Research on hierarchical routing technology of Automatic switched Optical Network

Automatic Switched Optical Network (ASON) is the core transfer technology of NGN. This technology is based on the traditional optical network (SDH, DWDM, OTN, etc.), by introducing the control plane to make it have intelligent function, that is, the optical transport network can according to the user's call request, Guided by the routing and signaling mechanism of the control plane, according to the user's business requirements (such as SLA for service level agreements), Automate the establishment of the optical transmission channel between the source end user and the destination user. In the process of realizing the automatic switching of optical transmission network, routing technology is one of the core technologies of Ason. To establish a connection between a routing domain or multiple routing domains, you can use a hierarchical route, Source Routing and step-by-step routing 3 basic routing algorithms. These 3 routing algorithms can achieve the fast connection of End-to-end channel spanning multiple routing domains by controlling the dynamic channel. Because the layered architecture is adopted in the transmission plane of Ason, in order to realize the routing, we can use the hierarchical routing method to realize the transmission plane of Ason Network connectivity (NC) that supports End-to-end business. Based on the analysis of the network structure of Ason and the routing structure of Ason, this paper focuses on the implementation of the hierarchical routing technology in Ason.

The layer network structure of Ason

It is suggested by g.805 that the transport network is layered, that is, the continuous vertical transmission network layer (i.e. layer network) superimposed, from top to bottom of the circuit layer, channel layer and transfer media layer, therefore, The transfer plane of Ason also adopts a layered approach. In addition, by g.8080, we also know that the implementation of Ason hierarchical routing of key functional components of the connection controller (CC) It works in the subnet of the Ason transmission plane layer network. Therefore, to understand the network structure of Ason is a prerequisite and basis for us to analyze the implementation of Ason hierarchical routing.

Layer Network (LN) is a topological element, which is generated by describing the information of special features, The transfer and termination of the transport entity and the transport processing function. In order to select the path and management, an LN can perform functional segmentation to form several subnets, and the subnet is a topological element for the selection of special feature information. Subnets can also be further segmented into lower-level subnets and subnet links, as well as sub-network Group (SNPP) links, The lowest level of recursive decomposition of a link is the transmission medium. Lower-level subnets can also continue to be split down until the matrix is in a single physical node. The matrix is also a topological element that represents the final limit of the recursive segmentation of the subnet, contained within a single network element, such as the Optical Connection controller interchange in Ason (OCC ) can be considered as the lowest level subnet. The logical combination of the network topological elements, such as LN, subnet, and subnet links, constitutes the logical topological structure of the transmission plane of Ason.

In ln in Ason, subnet and subnet link routing connection point (CP), terminal connection point (TCP), Sub Network (SNP) and sub-dot Group (SNPP) These reference points to define. Among them, CP is a component of the output node and another input node combination of points, its basic function is the connection function. TCP consists of a pair of "one-way TCP" in one place, which represents the combination of path terminals and two-way connections. The SNP represents an actual or potential CP or connection Terminal Point (CTP), or represents an actual or potential TCP or path terminal point (TTP). The difference between a SNP and other SNP forms a link connection (LC) and Subnet connection (SNC). LC represents a static connection between two SNP in different subnets. Is the subnet link, which describes the network topology relationship and the available transfer capacity that can be used for routing between subnets. There can be more than one link between a subnet. The two SNP (or multiple distribution-connected SNP) representing the same subnet boundary. ) is a dynamic connection relationship. SNC can be concatenated by a smaller subnet connection and a link connection, and the smallest SNC is a matrix connection in a mesh element, Its main function is to realize the transparent transmission of information within the subnet. To achieve the alternative, a SNP can also be combined with other SNPs to form SNPP. A snpp can also be subdivided into smaller snpp, representing different routes, or even different wavelengths. Connections between SNPP on different subnets form a SNPP chain The road. Finally, a series of link connections and subnets are connected in series to form a network connection across the entire LN, which realizes the transparent transfer of information end-to-end in Ln. So, how do you establish an End-to-end network connection in Ln in Ason? This is closely related to the routing structure and routing domain of Ason.

