Edge device

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Edge devices are routers, switches, routing switches, integrated access devices (IADs), multiplexers, and a variety of metropolitan area network (MAN) and wide area network (WAN) access devices that provide entry points into enterprise or service provider core networks. On an enterprise network, edge devices may connect Ethernet and token ring local area networks (LANs) to an Asynchronous Transfer Mode (ATM) backbone, where the ATM network provides a bridge between the edge networks. Edge devices also provide connections into carrier and service provider networks.

[edit] Introduction

In general, edge devices provide access to faster, more efficient backbone and core networks. The trend is to make the edge device smart and the core device(s) "dumb and fast". Consequently, core networks are being designed with switches rather than routers. ATM and Multiprotocol Label Switching (MPLS) provide examples of edge switches. While a core of all routers may be easy to manage (routing protocols self-configure routes), they are not scalable and do not support teletraffic engineering and other techniques that support Quality of Service (QoS) in large packet networks.

[edit] Translation

Edge devices may translate between one type of network protocol and another. For example, ATM networks send data in cells and use connection-oriented virtual circuits. An IP network is packet oriented; so if ATM is used as a core, packets must be encapsulated in cells and the destination address must be converted to a virtual circuit identifier. Edge devices are responsible for handling this conversion. There is an ingress (input) and egress (output) edge device for all connections. A number of techniques have been devised to move IP packets over switched network topologies.

[edit] Multiservice Units

An edge switch for a WAN may be a multiservice unit, meaning that it supports a wide variety of communication technologies, including Integrated Services Digital Network (ISDN), T1 circuits, frame relay, and ATM. An edge device may provide enhanced services, such as virtual private networking (VPN) support, Voice over IP, and QoS services.