1. OVERVIEW
MPLS-VPN (Multiprotocol Label Switching-Virtual private networks) technology is new substitute to private WANs (Wide area network). This technology is popular in company day by day rapidly. Enterprise customers are moving to service providers that offer MPLS VPNs. MPLS VPN provides any-to-any connectivity like (T1 link, Frame-relay, T3 link, ATM, DSL, and VOIP) and built in-security characteristic. We can use this MPLS VPN instead of WAN due to this any kind of connectivity and cost.
Quality of service (QOS) is more important task in customer enterprise network. Company has video, VOIP, live conferencing and data traffic on one network infrastructure.
In this Research paper, MPLS-VPN provides enterprise network customers and service provider customer to maintain quality of service (QOS) for voice, video over IP and information traffic over MPLS VPNs environment. To deliver consistent peer to peer QOS, service provider and the enterprise customer should work closely together and have to same policies to implement on both side because service provider pass customer route in MPLS VPN topology. We can use the DiffServ (Differentiated services) QOS model in MPLS-VPN topology. We would use 6- class model for service provider network and enterprise customer network to achieve end-to end service quality. We will also investigate QOS parameters (e.g. delay, jitter and packet loss) over MPLS VPNs environment.
MPLS VPN QOS design can be view in three parts
‘The customer enterprise subscribes MPLS VPN service from ISP.
‘The service provider provisioning edge of network
‘Quality of service within the MPLS VPN core network.
LIST OF FIGURES
Figure 2.1 QOS policy in MPLS VPN network
Figure 2.2 QOS deployed in layer 2 WAN design
Figure 2.3 QOS implement in MPLS VPN DESIGN (FULL-mesh connectivity core network)
Figure 7.1 pipe model
Figure 8.1 per Hop Behaviour (PHB)
Figure 8.2 EF bit pattern
Figure 8.3 Assured Forwarding
Figure 8.4 AF class values
Figure 8.5 class bit pattern
LIST OF SYMBOLS AND ABBREVIATIONS
QOS- Quality of Service
MPLS- Multiprotocol label switching
BGP- Border Gateway Protocol
EBGP- Exterior Border Gateway Protocol
PE- Provider Edge
CE-Customer Edge
PHB- Per Hop Behavior
ME-Mark Eligible
2. LOCATION OF QUALITY OF SERVICE IN MPLS VPN
MPLS VPN architecture is implemented on provider-edge- routers (PE), customer-edge-routers (CE), and core provider (P) routers. Here we require fully meshed connectivity between all core provider routers with the help of layer 3 routing protocols like (EBGP, IBGP, MPLS, and IP).
There are different policy on PE and CE Routers. PE Router has Marking ‘classification policy to deploy SLA. Qualities of service policy are optional on Core provider routers (P) .there is no such requirement additional policy of QOS with core routers. Some provider can be implement diff-serv. policy in core provider network. We can also deploy traffic-engineering (MPLS-TE) with reserve resource of network help of RSVP protocol. We can see in figure 2.1 where we implement QOS Policy in MPLS VPN network
‘Required QOS on
1) Egress of CE router (CE to PE)
2) Ingress of PE router (CE to PE)
3) Egress of PE router (PE to CE)
4) Ingress of CE router (CE to PE)
‘ Optional QOS on
1) Backbone core provider network routers
Figure 2.1 QOS policy in MPLS VPN network [1]
Private WAN use rarely due to high-cost, scalability, manageable traditional private WAN designs rarely use full-mesh models. We can use central hub model in place of Layer 2 WAN model. Quality of service is deployed on hub router of enterprise. QOS is defined in figure 2.2
Figure 2.2 ‘ QOS deployed in layer 2 WAN design
The only way to guarantee service levels in such a scenario is for the service provider to provision QOS scheduling that is compatible with the enterprise’s policies on all PE links to other branches. These change in QOS administration for full mesh topology. Customer networks and service providers must cooperate to jointly administer QOS over whole Network in figure.
we can deliverd gurantee service though different trafic class on based of provision. This policy can be share between provider edge router and customer edge router. These edge router should co-operate to deploy quality of serive in MPLS VPN NETWORK shown in figure 2.3 [1]
Figure 2.3 QOS implement in MPLS VPN DESIGN (FULL-mesh connectivity core network)
Queuing policies are mandatory on CE and PE routers because of the full-mesh topology in MPLS VPN network. PROVIDER EDGE routers also have same policy (and marking) on ingress through SLA.
3. QOS NETWORK ELEMENTS
Service providers define their network service with Quality to costumer. They offer Service-level-agreements (SLA) in which include details of all QOS parameters like delay, loss of packet and peer to peer jitter . QOS is mechanism that provides End – End intelligence to network devices to deploy different traffic that defined by class s level by SLA.