Routing structure in Ason

Typically, operators are based on specific operational strategies such as geography, Management and technical considerations) divide their networks into several parts. From a routing perspective, these sections can be viewed as route domains to provide routing services. In Ason, there is a relationship between a routing domain and a subnet: A routing domain exists in a single ln and consists of a set of subnets, The SNPP link connecting the subnet and the SNPP of the SNPP link Terminal point representing the route domain exit are defined. A routing domain can contain several smaller routing domains that are interconnected by SNPP links. The minimum limit for routing domain segmentation is to include only two subnets and one link in a routing domain. When a SNPP link crosses the boundary of a routing domain, a total All routing domains that enjoy public boundaries use a common SNPP identifier (SNPP ID) that determines the location of the SNPP link terminal point. The routing domain of Ason is based on its routing structure. The routing structure of Ason consists of routing controller (RC), Routing information Database (RDB), Link Resource Manager (LRM), The combination of components that perform routing functions, such as CC and protocol controller (PC), is formed. The function of RC is to respond to CC's request for channel or routing information in order to establish a connection. Including the equivalent RC Exchange routing information, this information can be end-to-end, can also be the next hop, and in the query RDB after the routing query (channel selection) to respond; To achieve network management purposes, RC is also responsible for loopback management network topology information needed (SNP and their properties). RC is not related to the protocol. The RC contains routing information within the routing domain under its jurisdiction, which is responsible for routing within the routing domain based on this information. This information includes the topology of the corresponding terminal system address in the given ln ( SNPP, SNP link connections, and SNP address (network address) information can also maintain the address information of other subnets (Peer-to-peer subnets) in the same ln, as well as a database on SNP status, For the implementation of restricted route selection. With this information, the RC can determine a route between two or more SNP (some of the routing restrictions also need to be considered). Detailed route selection information can have different programs, for example, provided by accessibility, should be distance vector (address and Next hop) of information; by network topology, you should have link state (address and topology bit ) information.

RDB stores a local topology, network topology, accessibility, and other routing information that may be the result of an update after routing information exchange, and may also include information that contains configuration. RDB can contain routing information for multiple routing domains. Rdb is not related to the protocol.

The main function of LRM is to provide all relevant SNPP link information to RC and to inform RC of any state change of its control link resources, and also to manage the SNPP link, including the allocation and removal of SNP link connections, Provides topology and state information. Currently, the main use of two LRM components, namely Lrma (A-terminal Link Resource manager) and LRMZ (z-end Link resource manager), while the SNPP chain routes a pair of Lrma and LRMZ components to manage each end of the link, the request to allocate a SNP link connection is only for the Lrma. LR M is also unrelated to the protocol.

CC is responsible for the coordination of routing controllers, link Explorer, and equivalent or next-level CC to enable the establishment and release of connections, the modification, management, and monitoring of existing connection parameters. 　　CC serves a separate subnet within the transport plane and provides a connection control interface (CCI) between the subnet and the control plane to create, modify, and delete the SNC directly. The PC handles the protocol-related messages, and what the message is, depends on the reference point for exchanging information (for example, E-nni, I-nni), and the PC passes the alternative primitives to the RC.

Implementation way of hierarchical routing in Ason

The hierarchical routing method of Ason works in subnets. The subnet is in accordance with the division of the LN in the transmission plane of Ason. In order to make the control plane of Ason correspond to the partition of the transmission plane's subnet, so as to facilitate the route selection and management, CC in the control plane of Ason, The RC and LRM routing control elements are also divided by subnets, That is, they are only responsible for the routing of the subnet to which they belong. Here, the implementation of CC is based on the distributed implementation, that is, the node-joint model is used to realize the hierarchical routing through the interactive communication between different grades of CC, and through the hierarchical routing, that is, through the call control and route selection of the control plane, the transmission plane of Ason can realize Link connection and subnet connection, finally realizes the network connection which supports End-to-end service in the Ason transfer plane. The network topology and signaling process for hierarchical routing are shown in Figure 1.

