Network

NSIS (Next Step in Signalling), is another new signalling system for IP network, which is expected to replace RSVP. NSIS is standardised by the IETF, and is envisioned to support various signalling applications that need to install and/or manipulate such state in the network. NSIS is expected to be generic and extensible. Therefore, NSIS protocols separate functionalities such as reliability, fragmentation, congestion control, and integrity; with signalling applications.

To fulfil it, two protocol layers are designed for NSIS:

• NSIS Transport Layer Protocol (NTLP), is utilised for layer messaging. It is called General Internet Signalling Transport (GIST) protocol and forms the building block of the framework. It transports applications layer messaging signal. GIST layer is transported over standard transportation and security protocols, such as UDP, TCP, SCTP, and DCCP. GIST provides all necessary means to detect signalling nodes and transport messages between them. Thereby, GIST provides a hop-by-hop transport fashion between the signalling nodes and re-uses well known transport protocols (like TCP, TLS over TCP) between the nodes to address problems like reliability, ordering, congestion control and security.
• NSIS Signalling Layer Protocols (NSLPs), each implements application-specific signalling functionalities, including arranging the rule and format of processing among NSLPs. Examples are QoS NSLP for QoS reservation signalling; NAT/Firewall NSLP for configuring middleboxes; and possibly special NSLP for metering configuration.

The difference between NSIS and RSVP, among others:

1. Transport. RSVP is transported over UDP or directly over IP. NSIS splits NTLP with NSLPS, which enables signalling separation. NTLP is transported over existing protocols, such as TCP or UDP.
2. Reservation Model. RSVP is initialised by the receiver, while NSIS QoS NSLP could be initialised by either the sender or the receiver. The usage of proxy is allowed, which means that initialisation and termination could also be performed not on the end of the flow. When RSVP must be end-to-end, NSIS could be end-to-end, edge-to-edge, host-to-edge, or edge-to-host.
3. Multicasting. Unlike RSVP, NSIS does not support multicasting. It reduces the complexity of applications, of which major part is, indeed, unicasting. However, it is possible that NSIS model will be extensible to IP multicasting too.
4. Two-ways Reservation. QoS NSLP enables two-ways reservation, by performing binding to the sessions on both ways. This could not be done with RSVP.
5. QoS Models. QoS NSLP enables any QoS model signalling.
6. Mobility. NSIS identifies signalling session with random session identifier, instead of flow identifier that includes IP address. Therefore NSIS would support mobility easier.
7. Security. Security issues has enhanced RSVP. However, security has been considered since the beginning of NSIS designing. Integration with standard security protocols, such as TLS or IPsec/IKEv2 has been done.

The framework of NSIS is described on RFC 4080. Working group documents could be referred here: tools.ietf.org/wg/nsis.