Ethernet services are what network operators provide their subscribers. Alcatel-Lucent 1665 DMX supports Private Line, Private LAN, Virtual Private LAN, and Virtual Private Line.
The Private services are transported over their own dedicated SONET time slots. If present, Ethernet switching functions may or may not be shared.
Subscribers of Virtual Private services share network bandwidth to take advantage of the efficiency of statistical multiplexing that is available due to the intermittent nature of data transmission. VLAN Tags are used to separate subscribers and maintain privacy. Alcatel-Lucent 1665 DMX supports VLANs in the 1–4093 range for customer identification and isolation.
Private Line services are point-to-point in nature while Private LAN services are multipoint. Private LAN services always involve internal Ethernet switching while Private Line services do not.
Private Line service provides a dedicated link between two locations. The Ethernet ports and SONET bandwidth are dedicated to the subscriber and not shared. Private line service is characterized by minimal provisioning - typically just the SONET cross-connection. A subclass, Fractional Private Line, is distinguished by less than Ethernet-line-rate SONET connectivity. It is a form of rate control that also improves efficiency by only consuming the required SONET bandwidth in STS-1 increments. For more information about how STS-1 tributaries can be virtually concatenated to provide Fractional Private Line service, see Virtual concatenation.
Another characteristic of Private Line service is little or no Layer 2 functionality. With Fast Ethernet, the physical layer must be terminated precluding transparency of auto-negotiation. In addition, performance of the Fractional Private Line may be improved by enabling flow control, a Layer 2 function. For more information about flow control, see Flow control.
MAC address learning is another function. For more information, see Ethernet LAN/VCG port density. Circuit packs that support multiple service modes For more information about Ethernet circuit packs, see Ethernet/SAN circuit packs.
Private LAN service extends the concept of Private Line to connect more than two locations in an extended Ethernet LAN. This is accomplished by introducing embedded Ethernet switching at each node. The SONET bandwidth is still dedicated to one subscriber. Because this is a switched service, the attendant QoS features are available.
VLAN tagging is an integral part of Private LAN service. VLANs are used to distinguish customers or organizations within customers. In the Transparent Mode, the service provider provisions a port tag, or customer ID, for each Ethernet port. This port tag is added to each incoming packet and carried with the Alcatel-Lucent 1665 DMX network in order to keep the traffic for each subscriber separate. When the packets exit the Alcatel-Lucent 1665 DMX network, the port tag is removed. Any subscriber-inserted VLAN tags within the packets are carried through the network unchanged.
In 802.1Q mode, the provider coordinates VLAN tags with the subscriber to further manage traffic flows. For example, some VLANs can limit traffic among particular groups of sites representing communities of interest while others may be used for traffic common to all. This can be coupled with QoS features such as PIR and priorities to optimize the Private LAN network. For more information about Quality of Service, see Quality of Service. For more information about Tagging modes, see Tagging Modes.
Virtual Private LAN service extends the concepts of Private LAN service to include bandwidth sharing among multiple customers. In this way, less SONET bandwidth can be used to serve customers by taking advantage of the efficiency of statistical multiplexing. VLAN tags or port tags are used to keep each subscriber's traffic private.
Virtual Private Line, a shared service between two points, is a special case of Virtual Private LAN. It requires the use of Ethernet switching functions and is therefore configured and managed in the same way as Virtual Private LAN.
Network topologies consist of two layers: the packet layer and the underlying SONET layer. Packet networks can be created over a variety of SONET topologies, and have different properties as a result. For example, a Private Line service uses a point-to-point packet topology, but may be carried over a SONET ring, which may in turn be configured with UPSR protection or no SONET protection.
The following packet topologies are supported:
The point-to-point topology is used to join two nodes. For example, a business may connect to an ISP via a point-to-point connection. Because of its simplicity point-to-point configurations have a variety of protection options available. They may use any of the SONET layer protection mechanisms. They may also forgo SONET protection and use data-layer protection such as Link Aggregation.
In a multipoint network all points converse with each other. Note that connecting three locations by two point-to-point connections is not the same as if done by a multipoint connection. The location in the middle of the point-to point connections would have to provide external switching to enable the outer locations to converse with each other.
