in NGN
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现代通信新技术导论 第二章 下一代网络与MPLS
NGN Impacts to IMS
• IMS can be mostly reused, as specified by 3GPP,
due to its large access independence
• A few changes are required:
– NAT traversal support in various points
– Relaxation of IMS constraints:
• SIP compression is no longer mandatory
• SIP timers are not “wireless” specific
• SIP preconditions (183, PRACK, UPDATE) are no longer
mandatory
• Support for ADSL access in P-Access-Network-Info header
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现代通信新技术导论 第二章 下一代网络与MPLS
IMS Architecture
• Call Session Control Function (CSCF):
– Establishes, monitors, supports and releases multimedia functions
– Three types of CSCFs: P-CSCF, I-CSCF, S-CSCF (same as in
3GPP IMS)
– But P-CSCF contains also:
• Application Level Gateway (ALG) to interface NAPT
• Interfaces the NASS to retrieve user’s physical location
• Media Gateway Control Function (MGCF):
– Controls a T-MGW
– Converts ISUP to SIP
– Functionality is equal to the 3GPP IMS MGCF
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现代通信新技术导论 第二章 下一代网络与MPLS
IMS Architecture
• Multimedia Resource Function Controller (MRFC):
– Controls an MRFP
– Together with the MRFP provides conference services,
announcement playback, and media transcoding
– Functionality is equal to the 3GPP IMS MRFC
• Breakout Gateway Control Function (BGCF):
– Selects the network in which PSTN breakout is to occur
– Or selects the MGCF
– Equal to the 3GPP IMS BGCF
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现代通信新技术导论 第二章 下一代网络与MPLS
PSTN/ISDN Simulation Services
• ETSI TISPAN considers two types of IMS
services:
– Basic PSTN/ISDN Simulation Services:
• Similar (but not equal) to PSTN/ISDN Supplementary Services
• Unlike in the PSTN, not all these services require network
support
• Services must interwork with the similar PSTN/ISDN
supplementary service and 3GPP supplementary service
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现代通信新技术导论 第二章 下一代网络与MPLS
PSTN/ISDN Simulation Services
• Multimedia services:
– New services, e.g., presence, multimedia instant
messaging, SIP services that do not require extra
standardization effort
• PSTN/ISDN Simulation Services defined in NGN
Release 1 with three priorities:
– Mandatory services
– Strictly recommended services
– Optional services
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现代通信新技术导论 第二章 下一代网络与MPLS
Main Contents
• Next Generation Network
–
–
–
–
Background of Next Generation Network (NGN)
Definition of NGN
Characteristics of NGN
Architectures of NGN
• 3GPP
• ETSI
• With Softswitch
• MPLS
61
现代通信新技术导论 第二章 下一代网络与MPLS
NGN
Architecture
with
Softswitch
62
现代通信新技术导论 第二章 下一代网络与MPLS
Access Layer
• Functions of access layer
– Connecting subscribers, AN & PABX and trunks from
PSTN, ISDN, and PLMN, etc
– Converting the format of information (circuits to packet or
packet to circuit) before transmitting it.
• Components on the access layer
– IP terminals (IP phones, IP PBX and software phones,
typically intelligent terminals based on either H.323 or SIP)
– Integrated access device (IAD) (used to access subscribers
(analog, ADSL, IP) in the NGN. Accesses data of subscriber
terminals, voice services and video services to the packet
network)
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现代通信新技术导论 第二章 下一代网络与MPLS
Access Layer
– Access gateway (AGW) (acts as the interface to the core
IP network and connects subscribers with analog
subscriber access, integrated services digital network
(ISDN) subscriber access, PABX and x digital
subscriber line (xDSL) access)
– Access network (AN) (provides connectivity between
the customer premises equipment and the access
gateways in the service provider's network)
– Access technologies could be cable, xDSL, wireless,
optical, ...
