- Transport Network Failures and Their Impacts
- Survivability Principles from the Ground Up
- Physical Layer Survivability Measures
- Survivability at the Transmission System Layer
- Logical Layer Survivability Schemes
- Service Layer Survivability Schemes
- Comparative Advantages of Different Layers for Survivability
- Measures of Outage and Survivability Performance
- Measures of Network Survivability
- Restorability
- Reliability
- Availability
- Network Reliability
- Expected Loss of Traffic and of Connectivity
This chapter is from the book
This chapter is from the book
This chapter is from the book
3.2 Survivability Principles from the Ground Up
As in many robust systems, "defence in depth" is also part of communication network survivbility. We will now look at various basic techniques to combat failures and their effects, starting right at the physical layer. Table 3-2 follows the approach of [T1A193] and identifies four levels at which various survivability measures can be employed. Each layer has a generic type of demand unit that it provides to the next higher level. As in any layering abstraction, the basic idea is that each layer exists to provide a certain service to its next higher layer, which need know nothing about how the lower layer implements the service it provides. Here it is capacity units of various types that each layer provides to the next to bear aggregations of signals or traffic formed in the next higher layer. It is important to note that although a layered view is taken it is not implied that one or more methods from each layer must necessarily be chosen and all applied on top of each other. For instance, if rings are implemented at the system layer, then there may be no survivability measures (other than against intra-system circuit-pack level of failures) implemented at the logical layer, and vice-versa. Additionally, certain service layer networks may elect to operate directly over the physical layer, providing their own survivability through adaptive routing. In contrast, however, certain physical layer measures must always be in place for any of the higher layers to effect survivability. In this framework it is usually the system and logical layers, taken together, that we refer to when we speak of "transport networking" in general.
Table 3-2. Layered view of networks for survivability purposes
|
Layer |
Elements |
Service and Functions |
Demand Units Generated |
Capacity Units Provided |
Generic Survivability Techniques |
|---|---|---|---|---|---|
|
Service |
IP routers, LSRs telephone switches, ATM switches, smart channel banks |
Circuit-switched telephony and data, Internet, B-ISDN private networks, multi-media |
OC-3, OC-12, STS-1s, DS-1s, DS-3s GbE, etc. |
n/a |
Adaptive routing, demand splitting, application re-attempt |
|
Logical |
OXC DCS ATM VP X-connects |
Services grooming, logical transport configuration, bandwidth allocation and management |
OC-48, OC-192, wavelength channels, wavebands |
OC-3, OC-12, STS-1s, DS-1s, DS-3s GbE, etc. |
Mesh protection or restoration DCS-based rings p-cycles |
|
System |
SONET OC-n TM, LTE, ADMs, OADMs WDM transmission systems |
Point-to-point bit-transmission at 10 to 40 Gbs/s Point-to-point fiber or wavelengths |
fibers, cables |
OC-48 OC-192 wavelength channels, wavebands |
1:N APS 1+1 DP APS, rings |
|
Physical |
Rights-of-way, conduits, pole-lines, huts, cables, ducts |
Physical medium of transmission connectivity |
n/a |
Fibers, cables |
Physical encasement, physical diversity |