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MPLS (Multiprotocol Label Switching)
What is MPLS?MPLS is a QoS (Quality of Service) protocol for managing bandwidth allocation for Internet media connections (e.g. a VOIP voice connection).
The most important thing to understand about MPLS is that it is not a service. It is a technique that can be used to deliver services like metro Ethernet to IP VPNs. It can also be used as a provision of optical services. Therefore, the services that carriers’ customers choose are not referred to as MPLS.
MPLS is a way of labeling packets that make it easier for routers to read. Originally, each packet that was sent through an IP network was sent through solo, which caused routers to have to read each one induvial. With MPLS, whenever a packet enters a network it labeled and assigned an FEC, which stands for forwarding equivalence class. This allows routers to be able to place the packets into a table, which allows them to sort them faster than having to read each one individually.
Overall, a MPLS network can handle packets more consistently, especially when it comes to packets that are carrying real-time traffic. Examples of real-time traffic packets are packets created by voice or video, which has become more popular over the years. In a MPLS network these types of packets are automatically mapped to the low-latency routes across entire networks, which conventional routing use to have issues with. The whole point of this system is to put additional information on each pack that flows through it.
Is MPLS a Layer 2 or a Layer 3?Over the years, a lot of people have been confused about MPLS systems. They are not sure if they are a Layer 2 or a Layer 3 service. The problem with this is the fact that MPLS is not easily placed into any type of OSI seven-layer hierarchy. This is one of the key benefits that MPLS offers those who uses it because it is a way of separating underlying data-link service from different forwarding mechanisms. The beauty of an MPLS system is that it can work with existing ATM or DLCI headers or with old type IP routers.
The bottom line behind choosing an MPLS service is that it allows network operators to offer their customers multiple services. There are two popular implementations of the MPLS service: Layer 2 VPNS and Layer 3 BGP/MPLS-VPNs.
The most popular VPNs that has been implemented by most major service provides are RFC 2547 VPNs. They are used by ISPs like Verizon, BT, and AT&T, which are some of the largest ISP providers in the business. When using the 2547, traffic is isolated into MPLS-VPNs whenever it enters a network.
Interior routers are not brilliant. They do not have any prior knowledge about IP information, besides the basic forwarding decisions that are found on the MPLS label. Most edge routers use BGP to exchange the knowledge they receive from VPNs. This is what allows services provides to isolate the traffic that is coming from multiple customers. The traffic could also come directly from the internet using a shared backbone.
When it comes to Layer 2 MPLS services, there are a few different flavors to choose from. However, all Layer 2 packets are encased in an MPLS header before being forwarded through to the MPLS core. After traveling and reaching their destination, the packets have their labels remove and it ends up at where it first entered the MPLS network. Due to how they work, Layer 2 MPLS services are usually used to extend services like frame relay across an IP WAN or Ethernet services.
Different Types of MPLS Service OptionsThe most popular MPLS version is called PWE3, which is known as Wire Edge to Edge Emulation. This version is used in ATM services and encapsulate connection-oriented frame relay services. The purpose of the PWE3 is to define point-to-point tunnels all the way across the MPLS backbone. Therefore, it works well with circuit-oriented networking protocols. Although it’s not preferred, PWE3 can be used to support connectionless LAN protocols.
If connectionless protocols are needed, the best MPLS version that should be used in VPLS, which is known as virtual private LAN service. VPLS can address more specific challenges that happen when extending Ethernet service across a WAN or metropolitan area. The T-MPLS, or the ITU’s transport – MPLS, was designed to help simplify the deployment of Ethernet services.
However, MPLS is not the only thing that can help with Ethernet services. There are a few vendors, like Extreme, Siemens, and Nortel, that promote a different approach to PBT, known as Provider Backbone Transport, when it comes to providing services to a larger metropolitan area.
Unlike MPLS, PBT uses existing IEEE 802.1 VLAN tags to help to deliver Ethernet services across an entire provider network. Unlike other types of services that have tried, PBT can compete with T-MPLS head to head, and it still hasn’t been determined which one will win.
GMPLS or Generalized Multiprotocol Label Switching system is a variant of MPLS. It can give routers that ability to signal optic layers intelligently, which allows provides to tear down, establish, or change optical links in real time.
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