Quality of service has different methods such as scheduling, marking, Classification, queuing, bandwidth defined and priority wise data is used widely in network to reach end-end services [2].
Quality of Service has to manage different following network-elements
1. Bandwidth: Maximum amount of information could be carried.
2. Delay: time between send data from Source-Destination.
3. Jitter: Variability in TIME (delay).
4. Reliability: how much data to be delivered to destination?
4. ISSUES OF QUALITY OF SERVICE (QOS) IN MPLS VPN NETWROK
Nowadays there are different types of application such as voice over IP, video over IP, live streaming, data packets and browsing data. Different applications have different level of sensitivities and different requirement. These applications run on same infrastructure so it is a challenge to fulfill the requirement of application as per requirements. Some applications are delay sensitive, some application requires more bandwidth, some applications require constant amount of bandwidth and some applications require less packet loss (reliability) [2].
There are distinct levels of service on internet (applications)
Some applications are time-sensitive like VOIP, live streaming
Some application needs much more bandwidth like video on demand
Internet needs constant amount of bandwidth or reliability (packet-loss)
Voice over IP (VOIP) and video over IP require following SLA details
‘ Jitter does not exceed over 30 ms
‘ END to END delay reside between 150 ms to 200 ms
‘ Packet loss < 1 percent
There are two type applications
1) TCP based application- if any packet drop then it has mechanism to retransmits these packets
2) UDP based application- there is no mechanism for acknowledgement and retransmission. Like VOIP, online-game, video on demand.
We have 4 big challenges in MPLS VPN network that are overcome by different methods
1. Bandwidth- marking, queuing.
2. Delay ‘ DSCP
3. Jitter-Diff. Services in QOS MPLS VPN
4. Reliability- Random Early Detection (RED), Tail Drop, Weighted Random Early Detection (WRED), Traffic policing and shaping.
5 QOS METHODS
There are 3 QOS Methods
1. Best-Effort
2. Integrated Services (Int. Serv.)
3. Differentiated Services (Diff. Serv.)
5.1 BEST-EFFORT METHOD
There is no QOS configuration in Best-Effort model. All different types of traffic are served in the same manner and equally important in this model. No Marking, classification and Policies are needed in this model. Example- Normal post service.
5.2 INTEGRATED SERVICES METHOD (INT SERV.)
It was developed to fulfill the requirement for real time applications and End to End delay. Basic idea was to store network-resources for applications through bandwidth, delay and loss of packet. Resource Reservation protocol (RSVP) is used for reserving resource of network for customers. It provides the signaling and reserves end-to-end network resources for the application. We can call hard QOS method. Use = virtual Circuit and flow-based model.
5.3 DIFFERENTIATED SERVICE METHOD (DIFFSERV)
Differentiated Service Method is alternatives of Int. Serv. QOS method. It beats the limitation of Int-Serv method. It does no need for call signaling, no need resource reservation, and no flow control. We can call Soft QOS model. It uses the per-hop-behaviors (PHB) instead of signaling protocols [3].
It is class based mechanism in which we can classify and mark packet as belongs to specific traffic class. Diff.serv aware routers implement through PHBs which define packet forwarding property associated with class of service. Example – low loss and latency
6. INTSERV – DIFFSERV DIFFERENCES AND RESTRICTION
Int Serv and Diff Serv are 2 methods to reach Quality of Services. There are distinct in their layout and configurations. Int Serv. method was the first attempt to achieve QOS. It is based on per flow operations and control to provide the guaranteed Quality of service for specific flow. It remarks bandwidth on network.
DiffServ uses resource reservation protocol (RSVP) for reservation of network resources. If RSVP reserves resource of network, then resource could not be used by other transmission. It works same as private leased lines and defined guaranteed QOS. One flow isolate from one another. It does not give guaranty QOS but it is much more flexible. It is class based mechanism in which we can mark and shaping this packer on each node.
7. MPLS VPN QOS
Quality of service can be defined in two models related to class of service in real time applications.
‘Hose model
‘Pipe model
7.1 HOSE MODEL
In this model, particular CE routers send and received traffic in same VPN. Consumer doesn’t have enough capacity to analyze and distribute traffic on core network.
Ingress-committed-Rate (ICR) = traffic received from CE routers
Egress Committed Rate (ECR) = traffic sent to CE routers.
7.2 PIPE MODEL
Figure 7.1 pipe model
A Service provider marks some QOS parameters at ingress router of PE router and matches this QOS policy at other PE side parameters at egress side. This pipe should be represented as tunnel between 2 CE customers. In this model traffic flows only one direction at a time .so, this model is called unidirectional model.