The network topology represents the resources of the basic transport plane with multiple entities in the control plane. The ln (recorded as subnet a) is divided into several subnets, recorded as subnets B, C, F and their connection links. Subnets B and C are further divided into smaller subnets, the subnet B is divided into subnet D and E, and the connection links between them, the subnet C is divided into subnet G and H, and the connection link between them. Hierarchical relationship between subnets or "parent" and "child" The relationship (that is, the containing relationship). Here, subnet A is an advanced subnet ("parent"), subnets B and C are low-level subnets ("children"), and in subnets B and C, can also be divided into "parent" and "child" level two subnet, namely Subnet B and C as "parent" subnet, subnet D, E and G, H are two subnets, "sub" subnet, And so on, recursion forms the hierarchical relationship between the LN's subnet. Here, subnets D, E, F, G, and H are the lowest-ranked subnets of LN, Can no longer be subdivided. In one ln, the formation of subnets and the hierarchical relationships between them are implemented through a number of device nodes, the hierarchical relationship between these device nodes determines the hierarchical relationship between subnets. Each subnet in the subnet hierarchy is associated with a separate device node that contains a single level of RC and several cc and LRM, for example, a child Device Node A, subnet B, and C ("Child") in Network A ("parent"), so that the unit nodes B, C, The device node is a separate node with routing function in the subnet. The main function of the device node is to divide an ln into a series of subnets, the RC contains the topology information of the subnet (SNP and SNP link), so that each subnet can realize its own dynamic connection control, the RC does not contain other subnets (above the layer , below, or other subnets of the same layer), the LRM contains link connection information between the smaller subnets within the subnet, Mainly responsible for the distribution and management of SNP links. The device node in the lowest level subnet (which can no longer be subdivided) contains only one cc, and the primary task is to implement the connection control between the two subnets by interacting with the CC at the top level. This shows that subnets D, E, F, The connection between G and H forms a transport entity for that Ln.

In general, the previous level of the device node and the corresponding next level of device nodes can be interactive communication between, There is no interaction between device nodes of the same level. In the hierarchical routing method shown in Figure 1, an end-to-end connection (d-e-f-g-h) across LN can be established through the interactive communication between CC, and its detailed procedures are shown in Figure 2.

The specific steps of the hierarchical route are as follows:

(1) When the network call controller (not pictured) sends a connection request message to CCA, CCA specifies a pair of SNP (A and Z-end) at the edge of subnet A.

(2) CCA to the RCA sent in A, z ends a request to establish a link connection required for routing messages (including messages to be routed through links and related subnets), CCA uses the SNP at the Z end to ask for RCA, and RCA returns the routing information of a set of links and related subnets to CCA, that is, Subnet B, C and F and the connection links between them.

(3) CCA to the local Lrma request link based on the resulting subnet B, C and F and the routing message between them connecting links, Lrma can return subnets B and F to CCA in any order (3a or 3b in Figure 2). Link connection information between F and C (includes connection link and SNP). When a connection link between subnets is assigned to a pair of SNP, a link connection is implemented, and the process between them is independent of the order in which they are established.

(4) CCA to CCB, CCC and CCF transmission of a pair of SNP (A and Z-end), the next level of subnet B, C can request a subnet connection, the operation of the process of repeated recurrence of the cycle, Until all the next subnet requests subnet connections. These sequence of operations are not fixed, the only requirement is to obtain a link connection before creating a subnet connection.

(5) The CCB in Subnet B uses the SNP at the Z-end of the subnet to ask RCB,RCB to return to the CCB subnet D, E and the connection link messages between them, so that a single route is determined between the pair of SNP (A and Z-ends) specified in the subnet; RCC determines a route between a pair of SNP (A and Z-ends) specified in Subnet C.

(6) The CCB is connected to the LRMB request link based on the resulting subnet D and E and the routing messages between them connecting links, LRMB can return the link connection information between Subnet D and E to the CCB in any order (such as 6a or 6b in Figure 2); Link connections in the next level of subnet C can be obtained from LRMC in any order (6a or 6b in Figure 2).

(7) The CC in the lowest rank subnet D, E, F, G and H completes the link connection and the subnet connection through the corresponding OXC device in the CCI control transfer plane, Finally, an end-to-end network connection (D-E-F-G-H) is formed. In this case, the lowest exchange does not include any routing or link configuration parts, providing only the necessary subnet connections.

(8) When the completion of this connection is established, CC in the lowest rank subnet D, E, F, G, and H will return the connection to the CCA of source node A to establish a successful verification signal (such as steps 8a, 8b and 9a, 9b and 9c in Figure 2), and finally, The CCA of source Node A will return the connection to the user network to establish a successful confirmation signal (step 10 in Figure 2).

Conclusion

Based on the analysis of ln structure and routing structure in Ason, The hierarchical routing technology in Ason is discussed in detail. Based on the discussion, we find that the hierarchical routing technology in Ason is based on the LN structure of Ason, which is similar to the Pnni technology in ATM network, and Pnni is also a kind of layered network technology. So, when we explore the related issues of Ason, if we can relate it to the existing network By comparing and analyzing the technology, we can understand and master the core technology of Ason in essence.