– SIP phone (a multimedia device working in the session
initiation protocol (SIP))
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现代通信新技术导论 第二章 下一代网络与MPLS
Access Layer
– H. 323 phone (a multimedia device working in the
H.323 protocol)
– Signaling gateway (SG) (provides signaling
interface between the IP network and the PSTN
signaling network, terminates SS7 links and
provides message transport part (MTP) Level 1
and Level 2 functionality)
– Trunk Media gateway (TMG) (resides between the
CS network and the IP network, converts format
between PCM signal flow and IP media flow, and
connects devices such as PSTN exchange, PBX and
BSC)
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现代通信新技术导论 第二章 下一代网络与MPLS
Access Layer
– Session border controller (SBC) (located at the administrative boundary of
an IP network) for enforcing policy on multimedia sessions). The functions
of SBC are
• Interworking
• Security
• Management of service level agreements
• Overload control
• NAT and firewall traversal
• lawful interception
• QoS management
• Protocol translation
• Call accounting
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NGN
Architecture
with
Softswitch
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现代通信新技术导论 第二章 下一代网络与MPLS
Transport Layer
• Composed of devices such as routers and Layer 3
switchers located in the backbone networks
• Packet switching
• Provides common and integrated platform for data
transport
• Ensures
– High reliability
– QoS assurance
– High Capacity
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NGN
Architecture
with
Softswitch
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现代通信新技术导论 第二章 下一代网络与MPLS
Control Layer
• Adopts software switching technologies to achieve
– Primary real-time call control
– Connection control
• Functions of softswitch
–
–
–
–
–
–
–
–
Call control
Media gateway access control
Signaling gateway control
Border gateway control
Resource allocation
Protocol processing
Routing
Authentication and charging
70
现代通信新技术导论 第二章 下一代网络与MPLS
NGN
Architecture
with
Softswitch
71
现代通信新技术导论 第二章 下一代网络与MPLS
Service Layer
• The components are
– Operation support system (OSS)
• Integrated charging, network operation and
management
– Application server
• Produces and manages value-added services and IN
services
• Provides a platform for third-party services
• Helps to develop supplementary services
72
现代通信新技术导论 第二章 下一代网络与MPLS
Service Layer
– Media server (MS)
• Service tone playing, conference services, IVR,
recorded announcement, …
– Service control point (SCP)
• Stores subscriber data and service logics
• Helps to realize various intelligent calls
– Video server
• Schedules, manages and provides video conferences
73
现代通信新技术导论 第二章 下一代网络与MPLS
Main Contents
• Next Generation Network
• MPLS
– Need for MPLS
– MPLS Architecture
• Label Switching
• MPLS Basics
– MPLS Labels
•
•
•
•
Label Forwarding
Label Distribution and Management
LSP Loop Detection
LDP
74
现代通信新技术导论 第二章 下一代网络与MPLS
Conventional IP Networks & Routing
• Client networks are connected to backbone via edge routers
– LAN, PSTN, ADSL
• Data packets are routed based on IP address and other
information in the header
• Functional components
– Forwarding
• Responsible for actual forwarding across a router
• Consists of set of procedures to make forwarding decisions
– Control
• Responsible for construction and maintenance of the forwarding
table
• Consists of routing protocols such as OSPF, BGP and PIM
75
现代通信新技术导论 第二章 下一代网络与MPLS
Need for MPLS
• Forwarding function of a conventional router
– A capacity demanding procedure
– Constitutes a bottle neck with increase in line speed
• MPLS simplifies forwarding function
– By introducing a connection oriented mechanism
inside the connectionless IP networks
76
现代通信新技术导论 第二章 下一代网络与MPLS
Main Contents
• Next Generation Network
• MPLS
– Need for MPLS
– MPLS Architecture
• Label Switching
• MPLS Basics
– MPLS Labels
•
•
•
•
Label Forwarding
Label Distribution and Management
LSP Loop Detection
LDP
77
现代通信新技术导论 第二章 下一代网络与MPLS
Why MPLS
R
X
X
Router
ATMControl
Switch Plane:
MPLS Router Forwarding Plane:
IP
Connectionless Oriented Connectionless Oriented
Layer 3 routing: Scalability and flexibility
Weak requirement of network topology
Layer 2 routing: Reliability and QoS guarantee
L3 routing
Low efficiency of routing
Poor QoS
Control Plane:
Forwarding Plane:
MPLS
Connectionless Oriented Connection Oriented
ATM
Control Plane:
Connection Oriented
L2 routing
QoS guarantee provided
N2 problem exists
Forwarding Plane:
Connection Oriented
78
现代通信新技术导论 第二章 下一代网络与MPLS
MPLS Architecture
LER
MPLS Domain
IP
LER
LSR
LSR
LER
LSP
LSR
MPLS
LER
• LSR：Label Switch Router
• LER：Label Edge Router
• LSP：Label Switch Path
79
现代通信新技术导论 第二章 下一代网络与MPLS
MPLS Architecture
Core LSR
LER
LER
IP
IP
Traditional
IP Forwarding
L1
IP
L2
Label Forwarding
IP
L3
IP
Traditional
IP Forwarding
80
现代通信新技术导论 第二章 下一代网络与MPLS
Main Contents
• Next Generation Network
• MPLS
– Need for MPLS
– MPLS Architecture
• Label Switching
• MPLS Basics
– MPLS Labels
•
•
•
•
Label Forwarding
Label Distribution and Management
LSP Loop Detection
LDP
81
现代通信新技术导论 第二章 下一代网络与MPLS
Label Switching
• Decomposition of network layer routing into
control and forwarding components
• Label switching forwarding component
algorithm uses
– Forwarding table
– Label carried in the packet
• What is a Label?
