Scheduling of Bursts at an OBS Node

THE JUMPSTART PROJECT 255 The common header consists of the subfields: protocol type 1 byte, protocol version 1 byte, header flags 1 byte, message type 1 byte, message length 2 bytes, softpath IEs offset 2 bytes. The signaling messages are not used exclusively for setting up and tearing down connections. They are also used by the routing and the network management protocols. The type of protocol used is indicated in the protocol type field. The message type indicates the message being carried, and the message length gives the length of the entire signaling message. Finally, the softpath IEs offset gives the offset from the end of the common header to the beginning of the softpath IEs field. This offset permits to directly access the softpath IEs field. The hardpath IEs field contains all of the IEs that are to be processed in hardware. The first subfield, IE mask, is a 32-bit vector that indicates which hardpath IE is present. Each bit is associated with a particular hardpath IE, and up to 32 different hardpath IEs can be accommodated. The IE mask subfield makes it easy for the hardware to parse the hardpath IEs field and determine invalid IE combinations. The hardpath IEs are a multiple of 32 bits; they are fixed and relatively inflexible in format. They are given immediately after the IE mask subfield. Some defined hardpath IEs include: source address, destination address, call reference number, burst descriptor, delay estimator, channel descriptor, QoS descriptor, remaining connection time, session scope, party address, cause, TTL, and bearer signal class. The softpath IEs field contains all of the IEs that are to be processed by software. Softpath IEs are structured using the type-length-value TLV format see Section 7.1.2. Unlike the hardpath IEs field, which permits the parser to see which particular IEs are present, the softpath IEs field simply contains a sequence of IEs. Thus, the software must scan the entire field before it knows which software IEs are present. As shown in Figure 10.13, the softpath IEs field consists of a subfield that gives the number of softpath IEs present, a flags subfield, and the TLVs of the softpath IEs. Finally, each signaling message is optionally appended with a CRC 32 for integrity verification. The CRC is made optional because the signaling message may be carried over a packet-switching network which provides its own CRC, thus making the CRC 32 field redundant.

10.3.3 Addressing

Jumpstart uses a hierarchical addressing scheme with variable length addresses similar in spirit to the NSAP address format see Section 5.5. Each address field is represented by an address LV length, value tuple. The maximum address length is 2048 bits 256 bytes. The hierarchical addressing schemes allows different administrative entities to be responsible for assigning their part of the address. They can decide on the length and the further hierarchical subdivision of the address space. Figure 10.14 shows a hierarchical network administrative structure that has three levels and eight administrative organizations. For presentation purposes the interconnectivity between the OBS nodes is not shown. The top level domain consists of the domains 0xA and 0xB, with four bits allocated to the top domain addressing level. The notation 0x indicates that the number following is in hexadecimal. Within domain 0xA, the second level is allocated 8 bits, and is subdivided into domains 0x01, 0x02 and 0x03. These are the lowest level domains, and OBS node addresses in these domains are allotted 8 bits. In domain 0xB, the second level domains are allotted 16 bits, and the OBS node addresses 256 OPTICAL BURST SWITCHING 0x1A 0x1B 0x01 0x02 0x0E 0x03 0x0B 0x001F 0x001 0x000F 0x035 Domain 0xA Domain 0xB OBS top domain Figure 10.14 Address hierarchy. within these domains are allotted 12 bits. As an example, the address of the OBS node in domain 0x001F is: 0xB.0x001F.0x035.

10.3.4 The Routing Architecture

In the Jumpstart OBS architecture there is a clear separation between the control plane and the data plane. The data plane is all optical and is responsible for transporting bursts. The control plane is an electronic packet-switching network and is responsible for signaling, routing, and network management. In the Jumpstart prototype network, an OBS node consists of an OXC which is a 2D MEMS switch fabric and a control unit which is known as the JITPAC controller [JITPAC] . The JITPAC controllers communicated with each other via an ATM network. Figure 10.15 shows the control and data planes. OXC OXC OXC OXC OXC JITPAC JITPAC JITPAC JITPAC JITPAC Data plane Control plane Figure 10.15 The data and control planes in Jumpstart.