Modern networks, such as access and aggregation networks, are moving towards Ethernet as the universal medium. However, Ethernet is not quite robust enough for carrier transport applications. Thus, a new variation termed “Carrier Ethernet” has been created. Carrier Ethernet is configured to provide Ethernet-based operations, administration, and maintenance (OAM). There are many variations of this type of Ethernet, for example Optical Transport Network (OTN) carriage of Ethernet is a form of carrier Ethernet. OTN can offer a form of tunneling, and in addition offers hardening features such as embedded forward error correction (FEC).
Referring to FIG. 1, an Ethernet frame 10 with Virtual Local Area Network (VLAN) tagging is illustrated in one instance of Carrier Ethernet. VLAN Tagging is defined in IEEE 802.1Q as a standard to allow multiple bridged networks to transparently share the same physical network link without leakage of information between networks (i.e. trunking). The Ethernet frame 10 in IEEE 802.1Q is not actually encapsulated. Instead, the EtherType value (for Ethernet II framing) in the Ethernet header is set to hex 8100, identifying this frame as an 802.1Q frame. Also, four extra bytes are added after the Ethernet header consisting of two-byte Tag Control Information (TCI). VLAN ID (VID) is a 12-bit field specifying the VLAN to which the frame 10 belongs. A value of “0” means the frame 10 does not belong to any VLAN (so that the 802.1Q header specifies only a priority), a value of “1” is used with bridges, and a value of hex FFF is reserved for implementation use; all other values can be used as VLAN identifiers, allowing up to 4093 VLANs.
VLAN tagging is a Media Access Control (MAC) option that provides three important capabilities not previously available to Ethernet network operators and users. First, it provides a quality-of-service (QoS) mechanism to expedite time-critical network traffic by setting transmission priorities for outgoing frames 10. Second, it allows stations to be assigned to logical groups to communicate across multiple LANs as though they were on a single LAN. For example, bridges and switches filter destination addresses and forward VLAN frames only to ports that serve the VLAN to which the traffic belongs. Finally, VLAN tagging simplifies network management and makes adds, moves, and changes easier to administer.
The VLAN header includes two fields: a reserved 2-byte type value, indicating that the frame is a VLAN frame, and a two-byte Tag-Control field 14 that contains both the transmission priority (0 to 7, where 7 is the highest) and a VLAN ID 12 that identifies the particular VLAN over which the frame is to be sent. The receiving MAC reads the reserved type value, which is located in the normal Length/Type field position, and interprets the received frame as a VLAN frame. If the MAC is installed in a switch port, the frame is forwarded according to its priority level to all ports that are associated with the indicated VLAN identifier. If the MAC is installed in an end station, it removes the 4-byte VLAN header and processes the frame in the same manner as a basic data frame. VLAN tagging requires that all network nodes involved with a VLAN group be equipped with the VLAN option.
Referring to FIG. 2, an Ethernet frame 20 for Provider Backbone Transport (PBT) according to IEEE 802.1ah is illustrated in another instance of Carrier Ethernet. PBT is a set of enhancements to Ethernet technology that allows the use of Ethernet as a carrier-class transport network. PBT uses the concepts of VLAN tagging as per IEEE 802.1Q, Q-in-Q as per IEEE 802.1ad and MAC-in-MAC as per IEEE 802.1ah (Provider Backbone Bridges (PBB)) but disables the concept of flooding/broadcasting and spanning tree protocol (SPT). The idea here is to use Ethernet for connection oriented purpose as is the case with present SDH/SONET transport by stripping down the complexity involved with the present Ethernet LAN. It simplifies the OAM, as in SDH/SONET world, by using additional extensions based on IEEE 802.1ag. It also provides extensions so as to provide path protection levels similar to the UPSR protection in SDH/SONET network.
In the Ethernet frame 20, the tunnel is encoded by the destination MAC address of the backbone egress switch (B-DA) as well as a 12-bit VLAN-tag (backbone tag, B-VID). PBT forms a topology of B-DA rooted trees and an independent sink-tree is configured for each <B-DA, B-VID> pair. Since no SPT algorithm has to be performed, the trees need not be spanning. Thus, up to 4096 different trees can be configured for one B-DA.
IEEE 802.1ad (Provider Bridges) is an amendment to IEEE standard IEEE 802.1Q-1998 (also known as Q-in-Q or Stacked VLANs), intended to develop an architecture and bridge protocols to provide separate instances of the MAC services to multiple independent users of a Bridged Local Area Network in a manner that does not require cooperation among the users, and requires a minimum of cooperation between the users and the provider of the MAC service. For example Q-in-Q can operate as follows: two VLAN tags are added to each customer Ethernet packet. The Ethernet VLAN tag includes both a 12-bit VLAN ID and a 3-bit priority tag. The inner VLAN is customer assigned, and the outer VLAN corresponds to the carrier's assignment of a tunnel in which customer traffic is carried. For example, multiple customer flows may be “clustered” into the outer VLAN. A part of the VLAN assignment can include a 3-bit p-bit priority marking per 802.1p. The VLAN assignment can indicate how the traffic is to be prioritized. Sometimes, the Ethernet packet priority is derived from the IP layer's DiffServ Code Point (DSCP) bits. The VLAN assignment can also indicate the shaping assigned to an Ethernet flow cluster.
In another example, PBT is used as a similar alternative to Q-in-Q except that two MAC addresses are used instead of two VLAN IDs. Each of these MAC addresses can be associated to a VLAN also, and as such has the priority markings. This is similar to the Q-in-Q except that the tunnel label field includes the MAC and that two MAC addresses are used instead of two VLANs. Another difference with PBT is that the management system normally assigns the MAC/VLAN labels along the tunnel path Ethernet switches. Once again, prioritization and clustering is done via the MAC+VLAN label.
Transport Multi-protocol Label Switching (T-MPLS) is an ITU-T defined network layer technology that uses a subset of the existing MPLS standards and is designed specifically for application in transport networks. T-MPLS offers a simpler implementation by removing features that are not relevant to connection-oriented packet-switched applications and adding mechanisms that provide support of critical transport functionality. For prioritization in T-MPLS, an MPLS shim header is used. In this scheme, the MPLS label is used to define a traffic engineered path for with the Ethernet frames must follow. The QoS can be explicit or implicit depending on the label implementation/policy.
Disadvantageously, all of the above described methods require prioritization to be marked in either the form of VLAN bits or MPLS labels, i.e. pre-determined or explicit. This leaves little flexibility in the grouping of individual Ethernet flows for the purpose of shaping and prioritization. For example, all Ethernet packets in one VLAN are treated with the priority of that VLAN.