Service availability in IP networks
One of the main challenges facing networking researchers is to improve
the Internet service availability. Availability has a different meaning
in different contexts. For example, for VoIP, it means that outages or
loss burst should not last more than 250ms. For a web users, it means
that the server is available to serve a request (not much constraints on
the lossiness of links).
Internet research has not made much effort to understand this issue. To
start with, there is not even a decent definition of availability for
Internet services. Using the POTS definition is wrong and their notion
of "5 nines" does not mean anything in a packet network. Since
restoration is now done at the IP level, routing protocols have a huge
impact on service availability:
- IGP restoration of service is in the order of seconds. Convergence is
even longer. Most of the link failures are very short and significantly
impact service availability.
- Interconnection provided by EGPs is flacky. There is no way to
guarantee that packets will be forwarded between to ASes if their ISPs
dont have commercial agreements. FOR EXAMPLE, a 911 VoIP call from a GBX
customer would not be forwarded by UUNET if the call receiver is not a
UUNET customer.
In addition, availability is limited by practices such as NAT, and
relies on services such as the DNS.
In summary, routing protocols should be designed in such a way that they
maximize service availbility in order to allow mission critical
applications to be deployed on packet networks. At the IGP level,
reducing the convergence time together with simple traffic engineering
should help. More significant changes are requested at the EGB level and
evolving BGP might not be an acceptable option. Instead, we have to
imagine now a routing architecture that will maximize service
availability in the Internet of the future. Therefore, the first step is
to agree on a defintion of service availability.
Details are available on
S. Bhattacharyya, G. Iannaccone, A. Markopoulou, C.-N. Chuah, C. Diot.
"Service availability in IP networks". Rejected from HotNets II. also
Sprintlabs Research Report RR03-ATL-071888. July 2003.