nt can request a disjoint backup to a primary route. 8.7.3 Addressing and Routing A client requesting a connection across an OTN needs to identify the end- points of the connection-the source and destination-using some address- ing scheme. Chapter 8 The O-UNI solution is supposed to use a new, distinct address space for UNI clients. In this strategy, the OTN assigns a single, globally unique address to each client endpoint. We refer to this type of address as a trans- port network assigned (TNA) address. Using an addressing scheme that is decoupled from both internal OTN and client protocol addresses has the following benefits: Internal OTN addresses are not revealed across administrative boundaries. Instead, clients address each other using TNA addresses, and mapping between the assigned address and internal switch addresses is done within the bounds of the OTN. (The alternative- revealing internal OTN addresses outside the OTN boundary-is viewed as a significant security risk.) The OTN can organize the TNA address to maximize the efficiency of routing and reachability calculations for its clients. By decoupling TNAs from client addresses, UNI can provide a seamless way for clients using different protocols to interwork. At the same time, the use of TNAs imposes certain responsibilities on the clients and Clients must register with the OTN to be assigned a TNA. The OTN must provide an address resolution service, which translates between a remote client protocol address and a remote TNA address. The OTN must be capable of distributing TNA address client mappings and reachability information to all edge nodes that provide the UNI (intradomain). Different OTNs must be capable of distributing addressing information between them (interdomain). One rejected addressing strategy was to use client protocol addresses. The key disadvantage of this strategy is that clients of the OTN are likely to use a variety of different address spaces and formats (such as Network Service Access Point [NSAP], IPv4, IPv6, and e.164), whic