– Short fixed length entity
82
现代通信新技术导论 第二章 下一代网络与MPLS
Main Contents
• Next Generation Network
• MPLS
– Need for MPLS
– MPLS Architecture
• Label Switching
• MPLS Basics
– MPLS Labels
•
•
•
•
Label Forwarding
Label Distribution and Management
LSP Loop Detection
LDP
83
现代通信新技术导论 第二章 下一代网络与MPLS
MPLS Basics
• A Label Switched Path (LSP) is set up for each
route
• A LSP for a particular packet P is a sequence of
routers,
<R1, R2, …, Rn>
for all i, 1< i < n, Ri transmits P to Ri+1
• Edge routers
– Analyze the IP header to decide which LSP to use
– Add a corresponding local Label Switched Path
Identifier, in the form of a label
– Forward the packet to the next hop
84
现代通信新技术导论 第二章 下一代网络与MPLS
MPLS Basics
• Subsequent nodes
– Just forward the packet along the LSP
– Simplify the forwarding function greatly
– Increase performance and scalability dramatically
• New advanced functionality for QoS, differentiated
services can be introduced in the edge routers
• Backbone can focus on capacity and performance
• Routing information obtained using a common intra
domain routing protocol such as OSPF
85
现代通信新技术导论 第二章 下一代网络与MPLS
TTL of MPLS
One hop for the whole MPLS domain
IP TTL -MPLS TTL＝255
MPLS TTL --
Entrance LER
LSR
IP TTL --
Exit LER
Count MPLS TTL to IP TTL
IP TTL -MPLS TTL＝IP TTL
MPLS TTL --
MPLS TTL -IP TTL＝MPLS TTL
Entrance LER
LSR
Exit LER
86
现代通信新技术导论 第二章 下一代网络与MPLS
Main Contents
• Next Generation Network
• MPLS
– Need for MPLS
– MPLS Architecture
• Label Switching
• MPLS Basics
– MPLS Labels
•
•
•
•
Label Forwarding
Label Distribution and Management
LSP Loop Detection
LDP
87
现代通信新技术导论 第二章 下一代网络与MPLS
MPLS Frame Format and Label
20
0
Label
L2 Header
23 24
EXP S
MPLS Header IP Header
31
TTL
Data
• For ATM and FR
– shim mode/frame mode
– Cell mode: VC (VPI/VCI for ATM and DLCI for FR) as the label
88
现代通信新技术导论 第二章 下一代网络与MPLS
The Location of Label
Ethernet/SONET/SDH
Header
Lable
L3 Data
ATM Header
Lable
L3 Data
Frame mode, ATM
Cell mode, ATM
VPI/VCI
L3 Data
89
现代通信新技术导论 第二章 下一代网络与MPLS
Label Stack
L2 Header
MPLS Header MPLS Header
MPLS Header IP Header
…
Data
• Theoretically, the nest of label stack is
unlimited to provide unlimited capacity
supporting new services.