8 DIFFERENTIATED SERVICES OVER MPLS VPN
We can select DiffServ QOS model and hose method to reach Quality of Services because it is used widely in Enterprises Company due to its scalability.
Diff. Serv QOS model can be defined as follow
‘Classification
‘Marking
‘Policy as per SLA
8.1 CLASSIFICATION
Classification is method of dividing the traffic into different category that is called a traffic class. Traffic becomes ready for further handling to reach Quality of service. Classification happen customer-edge router normally. It is basic part to achieve the QOS using DiffServ model.
It is implemented on below criteria [3]
1. Incoming-Interface
2. Differentiated service code point (DSCP)
3. IP precedence
4. Source and/ or destination IP address
5. Five-Tuple
8.2 MARKING
Marking is process in which we can sign color the packet in simply word. We can recognize packet. Marking is value which put in differentiated-services-code-point (DSCP) field in ip header. Network load is identified through to reach QOS. We can mark traffic on second layer and on Network layer [3].
8.2.1 DATA LINK LAYER MARKING
1. COS (class of services)
Three bits are reserved for QOS.
2. Multiprotocol Label Switching (MPLS) experimental bit
Three bit – MPLS EXP
3. Frame Relay
FECN
BECN
Discard eligible (DE) fields are used for congestion detection and avoidance.
8.2.2 NETWORK LAYER
1. Source or destination IP addresses
We can mark source – destination the IP packets.
2. IP precedence or DSCP on IP header
IP precedence and DSCP ‘8-bit field TOS in IP header.
We use DSCP 6 most significant bits. IP precedence uses 3 most significant bits.
8.3 PER HOP BEHAVIOR (PHB)
Per Hop Behavior (PHB) is a mechanism that is allocated x percent of network resource such as bandwidth delay, packet on each node. These PHBs are like building blocks and are grouped together to achieve QOS according to SLAs. PHBs are configured at each node in network in terms of buffer allocation and packet scheduling mechanisms. Figure-8.1 shows the bit pattern of PHB selector (DSCP field).
Figure 8.1′ per Hop Behavior (PHB)
There are four PHB which is defined below.
1. Default PHB: best-effort services.
2. Expedited Forwarding (EF): Used for low-delay service
3. Assured Forwarding (AF): Used for guaranteed bandwidth service
4. Class-selector PHB: Used for backward compatibility with non-DiffServ compliant device
8.3.1 EXPEDITED FORWARDING PHB
Figure 8.2 displays the bit pattern of Expedited Forwarding used in DSCP. It provides the following functionalities.
1. End-to-end delay.
2. Polices on bandwidth when congestion occurs.
3. guaranteed bandwidth.
Figure 8.2 EF bit pattern
8.3.2 ASSURED FORWARDING PHB
There is some functionality defined below
1. Allow extra bandwidth when available.
2. Provides some fix amount of bandwidth.
Figure 8.3 Assured Forwarding
These are 4 classes (AF1, AF2, AF3, and AF4). Each class has three level of drop probability which is LOW, MEDIUM and HIGH in figure 8.4
Figure 8.4 AF class values
Figure 8.5 class bit pattern
9. IMPLEMENTATION
9.1 TOPOLOGY [5]
Here I have created with one topology with MPLS VPN with Graphical Network Simulator [5]
Network configurations
CE1=customer edge network=10.1.12.0/24
PE1= provider edge network=192.168.14.1/24
P= core provider router =192.168.14.4/24
=192.168.41.4/24
PE1= provider edge network=192.168.41.1/24
CE2= customer edge network=10.1.21.0/24
9.2 CE1 ROUTER CONFIGURATION
Basic configuration on interfaces [5]
EBGP configuration between CE1-PE 1
Quality of service configuration [4]
Classification ‘ voice, video and call-signaling and IP
Policy- set bandwidth, dscp, priority value and apply it on CE1 egress.
9.3 PE1 ROUTER CONFIGURATION
Basic configuration on interfaces [5]
BGP configuration [4]
OSPF and MPLS configuration
Quality of service configuration
Classification ‘ voice, video and call-signaling and IP
Policy- set bandwidth, dscp, priority value and apply it on PE1 ingress.
REFERENCES
[1] MPLS-Enabled-Applications: ‘Emerging Developments and New Technologies Hardcover
Ina Minei (Author), Julian Lucek (Author)
[2] MPLS VPN with Diff-Serv QOS Performance research paper at Halmstad University
[3] Cisco website- www.cisco.com/c/en/us/support/docs/quality-of-service-qos/qos-packet-marking/10103-dscpvalues.html 18th april, 2014
[4] Cisco Learning Center -online learning center
[5] Graphical Network Simulator GNS version 3.0 – Implementation Network Topology