Enhanced optical line terminal controller

Abstract

An enhanced optical line terminal (OLT) controller capable of providing traffic processing features. The OLT controller comprises an Ethernet switch operable in a stacking mode and being capable of mapping between Ethernet addresses and passive optical network (PON) addresses. The Ethernet switch is connected to a PON medium access control (MAC) adapter via a stacking port and being capable of processing Ethernet frames relayed on the PON network. The mapping information is kept by the Ethernet switch in a forwarding table.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the invention and to see how it may be carried out in practice, some embodiments will flow be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

FIG. 1 is a diagram of a typical prior art PON;

FIG. 2 is a schematic block diagram of a prior art OLT;

FIG. 3 is a block diagram of an enhanced OLT controller disclosed according to one embodiment of the present invention;

FIGS. 4 a to 4d are schematic diagrams of a GEM header, a stacking tag, an upstream Ethernet packet header, and a downstream Ethernet packet header; and

FIG. 5 is a flowchart describing the process for learning the association between MAC addresses and port-IDs according to one embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

An embodiment of the present invention discloses an enhanced optical line terminal (OLT) controller capable of providing traffic processing features. The OLT controller comprises an Ethernet switch operable in a stacking mode and being capable of mapping between Ethernet addresses and passive optical network (PON) addresses. The Ethernet switch is connected to a PON medium access control (MAC) adapter via a stacking port and being capable of processing Ethernet frames relayed on the PON network. The mapping information is kept by the Ethernet switch in a forwarding table.

FIG. 3 is a block diagram showing the functionality of an OLT controller 300 disclosed according to one non-limiting embodiment of the present invention. The OLT controller 300 includes an Ethernet switch 310 having a plurality of input ports 312-1 through 312-N and a stacking port 314 connected to a PON MAC adapter 320. The PON MAC adapter 320 communicates with the ONUs 120 via a plurality of ports 322-1 through 322-M. Each port 322 is mapped to an address designated by a port-ID. The main function of the adapter 320 is to construct downstream frames compliant with at least the Gigabit PON (GPON) or Ethernet PON (EPON) standards. As illustrated in FIG. 4a, a GEM header 410 of a GPON downstream frame comprises at least the fields: a payload length indicator (PLI) 411 used for delineation, a port-ID 412, a payload type indicator (PTI) 413, and a cyclic redundancy check (CRC) 414. In addition, the CRC is computed over the PLI, port-ID, and PTI values and inserted in field 414. In addition, the PON MAC adapter 320 reconstructs upstream Ethernet packets from PON frames originated at ONUs 120.

Other embodiments of the OLT controller 300 may likewise be employed where the Ethernet switch 320 is replaced by a network processor, a custom ASIC, or any aggregation device supporting custom or proprietary tags (e.g., stacking tags).

The stacking tag is sent from the Ethernet switch 310 which is configured to operate in a stacking mode. Generally, stacking is the connection of two or more component Ethernet switches that may optionally be resident in the same chassis so that they behave as a single composite switch. As shown in FIG. 4b, a stacking tag 420 includes a switch number, a port number and preferably a priority tag. The combination of switch and port numbers determines the port-ID. Therefore, to encapsulate the GEM header 410 includes extracting the switch and port numbers from the stacking tag, computing the port-ID as a function of these numbers, and inserting the port-ID in the field 411. The priority tag defines the quality of service (QoS) assured to customer equipment (CPE) connected to an ONU 120.

As opposed to hitherto-proposed OLT controllers the mapping between Ethernet addresses (e.g., MAC address, VLAN tag, etc.) and port-IDs is based on the MAC destination address of incoming Ethernet packets. With this aim, the Ethernet switch 310 learns port-IDs of PON frames. The learning process will be better understood with respect to FIG. 5. At S510, an upstream Ethernet packet is received at the Ethernet switch 310. As depicted in FIG. 4c, a header 430 of an upstream Ethernet packet includes at least a MAC source address (SA), i.e., the address of a source CPE of an ONU, a MAC destination address (DA), i.e., the address of a destination terminal in a backbone network, and a port-ID, i.e., the ID of the source ONU. For simplicity of the description, other fields that may be included in header 430 are not shown. At S520, the port-ID and SA values are extracted from the received packet. At S530, a check is made to determine if the port-ID is included in a forwarding table maintained by the Ethernet switch. The forwarding table includes mapping information between MAC address of each CPE and a port-ID value. It should be emphasized that the extract port-ID is. derived from a switch and port numbers.

In one embodiment of the present invention the forwarding table may also include a priority tag that defines the QoS ensured for a respective CPE. If S530 results with an affirmative answer, execution terminates; otherwise, at S540, a new entry is allocated in the forwarding table and the extracted MAC address and port-ID are saved in the table. It should be noted that a single MAC address may have multiple port-IDs associated with it. It should also be noted that no new database is required in the Ethernet switch to maintain the forwarding table, as the present invention utilizes databases that in any case exist in conventional Ethernet switches to keep the mapping information.