90
现代通信新技术导论 第二章 下一代网络与MPLS
Main Contents
• Next Generation Network
• MPLS
– Need for MPLS
– MPLS Architecture
• Label Switching
• MPLS Basics
– MPLS Labels
•
•
•
•
Label Forwarding
Label Distribution and Management
LSP Loop Detection
LDP
91
现代通信新技术导论 第二章 下一代网络与MPLS
The Concept of Label Forwarding
• FEC（Forwarding Equivalence Class）
– Use the same LSP for packets with similar or identical
characteristics (bound to the same label)
• NHLFE（Next Hop Label Forwarding Entry）
– Includes the information of the next hop
– Action types: push/pop/swap/null
• FTN（FEC to NHLFE）
– Mapping FEC to NHLFE
• ILM（Incoming Label Map）
– Mapping MPLS label to NHLFE
92
现代通信新技术导论 第二章 下一代网络与MPLS
Label Forwarding
Action: pop
Action: push
Bind LSP
according to
the IP Header
FTN->NHLFE
Action: swap
ILM->NHLFE
E1
ILM->NHLFE
E2
A
Entrance LER
ILM->NHLFE
Find out the next
hop according to
the IP Header
Action: swap
E3
B
LSR
C
LSR
D
Exit LER
A:
FEC
10.0.1.0/24
NHLFE
Next Hop
Send to
Action
Others
B
E1
Push L1
…
•
To establish a LSP: With routing protocol and LDP, build the routing table and
FEC-Label mapping for FECs
•
Push the Labels for different FECs
93
现代通信新技术导论 第二章 下一代网络与MPLS
Label Forwarding
Action: pop
Action: push
Bind LSP
according to
the IP Header
FTN->NHLFE
Action: swap
ILM->NHLFE
E1
ILM->NHLFE
E2
A
Entrance LER
ILM->NHLFE
Find out the next
hop according to
the IP Header
Action: swap
E3
B
LSR
C
LSR
D
Exit LER
B:
Original Label
L1
•
NHLFE
Next Hop
Send to
Action
Others
C
E2
Swap, L1->L2
…
In the MPLS domain, forwarding is based on the Label and the
forwarding table
94
现代通信新技术导论 第二章 下一代网络与MPLS
Label Forwarding
Action: pop
Action: push
Bind LSP
according to
the IP Header
FTN->NHLFE
A
Entrance LER
Action: swap
ILM->NHLFE
ILM->NHLFE
ILM->NHLFE
Find out the next
hop according to
the IP Header
C
LSR
D
Exit LER
Action: swap
B
LSR
D:
Original Label
NHLFE
Next Hop
Send to
L3
Action
Others
Pop Label
…
• Remove the Label and forward
95
现代通信新技术导论 第二章 下一代网络与MPLS
Penultimate Hop Popping
Action: push
Bind LSP
according to
the IP Header
FTN->NHLFE
A
Entrance LER
Action: swap
ILM->NHLFE
B
LSR
Action: pop
ILM->NHLFE
Find out the next
hop according to
the IP Header
C
LSR
D
Exit LER
•
Pop the Label at the hop before the last hop, since the Label is not useful at the last
hop
•
In case of only one Label, use IP routing at the last hop, otherwise forward the
message according to other Labels.
96
现代通信新技术导论 第二章 下一代网络与MPLS
Establishing LSP
• LSP drivers
– Stream driven
• Establish LSP when message is received
– Topology driven
• Establish LSP based on the topology information (routing
information)
– Application driven
• Establish LSP based on the applications
• Signaling Protocol
– For Label allocation among LSRs, and establishing
LSP
– LDP, CR-LDP, RSVP-TE, MP-BGP, PIM
97
现代通信新技术导论 第二章 下一代网络与MPLS
Main Contents
• Next Generation Network
• MPLS
– Need for MPLS
– MPLS Architecture
• Label Switching
• MPLS Basics
– MPLS Labels
•
•
•
•
Label Forwarding
Label Distribution and Management
LSP Loop Detection
LDP
98
现代通信新技术导论 第二章 下一代网络与MPLS
Label Distribution and Management
• Label distribution modes
– DoD: downstream-on-demand
– DU: downstream unsolicited
• Label control modes
– Ordered
– Independent
• Label retention modes
– Conservative
– Liberal
99
现代通信新技术导论 第二章 下一代网络与MPLS
Label Distribution Mode: DoD
Trigger
Label 18 is allocated
to 172.68.1.0/24
Label 20 is allocated
to 172.68.1.0/24
171.68.4.0/24
171.68.1.0/24
LSR1
Sender
Request the Label for
dest-addr
172.68.1.0/24
LSR2
LSR3
Request the Label for
dest-addr
172.68.1.0/24
Receiver
100
现代通信新技术导论 第二章 下一代网络与MPLS
Label Distribution Mode: DU
Label 18
could be used
to get to
172.68.1.0/24
171.68.4.0/24
Sender
Label 20
could be used
to get to
