Реферат: Cisco Tag Switching Essay Research Paper Abstract

Cisco Tag Switching Essay, Research Paper

Abstract

The ever-increasing growth of the Internet and corporate Intranets are presenting a serious challenge to service providers and equipment vendors. This paradigm shift has transformed the way the world does business and defines new requirements for any business that wants to gain a competitive edge. Service providers, especially, are faced with the challenge of creating differentiated IP services and getting these new value-added services to market quickly. Cisco’ s Tag Switching technology is a key component in Cisco’ s plans for meeting these challenges. The two main components of Tag Switching are forwarding and control. This Tag Switching technology can retain the scaling properties of IP, and can help improve the scalability of IP networks. Tag Switching marries the performance of Layer 2 switching with the intelligence of Layer 3 routing to meet future growth demands. 4

Introduction

The continuous expansion of the Internet demands higher bandwidth within the Infrastructures of all corporations, not just Internet Service Providers (ISPs). Nevertheless, growth of the Internet is not the only driving factor for higher bandwidth; demand for higher bandwidth also comes from emerging multimedia applications. This demand for higher bandwidth requires higher throughput performance (packets per second) by routers, for both unicast and multicast traffic.

The expansion of the Internet also demands improved scaling properties of the Internet routing system. The ability to contain the magnitude of routing information maintained by individual routers and the ability to build a hierarchy of routing knowledge are essential to support a quality, scalable routing systems. 2

The requirements are growing for the need to:

X Improve scalability

X Improve forwarding performance

X Add routing functionality to support multicasting

X Allow for more flexible control over routing the traffic

X Provide the ability to build a hierarchy of routing knowledge 1

Cisco’ s multilayer switching technology, known as Tag Switching, provides an effective solution for meeting the aforementioned requirements. Tag switching in essence provides the functionality of a Network Layer router with the performance of an ATM switch. This technology is simple and based on the concept of “label swapping,” which uses a label (called a tag) for layer 3 packet forwarding. The simplicity of the tag switching forwarding component (label swapping) enables improved forwarding performance, while maintaining a competitive price performance ratio. 4

To enhance the flexibility of the system, Cisco chose to support multiple granularities within the definition of a tag. This enables a tag switch to forward data based on a wide variety of routing functions, such as multicast, destination-based routing, hierarchy of routing knowledge, and flexible routing control. Ultimately, a combination of all of these routing functions provided in tag switching enables a routing system that will be able to accommodate the demand made by emerging requirements in the corporate backbones as well as the Internet backbone. 7

In this article Cisco’ s Tag Switching will be described and defined by it’ s components, routing capabilities, ATM switching capabilities, and QoS implementation.

Tag Switching Elements and Components

Again, Tag Switching is an innovative technique for high performance packet forwarding that assigns “tags” to multi-protocol frames for transport across packet, or cell based networks. This technology is based on the concept of “label swapping,” where a packet or a cell, carry a short, fixed-length label that tells switching nodes how to process the data sent. 7

A Tag Switching internetwork consists of the following elements:

X Tag: A short fixed-length field header that is contained in a packet. Examples of a tag include the VPI and or VCI value in an ATM cell, or the DLCI header in a Frame Relay PDU, or a “shim” tag inserted between layer 2 and layer 3 addressing information in a packet1

X Tag Switching: The architecture, protocols, and procedures that bind network layer information to tags and forward a packet or cell using a label (tag) swapping mechanism.

X Tag Edge Routers: [TER] Located at the boundaries of a Tag Switching network, tag edge routers perform value-added network layer services and apply tags to packets at the ingress point of the network and removes tags at the egress point of the network. 1

X Tag Switch Routers: [TSR] A forwarding device that runs standard unicast and multicast routing protocols, is capable of forwarding packets or cells at layer 3 or layer 2 or via Tag switching (e.g. link layer independent). 1

X Tag Distribution Protocol: [TDP] A label binding distribution protocol. If the mapping of the FEC to next-hop mapping uses a link-state protocol, (e.g. OSPF, BGP), the distribution of tag binding information is provided via this separate protocol, known as TDP. 1

X Forward Equivalence Class: [FEC] an FEC can be mapped in tag switching to a set of labels along a routed path. 1

X Tag Stack: This is a technique that is roughly analogous to IP over IP encapsulation, and it enables a packet to carry more than one tag (e.g. multiple tags).

X Tag Switch Path: The ingress to egress switched path formed through a series of TSR devices by associating an FEC with a set of tags. 1

X Tag Forwarding Information Base: [TFIB] the TFIB is the connection or label swap table that is built and maintained in tag switching devices. The TFIB is the table used to index forwarded packets through a tag switch network. 1

X Piggybacking: Tag switching allows tags to be distributed using existing protocols. ( e.g. using existing protocols such as RSVP and PIM). 1

+ Figure 1. Tag Switching Example Diagram

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