In the downstream direction, the Ethernet switch maps between the DA of an incoming Ethernet packet, generates the stacking tag, and appends the tag to the packet's header. Specifically, the Ethernet switch 310 extracts the DA from the packet's header. Then, the switch 310 searches in the forwarding table a MAC address that matches the DA, and once such an address is found, its respective port-ID is retrieved. From the port-ID the switch number and port number are derived and inserted to the stacking tag 420. If the entry of the port-ID also includes a priority tag, then this tag may also be added to the tag 420. Subsequently, the stacking tag is attached to a header of an incoming Ethernet packet. As shown in FIG. 4d, the modified Ethernet header 440 includes a stacking tag 420, a MAC DA, a MAC SA, an Internet protocol (IP) address, and a frame check sequence (FCS). For simplicity of the description other fields that may be included in header 440 are not shown. The Ethernet packet including the header 430 is sent to the PON MAC adapter 320 over the stacking port 314.

It should be appreciated by a person skilled in the art that the ability to map addresses from Ethernet domain to the GPON domain allows the Ethernet switch to provide enhanced traffic processing features including, but not limited to, aggregation of multiple PON flows, Ethernet QoS, rate limitation, packets multicasting, and so oil. Specifically, the rate limitation allows controlling the amount of bandwidth that ingress the output ports 322. It further allows enforcing downstream traffic rates, per ONU, according to a predefined service level agreement (SLA). The Ethernet switch 310 replicates multicast traffic on its stacking port 314, i.e., creates a copy for each relevant port 322. The switch 310 forwards the multicast traffic, identified by the multicast group to the PON MAC adapter 320, which correlates between multicast group of packets to its corresponding multicast port ID.

In a specific embodiment, the OLT controller disclosed herein is applicable to operate in conjunction with the GPON and EPON standards. When operating in a GPON mode, the PON MAC adapter encapsulates the port-ID into a port-ID field in a GEM header (shown in FIG. 4a). When the OLT is configured to operate in an EPON mode the PON MAC adapter 320 encapsulates Ethernet packets within frames compliant with the EPON standards. In particular, a logical link ID (LLID) is derived from the switch and port number in the stacking tag and inserted in a LLID field in a preamble of a header of an EPON frame.

Claims

1. An optical line terminal (OLT) controller capable of providing enhanced traffic processing features, the OLT comprising: an Ethernet switch operable in a stacking mode and being capable of mapping between Ethernet addresses and passive optical network (PON) addresses; anda PON medium access control (MAC) adapter connected to the Ethernet switch via a stacking port and capable of processing Ethernet frames relayed on the PON network.

2. The OLT of claim 1, wherein the Ethernet switch maintains the mapping information in a forwarding table.

3. The OLT of claim 1, wherein the mapping information comprises at least one of: the association between MAC destination addresses and port-IDs, the association between MAC destination addresses and logical link IDs (LLIDs).

4. The OLT of claim 3, wherein at least one of: the LLIDs, the port-IDs are encapsulated in a stacking tag.

5. The OLT of claim 4, wherein the stacking tag includes a switch number and a port number.

6. The OLT of claim 5, wherein the port-ID and the LLID are determined using switch number and the port number.

7. The OLT of claim 6, wherein the stacking tag further includes a priority tag that defines a quality of service (QoS) assured to customer equipment (CPE) connected to an ONU.

8. The OLT of claim 1, wherein the PON comprises at least one of: a Gigabit PON (GPON), an Ethernet PON (EPON).

9. The OLT of claim 1, wherein the enhanced traffic processing features comprise at least one of: aggregation of multiple PON flows, Ethernet QoS, rate limitation, packets multicasting.

10. A method for providing enhanced traffic processing features by an optical line terminal (OLT) controller, the method comprising: generating a stacking tag based on mapping between Ethernet addresses and passive optical network (PON) addresses; andconstructing downstream frames compliant with the PON using address information encapsulated in the stacking tag.

11. The method of claim 10, wherein the mapping information comprises at least one of: the association between medium access (MAC) destination addresses and port-IDs, the association between MAC destination addresses and logical link IDs (LLIDs).

12. The method of claim 11, wherein the stacking tag includes a switch number and a port number.

13. The method of claim 12, wherein constructing the downstream frames further comprises: extracting the switch number and the port number from the stacking tag;determining a port-ID using the switch number and the port number; andinserting the port-ID to a header field of a downstream frame.

14. The method of claim 12, wherein constructing the downstream frames further comprises: extracting the switch number and the port number from the stacking tag;determining a LLID using the switch number and the port number; andinserting the LLID to a header field of a downstream frame.

15. The method of claim 12, wherein the stacking tag further includes a priority tag that defines a quality of service (QoS) assured to customer equipment (CPE) connected to an optical network unit (ONU).

16. The method of claim 11, further comprising learning at least one of port-IDs or LLIDs associated with the PON addresses.

17. The method of claim 16, wherein learning at least one of port-IDs or LLIDs associated with the PON addresses comprises: receiving an upstream packet;extracting a port-ID and an Ethernet source address from the upstream packet;determining if the port-ID is included in a forwarding table; andwhen a respective entry is not found in the forwarding table, inserting the port-ID together with the Ethernet source address to an entry in the forwarding table.

18. The method of claim 17, wherein the forwarding table includes mapping information between MAC address of each CPE and a port-ID value.

19. The method of claim 18, wherein the port-ID comprises a LLID.

20. The method of claim 10, wherein the PON comprises at least one of: a Gigabit PON (GPON), an Ethernet PON (EPON).

21. The method of claim 10, wherein the enhanced traffic processing features comprise at least one of: aggregation of multiple PON flows, Ethernet QoS, rate limitation, packets multicasting.