172.68.1.0/24
Trigger
171.68.1.0/24
Receiver
101
现代通信新技术导论 第二章 下一代网络与MPLS
Label Control Mode
Label
Request
Label
Request
Label
Request
Sender
Receiver
Label
Mapping
Label
Mapping
Label
Mapping
102
现代通信新技术导论 第二章 下一代网络与MPLS
Label Retention Mode: Conservative
• Only keep the Label from the next hop neighbor, while
discarding the other labels
– Advantages: Less memory space required
– Disadvantages: Slow convergence with changing topology
mapping
label 20
mapping
label 30
172.16.2/24
LSR1
LSR2
mapping
label 16
LSR3
LSR4
mapping
label 17
Not the label from the next hop
neighbor, discard it
LSR5
103
现代通信新技术导论 第二章 下一代网络与MPLS
Label Retention Mode: Liberal
• Keep the labels from any neighbor
– Advantage: Fast convergence with changing
topology
– Disadvantages: More memory space required
mapping
label 20
mapping
label 30
172.16.2/24
LSR1
LSR2
mapping
label 16
LSR3
LSR4
mapping
label 17
Not the label from the next hop
neighbor, keep it for future use
LSR5
104
现代通信新技术导论 第二章 下一代网络与MPLS
Main Contents
• Next Generation Network
• MPLS
– Need for MPLS
– MPLS Architecture
• Label Switching
• MPLS Basics
– MPLS Labels
•
•
•
•
Label Forwarding
Label Distribution and Management
LSP Loop Detection
LDP
105
现代通信新技术导论 第二章 下一代网络与MPLS
LSP Loop Detection
• Loop routing
– Very harmful
• Two ways to prevent loop routing
– Max hop
– Path vector
106
现代通信新技术导论 第二章 下一代网络与MPLS
Main Contents
• Next Generation Network
• MPLS
– Need for MPLS
– MPLS Architecture
• Label Switching
• MPLS Basics
– MPLS Labels
•
•
•
•
Label Forwarding
Label Distribution and Management
LSP Loop Detection
LDP
107
现代通信新技术导论 第二章 下一代网络与MPLS
Concept of LDP
• Label Distribution Protocol
– To generate dynamic labels, similar to dynamic routing
protocols (e.g., OSPF)
•
•
•
•
With messages
With neighbor discovery and maintenance
With the algorithm to obtain the results based on the information
The result of LDP is composed of labels, but the result of OSPF is
routing information
– Main functions
• Distribute Label-FEC mapping
• Establish and maintain the routing for label switch
• LDP uses UDP and TCP
108
现代通信新技术导论 第二章 下一代网络与MPLS
Messages in LDP
• Discovery message
– For informing and maintaining LSR
• Session message
– For establishing, maintaining and stopping the
session connection between LDP entities
• Advertisement message
– For creating, changing and removing FEC-Label
binding
• Notification message
– For notification of information and error
109
现代通信新技术导论 第二章 下一代网络与MPLS
LDP Session Establishment and Maintenance
LSR1
Neighbor Discovery: Sending hello messages (UDP/prot:646）
LSR2
TCP Connection Establishment: Initiated by the LSR with higher address
(TCP/port:646)
S
Session Initialization: Initialization message sent by Master, with
negotiation parameters.
S
M
M
Slave checks if the parameters are acceptable. If so, the initialization message
with the negotiation parameters, and the keepalive message are sent
S
Master checks if the parameters are acceptable, If so, the keepalive
message is sent
M
S
By receiving the keepalive message by both LSRs, the session is
established
M
S
Disconnect the TCP connection and stop the session at any error message
M
110
现代通信新技术导论 第二章 下一代网络与MPLS
A Brief Review
• Background of NGN
– Multi-service
– Mature of new technologies
– Flexibility
• Definition of NGN
– By ITU-T
• Characteristics of NGN
• Architectures of NGN
– With IMS by 3GPP
– By ETSI
– With Softswitch
111
现代通信新技术导论 第二章 下一代网络与MPLS
A Brief Review
• MPLS
– Simplifies forwarding function
– Integrates ATM and IP
• Label switching
– Decomposition of network layer routing into
control and forwarding components
• Label forwarding
• Label distribution and management
– Label distribution, control and retention
112