One useful case of multipoint configurations is a packet ring. In a closed-ring configuration all nodes may converse. An internal spanning tree may be configured for protection and loop prevention. This is independent of any spanning tree protocol that may be running on the subscriber's network. The spanning tree breaks one link, necessary with a ring of interconnected bridges. In the case of a link failure, the spanning tree algorithm restores connectivity by moving its break to coincide with the failed link.
A special case of multipoint configuration is where one node acts as a hub and all other nodes converse only with it. This hub configuration differs from a hub-and-spoke network only in that the spokes share bandwidth to reach the hub. It is more efficient and may be more practical because it conserves hub ports; only two VCG (WAN) ports are needed, regardless of the number of spokes. (In a packet ring configuration the broken link is placed between the two nodes most remote from the hub; because those nodes don't converse, there is no loss of useful bandwidth.) Both this topology and the hub-and-spoke described next are sometimes called point-to-multipoint.
The hub-and-spoke network is a hybrid between point-to-point and multipoint. Each node connects to the hub via a dedicated link; but, the links terminate on an embedded switch at the hub. In a typical back-haul application, the switch aggregates the traffic into a single Ethernet link for hand off. As in the multipoint hub network, tags are used to identify and direct traffic to and from the hub.
Ethernet applications are examples of what users can do with the services and topologies described in previous sections. The user can be the owner of the equipment or a client of the owner. For example, an ISP can have a private network or buy the services from an LEC to construct the application.
Alcatel-Lucent 1665 DMX supports the following applications:
Two or more enterprise LANs are interconnected. The LANs may be point-to-point Private Line connections, in which case Ethernet switching services are not provided. If Virtual private lines are desired, Ethernet switching is required. Even so, in a three-node LAN Interconnect application composed of Virtual private lines the middle node has two termination ports, one for each neighbor. This is different from a three-node LAN Extension (next application) using Virtual Private LAN in which the middle node may have only one (effectively a hub) port.
Sometimes called intranet or Layer 2 VPN, this extends an enterprise LAN to multiple locations via embedded Ethernet switching. Either Private LAN or Virtual Private LAN may be used.
Transparent LAN is a common form of LAN Extension in which the subscriber's traffic is transported without regard to the presence of subscriber VLAN tags. Transparency is achieved by the use of Port Tags, avoiding the need for the provider to administer VLANs with subscribers. The Port Tag is effectively a customer ID; only ports in the network assigned a particular customer ID will exchange traffic.
In Non-Transparent LANs, greater flexibility is available when the subscriber's 802.1Q tags are used for traffic management (802.1Q mode). For example, the priority bits within the tag can be used to give a portion of the traffic, for example VoIP, preferential treatment versus file transfer or other internet traffic. DSCP offers an alternative to priority bits. DSCP can also be used to give certain packets/data streams preferential treatment.
Although in a Virtual Private LAN service a Non-transparent LAN application requires the administration of VLAN Id's among customers, in a Private LAN where no other customers share the embedded Ethernet switch this is not necessary. For more information about priority bits, see Priorities.
In this application an ISP uses a provider's network to collect internet traffic. It is also an example of a trunking application, where traffic from multiple customers is handed off to the ISP router on a single trunk link for efficiency. The Virtual Private LAN service may be used to efficiently transport the best-effort internet traffic. It is typically done using the 802.1Q mode for separating the ISP's clients' traffic. If the ISP's router supports stacked VLANs then it can be done in Transparent Mode The trunk link may be GbE while the access links may be 10 or 100 Mb/s Ethernet.
In this application the ISP owns the network. In this case the clients' traffic is untagged. The ISP adds tags for customer separation using the 802.1Q mode. The ISP administers the tags directly, there is no third party involved.
Video distribution can be accomplished using Ethernet Multicasting. A Private LAN service is used to guarantee the bandwidth. Video traffic, generated at the head end, is sent using a multicast address. Transparent mode or 802.1Q mode may be used. At each node the traffic is dropped to its user and also duplicated and sent to the rest of the Private LAN.
An alternative is to use SONET drop-and-continue cross-connections to implement multicasting. This is a variation of the Private LAN service. Although it is limited to one-way video distribution, it supports full line rate throughput.
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